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Department of Sustainability and Environment Victoria, Australia

NATIVE GUIDELINE NO. 15

Summary This Guideline describes the recommended procedures for planning and conducting commercial, pre-commercial and ecological operations in the Box-Ironbark State in Victoria. It includes a brief history of thinning; the effects of thinning on the stand; and economic issues; and criteria for identifying stands that are suitable for thinning.

The Guideline outlines the main thinning methods and gives specifications to ensure the best results, according to whether the main objective is timber production or ecological improvement.

A Bibliography, a Glossary, and Appendices covering pre- and post-thinning stand assessment/audit procedures are also included.

Title: THINNING OF BOX-IRONBARK FORESTS

Authors: Peter Fagg (Forest Resources Branch, DSE, Melbourne) Paul Bates (North West Area, DSE, Maryborough)

Distribution: Regional Forest Managers All Work Centres

Date: 6 March 2009

Signed:

Janine Haddow Executive Director Natural Resources Division

Native Forest Silviculture Guidelines are official DSE documents that have State-wide application. ii

© The State of Victoria, Department of Sustainability and Environment, 2009

Published by the Department of Sustainability and Environment 8 Nicholson St East Melbourne, Vic. 3002

This publication is copyright. Apart from any fair dealing for private study, criticism or review as permitted under the Copyright Act 1968, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic or otherwise, without prior permission of the copyright owner.

This publication may be referenced as:

Fagg, P.C. and Bates, P. (2009) Thinning of Box-Ironbark Forests. Native Forest Silviculture Guideline No. 15, Natural Resources Division, Department of Sustainability and Environment, Victoria.

ISSN 1329-5918 ISBN 978-1-74208-896-9 (print) ISBN 978-1-74208-897-6 (online)

Inclusion in this document of the name of any supplier or equipment by name or trade designation does not constitute any endorsement of that supplier or equipment to the exclusion of any other.

The advice provided in this publication is intended as a source of information only. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular uses and therefore disclaims all liability for any error, loss, or other consequence which may arise from you relying on any information in this publication.

Layout and printing by SMA (Publications) Pty Ltd, Hawthorn. Printed on recycled paper. iii

CONTENTS

1. INTRODUCTION ...... 1

1.1 Aim of guideline ...... 1 1.2 What is thinning and why do it?...... 1 1.2.1. Commercial Thinning (CT)...... 1 1.2.2 Pre-commercial Thinning (PCT) ...... 2 1.2.3 Ecological Thinning (ET)...... 2 1.3 What and where is “Box-Ironbark” forest in Victoria?...... 2 1.3.1 Species and Species Groupings...... 2 1.3.2 Occurrence in Victoria...... 3 1.4 Brief history of Box-Ironbark thinning in Victoria ...... 4 1.4.1 Commercial thinning ...... 4 1.4.2 Pre-commercial thinning...... 5

2. EFFECTS OF THINNING ...... 5

2.1 Growth of retained ...... 5 2.1.1 Effect on basal area and diameter ...... 5 2.1.2 Effect on height ...... 7 2.1.3 Effect on volume response...... 7 2.1.4 Duration of response...... 7 2.1.5 Effect of tree age at thinning ...... 7 2.1.6 Effect on clear bole ...... 7 2.1.7 Stump/coppice survival ...... 7 2.2. Damage to retained trees ...... 8 2.2.1 Stain and decay of ...... 8 2.2.2 Epicormic development...... 8 2.3 Environmental issues...... 8 2.3.1 Observations and research findings ...... 8 2.3.2 Operational implications...... 9

3. COMMERCIAL THINNING...... 10

3.1 Economics ...... 10 3.2 Planning ...... 11 3.2.1 Developing a strategy ...... 11 3.2.2 Identification of areas available and suitable for thinning ...... 11 3.2.3 Constraints that may affect planning and scheduling of operations ...... 12 3.3 Commercial thinning equipment...... 12 iv

3.4 Commercial thinning specifications & monitoring...... 13 3.4.1 Basal area and stocking...... 13 3.4.2 Tree retention...... 13 3.4.3 Damage to retained trees...... 13 3.4.4 Utilisation...... 14 3.4.5 Monitoring...... 15 3.5 Fire risk and fuel reduction burning ...... 15

4. PRE-COMMERCIAL THINNING...... 15

4.1 Planning ...... 15 4.2 Pre-commercial thinning methods...... 16 4.2.1 Stem injection with herbicide...... 16 4.2.2 Chainsaws...... 17 4.2.3 Clearing saws and long-handled chainsaws...... 18 4.2.4 Axes ...... 18 4.3 Pre-commercial thinning specifications...... 18 4.4 Fire risk and fuel reduction burning ...... 19

5. ECOLOGICAL THINNING ...... 19

5.1 Planning ...... 19 5.2 Ecological thinning methods...... 20 5.3 Ecological thinning specifications...... 21 5.4 Fire risk and fuel reduction burning ...... 22

6. EQUIPMENT AND MATERIALS...... 22

7. REFERENCES ...... 23

ACKNOWLEDGEMENTS...... 25

GLOSSARY ...... 26

APPENDICES

1 Pre-thinning stand assessment – commercial thinning ...... 29 2 Post-thinning stand assessment – commercial thinning ...... 33

Thinning of Box-Ironbark Forests 1

1. INTRODUCTION

1.1 AIM OF GUIDELINE The aim of this Silviculture Guideline is to be a comprehensive guide to the conduct of thinning of Box-Ironbark in Victorian State forests. It is prepared specifically for and forest officers who plan and supervise such operations, although the Guideline may have applicability in conservation reserves where the main objective is forest health and wildlife habitat improvement.

The contents of this Guideline are consistent with the Sustainability Charter for Victoria’s State forests (DSE 2006b) and DSE’s policy statement Thinning in State forests (DSE 2008c).

