Santalum Album) Growth Rates, Heartwood and Oil Production, and Product Definition

Flood-irrigated Tropical Timber Trials in the North of Western Australia

NOVEMBER 2012 RIRDC Publication No. 12/044

Flood-irrigated Tropical Timber Trials in the North of Western Australia

by Dr Liz Barbour1,2, Professor Julie Plummer2 and Len Norris1,3

November 2012

RIRDC Publication No. 12/044 RIRDC Project No. PRJ-002676

ISBN 978-1-74254-493-9 ISSN 1440-6845

Flood-irrigated Tropical Timber Trials in the North of Western Australia Publication No. 12/044 Project No. PRJ-002676

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While reasonable care has been taken in preparing this publication to ensure that information is true and correct, the Commonwealth of Australia gives no assurance as to the accuracy of any information in this publication.

The Commonwealth of Australia, the Rural Industries Research and Development Corporation (RIRDC), the authors or contributors expressly disclaim, to the maximum extent permitted by law, all responsibility and liability to any person, arising directly or indirectly from any act or omission, or for any consequences of any such act or omission, made in reliance on the contents of this publication, whether or not caused by any negligence on the part of the Commonwealth of Australia, RIRDC, the authors or contributors.

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Researcher Contact Details

1Dr Liz Barbour and Len Norris 2Dr Liz Barbour and Prof Julie Plummer 3Len Norris Forest Products Commission University of Western Australia Dept Agriculture and Food WA Locked Bag 888 35 Stirling Highway Locked Bag 4 Perth BC WA 6849 Crawley WA 6009 Bentley delivery centre WA 6983

Email: [email protected] Email: [email protected] Email: [email protected]

In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form. RIRDC Contact Details

Rural Industries Research and Development Corporation Level 2, 15 National Circuit BARTON ACT 2600

PO Box 4776 KINGSTON ACT 2604

Phone: 02 6271 4100 Fax: 02 6271 4199 Email: [email protected]. Web: http://www.rirdc.gov.au

Electronically published by RIRDC in November 2012 Print-on-demand by Union Offset Printing, Canberra at www.rirdc.gov.au or phone 1300 634 313

Foreword

This report records a joint project between the Rural Industries Research and Development Corporation (RIRDC), the Forest Products Commission of Western Australia, Elders Forestry and the University of Western Australia to ensure that the original plantation trials and plantings of tropical tree species in the Ord River Irrigation Scheme (ORIS) on the Frank Wise Institute site were assessed and published. Sixteen trials were selected to provide scientific information on:

• sandalwood (Santalum album) growth rates, heartwood and oil production, and product definition

• African mahogany (Khaya senagalensis) growth rates

• teak (Tectona grandis) growth rates

• pongamia (Millettia pinnata) growth rates, seed production and seed oil quality

• identification of other tropical species that could either be used as a long-term host for sandalwood or as a tropical timber project for the north of Australia.

This set of trials holds valuable information which has and will assist in all aspects of the developing essential oil and plantation industry in the north of Western Australia and similar developing tropical forestry industries in Queensland and Northern Territory. The report provides a perspective of different tree systems and their performance in flood-irrigated systems.

The sandalwood trials selected demonstrate a variety of silviculture systems. Outstanding trees, far beyond expectations, were found within these trials. As with any plantation program, the aim of breeders and silviculturalists alike is to uniformly repeat this exceptional performance in every tree across each hectare of plantation. Tree distribution required to optimise a site for sandalwood performance was investigated and discussed. Prior to this report, sandalwood growth analyses were either on young plantations where inter-tree competition had not emerged as a parameter or on singled-out older trees. The analysis of each of these trials explores the average expected performance with different silviculture management systems.

New crop development is not encouraged when land valuation is as high as is presently being experienced in the ORIS. Whereas annual crops can be manipulated to produce multiple generations within a year, the first full-rotation commercial harvest of sandalwood will only occur in 2016 (a 15- year rotation) and similarly with other tropical species. Sandalwood oil, at present, has a high commercial potential that can support this slow development cycle. However, other tropical timber species need to confront a range of issues before being considered viable.

This report is an addition to RIRDC’s diverse range of over 2100 research publications and it forms part of our Essential Oils and Plant Extracts R&D program. RIRDC's vision for this program is of a profitable and sustainable industry producing essential oils and plant extracts of the quality and content that meets customers' evolving demands.

Most of RIRDC’s publications are available for viewing, free downloading or purchasing online at www.rirdc.gov.au. Purchases can also be made by phoning 1300 634 313.

Craig Burns Managing Director Rural Industries Research and Development Corporation

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About the Authors

The Forest Products Commission is a Western Australian state agency that was formed out of the Department of Conservation and Land Management in 2000. A number of researchers and technicians have been responsible at various stages for the establishment and management of a series of tropical tree trials at the Frank Wise Institute in the Ord River Irrigation Area. It is through this commitment by the West Australian State Government that demonstration trails, research information and germplasm has been made available to establish three budding tropical forestry industries: tropical sandalwood (Santalum album), African mahogany (Khaya senegalensis) and teak (Tectona grandis). The management and research associated with these trials provides continued support for these fledgling industries.

Dr Liz Barbour and Len Norris were the two researchers from the Forests Products Commission responsible for management and research program development during the period of this RIRDC- supported project. Dr Barbour is now with the University of Western Australia and Len Norris is seconded to the Department of Agriculture and Food in Western Australia.

Professor Julie Plummer is a plant scientist from the University of Western Australia. She has been studying production of tropical timbers and oil biosynthesis in sandalwood for most of the last decade. She is the chief investigator on the Australian Research Council Linkage Project (LP0882690) ‘Elucidation of genetic and physiological factors controlling biosynthesis of sesquiterpenoids in sandalwood, Santalum spp’, and the ARC Linkage Project LP100200016 ‘Molecular characterisation of the fungal disease defence response in tropical sandalwood (Santalum album)’.

Acknowledgments

We acknowledge and are grateful for the assistance provided by the following:

• Rural Industries Research and Development Corporation, especially Dr Ros Prinsley (former employee) and Ms Alison Saunders, for supporting this project so that these trials could be documented

• Forest Products Commission, especially Gavin Butcher, Peter Jones (former employee) and Grant Pronk (former employee), for ensuring the management of the site so that this work could be undertaken. John Streatfield (former employee) managed the site and assisted with the harvesting during the period of this project. Dr Andrew Lyon completed the acoustic time-of-flight measurement on sandalwood

• Elders Forestry for their financial and in-kind support for the project. This project was initiated with Dr Andrew Callister (former employee) and passed over to Dr Marie Connett

• PhD students at the University of Western Australia: Jessie Moniodis (University of Western Australia) for her technical assistance with the sandalwood oil analyses and Ni Luh Arpiwi for completing the seed oil analyses for Millettia

• Dr Chris Jones (University of Western Australia), Professor Joerg Bohlmann (University of British Columbia, Canada) and Dr Katherine Zulak (formerly University of British Columbia, Canada) for their thoughtful suggestions regarding aspects of sesquiterpene oil synthesis in this project and during its development and analysis

• Dr Andrew Callister of Treehouse Consulting who developed the individual tree-competition indices and undertook the analysis

• Craig Hallam of Enspec for undertaking the electrical impedance tomography.

Abbreviations

Institutions/Organisations

ACIAR Australian Centre for International Agricultural Research

CALM Conservation and Land Management with was formed from an amalgamation of the Forests Department, the wildlife section of the Department of Fisheries and Wildlife and the National Parks Authority. In 1990 it was split into the Department of Environment and Conservation and the Forest Products Commission.

DAFWA Department of Agriculture and Food, Western Australia

DEC Department of Environment and Conservation, Western Australia

FPC Forest Products Commission, Western Australia

Elders Forestry Integrated Tree Cropping Limited renamed Elders Forestry Limited

MU Murdoch University

ORIS Ord River Irrigation Scheme

ORIA Ord River Irrigation Area

TFS Tropical Forestry Services

UBC The University of British Columbia, Vancover, Canada

UWA The University of Western Australia, Perth, Western Australia

Parameters

BD Basal diameter HVT High-value timber

BR Basal radius LEA Large end area

CBD Crown break diameter LED Large end diameter

CSV Canopy stem volume LER Large end radius

DBH Diameter at breast height (130 cm MAI Mean annual increment above ground)

EBV Estimated bole volume SEA Small end area

ESV Estimated stem volume SED Small end diameter

HCI Host count index SER Small end radius

HSDI Host size-distance index SPH Stems per hectare

Contents

Foreword ...... iii About the Authors ...... iv Acknowledgments...... v Abbreviations ...... vi Executive Summary ...... xi 1 Introduction ...... 1 1.1 Background ...... 1 1.2 Tropical forestry history in the Ord River Irrigation Scheme ...... 3 1.3 Sandalwood as a crop ...... 12

2 Objectives ...... 16 3 Methodology ...... 16 3.1 General methods and formula ...... 17 3.2 Main species ...... 18

4 Sandalwood (Santalum album) trials ...... 20 4.1 Sandalwood host selection demonstration plots ...... 20 4.2 Sandalwood growth with Cathormion umbellatum ...... 27 4.3 Investigation of spatial competition analysis ...... 39 4.4 Sandalwood heartwood and oil development ...... 54

5 High-value timber trials ...... 79 5.1 A summary of Khaya senegalensis growth within trials of different age and silviculture, Trials 5, 7, 11, 12 and 15 ...... 79 5.2. Comparison of the growth of eleven high-value timber species, Trial 12 ...... 83 5.3 Growth assessment of high-value timber demonstration plots, Trials 10, 11, 13 and 15...... 88 5.4. The growth of teak (Tectona grandis) on levee soil, Trial 14 ...... 91 5.5 Growth, seed yield and oil characteristics of Millettia pinnata, Trial 16 ...... 96

6 Implications ...... 100 6.1 Sandalwood trials ...... 100 6.2 High-value timber trials ...... 101

7 Recommendations ...... 103 Appendix A ...... 104 References ...... 106

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Tables

Table 4.1 Growth parameters of sandalwood and hosts in Trial 5 when they were 11 years old ...... 21 Table 4.2 Measured and estimated growth parameters of 15-year-old Peltophorum and Cassia as sandalwood hosts in Trial 3 ...... 23 Table 4.3 Measured and estimated growth parameters of 15-year-old sandalwood with host species Peltophorum and Cassia in Trial 3 ...... 23 Table 4.4 Growth parameters of 18-year-old and 17-year-old sandalwood established in 1990 (Trial 1) and 1991 (Trial 2) respectively ...... 25 Table 4.5 Growth parameters of sandalwood in 1991 (Trial 2) when planted in dual host configurations ...... 25 Table 4.6 Growth parameters measured at 18 years and 17 years for host species established in 1990 (Trial 1) and 1991 (Trial 2) respectively ...... 26 Table 4.7 Sandalwood (S) and host (H) spacing and stocking for the six ratio treatments in the original planting design of Trial 9 ...... 28 Table 4.8 Trial 9 host (H) and sandalwood (S) stocking rates after culling of plots in 2003 ...... 29 Table 4.9 The within column spacing and stems per hectare (SPH) for the six stocking treatments of sandalwood and Cathormion umbellatum hosts in Trial 6 ...... 33 Table 4.10 Age and planting details of Cathormion host trials ...... 37 Table 4.11 P-values for model effects on sandalwood basal diameter using host count indices (HCI) in Trial 7 ...... 42 Table 4.12 Estimates for significant effects of host count index (HCI) on sandalwood basal diameter in Trial 7 ...... 43 Table 4.13 P-values for model effects on sandalwood basal diameter using host size-distance indices (HSDIs) in Trial 7 ...... 44 Table 4.14 Estimates for significant effects of host size-distance index (HSDI) on sandalwood basal diameter in Trial 7 ...... 45 Table 4.15 Summary of selected significant linear models explaining the relative growth of sandalwood with Peltophorum and Cassia hosts between 2001 and 2008 in Trial 3 ...... 50 Table 4.16 Summary of selected significant linear models explaining sandalwood stem volume with Peltophorum and Cassia hosts in Trial 3 ...... 52 Table 4.17 Summary of selected significant linear models explaining the stem volume of Peltophorum and Cassia in Trial 3 ...... 53 Table 4.18 Growth parameters for 30 trees destructively harvested after 8 years from Trial 8 ...... 57 Table 4.19 Total disc area and the area and percentage of heartwood and rot with discs located along the bole of 30 sample trees in Trial 8 ...... 58 Table 4.20 Field-determined parameters for the 40 trees sampled from Trial 4 ...... 63 Table 4.21 Parameters calculated from photographic analysis of the four discs along the boles from trees in Trial 4 ...... 63 Table 4.22 Mean estimated under-bark volume and heartwood volume and the percentage heartwood (± s.d.) for bole sections, canopy stem and total above-ground volume ...... 63 Table 4.23 Total oil yield (g/kg) and santalol composition of the five sample locations in 20 trees subsampled from Trial 4 ...... 64 Table 4.24 Proportion of alpha and beta-santalol in oil from the five sample locations in 20 trees subsampled from Trial 4 ...... 64 Table 4.25 Over-bark measurements for sandalwood trees growing with the three host treatments in Trial 7 ...... 69 Table 4.26 Core and cross-sectional parameters for sandalwood grown with the three host treatments in Trial 7 ...... 69 Table 4.27 Proportion and yield (g/kg) of alpha-santalol, beta-santalol and total oil from cores sampled at 30 cm from sandalwood with Cathormion, Dalbergia and Millettia hosts ...... 72

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Table 5.1 Summary description of trial plots in which Khaya senegalensis was planted ...... 80 Table 5.2 Khaya senegalensis growth measurements across Trials 5, 7, 11, 12 and 15. Results at the hectare level were calculated using surviving number of Khaya stems per hectare ...... 81 Table 5.3 Estimated parameters assessed for the nine high-value timber species surviving after 12 years (2008) in Trial 12 ...... 87 Table 5.4 Description of high-value timber demonstration plots in Trials 10, 11 and 15 ...... 89 Table 5.5 High-value timber growth measurements in Trials 10, 11, 13 and 15...... 90 Table 5.6 Growth parameters for teak aged 3, 8 and 10 years at Kununurra in Trial 14 ...... 94 Table 5.7 Proportion of teak trees infected with termites assessed 10 months after planting in Trial 14, DBH per pesticide treatment at 3 years of age and DBH with outliers/runts removed ...... 95 Table 5.8 Seed traits of Millettia pinnata ...... 97 Table 5.9 Correlations between measured seed variables of Millettia pinnata ...... 98 Table 5.10 Composition of fatty acids within oil derived from seed of Millettia pinnata ...... 98

Figures

Figure 1.1 Location of the ORIS, Kununurra (blue dot) in the north of Western Australia in relation to the state capital, Perth (red dot) ...... 2 Figure 4.1 Trial 5 layout showing within and between row spacing (distance across plot from corner) for sandalwood and hosts...... 21 Figure 4.2 Trial 9 planting layout of sandalwood (S) and Cathormion host (H), for the six ratio treatments. .. 29 Figure 4.3 Sandalwood tree height (cm), bole height (cm) and basal diameter (mm) within ratio treatments of sandalwood (S) with a Cathormion host (H) when Trial 9 was 1 year old (2001) ...... 30 Figure 4.4 Sandalwood (S) and Cathormion host (H) growth parameters in Trial 9 post culling (in 2003) measured in 2008 ...... 31 Figure 4.5 Trial 9 sandalwood (S) growth parameters measured in 2008 (8 years) of post culling treatments without hosts (H) based on original treatments (Table 4.7) ...... 31 Figure 4.6 Estimated stem volume (m3) of sandalwood for long-term host stocking treatments and intermediate host types within treatments after 9 years in Trial 6 ...... 34 Figure 4.7 Height (cm) of Cathormion umbellatum and sandalwood within the six stocking treatments after 9 years in Trial 6 ...... 34 Figure 4.8 Estimated sandalwood stem volume per hectare after 9 years in Trial 6 ...... 35 Figure 4.9 Relationship between the number of sandalwood per hectare and the mean individual tree estimated stem volume (ESV), and the mean estimated stem volume per hectare (ESVha) in Trial 6 after 9 years ...... 35 Figure 4.10 Basal diameter (cm) and estimated basal area per hectare (m2 ha-1) for Cathormion umbellatum within stocking treatments in Trial 6 after 9 years ...... 36 Figure 4.11 Diameter (a) and height (b) of sandalwood grown with Cathormion hosts generally at a 1:1 ratio with 462 sandalwood stems per hectare...... 38 Figure 4.12 Mean basal diameter of 8-year-old sandalwood trees estimated on an internal and whole-plot basis in Trial 7 ...... 41 Figure 4.13 Spatial representation of a subject sandalwood tree (solid star) surrounded by four neighbouring host trees (A–D: solid diamonds) within qualifying distance ...... 49 Figure 4.14 Stylistic representation of mean heartwood and rot areas within discs along the bole (a), and an example of non-uniform heartwood production with rot in the centre (b) from Trial 8 ...... 59 Figure 4.15 Relationships between the percentage of rot and aromatic wood within (a) all discs and (b) a comparison of discs with rot originating in the centre and other sites in boles from Trial 8 ...... 59 Figure 4.16 Basal diameter class distribution of the 40 trees sampled in Trial 4 ...... 62

Figure 4.17 Relationship between the height of the sampled disc within the tree (m) and (a) the total oil yield, and (b) the percentage composition of total santalol within the oil in 20 trees subsampled from Trial 4 ...... 65 Figure 4.18 Relationship between total oil yield (g/kg) of individual samples and (a) the cross-sectional disc and heartwood area (cm2), and (b) the percentage of heartwood in 20 trees subsampled from Trial 4 ...... 66 Figure 4.19 Estimated oil yield (g) for each of 20 subsampled trees in Trial 4, indicating the contribution of the root stump, lower third, middle third and upper third of the bole ...... 66 Figure 4.20 Relationships between sandalwood cross-sectional disc area (cm2) and (A) cross-sectional heartwood area, and (B) cross-sectional heartwood proportion (%) in trees from Trial 7 ...... 70 Figure 4.21 Relationships between heartwood % and (A) host size-distance index (HSDI) and, (B) host count index (HCI) in trees from Trial 7...... 71 Figure 4.22 The electrical impedance tomograms for the 8-year-old tree (Tree 1, left), and the extrapolated 3-D tomogram and extracted discs for the 8-year-old (centre) and 15-year-old tree (Tree 2, right) respectively ...... 75 Figure 4.23 Relationships between IML readings and (a) heartwood area with discs for 9-year-old trees from Trial 8 and (b) 15-year-old trees from Trial 4, heartwood diameter within discs for (c) 9-year-old and (d) 15-year-old trees, and percentage heartwood within discs for (e) 9-year-old and (f) 15-year-old trees ...... 77 Figure 5.1 Tree survival (%) for high-value timber species in Trial 12 from 1998 to 2008 ...... 84 Figure 5.2 Height (a) and DBH (b) for high-value timber species in Trial 12 from 1998 to 2008 ...... 85 Figure 5.3 (A) Survival-adjusted estimated stem volume per hectare (m3), and (B) mean annual increment for estimated stem volume of high-value timber species in Trial 12 between 1998 and 2008 ...... 86 Figure 5.4 Frequency (%) of high-value trees in Trials 10, 11 and 12 with one, two and three stems at breast height ...... 90

Plates

Plate 1.1 Cununurra clay showing the cracking ability of this clay soil ...... 2 Plate 1.2 Drilling a core from a sandalwood tree ...... 8 Plate 1.3 Santalum album tissue cultured shoots from juvenile tissue (The Tree Lab) ...... 11 Plate 1.4 Santalum album clonal plants used in the trial established in the ORIS (Nippon Paper) ...... 11 Plate 1.5 Testing the concept of Millettia pinnata hedges by directly sowing the seed...... 14 Plate 1.6 One lay-out for flood-irrigated sandalwood plantation establishment...... 15 Plate 4.1 Trial 1 showing the planting arrangement with the sandalwood and Cathormium ...... 24 Plate 4.2 The sandalwood block in Trial 2 showing the edge effect together with Cathormion ...... 26 Plate 4.3 Typical 8-year-old tree from this trial ...... 56 Plate 4.4 A sample of the 8-year-old wood assessed after the destructive harvest ...... 56 Plate 4.5 The plot combining sandalwood with the long-term host Dalbergia ...... 68 Plate 5.1 Examples of wind-swept boles (top left), crooked boles (top right), and a tree displaying favourable phenotype (bottom left), in a 9-year-old African mahogany plantation ...... 82 Plate 5.2 The teak trial showing the variability in performance ...... 93 Plate 5.3 The Millettia pinnata plot at the time the seed harvesting was completed for this report ...... 96

Executive Summary

What the report is about

This report records a joint project between the Rural Industries Research and Development Corporation (RIRDC), the Forest Products Commission (FPC) of Western Australia, Elders Forestry and the University of Western Australia (UWA) to ensure that 16 of the original plantation trials and plantings of tropical species established in the Ord River Irrigation Scheme (ORIS) by the Western Australian Government were assessed and published.

Who is the report targeted at?

The main target groups of this research are researchers and managers, especially within the Western Australian Government system, non-governmental organisations and commercial and private companies actively growing sandalwood in the ORIS. The included information on growth rates and essential oil production will be of interest to investors and consultants.

Where are the relevant industries located in Australia?

The tropical sandalwood industry is presently focused in the ORIS on the outskirts of Kununurra in the north of Western Australia. The biggest company in this sector is Tropical Forestry Services (TFS). Elders Forestry and TFS have experimented with sandalwood plantations in Queensland and there has been discussion of plantations starting in the Northern Territory. In addition there are private growers who have attracted private investment. A number of Aboriginal communities have considered tropical sandalwood as an enterprise. The tropical hardwood industry has been mainly developing in Queensland and the Northern Territory and includes both teak and African mahogany.

The focus FPC has requested of UWA is to transfer tropical sandalwood knowledge to the more ancient species, Australian sandalwood (Santalum spicatum). The ownership of these plantations covers a wider spectrum of land and investment options and ranges from the private farmer to foreign- owned managed investment schemes.

Background

Sandalwood, an otherwise insignificant hemi-parasitic tree, forms heartwood within its trunk that contains one of the most sought-after essential oils, sandalwood oil. The sesquiterpene components that make up the oil protect the tree’s core from fungal and insect attack. The oils are extracted and used in a number of niche products, such as the base note for the most expensive perfumes. There are also many products being discovered that address an increasing number of human health benefits.

In Western Australia in the 1980s, the concept of cultivating sandalwood was first considered in 1988. An agreement between the Department of Conservation and Land Management (CALM, formerly the Forests Department) and Department of Agriculture and Food Western Australia (DAFWA) was reached and a series of plantings looking at different host combinations were established at the Frank Wise Institute.

In 2000 the Forest Products Commission (FPC) was formed from the commercial activities within CALM. The Tropical Forestry project at Kununurra based at the Frank Wise Institute became the responsibility of FPC and was to work on a number of issues to do with sandalwood research, including understanding and recording each planting/trial at the Frank Wise Institute.

Aims/objectives

The 16 trials selected aimed to highlight information on: sandalwood (Santalum album) growth rates, heartwood and oil production and product definition; African mahogany (Khaya senagalensis) growth rates; teak (Tectona grandis) growth rates; pongamia (Millettia pinnata) growth rates, seed production and seed oil quality; and the identification of other tropical species that could either be used as a long- term host for sandalwood or as a tropical-timber project for the north of Australia.

Methods used

There are two main groups of trials: those concerned with sandalwood and its hosts; and those related to high-value timber species. Where possible, statistical analyses were completed using the original design elements of the trials; however, where trials were of a demonstrational nature or no longer conformed to the original design due to high mortality, only comparisons of descriptive results have been made. In addition to trial measurements, destructive harvesting of sandalwood was undertaken, and two non-invasive techniques were evaluated for their potential use in determining aromatic wood.

Results/key findings

Barbour (2008) indicated that the best hosts for tropical sandalwood were Cathormion umbellatum, Dalbertgia latifolia and Millettia pinnata and this was further supported by the analyses of these additional trials. Hosts producing lower sandalwood growth rates were Cassia siamea, Khaya senegalensis, Peltophorum pterocarpum and Swietenia mahogani.

Poor host performance was related to a fast-growing nature and spreading canopy that enabled dominant host occupation of the site and spatial competition with the sandalwood. An unexpected finding was that even when tropical sandalwood was growing with favourable hosts, spatial competition could negatively influence sandalwood growth. A specific trial designed to explore this aspect showed that 9-year-old sandalwood growing with Cathormion displayed a growth decline when sandalwood stocking rates were increased and when planted in different host-to-sandalwood ratios. Trial analysis using spatial competition indices indicated that increasing host and sandalwood stocking could produce a situation of negative competition effects on sandalwood growth rate. What was of importance was how the nature of these competition interactions varied between hosts.

Heartwood formation was found within 8-year-old sandalwood; however, the amount and development along the stem was generally low and highly variable between trees. In 15-year-old trees, heartwood development was more reliable, and in some cases extended as far as 3.5 m up the tree compared to a maximum of up to 1.8 m in 8-year-old trees. The calculated heartwood volume for 15- year-old trees was approximately 6.3 kg, with the majority (4.4 kg) occurring in the bole.

Oil extracted from 11-year-old and 15-year-old sandalwood samples was of high quality, as indicated by the alpha and beta-santalol composition standards required for S. album oil (ISO 3518:300E). Oil yields from a single core that included heartwood and sapwood taken at 30 cm above the ground were typically low (average of 1.3 per cent); however, after adjusting yield to reflect the sapwood-to- heartwood ratio within cores, the average yield of heartwood was approximately 3.8 per cent. Heartwood samples from 15-year-old sandalwood taken at five locations along the stem (from root stump to bole top), had an average oil yield of 5.5 per cent. The average estimated oil yield from 15- year-old sandalwood was approximately 300 g; however, it was noted that individual tree oil estimates were wide ranging (between 18 to 780 g).

African mahogany (Khaya senegalensis) displayed superior growth rates in comparison to other high- value timber species in the trials. The mean annual increment (MAI) for diameter at breast height (DBH) across trials aged 9 to 12 years ranged from 1.9 to 2.7 cm per year. Other species that demonstrated favourable growth rates included: teak (Tectona grandis), with an MAI of 2 cm per year at 10 years old; and mahogany (Swietenia macrophylla) with an MAI of 2.0 at 12 years old. The

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growth rate of Indian rosewood (Dalbergia latifolia) was moderate, but it was the only high-value timber species trialled that was able to promote good sandalwood growth.

In general, the observed stem form of all timber species was largely unfavourable for sawlog production, with stems often crooked or having short bole lengths and large branches. Given this, the recovery rates for sawlogs would be low and thus the concept of multiple products needs time to develop scientifically. Poor form was largely believed to be a result of poor genetics, lack of management and/or inappropriate silviculture. With inadequate silviculture records on the trials the cause could not be isolated.

Compared to other high-value timber species, Millettia pinnata (pongamia) fits into a different performance group, with its high-value product being seed (which is then used for producing biodiesel) not sawlogs. The concept of hedges of economically viable pongamia supporting tropical sandalwood growth is possible; however, whist Millettia pinnata seed oil has broadly been recognised as suitable for biodiesel production, the viability of the undertaking will largely depend upon oil quality and seed yield of the genetic resources used in a given environment.

Implications for relevant stakeholders

Industry

Sandalwood

The projected rotation length for commercial plantations of tropical sandalwood in the ORIS is 15 years. Trees assessed at this age under various silviculture treatments showed that Santalum album has converted 30 per cent of its bole to heartwood. This amount of sandalwood heartwood would not make the standard of a carving log (the highest-valued product from sandalwood); however, on oil alone and based on current sandalwood prices, the potential of the industry has not been over-stated.

Most of the trials assessed were planted prior to the commercialisation of tropical sandalwood in the ORIS and used silviculture systems and hosts that are different from what is seen in company plantations today. The two biggest differences are: the past use of the primary host Acacia trachycarpa which has been superceded by the dominant species Sesbania formosa; and the separation of sandalwood and primary host in one row from the secondary host in a separate row. The change in primary host had far greater implications on the choice and performance of the secondary host (long-term host) than was originally appreciated. The shading effect of Sesbania and the different management methods used to reduce the shading brought disease into the plantation as well as suppressing secondary-host growth of some species. Whereas Cathormium was an exemplary host with Acacia trachycarpa (producing the biggest trees on the Frank Wise Institute site), when the primary host was changed to Sesbania, all benefits of Cathormium as the secondary host were lost. This indicates that spatial host relationships need to be revisited and data from these trials infers that the density of secondary hosts is too high.

A plantation project has two major factors to consider for economic sustainability: product market value; and production per hectare. When entering high-value markets, the challenge of producing a standard product needs to be met. The sandalwood oil profile has been shown to be stable between trees and sites; a quality product can be extracted and sold that meets the ISO standard.

The second factor, production (either as tree wood volume or heartwood volume) per hectare, has been shown to have wide variation across each trial and indeed to vary excessively across a site. The challenge is to understand the key factors that control this variation and this report begins to look at optimising spatial relationships for maximum sandalwood growth. Heartwood formation, whilst related to growth, is regarded as a separate process. This is being explored through an Australian Research Council award and the outcomes of that research, as background knowledge, are referred to in this report.

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High-value timber species

African mahogany (Khaya senegalensis) is impressive both in its ability to survive and its growth rate in the ORIS. An intensive selection program is required to improve tree form and thus timber recovery. This could also be the case with teak (Tectona grandis) but growth rates are lower and teak is not as resistant to pests, particularly termites. The tree of most interest is rosewood (Dalbergia latifolia) as it is an excellent host for tropical sandalwood. Whilst it is highly sought after, the form of trees at the Frank Wise Institute does not make it a desirable timber tree and there are also problems with raising this species in present nursery systems.

Communities

Sandalwood provides an opportunity where forestry and agriculture can closely combine. The hemi- parasitic nature of sandalwood and competition indices indicate that intercropping with other valuable horticulture or agriculture crops may be a way to optimise sandalwood growth and meet food needs. However, sandalwood is a perennial plant, harvested after 15 years, and so for communities it is quite different from annual harvest agricultural systems. With companies managing plantations for investors, and local landowners either selling or leasing their land, the nature of the business is also unfamiliar in the ORIS.

Sandalwood will create an industry in which the product will be grown and processed in the ORIS before export. Sandalwood waste from harvesting, together with host biomass that will be removed at the site, may be a product itself and needs to further exploration. Like the rum industry, sandalwood could also attract a tourist trade. The industry will thus provide work for a varied range of skills.

Recommendations

The first outcome from this project was the discovery of heartwood rot within Santalum album at the Frank Wise Institute. The first recommendation to RIRDC was to further investigate the heartwood rot and this culminated in the RIRDC report Heartwood Rot Identification and Impact in Sandalwood (Santalum album) (Barbour et al. 2010).

This project additionally recommends that:

• Time-course studies of different planting designs are undertaken to quantify changing spatial relationships between hosts and sandalwood so that silviculture recommendations over the full 15- year rotation can be made.

• The exploration of new secondary hosts is continued; including the concepts of a hedge of Millettia pinnata and/or horticultural and/or agricultural inter-row integration.

• Studies are undertaken to understand heartwood formation.

• A selection program is initiated for the development of a timber product from African mahogany, teak and Dalbergia.

• Mechanical systems are developed for the selective harvest of sandalwood, the removal of clay, and the separation of heartwood and sapwood.

• The possibility of products from the non-sandalwood biomass at harvest is explored.

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1 Introduction

Sixteen trials/plantings established at the Frank Wise Institute in the Ord River Irrigation Scheme (ORIS) on behalf of the Western Australian Government were measured and analysed. These trials contributed a good portion of the information used by industry to develop the first tropical forestry plantation projects in the north with sandalwood, followed by teak and African mahogany.

1.1 Background

1.1.1 Ord River Irrigation Scheme history

The Ord River is 320 km long and located in the Kimberley region of Western Australia. The headwaters of the Ord River are located below Mount Wells and it initially flows east around the edge of Purnululu National Park before heading north through Lake Argyle. The river then passes west of Kununurra and discharges into the Indian Ocean in Cambridge Gulf.

The ORIS was constructed on the river in 1963 and opened on 30 June 1972. The scheme created Lake Argyle, which is Australia’s largest dam, covering an area of 741 km², and it generates power for the local community as well as providing a constant source of irrigation water. Lake Kununurra was also constructed as part of the project.

Allocation of the first 14 000 ha of farming land during Stage 1 of the project was completed in 1966. The 30 farms produced mostly cotton; however, pest problems soon became apparent. The early 1970s saw the application of large amounts of pesticides; mainly to control the Helicoverpa armigera caterpillar which then developed pesticide resistance. Pressure from pests resulting in low crop yields combined with a drop in world cotton prices and led to the suspension of the commercial cotton industry. In the 1990s the ORIS converted to sugar cane and a sugar mill was built on the outskirts of Kununurra to support the growing industry, based on plans for the scheme’s expansion to 30 000 ha. This land expansion did not occur and coupled with fluctuating market prices for sugar, the sugar mill closed in 2007. Whilst other crops were being experimented with, tropical sandalwood which was a fledgling industry, became the new dominant crop in the ORIS.

1.1.2 The challenges of the Ord River Irrigation Scheme

Remote north of Western Australia

The ORIS is located in a remote part of Australia with large distances to the main markets in the rest of the continent (see Figure 1.1). Kununurra is 3228 km north of Perth and 780 km south-west of Darwin. It is 1042 km north of Broome, which is the closest Western Australian town to Kununurra. Crops grown in the ORIS thus need to be partially processed into an easily transportable form and be of high value or grown in economically large quantities.

Figure 1.1 Location of the ORIS, Kununurra (blue dot) in the north of Western Australia in relation to the state capital, Perth (red dot)

Soil

The soils in the first ORIS land release are known as cracking clays, mainly made up of Cununurra clays (see Plate 1.1) and Aquitaine clays. The Aquitaine clays have higher clay content and while they can be very productive, require careful management and irrigation practices. Smaller areas of red- brown earths, red earths, brownish cracking clays, colluvial outwash slopes, rock outcrops and other soils also occur.

Cracking clay soils are often described as black soils or vertisols. They exhibit substantial shrinking and swelling properties; resulting in deep, open desiccation cracks into which vegetation will often fall. This vegetation then becomes incorporated into the soil mass, giving the dark grey or black colouration. Continuous movement due to moisture variations can result in slicken sides or polished surfaces within the soil profile.

Plate 1.1 Cununurra clay showing the cracking ability of this clay soil

Unless these cracking clays are continuously moistened, drying can cause cracks in the soil surface that are able to rip roots. Furthermore, the ‘sticking’ properties of the clay make any commodity harvested from the ground extremely difficult to extract and clean. All crops to date developed in the ORIS have been above-ground crops. Tropical sandalwood will be the first commodity harvested from below ground (i.e. the sandalwood roots) and it thus will have engineering challenges to overcome to be economically viable in an area where labour is at its most expensive in Australia.

The soil pH is generally above 7, indicating that alkaline soils are typical. This may not have a direct impact on tropical sandalwood as it is a hemi-parasite, but it may influence nutrient uptake and growth of other tropical trees investigated individually and as hosts.

Furthermore, the electrical conductivities of the subsoils are very high so there is a strong possibility of soil salting if groundwater is allowed to rise. Aquitaine clays in the northern part of the Weaber Plains are known to have high salt content at depth and irrigation must be carefully planned to prevent water seepage and subsequent water table elevation. Consequently, it is proposed that control be exercised over water application and that this is combined with groundwater monitoring and management. In this situation, tree crops have many advantages.

Climate

The climate is sub-tropical with two dominant seasons: the wet (monsoon or cyclone) season usually extends from November to April, while the dry season can be taken as May to October. During the wet season, temperatures and rainfall are relatively high with much of the rain activity coming from thunderstorms and cyclones formed in subtropical low-pressure systems off the coast. The average rainfall is 776 mm with around 90 per cent falling during the wet season. In contrast, the dry season is characterised by lower temperatures, low rainfall and lower humidity. Net evaporation rates are generally high, of the order of 2100 mm per annum and, during most months, evaporation exceeds precipitation.

The sub-tropical climate in northern Western Australia could provide market advantages for crops grown in the ORIS. Tropical fruits could use counter-seasonal marketing for improved profit, whereas annual crops grown in the dry season with irrigation would be relatively free of major pests and diseases as encountered in other parts of Australia and the world. A regional biosecurity plan is in place to further reduce the risk of incursions. Recent evidence indicates that for tropical sandalwood, infection by endemic fungi from surrounding bush is an additional threat to sustainability (Barbour et al. 2010).

1.2 Tropical forestry history in the Ord River Irrigation Scheme

There are a number of reviews of the development of the tropical sandalwood industry in the ORIS (Radomiljac 1993; Radomiljac et al. 1998b; Shea et al. 1998; Vernes and Robson 2002; Done et al. 2004; Barbour 2008; Barbour et al. 2010; Plummer et al. 2011).

1.2.1 A brief overview

Sandalwood once played an important role in the history of Western Australia, particularly in the south-west. With tropical sandalwood now dominating in the ORIS, the question is whether the crop is poised to tame the last frontier of the north for agriculture and forestry.

This otherwise insignificant hemi-parasitic tree forms heartwood within its trunk that contains one of the most sought-after essential oils, sandalwood oil. The sesquiterpene components that make up the oil protect the tree’s core from fungal and insect attack. The oils are extracted and utilised in a number of niche products, such as the base note for the most expensive perfumes. There are also many products being discovered that address an increasing number of human health benefits.

Prior to gold being discovered in Western Australia, it was the harvest and export of Australian sandalwood (Santalum spicatum) that kept the colony solvent. The demand for tea from China was compensated for by the sandalwood trade from Western Australia. This led to mass clearing of Australian sandalwood and the eventual introduction of legislative control to temper this destruction.

Santalum spicatum regeneration has a unique aspect which, with increased human occupation, has become its Achilles heel. The seed has to be buried for it to successfully establish. A sequence of wet and hot dry days cracks the seed shell, allowing for germination; but if the emerging seedling is not covered, it desiccates and soon dies. Seed dispersal is cleverly undertaken by a native marsupial, the woylie which buries the seed as a later food store. The introduction of foxes and cats has played havoc with woylie populations and even populations protected from these carnivores have mysteriously declined in recent drought years. Successful regeneration is also threatened by increasing numbers of goats on pastoral leases. Unless major human intervention occurs, the accumulating evidence points to extinction as the natural seed dispersal and regeneration cycle has been destroyed. The present age structure of the population certainly indicates an extinction trend.

Australia is no different from any other Pacific Rim country when it comes to exploitation of valuable trees. The story of over-extraction also was felt in India and was exasperated by the spread of sandalwood spike disease. The regulation of sandalwood sales from India caused a world shortage and prices ultimately doubled. To date, this shortage has been compensated for by the harvest of Osyris tenuifolia, East African sandalwood, as well as S. album from Indonesia, S. austrocaledonicum from Vanuatu and S. yasi from Fiji, but all these countries are putting conservation strategies in place.

The first thoughts of plantation forestry in Kununurra focused on firewood production. CSIRO planted two Eucalyptus camaldulensis trials at the Frank Wise Institute between 1976 and 1978. Whilst trial measurements were published, it was never followed up.

In the 1980s the concept of cultivating sandalwood was first considered and the Forest Department of Western Australia and the Australian Sandalwood Company sent a party to India to observe their sandalwood industry. From this trip, the first sandalwood seed was imported into Australia and thirty trees of sandalwood were established in Kununurra. This was followed by the planting of a series of small plots when seed could be attained. In 1988 an agreement between the Department of Conservation and Land Management (CALM formerly the Forests Department) and Department of Agriculture and Food Western Australia (DAFWA) was reached and a series of plantings looking at different host combinations were established at the Frank Wise Institute.

In this same period, Ian Richmond was awarded a Churchill Scholarship to go to India and learn more about sandalwood, especially the tissue culture systems. When he returned, he collaborated with Murdoch University to plant a series of three trials covering three different soil types, with a variety of hosts and using newly imported genetic material from India.

The concept of tropical sandalwood plantations as a solution to meet the growing demand for sandalwood wood and oil products was taking hold at this time. CALM invested in a dedicated research scientist, Andrew Radomiljac, and through his PhD studies at Murdoch University, produced the first solid research work on Santalum album in the ORIS. By the mid 1990s, promoters of a managed investment scheme to sell woodlots of S. album to investors approached CALM for technical support.

At this time negotiations for an Australian Centre for International Agricultural Research (ACIAR) project between CALM and the Forest Department in India were progressing. The collapse of this project and the loss of the research scientist from Kununurra left the research work at the Frank Wise Institute in limbo. Fortuitously, a partnership of Tanya Vernes and Pat Ryan in subsequent years established a few of the trials that were planned for the ACIAR project but the research aspect of the project began to flounder.

During this same period, the first managed investment scheme failed. This was blamed on a number of reasons including the rate of expansion in relation to system knowledge, use of the wrong hosts, and the many aspects of management that still needed to be investigated and understood for reliable tree growth and oil production.

Tropical sandalwood needs to be established successfully in a single pass. In-filling in the following seasons, a common forestry practice in the south-west, cannot be done in the tropical environment of the north due to the growth rates of hosts. Thus the key reason for the initial failure appeared to be the lack of appropriate nursery practices and the low quality of plants produced for establishment.

A number of different types of growers came onto the scene. The failed first plantings from the initial managed investment schemes (MIS) were purchased and managed for their African mahogany (which was the dominant host that suppressed tropical sandalwood). This approach created an interest in plantation African mahogany that spread across to the Northern Territory where land was cheaper than in the ORIS. This was the beginning of MIS’s in African mahogany.

Teak was another tree crop initiated in the ORIS that was adopted by managed investment scheme companies. Two trials were established in the ORIS, one by CALM at the Frank Wise Institute and the other by Elders Forestry. These were the basis of the industry which then moved across to Queensland, once again due to land prices.

New managed investment schemes for sandalwood came into the ORIS and eventually the market was dominated by Elders Forestry and Tropical Forestry Services (TFS). A number of private growers in the ORIS started growing tropical sandalwood and most of these plantations became private investment schemes. A combination of the collapse of the sugar industry, the sandalwood investment strategy and a gradual improvement of establishment systems has meant that the ORIS is now dominated by tropical sandalwood. In the single year of 2010, 4667 ha of tropical sandalwood was established.

In 2000 the Forest Products Commission (FPC) was formed from the commercial activities within CALM. The remainder of CALM was renamed the Department of Environment and Conservation (DEC). The Tropical Forestry project at Kununurra based at the Frank Wise Institute became the responsibility of FPC under Peter Jones. For a few years, the research program was subcontracted to DEC under Dr John McGrath but this changed with a review of the project by Richard Mazanec (Tree Breeder, DEC) and was transferred to Dr Liz Barbour (Seed Technologies) within FPC.

The research program on tropical forestry in FPC was to work on these issues:

• understand and capture the genetic diversity of Santalum album as it is difficult to get further accessions from other native populations

• find a non-destructive system of oil sampling that correlates with the whole tree so that genetic origins can be correlated to heartwood oil production for selection

• transfer the benefits discovered with S. album to S. spicatum

• develop a seed orchard system for out-crossed seed of the best selections captured through grafting

• develop a tissue culture system so that the best selections can be cloned and made available to the industry

• understand and record each planting/trial at the Frank Wise Institute.

1.2.2 Meeting the FPC research objectives

To meet these objectives, a number of collaborations were developed with industry, universities and federal funding bodies. This project, which started in July 2007, has provided background information for the projects numbered 4 onwards.

1. FPC-UWA: Chris Jones Honours Project (2004): ‘An accurate method for estimating the oil content and quality of Australian Grown Plantation East Indian Sandalwood, (Santalum album)’. Supervisors: A/Prof JA Plummer and A/Prof EL Ghisalberti (UWA).

2. UWA-FPC-DEC-ARC-Linkage Project (LP045191) (2005–2007): ‘Indian sandalwood: Genetic and oil diversity, and biochemistry of the Australian germplasm collection’. CIs: A/Prof JA Plummer and A/Prof EL Ghisalberti (UWA). PIs: Dr L Barbour (FPC) and Dr M Byrne (DEC). PhD: Chris Jones.

3. FPC-RIRDC No 08/138 (2007–2008): ‘Analysis of plant-host relationships in tropical sandalwood (Santalum album)’ (see Barbour, 2008).

4. UWA-FPC-UBC-ARC Linkage Project (LP0882690) (2007-2011): ‘Elucidation of genetic and physiological factors controlling sesquiterpenoid biosynthesis in Sandalwood, Santalum sp.’. CIs: A/Prof JA Plummer and A/Prof EL Ghisalberti (UWA). PIs: Dr L Barbour (FPC) and A/Prof J Bohlmann (UBC). Post Doc: Dr Chris Jones. PhD: Jessie Moniodis.

5. FPC-RIRDC No 10/179 (2008–2009): ‘Heartwood rot identification and impact in Sandalwood (Santalum album)’. (see Barbour et al. 2010).

6. UWA-RIRDC PRJ0068221 (2011): Workshop hosted by UWA ‘Sandalwood oil: genetic solutions developed to improve quantity and quality’ (see Plummer et al. 2011).

7. FPC-MU-Elders Forestry-RIRDC PRJ-4786 (2010–2013): ‘Tropical sandalwood silviculture management to minimise fungal attack’.

8. UWA-FPC-UBC-MU-Elders Forestry-ARC Linkage Project (LP100200016) (2011-2014): ‘Molecular characterisation of the fungal disease response in tropical sandalwood (Santalum album)’. CIs: A/Prof JA Plummer, A/Prof EL Ghisalberti, Dr L Barbour (UWA), Dr T Burgess (MU). PIs: G. Butcher (FPC) and A/Prof J Bohlmann (UBC). Post Doc: Kesserin Tungngoen, PhD.

9. UWA-FPC: Ni Luh Arpiwi PhD ‘Optimising Millettia pinnata seed production’. Supervisors: A/Prof JA Plummer, A/Prof G Yan and Dr L Barbour (UWA).

Other researchers involved:

• Dr Katherine Zulak (UBC), to investigate oil synthesis in S. austrocaledonicum, a sandalwood species from Vanuatu

• Dr Margaret Byrne (DEC) with Dr Melissa Millar, to develop microsatellites for DNA analysis

• Dr Liz Watkin (Curtin University), to screen and identify superior soil rhizobia for host nitrogen fixation.

Research outcomes

Below is a short discussion of the research outcomes for each of the objectives listed above. At times the outcomes didn’t follow the expected paths.

Understand and capture genetic diversity of Santalum album as it is difficult to get further accessions from other native populations

The genetic diversity of Santalum album was initially assessed using a reliable restriction fragment length polymorphism method (Jones et al. 2009). Surprisingly low levels of genetic diversity were present among the trees established at the Frank Wise Institute and the CALM arboretum. Reassuringly, the Timor-sourced sandalwood trees were distinct from the Indian-sourced trees, and exhibited a more ancestral genotype, indicating that the prehistoric source of S. album was indeed Timor. Thus, the common name ‘tropical sandalwood’, and not ‘Indian sandalwood’ is being used in this report. It was also noted that there were many trees within the plantings that were very closely related and genetically indistinguishable from each other.

The entire sandalwood genus appears to have originated in Australia (Harbaugh and Baldwin 2007; Jones et al. 2009). Santalum spicatum is one of the most ancestral species of the genus. Its confinement to the south-west of Western Australia is likely due to climatic cycling through the Pleistocene. Sandalwood isolated to the north became a melting pot of sandalwood diversification. Speciation is thought to have occurred through long-range dispersals to the Pacific and a small founder population north to Timor. Limited initial genetic diversity, a propensity to asexually propagate and a high occurrence of self-pollination are likely to be the main reasons for such low diversity. Most probably, humans transported S. album from Timor to India. Perhaps it was also this human selection pressure that has made the genetic diversity of S. album so narrow, with its static oil profile and high santalol content (Jones et al. 2006; Jones et al. 2007). In comparison, most other sandalwood species, including S. spicatum (Byrne et al. 2003), have greater genetic diversity and wide-ranging oil profiles, often accumulating less-favoured sesquiterpenes for commercialisation.

This information showed ORIS industry members that they needed to know the diversity of their tropical sandalwood plantings. This was for a number of reasons: (i) for the establishment of seed orchards (to maximise out-crossing); (ii) to understand the make-up of present plantations for disease susceptibility/resistance; (iii) for future security against disease and pest resistance; and (iv) for future product development (alternate genes) and for other products (for example, bark, seed pulp or kernels).

An alternate DNA technology for assessing genetic diversity using simple sequence repeats, or microsatellites was developed (Millar et al. 2011). This provided a service to industry and allowed the flexibility of adding further different selections into the FPC study. The microsatellite method permitted a few selections at a time to be added to the knowledge pool. This second screening showed somewhat higher diversity within the population, but compared to other tree species the diversity remains remarkably low.

Find a non-destructive system of oil sampling that correlates with the whole tree so that genetic origins can be correlated to heartwood oil production for selection

To select for high sandalwood-oil producing trees, a system of non-destructive sampling was required. The system needed to be relatively quick and inexpensive and also give a high correlation to whole- tree oil assessment. A system that had been developed for eucalypts to correlate density and pulp yield (Downes et al. 1997) was employed and involved extracting cores at breast-height diameter from the tree bole using a chainsaw-driven drill (see Plate 1.2).

Plate 1.2 Drilling a core from a sandalwood tree

Twenty-two 10-year-old sandalwood trees were used in this study; all were cored at 30 and 100 cm above the ground but only 10 trees destructively harvested. The oil quantity results were so diverse that no strong relationship between cored sub-samples and whole-tree oil content could be found (Jones et al. 2007). The oil profiles from these trees were surprisingly stable but, at this stage, this information could not be correlated to genetic diversity. It was further observed that a number of trees had no sign of heartwood production and related oil production. All trees selected were similar in external appearance and hence the quest to understand why there was this large variation in oil production (Jones et al. 2007).

Extending the oil sampling from different trees across a known genetic diversity, it was realised that S. album was producing the main sesquiterpene constituents in precisely the same proportions. Co- occurrence patterns indicated that several groups of sesquiterpenes might be synthesised by the same enzyme. Santalenes and santalols are the most valuable components of the sesquiterpene oils produced by S. album, and from this analysis a pathway for their biosynthesis was hypothesised and published in a key paper (Jones et al. 2006). Put simply, the biosynthetic pathway has two main steps: the conversion of farnesyl diphosphate into santalenes by santalene synthase; and the conversion of the santalenes to santalols by cytochrome P450 oxidase.

A bisabolene synthase and a germacrene D-4-ol synthase were the first terpene synthase genes from sandalwood to be cloned and biochemically characterised (Jones et al. 2008). As hypothesised earlier (Jones et al. 2006), the enzymes were multifunctional and produced mixtures of sesquiterpenes in unique, but consistent proportions. To further this path of gene discovery, a cDNA library from the RNA of an oil-producing sandalwood tree in the FPC plantings was made and this was comprehensively sequenced using conventional and massively parallel technologies. From this library, candidate genes in the oil biosynthetic pathway were selected, expressed and tested. On 1 April 2010, the santalene synthase from S. album was isolated and shown to convert the universal sesquiterpene precursor, farnesyl diphosphate into the three santalenes and bergamotene in exactly the same proportions as predicted (Jones et al. 2006).

Plate 1.2 Drilling a core from a sandalwood tree

A provisional patent was lodged for the santalene synthase gene and along with the kinetic parameters of the recombinant enzyme in the three main sandalwood species, S. album, S. spicatum and S. austrocaledonicum. Firmenich SA was first to patent the S. album santalene synthase (WO 2010/067309 A I (FIRMENICH SA)). Jones et al. (2011) showed that by exploring multiple species, the unique, highly conserved nature of santalene synthase in the genus can be recognised; and this has many evolutionary ramifications. The enzyme is a sequence of amino acids and less than 2 per cent of this amino acid sequence differs between the enzymes of the most advanced and the enzymes of the most ancestral of sandalwood species.

The conversion of santalenes to santalols can be done chemically but with poor efficiency. The ideal would to be to identify and isolate the cytochrome P450 oxidase gene, which is responsible for the conversion of santalenes to santalols.

These gene discoveries open doors to new technologies which enable the in vivo production of sandalwood oil in engineered microorganisms. Due of the shortage of sandalwood oil, some of the world’s largest fragrance and flavour companies have been searching for chemically synthesised compounds with similar organoleptic properties to those of the authentic oil. A number of synthesised compounds have been introduced to the market and they occupy a new niche of single, pure compounds that can be accurately included into a formula for reliable product repeatability.

The biosynthetic production of sesquiterpenes (santalenes and santalols) using the sandalwood genes in yeast constructs produces exactly the same sesquiterpenes as produced in sandalwood heartwood. Individually, these compounds are not dissimilar from the natural sesquiterpenes. The singular difference between biosynthetic sesquiterpenes and natural sandalwood oil is the overall composition. Natural sandalwood oil may contain up to 100 different components and, as a result, biosynthetic sesquiterpenes and natural sandalwood oil will occupy different markets.

Convert the benefits discovered with S. album to S. spicatum

The quality difference between S. album and S. spicatum is the frequent presence of the oil component farnesol in the latter species (see Figure 1.2). Analyses indicate that when levels of farnesol are high, santalols are typically low (Moniodis,pers. comm.). Farnesol is regarded as an irritant and thus S. spicatum oil does not make the ISO standard and cannot be mixed into products above a certain proportion. Farnesol separation from the essential oil is an expensive and inefficient process so selection and breeding may be a solution to select for oil profiles with low farnesol in S. spicatum.

50 45 S.spicatum 40 S.album 35 30 25 20 15

Composition (%) Composition 10 5 0

dendrolasin beta-santalol cis-lanceol * trans-nerolidol alpha-santalol alpha-santalene beta-santalene epi-beta-santalol missing oil comp epi-beta-santalene epi-alpha-bisabolol trans-beta-farnesene trans,trans-farnesol alpha-trans-bergamotene cis-beta-curcumen-12-ol cis-alpha-trans-bergamotol

cis-nuciferol, cis-gamma-curcumen-...

Figure 1.2 Typical sandalwood oil profile of Santalum album and Santalum spicatum

Develop a seed-orchard system for out-crossed seed of the best selections captured through grafting

To establish an S. album breeding population to enable deployment of seed orchards, the genetic diversity of the species needed to be understood. Because of poor accession records, DNA technologies were relied upon to unravel the relatedness of selections.

Two progeny trials had been established at the Frank Wise Institute. The first trial, established in 1996, captured a diverse range of S. album material which included selections from the Indian Forestry seed orchards (from their breeding program), selections of plus-trees from the Frank Wise Institute, Northern Territory trees and some selections from Timor. Whilst rigorously designed, the trial had no buffer and the host combination did not remain constant. The one common host, African mahogany has suppressed the sandalwood growth as well as other host trees and this trial is now lost.

The second trial, established in 2004, was from plus-tree selections from the Frank Wise Institute. The long-term host, Cathormium umbellatum, was planted over a 2-year period and it was also used as the buffer row. Initial sandalwood growth was exceptional and it was realised that the nursery technique used in Perth (of growing the seedlings in an organic medium, mainly composted bark, and using water that was of near neutral pH) enabled the seedlings to grow to a stem thickness not observed in Kununurra nurseries. Sandalwood growth was excellent until the Sesbania formosa started to die and adjacent sandalwood appeared stressed, aborting their leaves. A theory mooted was Sesbania may become allelopathic and kill surrounding trees as it dies to ensure seed propagation success. The removal of the Sesbania that were within the same row as the sandalwood forced the sandalwood trees into host-shock and it took 3 years before the sandalwood recovered through the eventual connection with the long-term host.

Clonal capture of mature selections was successfully achieved using the mango-grafting technique. This grafting method used scion material about 10 cm long with all the leaves removed. Success was attained when the stem was green to woody and the diameter matched that of the rootstock for cambium fusion. The cleft join was bound with grafting tape and the scion covered with a plastic bag left open at the base to ensure appropriate humidity. Once the shoots extended from the lateral buds, the plastic bag was removed. The removal of this bag had to occur in a high humidity environment or the young leaves had to be sprayed with an anti-transpirant to prevent leaf desiccation and abortion.

Enough grafts were successful to start establishing an archive and an area was cleared to extend this planting as more selections were captured. The industry also became successful in genetic capture using grafting and extensive seed production areas have been established.

Develop a tissue culture system so that the best selections can be cloned and made available to the industry

Tropical sandalwood has two aspects that favour tissue culture success: the seedling price is high and the species lends itself to somatic embryogenesis. Whilst the understanding of the regulation of the biosynthetic pathway for santalol is unraveling, the concept of cloning genotypes that have superior performance in ORIS conditions is attractive.

FPC did not have the facilities to undertake tissue culture on a commercial basis. However, it was able to capture material in sterile cultures and hence relationships were developed with The Tree Lab (New Zealand) and NIPPON Paper (Collie, Western Australia) to explore the commercial tissue culture option (see Plates 1.3 and 1.4). Both companies came to the conclusion that only S. album material sourced from seed (juvenile) could be propagated through to rooting. Clones initiated, either through micropropagation or somatic embryogenesis, from mature tissues could not be rooted reliably. So whilst initiation, multiplication and shoot production are well-developed, the final stage of rooting remains a challenge.

Plate 1.3 Santalum album tissue cultured shoots from juvenile tissue (The Tree Lab)

A clonal trial was established with the clonal material produced by Nippon Paper which will be of value in future years.

Plate 1.4 Santalum album clonal plants used in the trial established in the ORIS (Nippon Paper)

Clones could be initiated from seedling material and the callus material cryo-preserved whilst the clones are being field-tested, as is the case with Pinus radiata. This would provide an opportunity to mass produce high-performing clonal lines for the ORIS.

Understand and record each planting/trial at the Frank Wise Institute

This RIRDC project and Barbour (2008) began the recording of each of the trials/plantings that were established in the ORIS over the last 20 years. Management of the Frank Wise Institute Tropical

Forestry project has been transferred between three different organisations and locations, and unfortunately many of the records were misplaced. The first challenge for this research objective was to review the information available so that a history of each trial could be collated.

The trials are split into two broad types: general silviculture trials and genetic conservation trials. The trials presented in this report are the silviculture trials, which are either monoculture trials of different species or combination trials to understand and optimise the sandalwood–host relationships.

1.3 Sandalwood as a crop

1.3.1 The hemi-parasitic nature of sandalwood

Tropical sandalwood (Santalum album) is a small tropical tree from the Santalaceae family. The species occurs from India through to the South Pacific and to the northern coast of Australia. These evergreen trees reach a height of between 4 and 10 m and can live for 100 years. They can flower from the first year producing very small, blood-red flowers that attract a variety of pollinators such as bees, flies and butterflies. Once pollinated, flowers produce a berry which attracts and is eaten by birds or alternatively falls to the ground. The berry pulp inhibits germination and so must rot off, be consumed by a bird, or be abrasively removed by soil or manually before the seed can germinate within accumulated mulch.

The ability of sandalwood trees to re-sprout from roots left in the ground after a tree has been removed may contribute to the observed lack of genetic diversity. The thicket of sprouts eventually thins to two or three trees which, if there are enough hosts nearby, successfully continue their growth through to mature trees. An out-crossing study with S. spicatum indicated that this species preferentially out-crosses (Muir et al. 2004) but if there was no choice, as in a case where clonal material dominates, inbreeding would be the only reproductive strategy available.

With this reproductive plasticity, the need for sandalwood to be a hemi-parasite is a prominent question. The definition of a hemi-parasitic tree implies that sandalwood is photosynthetic but that additional water, mineral nutrients and organic substances are acquired via the host plant (Radomiljac et al. 1998c, Radomiljac et al. 1999b). It does this by parasitising other trees by connecting with their roots by means of haustoria from its own roots. So aggressive is sandalwood in finding hosts to connect with that within 30 days from germination 70 per cent of seedlings have generated haustoria (Nagavai and Srimathi 1985).

There are a number of common factors that determine the distribution of tropical sandalwood. One of these relates to the ability of trees to adapt to alkaline soils. The Cununurra clays are alkaline and this is also common to Timor soils and the red soils of India where sandalwood is dominant. A high pH affects nutrient availability, making some micro-nutrients inaccessible to plants. The red soils in India have high iron levels but lack nitrogen, phosphorous and potassium. The ORIS soil is poor in nitrogen and phosphorous and the micro-nutrients iron, copper and zinc are present only in marginal concentrations. Soil composition and variation in tolerance of the host species will affect what is made available to sandalwood and hence it is not surprising that a range of nutrients have been found to be supplied by a variety of hosts to sandalwood: calcium and iron (Sreenivasan Rao 1933); nitrogen and phosphate (Iyengar 1960): and potassium, phosphate and magnesium (Rangaswamy et al. 1986).

The classic definition of a hemi-parasite neglects to acknowledge the structural benefits hosts can provide. In the harsh climates of the Kimberley, India and Timor, being amongst other trees that provide sun, wind and grazing protection would certainly be a survival advantage. The need for sun protection on the juvenile sandalwood stem is a key factor highlighted in Barbour et al. (2010). When bark is damaged via sun-scorch, it provides a heartwood rot entry point that sandalwood has difficulty in defending. A balance between protection of the tree bole from the sun and access to sunlight for

photosynthesis is required for optimum sandalwood growth and survival (Barbour 2008). The compatibility of the host structure in relation to sandalwood growth is a key factor contributing to the success of the hemi-parasitic relationship. If sandalwood is grown with a host that dominates this spatial balance preventing photosynthesis, either an intervention is needed (pruning or culling of the host) or the sandalwood will cease growing and eventually die. The concept of defining this relationship is a dominant theme throughout this report.

The silviculture system devised in the ORIS utilises three hosts: a pot host, a short-term host and a long-term host. The first, the pot host, is a prostrate herbaceous plant introduced to the container- grown sandalwood 1 month prior to field planting. Early research (Barbour and Broadbent, pers. comm.) showed that the success of this pot host is proportionally based to its vigour. The vigour of the most popular pot host, Alternanthera nana, needs to be balanced with the timing of its introduction into the pot so that it does not over-grow and suppress the sandalwood seedling (Radomiljac 1998; Radomiljac and McComb 1998a; Radomiljac et al. 1998a). If Alternanthera is introduced too early and dominates the sandalwood seedling, expensive manual pruning has to occur.

The short-term host enables rapid sandalwood growth, and hosts selected to date die 2–4 years after establishment leaving the long-term host to grow and support the sandalwood over its production life. In the ORIS, the most successful short-term hosts have been legumes that fix nitrogen and with the ORIS soils lacking nitrogen this should be expected. Radomiljac et al. (1998c) demonstrated the successful translocation of nitrogenous compounds between host and sandalwood.

Short and long-term hosts are planted at the same time as the sandalwood, with plantation establishment usually occurring in May–June, or at least before summer temperatures escalate. The growth rate of the short-term host demands a one-pass establishment with no in-filling.

Similar to the pot host, short-term host success is related to its vigour. Two host species have dominated ORIS plantings, Acacia trachycarpa and Sesbania formosa. Both species are native to the region and are short-lived legumes. Sesbania formosa is the species that now prevails for a number of reasons: it is the more vigorous, it is a prolific seeder and it is easy to propagate in the nursery system in Kununurra. The downside is that, due to its vigour, its introduction has suppressed the growth of some secondary hosts. Cathormion umbellatum is notable example of this. In the first trials in the ORIS which used Acacia trachycarpa as the short-term host, the growth of both sandalwood and secondary-host Cathormion was magnificent. Later trials that used Sesbania with Cathormium were not as successful; the fast-overshadowing, vertical growth of Sesbania suppressed Cathormion growth and hence the Cathormion was not of sufficient size to support the sandalwood when the Sesbania died. The initial response to maintaining the use of Sesbania as a short-term host and Cathormion as the long-term host was to prune Sesbania. Due to the extent of the sandalwood plantations, mechanical vertical and horizontal pruning occurred which appeared to extend the life of the tree; but a build up of fungal disease over time increased Sesbania death, and this practice has since been discontinued.

The long-term host trials require a full-rotation for the relationship between host and sandalwood to be assessed. This was highlighted in Barbour (2008) and the discussion will continue with further trials being assessed in this report.

Present knowledge highlights that the success of a host–sandalwood relationship starts with the soil. It is the interaction between host and soil that determines what is passed from host to sandalwood in terms of water and nutrients, and in the case of the ORIS, nitrogen. The sandalwood itself needs to photosynthesise but this demand is complicated by the need for sun protection of the bark, as the bark is the critical pest and disease barrier for the tree. The analysis of these trials will show how these relationships unravel and their influence on sandalwood growth and ultimately on heartwood oil production.

1.3.2 Adding value to the long-term host

Many of the trials at the Frank Wise Institute were established to identify and develop a valuable secondary host. The hypothesis was that if additional worth could be attained from the secondary host, the productivity and profitability of the plantation would be greatly increased or hedged when sandalwood prices fluctuate.

Long-term host species selection was based upon a high-value sawlog product. The ORIS’s unusual soils, temperatures and flood irrigation meant that the selection process needed to start with species that had both potential economic value and good survival under these conditions. The classic forestry approach is to establish provenance trials of each species and then when species and superior provenances were identified, initiate a breeding program. This has certainly been true of the successful plantation species across Australia (Pinus pinaster, P. radiata, Eucalyptus globulus, E. nitens and the RIRDC-funded Australian Low Rainfall Tree Improvement Group). Poor accession records did not allow this methodical process in the ORIS. Two species, African mahogany and teak, were identified early in their plantation cycle; both survived the harsh conditions and showed exemplary initial growth that was recognised as being worthy of further development.

The inclusion of African mahogany and teak in sandalwood plantations as secondary hosts was a disaster. African mahogany clearly suppressed sandalwood growth (Barbour, 2008) and was the main cause of the collapse of the first managed investment scheme. Teak was used by Elders Forestry and when its negative impact was realised, the trees were removed from sandalwood plantations. Fast- growing, dominant sawlog species appear to be unsuitable long-term hosts in a sandalwood plantation system.

Silviculture management of a sawlog species in a multi-species plantation would have to be developed. Silviculture regimes in a monoculture plantation are severe and include a cull of approximately 6:1 selection pressure. This enables the use of lower-level genetics compared to when plantations are established for final stocking. In a multi-species plantation, the risk of damage to the sandalwood if the host species was thinned would be high. This suggests that for a reasonable return from a sawlog species within a sandalwood plantation system, a clonal system should be considered.

Plate 1.5 Testing the concept of Millettia pinnata hedges by directly sowing the seed.

Another option is that secondary hosts do not have to be tall, solid trees. The introduction of pongamia (Millettia pinnata), the biodiesel tree, has opened a new way of thinking (see Plate 1.5). This species was identified as a successful host of sandalwood (Barbour 2008). A hedge of pongamia producing easy-to-harvest seed pods may be just as effective as a secondary host for sandalwood as uniformly spaced trees.

Sandalwood is in focus at present but the woody biomass that will need to be removed from the site at harvest may have value as a quite different product than the first envisaged sawlog. With wood chemistry reaching new levels that crosses boundaries into food and fibre products, this may well become the high-value secondary product that cements trees again as a new frontier industry in Australia.

1.3.3 Tropical sandalwood plantations after 15-years growth

The most pertinent question for the developing tropical forestry industry in the ORIS is the quantity and quality of trees in sandalwood plantations when they are 15 years old. There are not many examples of trees this old in the ORIS, and those plantings that are this age were undertaken with quite different silviculture systems than what the valley is presently experimenting with. Nevertheless, knowing how much sandalwood and other biomass produced from each hectare in the ORIS will help with planning.

The standard layout of sandalwood plantations in the ORIS is with rows 3.6 m wide and this is due to an historic development from agriculture and the flood and drain system. Normally sandalwood is planted 3 m apart down every second row with a Sesbania planted between the sandalwood. Thus sandalwood is planted at approximately 460 stems per hectare (SPH). The secondary host is planted in the alternate row and normally 6 m apart. In some cases two sandalwood rows are planted at 1.8 apart with only one secondary host row (see Plate 1.6). A present overview of the ORIS would show many computations of these planting models. Understanding the trials in this report may identify the final parameters of sandalwood and its possible hosts in the establishment of a hectare of plantation in the ORIS.

Plate 1.6 One lay-out for flood-irrigated sandalwood plantation establishment. Mounds are formed every 1.8 m but only the second row planted.

2 Objectives

The project involves the measurement and analysis of 16 trial plots (Appendix A) at the Frank Wise Institute, in the Ord River Irrigation Area near Kununurra, Western Australia. The over-arching objectives were to provide information and outcomes for the following:

• sandalwood (Santalum album) growth rates, heartwood and oil production and product definition

• African mahogany (Khaya senegalensis) growth rates

• teak (Tectona grandis) growth rates

• pongamia (Millettia pinnata) growth rates, seed production and seed oil quality

• identification of other tropical species that could either be used as a long-term host for sandalwood or as a tropical timber project for the north.

3 Methodology

There are two main groups of trials, those concerned with sandalwood and its hosts (Chapter 4), and those related to high-value timber species (Chapter 5). Where possible, statistical analyses were completed using the original design elements of the trials, however, where trials were of a demonstrational nature or no longer conformed to the original design due to high mortality, only comparisons of descriptive results have been made. In addition to trial measurements, destructive harvesting of sandalwood was undertaken, and two non-invasive techniques were evaluated for their potential use in determining aromatic wood.

During project planning, the only methods to be used were basic tree allometry together with tree coring to non-destructively assess heartwood formation and oil quantity and quality. Minimal destructive harvest was to occur so that trials could be preserved.

Basic growth analysis indicted that competition relationships occurred between the trees; and competition indices, a statistical technique never before used on hemi-parasites, was explored for greater spatial understanding.

Furthermore, the FPC’s need to remove some plantings provided the opportunity for greater destructive harvesting than was initially planned. Destructive harvests of 8-year-old and 15-year-old sandalwood was completed and revealed the presence of a fungal heartwood rot. This became a separate study published by RIRDC (Barbour et al. 2010). Understanding that this heartwood rot was mainly caused through the breaking of the bark (as would occur with coring), the coring aspect of the project was stopped. Alternate methods of non-destructive assessment of heartwood oil were then explored. This introduced experimenting with acoustic time-of-flight measurement as well as electrical impedance to detect heartwood and heartwood rot formation.

As fungal infection changed the internal heartwood core profile from circular to a multitude of shapes, a photographic system was developed to estimate heartwood production.

All sandalwood oil analyses were done with a hexane extraction and assessed using gas chromatography methodologies.

3.1 General methods and formula

A number of standard measurements and calculations were used in the assessment and analysis of sandalwood and high-value timber trials and these are explained below.

• basal diameter (BD): the diameter at the base of the stem, approximately 10 cm from ground level

• basal area: the cross-sectional area at the base of the stem, calculated from basal diameter as:

Basal area (m2) = π x (BD/200)2

• diameter at breast height (DBH): the diameter of the stem, over bark, measured at 1.3 metres. Where more than one stem was present a combined DBH was calculated using the following formula:

2 2 2 Combined DBH = ∑(DBH1 + DBH2 + DBHi )

• crown break diameter (CBD): the diameter of the stem where it separated into multiple branches. Where there were multiple stems from the base of the tree, CBD was equal to basal diameter

• bole length: the length (or height) of the stem from ground level to where it separated into multiple branches

• tree height: height of tree from ground to highest visible leader or branch, measured with either a height pole or Vertex III (Haglöf, Sweden)

• bole volume: unless otherwise specified, bole volume was calculated using Smalian’s formula, using a basal radius (BR) and crown break radius (CBR) taken from the respective diameter measurements:

Bole volume = (π BR2 + π CBR2) x bole length 2

Estimated stem volume (ESV) differed for high-value timber species and sandalwood:

• unless otherwise stated, high-value timber (HVT) volume was estimated using a single conical volume calculation:

HVT ESV (m3) = π (DBH/200)2 x tree height 3

• unless otherwise stated, sandalwood volume was estimated as the sum of bole volume and the above bole conical volume to the top of the tree:

Sandal ESV (m3) = bole vol + (π (CBD/200)2 x (tree height-bole length)) 3

3.2 Main species

3.2.1 Primary hosts

Acacia trachycarpa E.Pritz. Fabacaea subfamily Mimosoideae: Known as Sweet-scented Minnieritchie, the species is an arid-to-tropical Australian shrub or small tree ideal for planting in frost-free regions. It grows in neutral to alkaline soils in 120–400 mm rainfall zones but in the drier parts of its distribution it becomes riverine, growing in dry creeks. The tree can reach 15 m in height with a spreading crown of up to 10 m in diameter. The trunk has a curling, ‘minni ritchi’ bark texture with a pine scent which is unique and interesting for an arid tree. The leaf is made up of soft, pine- needle-like, narrow phyllodes, 12–50 mm long. It produces yellow, rod-shaped flowers in spring. It propagates by seed and its coppicing is assumed weak.