1.2 WHAT IS THINNING AND WHY DO IT? Thinning is the selective removal of designated trees in a forest stand in order to achieve one or more of the following objectives:

(i) the concentration of future growth on to a reduced number of selected trees; (ii) a yield of timber early in the life of the stand; (iii) improved wildlife habitat such as faster hollow development; (iv) increased water yield from a catchment (due to reduced transpiration); and (v) an improvement in health of the remaining trees (due to reduced competition),

The Box-Ironbark Forests and Investigation Report (ECC 2001) states: “carefully conducted thinning … has an important role in producing timber for harvest and achieving…stands with more than the present density of large diameter trees”.

The three main categories of thinning in the Box-Ironbark forests: • commercial; • pre-commercial thinning; and • ecological thinning, are described below.

1.2.1. Commercial Thinning (CT) Commercial thinning, usually described as ‘Thinning from Below’ (abbreviated ‘THB’), is the harvesting of the smaller merchantable trees in the stand. Many trees removed in a ‘thinning from below’ will be those which would have died or be very suppressed in their growth through inter-tree competition before the final . As such, thinning can be seen as a type of ‘salvage’ harvest that increases the overall per hectare commercial timber production from the stand.

Thinning should not be confused with the ‘Single Tree Selection’ silvicultural system, which is the harvesting of scattered mature individual trees, at intervals over the rotation.

The Plan for the Bendigo Forest Management Area (DSE 2008a) identifies thinning as a means ‘to improve forest stands for future sawlog production and for ecological purposes’.

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In recent years, approximately 1200-1500 ha has been commercially thinned on an annual basis in the Box-Ironbark forests to produce firewood and residual sawlogs (Box-Ironbark sawlogs grade 2), predominantly in the Bendigo Forest Management Area (FMA) and less so in the North East FMA.

Approximately 12,000 m3 of firewood (for sale to the public for domestic consumption) is produced annually by DSE crews in Victoria and 1,500 m3 of firewood is produced by private cutters with commercial licences.

1.2.2 Pre-commercial Thinning (PCT) Pre-commercial thinning is thinning where none of the removed trees are used or sold, the operation being carried out primarily to promote the growth of the retained trees. There is the expectation that the stand will be commercially thinned 15-25 years later. PCT is sometimes described as ‘Early Spacing’ (abbreviated ‘ESP’). Economic analyses (e.g. Kerruish et al 1991) show that investment in PCT on Ash sites may have a high present net worth value – in terms of accelerating future timber returns. On other sites or tenures, PCT may be used to promote forest health or ecological values.

Given the relatively high up-front cost of pre-commercial thinning, associated with long time frames before the investment is realised, PCT has usually only been undertaken in Box-Ironbark regrowth when labour and funds are available.

1.2.3 Ecological Thinning (ET) The main objective of Ecological thinning is to enhance fauna habitat and biodiversity values. Depending on the type of habitat being aimed for, ET may or may not involve utilisation of the removed trees.

In the period 2005-07, about 360 ha was ecologically thinned as part of a long-term trial conducted by Parks Victoria in nature conservation reserves around Maryborough, Bendigo and Castlemaine. The trial is aiming to accelerate the return of these forests to their pre-European condition, thought to have been large trees at low density, by heavily reducing the current tree density and assisting the development of arboreal habitat features such as hollows and cavities in the retained trees.

1.3 WHAT and WHERE IS “BOX-IRONBARK” FOREST IN VICTORIA?

1.3.1 Species and species groupings “Box-Ironbark” species in this Guideline includes the eucalypts listed in Table 1.

Table 1. Eucalyptus species found in Victorian Box-Ironbark forests

Main species Common name Minor species Common name E. tricarpa Red Ironbark E. melliodora Yellow Box E. sideroxylon Mugga Ironbark (NE Vic) E. albens White Box E. leucoxylon Yellow Gum (or White Ironbark) E. goniocalyx Long-leaved Box E. microcarpa Grey Box E. macrorhynca Red Stringybark E. polyanthemos Red Box Thinning of Box-Ironbark Forests 3

The main relevant Ecological Vegetation Classes (EVC) are:

• Box-Ironbark Forest and Heathy Dry Forest – mainly Central Victoria (e.g. Bendigo; Dunolly; Rushworth; Heathcote; Maryborough; Clunes; St Arnaud; Stawell; Pyrenees); • Box-Ironbark Forest and Grassy Dry Forest –mainly NE Victoria (e.g. Killawarra; Chiltern; Barambogies); and • Foothill/ Box-Ironbark Forest – mainly Gippsland (e.g. Heyfield; Mt Taylor).

These occur in either an open forest formation (30-70% crown cover, and 15-28 m height range) or formation (10-30% crown cover and 15-28 m height range) (NRE 1998).

1.3.2 Occurrence in Victoria Figure 1 shows the extent of land (public and private) in Victoria where the predominant forest type is the Box-Ironbark Forest EVC (Number 61). The extent of Heathy Dry Forest (Number 20) and Grassy Dry Forest (Number 22), which also contain some species listed in Table 1, is not shown.

Figure 1. Extent of the Box-Ironbark forest EVC in Victoria

The main contiguous area is the country between the Northern Plains and the Great Dividing Range which is drained by the middle reaches of the Goulburn, Campaspe, Loddon, Avoca and Wimmera Rivers (NRE 1998). It is interspersed with associations of mixed and mallee eucalypt species.

E. sideroxylon is now largely confined to areas managed by Parks Victoria in the Warby Ranges and Chiltern areas, although current thinning in North East Victoria in the Box-Stringybark State forests in is covered by this Guideline.

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Soils are generally shallow or skeletal clay loams largely derived from Palaeozoic slates and sandstones and are low in fertility and permeability.

Mean average rainfall varies from 400 mm in the north to 750 mm in the south with a winter maximum. Run-off on the generally undulating topography is rapid after rainfall and follows seasonal or intermittent drainage lines (NRE 1998).

E. tricarpa also occurs (usually in mixtures with other eucalypt species) in State forests in several East Gippsland localities, such as Heyfield, Mt Taylor and Waygara.

Some forests around Stawell and Edenhope in western Victoria are predominantly E. leucoxylon, and these should be treated as outlined in this Guideline.

“Box-Ironbark forest” in this Guideline covers both uneven-aged and even-aged stands. This includes stands naturally regenerated from coppice or seed but may also include planted stands.