Sesbania formosa (F.Muell.) N.T.Burb.: Very-fast-growing, a native Western Australian tree that is distributed from Karratha up north to Broome and across to Halls Creek. The tree is 2.5–13 metres tall with white to cream pea-shaped flowers which appear between May to September. It is commonly known as the White Dragon Tree with pale-grey bark which is furrowed and corky. The leaves are pinnate 15–40 cm long with 5–20 or more pairs of leaflets. The trees can grow in a variety of environments. The species tolerates saline and waterlogged conditions. They are short-lived, lasting from between 3 and 5 years.

3.2.2 Secondary hosts or timber species

Cathormium umbellatum (Vahl.). Fabaceae subfamily Mimosoideae: A native species distributed in the most northern areas of Western Australia around Kununurra through to the Northern Territory. The species grows in alluvial soils, wet river sites, mangroves, dune swales, sandstone screes and rainforest and is described as a tree or shrub 3–24 m high. Leaves are bipinnate with opposite leaflets. The tree produces cream flowers between September and October, which develop into a pod with one seed.

Cedrela odorata L. Meliaceae: Known as Cedro Hembra or Spanish, Mexican or Cigar-box cedar, the species is one of the world’s most important timber species and occurs naturally from the Mexican Pacific coast, through Central America and the West Indies to its southern limit in Argentina. The species prefers well-drained soils, occasionally limestone and is able to tolerate a long dry season. It does not flourish in areas of rainfall greater than 3000 mm or on sites with water-logged soils. The species is a monoecious, semi-deciduous tree ranging in height from 10 to 30 m with pinnate compound leaves grouped towards the end of the branches.

Dalbergia latifolia Roxb. Fabaceae subfamily Faboideae: Dalbergia is a large genus of approximately 500 species from small to medium-sized trees, shrubs and lianas with a wide distribution. It is native to the tropical regions of Central and South America, Africa, Madagascar and southern Asia. Dalbergia latifolia is known as (East) Indian rosewood or sonokeling and can be found in India, Nepal and Malaysia. Naturally, the species can receive a rainfall between 750 and 5000 mm and survive maximum temperatures of 37–50°C. The species grows best on deep loams or clays containing lime; poor drainage causes stunting of tree growth. The tree is predominantly a single- stemmed deciduous tree with a dome-shaped crown of lush, green foliage. The bark is grey, thin with irregular short cracks, and it has a root system that will produce suckers when near the surface. The trees can reach a height of 20–40 m and a girth of 1.5–2 m.

Khaya senagalensis Meliaceae: Khaya is a genus of seven species of trees in the mahogany family Meliaceae, native to tropical Africa and Madagascar. K. senegalensis is known as the Dry Zone Mahogany and is distributed from the Congo across to Senegal. A deciduous tree, usually 15–20 m tall with a diameter up to 1.5 m, it can have 8–16 m of clean bole and often is buttressed at the base.

The leaves are pinnate, with 4–6 pairs of leaflets and the terminal leaflet absent; each leaflet is 10–15 cm long and is abruptly rounded toward the apex but often with an acuminate tip. The flowers are produced in loose inflorescences, each flower small, with four or five yellowish petals and ten stamens. The fruit is a globose four or five-valved capsule 50–80 mm diameter, containing numerous winged seeds.

Pongamia pinnata (L.). Fabaceae (recently renamed Millettia pinnata): Indian Beech is an Indo- Malaysian species common on alluvial and coastal situations to 1200 m altitude from India to Fiji. The species can withstand temperatures from slightly below 0°C to as high as 50°C and an annual rainfall of 500–2500 mm. The tree grows wild on sandy and rocky soils including oolitic limestone, but will grow in most soil types even with its roots in salt water.

The tree is described as a fast-growing deciduous tree up to 25 m tall. The trunk can reach 60 cm in diameter with smooth grey bark. Leaves are imparipinnate, with young leaves showing a pinkish-red tinge which matures into a glossy, deep green and grouped into 5–9 leaflets with the terminal leaf larger than the others. Flowers are fragrant, white to pinkish, paired along a rachis in axillary, pendent, long racemes of panicles reminiscent of wisteria. The pod is stalked, oblique-oblong, flat, smooth, thickly leathery to sub-woody, indehiscent with one reinform seed per pod.

The wood is yellowish-white, coarse, hard and beautifully grained but is not durable; limiting its use to cabinet-making and fuel. The wood has a calorific value of 4600 kcal per kg. The tree has been used extensively in folk medicine with both the oil and residues being toxic; containing a high level of alkaloids. The seed contains pongam oil, a bitter red-brown, thick, non-drying oil which lends itself for use in the leather tanning process, in soap, as a linament for treatment for scabes, herpes and rheumatism and as an illuminating oil. Recently it has been recognised for its bio-diesel potential. Trees reach seed bearing at the age of 4–7 years with a single tree able to yield between 9 to 90 kg seed per tree of which approximately 25 per cent of this weight is pongam oil.

Pterocarpus indicus (Willd.). Fabacaea: This species comes from the western limit of southern Burma, extending eastwards through to Solomon Islands and can tolerate an annual precipitation of 960–2180 mm and a pH range of 4.0–7.5. It is able to tolerate water-logging but cannot tolerate shallow soils and stiff clays.

The tree is a large deciduous tree, 30 m or more high with large and high buttresses. Leaves are 12–22 cm long in all with 5–13 leaflets and greyish brown to green in colour. Seeds are winged with the seed-bearing part covered by a woody protection. The seed is dark brown and smooth in appearance and ripens within 4–6 months. The wood harvested from these trees is regarded as one of the best furniture timbers; it has a density of 625 kg per m3 and can be air-dried with no difficulty.

Tectona grandis. This is one of the three species in the genus Tectona. The other two species, T. hamiltoniana and T. philippinensis, are endemics with relatively small native distributions in Myanmar and the Philippines respectively. Tectona grandis is native to India, Indonesia, Malaysia, Myanmar, northern Thailand, and northwestern Laos but is naturalised and cultivated in many countries, including those in Africa and the Caribbean. Tectona grandis is a large, deciduous tree that is dominant in mixed-hardwood forests. It has small, fragrant, white flowers and papery leaves that are often hairy on the lower surface.

4 Sandalwood (Santalum album) trials

4.1 Sandalwood host selection demonstration plots

The trials detailed below are those that did not have experimental designs. It is possible that these trials formed part of plantation-establishment research or were done for other experimental purposes, but there were no adequate extant records to indicate objectives. These trials provided an established resource to examine the growth of sandalwood up to 18 years of age in combination with various host species and different planting patterns. Given the close proximity of all trials within the Frank Wise Institute, the soil type and climate experienced by each trial was largely similar, and it is likely the irrigation regime did not differ considerably across trials. It is suggested that indirect comparisons of growth results across trials could be made with some confidence regarding the utility of particular host species or planting designs.

4.1.1 Sandalwood aged 11 years (1997), Trial 5

Method

Trial description

The trial was established to demonstrate sandalwood growth in a multi-species plantation with high- value timber hosts. Host species used were Khaya senegalensis, Cathormion umbellatum, Swietenia mahogani and Cassia siamea. A total of 15 rows were planted in an area of 0.89 ha, with the planting design used shown in Figure 4.1. The middle row of each 3-row group was a host-only row where species were planted in the same repeated order along the length of each row. This planting was not established with a short-term host species and instead Cathormion was planted within the sandalwood rows. Initial stocking was equivalent to 470 sandalwood stems per hectare, 480 Cathormion, 150 Khaya, 125 Swietenia and 235 Cassia with a total of 1460 SPH. The sandalwood-to-host ratio at establishment was approximately 1:2.

Measurement

In 2001 records were found where only the BD, DBH and height of only the sandalwood were measured. In 2008 when the trees were 11 years old, measurements included both sandalwood and hosts, with BD, DBH, bole height, CBD and tree height recorded.

Results

Between 5 and 11 years from planting, 15 sandalwood plants died, reducing survival from 79 to 75 per cent or 352 SPH. The total number of host and sandalwood stems surviving at 11 years was equivalent to 806 SPH, or 55 per cent of the original planted trees. The ratio of sandalwood to host at 11 years of age had changed to 1: 1.3.

Rows 18 S SWE S Guard S SWE S Guard S SWE S 15 C CAS C C CAS C C CAS C 12 S K S S K S S K S 9 C CAS C C CAS C C CAS C 6 S SWE S S SWE S S SWE S 3 C K C C K C C K C 0 1 2 3 4 5 6 4 5 6 Meters 0 1.8 3.6 5.4 7.2 9 10.8 12.6 14.4 16.2 18

Figure 4.1 Trial 5 layout showing within and between row spacing (distance across plot from corner) for sandalwood and hosts. C = Cathormion, K = Khaya, SWE = Swietenia, CAS = Cassia, S = sandalwood, and guard rows were vacant.

At 5 years of age this sandalwood had a BD of 6.1 ± 1.8 cm, DBH of 3.6 ± 1.3 cm and trees were 4.2 m tall. Mean growth parameters (Table 1.1) indicated that sandalwood growth rates up to 11 years of age were low. The average basal diameter of sandalwood increased by 2.8 cm, a rate of less than 0.5 cm per year between age 5 years and 11 years. The stem basal area occupied by all species on the site was equivalent to 26.9 m2 per hectare, of which 8 per cent was attributed to sandalwood. Khaya was the dominant species on the site and contributed 53 per cent of total stem basal area and 69 per cent of the total estimated stem wood production for the site, despite only accounting for 10 per cent of stems initially established.

The largest parameters recorded for an individual sandalwood plant at 11 years of age were 20.6 cm for basal diameter, 12.9 cm for DBH, 5.5 m bole height, 9.5 m tree height and maximum calculated bole and estimated stem volumes for individual trees were 0.050 m3 and 0.079 m3 respectively.

Table 4.1 Growth parameters of sandalwood and hosts in Trial 5 when they were 11 years old (mean ± s.d.) Santalum Cathormion Cassia Khaya Swietenia Parameter album umbellatum siamea senegalensis mahogani No. observations 314 71 111 130 91 Survival (%) 75.1 16.5 52.9 96.3 82.7 Basal diameter (cm) 8.9 ± 3.1 7.1 ± 3.3 26.1 ± 6.2 35.4 ± 5.6 9.8 ± 3.0 DBH (cm) 6.4 ± 3.0 4.8 ± 2.8 18.9 ± 4.6 26.4 ± 5.6 6.8 ± 2.7 Bole height (m) 0.92 ± 0.70 0.71 ± 0.65 0.88 ± 0.78 2.7 ± 1.3 1.1 ± 0.64 Tree height (m) 5.2 ± 1.4 3.3 ± 1.4 9.3 ± 2.3 13.6 ± 2.4 5.4 ± 1.7 Basal area/ha (m2 ha-1) 2.20 0.32 6.67 14.38 0.77 Bole vol (m3) 0.006 ± 0.006 0.003 ± 0.004 0.037 ± 0.039 0.114 ± 0.062 0.007 ± 0.006 ESV (m3) 0.014 ± 0.012 0.008 ± 0.013 0.172 ± 0.113 0.312 ± 0.175 0.016 ± 0.014 ESV/ha (m3 ha-1) 2.1 0.2 4.6 16.7 0.7 Surviving SPH 353 80 125 146 102 DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.

Discussion

The combination of host species used here produced low sandalwood growth at age 11. Two of the host species, Khaya and Swietenia, belong to the Meliaceae family, which has been broadly indicated as providing poor long-term hosts (Barbour 2008). Leguminous species often make better hosts in the Cununurra clays (Barbour 2008; Radomiljac and McComb 1998b; Radomiljac et al. 1999a; Radomiljac et al. 1999b) probably because symbiotic relationships with rhizobia enable legumes to fix atmospheric nitrogen and nitrogen-containing compounds are transferred to sandalwood (Radomiljac et al. 1998c). The potential nutritional benefit gained from the two legume species used, Cassia and Cathormion, was insufficient to allow the slower-growing sandalwood to compete for resources, particularly against Khaya which dominated the site in terms of basal area production. The tree size and the proportion of the site occupied by Cassia suggest it could also have negative competition effects on sandalwood growth. Both Cassia and Khaya were nearly or more than double the height of sandalwood and dense shading by these trees, especially Khaya, appeared to be a major factor. The effects of competition on sandalwood growth are more thoroughly discussed in Section 4.3.

4.1.2 Sandalwood aged 16 years (1993), Trial 3

Method

Trial description

The planting consists of separate host species blocks with no experimental design applied. Long-term host species used for this trial were Peltophorum and Cassia. The Peltophorum block had four rows with hosts at 9 m spacing and sandalwood planted at 3 m either side of each host within the row. The sandalwood-to-host ratio at establishment was 2:1 with stocking of 1235 SPH for sandalwood and 617 SPH for hosts. The area of this block was 0.13 ha. The Cassia block contained 10 rows, odd- numbered rows had alternate positions of host and sandalwood at 3 m spacing, and even-numbered rows were planted only with sandalwood spaced at 3 m. The planting ratio of sandalwood to host was 3:1 with sandalwood stocked at 929 SPH and hosts at 309 SPH. The area of this block was 0.41 ha.

Measurement

In 2001 (8 years old) sandalwood DBH, basal diameter, bole height and tree height were measured. Measurements in 2008 (15 years old) recorded sandalwood DBH, basal diameter, bole height, crown break diameter (CBD) and tree height for both sandalwood and host. Calculated parameters of basal area, bole volume and estimated stem volume (ESV) were done on an individual tree and per hectare basis.

Results

At 15 years of age, sandalwood survival was very poor with Peltophorum as a host. There was better survival with Cassia but sandalwood survival was still low. Within the Peltophorum block, two thirds of hosts survived (67.3 per cent) but few sandalwood (6.9 per cent). In the Cassia block, most hosts survived (92.1 per cent) and only a quarter of sandalwood trees (25.2 per cent).

Cassia trees were considerably larger than Peltophorum after 15 years (Table 4.2). Cassia trees were taller with wider trunks and the estimated stem volume was four times greater. Combined with greater survival rates of Cassia, the estimates of stem volume per hectare were seven times greater than for Peltophorum.

Sandalwood trees were much smaller than their associated hosts (Table 4.3). Differences in growth parameters between sandalwood in association with the two hosts were relatively small, however because of more favourable sandalwood survival in association with Cassia the estimated stem volume per hectare was close to four times that with Peltophorum as the host. Despite sandalwood

having an initial stocking two and three times higher than Peltophorum and Cassia respectively, the proportion occupied (basal diameter) per hectare was less than 13 per cent of the area occupied by the hosts.

Table 4.2 Measured and estimated growth parameters of 15-year-old Peltophorum and Cassia as sandalwood hosts in Trial 3 (mean ± s.d.) Parameter Peltophorum block Cassia block DBH (cm) 18.44 ± 4.65 28.61 ± 9.07 Basal diameter (cm) 25.49 ± 5.61 43.86 ± 13.18 Basal area (m2) 0.0535 ± 0.0216 0.1645 ± 0.0917 Basal area/ha (m2 ha-1) 12.52 68.27 Tree height (m) 8.96 ± 1.74 12.90 ± 2.74 Bole height (cm) 181.52 ± 66.51 119.22 ± 125.91 Bole volume (m3) 0.0690 ± 0.0356 0.1199 ± 0.0976 ESV (m3) 0.1360 ± 0.0819 0.5803 ± 0.3905 ESV/ha (m3 ha-1) 31.82 240.82 Surviving stems (SPH) 234 415 DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.

Table 4.3 Measured and estimated growth parameters of 15-year-old sandalwood with host species Peltophorum and Cassia in Trial 3 (mean ± s.d.) Parameter Peltophorum block Cassia block DBH (cm) 10.84 ± 3.75 11.95 ± 3.10 Basal diameter (cm) 14.47 ± 4.82 18.15 ± 5.72 Basal area (m2) 0.0181 ± 0.013 0.0284 ± 0.0193 Basal area/ha (m2 ha-1) 1.54 6.65 Tree height (m) 6.18 ± 2.69 7.35 ± 1.37 Bole height (cm) 168.18 ± 95.58 120.29 ± 98.70 Bole volume (m3) 0.0229 ± 0.019 0.0237 ± 0.0252 ESV (m3) 0.0433 ± 0.041 0.0598 ± 0.0468 ESV/ha (m3 ha-1) 3.68 13.99 Surviving stems (SPH) 85 234 DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.

Discussion

In the planting arrangements used here, Peltophorum and Cassia performed poorly as hosts for sandalwood based on survival, and at best produced moderate growth rates. To put the growth in perspective Barbour (2008) indicated that the average sandalwood DBH for moderate to good hosts ranged from 9 to 10.8 cm at 9 years, compared to only 10.8 to 11.95 cm at 15 years achieved here. With the absence of comparable experimental treatments it was difficult to identify the degree to which the poor sandalwood performance was contributed to by species or planting design. In seedling trials, sandalwood grown with Cassia siamea produced similar growth to those with Dalbergia latifolia and Millettia pinnata (Rai 1990), which have been identified as good hosts in plantation trials (Barbour 2008). This suggests Cassia was functionally capable of providing requirements for sandalwood growth, but over time its growth rate and size produced negative competition effects. The planting design had sandalwood initially stocked at 1235 stems per hectare and hosts at 617 stems per

hectare giving a 2:1 ratio, so that there were substantially fewer hosts for each sandalwood tree than the trial used by Barbour (2008) where sandalwood and hosts were in a 1:1 ratio and stocked at 462 stems per hectare. The higher stocking of sandalwood and lower host ratios would elevate intra- specific competition and potentially the level of parasitism between individual sandalwood, and these factors were likely to contribute to the low survival and growth rates. Further examination of competition within this trial is detailed Section 4.3.

4.1.3 Sandalwood aged 17 years and 18 years, Trials 1 (1990) and 2 (1991)

Methods

Trial establishment

Both Trial 1 and Trial 2 were located in the same block at the Frank Wise Institute with Trial 1 positioned about 85 m to the south of Trial 2. The trials were established on Cununurra clay, using land preparation for flood irrigation with mounded rows and with a long-term host-to-sandalwood ratio of approximately 1:1. The sandalwood and long-term hosts were spaced at 3 m within alternating rows. Planting density of sandalwood and host together was approximately 460 SPH.

Trial 1 included the long-term host Cathormion umbellatum, and covered an area of around 0.4 ha with only three rows of both sandalwood and hosts remaining. It appeared as though it was a remnant from a larger trial. There was a gap of 10–15 m between this trial and the next trees (see Plate 4.1).

Plate 4.1 Trial 1 showing the planting arrangement with the sandalwood and Cathormium

Trial 2 was planted over 1.3 ha and tested three long-term host species: Acacia aneura, Bauhinia cunninghamii and Cathormion umbellatum. The trial was split longitudinally into three blocks approximately 70 m long, with each host represented once within a row in a randomised pattern. Poor sandalwood survival with the Acacia and Bauhinia hosts made statistical analysis using the original design impossible.

Measurement

Both trials were assessed in 2008 at ages 18 years and 17 years for the 1990 and 1991 trials respectively. Sandalwood diameter at the base, breast height and bole break were measured, as were the bole height and tree height. The host basal diameters and tree height were measured.

Results

Sandalwood survival in Trial 1 was 30 per cent (139 SHP) and Cathormion umbellatum 51 per cent. There was one row in which only one sandalwood survived, compared to approximately 30

sandalwood in the each of the other two rows, and it is not known whether this mortality occurred naturally or by design to benefit the remaining sandalwood. With this row excluded in the analysis, sandalwood survival increases to 43 per cent.

Sandalwood survival in Trial 2 was 35 per cent (162 SPH). When the sandalwood was planted alongside one row of Cathormion, sandalwood survival was 50 per cent compared to 33 per cent with Acacia and Bauhinia. In this mixed host planting, 56 per cent of sandalwood survived when planted with Bauhinia and Cathormion combination. Only 11 per cent of planted Acacia aneura were surviving at 17 years of age, compared to 73 per cent of Bauhinia cunninghamii and 83 per cent of Cathormion umbellatum.

The sandalwood in Trial 1 was larger than those in Trial 2 (Table 4.4), and had a basal diameter of 1.4 compared to 1.1 MAI (cm per year). The mean growth of sandalwood in combination with different hosts in Trial 2 varied (Table 4.5) and those growing next to at least one row of Cathormion were superior to those without Cathormion. The mean over-bark estimated stem volume, adjusted for survival, of sandalwood in Trial 1 was 27.2 m3 per hectare compared to 9.9 m3 per hectare for Trial 2. The best performing host combination in Trial 2, Bauhinia and Cathormion, had an estimated stem volume of 17.3 m3 per hectare.

Cathormion in Trial 1 had basal diameter MAI of 1.5 cm per year compared to 1.2 cm per year in Trial 2 (Table 4.6). The surviving Acacia hosts in Trial 2 were smaller compared to Bauhinia and Cathormion, which on average had grown to a similar size.

Table 4.4 Growth parameters of 18-year-old and 17-year-old sandalwood established in 1990 (Trial 1) and 1991 (Trial 2) respectively (mean ± s.d.) Trial 1 (1990) Trial 2 (1991) Parameter Mean Min Max Mean Min Max Basal diameter (cm) 25.6 ± 8.1 11 58 17.9 ± 4.9 6.5 35.2 DBH (cm) 18.7 ± 5.7 7.2 33.1 13.8 ± 4.2 4.8 28.6 Crown break diam. (cm) 22.9 ± 9.1 8.3 58 14.7 ± 4.9 4.5 32.1 Bole height (cm) 195.2 ± 78.3 0 480 148.6 ± 58.5 0 420 Tree height (cm) 767.9 ± 146.5 441 1100 549.6 ± 118.5 300 950 Bole volume (m3) 0.089 ± 0.061 0 0.378 0.033 ± 0.025 0 0.212 Stem volume (m3) 0.196 ± 0.155 0.015 0.812 0.061 ± 0.048 0.003 0.309

Table 4.5 Growth parameters of sandalwood in 1991 (Trial 2) when planted in dual host configurations (mean ± s.d.) Basal diam. DBH Height Bole volume Stem volume Hosts n (cm) (cm) (cm) (m3) (m3) A/A 4 17.6 ± 2.6 14.7 ± 3.8 500.0 ± 40.8 0.033 ± 0.008 0.060 ± 0.024 A/B 51 16.1 ± 4.4 12.3 ± 3.7 503.9 ± 116.6 0.028 ± 0.021 0.048 ± 0.039 A/C 36 18.5 ± 4.4 14.7 ± 4.4 556.9 ± 119.0 0.034 ± 0.019 0.067 ± 0.043 B/B 8 15.9 ± 3.8 11.8 ± 3.8 500.0 ± 116.5 0.019 ± 0.018 0.039 ± 0.026 B/C 52 18.8 ± 4.7 14.7 ± 4.2 570.2 ± 79.4 0.037 ± 0.020 0.066 ± 0.039 C/C 43 18.0 ± 3.9 13.6 ± 3.2 617.4 ± 110.7 0.038 ± 0.032 0.062 ± 0.041 Hosts: Acacia aneura (A), Bauhinia cunninghamii (B) and Cathormion umbellatum (C).

Table 4.6 Growth parameters measured at 18 years and 17 years for host species established in 1990 (Trial 1) and 1991 (Trial 2) respectively (mean ± s.d.) Established Host Survival (%) Basal diameter (cm) Tree height (cm) Trial 1 Cathormion umbellatum 51 26.7 ± 11.5 704.0 ±166.2 Acacia aneura 11 12.7 ± 3.8 482.4 ± 95.1 Trial 2 Bauhinia cunninghamii 73 19.6 ± 6.4 592.7 ± 132.6 Cathormion umbellatum 83 20.3 ± 6.1 529.2 ± 138.9

Discussion

Survival of sandalwood varied with host combinations and indicated that neither Bauhinia cunninghamii nor Acacia aneura were suitable as sole long-term hosts. At 17 and 18 years of age, Cathormion umbellatum was able to sustain between 40 and 50 per cent of sandalwood trees when established at an initial density of 463 stems per hectare at a 1:1 host-to-sandalwood ratio. Sandalwood survival was lower than desirable for a commercial plantation and may be related to the less-than-optimised nature of the silviculture and management practices applied across the trials. It could also be that the initial 1:1 host-to-sandalwood ratio was inadequate for long-term sandalwood survival and resource competition contributed to high mortality. Unfortunately early survival data was not available and the timing of the mortality undetermined, which may have elucidated causal factors.

The differences in growth parameters between the 17-year-old and 18-year-old sandalwood were considerably larger than what would be expected of one year’s growth. Even when sandalwoods grown with Cathormion hosts were compared between Trial 1 and Trial 2, the large difference could not be accounted for. Trial 1 was only six rows wide and sandalwood trees would therefore benefit from strong edge effects. The positive impact of edge effects on sandalwood growth was also displayed in Trail 2 (see Plate 4.2). The 35 surviving sandalwood in the first two edge rows planted adjacent to least one row of Cathormion had an estimated stem volume of 23.8 m3 per hectare. This closely resembled the estimated 27.2 m3 per hectare for sandalwood in Trial 1. This space requirement for sandalwood when grown with Cathormion is further confirmed later in this report (Section 4.2.2, Trial 6). The strong influence of planting density reinforces the understanding required to achieve the correct balance between host and sandalwood stocking and their spatial arrangement to obtain optimal sandalwood growth in a plantation system.

Plate 4.2 The sandalwood block in Trial 2 showing the edge effect together with Cathormion

This is the first report on the growth performance of plantation-grown 17-year-old and 18-year-old sandalwood. Taking into account the unknown history of the Trials as well as their final stocking rate, it is questioned whether they are representative of future plantations of a similar age. The growth rates, as indicated by basal diameter MAIs of 1.4 cm in Trial 1 and 1.0 cm for Trial 2, were not dissimilar to those reported for younger sandalwood. Barbour (2008) reported mean basal areas for sandalwood equivalent to basal diameters of 14.4 cm (1.6 MAI) when grown with Cathormion, and up 15.8 cm (1.8 MAI) with the best host species after 9 years at an established density of 463 stems per hectare. At 14 years, sandalwood has an average basal diameter of 13.3 cm (~1.0 MAI) when grown with Acacia mangium at the Frank Wise Institute, and up to 18.1 cm (1.3 MAI) at Carnarvon (24°532 S 113°39’39 E) when grown with Azaderachta indica (neem) (McComb 2009). This previous work indicates that single-tree sandalwood growth performance in Trial 1 is higher than expected when using Cathormion as a long-term host. Survival could be greatly enhanced with silviculture improvements but whether this would correlate to increased total wood yield per hectare is questionable knowing there are sandalwood growth limitations based on its spatial requirements, especially with Cathormion as a host.

Trial 2 demonstrated that there was a sandalwood growth benefit when grown with dual host species compared to growth with a single host species. Sandalwood grown with a combination that included Cathormion with another species was better than Cathormion on its own, even when the other species was Bauhinia cunninghamii and/or Acacia aneura which are singularly poor performing hosts. This finding is supported in other trials (Section 4.3.1, Trial 7). The additive effect on sandalwood growth of these mixed-host environments is unclear. It is hypothesised that as the composition of sandalwood sap flow varies with different host species (Radomiljac et al. 1998c), it is possible that in a mixed-host environment sandalwood takes up a broader range of host organic and mineral solutes which ultimately better satisfies growth requirements. Many commercial plantations are currently being established with mixed-host combinations. This spreads the risk of host loss by insect pests and disease and natural ageing, which in turn lowers the risk of reduced sandalwood growth due to inadequate nutrients from hosts. Further research is required to understand the dynamics of the interactions in mixed-host sandalwood plantations and to quantify the improvements to sandalwood growth.

4.2 Sandalwood growth with Cathormion umbellatum

Cathormion umbellatum Fabaceae is a shrub to small tree native to northern Australia (Florabase 2011), and it was identified as a candidate host because of its ability to fix nitrogen. During the initial stages of research into sandalwood cultivation in the Ord River Irrigation Area (ORIA) in the early 1990s, Cathormion was classified as a ‘satisfactory’ intermediate host compared to other species, such as Albizzia and Khaya (Done et al. 2004). Subsequently Cathormion was broadly utilised as a long- term host species in a large number of the initial commercial plantations. More recently, plantation systems have incorporated multiple host species, yet Cathormion remains an important species in the host mix and could be considered somewhat of a ‘benchmark’ against which the effectiveness of other hosts is judged. This section examines the impact of different host ratios and spatial configurations on sandalwood grown with Cathormion.

4.2.1 Effect of host ratio on sandalwood growth with Cathormion umbellatum as the primary host, Trial 9

Methods

Trial establishment and design

Planted in 2000 with sandalwood and long-term host, Cathormion umbellatum in six ratio treatments (Table 4.7) with Sesbania formosa as the short-term host (Radomiljac et al. 1999a). Land was

prepared for flood irrigation and mounds made 1.8 m apart. Ratio treatments were allocated randomly to plots 18 m wide by 36 m long, with six replicates. Planting configurations varied according to ratio treatment (Figure 4.2), however each plot was planted in three ‘columns’ each of three rows, with a constant 1.8 m between rows and 3.6 m between ‘columns’. In 2003, when trees were aged 3 years, the original planting design was considered overcrowded and rows 2, 5 and 8 in each block were removed thus altering the sandal treatment ratios (Table 4.8).

Table 4.7 Sandalwood (S) and host (H) spacing and stocking for the six ratio treatments in the original planting design of Trial 9 Host Sandal Total spacing Ratio spacing in Sandalwood/ sandal/ Sandal in row Host/ Total host/ Host Treat. (S:H) row (m) plot treatment SPH (m) plot treatment SPH 1 1:8 9 12 48 185 3 96 384 1481 2 1:4 6 18 72 278 3 72 288 1111 3 1:2 3 36 144 556 3 72 288 1111 4 1:1 6 54 216 833 6 54 216 833 5 2:1 3 72 288 1111 3 36 144 556 6 4:1 3 72 288 1111 6 18 72 278

Measurement

Sandalwood trees were first measured in 2001 (1 year old), with a second measurement of host and sandalwood in November 2008 (8 years old). In 2008 only the internal blocks were measured to avoid edge effects from surrounding plots. Only Treatments 1, 4, 5 and 6 were measured because of the repetitive nature of treatments existing post-culling (Table 4.8). Basal diameter and height were measured for sandalwood and host, with DBH, crown break diameter and bole height, measured for sandalwood only. Sandalwood growth data from 2001 was subjected to an analysis of variance. Only descriptive means were computed for the 2008 data because the host culling in 2003 changed planting arrangements, resulting in an imbalance in the original experimental design.

H H H H H H H H H H H H H H H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H H H H H H H H H H H H H H H H S H H S H H S H H H H H H H H H H H S H H S H H S H H S H H S H H S H H S H H S H H S H H H H H H H H S H H S H H S H H H H H H H H H H H S H H S H H S H H S H H S H H S H H H H H H H H H H H H H H H H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H S H H H H H H H H H H H H H H H H H S H H S H H S H H H H H H H H H H H S H H S H H S H H S H H S H H S H H S H H S H H S H H H H H H H H S H H S H H S H H H H H H H H H H H S H H S H H S H H S H H S H H S H Treatment 1 (1:8) Treatment 2 (1:4) Treatment 3 (1:2) H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S H S H H S H H S H S H S S H S S H S S S S S S S S H S S H S S H S S H S S H S S H S S H S S H S S H S Treatment 4 (1:1) Treatment 5 (2:1) Treatment 6 (4:1) Figure 4.2 Trial 9 planting layout of sandalwood (S) and Cathormion host (H), for the six ratio treatments. Intermediate hosts were planted at 1.5 m either side of each sandalwood.

Table 4.8 Trial 9 host (H) and sandalwood (S) stocking rates after culling of plots in 2003

Post-culling of hosts in 2003 Original Total Total ratio Sandal/ sandal/ Sandal Host/ host/ Host Current 2008 Treat. (S:H) plot treatment SPH plot treatment SPH treatment measure 1 1:8 0 0 0 72 288 1111 All host Yes 2 1:4 0 0 0 72 288 1111 All host No 3 1:2 0 0 0 72 288 1111 All host No 4 1:1 36 144 556 36 144 556 1:1 Yes 5 2:1 72 288 1111 0 0 0 All sandal Yes 6 4:1 72 288 1111 0 0 0 All sandal Yes

Results

At 1 year, the trial showed no difference in the mean sandalwood basal diameters between ratio treatments (P = 0.146) (Figure 4.3). There were however differences between sandalwood tree height (P <0.001) and bole height (P <0.001) between treatments. Generally sandalwood trees in treatments

with a higher proportion of hosts were shorter than with those with higher proportion of sandalwood (i.e. lower proportion of hosts). More specifically sandalwood were shortest under a sandalwood-to- host ratio of 1:8 (Treatment 1) compared to all other treatments, except where sandalwood was in a 1: 4 ratio with Cathormion (Treatment 2). The tallest sandalwood were in treatments where there were more sandalwood (S) than hosts (H) such as Treatments 5 (1S:1H) and 6 (4S:1H). Bole height under the 1:8 ratio of sandalwood to Cathormion (Treatment 1) was also shorter than most other ratios (Treatments 4, 5 and 6). Sandalwood basal diameter followed a similar trend to tree height and it increased as the ratio shifted from many hosts per sandalwood to many sandalwood per host.

250 40

35 200 30

150 25 20

100 15 Diameter (mm) Height (cm)Height 10 50 5

0 0 T1 1S:8H T2 1S:4H T3 1S:2H T4 1S:1H T5 2S:1H T6 4S:1H Treatment Tree Ht Bole Ht Basal dia

Figure 4.3 Sandalwood tree height (cm), bole height (cm) and basal diameter (mm) within ratio treatments of sandalwood (S) with a Cathormion host (H) when Trial 9 was 1 year old (2001) (mean ± s.d.)

When Trial 9 was measured after 8 years (2008), sandalwood in treatments with all hosts removed (Treatments 5 and 6) were considerably smaller than those sandalwood where a 1:1 ratio with Cathormion hosts remained (Treatment 4; Figure 4.4). All measured parameters were lower in these treatments and this resulted in an estimated wood volume of 0.0127 ± 0.0061 m3 for sandalwood without hosts compared to 0.0271 ± 0.0134 m3 for sandalwood with hosts at a 1:1 ratio. Cathormion growth was similar with or without sandalwood. Where Cathormion was a host for sandalwood at a 1:1 ratio, there was on average less than less than 5 mm difference in basal diameter and 10 cm in tree height, when growth with and without the parasite were compared.

There was little difference in sandalwood growth between Treatments 5 and 6, which had no hosts since culling. There was a slight trend for smaller trees with the higher pre-culling sandalwood-to-host ratio (4S:1H, Treatment 6) than with the lower ratio (2S:1H, Treatment 5) but basal diameter and DBH were less than 1.5 cm apart and there was only 2.3 cm difference between bole and 7.5 cm in tree height (Figure 4.5). Estimated stem volumes reflected this similarity and Treatment 5 was only 0.0257 m3 larger than Treatment 6. Presumably growth rates post culling would be similar for both treatments and their similarity in 2008 reflects similar growth at one year (Figure 4.3) and probably at 3 years of age when culling occurred.

A 25 B 6

5 20

4 15 3

10 (m)Height

Diameter (cm) 2

5 1

0 0 S - 1S:1H Sandal only H - 1S:1H Host only S - 1S:1H Sandal only H - 1S:1H Host only Treatment Treatment Basal dia DBH CBD Tree Ht Bole Ht

Figure 4.4 Sandalwood (S) and Cathormion host (H) growth parameters in Trial 9 post culling (in 2003) measured in 2008 (mean ± s.d., CBD = canopy break diameter)

A B 5 14 4.5 12 4

10 3.5 3 8 2.5 6 Height (m)Height 2 1.5 Diameter (cm) 4 1 2 0.5 0 0 T5 2S:1H T6 4S:1H T5 2S:1H T6 4S:1H Original Treatment Original Treatment Basal dia DBH CBD Tree Ht Bole Ht

Figure 4.5 Trial 9 sandalwood (S) growth parameters measured in 2008 (8 years) of post culling treatments without hosts (H) based on original treatments (Table 4.7) (note, all hosts culled in Treatment 5 (2S:1H) and Treatment 6 (4S:1H) in 2003, Figure 4.2, Table 4.8, mean ± s.d.) Discussion

Successful sandalwood plantations will require a balance between the growth of sandalwood and hosts. Achieving this balance is complicated by the parasitic interactions, via haustoria, but also by competition for resources including water, nutrients and light for photosynthesis and shading, which protects bark from damage by the sun. Here this was further complicated by the presence of the intermediate host Sesbania formosa in addition to the long-term host Cathormion umbellatum and the distances between sandalwood and hosts. During early establishment, increasing the Cathormion umbellatum host ratio beyond four per sandalwood was detrimental. At this early stage it was unlikely that Cathormion had any positive host effects, particularly in Treatments 2, 3, 5 and 6 that had separate long-term host rows. Sandalwood haustoria were most likely to first intercept and parasitise the roots of the intermediate host, Sesbania formosa, which was planted within rows at a constant spacing of 1.5 m either side of sandalwood throughout the trial. Presumably haustorial connections and resources for these intermediate hosts were relatively constant. Differences in growth must

therefore be a function of competition for resources between growth of the long-term host (Cathormion) and sandalwood. Unfortunately without early host growth data this can not be further investigated.