For thinning of mixed species regrowth, such as Stringybarks, Peppermint and Gum eucalypts, see Native Forest Silviculture Guideline No. 14 (Sebire & Fagg 1997).

1.4 BRIEF HISTORY OF BOX-IRONBARK THINNING IN VICTORIA

1.4.1 Commercial thinning The Box-Ironbark forest was subject to heavy exploitation during and after the gold rush period in Victoria (1851-1880) when large areas in central Victoria were essentially clear-felled at least twice (Newman 1961).

The first regulated commercial operations started in 1891 when licensed operators produced mining timbers and firewood on ‘thinning blocks’ marked by forest officers (Perrin 1891, Newman 1961). Silvicultural thinning was also extensively carried out by government employees from this time through to the 1950s, depending on the availability of labour and funding.

From 1928, Working Plans that set out the objects and methods of forest management were developed and implemented (Newman 1961). Within the ‘Selection Working Circle’1, four types of silvicultural treatment were planned:

• – for all age classes from young coppice upwards; • Regeneration fellings – heavy felling where trees were unhealthy or of poor form - leading to a ‘coppice with standards’ system; • Liberation treatment – felling or ringbarking of overwood that was inhibiting younger age classes; and • – knocking coppice shoots from stumps to minimise competition with the crop trees.

Harvesting was greatly accelerated in the 1930s during the world-wide economic depression when large numbers of otherwise unemployed men were involved in thinning and cull treatment works. The war years of the 1940s saw further high activity to meet the demand for firewood, sleepers and (NRE 1998). Kellas (1991) reported that approximately 1000 ha were

1 That part of a Forest District that was managed under selection silvicultural systems. Thinning of Box-Ironbark Forests 5 thinned annually in the 1980s. Where the demand for firewood has been very high, a cutting cycle of 30-40 years has meant that regrowth has been harvested three or four times since 1851 (Vearing 2002).

1.4.2 Pre-commercial thinning Pre-commercial thinning (PCT) was carried out in several places in the early 1930s (due to the availability of cheap labour during the Great Depression). This mainly involved removing all but 1 or 2 coppice stems per stump, using axes.

In the period 2003-05, approximately 1500 ha were pre-commercially thinned using small chainsaws in the Box-Ironbark forests, predominantly in the Bendigo FMA. The main area treated was coppice regrowth from the 1985 , mainly in the Maryborough District (pers. comm. Jim Allen, DSE Bendigo).

2. EFFECTS OF THINNING

There have been relatively few studies of thinning in Box-Ironbark stands. There has been, however, considerable research into the effects of thinning in other forest types, and some principles found in these studies may be applied to Box-Ironbark thinning.

2.1 GROWTH OF RETAINED TREES

2.1.1 Effect on basal area and diameter In general, after a stand is thinned, retained trees will grow to a given size in a shorter period of time or will grow to a larger size in any given period of time. As such, there is the potential for shorter rotations if a stand is thinned or for higher value trees (e.g. veneer logs) if the planned rotation is retained.

The Box-Ironbark Timber Assessment Project (NRE 1998) in the Bendigo Forest Management Area measured increment on 852 trees in a range of thinned and unthinned stands. Averaged over the different species and size classes, the northern districts2 showed an average diameter increment of 3.8 mm/year, compared with the southern districts3 of 3.2 mm/year.

Another study showed that removal of competing coppice stems can increase Basal Area (BA) increment of retained stems by at least 25% (Kellas et al 1982). This 8-year study (north-east of Heathcote) showed that two steps are needed where accelerated growth of regrowth is required:

• significant reduction of any overwood (greater than 20 cm dbhob) present (retaining necessary habitat trees); and • thinning from below of at least 50 percent (by BA) of the regrowth (less than 20 cm dbhob).

Resultant BA increment of the regrowth was estimated to increase from 0.5 m2/ha/year to 0.8 m2/ha/year.

2 Includes forests around St Arnaud, Inglewood, Dunolly, Bendigo, Heathcote and Rushworth 3 Includes forests around Avoca, Maryborough, Talbot and Castlemaine

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A thinning trial in a 71-year E. tricarpa at Dargile (north-west of Heathcote) examined 3 levels of retention with and without coppice control (Murphy & Forrester 2008 in prep.). Table 2 shows the results after 10 years of growth. Thinning heavier than 50 percent was required to achieve a significant BA response. Coppice control on the 33 percent retained treatment promoted significantly extra growth in the largest 100 retained trees – see Fig. 2.

Table 2. Basal area of the 100 largest trees per ha (in order of decreasing response)

% of initial Coppice Mean basal area BA retained control (m2) 33 yes 9.6 c

33 no 9.1 b

50 yes 8.8 a 60 no 8.6 a 100 n/a 8.4 a

Note: Means sharing different letters are significantly different

Although the stand is not typical of the majority of Box-Ironbark regrowth in that it was relatively old and closely spaced when thinned, the result indicates that a heavy thinning is needed to get a measurable response. Analysis of the data using total stand BA showed no significant differences, indicating that smaller trees did not respond as well as the larger ones.

Figure 2. Thinning Trial in Red Ironbark at Dargile (near Heathcote) – 4 years after thinning. Note the coppice development. 2001

Thinning of Box-Ironbark Forests 7

2.1.2 Effect on tree height Moderate to heavy thinning may reduce ultimate height growth, as the growing tree extends its crown more sideways rather than upwards.

2.1.3 Effect on volume response Average Mean Annual Increment (MAI) rate for Box-Ironbark regrowth stands of around age 60 years is about 0.8 -1.5 m3/ha/year (Newman 1961).

As the rate of diameter growth is increased by thinning, volume growth will increase as volume is a function of diameter and height.

2.1.4 Duration of response The duration of growth response after thinning is determined by:

• the intensity of the thinning; • the rate at which the removed basal area is replaced; and • the age at which thinning is implemented.

Brown (1997) reported for E. obliqua that a response after heavy thinning continued for 25 years in the 75 largest stems/ha. However, this may not apply in Box-Ironbark.

2.1.5 Effect of tree age at thinning Older stands respond more slowly to thinning than young stands. However the response period may be longer in older stands (Brown 1997).