After culling, the sandalwood in no host plots (Treatments 5 and 6) would only have had weeds and other sandalwood to parasitise because the intermediate host, S. formosa, that was planted within sandalwood rows tends to die out after 3 years. This resulted in clear differences at 8 years and every measured growth parameter was larger for sandalwood grown with long-term hosts at a 1:1 ratio (Treatment 4) than for sandalwood grown without hosts. To highlight the differences between them, the estimated wood volume per hectare, based on surviving stems, was 11.34 m3 for sandalwood with hosts compared to 6.99 m3 for those without hosts, even though these treatments initially had twice as many sandalwood plants.

The original planting ratios of 2S:1H and 4S:1H (Treatments 5 and 6 respectively) present during the first 3 years before culling did not have a residual effect on sandalwood growth at 8 years. Both treatments displayed very similar growth patterns between 1 and 8 years of age. These treatments were both planted so that sandalwood and long-term hosts were in separate rows, and it is possible that the similarity in growth patterns reflect the lack of early long-term host influence, and the constant intermediate host (S. formosa) effect up to 3 years of age in this planting configuration. The immediate availability of S. formosa roots along mounds, and intermittently waterlogged conditions from irrigation water that flows between mounds, may provide an environment in which roots initially grow along and not across rows, and thus connections to long-term host roots may not occur in the first 3 years.

4.2.2 The effect of spacing and host-parasite ratio on sandalwood growth with Cathormion umbellatum as the primary host, Trial 6

Methods

Trial establishment design

Trial 6 was planted in 1999. Six stocking treatments consisting of different spacing and two host-to- sandalwood ratios (Table 4.9) were planted in blocks of five plots. The 2:1 ratio was planted in plots consisting of paired columns with sandalwood and Cathormion umbellatum (long-term host) planted in separate columns, and the 4:1 ratio was planted in plots consisting of three columns with long-term hosts in the two outer columns and sandalwood in the middle column. Each column within a plot was 1.8 m apart and there was 3.6 m between plots. Within treatment blocks, intermediate hosts Sesbania formosa and Acacia trachycarpa were planted in alternating sandalwood columns, midway between the sandalwood, such that there were three columns with Sesbania and two columns of Acacia per block. Treatments were arranged from one to six across the site with no true replication applied.

Table 4.9 The within column spacing and stems per hectare (SPH) for the six stocking treatments of sandalwood and Cathormion umbellatum hosts in Trial 6

No. of Sandal Sandal Cathormion Cathormion Host:sandal spacing stocking Cathormion stocking Treatment columns ratio (m) (SPH) spacing (m) (SPH) 1 1 2:1 3 617 1.5 1234 2 1 2:1 4 462 2 924 3 1 2:1 6 308 3 616 4 2 4:1 3 462 1.5 1848 5 2 4:1 4 347 2 1388 6 2 4:1 6 231 3 924

Measurement

In 2008, when Trial 6 was 9 years old the six treatments were divided into four measurement areas, or pseudo replicates, 25 m long. Only four of the five plots within each block were measured to maintain a balanced number of primary host columns. Sandalwood height, basal diameter, DBH, crown break diameter and bole height were measured. Values for stem basal area, crown break area, estimated bole volume (EBV) and estimated stem volume (ESV) were calculated. Cathormion basal diameter and height were measured. Intermediate host species were no longer living at the time of measurement.

Statistical analyses were carried out using the pseudo replication structure, and these examined the fixed effects of treatments and intermediate hosts, along with their interaction. A linear mixed model approach was used to accommodate the design of the study. All analyses were carried out for the mean treatment at a tree level and the sums which gave output at the replicate level allowing adjustments to be made for the number of surviving trees, and also percentage survival.

Results

After 9 years, overall sandalwood survival from the sampled area was 77.6 per cent. Intermediate hosts influenced survival (p = 0.03) and more sandalwood survived with S. formosa (82.3 per cent) than A. trachycarpa (72.9 per cent). There were no significant differences in sandalwood survival between treatments, however for treatments with equivalent sandalwood spacing (1 and 4; 2 and 5; 3 and 6) the survival of the 4:1 ratio treatment was always equal to or higher than the 2:1 ratio treatment. Survival of Cathormion was 73.1 per cent across all treatments and ranged from a low of 68.1 per cent for Treatment 1 to a high of 81.8 per cent for Treatment 2.

Stocking rates influenced (P = 0.001) sandalwood basal diameter, but there was no interaction with treatments. Sandalwood in Treatment 3 had the largest basal area (16 ± 3 cm2) and Treatment 1 the smallest (13.7 ± 3.2 cm). A significant effect of treatment was found (P = 0.0014) for sandalwood DBH but not between intermediate hosts. Sandalwood DBH was larger in Treatment 6 (12.7 ± 2 cm) compared with Treatments 1, 2 and 4, and Treatment 1 had the smallest DBH (9.85 ± 2.50 cm). Intermediate host species did not influence sandalwood DBH at 9 years of age. Sandalwood were generally 550–600 cm tall but were tallest in Treatment 6 (616 ± 73 cm; P = 0.02) and shortest in Treatment 2 (549 ± 91 cm) (Figure 4.7).

Sandalwood bole volume was effected by treatment (P<0.0001), whilst the effect of intermediate host was marginal (P = 0.06). Treatment 6 (0.033 ± 0.015 m3) and Treatment 3 (0.028 ± 0.013 m3) had the greatest sandalwood bole volume and Treatment 1 the smallest bole volume (0.020 ± 0.016 m3). Estimated wood volume of sandalwood varied between stocking rates (p<0.0001) (Figure 4.6), but there was no intermediate host effect. Estimated sandalwood stem volume per hectare was greater in

Treatments 6 (0.049 ± 0.031 m3) and 3 (0.044 ± 0.019 m3) than all other treatments except Treatment 5, and Treatment 1 had the smallest mean wood volume (0.031 ± 0.016) (Figure 4.6). Sandalwood grown in treatments with a 2:1 host ratio (see Table 4.9 for treatment descriptions) had lower estimated stem volume than those grown in the equivalently spaced treatments with a 4:1 ratio (i.e. Treatments 1 versus 4, 2 versus 5, 3 versus 6).

0.06

0.05 ) 3 0.04

0.03

0.02 Est. stem volume (m 0.01

0 1 2 3 4 5 6 Treatment AT SF All Data

Figure 4.6 Estimated stem volume (m3) of sandalwood for long-term host stocking treatments and intermediate host types within treatments after 9 years in Trial 6 (mean ± s.e., AT = Acacia trachycarpa, SF = Sesbania formosa, refer to Table 4.9 for treatment descriptions)

700

600

500

400

300 Hieght (cm)Hieght 200

100

0 1 2 3 4 5 6 Treatment Cathormion Sandalw ood

Figure 4.7 Height (cm) of Cathormion umbellatum and sandalwood within the six stocking treatments after 9 years in Trial 6 (mean ± s.e., refer to Table 4.9 for treatment descriptions) The difference between estimated sandalwood volume per hectare between the highest and lowest stocking treatments of 617 SPH (Treatment 1) and 231 SPH (Treatment 6) was 4.58 m3 (Figure 4.8). Despite producing the smallest trees on an individual basis, Treatments 1 and 4 had the highest sandalwood stem wood productivity per hectare. Even though Treatment 6 produced the largest individual trees, it had lower productivity per hectare than all other treatments as a result of the low sandalwood stocking rate. Across all stocking treatments the estimated volume per hectare was lower when sandalwood was grown with Acacia (Figure 4.8) compared to Sesbania, with the greatest difference being 3.28 cm3 per hectare for Treatment 5.

There was an opposing trend of individual and block yield with the number of sandalwood stems per hectare (Figure 4.9), such that as stocking rate increased the individual tree yield declined but block yield increased. In both cases the relationships were most strongly described by logarithmic regressions with R2 values of 0.986 and 0.725 for mean estimated stem volume and mean estimated stem volume per hectare respectively (Figure 4.9).

16.0

) 14.0 -1 ha

3 12.0 10.0

8.0 6.0 4.0

2.0 Est. stem volume stem Est. (m 0.0 1 2 3 4 5 6

AT SF All Data Treatment

Figure 4.8 Estimated sandalwood stem volume per hectare after 9 years in Trial 6 (note, Acacia trachycarpa (AT) and Sesbania formosa (SF) were intermediate hosts within the six Cathormion umbellatum stocking treatments, see Table 4.9 for treatment details)

0.060 16

14 0.050 ) 3 )

12 3

0.040 (m 10 -1

0.030 8

6 0.020

4 Est stem vol ha Mean estMean stem vol (m 0.010 y ESV = -0.0181Ln(x) + 0.1472 y ESVha = 4.2603Ln(x) - 13.48 2 R2 = 0.9864 R = 0.7246 2 0.000 0 200 250 300 350 400 450 500 550 600 650

-1 ESV ESV ha Established Sandalwood stems ha

Figure 4.9 Relationship between the number of sandalwood per hectare and the mean individual tree estimated stem volume (ESV), and the mean estimated stem volume per hectare (ESVha) in Trial 6 after 9 years Cathormion basal diameters differed between treatments (P <0.001) and Treatment 3 (16 ± 5 cm) had the largest diameter, and Treatments 4 (12 ± 4 cm) and 5 (13 ± 4 cm) the lowest (Figure 4.10). Cathormion basal diameters were larger for 2:1 host-to-sandalwood ratio treatments (see Table 4.9 for treatment descriptions), compared with the equivalently spaced treatments with a 4:1 ratio. This trend was reversed when examined on a per hectare basis, where the higher host stocking rate in the 4:1 treatments resulted in a larger basal area compared to the equivalently spaced 2:1 configurations

(Figure 4.10). Mean height of Cathormion was very uniform (Figure 4.7) and only varied by 22 cm between treatments.

18.0 18.0 16.0 16.0

14.0 14.0 ) -1

12.0 12.0 ha 2 10.0 10.0 8.0 8.0 6.0 6.0 Basal diameter (cm) 4.0 4.0 Basal area (m 2.0 2.0 0.0 0.0 1 2 3 4 5 6

Basal diameter Basal area Treatment

Figure 4.10 Basal diameter (cm) and estimated basal area per hectare (m2 ha-1) for Cathormion umbellatum within stocking treatments in Trial 6 after 9 years (see Table 4.9 for treatment descriptions) Discussion

Sandalwood survival was higher where Sesbania formosa was used as the intermediate host. Growth of sandalwood was similar with either of the intermediate hosts, S. formosa or Acacia trachycarpa. Thus sandalwood planted with S. formosa would have greater yield per hectare compared to A. trachycarpa within this trial.

Sandalwood were consistently larger on an individual basis when planted in treatments with a 4:1 host-to-sandalwood ratio (Treatments 4, 5, 6) compared to the equivalently spaced 2:1 ratio treatments (Treatments 1, 2, 3). This may be due to greater availability of host roots, which presumably increased the frequency of haustorial connections, and an associated rise in solute uptake which could improve sandalwood growth. Whilst higher host availability improved sandalwood growth, the results within sandalwood-to-host ratio treatments indicated a trend of increased sandalwood growth when spacing between trees was further apart. So even ‘good’ hosts acted as competitors within the plantation environment and could be detrimental to growth with increasing planting density. Further to this, the short distance between sandalwood within high stocking treatments increased the direct competition and parasitism between sandalwood trees, and this may have contributed to the reduced individual sandalwood growth in these treatments.

Total sandalwood productivity at the stand level ran counter to the individual tree productivity for equivalently spaced treatments, as sandalwood grown under high stocking rates outweighed the yield of fewer, but larger trees. In terms of maximising total wood yield, Treatments 1 and 4, with sandalwood stocking rates of 617 and 462 SPH respectively, were the preferred planting design. However, ultimately the commercial value of sandalwood lies in heartwood production and oil yield and thus plantation design should be aimed at optimising this component. Clearly external sandalwood size can be manipulated by altering stocking rates and host ratios when sandalwood is planted with C. umbellatum as the primary host, however the impact, if any, of the treatments on heartwood remains unclear. In the future, monitoring aromatic wood yield in addition to growth data should allow for a more precise economic evaluation of the different planting designs.

Cathormion growth was not reduced by increasing parasitic load from a 4:1 ratio to equivalently spaced 2:1 ratio treatments. Indeed Cathormion trees planted at 2:1 were wider and taller than in the

equivalent 4:1 treatments, indicating that the effects of competition between hosts for environmental resources were potentially greater than any detrimental parasitic effects.

4.2.3 Compilation of sandalwood growth with Cathormion umbellatum as primary host

Methods

Mean height and basal diameter data was compiled from the Cathormion host trials presented within this report, except for Trial 7 age 3, which used the data presented by Barbour (2008). Trials and treatments within trials were selected based upon the most common stocking arrangement where sandalwood and Cathormion were planted at a 1:1 ratio, with 462 stems per hectare of each (Table 4.10). Where trials contained multiple treatments, the treatment with the closest parameters to these was chosen. All the trials, except Trial 7, had sandalwood and Cathormion planted in separate and alternate rows. Scatter plots were used to graphically represent the growth curve of sandalwood basal diameter and height between 2 and 18 years old, with relationships determined by the Excel trendline function.

Table 4.10 Age and planting details of Cathormion host trials Established Surviving Tree age Number of Host: sandal sandalwood sandalwood Surviving host Trial # (years) samples ratio SPH SPH SPH 9 1 208 1:1 556 533 - 7 3 209 1:1 462 402 420 9 8 60 1:1 556 417 403 6 9 66 2:1 462 319 378 2 10 143 1:1 462 231 - 7 11 45 1:1 462 370 322 2 17 143 1:1 462 217 383 1 18 61 1:1 462 199 236

Results

Sandalwood basal diameter and height increased with age (Figure 4.11). Log functions fitted to the data accounted for approximately 90 per cent of the variation in basal diameter and height. Growth was rapid between 1 and 7 years after which thegrowth rate slowed. The lack of data for trees aged 4 to 7 years reduced confidence in the growth curve during this period. However, despite gaps in the data, there was a consistent growth pattern between age 8 years and 11 years suggesting that conditions in the selected trials generally promoted similar sandalwood growth rates, and potentially similar growth curves. The exception was a substantial difference in size between sandalwood at 17 and 18 years of age and with limited data after 11 years it is difficult to know which curve is more representative of growth. This is further complicated by a potential edge effect in Trial 1 (age 18 years), and as such a more conservative trend should be considered normal.

For both basal diameter and height the power trendline function provided a stronger fit, 0.98 and 0.96 respectively, compared to the log relationships (Figure 4.11). However the trend lines of power functions at 18 years were closer to the upper data point of Trial 1 and this was considered unusually high due to edge effects and so the more-conservative log relationships were presented. At harvestable age (15 years) the difference between log and power function was less than 2 cm for basal diameter and 30 cm for height, however differences in the log and power relationships were very apparent in

comparisons beyond the bounds of the available data. At 25 years the power function gives a basal diameter of 31 cm compared to 23 cm for the log function. Accurate modelling of sandalwood growth curves would require data across a longer time scale that encompassed the juvenile fast growth phase, the mature steady growth phase and senescence.

a 30 b 9 8 25 7 20 6 5 15 4 10 3 Tree (m) height

Basal diameter (cm) y = 7.038Ln(x) + 0.4005 2 5 2 y = 2.0374Ln(x) + 0.8263 R = 0.8972 1 R2 = 0.9027 0 0 0 5 10 15 20 0 5 10 15 20 Age Age

Figure 4.11 Diameter (a) and height (b) of sandalwood grown with Cathormion hosts generally at a 1:1 ratio with 462 sandalwood stems per hectare (see Table 4.10 for trial details) Discussion

The parasitic nature of sandalwood means it is not plausible to establish a ‘standard’ free-growing growth rate or growth curve that is applicable to plantation forestry. Hence, an alternative growth standard is required so that performance of different host species, spacing and designs can be put into context. We suggest that a 1:1 Cathormion host-to-sandalwood ratio, established at 462 sandalwood stems per hectare with a spatial arrangement of 3 m within rows and 7.2 m between rows could provide a benchmark for sandalwood plantation production.

For a benchmark to succeed good data is required, however, there are some inherent issues with the dataset presented. The data was compiled across different trials established as much as 11 years apart and so these growth curves may not accurately represent sandalwood growth through time with Cathormion as the primary host. A complete time series of growth was not kept for these trials and a maximum of two time points (approximately 7 years apart), were available for any one trial. Where more age data was available, such as trees aged 8 to 11 years, growth rates were consistent, but growth curves of individual trials may vary through time or at particular points in time. In addition, mortality increased with trial age and thus reduced stocking of both Cathormion and sandalwood, was inherently linked with growth rates in older trials, and it is possible larger trees with more extensive root networks were more likely to survive, biasing the results. For all trials, active management included pruning, weed and insect control, and irrigation; but inadequate records do not allow accurate comparisons with current practices in commercial plantations. Declining survival of sandalwood and Cathormion per hectare with age (Table 4.10) could be related to sub-optimal management practices, as indeed these have improved with experience, and so these results represent a baseline. Alternatively, the decline in survival could indicate increasing stress from competition, as the demand on resources for survival and growth increase with the size of trees.

None-the-less, the growth curves presented for sandalwood planted at 462 stems per hectare in a 1:1 ratio with Cathormion in a 3 x 7.2 m spacing, represent the best available baseline data for plantation production at this time. These generalised growth curves provide a dataset for comparing the relative effectiveness of different hosts, spatial arrangements and plantation management over the expected plantation rotation.

4.3 Investigation of spatial competition analysis

The hemi-parasitic nature of sandalwood dictates that the majority of plantations are by necessity mixed-species environments. Standard sandalwood silviculture employs an herbaceous pot host, an intermediate ‘woody’ host and a long-term host. Hosts may consist of multiple species, so at any one time there can be between two and five tree species in a plantation. In mixed-species environments there are three interactions resulting in different growth outcomes and these are: competition (where one species exerts negative effects on another and reduces its growth); competition reduction (where inter-specific competition is lower than intra-specific competition and results in improved growth for all species); and facilitative production (where one species positively impacts another and improves their growth) (Vandermeer 1989). The complexity of these interactions within mixed-species plantations is highlighted in reviews by Forrester et al. (2006) and Kelty (2006), and it is foreseeable that the parasitic nature of sandalwood would increase this complexity.

For sandalwood to grow successfully in plantations, positive facilitative production effects (primarily via parasitism of hosts but also through environmental benefits) must outweigh the negative effects of host competition for resources such as light, space, water and soil nutrition. In turn, the host must be able to successfully withstand the parasitic draw of water and nutrients as well as the spatial and environmental competition, to sustain sandalwood throughout the rotation. Variation in the interactions between sandalwood and hosts will result from differences in the amount and constitution of solute uptake (Radomiljac et al. 1998c), and the size and structure of hosts (Barbour 2008) and thus it is likely that spatial requirements for successful sandalwood growth will vary between host species. There is a lack of quantitative knowledge on variation in competitive interactions and the impact of spatial parameters between sandalwood and its host species and how these may effect growth. Decisions for plantation designs to date have been largely based on the best estimation or from trial and error experimentation.

Competition indices can provide insight into spatial parameters and the impact on growth of inter- and intra-specific interactions between trees in native forest (von Oheimb et al. 2011; Zhao et al. 2006) and mixed-species plantation environments (Bristow 2006; Vanclay 2006b). Analysis of tree growth using competition indices aims to account for the impact of relative size and/or density of neighbouring trees, within a specific horizon of influence around target trees. The ability to account for spatial effects as well as species differences simultaneously could provide a level of understanding of host–sandalwood interactions within plantations not yet achieved. The analysis completed here across two trials aimed to provide a preliminary examination of the utility of spatially explicit competition indices to explain differences in sandalwood growth with different host species.

4.3.1 Spatially-dependent host effects on sandalwood size when grown with six host species, Trial 7

Methods

Trial establishment and design

Trial 7 was established in 1999 to test sandalwood growth with six long-term hosts: Khaya senegalensis and Cedrela odorata from the Meliaceae family; and Cathormion umbellatum, Dalbergia latifolia, Millettia pinnata (syn. Pongamia pinnata) and Pterocarpus indicus from the Fabaceae family. The short-term host was Acacia trachycarpa and Alternanthera was used as the pot host. The six long-term host treatments were planted in a randomised complete block design replicated five times. The ratio of sandal to intermediate host was 1:1, and the sandal to long-term host ratio was initially established at 1:2; however, in 2003 hosts were removed from every second row so that a ratio of 1:1 was achieved. Post-thinning treatment blocks were eight rows wide by 12 positions long with sandalwood and long-term hosts alternating at 3 m spacing within each row.

Measurement and statistical analysis

In January 2008, when trees were 8 years old, plots within the trial were measured and statistical analysed (Barbour 2008). Individual tree data from these measurements was then used for further analysis here. This approach, used in mixed-species analysis, was experimental in its application to the complex interactions of spatial host relationships in sandalwood plantations. Two host competition indices were calculated for individual sandalwood within five competition horizons (x); 6, 9, 12, 15, and 18 m (i.e. hosts within this distance from an individual sandalwood tree), using Simile modelling environment software (Simulistics, Edinburgh). The indices were calculated as:

• host count index (HCIx) = number of host trees within x metres (horizon) of the subject sandalwood tree

• host size-distance index (HSDIx) = ∑i BAi/Di, where BAi is the basal area of host tree i and Di is the distance from host tree i to the subject sandalwood tree, for all host trees within x metres of the subject sandalwood tree.

Host treatment plots were segregated into two areas: interior (the inner four rows x eight planting positions); and periphery (outer two rows on each side and outer two planting positions on each end). This division allowed for modelling interior sandalwood diameter as if they were growing with a single host species, while considering peripheral trees as being under the potential influence of host species in neighbouring treatment plots.

A mixed-model analysis using ASReml (VSN International, Hemel) was completed to determine the effect of the indices on sandalwood basal diameter. Host treatments, plot interior host indices, plot periphery host indices and treatment by interior index interaction were fitted as fixed effects in the model. The row and position of individual trees and the plot column of the host treatment were fitted as random effects to model environmental effects across the site.

Results

Host count indices

Host count indices (HCIs) were not significant determinants of the size of sandalwood in plot interiors regardless of the horizon used, indicating that the type of host and not the number of hosts was more influential within the single species environment of a plot interior. There were substantial differences between hosts, and the predicted basal diameters of sandalwood grown in Dalbergia and Millettia plots were slightly larger than those grown with Cathormion, and in turn, these were larger than sandalwood grown with Pterocarpus or Cedrela, followed by Khaya (Figure 4.12). There were slight differences to host species ranks when sandalwood basal diameter was estimated using whole plots or only plot interiors. For all species except Cathormion, there was an increase in predicted diameter suggesting positive edge effects or benefits of host diversity.

In the plot periphery, different host species appeared to have different horizons of influence (Table 4.11). Millettia appeared to have an influence when in close proximity (6 to 9 m), Pterocarpus when further away (12 to 15 m) and Dalbergia and Khaya were influential across a wide range of distances (6 to 18 m). The significant effects from the analysis (Table 4.11) were further fitted together in a linear model, which was subsequently reduced to provide a final estimate of the most significant effect of host count indices on sandalwood growth for each species (Table 4.12).

Predicted basal diameter (cm) 4

0 Dal Cath Mil Pt Ced Kh Internal plot Whole plot

Figure 4.12 Mean basal diameter of 8-year-old sandalwood trees estimated on an internal and whole-plot basis in Trial 7 (long-term hosts: Dal = Dalbergia, Cath = Cathormium, Mil = Millettia, Pt = Pterocarpus, Ced = Cedrela, Kh = Khaya)

The effects of host count indices for each host in the periphery of their own plots were mostly significant, and reflected the ranking of host treatments determined from the plot interiors. For example, it was estimated that for each Dalbergia tree within 6 m, basal diameter of sandalwood within Dalbergia plots was increased above the mean by 0.64 cm, whereas for each Khaya tree within 9 m, basal diameter of sandalwood within Khaya plots was reduced below the mean by 0.92 cm (Table 4.12). These mirrored the host-treatment effects on sandalwood in the plot interiors, where for Dalbergia this was estimated as 1.23 cm greater than the trial mean and estimated as 7.55 cm lower than the trial mean for Khaya.

The positive effect of the plot periphery on sandalwood growth within plots of host species suggests a positive influence of certain multi-host environments. For example, there appeared to be favourable reciprocal interaction between Cedrela and Millettia on sandalwood basal diameter. Each Cedrela tree within 12 m of sandalwood in a Millettia plot increased basal diameter by an estimated 1.2 ± 0.4 cm, and in the Cedrela plots each Millettia tree within 12 m of a sandalwood increased basal diameter by an estimated 1.5 ± 0.4 cm. The predicted basal diameter of a sandalwood in the periphery of a Millettia plot with 12 Millettia and 2 Cedrela available as hosts within 12 m was 17.5 cm. This was substantially greater than the predicted treatment mean in the interior of Millettia plots (14.4 cm) or Cedrela plots (9.5 cm). Cedrela and Dalbergia also appeared to have a strong positive interaction; however, this was only significant for sandalwood with Cedrela present in the periphery of Dalbergia plots.

There were also negative interactions between host species. For example sandalwood growth was reduced when its host included a mix of Pterocarpus and Millettia. Each Millettia tree within 12 m of a sandalwood in a Pterocarpus plot reduced the estimated basal diameter by 0.5 ± 0.2 cm. A sandalwood in the periphery of a Pterocarpus plot with 20 Pterocarpus within 15 m and 4 Millettia within 4 m was predicted to have a basal diameter of 10.4 cm, which is substantially smaller than the predicted treatment mean for the interior of Pterocarpus (11.8 cm) or Millettia plots (14.4 cm).

Table 4.11 P-values for model effects on sandalwood basal diameter using host count indices (HCI) in Trial 7

Effect 6 m 9 m 12 m 15 m 18 m horizon horizon horizon horizon horizon m (overall mean) < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 Effects on basal diameter of sandalwood in the plot interior Treatment 0.008 0.075 0.233 0.015 0.003 HCI Cathormion 0.070 0.410 0.411 0.258 0.641 HCI Cedrela 0.789 0.132 0.869 0.824 0.735 HCI Dalbergia 0.142 0.196 0.250 0.087 0.250 HCI Khaya 0.544 0.913 0.825 0.972 0.821 HCI Millettia 0.808 0.475 0.867 0.957 0.734 HCI Pterocarpus 0.263 0.974 0.785 0.085 0.174 Effects on basal diameter of sandalwood in the plot periphery HCI Cathormion 0.139 0.513 0.696 0.490 0.270 HCI Cedrela 0.490 0.474 0.252 0.063 0.395 HCI Dalbergia < 0.001 < 0.001 0.051 0.197 0.015 HCI Khaya < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 HCI Millettia < 0.001 0.021 0.113 0.613 0.257 HCI Pterocarpus 0.458 0.079 0.036 0.013 0.120 Effects on basal diameter of the host-species treatment by HCI interaction Treatment x HCI Cathormion 0.857 0.314 0.477 0.68 0.684 Treatment x HCI Cedrela 0.701 0.080 0.028 0.078 0.019 Treatment x HCI Dalbergia 0.020 0.128 0.109 0.186 0.389 Treatment x HCI Khaya 0.129 < 0.001 < 0.001 < 0.001 0.003 Treatment x HCI Millettia 0.653 0.003 < 0.001 0.005 0.009 Treatment x HCI Pterocarpus 0.363 0.081 0.302 0.221 0.39

Error Variance 9.3 9 8.9 8.9 8.9 All effects were fitted simultaneously for each horizon, where data for plot interior was excluded because differences were not significant. P-values < 0.05 are presented in bold. (Note Millettia pinnata syn. Pongamia pinnata.)

Host size-distance indices

Results from fitting the host size-distance indices (HSDIs) were generally similar to those from fitting the host count indices, particularly within the plot periphery where Dalbergia, Khaya and Millettia again had significant effects on sandalwood diameter across most horizons (Table 4.13). Also the interaction effects of host species within the plot periphery had a similar pattern, with the exception that Dalbergia interactions were significant up to 12 m for the HSDI compared to only 6 m for the HCI. However, there was one important difference between the indices, in that the HSDI displayed significant negative effects on sandalwood basal diameter within the plot interiors of two treatments, Cathormion and Millettia (Table 4.14). This indicated that an increase in the relative size of the host (as indicated by the HSDI) within the plot interior neighbourhoods, resulted in a decline in basal diameter of sandalwood with Cathormion and Millettia hosts.

Final reduced models for each species treatment were again produced using only the most significant horizons (Table 4.13), with the estimated effect on sandalwood diameter of the final model indicated (Table 4.14).

Table 4.12 Estimates for significant effects of host count index (HCI) on sandalwood basal diameter in Trial 7 Effect Level Estimate SE mu (overall mean) na 13.96 0.51 Effects on basal diameter of sandalwood in the plot interior Dalbergia 1.23 0.57 Pterocarpus -2.16 0.58 Host-species treatment Cedrela -4.42 1.06 Khaya -7.55 0.78 Effects on basal diameter of sandalwood in the plot periphery Treatment-specific Cedrela -0.15 0.05 HCI Cedrela 12 m Millettia 1.17 0.42 Treatment-specific Cedrela 5.63 1.62 HCI Dalbergia 6 m Dalbergia 0.64 0.19 Treatment-specific Dalbergia -0.48 0.19 HCI Khaya 9 m Khaya -0.92 0.08 Cedrela 1.46 0.4 Treatment-specific Millettia 0.1 0.04 HCI Millettia 12 m Pterocarpus -0.46 0.18 Estimates are made using the final reduced model containing the most significant horizons displayed in Table 4.11.

Table 4.13 P-values for model effects on sandalwood basal diameter using host size-distance indices (HSDIs) in Trial 7

Effect 6 m 9 m 12 m 15 m 18 m horizon horizon horizon horizon horizon Mu (overall mean) < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 Effects on basal diameter of sandalwood in the plot interior Treatment < 0.001 0.01 0.01 < 0.001 0.002 HSDI Cathormion 0.02 0.03 0.07 0.10 0.23 HSDI Cedrela 0.32 0.41 0.18 0.15 0.24 HSDI Dalbergia 0.18 0.26 0.14 0.06 0.09 HSDI Khaya 0.36 0.46 0.80 0.84 0.94 HSDI Millettia 0.04 0.48 0.42 0.22 0.24 HSDI Pterocarpus 0.33 0.65 0.79 0.37 0.28 Effects on basal diameter of sandalwood in the plot periphery HSDI Cathormion 0.38 0.99 0.58 0.22 0.20 HSDI Cedrela 0.09 0.13 0.34 0.38 0.64 HSDI Dalbergia < 0.001 < 0.001 0.001 0.002 0.001 HSDI Khaya < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 HSDI Millettia 0.003 0.05 0.03 0.06 0.06 HSDI Pterocarpus 0.06 0.02 0.11 0.23 0.29 Effects on basal diameter of the host-species treatment by HSDI interaction Treatment x HSDI Cathormion 0.65 0.40 0.24 0.27 0.28 Treatment x HSDI Cedrela 0.52 0.98 0.15 0.08 0.04 Treatment x HSDI Dalbergia 0.04 0.04 0.03 0.08 0.16 Treatment x HSDI Khaya 0.08 0.002 0.002 < 0.001 0.001 Treatment x HSDI Millettia 0.47 0.003 0.003 0.004 0.01 Treatment x HSDI Pterocarpus 0.13 0.09 0.15 0.07 0.09

Error variance 9.3 9.1 8.9 8.8 8.8 All effects were fitted simultaneously for each horizon. P-values < 0.05 are presented in bold.

A positive interaction was again observed between Cedrela–Millettia and Cedrela–Dalbergia (Table 4.14). An increase in the relative size and density of Millettia trees within 12 m of sandalwood in Cedrela plot increased basal sandalwood diameter by 1.77 ± 0.43 cm per HSDI unit, and by 2.16 ± 0.64 cm for each unit increase in HSDI of Dalbergia hosts within 9 m of a Cedrela plot. Unlike for the HCI the benefit was not reciprocal and was only statistically significant when the subject sandalwood was located in a Cedrela plot. A significant negative interaction was again observed between Millettia and Pterocarpus.

Table 4.14 Estimates for significant effects of host size-distance index (HSDI) on sandalwood basal diameter in Trial 7 Effect Level Estimate SE Mu (overall mean) na 13.47 0.48 Effects on sandalwood basal diameter in plot interior positions Cathormion 3.61 1.18 Cedrela -3.64 1.05 Dalbergia 4.45 1.52 Host treatment effects Khaya -6.98 0.78 Millettia 3.48 1.30 Pterocarpus -1.64 0.56 HSDI Cathormium 6m -1.03 0.42 HSDI Millettia 6m -0.49 0.24 Effects on sandalwood basal diameter in plot periphery positions Treatment-specific Cedrela -0.19 0.06 HSDI Cedrela 12 m Cedrela 1.77 0.43 Treatment-specific Dalbergia 0.48 0.11 HSDI Dalbergia 9 m Khaya 1.11 0.45 Treatment-specific Dalbergia -0.29 0.10 HSDI Khaya 9 m Khaya -0.44 0.04 Cathormion 0.37 0.38 Treatment-specific Cedrela 2.16 0.64 HSDI Millettia 12 m Millettia 0.16 0.06 Pterocarpus -0.69 0.29 Estimates are made using the final reduced model containing the most significant horizons displayed in Table 4.13.

Discussion

Host species within plot interiors were more influential in determining sandalwood growth than the effect of the number and relative size of hosts as indicated by the two competition indices used here. The host-species effects displayed here were in general agreement with the analysis using the original trial design elements completed by Barbour (2008) that indicated sandalwood was larger with Dalbergia and Millettia followed by Cathormion. However, the analysis used here revealed more about the nature of interactions between hosts in their support of sandalwood size within single and multi-species environments that were not previously detected or confirmed. For example, the resilience of Dalbergia as a host was highlighted by Barbour (2008), as it was able to promote superior sandalwood growth even when lower host survival reduced the ratio of sandalwood to hosts to 1:0.6, compared to a 1:1.2 ratio for Millettia. The analysis here further complements this finding by indicating significant positive effects of the number and relative size of Dalbergia on sandalwood growth in all plot periphery horizons (excluding 15 m HCI). Importantly, this confirms that sandalwood size was improved by the presence of Dalbergia hosts, and not as a result of increased availability of space and reduced host competition. As such, it could be predicted that sandalwood growth would have been further improved if Dalbergia survival had been greater.

In contrast to Dalbergia, the HSDI, the sum of host relative basal diameters, of Millettia and Cathormion had a significant negative effect on sandalwood size within a 6 m radius of sandalwood.

This indicated that these two species were more aggressive competitors than Dalbergia when in close proximity to sandalwood. Interestingly, the number of hosts (HCI) did not display the same negative effect at this proximity, which suggests suitable plantation management to increase sandalwood growth with these two host species may be to retain host stocking but modify host structure, for example by canopy pruning.

Another benefit of the analysis was the ability to determine sandalwood response in a multiple-host environment that existed beyond the structured blocking used in the original experimental design. Visual observation of sandalwood within the boundaries of Millettia and Dalbergia plots suggested there could be a positive ‘combining effect’ of the two superior host species; however, somewhat surprisingly, the analysis displayed a lack of significant growth response above that in single-host environments. This is an example of the imbalance that can occur between observation and quantitative results, and highlights the utility of the analysis technique in maximising information gained from sandalwood trials. Other species combinations, notably Cedrela–Millettia and Cedrela– Dalbergia, did display positive effects on sandalwood growth despite Cedrela being a very poor host in a single-species environment. Using a low ratio of Cedrela within a host mix could be further investigated.