2.1.6 Effect on clear bole Maintenance of, or increase of, clear bole length is important when thinning is designed to maximise sawlog yield. Webb (1966) reported that in Mountain Ash stands thinned by 40% or more basal area reduction, clear bole length does not subsequently increase much.

This is almost certainly the case in Box-Ironbark due to the more open nature of the stands. Accordingly, the stand selection criteria require that the clear bole be at least 5 m on dominants and co-dominants before commercial thinning is considered or undertaken (see Table 3).

2.1.7 Stump/coppice survival Factors affecting stump survival following thinning include age of stump (some may be 150 years old and thus have a significant amount of rot), soil moisture, and browsing by wallabies. Surveys of stumps after harvesting in the Bendigo area have shown generally high survival rates (up to 88%) but other surveys during the current low rainfall period have shown that in some areas 50% of stumps had not coppiced or had died within 3 years of the harvesting.

As indicated above, the majority of stumps of all the Box-Ironbark species re-sprout (coppice) within a few months of cutting resulting in a vigorous clump of 3-6 stems. Without treatment, these stems will grow on and compete strongly with the retained trees (see Section 2.1.1). Thus, there is a case for treating a proportion of the stumps or young coppice with herbicide to

8 Native Forest Silviculture Guideline No. 15 reduce this competition. However, since coppice is the main way that Box-Ironbark species regenerate:

• a maximum of 25% of stumps may be treated in commercial or pre-commercial thinning operations; although • greater than 25% may be treated in ecological thinning, depending on the desired future density.

However, in areas where is a high rate of natural mortality, herbicide treatment of stumps or coppice would not be recommended.

2.2. DAMAGE TO RETAINED TREES

2.2.1 Stain and decay of wood The wood of Ash type eucalypts may be degraded following accidental bark removal from the bole, or breakage of the bark-wood bond - even if the bark is not removed (White & Kile 1991). Such breakage may be caused by a severe bump by a log or by machinery.

The thick tough bark of the Ironbarks generally limits bark damage. The Box and Gum species, however, are more prone to breakage of the bark.

If damage does occur, the initial reaction of a damaged tree is to produce chemicals to protect itself against micro-organisms. Next, organisms which are tolerant of these chemicals begin to invade the wood, causing staining. In the third stage, brown and/or white rotting fungi begin to actively degrade the walls of the wood cells.

2.2.2 Epicormic development In Ash and mixed eucalypt species, epicormic shoots may develop on boles if greater than 50 percent of the initial basal area is removed in thinning. Such shoots persist for several years, thus creating knots and sometimes kino pockets in sawn timber. In Box-Ironbark, however, epicormic growth following thinning is very uncommon.

2.3 ENVIRONMENTAL ISSUES The following section draws on research findings (which are relatively limited) and observations to review the environmental impacts and benefits of thinning.

2.3.1 Observations and research findings Soils It is known that soil compaction varies with soil moisture, number of machinery passes and slash cover. In Ash thinning, soil compaction on tracks and outrows covered with slash generally remained within the limits considered to be desirable for root development (Roberts and McCormack 1991). In Box-Ironbark areas, however, the soils are naturally heavy and difficult to compact, especially with the light machinery used in thinning.

Thinning of Box-Ironbark Forests 9

Water Hydrological studies undertaken in Ash and mixed eucalypt water catchments have consistently shown that moderate thinning increases stream flow, although this may not apply in Box- Ironbark areas due to the generally low rainfall.

Flora Thinning may result in crushing of some of the understorey but in the relatively sparse understorey in Box-Ironbark forests this is unlikely to be a significant issue, except where threatened species occur. In this case, thinning is unlikely to be scheduled.

Fauna There are few studies on the impact of thinning on fauna in Box-Ironbark forests. However, significant numbers of habitat trees must be retained in all harvested areas (see prescriptions – Section 2.3.1) so hollow-dependent species such as possums and parrots, would generally not be negatively affected.

Coarse woody debris (CWD) lying on the forest floor is habitat and food for various ground and soil-dwelling animals. Prescriptions, see next Section, for the retention of CWD must be followed.

2.3.2 Operational implications Habitat retention Like any timber harvesting operation, thinning operations must follow the Code of Practices for Timber Production (DSE 2007a) and the relevant environmental guidelines and prescriptions in the relevant Forest Management Area (FMA). The Bendigo FMA Prescriptions to maintain habitat in timber harvesting areas are:

1. Permanently retain: 1.1 All trees with visible stem or branch hollows (both standing dead and living) greater than 20 cm DBHOB (diameter at breast height (1.3 metres) over bark), where safe and practicable to do so. These trees may count towards retention requirements under prescriptions 1.2 and 1.3. 1.2 At least 10 living trees per hectare between 30 and 39.9 cm DBHOB. 1.3 Where they exist: 1.3.1 two trees per hectare between 40 cm and 49.9 cm DBHOB inclusive. 1.3.2 two trees per hectare between 50 and 59.9 cm DBHOB inclusive. 1.4 All trees greater than 60 cm DBHOB in sawlog harvesting operations and greater than 40 cm DBHOB in non-sawlog operations and sawlog harvesting operations in Special Management Zones. 1.5 All standing dead trees greater than 40 cm DBHOB. 1.6 All living Yellow Box, Fryers Range Scent-bark and Bealiba Ironbark trees. These trees may count towards retention requirements under prescriptions 1.2 and 1.3. A whole of coupe approach should be adopted (numbers averaged over coupe area) to ensure that the best habitat trees are retained, including where these occur in groups. 2. Retention of : 2.1 Firewood harvesting within a Special Management Zone must be managed to ensure coarse woody debris levels are not reduced below pre-harvest levels. 2.2 All log sections larger than 40 cm diameter with hollows larger than 10 cm diameter must be retained. Note: the above prescriptions apply to all harvesting operations, not just thinning.

10 Native Forest Silviculture Guideline No. 15

In addition to this, the potential for any significant detrimental effects on the environment may be minimised by adopting other measures such as retention of non-eucalypt trees; limiting soil compaction; or controlling weeds.