The original trial design had trees positioned on a repeated rectangular grid with constant spacing between hosts and sandalwood for all host species, where differentiation in spatial arrangement only occurred through tree mortality. Competition indices improve the outcomes of analysis in trials where mortality has modified the original design (Bristow et al. 2006), but Vanclay (2006a) warns common forestry trial designs, such as that used here, rarely provide a good basis for maximising the information gained from competition indices. In addition, basal area was used as the physical parameter for the calculation of HSDI, but it may not be the optimal parameter of competition evaluation in sandalwood plantations. Canopy parameters may provide a better indicator of competition in sandalwood trials because they display a more ‘plastic’ response to competition (von Oheimb et al. 2011). Further investigation using alternative trial designs (Vanclay 2006a), index calculation, and methods for horizon calculation (von Oheimb et al. 2011; Rivas et al. 2005) should improve the methodology. The goal of such work would be to provide a response surface of sandalwood growth in relation to various host, stocking and spatial regimes to predict optimal plantation arrangements, as demonstrated by Vanclay (2006b) for mixed Acacia and Eucalyptus plantations. This approach would narrow plantation design and host species options so that more efficient field testing could be completed, as opposed to a ‘trial and error’ approach.

The aim of this study was to provide a preliminary investigation of the utility of spatial competition indices in providing insight into the effect of interactions between sandalwood and hosts on tree growth at the individual tree level. The two indices used here, host count index (HCI) and host size- distance index (HSDI) produced similar results and were able to show some differentiation in the response of sandalwood to competition from different host species. Whilst not definitive, these results offer reasons to suggest that considerable scope exists to improve the analysis technique for use in sandalwood plantations.

4.3.2 Spatially-dependent host effects on sandalwood size within a trial without an experimental design, Trial 3

Method

Trial description

Trial 3 was planted in 1993. The planting consists of separate host-species blocks with no experimental design applied. The Peltophorum block had four rows with hosts at 9 m spacing and sandalwood planted at 3 m either side of each host within the row. The sandalwood-to-host ratio at establishment was 2:1 with stocking of 1235 SPH for sandalwood and 617 SPH for hosts. The area of

this block was 0.13 ha. The Cassia block contained 10 rows. Odd-numbered rows had alternate positions of host and sandalwood at 3 m spacing, and even-numbered rows were planted only with sandalwood spaced at 3 m. The planting ratio of sandalwood to hosts was 3:1 with sandalwood stocked at 929 SPH and hosts at 309 SPH. The area of this block was 0.41 ha.

Measurement

In 2001 (8 years old) sandalwood DBH, basal diameter, bole height and tree height were measured. Measurements in 2008 (15 years old) recorded sandalwood DBH, basal diameter, bole height, crown break diameter (CBD) and tree height for both sandal and host. Calculated parameters of basal area, bole volume and estimated stem volume (ESV) were done on an individual tree and per hectare basis.

Data preparation

Data from 2001, when only sandalwood parameters were measured, was used to determine relative growth. Tree height, basal area and total stem volume were used as variables in the analysis. The position of each tree in two-dimensional space was also recorded as the distance (meters) between trees within and across rows.

The usual application of competition indices is to quantify the competition environment of subject trees as a potential determinant of growth in the forthcoming period. Applying this would involve using competition indices formulated with the 2001 data as potential determinants of growth from 2001 to 2008. However, because host size data was not available from the 2001 assessment, an assumption was therefore made that tree height of each host tree in 2001 was 0.7 times tree height at 2008, and that basal area of each host tree in 2001 was 0.5 times basal area in 2008. These assumed host data were only used for the calculation of interaction indices, not for analysis of host tree growth. Relative growth in the period of 2001–2008 was estimated following Causton and Venus (1981):

Relative growth = ln(basal area in 2008) – ln(basal area in 2001) Equation 1

Development of tree-tree interaction indices

The indices of tree-tree interaction between sandalwood and hosts cannot strictly be termed competition indices because the parasitic nature of the relationship means that a host is a potential resource as well as a competitor in the plantation environment. As such the indices between host trees and sandalwood will be referred to as either ‘hosting indices’ or ‘parasitism indices’, as a measure of the effect of hosts on sandalwood, and sandalwood on hosts respectively. The term competition indices can refer to host-host and sandalwood-sandalwood interactions.

The indices used in the analysis can be characterised by three parameters which define the relationship described by an index, these are:

• distance, where indices can either be distant-independent or distant-dependent where the index includes the distance between subject tree and interacting trees

• competitor size, where indices are either size-independent or size-dependent if the index includes a relative measure of the size of competitor (host) trees

• subject size, where indices are either subject-independent or subject-dependent if the index includes the size of the subject tree.

A critical aspect of competition analysis is correctly identifying which neighbouring trees are interacting with the subject tree. Typically, neighbouring trees are considered to be interacting with a subject tree if they are located within a specified distance. For the present analyses, the neighbourhood distance has been defined as:

Ds = Ks*(subject tree height + neighbouring tree height) Equation 2 where Ks is a variable coefficient between 0 and 1, used to modify the size of the neighbourhood horizon. For example a Ks of 0.5 indicates a neighbourhood of half the sum height of the target tree and neighbour.

The well-established Hegyi competition index was applied to the prediction of sandalwood relative growth by tree-tree interactions in 2001:

IHegyi = ∑i BANi/BAs x Di Equation 3 where BANi is the basal area of neighbouring tree i, BAS is the basal area of the subject tree and Di is the distance from the subject tree to the neighbouring tree for all trees I, where Di

ISIndep = ∑i BANi/Di Equation 4

HIhost count = n(hosts) Equation 5

1 HIhost ratio = ∑i /ns Equation 6 where ISIndep is a subject-independent, size-dependent and distance-dependent index derived from the Hegyi index. HIhostcount is a count of host trees within qualifying distance Ds to subject sandalwood trees. HIhostratio is an index of the effective host-to-sandalwood ratio experienced by subject sandalwood trees where ns is a count of the number of sandalwood trees within qualifying distance Ds of host tree I, see Figure 4.13 in which host A has the subject sandalwood and two other sandalwood trees (open stars) within qualifying distance Ds.

The program Simile (Simulistics, Edinburgh) was used for calculating interaction indices. Each index was estimated with a range of Ks values to infer the effective distances over which tree-tree interactions could be detected. ISIndep was analysed with respect to competition, hosting and parasitism, whereas HIhostcount and HIhost ratio were only considered as hosting indices.

Statistical analysis

Interaction indices were treated as covariates in linear models to explain growth and stem volume using S-Plus V.6.0. Dependent variables were transformed when necessary to satisfy normality of residuals, and outliers were occasionally removed to ensure residuals were homoscedastic. Row number and within-row position were included as covariates or factors when their effect was significant.

Figure 4.13 Spatial representation of a subject sandalwood tree (solid star) surrounded by four neighbouring host trees (A–D: solid diamonds) within qualifying distance Results

Sandalwood relative growth

Only 11 sandalwood trees survived to 2008 in the Peltophorum block and the statistical power for analyses of their growth or volume was accordingly weak. Nevertheless, tree-tree interactions appeared to be more marked in this smaller block than in the Cassia block.

Hegyi competition indices (CIhegyi) with Ks between 0.6 and 0.8 explained significant variation in sandalwood relative growth (Table 4.15). The growth response to competition indices was negative, suggesting significant competition for resources between sandalwood up to an average distance of 10.8 m (equivalent to Ks = 0.8 in 2001). Hegyi hosting indices (HIhegyi) also displayed negative relationships with sandalwood relative growth where indices with Ks were between 0.3 and 0.8 (Table 4.15). This suggests that sandalwood growth was reduced as the combined size of the Peltophorum host trees in their neighbourhoods increased. Multiple regression models including CIhegyi and HI hegyi indices explained more variation (up to R2 of 0.75) in relative growth than univariate regressions (Table 4.15). The optimum Ks for CIHegyi in multiple regressions was 0.8 (average interaction limit 10.6 m) whereas the Ks for HIHegyi was optimised at either 0.3 (average 4.7 m) or 0.8 (average 12.5 m).

The size-independent index HIhostratio with Ks = 0.6 (average interaction limit 12.1 m) explained a similar proportion of variance in sandalwood relative growth in the Peltophorum block to the best multiple regression of Hegyi indices (Table 4.15). The host ratio index was superior to the Hegyi indices in this comparison as the excluded outlier in the Hegyi regression was well-predicted by the host ratio index. Unlike for the Hegyi indices, sandalwood growth from 2001 to 2008 was positively related to HIhostratio. This suggests that subject sandalwood trees with greater numbers of available Peltophorum hosts (i.e. hosts without or with few nearby sandalwood trees) were at a growth advantage.

Table 4.15 Summary of selected significant linear models explaining the relative growth of sandalwood with Peltophorum and Cassia hosts between 2001 and 2008 in Trial 3 Independent Sign of Effect Model Model Host variable(s) Ks Outliers coefficient P-value P-value R2 Peltophorum CIHegyi 0.5 0 negative 0.06 0.058 0.35 0.6 0 negative 0.01 0.013 0.50 0.7 0 negative 0.01 0.013 0.50 0.8 0 negative 0.02 0.024 0.45 HIHegyi 0.3 1 negative 0.02 0.016 0.53 0.4 1 negative 0.04 0.035 0.45 0.5 1 negative 0.02 0.020 0.50 0.6 1 negative 0.03 0.029 0.46 0.7 1 negative 0.01 0.008 0.61 0.8 1 negative 0.01 0.006 0.62 CIHegyi 0.8 1 negative 0.04 0.008 0.75 HIHegyi 0.3 0.01 CIHegyi 0.8 1 negative 0.11 0.008 0.75 HIHegyi 0.8 0.02 HIhost ratio 0.6 0 positive 0.00 0.009 0.69 row (covariate) 0.15 Cassia HIhost ratio 0.7 1 positive 0.01 0.019 0.08 row (covariate) 0.09 HIhost ratio 0.8 1 positive 0.00 0.006 0.10 row (covariate) 0.04 HIhost ratio 0.9 1 positive 0.00 0.010 0.13 row (covariate) 0.02 HIhost ratio 1 1 positive 0.00 0.007 0.10 row (covariate) 0.04 Where CI and HI indicate indices representing effects of sandalwood-sandalwood and host-sandalwood interactions respectively.

Interaction indices provided less prediction of sandalwood growth in the Cassia block than in the Peltophorum block. None of the Hegyi indices were statistically significant either singly or in multiple regression combinations. Host ratio indices were significant with Ks values between 0.7 and 1.0 although they explained only 8 to 13 per cent of variation in sandalwood growth, which was considerably less than in the Peltophorum block.

Sandalwood stem volume

It would be inappropriate to predict stem volume with subject-dependent indices, as the dependent variable would be represented in the denominator of the predictive variables. Therefore, only subject- independent indices were evaluated as explanatory variables for stem volume in 2008.

The subject-independent hosting index derived from the Hegyi index (HISIndep) was a significant predictor of sandalwood volume in the Peltophorum block at two values of Ks: 0.4 and 0.5 (Table 4.16). This neighbourhood equates to an average tree-tree distance of 10.1 m. The relationship between HISIndep and sandalwood volume was negative which supports the findings of the analysis of

sandalwood growth using the Hegyi hosting index that large Peltophorum host trees can negatively impact sandalwood growth within a neighbourhood of 10 m.

The subject-independent competition index was not significant with Ks between 0.2 and 1.0. The host count index (HIhostcount) was the simplest index used, derived from a count of hosts within the neighbourhood; it proved to be the most powerful predictor of sandalwood stem volume in the Peltophorum block. This index accounted for approximately 60 per cent of the variation in the data when using Ks of 0.8 to 1.0 (Table 4.16). This relationship was positive, implying that increasing numbers of Peltophorum hosts within the neighbourhood of sandalwood were beneficial in increasing sandalwood stem volume. These results support the conclusion drawn from the growth analysis with Hegyi indices; that the number rather than the size of nearby Peltophorum hosts was beneficial to sandalwood.

The larger dataset of sandalwood stem volume in the Cassia block offered greater power to detect significant effects of interaction indices. All HIhostcount and HIhostratio indices with Ks between 0.2 and 1.0 were statistically significant, although only the best models for each index type are presented 2 (Table 4.16). The index with best explanatory power was HIhostratio with Ks of 0.8 (R =0.36, P<0.0001). Sandalwood volume was positively related to the presence of ‘available’ Cassia host trees (i.e. those without other nearby sandalwood trees) within an average of 13 m, which is equivalent to Ks of 0.8 for this index.

Size-dependent indices were only significant for sandalwood stem volume in the Cassia block when a hosting index (HISIndep) and competition index (CISIndep) were combined in multiple regression. The optimum Ks in such multiple regression models was 1.0 for HISIndep and 0.4 for CISIndep (Table 4.16), which equate to an average Cassia-sandalwood interaction limit of 16.3 m and an average sandalwood-sandalwood interaction limit of 6.5 m. The hosting index was positively related to sandalwood volume and was more significant in this model than the competition index, which was negatively related to sandalwood volume. These results support the conclusions drawn from evaluation of the host ratio index, that sandalwood stem volume is increased when the number of available hosts increases within the neighbourhood.

Host stem volume

Host tree volume could be reduced by parasitism from nearby sandalwood and by competition from other nearby hosts. Both of these effects were statistically significant on Peltophorum as represented by size-dependent parasitism indices and competition indices (Table 4.17). As univariate predictors of Peltophorum stem volume, parasitism (PISIndep) and competition (CISIndep) indices were most significant at Ks = 1.0 (Table 4.17). However, the best model of Peltophorum volume included both PISIndep and CISIndep in multiple regression, explaining 45 per cent of variation in the data (Table 4.17). The average neighbourhood limits for Peltophorum-sandalwood and Peltophorum-Peltophorum interactions accounted in this model were 14.1 m and 25.8 m respectively.

Table 4.16 Summary of selected significant linear models explaining sandalwood stem volume with Peltophorum and Cassia hosts in Trial 3 Independent Sign of Effect Model Model Host variable(s) Ks Outliers coefficient P-value P-value R2 Peltophorum HISIndep 0.4 0 negative 0.00 0.001 0.36 0.5 0 negative 0.02 0.020 0.46 HIhost count 0.7 0 positive 0.01 0.013 0.51 0.8 0 positive 0.00 0.004 0.61 0.9 0 positive 0.00 0.004 0.63 1.0 0 positive 0.01 0.005 0.60 HIhost ratio 1.0 0 positive 0.04 0.040 0.39 Cassia HISIndep 1.0 1 positive 0.00 0.005 0.13 CISIndep 0.4 0.04 row (covariate) 0.00 HIhost ratio 0.9 1 positive 0.00 <0.001 0.22 row (covariate) 0.00 position (covariate) 0.17 HIhost ratio 0.8 1 positive 0.00 <0.001 0.36 row (factor) 0.01 position (covariate) 0.01 Where CI and HI indicate indices representing effects of sandalwood-sandalwood and host-sandalwood interactions respectively.

Variation in Cassia stem volume was best explained by positive effects of PISIndep and CISIndep in multiple regression (Table 4.17). A possible explanation for positive correlations between the size of subject trees their neighbours is that these indices were registering spatial autocorrelation due to shared environment, rather than tree-tree competitive interactions. Alternatively, the positive sign of these relationships for Cassia compared with the negative sign for Peltophorum may indicate that Cassia stem volume is more resilient to the effects of parasitism and/or intra-specific competition. However, lack of replication in the experimental design means that the parasitism, competition and species effects could not be separated from the potential environmental effects within the trial.

Table 4.17 Summary of selected significant linear models explaining the stem volume of Peltophorum and Cassia in Trial 3 Independent Sign of Effect Model Model Species variable(s) Ks Outliers coefficient P-value P-value R2 Peltophorum PISIndep 0.4 0 negative 0.05 0.049 0.07 0.5 0 negative 0.04 0.037 0.08 0.6 0 negative 0.03 0.030 0.09 0.7 0 negative 0.02 0.016 0.20 0.8 0 negative 0.01 0.012 0.12 0.9 0 negative 0.01 0.008 0.13 1.0 0 negative 0.00 0.002 0.28 CISIndep 0.9 0 negative 0.05 0.047 0.07 1.0 0 negative 0.03 0.025 0.09 PISIndep 0.7 1 negative 0.04 <0.001 0.45 CISIndep 1.0 0.02 row (covariate) 0.00 Cassia PISIndep 0.4 1 positive 0.04 0.036 0.04 0.5 1 positive 0.01 0.014 0.05 0.6 1 positive 0.01 0.009 0.06 0.7 1 positive 0.01 0.005 0.07 0.8 1 positive 0.01 0.005 0.07 0.9 1 positive 0.01 0.005 0.07 1.0 1 positive 0.01 0.007 0.06 CISIndep 0.3 1 positive 0.00 0.000 0.13 0.4 1 positive 0.00 0.000 0.11 0.5 1 positive 0.01 0.006 0.06 0.6 1 positive 0.00 0.004 0.07 0.7 1 positive 0.01 0.013 0.05 0.8 1 positive 0.04 0.042 0.04 PISIndep 0.8 1 positive 0.07 <0.001 0.38 CISIndep 0.4 0.00 row (factor) 0.00 CI and PI indicate indices representing effects of host-host effect and sandalwood–host effect (parasitic effect) respectively.

Discussion

The preliminary analysis using interaction indices has given an indication to their potential utility in examining and comparing the nature of the intra-specific, parasitic and hosting relationships within the sandalwood plantation environment. Notwithstanding the problems associated with lack of replication at the species level and limited data available with the Peltophorum block, some comparison can be made between Peltophorum and Cassia as hosts for sandalwood.

In both cases, sandalwood growth and volume were improved by proximity to host trees that had a lower number of nearby sandalwood. This would seem to indicate that both species are functional hosts and provide some facilitative effect that is beneficial to sandalwood growth. However, sandalwood relative growth and volume in the Peltophorum block were negatively associated with size-dependent hosting indices. This relationship indicates that where Peltophorum size increases the

facilitative benefits of the host, it is increasingly outweighed by an increase in the competition for primary resources within the environment, which results in lower sandalwood growth. Despite Cassia being considerably larger than Peltophorum, it did not appear to have the same size-dependent detrimental effect on sandalwood relative growth or stem volume.

The sandalwood to sandalwood competition in the Peltophorum block appeared to have a stronger negative effect on growth between 2001 and 2008 than within the Cassia block. This occurred despite the number of sandalwood on a per hectare basis being over 2.5 greater in the Cassia block. Whilst the data does not provide direct insight into the cause of such an anomaly, it does provide a stimulus for further investigation as to why it may occur. For example it could be hypothesised that the Cassia has a higher availability of roots within a compatible soil horizon which could increase the number of sandalwood–host connections, potentially limiting sandalwood-sandalwood parasitism. Other explanations relating to root physiology, differentiation in nutrient draw from hosts, and competition for primary resources could be investigated to further the understanding of factors that contribute to a successful host.

In the analysis presented here, neighbourhood areas were defined in terms of tree heights rather than discrete distances. This should have the advantage of accounting for the asymmetrical nature of above-ground competition, in that larger trees will have greater spheres of influence within the environment. The spatial extent of tree-tree interaction limits revealed by the analysis was surprisingly large, with few significant indices extending to less than an average of 10 m. For example the average sandalwood-host interaction limited for the most significant relationship between the Peltophorum count index and sandalwood volume was 18 m at a distance coefficient of 0.9 (Table 4.16). The specific combination of the tallest Peltophorum and sandalwood trees within the analysis (18.7 m and 10.5 m respectively) equated to an interactive neighbourhood of over 26 m. Such observations have important ramifications for the experimental design of sandalwood host trials and plantations. In particular, large plots to separate out treatment effects are required if tree-tree interaction indices are not used as part of the analysis.

4.4 Sandalwood heartwood and oil development

The commercial value of Santalum album is largely dependent on its fragrant heartwood. This heartwood is used in joss sticks and carvings, and the sandalwood oil extracted from it is sought after for a number of aromatic, flavour and health-based products. The majority of the oil is composed of sesquiterpene alcohols, dominated by α (alpha) and β (beta)-santalol (Verghese et al. 1990; Jones et al. 2006) which are the primary indicators of oil quality. Whilst the control of oil production at the molecular level is starting to be uncovered (Jones et al. 2006; Jones et al. 2008; Jones et al. 2011), the factors involved in initiation and regulation of heartwood and oil development are not well understood but like most tree characteristics are likely to be the result of genetic and environmental interactions.

Although traditional estimates of the heritability of heartwood and oil have not been established, the FPC sandalwood germplasm has relatively low levels of genetic diversity compared to natural stands in India (Suma and Balasundaran 2003), yet it displays substantial phenotypic variation in heartwood (Jones et al. 2009). Whilst there may well be genotypes with a predisposition for heartwood and oil production, the environmental component is likely to be highly influential in the stimulation of heartwood and oil deposition. It is possible that differences in heartwood and oil directly relate to variation in uptake of assimilates between host species (Radomiljac et al. 1998c), as well as the potential transfer of species-specific compounds between host and root hemi-parasites (Loveys et al. 2001). In addition, differences in host root and canopy structure and competition may indirectly affect heartwood and oil content by modifying the immediate environment. This could result in differential exposure to stress factors such as amount of sunlight and pathogens, which have been implicated, but not confirmed, as contributors to heartwood initiation and/or development (Rai 1990; Barbour et al. 2010). To date host species selection has been conducted primarily on the basis of optimising growth performance, and there is a need to complement this work with data on heartwood formation.

Heartwood occurrence in plantation trees has largely been monitored using non-destructive core sampling at one or two heights within the stem (Brand et al. 2006; Brand et al. 2007; Jones et al. 2007). Some heartwood has formed in some 10-year-old trees in plantations (Rai 1990; Jones et al. 2007), with most trees producing heartwood by 14 years (Brand et al. 2006; McComb 2009). Destructive harvesting from natural forests indicates heartwood formation can be delayed to 14-46 years and even in mature trees the amount and proportion of heartwood is highly variable (Rai 1990; Haffner 1993; Venkatesan et al. 1995), Whilst non-destructive core sampling allows for the assessment of the presence of heartwood and oil, it has not provided a clear assessment of the amount (volume) and pattern of heartwood development and there is a need to better quantify the heartwood and oil development within plantation-grown sandalwood trees. This will aid plantation managers in estimating plantation yield and in decision making for host selection, planting designs, thinning programs and rotation lengths.

Core sampling within the FPC trials has in some cases proved not entirely ‘non-destructive’. The invasive nature of the method provides an entry point for pathogens that are damaging to wood quality, and possibly long-term tree health (Barbour et al. 2010). The ability to confirm the presence and estimate the volume of heartwood in standing trees is required to improve plantation management and estimate harvest yield but to reduce the risk of tree damage, alternative techniques of heartwood evaluation are necessary. Non-destructive methods to evaluate wood properties have been around since the 1940s. Advances in technology have seen a suite of methods developed and some of these may be adapted for use in analysis of standing trees (Bucur 2003). Two of these methods, electrical impedance tomography and acoustic time-of-flight, utilise a portable device that, once calibrated to a species and environment, would provide data capture at a rate similar to core sampling. The methods are based on different signals to determine wood characteristics: electrical impedance uses electrical current that responds to variations in chemical properties of wood, specifically moisture content; and acoustics utilise sound waves that respond to the mechanical properties of wood. The ability of these methods to determine heartwood characteristics in sandalwood is untested, but if successful they would provide useful tools to improve plantation evaluation and management.

This section presents results from destructive harvesting and non-destructive sampling of sandalwood between 8 and 15 years of age. Destructive harvests aimed to describe wood volume and pattern of heartwood production within trees aged 8 and 15 years, whilst core sampling was used to examine the occurrence of heartwood and oil within 11-year-old sandalwood grown with different host species. In addition to measurements of the usual heartwood, fungal rots in these trees were often associated with an encapsulation that has been shown to contain heartwood (Barbour et al. 2010), but did not appear to be part of the normal heartwood formation process. A preliminary investigation of two non- destructive wood-evaluation methods, electrical impedance and acoustic time-of-flight, was also undertaken.

4.4.1 The destructive harvest of 8-year-old sandalwood, Trial 8

Method

Trial establishment

Trial 8 was originally established in 2000 to assess the growth response of S. album in a multi-species plantation environment. Primary, short-lived host species included Sesbania formosa, Acacia auriculaformis and A. crassicarpa, with secondary, long-term hosts being Cathormion umbellatum, Castenospernum australe, Dalbergia latifolia and Dalbergia retusa. A primary host-to-sandalwood ratio of 2:1 was planted with sandalwood in every second row with a primary host either side. Rows were 3.6 m apart with 3 m spacing between sandalwood and secondary host trees within rows. During 2002 an inappropriate application of herbicide overspray resulted in widespread deaths of both host and sandalwood. The remaining trees were retained and received little management except for bole pruning and regular irrigation during the dry season.

Plate 4.3 Typical 8-year-old tree from this trial Destructive harvest

At 8 years of age, 30 trees with clear boles were selected for harvesting and were pulled out by their roots (see Plates 4.3 and 4.4). The trees were laid on the ground and measured for height, basal diameter, breast height diameter, crown break diameter and bole length. Trees were then sectioned into roots, bole and crown and each section weighed. Discs were then cut from the bole section at the base, lower third, upper third and top, and green weight recorded. After air-drying for 8 weeks a dry weight was obtained. Image analysis of disc photographs with Image J (NIH, USA) was used to determine under-bark disc area, heartwood area, and area of wood rot for manually outlined areas on each disc. Whilst wood rot data is presented here, a more comprehensive analysis of rot, including fungal isolation and identification, was undertaken within a separate RIRDC project (Barbour et al. 2010).

Plate 4.4 A sample of the 8-year-old wood assessed after the destructive harvest

Simple and multiple linear regressions were used to determine relationships between measured variables (XLStat, 2006). For multiple regression, model selection was determined by comparing the

coefficient of determination (R2) and Akaike information criteria (AIC). The normal distribution of residuals was checked using the Kolmogorov-Smirnov test.

Results

A typical tree from this 8-year-old trial was 4.9 m tall with a bole 1.8 m long with a basal diameter of 14.7 cm, which gradually tapered to 10.2 cm at breast height diameter and to 9.9 cm just prior to crown break (Table 4.18). These 8-year-old trees on average weighed 60.9 kg which was made up of 15.1 kg of stump, 17.5 kg of bole with the remainder being the branches (Table 4.18). The commercially valuable portion of the tree, roots and bole, typically made up 54 per cent of total mean tree weight.

The mean water content of the 120 discs as indicated by weight loss after air drying was 33.1 ± 6.7 per cent, and was lowest in the basal discs with 29.5 ± 10.1 per cent, and highest in the upper third disc with 34.8 ± 4.7 per cent. For individual trees, mean weight loss ranged from 15.4 ± 3.0 to 38.7 ± 5.1 per cent.

Table 4.18 Growth parameters for 30 trees destructively harvested after 8 years from Trial 8 (mean ± s.d., minimum and maximum) Parameter Mean Minimum Maximum Tree height (m) 4.9 ± 0.6 3.64 6.50 Bole length (m) 1.8 ± 0.16 1.01 2.54 Basal diameter (cm) 14.7 ± 1.1 11.90 17.00 DBH (cm) 10.2 ± 1.5 8.30 15.10 Crown break diameter (cm) 9.9 ± 1.7 7.00 15.10 Weight of tree bole (kg) 17.5 ± 3.1 11.26 24.70 Weight of tree crown (kg) 28.2 ± 13.4 8.00 70.00 Above ground tree weight (kg) 45.7 ± 14.7 18.30 85.33 Root weight (kg) 15.1 ± 4.0 5.58 22.80 Total tree weight (kg) 60.9 ± 16.0 33.54 106.11

The production of heartwood within the tree bole was highly variable as highlighted by standard deviations that were larger than sample means of the aromatic wood within the discs (Table 4.19). Among the 120 discs, 59 did not have any heartwood and three trees had no heartwood. Heartwood was clearly most prevalent in the basal disc of the bole, however within eight trees there was no heartwood in the basal disc.

The highest mean aromatic wood area from the four discs within an individual tree was 23.9 cm2 ± 16.5, some 18.6 ± 20.1 per cent of the bole wood. The single highest area and percentage of heartwood within a single disc was 67.0 cm2, 45.2 per cent of the disc area. The area of heartwood in basal discs did not display a linear relationship with disc area (P = 0.313, R2 = 0.048), that is discs with larger cross-sectional area did not have a larger area of heartwood.

Table 4.19 Total disc area and the area and percentage of heartwood and rot with discs located along the bole of 30 sample trees in Trial 8 (mean ± s.d.) Disc area Heartwood area Rot/damage Heartwood Rot/damage Disc position (cm2) (cm2) area (cm2) (%) (%) Top bole 53.9 ± 20.7 3.1 ± 6.2 1.9 ± 4.0 4.2 ± 7.8 3.1 ± 6.7 Upper 3rd bole 57.5 ± 15.0 1.6 ± 3.3 1.8 ± 3.6 3.0 ± 6.7 3.5 ± 7.2 Lower 3rd bole 77.6 ± 19.5 2.71 ± 4.5 3.1 ± 5.8 3.2 ± 4.5 3.6 ± 6.5 Base 1245.0 ± 22.8 14.5 ± 17.3 4.0 ± 8.03 11.2 ± 3.0 3.0 ± 5.8

There was a taper of the bole from base to crown break (Figure 4.14a), where the disc area declined from 100 per cent at the base to 62 per cent in the lower third, 46 per cent in the upper third and 43 per cent at the top of the bole. The taper of heartwood within the bole was more rapid. At the base, the heartwood accounted for 11.2 per cent of the disc; this heartwood declined rapidly to 3.2 per cent in the lower third (approximately 60 cm up the bole) and did not change from this level up the bole of the tree.

No significant linear relationship was found between the percentage of heartwood in basal discs and that of lower third discs (P = 0.118, R2 = 0.124). Heartwood shape was often irregular due to its association with heartwood rot (Figure 4.14b) and variability in longitudinal development of heartwood along the bole in 8-year-old trees.

The occurrence of rot within the bole was highly variable between trees (Table 4.18). Among the 120 discs, 73 had no rot and seven trees were free of rot. The proportion of heartwood rot within a disc was as high as 20.4 ± 12.1 per cent of the disc area. Within the 47 discs with rot damage, 14 had no aromatic heartwood and only one of these was from the base of the bole.

Analysing the discs with both rot and heartwood indicated a weak but significant (P = 0.008, R2 = 0.209) linear relationship between rot and heartwood (Figure 4.15a). As the presence of rot increased, the amount of heartwood increased.

The discs were clearly separated into two groups; those with the heartwood rot originating from the centre of the tree and those with rot originating in another area of the disc (Figure 4.15b). These separate relationships were both highly significant (P<0.001) and accounted for a high proportion of the variation in the data. Discs with rot in the centre of the bole included a large number of basal discs (nine of 20 samples) compared to discs with non-centre damage which included only one basal disc in 13 samples.

a b total area heartwood area Rot/dam. area

Figure 4.14 Stylistic representation of mean heartwood and rot areas within discs along the bole (a), and an example of non-uniform heartwood production with rot in the centre (b) from Trial 8

a 50 y = 7.43 + 0.61x b 50 45 R2 = 0.209 45 y = 7.18 + 1.47x 2 40 R = 0.758 P = 0.008 40 P <0.001 35 35 30 30 25 25 y = 1.81 + 0.26x 2 20 20 R = 0.764 15 P <0.001 Disc heartwood % heartwood Disc 15 Disc heartwood % heartwood Disc 10 10 5 5 0 0 0 10 20 30 40 0 10 20 30 40 Disc Rot/Damage % Disc Rot/Damage %

Figure 4.15 Relationships between the percentage of rot and aromatic wood within (a) all discs and (b) a comparison of discs with rot originating in the centre and other sites in boles from Trial 8

Discussion

This trial did not follow typical silvicultural practices for a tropical sandalwood plantation in Kununurra. Selecting the dominant trees ensured that each of these trees had sufficient hosts for optimum growth, and final stocking after the chemical damage meant that there was minimal spatial competition. Sun-scorch may have been a compounding issue as this can damage the bark allowing disease entry and restricting growth.

There were two sites for fungal disease entry into the bole of trees. The first entry site appeared to be through the centre of the tree via the juvenile wood and this resulted in cavity formation. This entry site positively stimulated heartwood production (Figure 4.15b). The second type of infection entered via entry sites other than the centre of the tree. Whilst this infection also increased heartwood in

relation to area damaged, there was only a relatively small increase in heartwood. For example, for a 25 per cent loss of heartwood area due to infection in the centre of the tree (juvenile wood) was on average associated with a response that produced heartwood in 45 per cent of the disc area, whereas when the fungus entered via at a site other than the centre (via the sapwood), the tree responded with production of heartwood in only 7 per cent of the disc area (Figure 4.15b). A more comprehensive appraisal of rot and identification of candidate fungal species in sandalwood have been undertaken, in which fungal species from at least 11 genera were isolated from rot sections and implicated as potential causal agents (Barbour et al. 2010).

Under silviculture conditions described here, 8-year-old sandalwood trees had an average total fresh weight of 60 kg of which around 33 kg, or approximately 22 kg of air dry wood, was from the root and bole wood. Heartwood was observed at the bole base of three-quarters (73 per cent) of 8-year-old trees and this could provide a commercial opportunity for thinning programs. The mid and upper sections of the tree contained sapwood, but the root stump and lower-third section of the bole contained up to 11 per cent heartwood and could have value as wood for the incense/agarbhartti industries. The cost associated with processing (de-sapping) trees at 8 years of age, which contain only small amounts of heartwood, may restrict profitability of these value-added products (principally oil from extraction).

4.4.2 The destructive harvest of 15-year-old sandalwood, Trial 4

Method

Trial establishment

Trial 4 was planted in 1994 originally to determine the suitability of three long-term hosts, Cassia siamea, Acacia mangium and Peltophorum sp., each planted in separate blocks with sandalwood. The original planting had 926 sandalwood per hectare planted in two out of three rows with 232 long-term hosts per hectare planted in the remaining row. Sandalwood rows were 3.6 m apart with the host row in the middle equidistant from the sandalwood trees. Poor sandalwood and host survival was observed at 8 years of age and so regular irrigation ceased in 2002. Generally only edge trees, close to water channels, survived.

Destructive harvest

Whilst random sampling is the preferred option, because of the low-maintenance regime and poor host survival, the largest 40 trees in the trial were selected for harvesting to provide a sample more representative of growth from a maintained plantation. Analysis indicated that the selected sample followed a normal distribution based on basal diameter and DBH (Figure 4.16). Among those selected, 19 were within 20 m from the end irrigation channel, 14 between 20 and 40 m, and 7 between 60 and 40 m from the channel.

Trees were cut at the bole base before tree height and diameter of up to three large branches dividing from crown break were measured. The tree was then divided into bole and canopy sections. The whole canopy was weighed followed by a sub-sample of canopy branches with a diameter greater than 4 cm. When heartwood was visible where a branch had been cut from the bole, the large end diameter (LED) and branch length was measured and then cut at approximately 15 cm intervals from the small end diameter (SED) until heartwood was visible. Heartwood was clearly distinguishable from sapwood as a dark yellow to brown colouration of wood. End discs were then labelled and photographed with a scale. The length and weight of the heartwood branch section was then measured, and discs taken from the LED and SED ends of the branch.

The bole was weighed and measured for total length and basal, breast height and crown break diameters. Boles were then cut into thirds, and 5 cm width discs were cut from the bole base, lower

third, mid third and at crown break. All discs were then labelled and photographed from above with a ruler scale at the disc surface. The disc parameters: total disc area over-bark, area under-bark, heartwood and rot area, were measured sing Image J software (NIH, USA). Disc parameters were interpreted, their outline manually traced and the cross-sectional areas were calculated by the image analysis package.

The root mass was divided into two sections, termed butt and roots, for volume estimation. The butt referred to the continuation of the bole from ground level to where the lateral roots emerged, and the root section was the lower mass which included the region where lateral roots emerged. A sub-sample of 20 root masses were cut vertically through the centre of the butt to where the lateral roots emerged, then horizontally through to this vertical cut. A photograph was taken of the vertical and horizontal face of each root section. Image analysis was then used to determine butt length and heartwood taper from top to bottom of butt, half-disc area and half-disc aromatic wood area.

Volume estimation

Bole volume under-bark was modelled for each tree using Smalian’s formula, using either total bole length (Equation 7) or the sum of sectional third volumes (Equation 8):

Bole vol (cm3) = (((3.142 x LER2) + (3.142 x SER2))/2) x bole length Equation 7

3 2 2 Bole vol (cm ) = ∑ ((((3.142 x LER1 ) + (3.142 x SER1 ))/2) x section length1) + ((((3.142 x 2 2 2 2 LER2 ) + (3.142 x SER2 ))/2) x section length2) + ((((3.142 x LER3 ) + (3.142 x SER3 ))/2) x section length3) Equation 8 where LER and SER are the large end radius and small end radius respectively, of the three bole sections.

Canopy stem volume (CSV) was modelled as a cone using either the end area of the crown break, or the end areas of up to the three largest branches dividing from crown break as in Equation 9:

CSV (cm3) = (((3.142 x LER2) x (tree height – bole height))/3 Equation 9 where LER is the diameter at crown.