Retention of non-eucalypt trees Acacia species (Wattles) are an important food and shelter resource for many native animals and their removal should be minimised. Other non-eucalypt tree species should be retained for biodiversity reasons and given the open nature of the forest, this is easy to implement. In Box- Ironbark forests, such trees and larger shrubs include Exocarpos cupressiformis (Cherry Ballart), Callistemon spp (Bottlebrushes) and Cassinia arcuata (Drooping Cassinia).

Limiting soil compaction Low ground pressure machinery should be employed and slash (branches and bark) should be retained on tracks where possible to help minimise soil compaction.

Controlling weeds If problem weed species are present where thinning is planned, control treatment prior to thinning is recommended to reduce the chances of the thinning machinery spreading these weeds elsewhere. The Management Procedures for Timber Harvesting and Associated Activities in State Forests (DSE 2007b) in relation to forest hygiene must be followed.

3. COMMERCIAL THINNING

Commercial thinning, usually described as ‘Thinning from Below’, is the harvesting of the smaller merchantable trees in the stand to produce firewood, fence posts or small sawlogs.

3.1 ECONOMICS Productivity of hand-felling by DSE crews is about 1.2-1.5 ha/person/day, yielding about 20 m3/ha. With an excavator-based feller-buncher, productivity would be about 1.5-3 ha/day depending on tree density and terrain. The context of the following section is mainly mechanised harvesting, although machine falling is not currently used in the Box-Ironbark forests.

The economic viability of a commercial thinning operation is affected by:

• Tree size/stand yield. The larger the tree/log size, the higher the productivity. If average removed tree volume is less than 0.05 m3, thinning costs per cubic metre rise rapidly. The minimum box-ironbark thinning yield is about 10 m3/ha. • Site factors. Ground obstacles, such as rock and logs, dense understorey and steeper slopes will slow the operation but in box-ironbark these factors are relatively uncommon. • Skill levels of operators. Skilled and experienced operators will produce more timber per day and will cause less damage to retained trees. • Machinery type. The type and cost of the harvesting equipment will clearly affect the economic viability. Currently farm-type tractors and small trucks are used for snigging loading and cartage. While a fully mechanised operation will produce more wood per day, the high purchase and operating costs might be difficult to justify. • Coupe size and location. Generally, a minimum coupe size of 10 ha is needed for an economically viable operation. Thinning of Box-Ironbark Forests 11

3.2 PLANNING Planning for sustainable thinning operations is a task that includes:

• consideration of any thinning strategy in the relevant Forest Management Plan; • identification of the stands suitable for the type of thinning proposed; • taking into account any planning constraints; and • data collection before, during, and after the thinning operation.

These factors, which are considered in more detail below have been mainly developed for commercial thinning operations in East Gippsland (Sebire 2002).

3.2.1 Developing a strategy Where there is no documented thinning strategy, some matters to consider in developing a strategy include:

• Thinning may be concentrated on older or younger stands depending on matters such as regional forest age structure and markets for particular products. • Where the area available for timber production is decreased for any reason, thinning to promote sawlog growth may assist in minimising the impacts. • The earlier the age of thinning, the earlier will be the growth response. This would be an advantage where a shorter rotation is desired to grow trees of a given size.

3.2.2 Identification of areas available and suitable for thinning A pre-thinning assessment of each stand proposed for thinning should be carried out in order to ensure that:

• the stand meets the criteria for thinning suitability – see Table 3; • stands with better growth potential can be identified and prioritised; and • the need for any specific prescriptions can be identified.

Recommended assessment procedures are given in Appendix 1. Criteria that describe stands suitable for commercial thinning are given in Table 3.

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Table 3. Suitability of Box-Ironbark stands for commercial thinning (includes thinning for firewood)

Criterion Preferred Requirement Reason(s) 1. Slope Generally <100O For ease and safety of thinning and product removal operations, and to help minimise tree damage. 2. Basal area Generally more than 12 m2/ha To allow an economic volume yield from the operation 3. Tree size & Most trees to be removed to be To improve the economics of the volume/ha at least 0.05 m3. Minimum operation. Firewood is defined as volume of thinnings for firewood material not suitable as logs down to a to be not less than 10 m3/ha; for small end DUB of 10 cm. BIB sawlog Class 2 to be not less than 2 m3/ha 4. Height to first Average not less than 5 m on To ensure a good, clear log length as green branch dominant & co-dominant trees. thinning may encourage branch retention. 5. Area Minimum of 10 ha To improve the economics of the operation. 6. Overwood4 Generally less than 6 m2/ha To ensure maximum response from basal area thinning.

3.2.3 Constraints that may affect planning and scheduling of operations Certain constraints influence the selection of coupes for thinning and the scheduling of those coupes. These include:

ƒ Coupe planning and approval processes. All the same issues have to be covered as for any other harvesting operation. All coupes need to be included in the Wood Utilisation Planning process and must follow the relevant Departmental guidelines. ƒ Flora and fauna conservation. There may be areas of the General Management Zone where special conditions should apply to protect certain flora and fauna species. ƒ Seasonal conditions. Normally seasonal weather conditions are not a constraint in Box- Ironbark, but very wet conditions may bring operations to a temporary halt. ƒ Markets/economics. Some types of logs produced in thinning may be unacceptable for some markets and this will limit the ability to schedule those areas.

3.3 COMMERCIAL THINNING EQUIPMENT Currently, a typical thinning operation involves hand-falling using chainsaws and agricultural- type tractors used to snig the logs.

Mechanical harvesters with felling heads are currently not used in the Box-Ironbark regrowth, but could be an option in the future. See also Section 3.1.

4 All trees >60 cm dbhob, all other habitat trees and current sawlog trees. Thinning of Box-Ironbark Forests 13

3.4 COMMERCIAL THINNING SPECIFICATIONS & MONITORING

3.4.1 Basal area and stocking

Up to 60% of the live basal area (BA) may be removed provided that the total retained average basal area does not fall below 8 m2/ha (regrowth and overwood/retained habitat included).

In the case of salvage operations, which normally involve heavier cutting, the retained basal area may be as low as 4 m2/ha but the operation may be better termed ‘clear-felling’ or ‘seed tree’ if the retained BA is lower than this level.

Stocking (retained trees/ha) of thinned stands will vary widely, depending on the average tree size. Removal of up to 60% of BA will usually mean that 70-80% of trees will have been removed, as generally the smaller stems are removed and the larger ones are left.

The relevant pre- and post-thinning BA must be recorded on the Forest Coupe Plan.

3.4.2 Tree retention In Box-Ironbark type forests, the normal thinning method is ‘uniform’ thinning, rather than the ‘outrow-bay’ method (see Glossary). Unlike outrow-bay operations, uniform thinning allows retention of all potential crop trees because the spacing between trees is greater (see Figure 3).

Selection of trees to remove or leave must consider the following matters:

• crop tree retention – in ‘thinning from below’, all dominants and most co-dominants must be retained, unless a Forest Officer directs otherwise, on the basis of defect/form. Intermediate class trees may be retained to fill gaps if needed. ‘Crop’ trees are those that contain, or are likely in the future to contain, merchantable timber. • habitat value – trees with hollows or other features that makes them suitable for wildlife should be retained5, according to the prescriptions listed in Section 2.3.2 (at least in the Bendigo FMA) or in DSE (2007b). • spacing – all dominant trees with sawlog potential should be retained even if they appear to be too close together, unless directed otherwise by a Forest Officer. • species mixture – where more than one eucalypt species occurs on the coupe to be thinned, the retained trees must reflect a similar proportion to the initial composition. • damaged trees - potential final crop trees damaged in thinning operations should not be removed. A dominant with a butt injury will still yield more timber than an undamaged smaller tree.

3.4.3 Damage to retained trees During thinning operations, damage to retained trees may be caused if trees being felled or processed hit retained trees. Damage can also be caused by machinery contacting trees. Damage must be minimised as exposed wood allows the invasion of decay-causing fungi, thus downgrading future log quality and future tree health.

5 Many old trees which have abundant hollows may drop branches. In the interests of safety, public collection of firewood on the ground near such trees should be avoided.

14 Native Forest Silviculture Guideline No. 15

Damage inflicted (by the current operation) must be restricted to no more than an average of 10 % of retained 'crop' trees. Damage is defined as – (i) breakage or splitting of the bark-wood bond, of more than 100 cm2, on the main bole, whether bark is removed (‘open’ wound) or not (‘closed’ wound) (ii) breakage or removal of greater than 30 percent of the original crown.

Damage is assessed during the post-thinning check, as described in Appendix 2.

3.4.4 Utilisation In State forests, operators must comply with relevant sections of the Timber Harvesting Operators Procedures (DSE 2008b) and the Management Procedures - Section 1.3 (DSE 2007b). Specifically, for thinning:

• stumps heights must not exceed 1/3 of DBHOB for all Box-Ironbark trees; • the Harvesting Team leader must ensure that no felled timber that meets licence specifications remains in the coupe on completion of harvesting; and • all logs are to be debarked "at the stump" or at a landing. If bark is removed at a landing, it must be re-distributed as evenly as practicable over the coupe by the thinning contractor in piles not exceeding 1 m3. This is to maintain the nutrition of the stand and to protect the soil.

Figure 3. Firewood obtained (34 m3/ha) from thinning a Grey Box stand. Walmer State Forest, near Castlemaine. 2004

Thinning of Box-Ironbark Forests 15

3.4.5 Monitoring During thinning, regular post-thinning assessments must be carried out by the supervisor to ensure that the prescriptions in this section are being complied with. Timely collection of data allows the supervisor to provide feedback to crews in relation to thinning intensity, damage incidence and choice of trees to retain.

These assessments (1x BA sweep plot per 3 ha in 9 ha sections) should be carried out progressively as the coupe is thinned, according to the procedures in Appendix 2.

Boundaries of harvested areas must be mapped annually for History following the departmental guideline (see DSE 2006).

3.5 FIRE RISK and FUEL REDUCTION BURNING Thinning will produce a short-term (1-2 years) increase in fire hazard in regrowth stands due to the increase in on-ground slash left after the thinning. After 2-3 years, the fine fuels (leaves and twigs) will have broken down, leaving a reduced ignition hazard (Les Vearing pers. comm.)

In thinned coupes, to minimise serious stem or crown damage to retained trees, fuel reduction burning should be carried out either:

• 2-3 years after thinning (the heads will have broken down by then, thus reducing potential scorch height)6; or • when the regenerating coppice is at least 8 m tall (to escape most scorch).

4. PRE-COMMERCIAL THINNING

Pre-commercial thinning is where the removed trees are not used or sold, the operation being carried out to promote the growth of the retained trees.

4.1 PLANNING

The planning process is similar to that described in Section 3.2 for commercial thinning.

Table 4 gives broad criteria for selection of stands suitable for pre-commercial thinning. If the assessment shows that the stand meets the majority of these criteria, plans may then be drawn up for the thinning treatment. Coppice or seedling regrowth originating from wildfire, regeneration or may be suitable for pre-commercial thinning.

6 This burning will set the coppice back 1-3 years but that will be a secondary consideration as the coppice will re-shoot.

16 Native Forest Silviculture Guideline No. 15

Table 4. Suitability of Box-Ironbark regrowth for pre-commercial thinning

Criterion Preferred Requirement Reason(s) 1. Age Generally 5-20 years Regrowth will be of a suitable size, but not generally of merchantable size. 2. Slope Generally <10O Low-moderate slopes are safer and easier for work crews. 3. Site quality Medium to high site quality. Likelihood of better future growth Regrowth is of good form returns from the thinning. 4. Area Minimum of 10 ha Assists viability of later commercial thinning. Cost per ha rises if area is <10 ha. 5. Overwood Average <4 m2/ha Higher level will suppress regrowth basal area (but may be treated during commercial thinning of regrowth) 6. Stocking 2,000-5,000 stems/ha (will vary with age)

Useful suggestions for work organisation include:

• Use existing tracks to break the area into units of 5-8 ha; • Allow a maximum of 100 m return journey from the access track; • Minimum crew size is 2 and the maximum is 4; • Crews should work in a staggered line; and • Mark trees for retention (at start of operations only, and if crew is inexperienced).