Above-ground stem volume (under-bark) was modelled as the sum of bole volume and canopy stem volume.

Heartwood volume within the bole of each tree was modelled as the sum of the third sectional volumes calculated using cross-sectional areas from discs with each third having a large end area (LEA) and small end area (SEA), as per Equation 10:

3 Heartwood vol (cm ) = ∑ (((LEA1 + SEA1)/2 x section length1) + ((LEA2 + SEA2)/2 x section length2) + ((LEA3 + SEA3)/2 x section length3)) Equation 10

Where heartwood was not present at the small end diameter of a section a conical volume was used, with the LEA of the heartwood and section length substituted into the formula of Equation 9. Heartwood within the branches was calculated as per Equation 7, with bole length substituted by the length of heartwood within the branch.

Oil analysis

The 20 trees selected for root sampling were also used for oil analysis. Wood samples were taken from the root stump at 15 cm below stump top, from the basal disc, and then each bole third disc that contained heartwood. Heartwood shavings were collected from three holes made vertically through the disc with a 10 mm drill bit, one in the centre of the heartwood, and the other two at two-thirds

distance to the heartwood edge. Where the heartwood was too small for three holes, either one or two were made, making sure that only heartwood was sampled. Samples were placed in labelled envelopes and sent to Australian Botanical Products (Horsham, VIC) for oil extraction and gas chromatography analysis. Methods used by Australian Botanical Products are described in Brand et al. (2007).

Results

Growth and heartwood

14 12 10 8 6 Frequency 4 2 0 0-10.7 10.8- 13.0- 15.2- 17.4- 19.6- 21.8 + 12.9 15.1 17.3 19.5 21.7 Diameter class

Figure 4.16 Basal diameter class distribution of the 40 trees sampled in Trial 4 Measured growth parameters for the 40 trees indicated that on average bole weight accounted for around 37 per cent of total above-ground fresh weight, with branches greater than 4 cm diameter accounting for 31 per cent of the crown weight and 19.5 per cent of total above-ground fresh weight (Table 4.20). There was substantial variation within each parameter, bole fresh weight varied from 10 to 63 kg and root mass from 10 to 57 kg. Total crown weight varied from 10 to 153 kg with the subsample of branches greater than 4 cm diameter ranging between 3 and 61 kg.

Field measurements for the basal diameter and crown break diameter were 1.61 cm and 0.95 cm larger than those measured during photographic analysis respectively (Table 4.21). Disc photographic analysis showed average bark thickness varied between 7.8 and 8.4 mm along the bole, with an overall mean bole bark thickness of 8.0 ± 1.60 mm. The proportion of heartwood within disc cross sections decreased along the stem and at the base the mean area was 44.99 ± 25.80 cm2 compared to 5.83 ± 8.21 cm2 at crown break. The variability of heartwood also increased along the bole as indicated by the larger proportional standard deviations of the means. Heartwood was observed in all basal discs, declining to 36 discs at the first third, 29 at the second third, 28 at bole break and it was only present in the branches of 21 trees. The basal discs had a considerably lower proportion of rot compared to other bole locations, but there was no trend for rot occurrence further along the bole.

Total above-ground wood volume, and sapwood and heartwood volumes were estimated (Table 4.22). Heartwood was estimated to account for 19.9 per cent of the bole volume and 14.3 per cent of total stem volume. Heartwood proportion declined along the stem, and the lower-third bole accounted for 58 per cent of above ground heartwood compared to less than 6 per cent in the canopy stem. Stem volume varied according to the measurements used. Here the under-bark photographic analysis measurements were used to calculate the sum of sectional bole volumes. This method was considered more accurate as it accounted for changed taper along the stem. The method more likely to be used in large-scale measurements would be a full-length bole volume with canopy branch volume estimated using crown-break diameter, adjusted for under-bark measurements using mean bark thickness. This method gave a mean stem volume of 45963.7 ± 23640.2 cm3, which was 127 per cent the volume estimated using the method applied here.

The estimated root stump volume of the 20 tree subsample was 4972.1 ± 2797.3 cm3, with an estimated 1566.8 ± 969.5 cm3 of aromatic wood, or 31.5 per cent of total estimated volume. The mean whole-stem tree under-bark stem volume was 39579 ± 30444 cm3, with total heartwood of 6959 ± 5171 cm3 or 17.6 per cent of volume.

Table 4.20 Field-determined parameters for the 40 trees sampled from Trial 4 Parameter Mean ± s.d. Basal diameter (cm) 15.7 ± 2.8 Breast height diameter (cm) 11.9 ± 2.2 Crown break diameter (cm) 10.4 ± 3.0 Branch diameter (cm) 10.8 ± 2.7 Bole length (cm) 279.8 ± 80.2 Tree height (cm) 637.0 ± 115.2 Total crown (kg) 53.7 ± 30.9 Branch >4 cm (kg) 16.8 ± 12.9 Bole (kg) 31.6 ± 12.5 Total above ground (kg) 85.3 ± 39.1 Root stump (kg) 22.2 ± 10.4 Whole tree (kg) 107.5 ± 48.6 All weights (kg) are fresh weight.

Table 4.21 Parameters calculated from photographic analysis of the four discs along the boles from trees in Trial 4 (mean ± s.d.) Over-bark Under-bark Bark thickness Heartwood area Rot area Disc position diameter (cm) diameter (cm) (cm) (%) (%) Base 14.1 ± 2.6 13.2 ± 2.5 0.837 ± 0.150 30.6 ± 12.4 1.5 ± 2.4 Lower 3rd 11.2 ± 2.0 10.4 ± 1.9 0.778 ± 0.144 17.5 ± 12.6 6.1 ± 11.3 Upper 3rd 9.8 ± 1.7 9.0 ± 1.6 0.806 ± 0.160 12.0 ± 11.3 5.2 ± 11.2 Crown break 9.5 ± 4.6 8.7 ± 2.1 0.777 ± 0.176 7.2 ± 8.4 5.5 ± 13.3

Table 4.22 Mean estimated under-bark volume and heartwood volume and the percentage heartwood (± s.d.) for bole sections, canopy stem and total above-ground volume Under-bark volume Sapwood volume Heartwood volume Heartwood Tree section (cm3) (cm3) (cm3) (%) Upper third 5959.1 ± 2415.0 5305.1 ± 2079.2 654.0 ± 722.6 11.0 Middle third 7302.9 ± 3151.5 6102.5 ± 2012.9 1200.4 ± 995.4 16.4 Lower third 11138.8 ± 5251.1 8122.5 ± 3973.3 3012.3 ± 1935.8 27.0 Total bole 24400.8 ± 13015.3 19534.1 ± 8408.6 4866.7 ± 3296.4 19.9 Canopy stem 11635.7 ± 9715.4 11343.1 ± 9413.5 292.7 ± 451.5 2.6 Total stem 36036.6 ± 17556.7 30877.2 ± 14929.9 5159.4 ± 3568.2 14.3

The whole-tree mean weight of the 20 tree subsample was 109.47 ± 54.31 kg, of which 49.8 per cent was contributed by the root stump and bole with mean weights of 22.95 ± 12.00 kg and 31.53 ± 14.38

kg respectively. These parameters were similar to those of the broader 40 tree sample, which indicated that the results of the root sampling were indicative of all sampled trees.

Oil analysis

The average oil yield of the 79 samples of pure heartwood from the five sample locations was 55.4 ± 23.7 g per kg, or 5.5 per cent. The highest average oil yield across sample locations was 68.6 ± 18.5 g per kg in the root stump, and the average yield declined at each section along the stem to the lowest mean yield of 34.3 ± 11.7 g per kg at the top of the bole (Table 4.23). Oil yield within individual trees did not strictly follow the pattern of decline along the stem, for example the maximum single sample yield of 122.6 g per kg occurred at the second-third disc location (Table 4.23). Across the nine trees that had heartwood at all five sample locations, the average oil yield per tree ranged from 36.0 ± 11.8 to 64.8 ± 17.8 g per kg.

The average yield of alpha and beta-santalol within the oil followed the same distribution pattern as total oil (Table 4.23), and there were only slight changes in their contributions to the composition of the oil at the five sample locations (Table 4.24). The 79 samples of oil on average contained 70.3 ± 6.0 per cent of combined alpha and beta-santalol, with individual contributions of 48.9 ± 3.8 per cent for alpha-santalol and 21.5 ± 2.5 per cent for beta-santalol.

Table 4.23 Total oil yield (g/kg) and santalol composition of the five sample locations in 20 trees subsampled from Trial 4 (mean ± s.d.) Yield (g/kg) Sample Alpha- Beta- Total Minimum Maximum location n Total oil santalol santalol santalol total oil total oil Root 20 68.6 ± 18.5 33.2 ± 7.0 14.6 ± 3.2 47.7 ± 10.2 41.1 99.8 Bole base 20 63.9 ± 22.1 31.3 ± 10.3 14.2 ± 5.0 45.4 ± 15.3 32.2 108.7 Bole 1st 17 50.6 ± 16.4 24.6 ± 8.4 10.9 ± 4.0 35.5 ± 12.4 20.4 89.7 third Bole 2nd 13 43.3 ± 30.6 20.8 ± 15.1 9.2 ± 7.1 30.0 ± 22.2 9.6 122.6 third Bole top 9 34.3 ± 11.7 16.6 ± 5.6 6.8 ± 2.6 23.4 ± 8.2 23.7 53.5

Table 4.24 Proportion of alpha and beta-santalol in oil from the five sample locations in 20 trees subsampled from Trial 4 (mean ± s.d.) Composition (%) Sample Alpha Beta Total Minimum total Maximum total n location santalol santalol santalol santalol santalol Root 20 49.3 ± 5.0 21.7 ± 2.4 71.0 ± 7.3 52.8 78.4 Bole base 20 49.3 ± 2.8 22.3 ± 2.2 71.7 ± 4.7 59.7 78.9 Bole 1st third 17 48.7 ± 3.6 21.5 ± 2.6 70.2 ± 6.0 56.5 77.8 Bole 2nd 13 48.2 ± 4.0 20.9 ± 2.8 69.1 ± 6.5 52.4 77.0 third Bole top 9 48.4 ± 3.1 19.7 ± 1.7 68.1 ± 4.6 57.2 73.7

The pattern of declining oil yield along the tree was examined further using linear regression. Heartwood within the root stump was sampled at a fixed height of –0.15 m, basal discs fixed at zero metres, and the bole third sampling heights were calculated by the division of total length (m) by three. There was a moderately weak (R2 = 0.261) but significant (P<0.001) relationship such that for every 1 m along the tree the oil yield declined by 12.9 g per kg (Figure 4.17a). There was no trend apparent between sample location height and total alpha and beta-santalol composition (Figure 4.17b).

There was also no trend between sample oil yield and the stem or heartwood cross-sectional area of the corresponding disc (Figure 4.18a). Similarly, the proportion of heartwood cross-sectional area did not appear to influence oil yield (Figure 4.18b). That is, the stem size, the amount and percentage of cross-sectional heartwood, was not an indicator of the of oil yield at a given location.

Estimates of oil yield per tree were calculated by converting the geometric volumes to kilograms using a heartwood density of 0.9 (Rao et al. 1998), then multiplying the root stump and bole sections by the average oil yield (g per kg) of the samples taken from either end of the section. For root stumps only the single sample was used to determine yield. The mean estimated total oil yield per tree was 307.3 ± 215.9 g, with individual trees ranging from 18 to 778 g (Figure 4.19). On average, the lower third of the bole accounted for the highest proportion of oil yield at 50.7 per cent per tree, followed by 28.4 per cent in the root stump, 15.5 per cent in the middle third of the bole and 5.4 per cent in the upper third.

a 140 b 85 y = 64.56 -12.931x 80 120 R2 = 0.261 P<0.001 75 100 70 80 65 60 60

% composition 55

Total oil yield (g/kg) yield Total oil 40 50 20 45 0 40 -0.25 0.25 0.75 1.25 1.75 2.25 2.75 3.25 -0.25 0.25 0.75 1.25 1.75 2.25 2.75 3.25 Sample height (m) Sample height (m)

a 140 b 140

120 120

100 100

80 80

60 60

Total oil yield (g/kg) yield Total oil 40 Total oil yield (g/kg) yield Total oil 40

20 20

0 0 0 100 200 300 400 0 20 40 60 2 Dis c HW Cross sectional area (cm ) % of heartw ood in disc

Figure 4.18 Relationship between total oil yield (g/kg) of individual samples and (a) the cross- sectional disc and heartwood area (cm2), and (b) the percentage of heartwood in 20 trees subsampled from Trial 4

800 700 600 500 400 300 200

Est. oil yield per tree (g) tree per oil yield Est. 100 0 1 2 3 4 8 9 14 16 17 21 23 25 26 27 30 32 35 36 37 40

roots low er mid upper Tree identity

Figure 4.19 Estimated oil yield (g) for each of 20 subsampled trees in Trial 4, indicating the contribution of the root stump, lower third, middle third and upper third of the bole Discussion

All 40 of the 15-year-old sandalwood trees harvested produced at least some heartwood, evaluated as a yellow to brown colouration of wood within cross-sectional discs. On average these trees were 6.37 m tall, had a bole length of 2.78 m with a basal diameter of 15.7 cm and crown break diameter of 10.4 cm. Heartwood was estimated as 31.5 per cent of the stump volume and 21.5 per cent of the bole volume, with inconsistent and low amounts of heartwood extending up into the canopy stem and branches.

This harvest only considered one planting, grown in what could be considered adverse conditions, where the number of hosts and water availability may have been limiting since age 10. The results may not necessarily reflect those that would occur in intensively managed plantation-grown sandalwood, where sandalwood may be larger than those sampled here at 15 years of age. For example, earlier in this report the (Section 4.2.2, Trial 6) sandalwood grown with long-term host

Cathormion umbellatum, at 9 years of age had a mean basal diameter of 13.7 cm when stocked at 617 stems per hectare, or 16.2 cm when stocked at 231 stems per hectare, compared to 15.7 cm measured for these 15-year-old trees. In plantations it is assumed that long-term host stocking, spacing and water availability will remain largely constant throughout the rotation and should provide an advantage to growth given a suitable host species is used and stocking rates do not promote excessive competition.

A general pattern of decline in oil yield was observed from the roots to crown break across the 20 tree subsample. Heartwood from the crown break had on average only half of the yield found in root stumps. This trend occurs in sandalwood trees grown in forests in India (Rai 1990) and more specifically in studies on 10-year-old and 14-year-old plantation trees grown at Kununurra (McComb 2009; Jones et al. 2007). Oil composition, particularly in regard to santalols, did not vary greatly along the stem suggesting that oil quality was relatively stable within trees. The level of alpha and beta- santalol were within the range specified by the ISO standard (ISO 3518:300E) of 41–55 per cent alpha-santalol and 16–24 per cent beta-santalol, and thus confirm that high-quality oil was produced in 15-year-old trees.

The oil yields here of 6.9 per cent at the stem base were higher than earlier reports from plantation trees grown at Kununurra (McComb 2009; Brand et al. 2006; Brand et al. 2007) which had an average oil yield ranging between 2.3 to 3 per cent at the base of trees aged 14 to 15 years. Brand et al. (2006, 2007) undertook analyses on samples containing both heartwood and sapwood from cross-sectional core sampling and thus oil yield from pure heartwood would be expected to be higher. Interestingly, oil yields were within the range expected of older trees in natural stands in India, as broadly suggested by Rai (1990) and more explicitly in a study by Jayappa et al. (1995) where root oil yield is 6.5–8.5 per cent declining to 2.5–5.5 per cent further up the tree. The oil yields here could be influenced by point sampling compared with whole-disc heartwood sampling. Alternatively, yields may be influenced by the somewhat adverse environmental conditions, such as increased exposure to sunlight and lower water availability, compared to trees in a forest or under better plantation management. Such environmental stresses have been proposed as potential factors affecting the initiation and development of heartwood (Rai 1990). However, the most likely cause of lower yields is the younger age of trees.

The estimates of whole-tree oil yields indicated that an average of 330 g of oil could be solvent extracted from 15-year-old trees grown under similar environmental and silvicultural conditions. However, because the methodology used here is based on a relative small sample of 20 trees using geometric-modelled heartwood volume and point oil analysis, as opposed to whole-heartwood extraction, the results should be viewed as an approximation of actual yields from these trees. This study, however, clearly indicates that a large variation in tree size and heartwood oil yield can be expected in plantation-grown sandalwood at 15 years of age.

4.4.3 Characterisation of heartwood and oil development in 11-year-old sandalwood with three host species, Trial 7

Method

Trial establishment and design

Trial 7 establishment and design has been previously reported in detail by Barbour (2008). Three species, Cathormion umbellatum, Dalbergia latifolia and Millettia pinnata which promote better sandalwood growth and survival at 9 years of age, were used as long-term hosts for sandalwood which were selected for core sampling (see Plate 4.5). For each host-species treatment, sampled sandalwood trees were selected to reflect a normal distribution of the basal diameters measured in 2008. Fifteen sandalwood trees were selected for each host treatment, with three chosen from each of the five replicates to equally represent the environment across the site.

Plate 4.5 The plot combining sandalwood with the long-term host Dalbergia

Measurement and core sampling

Prior to coring, basal diameter, diameter at breast height, diameter at crown break and bole length of the sandalwood were measured. Sandalwood were cored at 30 cm above ground level using a 0.5 cm diameter hand-increment corer. Cores were extracted in an east to west orientation (along row) through the centre of the tree and a polymer sealant was used to cap the core hole. Cores were gently sanded on one side to allow for a clear distinction between sapwood and heartwood, which was defined as a yellow to brown discolouration possessing a typical sandalwood aroma. Total core and heartwood length (diameters) were measured and the hypothetical cross-sectional areas and heartwood percentage were calculated.

Whole-increment cores were air dried, ground with a coffee grinder and then weighed to four decimal places. Oil was extracted from samples into ethanol for 7–14 days with isobutyl benzene as an internal standard (12 mM). A standard curve was constructed using oil from S. album (Sigma Aldrich) to estimate total oil content in each sample. The chemical composition was determined by gas chromatography with flame ionization detection (GC-FID) using a Shimadzu GC-17 A instrument equipped with a DB-WAX column (Alltech, 30 m, 0.25 mm inside diameter, 0.25 µm film thickness) and a flame ionisation detector. Injection volume was 1.0 µL, the injection port temperature was 200°C and detector temperature was 250°C. Helium (2.4 ml per min) was the carrier gas and a split ratio of 10:1 was used. Oven temperature was held at 40°C for 5 min before ramping to 230°C at 10°C per min and held for 20 min (total run time was 45 min). Peak identification was facilitated by calculating retention indices and previous MS data. Integration was performed using Shimadzu GC- Solutions software. Areas were recorded for all detectable peaks and per cent composition was calculated by taking the area of the peak divided by total chromatogram area x 100. Samples which contained small amounts of total oil tended to overestimate the proportion of the major components.

Statistical analysis

Differences in sandalwood heartwood and oil parameters between host treatments were tested using ANOVA. Linear regression was used to test for relationships between total core, disc parameters and aromatic wood parameters, and proportional data was angular transformed to satisfy the normality assumption. Trends between heartwood traits and the interaction indices host count index (HCI) and host size-distance index (HSDI) (see Section 4.3.1, Trial 7) were examined with scatter plots at search

horizons of 6, 9, 12 and 15 m from the target sandalwood. Those displaying visible trends were further examined using linear regression. In this scenario it was thought that the interaction indices could be representative of environmental conditions, such as light and host root availability, and that these resources could influence heartwood development.

Results

Over-bark sandalwood parameters for the host treatments did not vary substantially (Table 4.25). Sandalwood growing with either Dalbergia or Millettia were of a similar size, based on bole volume, whilst on average sandalwood in the Cathormion treatment had around 69 per cent of the bole volume of sandalwood grown with Millettia.

Table 4.25 Over-bark measurements for sandalwood trees growing with the three host treatments in Trial 7 (mean ± s.d.) Base diameter DBH CBD Bole Length Bole volume Host treatment (cm) (cm) (cm) (cm) (cm3) Cathormion 15.9 ± 3.7 10.1 ± 3.6 10.7 ± 4.4 174.0 ± 55.5 26390.8 ± 14446.9 Dalbergia 17.1 ± 3.8 11.8 ± 2.6 11.5 ± 2.9 204.8 ± 49.5 35898.3 ± 18288.2 Millettia 16.7 ± 2.8) 12.0 ± 2.2 10.8 ± 2.5 238.9 ± 76.4 38361.1 ± 17570.3

Heartwood was present in 35 of the 45 sandalwood sampled. There was only one sandalwood tree grown with Dalbergia without aromatic heartwood, compared to four and five sandalwood without aromatic heartwood with Cathormion and Millettia hosts respectively. Core and heartwood properties of sandalwood with the three host species did not vary greatly (Table 4.26). Sandalwood sampled with Dalbergia hosts had the longest mean cores, core aromatic heartwood length and percentage, and the largest cross-section disc heartwood percentage, although none of these variables were statistically significant (P<0.05). The largest aromatic heartwood diameter for Cathormion, Dalbergia and Millettia was 8.7, 7.3 and 10.1 cm respectively, and the highest proportion of aromatic heartwood calculated on the basis of hypothetical discs was 33.6, 41.7 and 43.0 per cent respectively. Whilst Dalbergia and Millettia had very similar mean aromatic heartwood area and percentage area, sandalwood hosted with Dalbergia displayed more consistent heartwood production across the sampled trees than Millettia.

Table 4.26 Core and cross-sectional parameters for sandalwood grown with the three host treatments in Trial 7 (mean ± s.d.) Heartwood Total cross- Heartwood Cross-sectional Host Core length length sectional area area heartwood area treatment (cm) (cm) (cm2) (cm2) (%) Cathormion 11.4 ± 3.1 3.0 ± 2.5 109.2 ± 55.4 12.2 ± 15.6 9.0 ± 9.1 Dalbergia 13.0 ± 2.9 4.0 ± 1.9 138.2 ± 57.9 15.5 ± 12.7 11.5 ± 9.8 Millettia 12.5 ± 2.2 3.2 ± 3.2 126.4 ± 45.3 16.3 ± 23.3 11.2 ± 14.2

There was a positive linear relationship between cross-sectional disc area and cross-sectional heartwood area (P = 0.001, R2 = 0.225), and a very weak but significant relationship between disc area and heartwood percentage (P = 0.049, R2 = 0.087). Examination of scatter plots revealed that for each host treatment there was one outlier. With the outliers removed significant relationships between disc area and heartwood were found for sandalwood with Cathormion (P>0.001, R2 = 0.658), Millettia (P = 0.003, R2 = 0.527) and Dalbergia (P = 0.015, R2 = 0.403) host treatments. Cathormion was the only treatment where sandalwood displayed a significant relationship between disc area and heartwood

percentage (Figure 4.20B). The nature of the relationships between disc and heartwood area, as indicated by the regression coefficients (slope), suggested that the response of heartwood area in relation to disc area occured most rapidly in Millettia, followed by Cathormion and then Dalbergia. For example, a cross-section area increase of 100 cm2 at the stem base for sandalwood when hosted with Millettia would be expected to have an increase of around 52 cm2 in heartwood area, compared to 12 cm2 when Dalbergia is the host.

A 90 B 0.8 yCath= -14.401 +0.272x yDal =-3.456 + 0.122x yCath =-0.064 + 0.0032x 80 2 2 0.7 2 R = 0.658 R = 0.403 R = 0.702

) 70 P >0.001 P = 0.015 2 0.6 P>0.001 60 yMil = -43.901 + 0.510x R2 = 0.527 0.5 50 P = 0.003 0.4 40 0.3 30

Heartwood area (cm 20 0.2 10 0.1 Heartwood % (transformed units) 0 0.0 0 50 100 150 200 250 0 50 100 150 200 250 2 2 Cath Dal Mil Disc area (cm ) Cath Dal Mil Disc area (cm )

Figure 4.20 Relationships between sandalwood cross-sectional disc area (cm2) and (A) cross- sectional heartwood area, and (B) cross-sectional heartwood proportion (%) in trees from Trial 7 (note, a single outlier was removed for each host treatment, and heartwood % was in angular transformed units to normalise residuals) Trends between heartwood traits and the host size-distance index (HSDI) were more visually identifiable compared to host count indices (HCI). Despite identifying potential trends there was only one significant linear relationship, which was found between heartwood percentage and HSDI for the Cathormion treatment at the 15 m horizon (P = 0.042, R2 = 0.302; Figure 4.21A). Whilst definitive relationships suitable for heartwood prediction were not found, the nature of the trends visible between interaction indices and heartwood traits generally varied between host treatments (Figure 4.21B). The Cathormion treatment displayed a negative trend where heartwood traits declined as the number (HCI) and relative size of hosts (HSDI) increased, as opposed to the positive trends indicated for Dalbergia. The strength of relationships with regard to the search horizon also had an opposing trend. In the Cathormion treatment the strength of the relationship with heartwood parameters increased as the search horizon broadened from 6 m (R2 = 0.019), to 9 m (R2 = 0.123), to 15 m (R2 = 0.302); this contrasted with the Dalbergia treatment where relationships weakened as the search horizons increased from 6 m (R2 = 0.186), to 9 m (R2 = 0.173), to 15 m (R2 = 0.004). Trends were not observed between heartwood and competition indices for sandalwood within the Millettia treatment.

Multiple linear regressions examined the relationships between heartwood parameters, area and proportion, with two explanatory variables, disc cross-sectional area and HSDI. Only the HSDI horizon that displayed the strongest relationship with heartwood area and proportion, as a single regressive variable for each host treatment, was used. Heartwood area displayed significant relationships for all treatments, and Cathormion had the strongest relationship (P <0.001, R2 = 0.708), followed by Millettia (P = 0.015, R2 = 0.534) and Dalbergia (P = 0.048, R2 = 0.423). Cathormion was however the only treatment to improve the predictive strength (based on adjusted R2 values) compared to the explanatory variable in single regressions. Heartwood proportion was only significant for the Cathormion treatment (P <0.001, R2 = 0.792), which provided a stronger predictive model compared to the explanatory variables in single regressions.

A 0.8 B 45 y 0.623 + -0.0003x Cath 40 0.7 R2 = 0.302 35 0.6 P = 0.042 30 0.5 25 0.4 20

0.3 Heartwood % 15 0.2 10 Heartwood % (transformed) 0.1 5 0.0 0 0 500 1000 1500 2000 5 10 15 20 25 30 35 40 Size dependent index (HSDI) Host count index (HCI) Cath 15m Dal 9ml Mil 15m Cath 15 m Dal 15m Mil 15m

Figure 4.21 Relationships between heartwood % and (A) host size-distance index (HSDI) and, (B) host count index (HCI) in trees from Trial 7. (A) displays significant linear regression for Cathormion and (B) displays general trend lines. Note that (A) displays heartwood % in angular transformed units to normalise residuals of linear regression.

The percentage oil yields from ground sandalwood cores taken from 30 cm above ground were similar between host treatments (P = 0.219), with means ranging from 1 per cent for Cathormion to 1.7 per cent for Dalbergia (Table 4.27). The maximum oil yield from single trees for host treatments was 2.6 per cent, 3.1 per cent and 4.3 per cent for Cathormion, Dalbergia and Millettia respectively. The ten core samples that did not appear to contain heartwood had a mean oil yield of 0.08 ± 0.04 per cent, compared to those containing heartwood which had an average of 1.7 ± 1.0 per cent. The proportion of santalols within the oil was not different between host treatments for alpha-santalol (P = 0.5), but beta-santalol varied (P = 0.019) and sandalwood in the Dalbergia treatments had a greater proportion than those from the Cathormion treatment. Santalol proportions across all samples ranged from 42 to 60 per cent for alpha-santalol and 19 to 30 per cent for beta-santalol.

There were no differences between the amount (g per kg) of oil extracted from host treatments (P = 0.220), nor for the amount of alpha-santalol (P = 0.246) and beta-santalol (P = 0.190) (Table 4.27). The maximum alpha and beta-santalol yield for individual samples within host treatments was 13.5 g per kg and 6.4 g per kg respectively for sandalwood with Cathormion, 16.5 g per kg and 8.0 g per kg for Dalbergia, and 22.6 g per kg and 11.1 g per kg for Millettia. The mean oil yields when samples without heartwood were excluded were 12.8 ± 8.2 g per kg for Cathormion treatment, 17.8 ± 8.9 g per kg for Dalbergia, and 19.0 ± 12.5 g per kg for Millettia.

There was a moderately strong and significant relationship (R2 = 0.60, P <0.001) between oil yield and the proportion of heartwood within core samples. Because core samples contained sapwood and heartwood in uneven proportions, oil yields (g per kg) were adjusted by multiplying original gas chromatograph yield by a dilution factor equal to the ratio of sapwood to heartwood within core samples. The mean sandalwood oil yield after applying the dilution factor was 37.9 ± 27.9 g per kg (3.8 per cent), and these oil yields varied between host treatments (P = 0.045). The Dalbergia treatment had a mean of 51.8 ± 26.3 g per kg (5.2 per cent), which was higher than 27.5 ± 21.8 g per kg (2.2 per cent) for the Cathormion treatment, but not different from 34.4 ± 27.9 g per kg (3.4 per cent) for the Millettia treatment.

Table 4.27 Proportion and yield (g/kg) of alpha-santalol, beta-santalol and total oil from cores sampled at 30 cm from sandalwood with Cathormion, Dalbergia and Millettia hosts (mean ± s.d.) Percentage composition Yield (g/kg) No. alpha- beta- alpha- beta- Oil yield Host samples santalol santalol santalol santalol (%) Cathormion 15 51.9 ± 2.7 25.1 ± 2.1 5.0 ± 4.6 2.4 ± 2.2 0.97 ± 0.88 Dalbergia 15 50.9 ± 2.8 25.8 ± 2.0 8.4 ± 4.9 4.3 ± 2.5 1.67 ± 0.96 Millettia 15 50.6 ± 4.5 23.6 ± 2.6 6.5 ± 6.9 3.2 ± 3.5 1.30 ± 1.30 Total 45 51.1 ± 3.5 24.8 ± 2.4 6.6 ± 5.6 3.3 ± 2.8 1.31 ± 1.09

Discussion

The rate of heartwood development in relation to overall wood production and heartwood proportion was similar between sandalwood planted with the three host species. This contrasts to the findings of McComb (2009) where the proportion of heartwood at the stem base of 14-year-old clonal sandalwood ranged from 17.5 to 34.9 per cent between host species. The difference in the cross- sectional heartwood area, whilst still not statistically significant, was noticeably larger between host species compared to heartwood proportion. The cross-sectional heartwood area of sandalwood grown with Cathormion was on average only 78per cent and 74 per cent of those grown with Dalbergia and Millettia respectively. If it is assumed that longitudinal heartwood development was constant across host species, then sandalwood grown with Cathormion could have around 250 kg less heartwood per harvested tonne compared to those grown with Dalbergia or Millettia. If for example heartwood yield at 15 years of age was an arbitrary 10 kg per sandalwood tree when grown with Millettia, the total yield per hectare could be reduced by as much as 1.2 tonnes per hectare when using Cathormion hosts at a stocking rate of 462 sandalwood stems per hectare.

The variability of heartwood production displayed for Cathormion and Millettia may also negatively impact the number of commercially valuable trees within a plantation. If the samples here were indeed representative of the broader plantation population, the number of trees containing heartwood would be considerably higher for sandalwood grown with Dalbergia which had 93 per cent of samples with heartwood compared to 67–74 per cent of sandalwood planted with Cathormion and Millettia. At a stocking rate of 462 stems per hectare, as used in this trial, the number of sandalwood with heartwood at 11 years of age could range from 429 when grown with Dalbergia, compared to between 310 and 342 when grown with Cathormion and Millettia respectively. In the destructive harvest of 8-year-old sandalwood earlier in this section, 26 per cent of the sample did not have heartwood at the base of the stem, and similar proportions of trees without heartwood at 30 cm have been reported at the age of 10 years (Jones et al. 2007) and 14 years (Brand et al. 2006). These studies have provided increasing evidence that a considerable proportion of up to 20 per cent of sandalwood will not develop substantial amounts of heartwood within the 15-year rotation envisaged by the plantation industry. If the selection of host species can reduce the proportion of low-value trees and maintain competitive external growth rates and heartwood proportion, as displayed by Dalbergia here, it would be very valuable to the industry.

The relationships between disc area and heartwood traits indicated that it was the amount and not proportion of heartwood that was more consistently and strongly related to sandalwood diameter. The results confirm that the amount of heartwood in cross section at the stem base diameter was only moderately accounted for by the external diameter of trees aged 11 years. There also appeared to be differences in the strength and nature of these linear relationships when sandalwood was grown with the different host species, which suggests that applying a universal predictive equation for heartwood across host species may not achieve a large degree of accuracy.

The examination of a possible relationship between tree-tree interaction indices and heartwood traits was an attempt to account for a proportion of the environmental component of heartwood formation and development. The indices used here indicated the number (HCI) and relative size (HSDI) of hosts within specified neighbourhoods of target sandalwood, and this helped to explain differences in the competition environments within and between host species. In this trial there was visual differentiation in the response of heartwood formation to interaction indices to the three host species. Broadly speaking, as the number and size of hosts increased within a 15 m radius of sandalwood, heartwood traits (amount and proportion) declined for the Cathormion treatment, increased for Dalbergia, and displayed no discernable impact on sandalwood with Millettia. The analysis did not however offer direct insight into reasons for these differences. The indices provided an indication of the physical size and density of trees in the environment, but it was more likely that differences were more strongly defined by physiological changes in the relationships that occur between host and sandalwood as a result of competition.

The oil extracted from sandalwood cores taken at 30 cm above the ground all met the minimum level specified within the ISO standard for Santalum album oil (ISO 3518:300E) for alpha-santalol (41–55 per cent) and beta-santalol (16–24 per cent). This indicates a quality oil product is possible from 11- year-old plantation-grown sandalwood. The oil yield was however relatively low at around 1.3 per cent, a range of less than 0.5 per cent to just over 4 per cent for individual samples. This is relatively similar to the findings of Jones et al. (2007) where core samples from 10-year-old sandalwood growing at Kununurra displayed oil yield ranging from less than 0.5 per cent to just less than 5 per cent. As the core samples included both sapwood and heartwood, the results will be lower than for pure heartwood samples, and after yield was adjusted using a dilution factor of the sapwood-to- heartwood ratio, the average heartwood oil yield was calculated to be around 4 per cent. It is important to note that such calculated values should only be seen as approximations and the preferred method would be to extract and analyse pure heartwood samples. The method used here was because the amount of heartwood within core samples was rarely over 1 g, with many samples having less than 0.5 g of heartwood, which made them difficult to work with.

The differences displayed in mean oil yield between the three host treatments was low when examining the raw gas chromatogram results. However, considering the unequal heartwood proportions in the samples and the moderately strong linear relationship that existed between heartwood proportion and oil yield, it is possible that the oil yields tended to reflect the differences in heartwood development between host species, and not necessarily differences in the rate of oil production per unit of heartwood. The dilution-adjusted average oil yield of the three host species did display more variation, and sandalwood with Dalbergia had an average yield 3 per cent higher than the Cathormion treatment. This difference may be a function of the more consistent sandalwood heartwood production as well as improved growth, and an associated positive relationship with heartwood development (Figure 4.20), when hosted with Dalbergia compared to Cathormion. Other potential causes for the differences, such as variability in compounds extracted from hosts (Radomiljac et al. 1998c), would require further research to confirm that there are specific host effects on oil production beyond those attributed to influences of host species on sandalwood size.

The observed variation in heartwood occurrence and development of the sandalwood suggested large differences in heartwood yield at the plantation level could occur as a result of host choice. Furthermore, the differentiation of relationships between heartwood traits and the diameter and tree- tree interaction indices could indicate fundamental differences in the response of heartwood production in sandalwood grown with different host species. The differences in oil yield between host species would likely be secondary to overall oil productivity compared to the host affect on heartwood production. That is, a host species that is able to produce bigger sandalwood is likely to produce more heartwood and thus a greater ability to produce oil. Currently there is limited knowledge to explain why differences in heartwood and oil can occur between host species, and considerable scope exists for investigations into the physical parameters and physiology of host-sandalwood interactions to identify how and why these differences occur.

4.4.4 Preliminary evaluation of non-invasive methods for aromatic wood determination in Santalum album, Trials 4 and 8

Methods

Electrical impedance tomography

The electrical impedance of three standing sandalwood trees, one aged 8 years (Trial 8) and two aged 15 years (Trial 4), was measured using a PiCUS Treetronic (Argus, Rostock) instrument. Within each tree, measurements were recorded at 100, 300, 500, 750 and 1000 mm along the bole. At each site 24 electrodes (nails) were hammered into the tree at points equidistant around the diameter. An electrical current was applied through two electrodes to produce an electrical field measured by the electrodes through the cross section of the tree. The shape of the electrical field was determined by the resistivity of the wood through the cross section, indicated by differences in voltage between pairwise electrodes (Rust et al. 2007). The data was then interpreted by experienced technicians using the instrument software (PiCUS Q72) to produce tomograms of each test site along the bole.

After data acquisition, the trees were felled and discs approximately 4 cm in width were taken from sites along the bole. A photograph of each disc was taken and each electrode was labelled so that the photograph could be aligned with the corresponding tomogram.

The tomograms were then visually compared with the disc photographs to identify if the physical traits recognised as heartwood or rot on the discs were interpreted by electrical impedance.

Acoustic time-of-flight

An IML Hammer (Instrumenta Mechanic Labor GmbH, Germany) was used to measure the stress wave velocity of four cross sections at different heights along the bole of eight standing sandalwood trees, four aged 9 years (Trial 8) and four aged 15 years (Trial 4). The IML hammer applied an acoustic stress wave and recorded the time taken for the signal to pass through two transducers located on opposite sides of the tree. The velocity was calculated by dividing the distance the signal traveled by the time recorded to pass through both transducers and as such the method is often referred to as a ‘time-of-flight’ measurement (Searles and Moore 2009).

The four 9-year-old trees were tested at approximately 130, 450, 830 and 1120 mm and the four 15- year-old trees were tested at 160, 500, 940 and 1325 mm. At each height, measurements were taken along two axes, one along the row (R IML) and the other across the row at 90 degrees to this (A IML).

After the acoustic measurements were recorded, the trees were felled and discs approximately 4 cm wide were taken from each of the sampled heights along the stem. The discs were then photographed with a scale set at the discs’ face in preparation for image analysis. The program Image J (NIH, USA) was used to manually trace the physical traits of the discs from photographs to calculate values for over-bark disc area, under-bark disc area, heartwood area, disc rot area, as well as the diameter of the disc and heartwood through the disc centre.

The relationships between the IML readings (R IML and A IML) and the heartwood area, diameter and percentage traits of the discs were then examined using simple linear regression (Xlstat).

Results

Electrical impedance tomography

The tomograms produced (Figure 4.22) did not correspond to a large degree of accuracy with the visual features identified as heartwood on the extracted discs. For example, in Tree 1 (Figure 4.22) the tomogram at 1000 mm along the bole appeared to display the small area of heartwood, albeit in an

exaggerated state, as an area of high impedance (red), however at the base (100 mm) of the bole the similar colouration on the tomogram was not verified as heartwood on the disc. On Tree 2 (Figure 4.22), heartwood was clearly defined and consistent throughout the bole length, yet the 3-D tomogram does not appear to provide a clear distinction between sap wood and heartwood and thus the ability of the technique to determine heartwood content or proportion was compromised.

Overall there was a large degree of ambiguity in the tomograms which could not be easily interpreted without completing a destructive harvest. This method may be useful in identifying trees that deviate from the norm. It would be hoped that a typical tree was represented by Tree 2 (Figure 4.22), with constant aromatic wood along the bole. Deviations from the corresponding typical tomogram, particularly inconsistent colouration, would be used to indicate trees that lack heartwood and/or the presence of wood rot or other damage. However, considerably more testing would be required ensure typical trees display consistent tomograms.

Figure 4.22 The electrical impedance tomograms for the 8-year-old tree (Tree 1, left), and the extrapolated 3-D tomogram and extracted discs for the 8-year-old (centre) and 15- year-old tree (Tree 2, right) respectively (note, area of blue indicates low impedance (higher moisture content) and area of red indicates high impedance (lower moisture content))

Acoustic time-of-flight

The linear relationships between IML reading and heartwood parameters measured had weak coefficients of determination (R2) when the 16 discs sampled from 9-year-old trees were used (Figure 4.23). The strongest relationship was between the A axis IML and heartwood diameter, and this had

an R2 of 0.362 (P = 0.014) (Figure 4.23c). Removing the discs without heartwood produced stronger relationships between measured heartwood parameters and IML readings along the R axis. For example, the R2 of the relationship with heartwood diameter within the discs increased to 0.768 (P = 0.004) compared to 0.207 (P = 0.076).

The discs from 15-year-old trees had generally stronger linear relationships between IML readings and heartwood parameters than in 9-year-old trees. Similar to the 9-year-old samples, the measurements along the A axis produced stronger relationships compared to the R axis. The strength of these relationships along the A axis ranged from moderately weak, with R2 of 0.335 (P = 0.019) and R2 = 0.385 (P = 0.0.01) for heartwood and percentage respectively, to a moderate R2 value of 0.501 (P = 0.002) for heartwood diameter. The strength of the relationships may have been negatively influenced by the small sample size, where potentially a large variation in underlying wood properties between trees could be skewed compared to a larger sample. Indeed the relationships between heartwood diameter and A IML within individual trees were considerable stronger when using all data, with three of the four trees sampled having an R2 greater than 0.740.

The weaker relationships between IML reading heartwood parameters in the 9-year-old compared to 15-year-old trees may be a result of the lack of consistent heartwood production within the younger trees. In the younger trees it is likely the low amount of heartwood prevented it from registering a consistent acoustic signature, and instead it responded to other wood properties independent of heartwood.

a 1500 b 1700 1400 1600 1300 1500 1200 1400 1100 1300 1000 1200 IML reading 900 IML reading 1100 800 1000 700 900 600 800 0 2 4 6 8 0 50 100 150 200 250 Heartw ood area w ithin disc (cm2) Heartw ood area w ithin disc (cm2)

c 1500 d 1700 Cont’d 1400 1600 1300 1500 1200 1400 1100 1300 1000 1200 IML reading 900 IML reading 1100 800 1000 700 900 600 800 0 2 4 6 0 10 20 30 Heartw ood diameter (cm) Heartw ood diameter (cm)

e 1500 f 1700 1400 1600 1300 1500 1200 1400 1100 1300 1000 1200 IML reading IML reading 900 1100 800 1000 700 900 600 800 0 5 10 15 20 20 30 40 50 60 Heartw ood % w ithin disc Heartw ood % w ithin disc R IML A IML

Figure 4.23 Relationships between IML readings and (a) heartwood area with discs for 9-year- old trees from Trial 8 and (b) 15-year-old trees from Trial 4, heartwood diameter within discs for (c) 9-year-old and (d) 15-year-old trees, and percentage heartwood within discs for (e) 9-year-old and (f) 15-year-old trees

Discussion

Neither method was able to accurately determine heartwood yield within discrete cross sections along the length of the bole in the limited sample tested. Because of the very limited sample size and scope of the testing, however, it could not be concluded that these methods are not able to determine aromatic wood within standing trees.

In the case of electrical impedance, it may be that further manipulation of the recorded data using the product software was required to provide an image output that reflected the specific chemical structure of heartwood. Indeed the operators were encouraged by initial results and expressed an interest in continuing further analysis. This more intensive testing and calibration was beyond the scope of the project, however, industry may decide that it is worthwhile pursuing this method.

The acoustic time-of-flight testing did not provide definitive results, but trends in the data were encouraging enough to suggest the possibility for it to be used in estimating heartwood or closely related parameters. In particular, the stronger positive relationships with heartwood of the 15-year-old compared to the 9-year-old trees, which had considerably less heartwood, suggested that acoustics could be detecting mechanical wood parameters related to heartwood. Also, the stronger positive relationships along the four bole sample sites within individual trees indicated that with a reduction in noise created by the differing wood properties between trees, heartwood appeared to register stronger relationships with the acoustic tool.

Of the two methods the acoustic time-of-flight is likely to be the easier to deploy in the field, and provide faster data interpretation. It appeared as though the data interpretation of electrical impedance required not only considerable experience with the product software, but also a familiarity with common patterns of electrical impedance within trees. Whilst time-of-flight instruments, such as the IML hammer, required expertise to use, they have been designed with in-field use by foresters in mind. Once a validated calibration has been made for a trait within a species and environment, the established equation could then be used to determine result.

The presence of heartwood was indicative of the presence of oil; however, the proportion of oil within the wood was indeterminable by visual inspection. Core sampling has been a desirable method in the past because it allows for a direct measure of oil yield and heartwood yield within a chosen cross section. If the methods used here can indeed be calibrated to provide estimates of heartwood, even further estimation would be required to determine an approximate oil yield. If further sampling is undertaken to verify these methods, the addition of oil yield is recommended because the extra information may provide clarity to the analysis.

5 High-value timber trials

Early sandalwood silvicultural research in the late 1980s tested several timber species in conjunction with sandalwood including: Azaderachta indica, Cassia siamea, Dalbergia sissoo, Khaya senegalensis, Pterocarpus indicus, Terminalia pilularis and T. platophylla (McKinnell 1990). With an aim to discover suitable hosts for sandalwood it was hoped that some species could provide an additional commercial product. Under this scenario sandalwood growth was not always favourable; however, the encouraging growth rates of some host species stimulated the planting of trial plots for timber species monoculture. This chapter summarises the growth performance of species planted with the aim of provide valuable wood or forest products, such as oil seeds, when planted in monocultures or with sandalwood.

5.1 A summary of Khaya senegalensis growth within trials of different age and silviculture, Trials 5, 7, 11, 12 and 15

African mahogany, Khaya senegalensis, belongs to the family Meliaceae, and is in one of two genera, the other being the true mahoganies Swietenia, in the subfamily Swietenioideae. Khaya senegalensis is native to tropical Africa in a band extending east to west between latitudes of 8oN and 15oN (Arnold et al. 2004). It is a deciduous tree that when fully grown reaches 15 to 20 m tall with a diameter up to 1.5 m and a clean bole length typically of between 8 to 16 m (Jøker and Gaméné 2003). Across its natural range it is used for medicinal purposes, fuel wood, fodder and as amenity or shade tree (Arnold 2004). Beyond traditional uses it has also gained commercial value because of its richly coloured wood that resembles that of the true mahogany, Swietenia macrophylla, and it has been utilised as a replacement for this species in high-quality furniture, cabinetry, joinery and flooring. With the increasing scarcity of true mahogany and social and ecological pressures to reduce its use, replacement timbers such as African mahogany are becoming more widely accepted and used (Arnold 2004). This inevitably places pressure on the natural resource and there is an increasing requirement for plantations meet demand.

African mahogany was introduced into northern Australia as a street tree in the 1950s, with species evaluation trials first being established in the 1960s and 1970s in the Northern Territory and Queensland (Arnold et al. 2004; Nikles et al. 2004). Its initial introduction to Kununurra at the Frank Wise Institute occurred within trial plots, testing its suitability as a host for sandalwood plantations during the early 1990s. However, it did not prove to be a suitable host because of its rapid growth, which enabled it to occupy the site, dominate the canopy and ultimately suppress sandalwood growth (Barbour 2008; Done et al. 2004). It is this vigour, as well as the aforementioned timber qualities, that has given rise to its recognition as a prime candidate for a plantation species in Kununurra and the broader northern-Australia region and resulted in the commencement of research programs and commercial plantations (Nikles et al. 2004; Armstrong et al. 2007). A summary of the growth of the African mahogany in FPC trial plots at Kununurra is presented.

Methods

Trial establishment

Five trials containing African mahogany were measured during the course of this project. The age and planting configurations varied between trial plots (Table 5.1). Trial plots 5, 11 and 15 were planted as demonstration plots with no treatment comparisons intended and thus no experimental design was employed, whereas Trial plots 7 and 12 were planted as treatments within a broader experimental design. All trial plots were established on the Cununurra cracking clay soils at the Frank Wise Institute, where the land was laser levelled and mounded for flood irrigation. All plots received

minimal silviculture with limited stem pruning, no thinning and no fertiliser application. Flood irrigation was applied approximately once a month during the dry season since establishment.

Measurement

The specific measurements taken for each trial plot were as follows:

• Trial 5: all African mahogany within the trial were assessed, with basal diameter, DBH, bole length and tree height measured

• Trial 7: basal diameter, diameter at breast height, and tree height were measured for all trees within the five replicated block plots

• Trial 11: a subplot of four rows by 120 m was selected from the larger block of eight rows by 200 metres, and the diameter at breast height and bole length measured

• Trial 12: basal diameter, diameter at breast height, bole length and tree height were measured for the four internal rows of each of the five block plots replicated within the experimental design

• Trial 15: an internal subplot of four rows by seven trees was selected from the larger block planting of six rows by 10 trees; the DBH, bole length, and tree height were measured.

Survival percentage, basal area (using DBH) and diameter increment were calculated for each trial and where applicable bole and stem volume was estimated using Smalian’s and conical volume formula respectively. Growth at the hectare level was then calculated by multiplying mean data by the number of surviving stems per hectare.

Table 5.1 Summary description of trial plots in which Khaya senegalensis was planted Age Trial spacing when (between x Total Khaya Trial Year measured within row) SPH SPH Design note Multi-species plot with sandalwood, 5 1997 11 2.7 m x 3 m 1235 154 Sweitenia, Cassia & Cathormion, established host:sandal ratio 2:1 Block plantings with sandalwood, 7 1999 9 3.6 m x 3 m 926 463 established host:sandal ratio 1:1 Alternating line planting at 1:1 ratio 11 1996 12 3.6 m x 4 m 1389 694 with Enterolobium sp. 12 1996 12 2.7 m x 3 m 1235 1235 Single species block planting

15 1999 9 3.6 m x 3 m 926 926 Single species block planting

Results

African mahogany had good survival under Kununurra conditions. More than 90 per cent of trees survived within all trial plots assessed (Table 5.2).

The growth rates (DBH MAI) across trials was relatively constant at between 2.4 and 2.8 cm per year (Table 5.2), with the exception of Trial 12 which had a markedly lower growth rate. However, in Trial 12 although African mahogany had the best growth performance, most of the 10 species planted had lower tree health and condition compared to other plantings at the Frank Wise Institute. Climatic factors and watering regimes were consistent across all trials and so localised soil conditions may

have been a contributing factor to the low growth rate; however, detailed site evaluations would be required to confirm this suggestion. No accurate records of seed source were held across trials, so it is possible that an inferior genetic resource was used to establish this particular trial.

Table 5.2 Khaya senegalensis growth measurements across Trials 5, 7, 11, 12 and 15. Results at the hectare level were calculated using surviving number of Khaya stems per hectare

Basal DBH Basal Bole Survival Survival diameter DBH MAI area length Height ESV ESV Trial (%) (SPH) (cm) (cm) (cm yr-1) (m2 ha-1) (m) (m) (m3) (m3 ha-1) 35.4 ± 26.4 ± 2.7 ± 13.6 ± 0.312 ± 5 95 146 2.4 8.0 45.6 5.6 5.6 1.3 2.5 0.175 33.6 ± 24.3 ± 1.7 ± - 7 97 449 2.7 20.8 - - 7.2 5.7 0.7 33.6 ± 3.4 ± - 11 90 624 - 2.8 55.3 - - 6.6 1.9 26.8 ± 22.3 ± 3.5 ± 11.2 ± 0.173 ± 12 92 1136 1.9 44.4 196.5 9.4 8.3 1.6 2.4 0.141 24.7 ± 4.7 ± 12.8 ± 0.202 ± 15 90 833 - 2.7 39.9 144.1 5.0 1.7 1.3 0.093

Discussion

Despite often occurring as solitary trees in its native range, African mahogany coped well with the competitive plantation environment. This supports earlier observations, for example a trial in the Northern Territory had 91 per cent survival after 34 years with trees planted in an un-thinned stand at over 4000 stems per hectare (Nikles et al. 2004). Trees coped equally well across trials with a range of competitors and various stocking regimes. For example, when planted with Enterolobium sp. as a direct competitor within rows (Trial 11), African mahogany produced the highest MAI (2.8) of the surveyed trials. Also in comparing the two trials aged 9 years (Trials 7 and 15), the mean DBH was the same despite different growth environments: in Trial 7 it was grown with sandalwood at half the stocking rate of Trial 15, which had high inter-specific competition. The ability of African mahogany to survive and grow well in a range of competitive environments, including presumed parasitism from sandalwood, should allow for flexible silviculture regimes with various stocking and thinning options likely to produce desirable growth rates.

Whilst there was no formal measurement/assessment made of stem straightness, it was widely observed across all trials that a large proportion of trees had crooked stems with very few trees displaying apical dominance (Figure 5.1), and this is similar to observations in other studies across northern Australia (Nikles et al. 2004). These problems are likely to be prevalent due to establishment with unimproved genetic stock and application of less than optimised silviculture. For example, historical trial notes indicate that African mahogany was susceptible to damage from strong seasonal winds, because of the early development of a large broad crown. This frequently caused trees to bend and/or shift within mounds, particularly after heavy rain or irrigation, which reduced stem form quality across trials (Figure 5.1). Current research programs in the Northern Territory are expected to yield improvements in genetics and silviculture (Nikles et al. 2004) and similar methods could be applied to improving the performance of future plantations in the Kununurra region, or by gaining access to seed produced by such programs. At the simplest level, the establishment of plantations using seed collected from trees displaying a superior phenotype for bole straightness and apical

dominance (Plate 5.1) will provide a better chance of yielding a larger proportion of acceptable stems across a plantation than deploying indiscriminately collected seed.

Plate 5.1 Examples of wind-swept boles (top left), crooked boles (top right), and a tree displaying favourable phenotype (bottom left), in a 9-year-old African mahogany plantation

In an economic evaluation of a potential African mahogany plantation industry in the Northern Territory, Whitbread (2003) considered a target of 40 to 50 cm DBH achievable over a 20-year rotation on average sites with thinning to a final stocking rate of 100 to 105 stems per hectare. Based on these parameters African mahogany gave positive internal rates of return even for 2 ha stands when some level of value adding (sawing and/or drying) was undertaken. The growth rates seen here were on par or exceeded trials at the same age in the Northern Territory, upon which Whitebread (2003) based his growth assumptions. It is thought that with appropriate silviculture African mahogany could meet the growth targets outlined in the analysis, but the economic viability of plantations under flood irrigation in the ORIA will be dependent on a different set of commercial sensitivities than those found in the Northern Territory.

5.2. Comparison of the growth of eleven high-value timber species, Trial 12

Method

Trial establishment

Trial 12 was established in 1996 to test the growth performance of 11 high-value timber species on flood-irrigated Cununurra cracking clay soil. The species were: Dalbergia melanoxylon, Dalbergia cochinchinensis, Dalbergia latifolia, Swietenia macrophylla, Khaya senegalensis, Khaya anthotheca, Cedrela odorata, Toona australis, Intsia bijuga, Castanospermum australe and Swietenia mahogani.

Land was prepared for flood irrigation with rows mounded in pairs 1.8 m apart, with 3.6 m between row pairs. Seedlings were planted into mounded rows at spacing of 3 m in separate species blocks of six rows wide by five trees long, the equivalent of 1235 SPH (stems per hectare). Each species was randomly allocated to plots across the four replicates. Because of low seedlings numbers, Dalbergia latifolia and Swietenia macrophylla were only planted in two of the replicates.

The trial was kept weed-free through chemical and physical means across the life of the trial. Records of fertiliser application were not kept and it is unknown if and when it was applied. Form pruning was reported to have occurred when trees were 4 years old.

In 2001 Dalbergia melanoxylon blocks were removed from the trial as field staff had recognised it as having potential to become a weed (see Randal 2002). At this time Intsia bijuga had only 6 per cent survival and no further measurements were recorded.

Measurement

The trial was assessed in 1998 for survival and height, with the addition of DBH to assessments in 1999, 2000 and 2001. In 2008 and internal subplot of four rows of each treatment plot was assessed to exclude edge effects and inter-specific competition. Survival, basal diameter, DBH and height were measured. Stem straightness was assessed using a five-point scoring system, with ‘1’ being worst in the trial and ‘5’ the best in the trial, with the aim for category frequencies to approach a normal distribution.

Data from 2008 was analysed using a linear mixed model to estimate mean growth parameters where replicate and species were fixed effects and plot a random effect. Raw data from the early measure in 2001 was not available, and results calculated previously by department researchers were presented here.

Results

Both species of Khaya had very high survival at 12 years of age and Dalbergia latifolia, Swietenia macrophylla and Cedrela odorata also had strong survival (Figure 5.1). Intsia bijuga had no surviving trees after 12 years and poor survival was experienced by Toona australis. All species except Intsia bijuga and Dalbergia melanoxylon, which was removed from the trial in 2001, had moderate to strong survival at 5 years of age. Dalbergia cochinchinensis and Toona australis were the only species to display a marked decline in survival from 5 to 12 years of age.

120.0 120.0 100.0 100.0 80.0 80.0 60.0 60.0

Survival (%) 40.0 40.0

20.0 20.0

0.0 0.0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 6 7 8 9 1 2 3 4 5 10 11

Figure 5.1 Tree survival (%) for high-value timber species in Trial 12 from 1998 to 2008 (Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2), Dalbergia latifolia (3), Swietenia macrophylla (4), Khaya senegalensis (5), Khaya anthotheca (6), Cedrela odorata (7), Toona australis (8), Intsia bijuga (9), Castanospermum australe (10), and Swietenia mahogani (11))

The height after 2 years was relatively constant between six species that were around 200 cm tall (Figure 5.2a). The main exceptions were Khaya senegalensis, which was 126 cm taller than the nearest species, and Intsia which was 48 cm shorter than the next closest species. Within the first 5 years there was considerable variation in height growth rates and rank height between and within species, for example Khaya anthotheca was ranked fourth at 1 year old and shifted to first at 5 years and Toona australis went from eighth after 1 year to fifth at 5 years. However, after 12 years the rankings for height reflect those at 5 years, with only Swietenia macrophylla and Khaya anthotheca switching rank from third to first, and first to third respectively.

The ranking for mean DBH over the first 5 years was relatively constant compared to ranks for mean height (Figure 5.2b). However, the rank in DBH at12 years generally did not reflect those at 5 years as was the case for height ranks, with the exception of three species, Khaya senegalensis, K. anthotheca and Swietenia macrophylla.

1500 1500

1250 1250

1000 1000

750 750 Height (cm)Height 500 500

250 250

0 0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 6 7 8 9 a 1 2 3 4 5 10 11

25 25

20 20

15 15

DBH (cm)DBH 10 10

5 5

0 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 6 7 8 9 1 2 3 4 5 10 11 b

Figure 5.2 Height (a) and DBH (b) for high-value timber species in Trial 12 from 1998 to 2008 (Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2), Dalbergia latifolia (3), Swietenia macrophylla (4), Khaya senegalensis (5), Khaya anthotheca (6), Cedrela odorata (7), Toona australis (8), Intsia bijuga (9), Castanospermum australe (10), and Swietenia mahogani (11))

The estimated stem volume per hectare (Figure 5.3A) combined survival with mean height and DBH, and therefore was an indicator of total productivity of each species at the trial site. The rank estimated that volume of each species was relatively consistent across all assessment years, and the performance at 5 years was strongly reflected in the yield at 12 years. Toona australis was the only species that declined in productivity between 5 and 12 years of age, because its high mortality over this period outweighed growth. Swietenia macrophylla and Khaya senegalensis displayed noticeably higher productivity at 12 years with an estimated stem volume of 166 and 161 m3 per hectare respectively, which was around 60 m3 per hectare higher than the closest moderately productive species Khaya anthotheca and Cedrela odorata.

The mean annual increment between age 1 year to age 5 years was greater than that for the period between 5 years to 12 years for Dalbergia cochinchinensis, Dalbergia latifolia, Swietenia macrophylla, Castanospermum australe and Swietenia mahogani, indicating that these species had lower growth rates during the initial establishment phase compared to that experienced once they were established (Figure 5.3B). The remaining species displayed the reverse of this trend where growth was more rapid in the first years after establishment than in later years.

180 180 160 160 ) 3 140 140 (m -1 120 120 100 100 80 80 60 60 40 40 Est. stem volume ha 20 20 0 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

A 1 2 3 4 5 6 7 8 10 11

16 16

14 14

12 12

10 10

8 8

6 6 4

MAI ESV ha-1 (m3) 4

2 2

0 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

B 2 3 4 5 6 7 8 10 11

Figure 5.3 (A) Survival-adjusted estimated stem volume per hectare (m3), and (B) mean annual increment for estimated stem volume of high-value timber species in Trial 12 between 1998 and 2008 (Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2), Dalbergia latifolia (3), Swietenia macrophylla (4), Khaya senegalensis (5), Khaya anthotheca (6), Cedrela odorata (7), Toona australis (8), Castanospermum australe (10), and Swietenia mahogani (11))

Estimated means for growth parameters and stem straightness scores varied with species at age 12 years (Table 5.3). Estimates for all parameters were significantly different (P<0.001) between species. Khaya senegalensis and Swietenia macrophylla had the largest basal diameter, DBH and height. Bole height was greatest for Khaya anthotheca followed by K. senegalensis, indicating that these species may have superior form compared to the other species for sawn timber production. There was no outstanding mean stem straightness displayed by any of the species and mean scores were low, to at best, moderate. Dalbergia cochinchinensis and Castanospermum australe had particularly poor mean scores which reflected the 70 and 77 per cent of individual trees which scored 1 and 2 for these species respectively. The species with highest proportion of scores above 4 were Cedrela odorata and Swietenia macrophylla with 35 and 31 per cent respectively. These species would display greater improvements in stand stem straightness and form if selective thinning was employed compared to the next best species, Toona australis (19 per cent).

Table 5.3 Estimated parameters assessed for the nine high-value timber species surviving after 12 years (2008) in Trial 12 (means ± error of estimate) Basal diameter DBH Bole height Tree height Species (cm) (cm) (m) (m) Straight score Dalbergia 22.0 ± 1.4 18.0 ± 1.2 1.9 ± 0.4 9.5 ± 0.6 1.9 ± 1.1 cochinchinensis Dalbergia latifolia 25.2 ± 3.4 18.5 ± 2.9 1.4 ± 0.8 9.4 ± 1.3 2.14± 1.2 Swietenia macrophylla 27.2 ± 4.0 20.1 ± 3.4 2.1 ± 1.0 14.2 ± 1.5 2.5 ± 1.2 Khaya senegalensis 27.2 ± 3.0 22.0 ± 2.5 3.1 ± 0.7 11.5 ± 1.1 2.3 ± 1.2 Khaya anthotheca 23.5 ± 3.0 17.0 ± 2.6 5.0 ± 0.7 11.2 ± 1.1 2.4 ± 1.2 Cedrela odorata 24.7 ± 3.0 18.5 ± 2.6 2.9 ± 0.7 10.2 ± 1.1 2.7 ± 1.2 Toona australis 21.0 ± 3.6 17.6 ± 3.0 2.1 ± 0.8 7.3 ± 1.3 2.2 ± 1.2 Castanospermum 15.9 ± 3.3 11.4 ± 2.8 2.1 ± 0.8 8.2 ± 1.2 2.0 ± 1.2 australe Swietenia mahogani 17.4 ± 3.1 13.7 ± 2.7 1.6 ± 0.7 8.1 ± 1.1 2.2 ± 1.1

Discussion

The survival and growth results provide a comparative guide of the potential of these species to establish and grow in flood-irrigated plantations in the ORIA. The species were grouped, based on their performance, into poor (Dalbergia cochinchinensis, Intsia bijuga, and Swietenia mahogani), moderate (Dalbergia latifolia, Khaya anthotheca, Cedrela odorata, Toona australis and Castanospermum australe), and good (Swietenia macrophylla and Khaya senegalensis) performers.

There were no records of the seed source used for each species and like most other timber plantings at the Frank Wise Institute it was likely that the seed was sourced from bulk lots of unimproved seed available commercially at the time. Therefore the growth performance may not necessarily be representative of the full potential of the species, especially considering the generally widespread geographical distributions of the species tested and the potential for improvement through selection and matching of superior genotypes to the site. For example, highly significant differences in mean diameters and height were found for Swietenia macrophylla in three trials in Costa Rica, where at one site the smallest family had only achieved approximately 62 per cent of the diameter of the largest family at 4.5 years (Navarro and Hernández 2004). Further to this Patiño (1997) suggested that the large differences in the morphology of leaves, fruits and wood properties between provenances of Swietenia could point to the existence of biotypes that are adapted to a range of habitats. The selection of specific provenances or biotypes suitable to northern Australia within the tested species would be likely to improve growth performance.

The tree form of all species was generally poor and characterised by swept and crooked stems, low bole break and unfavourable branching. Neither of the high performing species, Khaya senegalensis or Swietenia macrophylla displayed ideal form traits for sawlog production; however, Swietenia did have superior stem straightness compared to African mahogany, and also had a high enough number of comparatively straight stems (31 per cent) for selection of superior phenotypes in a thinning regime. Poor form is not uncommon for African mahogany as observed within trials across northern Australia (Nikles et al. 2004; Reilly et al. 2005), however, it is not an insurmountable problem with considerable improvements expected through the implementation of selection and breeding programs (Nikles et al. 2004). The plantation deployment of genetic material showing favourable form characteristics should be a priority for these fast-growing species. Among species with moderate growth, Cedrela odorata and Khaya anthotheca displayed the most potential because of favourable bole length and straightness, making them more suitable for sawlog production. The lack of knowledge about application and suitability of form pruning, the use of less than optimal silviculture,

as well as potentially poor genetic stock, precludes rejection of any of these species based on form traits alone.

Khaya senegalensis has gained recognition as a potential plantation species across northern Australia through the impressive growth rates achieved across multiple trial plantings throughout the region. The diameter mean annual increment of Khaya in this trial was low compared to other similarly aged plots at the Frank Wise Institute (Section 5.1), however its favourable growth compared to other species provides further evidence of its suitability as a plantation species in the ORIA. Swietenia macrophylla, has not been tested to the same extent across northern Australia, but results of Reilly et al. (2005) suggest moderate performance up to 5 years of age compared to African mahogany on un- irrigated sites in the Northern Territory. The similar growth rates and favourable form compared with African mahogany within this trial suggest further research may be warranted in the ORIA and potentially across broader northern Australia, especially where irrigation is available. Swietenia macrophylla should have good commercial potential as a plantation species, as a continued expansion of sustainable resources is required to alleviate the decline in the natural population caused by deforestation and exploitative logging within its natural distribution (Patiño 1997). Swietenia plantations have largely been concentrated in Oceania (Fiji, Solomon Island) and Asian regions (Indonesia, Phillipines and Sri Lanka) (Odoom 2001) and this could provide the opportunity to tap into the ready-made markets established by these neighbouring countries.

Despite its poor form, Dalbergia latifolia remains a species of considerable interest as a result of its ability to promote excellent sandalwood growth (Barbour 2008). The selection of host species that have their own commercial value is a desirable outcome for the sandalwood industry, and one that has not yet been widely achieved in plantations. Dalbergia latifolia is valued due to its very dense golden brown to dark brown wood, commonly traded as Indian, or East Indian rosewood (Lemmens 2008). It is suited to furniture and cabinetry and is widely used as a tone wood in high-end acoustic guitars and it can demand prices similar to teak (Lemmens 2008). Dalbergia is known to have a branching habit with short boles when grown under wide spacing (Lemmens 2008), as observed here, and the manipulation of branching and stem straightness through silvicultural practices within sandalwood plantations may be limited due to the required spatial arrangement of hosts to ensure maximised sandalwood growth. It would thus be desirable to select and deploy genotypes that display a favourable form when grown in spatial configurations commonly used in sandalwood plantations. The commercial return from Dalbergia would be dependent on the amount of heartwood the tree is able to produce. In this trial Dalbergia displayed moderate growth and projections could see an estimated average breast height diameter of around 20 cm at the 15-year rotation length for sandalwood. Future harvesting trials are required to determine whether the properties of Dalbergia wood grown in short rotations, as part of sandalwood plantations, meet the market expectations for the species.

5.3 Growth assessment of high-value timber demonstration plots, Trials 10, 11, 13 and 15

Methods

Trial establishment

All trials were established on land prepared for flood irrigation, with mound and tree spacing as indicated in Table 5.4. Historical watering schedules have not been maintained for these trials; however, they would have likely followed the regular routine of at least one application every 2 months during the dry season, reducing to an as-required basis as they aged. There was no evidence of form pruning in Trials 10 and 11, and scarring on stems in Trials 13 and 15 suggest at least one pruning had occurred prior to current management taking over the site in 2006. No thinning was undertaken on these trials.

Measurement

Assessment of tree height, DBH and bole length in the trials occurred in 2008. In Trials 10, 11 and 15 at least two subplots, representing opposite ends of the trial, were measured except for Castanospermum where only a single plot was possible. For Swietenia and Dalbergia plots the entire internal block was measured.

Table 5.4 Description of high-value timber demonstration plots in Trials 10, 11 and 15

Trial spacing Year (between x Trial Species planted Age within row) SPH Design note 10 Gmelina arborea 1993 15 3.6 x 3 926 Single species block Enterolobium Alternating line planting 11 1996 12 3.6 x 4 694 cyclocarpum at 1:1 ratio with Khaya Swietenia 1997 11 2.7 x 3 1235 Demonstration plots, 13 mahogani single species blocks Dalbergia retusa 1997 11 2.7 x 3 1235 Pterocarpus 1999 9 3.6 x 3 926 indicus Demonstration plots, 15 Cedrela odorata 1999 9 3.6 x 4 927 single species blocks Castanospermum 1999 9 3.6 x 5 928 australe

Results

Survival varied across species and Swietenia, Pterocarpus and Castanospermum displayed the poorest survival (Table 5.5).

Enterolobium had a diameter that was 2.5 times larger than Swietenia and Dalbergia, which were just 1 year younger, and 1.7 times larger than Gmelina which was 3 years older (Table 5.5). Pterocarpus and Castanospermum displayed growth rates that resulted in mean diameters equal to Gmelina six years earlier. These growth rates may underestimate the potential of these species within a sawlog regime as the trials were not thinned, and the smaller trees that would be targeted for removal, reduce the means. For example, if Gmelina was reduced to one-third of the original stocking rate (308 SPH) by 15 years, the mean DBH of the remaining trees in the subplots after thinning would be 25 ± 3 cm and the estimated stem volume would be 0.210 m3 per tree.

Form of the trees was evaluated by a combination of the mean bole length (Table 5.5) and the number of stems at breast height (Figure 5.4). Castanospermum and Gmelina displayed superior form compared with the other species, with average bole length equal to around one-third of total tree height, and around 80 per cent of trees had single stems at breast height. Dalbergia had the worst stem form with a very short bole length and a high proportion of multiple stems at breast height. The other species had comparatively moderate form with a bole length around 20 per cent of total height.

Table 5.5 High-value timber growth measurements in Trials 10, 11, 13 and 15. Results at the hectare level were calculated using surviving number of stems per hectare.

DBH Basal MAI area Bole Tree ESV Survival Survival DBH (cm (m2 length height ESV (m3 Trial Species (%) (SPH) (cm) y-1) ha-1) (m) (m) (m3) ha-1) 18.1 3.1 0.115 10.1 ± 10 Gmelina arborea 78.3 725 ± 1.3 18.7 ± ± 83.4 1.9 7.5 0.2 0.125 31.2 2.0 Enterolobium 11 80 1111 ± 2.6 85 ± - - - cyclocarpum 8.6 4.9 12.3 1.2 0.038 Swietenia 6.5 ± 48.3 597 ± 1.1 7.1 ± ± 22.7 mahogani 1.9 6.1 0.6 0.048 13 12.6 0.3 0.040 8.2 ± Dalbergia retusa 85 1050 ± 1.1 13.1 ± ± 42.0 2.3 4.8 0.8 0.042 18.2 1.7 0.086 Pterocarpus 8.8 ± 58.8 544 ± 2.0 14.2 ± ± 46.8 indicus 1.3 5.1 1.2 0.056 14.3 1.0 0.034 5.5 ± 15 Cedrela odorata 79 732 ± 1.6 11.8 ± ± 24.9 1.1 4.6 0.8 0.028 18.4 3.3 Castanospermum 11.3 ± 0.103± 66.7 618 ± 2.0 16.4 ± 63.7 australe 1.0 0.032 2.9 1.2

100%

80%

60%

40%

20%

0% Cedrela Gmelina Dalbergia Swietenia Pterocarpus Enterolobium

1 2 3 Castenospernum

Figure 5.4 Frequency (%) of high-value trees in Trials 10, 11 and 12 with one, two and three stems at breast height

Discussion

Swietenia mahogani, Dalbergia retusa and Cedrela odorata performed poorly and did not appear suitable to the flood-irrigated Cununurra clay. Enterolobium cyclocarpum, Pterocarpus indicus and Castanospermum australe performed much better than these species and displayed acceptable growth in comparison with other high-value timber species trials at the Frank Wise Institute which are shown elsewhere in this chapter. These species have not been commonly planted for commercial or trial purposes in Australia but the limited results available indicated growth was at least equivalent to, or better than, those reported elsewhere. For example, Castanospermum had an average diameter of 5.7 cm and a height of 4.8 m at 6 years old in sub-tropical Queensland (Lamb and Borschmann 1998), and up to 5.07 cm diameter in a trial series in the Northern Territory (Clark et al. 2009). In the same trial series Pterocarpus indicus had average diameters of 11.5 to 12.3 cm at different sites when aged 5 to 6 years. These other trials did not have the benefit of irrigation. These positive comparisons indicated that further testing to more accurately evaluate and compare the performance of fast growing species would be justified.