4.2 PRE-COMMERCIAL THINNING METHODS

4.2.1 Stem injection with herbicide Where one or two stems are to be retained on a multi-stemmed stump, stem injection may result in kill of the untreated stem(s) and thus should not be used until research with Box- Ironbark species shows otherwise7.

Where single stems or all stems on a stump are to be treated, injection with herbicide is likely to be the most effective and efficient thinning method. Re-sprouting will be prevented, compared with non-chemical methods and treatment at waist height makes it easier on the operator.

The recommended technique for stem injection is as follows:

• Use a tomahawk or similar tool to make cuts spaced evenly around the trunk at about 13 cm centres at about waist height (Figure 4). The angled cut must go through the bark and well into the sapwood to create a notch to receive the herbicide.

7 A small trial, however, in older coppice of E. bicostata (Blue Gum) and E. obliqua (Messmate) showed that mortality of retained stems was minimal following nick & squirt treatment of with glyphosate (Shurvell 1999) Thinning of Box-Ironbark Forests 17

• Use a ‘spot-gun’ or similar tool to deliver the required amount of herbicide. The Velpar Spot-Gun, which is a single–handed operation, may be used (see Section 5, “Equipment & Materials”). • Use a ‘frog-friendly’ glyphosate product, such as “Roundup Bi-Active” (see Section 5). This herbicide is registered for eucalypt stem injection and is safe for operators to use. The recommended rate is undiluted 1 mL/cut (at 13 cm intervals) - although this may have to be modified for Box and Ironbark eucalypt species.

Figure 4. Stem injection using a tomahawk and a spot-gun. Forrest area, 2001

This technique is most efficient where less than 5,000 stems per hectare are to be removed in young stands with diameters of 4-8 cm.

Injection timing. Although the recommended herbicide (glyphosate) is effective all year round, spring and summer are the best seasons for injection work.

Injection treatment should cease when rain begins to fall, as stem-flow could dilute the chemical. The herbicide should be dyed red to help identify spills, leaks or if an injection pocket has been treated or not.

Note - the frequency of occurrence in BIB of ‘flash-over’ or ‘flash-back’, which is the transfer of herbicide via root grafts from a treated tree to a nearby untreated tree, has been observed for E. polyanthemos (Red Box), but is uncommon.

4.2.2 Chainsaws Small chainsaws can be used to pre-commercially thin stands where mean diameter at breast height over bark (dbhob) of stems to be removed are generally greater than 8 cm, and where

18 Native Forest Silviculture Guideline No. 15 less than 3,000 stems per ha are to be removed (Roberts & McCormack 1986). Chainsaws are recommended where retention of one or two stems on a stump is required.

The productivity of this system, however, is low (about 40% of the stem injection rate) mostly due to the need to create a safe working space at most trees (Fagg and Roberts 1987).

4.2.3 Clearing saws and long-handled chainsaws

Roberts & McCormack (1986) and Incoll (1978) investigated the use of clearing saws (brush- cutters) for ash regrowth thinning. These saws are designed to allow stems (generally less than 7 cm diameter) to be cut close to the ground while the operator maintains an upright posture. The long drive shaft allows the operator considerable reach and keeps the rotating blade at a safe distance.

Long-handled chainsaws, as used by , have been used for thinning coppice. Trials showed that they were more effective than clearing saws (Ron Hateley, University of Melb. pers. comm.).

4.2.4 Axes Axes can be effective tools for pre-commercial thinning. The blade can be used to cut off the unwanted stems or the back of the axe can be used to knock unwanted stems off the coppicing stump.

Most stems need to be less than 5 cm dbhob for axes to be most effective. Like chainsaws and clearing saws, axe users need to be aware of the safety risks involved and take precautions to prevent any injuries.

4.3 PRE-COMMERCIAL THINNING SPECIFICATIONS In stands that meet the criteria (see Table 4), Table 5 should be used as a guide for PCT in Box-Ironbark regrowth.

Table 5. Density & spacing specifications for pre-commercial thinning in Box- Ironbark regrowth

Age of regrowth Approx. mean Equivalent average (yrs) retained density of square spacing # future crop trees* (no./ha) 5-8 1100 3.0 m x 3.0 m 9-13 800 3.5 m x 3.5 m 14-20 500 4.5 m x 4.5 m

Notes: * ‘Future crop trees’ are dominant and co-dominant trees with good form. Intermediate-crown trees may be retained to fill gaps where there are no other eucalypts. # Where more than one stem is retained on a coppicing stump, these spacings will not be relevant.

Thinning of Box-Ironbark Forests 19

Selection of trees for retention

Retained trees in PCT operations should have stem and crown characteristics likely to produce sawlogs in future harvests. Factors to consider, in priority order, are:

• Tree form. Straight stems, not forked, with no live branches >20 mm in diameter on the bottom 3 metres of the trunk. • Dominance. Retained trees should include all dominants and a proportion of co- dominants. Sub-dominants (intermediates) should only be retained if there are not enough suitable dominants or co-dominants. • Spacing. This factor comes after form and dominance are considered (see Table 5).

Regular checks must be carried out by the supervisor to ensure that the prescriptions in this section are being complied with. Completed works must be recorded in the Coupe Information System.

4.4 FIRE RISK AND FUEL REDUCTION BURNING Based on observation, it is believed that fire risk is less where trees are left standing (i.e. stem injection operations) because the dry fuel load is not concentrated as occurs in a felling operation. Alternatively, if stems are cut and left on the ground, there will be a short-term increased fire risk associated with increased fuel loads.

In areas thinned by felling, to minimise serious stem or crown damage to retained trees, fuel reduction burning should not be carried out until the retained trees are at least 8 metres tall.

5. ECOLOGICAL THINNING

As explained in Section 1.2.3, ecological thinning (ET) is appropriate in Box-Ironbark forests where the main objective is to improve fauna (and understorey flora) habitat rather than future timber production. Suitable areas for treatment would include conservation reserves as well as overstocked State forest areas of lower site quality.

Although ET will usually produce wood which may have value as firewood, it may, depending on the fauna that are being encouraged, have more habitat value as ‘coarse woody debris’ left on the forest floor.