Growth rates alone will not be the only consideration for the selection of species suitable for further investigation. Enterolobium for example, produced the most promising growth rate of these species; however, it may not be suitable as a sawlog species because of its poor form characterised by multiple, or basket leaders occurring at crown break. In this trial Enterolobium was planted as a nitrogen-fixing companion tree with Khaya senegalensis in an attempt to provide a facilitative effect from increased nitrogen resources. It appeared as though this may have been successful as growth of Khaya was better in this configuration (Trial 11) than in other trials described earlier in the Khaya summary section (see Table 5.2).Commercial multi-species plantations have not been widely established in Australia despite considerable research displaying the benefits of these arrangements (Nichols et al. 2006), and as such it is not foreseeable that Enterolobium would be widely used in such a capacity on the high-value land in the ORIA. Elsewhere it has mainly been grown to be utilised as an amenity tree, for shade in agroforestry or as livestock fodder for which it is well-suited because of its large spreading crown. However, its timber has also been used for veneers, cabinetry and boat construction (Hughes and Stewart 1990). The market demand for Enterolobium timber is likely to be limited compared to the more commercially acceptable species tested here, including Pterocarpus indicus which is well known in the international timber trade as Narra (Thomson 2006). Low land availability and its high cost limit further evaluation of timber species in the ORIA and so future trials should be targeted at species with tangible market value.

The growth and form characteristics of the species assessed here will need to be supplemented by the evaluation of the physical, mechanical and aesthetic wood properties as the trials approach a commercial rotation age of between 20 to 25 years. In particular it is important that the aesthetic characteristics of colour, grain and figure, which largely endow these species with commercial value for use as craft wood, approach the standards of the wood currently traded from native or more mature plantations.

5.4. The growth of teak (Tectona grandis) on levee soil, Trial 14

Teak, Tectona grandis L.f., is a large deciduous tree belonging to the Verbenaceae family that naturally occurs in India, Myanmar, Laos and Thailand. Its heartwood has a fine grain, is golden in colour and is resistant to damage by weathering termites and fungus. These qualities make it well suited to the manufacturing of high-value timber products, such as furniture, flooring and boats (Pandey and Brown 2000). It has been widely established in commercial plantations in areas across its natural range as well as in tropical Asia, northern Africa, Latin America (Pandey and Brown 2000) and more recently in northern Australia.

Teak tolerates a variety of conditions but prefers deep well-drained soils in warm moist tropical climates with a marked dry season (Pandey and Brown 2000). An opportunity existed for the FPC

(then Department of Conservation and Land Management) to plant a demonstration teak trial on the levee soils at the Frank Wise Institute. Levee soils in the Kununurra region are typically brown or red with a fine sandy to loam texture changing to a fine sandy clay loam at depth, and they have a neutral pH (Schoknecht and Grose 1996). This soil type was believed to be better suited for teak growth compared to the Cununurra cracking clays. Trial 14 was established in 1998 to determine the suitability of the Kununurra climate, and the levee soil for growing teak. The management and growth performance of the plantation was assessed over a 10-year period.

Methods

Trial establishment

Trial 14 was established in December 1998 from tissue-cultured clones sourced from Thailand. The pedigree and number of clonal lines were unknown. A total of 0.88 ha was established with rows deep-ripped at 4 m apart and trees spaced at 4 m within rows, the equivalent of 625 stems per hectare (SPH). The trial was watered by drip irrigation two to three times a week which delivered approximately 10 ml per tree per day during the dry season and no irrigation was applied during the wet season.

At planting an experiment was conducted to determine an effective chemical control for the termite species Mastotermes darwiniensis. Two pesticides, Dursban containing chloropyryphos and Termidor containing fipronil, were used and tested against a control (no treatment). Two concentrations were used for both chemicals with 20 ml and 40 ml of Dursban per tree, and 0.4 ml and 0.8 ml Termidor per tree. These treatments were not arranged with any experimental design within the plantation. Since undertaking this trial the control of termites appeared to have occurred on a somewhat ad hoc basis with the few records maintained showing that chemical application usually occurred in response to evidence of infestation.

During the first year, an herbicide spraying program was employed to reduce weed competition. An outbreak of the defoliation insect, Hyblaea puera, occurred approximately 6 weeks after planting and this was treated with carbaryl. Another outbreak of H. puera occurred in 2000 with no further records found to indicate an ongoing problem.

The first pruning was done at 4 months to remove side branching that appeared on the lower half of the stem. Further records of pruning were not recorded up until 2006 when the trees were pruned and the trial selectively thinned to the current stocking of 326 SPH. Selection for thinning was done to remove small and malformed trees (see Plate 5.2).

Plate 5.2 The teak trial showing the variability in performance

Measurement

The trial was measured for DBH and height in 2001 and 2006. In 2008 commercial bole height and DBH were recorded for an internal block of 18 rows by 18 positions.

Results

Growth

Survival at 3 years was 78 per cent, decreasing to 72 per cent at 8 years before thinning occurred. There was no tree deaths post thinning at age 10 years.

The growth performance was measured and estimated for parameters at age 3, 8 and 10 years (Table 5.6). The ESV per hectare for standing trees (per hectare data for final stocking, Table 5.6) at 3 and 8 years old was 8.54 ± 0.22 m3 and 47.98 ± 1.4 m3. Estimated wood volume was compared for trees selected and unselected for thinning at 8 years old and this indicated an improvement in ESV per hectare of 2.079 m3 based on a final stocking of 326 SPH. This rather small improvement is testament to the uniformity of tree growth of the clonal material used in the planting.

The MAI of DBH at the three measurements times indicated that trees were growing fastest at 3 years of age when mean diameters increased by 3.33 ± 0.056 cm, compared with 2.22 ± 0.029 cm and 1.93 ± 0.025 cm at ages 8 and 10 respectively. The mean change in DBH between individual trees at age 8 to 10 was only 0.97 ± 0.057 cm. This represents an annual increment over the 2-year period of 0.485 cm compared to the DBH MAI of 1.93 ± 0.25 cm for 10 years of growth, which suggested tree growth was in decline.

Table 5.6 Growth parameters for teak aged 3, 8 and 10 years at Kununurra in Trial 14 (mean ± s.e.) 2001 2006 2008 Parameter 3 years old 8 years old 10 years old DBH (cm) 9.9 ± 0.1 17.8 ± 0.2 19.3 ± 0.3 Height (m) 642.3 ± 7.7 12.5 ± 0.1 - Bole length (cm) - - 4.7 ± 0.4 Basal area (m2) 0.008± 0.0002 0.0258 ± 0.0005 0.0301 ± 0.0008 ESV (m3) 0.019± 0.0005 0.108 ± (0.003) - EBV (m3) - 0.140 ± 0.0033 Basal area/ha (m2 ha-1) 2.69 8.36 9.83 ESV/ha (m3 ha-1) 6.214 35.210 - EBV/ha (m3 ha-1) - - 45.49 MAI (ESVm3 ha-1) 2.07 4.40 - MAI (EBVm3 ha-1) - - 4.55 All per hectare results are based on final stocking rate (326 SPH at 10 years).

Termite control

At 10 months of age a total of 10.26 per cent of the trial had evidence of termite infestation. The chemical experiment (Table 5.7) indicated that Termidor (a.i. Fipronil) appeared to have been more effective than Dursban (a.i. Chloropyryphos) in preventing termite infestation at the trial site. However, the lack of experimental design and the potentially biased placement of treatments do not allow for fair comparisons and definitive conclusions. For example, both of the double-rate treatments were placed on outside rows possibly closer to the termite source and as a result they included more infested trees than the single-rate applications of internal rows.

There did not appear to be any consistant trends in mean DBH at 3 years of age amongst the chemical treatments. This indicated that early termite infestation reduced growth up to this age (Table 5.7). Runts present within the treatments also influenced results. Indeed a box plot analysis indicated that 24 trees with a DBH of less than 4 cm were outliers (runts), and once removed the difference in mean DBH between chemical treatments reduced to 0.96 cm from 1.99 cm before outlier removal (Table 5.7). The number of outliers/runts per treatment did not appear to be related to termite infestation at an early age, for example the double-rate Dursban treatment had the highest level of infestation but only had one outlier.

Table 5.7 Proportion of teak trees infected with termites assessed 10 months after planting in Trial 14, DBH per pesticide treatment at 3 years of age and DBH with outliers/runts removed (mean ± s.e.)

Trees infected 2001 2001 Number Rows with termites 3 yr old DBH outlier adjusted of Treatment treated (%) (cm) DBH (cm) outliers Control 13 & 14 10.5 9.7 ± 0.3 10.1 ± 0.3 1 Double rate Dursban 25 & 26 25 9.3 ± 0.8 9.7 ± 0.8 1 Double rate Termidor 1 & 2 9.5 9.9 ± 0.3 9.7 ± 0.3 6 Dursban 15 to 24 11.7 8.4 ± 0.5 10.3 ± 0.2 11 Termidor 3 to 12 5.9 10.4 ± 0.2 10.6 ± 0.1 5

Discussion

Growth results for teak in Trial 14 were probably an indication of not more than moderately good growth potential for similar sites in the region because of the ad hoc management of the trial, including pruning, termite control and a late thinning. A more controlled silvicultural regime would have produced better results. For example, observations of the early occurrence and rapid growth of lateral branches, which required the first pruning at 4 months, indicated that the planting density used was less than ideal. Whilst teak has been successfully grown in planting designs ranging from 1.8 m x 1.8 m to 4m x 4m (Kaosa-ard 1998), it was possible the spacing used here promoted early lateral branching and potentially reduced growth by diverting resources away from the main stem (Krishnapillay 2000). In addition to this, the lack of early thinning was likely to have negatively impacted growth rates through increased competition. Teak is commonly planted at a higher density of around 1111 SPH and is thinned twice within the first 10 to 12 years, firstly when the trees are between 8 to 9 m tall (3–4 years) and secondly once trees reach 15 to18 m (Kaosa-ard 1998; Krishnapillay 2000). However, extra establishment and management costs would need to be factored in if employing such a system.

With no other teak trials or plantations in the Kununurra region, the closest data of comparable age comes from the Northern Territory where Robertson and Reilly (2005) compared the growth of teak plantations across different sites and various management regimes. The conditions most similar to those in Kununnura were at Katherine where the trial was drip irrigated and planted on river levee soils. At the Katherine site at 2.5 years, trees had a diameter of 4.5 cm and height of 4.7 m increasing to 9.9 cm and 8.2 m respectively at 4.5 years. These figures are somewhat lower than the growth experienced in this trial where mean DBH reached 9.9 cm at 3 years. On a broader scale the results seemed to fall within the expected early growth rates seen in countries such as Malaysia (Krishnapillay 2000).

Although comprehensive records have not been kept on termites, it did appear that the occurrence and severity of termite infestation reduced as the trial aged. Robertson and Reilly (2005) also suggest in the Northern Territory that termites only appear be a problem during the early growth of teak to around 5 years of age. However, the last appearance of termites within this trial was at age 9, and therefore chemical treatment was still periodically required. Whilst early growth rates did not appear to be adversely impacted by termites, the full effect will not be known until harvest where damage to heartwood can be assessed. Observations during thinning at 8 years suggested it was likely at least a moderate proportion trees will have some heartwood damage.

5.5 Growth, seed yield and oil characteristics of Millettia pinnata, Trial 16

Methods

Millettia pinnata (syn Pongamia pinnata) is a medium-sized leguminous tree found naturally in India, across tropical south-east Asia and into the Pacific including northern Australia (Scott et al. 2008). It was introduced into cultivation at Kununurra as an experimental host for sandalwood, where it successfully promoted early growth of the parasite (Barbour 2008). In addition, the oil derived from Millettia seed is well recognised for its potential use in biodiesel production (Scott et al. 2008), and it may provide an opportunity for a stand-alone plantation industry and a diversified revenue stream for sandalwood growers. Whist Millettia pinnata seed oil is broadly been recognised as suitable for biodiesel production, the viability of the undertaking will largely depend upon oil quality and seed yield of the genetic resources used in a given environment. Within this section Millettia growth, and seed and oil yield within the FPC plantation collection are assessed to aid in determining the suitability of the current Millettia pinnata genetic resource and silviculture practices for seed and oil production.

Trial establishment

Millettia pinnata seedlings were established in 1999 in mounded Cunnurra clay prepared for flood irrigation. Trees were spaced at approximately 3 m within each row and 5.4 m between rows, a stocking of 617 stems per hectare across 0.3 ha. Trees were measured in October 2008, where diameter at breast height was recorded for up to five stems, and total tree height was measured. Where seed was present it was hand collected and weighed. Bee hives were introduced at the trial site in January 2009 and seed was collected from a random sample of 20 trees in October 2009.

Plate 5.3 The Millettia pinnata plot at the time the seed harvesting was completed for this report

Measurement and collection

Mature seed pods were hand collected (Plate 5.3) from 109 mature Millettia trees that had set seed within the FPC Trials 4, 7 and 16 (see Appendix A for trial details) at the Frank Wise Institute in October 2008. Seeds were extracted from the pods and the physical parameters of length, breadth,

thickness, and average weight of 100 seed were measured. Trees in Trial 4 were 14 years at seed collection, with Millettia established in a mixed-species arboretum planting with low density sandalwood. At collection trees in Trial 7 were 9 years old and were established with sandalwood at a host-to-sandalwood ratio of 1:1.

Seeds were dried and ground before oil was extracted in n-hexane using the methods of Kesari et al. (2008) and results were expressed as the proportion of oil per dry weight of seed. The fatty acid composition of seeds from a sample of 23 trees selected from across the range of oil content was analysed using a gas chromatograph fitted with flame ionization detector following a method adapted from Mukta et al. (2009).

Results

Survival of Millettia was approximately 70 per cent at 9 years in Trial 16. The mean DBH was 22.1 ± 6.7 cm with a range between 5.3 to 39.4 cm. Tree height averaged 9.8 ± 2.3 m and ranged between 3.9 to 15.2 m. The average number of stems at breast height was 2.4 and 12 per cent of trees had a single stem, 42 per cent had two stems, 36 per cent had three stems and 9 per cent had four or more stems.

Seed was produced by 37 per cent of trees in Trial 16 (44 of 133), 26 per cent in Trial 7 (58 of 220) and 83 per cent (10 of 12) in Trial 4. The mean weight of seed pods collected in 2008 from Trial 16 (age 9 years) was 1015 ± 1050 g per tree, 812 ± 242 g for Trial 7 (age 9 years) and 8012 ± 3372 g for Trial 4 (age 14 years). Seed comprised 40 per cent of the total fresh weight of pod and seed, which equated to a pure weight of approximately 406 g per tree, or 312 seeds (based on weight in Table 5.8) for Trial 16. In 2009 with the presence of bee hives, the total weight of the 20 tree sample was 248 kg, an average of 12443 ± 23872 g per tree. This was greater than a 10 fold increase in average yield per tree, with an approximate pure seed weight of 4977 g per tree. The highest total pod-on weight for an individual tree was 5 kg in 2008 and 91 kg in 2009, approximately 2 kg and 36 kg of pure seed respectively.

Physical seed traits from 109 trees were assessed from across the FPC trials (Table 5.8). Oil content of seed averaged 37.5 ± 2.8 per cent of dry weight, and ranged from 31 to 45 per cent between trees. There was little variation in the physical traits of seeds across trials, culminating in mean 100 seed weight of 146 ± 18 g, 129± 27 g and 130 ± 28 g for Trials 4, 7 and 16 respectively. Similarly there was little variation in oil content of seed between trials with means of 40 ± 2 per cent, 38 ± 3 per cent and 37 ± 3 per cent for Trials 4, 7 and 16 respectively.

There were significant positive correlations between physical seed variables and the mean weight of 100 seeds (Table 5.9). However, increased seed size was not correlated to an increase in the proportion of oil content.

Table 5.8 Seed traits of Millettia pinnata (n = 109, mean ± s.d.) Seed trait Minimum Maximum Mean Length (mm) 18.2 25.6 22.0 ± 1.6 Breadth (mm) 12.5 18.4 15.1 ± 1.3 Thickness (mm) 4.4 8.2 6.7 ± 0.8 100 seed weight (g) 66.7 184.6 130.5 ± 27.2 Oil content (%) 31.0 45.0 37.5 ± 2.8

Table 5.9 Correlations between measured seed variables of Millettia pinnata (n = 109)

Seed Seed Seed 100 seed Oil Variable length breadth thickness weight content Seed length 1 0.343 0.491 0.603 0.125 see breadth <0.001 1 0.315 0.584 0.158 seed thickness <0.001 0.001 1 0.744 0.234 100 seed wt <0.001 <0.001 <0.001 1 0.086 Oil content 0.195 0.101 0.014 0.375 1 Note: correlations above the diagonal, p value of Pearson correlation at α = 0.05 below the diagonal.

Gas chromatography indicated the presence of nine fatty acids from the seed samples. More than half (53 per cent) of the fatty acid component was oleic (a C18:1 compound), followed by linoleic (C18:2) at 16 per cent, palmitic (C16:0) at 10 per cent, stearic (C18:0) at 6 per cent, and very small proportions of linolenic, arachidic, behenic, lignoceric, and 11-eicosanoic (Table 5.10).

Table 5.10 Composition of fatty acids within oil derived from seed of Millettia pinnata (n = 23, mean ± s.d.) Minimum Maximum Mean Fatty acid (%) (%) (%) Palmitic 8.7 11.3 10.1 ± 0.1 Stearic 4.9 8.0 6.3 ± 0.7 Oleic 50.1 56.7 53.9 ± 1.9 Linoleic 12.3 18.4 15.8 ± 1.6 Linolenic 2.1 4.4 2.7 ± 0.6 Arachidic 1.3 2.1 1.5 ± 0.2

Discussion

Millettia pinnata grew faster in monocultures than as a host for sandalwood. At 9 years of age Millettia growing in a pure stand at a density of 617 stems per hectare had an average diameter at breast height of 22 cm. This diameter is greater than the 14.5 cm reported by Barbour (2008) for 9- year-old Millettia planted at 462 stems per hectare in a mixed stand with sandalwood (926 SPH total) (Trial 7). Considering the two trials shared similar environments (separated by 200 m) and were from the same genetic source, the disparity in growth suggests that sandalwood has some detrimental effect on the growth of Millettia. The parasitic nature of sandalwood did not greatly influence seed size characteristics, oil content or seed yield. The pure stand of Millettia had marginally larger seed and higher yield, but they had slightly lower oil content, than those growing with sandalwood.

Fatty acid composition is important in determining the suitability of oils derived from seed for biodiesel production, influencing cetane number (ignition quality), viscosity, cloud point and cold- filter plugging point, which are important considerations for storage and use (Knothe 2008). The composition of oil seed from Kununurra conforms to the ranges of major fatty acids suggested by Scott et al. (2008) for Millettia; palmitic (5–15 per cent), stearic (5–10 per cent), oleic (40–55 per cent) and linoleic (15–20 per cent), with smaller amounts of linolenic and arachidic acid (Arpiwi et al. 2011). Some of the large seed had high oil content with more than half the fatty acid as oleic acid. Hence the FPC genetic resource and the Kununurra growing environment appeared suitable for producing oil seed with the same qualities that have seen Millettia seed recognised as a candidate for biodiesel feedstock, and selection of superior lines is possible within the Kununurra collection.

Given the suitability of the oil composition and relative consistency of oil yield from seeds between trees and across trials seen here, the viability of commercial biodiesel production would largely depend upon seed yield. Seed yield within and between the three trials was highly variable, and the older 14-year-old trees (Trial 4) had a substantially higher average yield compared to the two 9-year- old trials. There is little information available regarding Millettia seed yield and patterns of production. In Kununurra, bee hives enhanced average yield in 2009 to around 5 kg of pure seed per tree, but this was still substantially lower than the agronomic estimates made by Scott et al. (2008) that equate to annual production of 36 kg per tree. The presence of bee hives improved seed production, but only a few individual trees produced a substantial amount of seed. Monitoring of annual seed production patterns in the future would allow for the selection of fecund individuals that could provide the basis of a deployment population aimed at decreasing variability and improving yield at the plantation level.

6 Implications

6.1 Sandalwood trials

Sandalwood host selection demonstration plots

• Cassia siamea, Khaya senegalensis, Peltophorum pterocarpum and Swietenia mahogani were not suitable hosts for sandalwood, producing poor growth and survival rates when planted in multi or single-host environments. Without knowledge of the physiological limitation of these host species, the development of large canopy structures appears to be the primary limiting factor of these species as successful hosts for sandalwood in the planting configurations used here. The broad and dense canopies that were evident with these hosts in the trials were thought to create an environment in which the shade tolerance of sandalwood was exceeded, thus suppressing growth and increasing mortality. Other species such as Bauhinia cunninghamii and Acacia anuera were not successful hosts but their growth habit is not thought to be limiting.

• At 17 years and 18 years sandalwood established in trial plantations at an initial stocking of 462 stems per hectare had a mean annual basal diameter increment of between 1.1 and 1.4 at age 17 and 18 when grown with Cathormion umbellatum. Sandalwood survival at this age was between 30 and 56 per cent, equivalent to 140 and 259 stems per hectare respectively.

Sandalwood growth with Cathormion umbellatum

• Because of it historical use and consistent performance as a host, it is proposed that Cathormion umbellatum be used as a benchmark species against which sandalwood growth comparisons can be made. At 15 years old, a plantation with sandalwood and host planted at a 1:1 ratio, 462 stems of each, could be expected to produce sandalwood with an average basal diameter between 19 and 22 cm and a height of 6 to 6.5 m.

• Sandalwood size was considerably affected by stocking density when planted with Cathormion hosts at 9 years old, where there was a trend of increased average sandalwood size with declining density. For example, those established at 231 stems per hectare had stem volumes that were 1.6 times greater than those established at 617 stems. Plantation yield (stem volume) did however generally increase with higher density, where higher stocking rates outweighed the benefits of the larger average individual trees in lower density plantings. The commercial implications of various stocking rates will be depend not only on final wood yields but also on balancing the costs of establishment, management, harvesting and post-harvest processing, including de-barking and de- sapping between a lower number of larger sandalwood compared to a higher number of smaller sandalwood. The impact of stocking on heartwood development and yield has not been assessed and monitoring this should be considered in the future.

Investigation of spatial competition analysis

• This report contains the first documented attempt to utilise spatial competition indices in sandalwood plantations. Two different methods have be utilised, one in a trial with no formal design and the other as a supplement to more common analysis of a randomised complete block design. There are certainly limitations in the interpretation of the results; however, as a preliminary investigation of competition indices it has provided evidence that considerable scope exists to improve the understanding of sandalwood-host interactions in plantations. Improvements to the method are also possible as there is large number of alternative competition indices and neighbourhood calculations cited in the literature, as well as using different tree parameters as indicators of competition.

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• The use of spatial competition indices has shown there is differentiation in the competitive nature of host species and their effect on sandalwood growth. The more common approach to trial analysis generally indicates a hierarchical result of effectiveness, that is, host species are good, average or poor. Despite some limitation the spatial competition analysis provided some evidence as to why the host performed in a particular way and in doing so offered insight in potential improvements in utilising the hosts. For instance, there were general trends of decreasing sandalwood growth where the relative size of Cathormion and Mellettia hosts increase, but the same did not occur in relation to the number of hosts. This indicates that retaining host number but altering host size, for example by canopy pruning, may improve host effectiveness.

Sandalwood heartwood and oil development

• Destructive harvesting showed that heartwood occurred in 8-year-old sandalwood, however, the amount and longitudinal development was generally low and variable between trees. At 15 years heartwood was present at least at the base of all 40 trees sampled and had improved to an average of 30 per cent of basal area compared to 11 per cent at age 8 years. There was also considerably more consistent longitudinal development of heartwood along the stem with heartwood still being observed in several trees at greater than 3.5 m along the stem, where at 8 years heartwood was not found over 1.8 m. The heartwood volume at 15 years was estimated to be on average around 1.6 L in the root stump, 4.9 L in the bole and 0.3 L in the canopy stem, or approximately 18 per cent of total stem volume.

• The oil yield typically increased with distance along the stem with the highest proportion being an average of greater than 6 per cent in the root stump and lower bole. Oil quantity further along the stem was still reasonably good with an average yield of 3.4 per cent recorded for trees with heartwood at crown break. The average proportion of alpha and beta-santalol within the oil indicates a high quality product meeting the criteria of the ISO standard for Santalum album oil (ISO 3518:300E). The oil composition varied only slightly at sample sites along the stem with the average total santalol levels ranging from 68 to 72 per cent, suggesting that wood products would not need to be separated before distillation to retain a quality product.

• Average estimated stem oil yield per tree was 307 grams at 15 years old, but as would be expected the oil yields were similar to heartwood volume in that they were highly variable between trees, with a low of 18 grams and a high of around 780 grams. The lower-third portion of the bole accounted for some 50 per cent of total average estimated oil yield compared to 28 per cent in the root stump. Given that oil quality is stable across the tree the lower-third of the bole would be of higher commercial value than the root stump section which would contribute a larger proportion of total harvesting and processing costs.

• Heartwood was present in 78 per cent of sandalwood core sampled at 11 years old, where only one of 15 sandalwood sampled with Dalbergia latifolia did not have heartwood compared to four and five for Cathormion umbellatum and Millettia pinnata respectively. The amount and proportion of heartwood was not significantly different between sandalwood with the three host species. However, if the differences in heartwood occurrence and yield held true at the plantation scale there would be substantial differences in the number of sandalwood containing heartwood and the total yield with different host species. Further research is required to confirm these initial findings and also to investigate the causes, whether environmental or physiological, of the variation in heartwood formation and yield with different host species.

6.2 High-value timber trials

• With the high growth rates observed in the ORIA, a small African mahogany plantation industry has emerged in the region. This current project has confirmed the superior growth rates, but has also reinforced the poor form characteristics that have been expressed in trials across northern

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Australia. To aid the development of the industry, additional research is required to identify and deploy genotypes that exhibit superior form. An immediate response of plantation managers should be to deploy material, by seed or clonally, from trees displaying a superior phenotype.

• Indian rosewood, Dalbergia latifolia, is the only species valued for its timber product that has proved successful as a host for sandalwood. Its current uptake as a host species in plantations is increasing and thus could provide an option for income diversification. There is a need to investigate whether the Indian rosewood grown in short rotation is able to produce wood with physical and appearance qualities that make it desired, particularly as a tone wood for guitars and other stringed instruments.

• Because of the limited availability and high cost of land any future timber research trials should consider only those species with potential to produce high-value products with well-established markets. Trials of such species should aim to evaluate the growth and form characteristics of several provenances from ‘best bet’ sources based on matching soils and climate data. The genetic base of species tested to date has been narrow and used generic seed which has limited the ability to identify their potential.

• One of the deficiencies in the timber trials reported on here is the lack of applied silviculture, management and record keeping. In future, trials should follow a prescribed silviculture regime throughout the rotation as to better reflect the potential growth and yield that would occur in a commercially managed plantation. As part of this, records must be kept of actions such as fertilising, pruning, thinning and irrigation so that there can be a more accurate evaluation of both system and tree performance.

• The oil quality and quantity of Millettia pinnata seed at Kununurra is within the range reported to have identified the species a candidate feedstock for biodiesel production. However, seed production appears to be a major limiting factor with the highest pure seed yield per tree at only approximately 36 kg. There was also considerable variation in production between trees, and whilst the presence of bee hives improved seed production only a few individual trees produced a substantial amount of seed.

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7 Recommendations

RIRDC supported this project so that 16 silviculture trials could be measured and reported on that were grown in the ORIS in the north of Western Australia with flood irrigation.

The first outcome was the discovery of the heartwood rot within Santalum album at the Frank Wise Institute. The first recommendation to RIRDC was to further investigate the heartwood rot and this culminated in RIRDC report Heartwood Rot Identification and Impact in Sandalwood (Santalum album) (Barbour et al. 2010).

This project additionally recommends that:

• Time-course studies of different planting designs is undertaken to quantify changing spatial relationships between hosts and sandalwood so that silviculture recommendations over the full 15- year rotation can be made.

• The exploration of new secondary hosts is continued. The concept of a hedge of Millettia pinnata or the inter-row integration of horticulture and agriculture needs further exploration.

• Studies are undertaken to understand heartwood formation as this is a key to regulating its production within the bole of the tree and the amount of final product produced.

• A selection program (using new technologies that correlate to wood quality) is initiated for the development of a timber product from African mahogany, teak and Dalbergia. The latter species also requires a review of current germplasm in relation to its natural distribution and current nursery techniques.

• Mechanical systems are developed for the selective harvest of sandalwood, the removal of the clay, and the separation of heartwood and sapwood.

• The possibility of products from the remaining biomass at harvest is explored.

• A method for non-destructive assessment of heartwood and heartwood rot would be extremely useful in tree selection and thus optimisation of tree value. The first assessment of acoustic time- of-flight measurement and electrical impendance techniques did not give clear answers but there are many other permutations of these that still need to be explored.

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Appendix A

A summary of sandalwood and high-value timber trial plantings assessed during the project. (LH = long-term host, IH = intermediate host, HVT = high-value timber)

Sandalwood plantings

No. Year Species Design Original aim Notes S. album & LH Cathormion umbellatum & IH 1 1990 No statistical design Demonstration plot Acacia ampliceps Original design redundant as result of poor 2 1991 S. album & LH Cathormion umbellatum, Randomised LH species Evaluate S. album survival. Host infill with Millettia has occurred at Bauhinia cunninghamii, Acacia aneura blocks with 7 replicates growth with three LH various stages 3 1993 S. album & LH Cassia siamea, Peltophorum sp. No statistical design, Demonstration plot

& IH Acacia trachycarpa, Sesbania formosa separate LH blocks with HVT host 104 Blocks of a single LH with Comparison of LH Original design redundant as result of poor early 4 1994 S. album & LH Acacia mangium, Cassia unknown randomised IH and IH effect on S. survival. Irrigation ceased in 2003. Trial used for siamea, Peltophorum sp. & IH various treatments album destructive harvest. S. album & LH Cathormion umbellatum, Demonstration plot of 5 1997 No statistical design. Cassua siamea, Swietenia mahogani, Khaya sandalwood with Mixed host design senegalensis mixed HVT hosts Six stocking and parasite Evaluate S. album 6 1999 S. album & LH Cathormion umbellatum & IH host ratios. No Trial was analysed using a pseudo-replicate growth in different Acacia trachycarpa, Sesbania formosa randomisation or structure. host environments replication S. album & LH Cathormion umbellatum, 7 1999 Cedrela odorata, Dalbergia latifolia, Khaya Randomised LH species Evaluate S. album Trial previously reported in RIRDC publication senegalensis, Melletia pinnata, Pterocarpus blocks with 5 replicates growth with three LH No.08/138 (Barbour 2008). indicus & IH Acacia trachycarpa

S. album & LH Castenospernum australe, Evaluate S. album Herbicide use in early development caused many 8 2000 Cathormion umbellatum, Dalbergia retusa, Randomised LH species growth with several deaths. Design redundant, trial used for Sweitenia humilis, Tectona grandis & IH blocks with 7 replicates LH species destructive harvest. Sesbania formosa

6 host-to-parasite ratio Identify host ratio to Overcrowding was identified in 2003 and 3 rows 9 2001 S. album & LH Cathormion umbellatum & IH treatments randomised optimise S. album per block were removed. Three treatments no Sesbania formosa with 6 replicates growth exist, all host, all parasite, 1:1 ratio.

High-value timber plantings (HVT) No. Year Species Design Original aim Notes

No statistical design. 10 1993 Gmelina arborea Demonstration plot No silvicultural treatments. Single species block plot No statistical design. 11 1994 Khaya senegalensis and Enterolobium Mixed species plot at 1:1 Demonstration plot No silvicultural treatments. cyclocarpum ratio within rows 105 Dalbergia cochinchinensis, Dalbergia latifolia, Swietenia macrophylla, Khaya senegalensis, Single species randomised Comparison of HVT Dalbergia melanolxylon was established but later 12 1996 Khaya anthotheca, Cedrela odorata, Toona block plots with 4 timber growth in removed as it posed a weed threat. australis, Castnospermum australe, Swietenia replicates cracking clay soil Trees pruned at 4 years old. mahogani

13 1997 Khaya senegalensis, Swietenia mahogani, No statistical design. Demonstration plot Dalbergia melanolxylon was established but later Dalbergia retusa Single species block plots for HVT selection removed as it posed weed threat.

No statistical design. Demonstration Pruned at 4 months and again at 8 years before 14 1998 Tectona grandis Single species block plots planting on levee soil thinning. Demonstration plot Castnospermum australe, Cedrela odorata, No statistical design. 15 1999 displaying HVT No silvicultural treatments. Pterocarpus indicus & K. senegalensis. Single species block plots species growth Demonstration plot No statistical design. 16 1999 Melletia pinnata (pongamia) and seed collection Single species block plots area

References

Arpiwi, NL, Yan, G, Barbour, EL & Plummer, JA 2011, ‘Genetic diversity, seed traits, and salinity tolerance of Pongamia (Millettia pinnata (L.) Panigrahi), a biodiesel tree’, (manuscript in preparation).

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111 Flood-irrigated Tropical Timber Trials in the North of Western Australia by L. Barbour, J. Plummer and L. Norris Pub. No. 12/044 This report records a joint project between the Rural Industries Research and Development Corporation, the Forest Products Commission of Western Australia, Elders Forestry and the University of Western Australia to ensure that 16 of the original plantation trials and plantings of tropical species established in the Ord River Irrigation Scheme (ORIS) by the Western Australian Government were assessed and published. The main target groups of this research are researchers and managers, especially within the Western Australian Government system, non-governmental organisations and commercial and private companies actively growing sandalwood in the ORIS. The included information on growth rates and essential oil production will be of interest to investors and consultants. RIRDC is a partnership between government and industry to invest in R&D for more productive and sustainable rural industries. We invest in new and emerging rural industries, a suite of established rural industries and national rural issues.

Most of the information we produce can be downloaded for free or purchased from our website .

RIRDC books can also be purchased by phoning 1300 634 313 for a local call fee.

Phone: 02 6271 4100 Fax: 02 6271 4199 Bookshop: 1300 634 313 Email: [email protected] Postal Address: PO Box 4776, Kingston ACT 2604 Street Address: Level 2, 15 National Circuit, Barton ACT 2600

www.rirdc.gov.au

Plate 4.3 Typical 8-year-old tree from this trial Destructive harvest

Plate 4.4 A sample of the 8-year-old wood assessed after the destructive harvest

Simple and multiple linear regressions were used to determine relationships between measured variables (XLStat, 2006). For multiple regression, model selection was determined by comparing the

Plate 4.5 The plot combining sandalwood with the long-term host Dalbergia

Measurement and core sampling

Statistical analysis

68 Flood-irrigated Tropical Timber Trials in the North of Western Australia by L. Barbour, J. Plummer and L. Norris Pub. No. 12/044 This report records a joint project between the Rural Industries Research and Development Corporation, the Forest Products Commission of Western Australia, Elders Forestry and the University of Western Australia to ensure that 16 of the original plantation trials and plantings of tropical species established in the Ord River Irrigation Scheme (ORIS) by the Western Australian Government were assessed and published. The main target groups of this research are researchers and managers, especially within the Western Australian Government system, non-governmental organisations and commercial and private companies actively growing sandalwood in the ORIS. The included information on growth rates and essential oil production will be of interest to investors and consultants. RIRDC is a partnership between government and industry to invest in R&D for more productive and sustainable rural industries. We invest in new and emerging rural industries, a suite of established rural industries and national rural issues.

Most of the information we produce can be downloaded for free or purchased from our website .

RIRDC books can also be purchased by phoning 1300 634 313 for a local call fee.

Phone: 02 6271 4100 Fax: 02 6271 4199 Bookshop: 1300 634 313 Email: [email protected] Postal Address: PO Box 4776, Kingston ACT 2604 Street Address: Level 2, 15 National Circuit, Barton ACT 2600