5.1 PLANNING Given that ET is currently not widely practised, experience with planning such thinning is relatively limited. However, the choice of compartments or blocks of forest to thin should consider the following issues:

• The species or group of animal (& plant) species being considered for habitat enhancement; • The current condition of the forest and its potential (see Section 5.2); and • The resources (human and financial) available to undertake the ET, which is often slow and costly when stands are dense.

20 Native Forest Silviculture Guideline No. 15

Once this strategic assessment has been completed, a pre-thinning assessment of each stand proposed for ET should be carried out in order to ensure that the stand meets the majority of the criteria (Table 6) for thinning suitability and to decide on the most appropriate thinning technique. Regrowth originating from either wildfire or regeneration after harvesting may be suitable for ET.

Table 6. Suitability of Box-Ironbark regrowth stands for ecological thinning

Criterion Preferred Requirement Reason(s) 1. Age Generally 5-40 years Treatment earlier in the life of the stand will maximise the period of growth response, but it may be preferred to start with trees of some size. 2. Slope Generally <10O Low-moderate slopes are safer and easier for work crews. 3. Site quality Low to moderate Avoids areas of high potential for timber production. 4. Area Minimum of 10 ha If area is <10 ha, cost per ha rises and value for fauna habitat is less. 5. Overwood Preferably 4-8 m2/ha Higher level will suppress regrowth, but some overwood is desirable to provide a more diverse stand structure. 6. Stocking 1,500-6,000 stems/ha (will Very dense stands are expensive to treat. vary with age)

5.2 ECOLOGICAL THINNING METHODS The methods applicable to pre-commercial thinning (see Section 4.3) are also suitable for ecological thinning in stands where tree density is in the range 3,000 - 6,000 per ha.

Where trees are older (greater than 20 years) and thus larger, falling with chainsaws is effective (see Figure 5).

Where herbicides are used to prevent stumps re-sprouting, care needs to be taken so that ‘flash-back’ is avoided. Herbicides such as glyphosate should only be sprayed or brushed on to cut stumps which do not also support a live stem.

Stem injection could be used provided that trials (still to be set up at time of writing) show minimal impact on retained stems where other stems on the same stump are injected. Experience to date indicates that root-to-root contact results in very little ‘flash-back’ (P. Pigott, Parks Victoria, pers. comm.).

Thinning of Box-Ironbark Forests 21

Figure 5. Ecological thinning trial conducted by Parks Victoria. This plot, at Pilchers Bridge (south of Bendigo) was thinned by hand in 2005 (50% basal area reduction with retention of an unthinned patch) with debris retained. 2008

Mechanised methods of thinning using ‘felling heads’ attached to excavator-type machines potentially offer much faster and safer means to thin larger areas of regrowth. The downside of using this method is that a more informed choice of trees to be removed or to retain is more difficult, and that such machines, to get access to the stand, might have to fell some trees that would normally be retained.

5.3 ECOLOGICAL THINNING SPECIFICATIONS As with both commercial and pre-commercial thinning, ‘thinning from below’ (in which the larger trees are retained and the smaller ones are removed) is the appropriate silvicultural method, given that the aim is to increase the proportion of bigger trees in the stand.

The suggested density of retained eucalypt trees in Table 7 reflects this aim. This Table will need to be refined after the results of the current trials are fully evaluated. The densities are less than those used in thinning for timber production (see Table 5).

Table 7. Suggested tree retention density in ecological thinning in Box-Ironbark type forests

Age of Approx. mean density of retained trees regrowth (yrs) 5-13 Retain 700 stems/ha 14 - 30 Retain 400 stems/ha >30 Retain BA minimum of 6 m2/ha (remove up to 70% of pre-thinning BA)

22 Native Forest Silviculture Guideline No. 15

If a 20-yr old stand is thinned to 400 retained stems/ha, it would be expected that the density would naturally decrease over time, so that at about age 80 yrs it could be about 150/ha. However, a second thinning (at 20-25 yrs after the first thinning) could be carried out to give a further boost to tree growth.

In ecological thinning, there will be increased requirements:

• to keep all larger trees regardless of their form, live or dead; • retain all hollow-bearing trees; • to avoid damage to understorey elements; and • to retain trees containing mistletoes8.

5.4 FIRE RISK and FUEL REDUCTION BURNING As with commercial and pre-commercial thinning, the fire hazard within the treated area will increase in the short term due to an increase in the amount of fine, elevated fuel on site. However, this hazard will reduce within 2-3 years.

Where cut trees are left lying on the ground for habitat value, ecological thinning will result in treated stands carrying a higher fire risk than where the timber was removed. This risk will also last longer. This may mean that fire protection measures (e.g. fuel reduction burning, firebreaks) need to be increased. However, given that timber production is not important in ET stands, some damage caused by fuel reduction burning is probably not of great concern.

Where a fire does occur, fire suppression activities, especially first-attack, may be more difficult due to access problems caused by the felled material on the ground.

However, if the thinning was carried out by stem injection (compared with felling), the fire risk would be lower because the fuel is not concentrated on the ground and access problems when occurred would be minimal.

6. EQUIPMENT AND MATERIALS

Name/description Potential suppliers Approx. cost (as at Oct 2008) Injector E E Muir & Sons Pty Ltd $137 + GST (Govt) Velpar Spot Gun & 5 L back- 542 Footscray Rd $156 + GST (Retail) pack Footscray. Vic. 3011 (03) 9687 6836 Herbicide: E E Muir & Sons Pty Ltd $343 +GST glyphosate (preferably as (as above) per 20 L drum (Govt) ‘Roundup Bi-active’) or IAMA Pty Ltd $370 +GST 29 Beverage Drive, per 20 L drum (Retail) Tullamarine. Vic. 3043 03) 9335 1911

8 Note that trees with heavy mistletoe infestation may die (see Fagg 1997) so some judgement is needed on tree selection where mistletoe is prevalent.

Thinning of Box-Ironbark Forests 23

7. REFERENCES

Brown, G. (1997) Growth responses to thinning in eucalypt regrowth forests. Tasforests 9:105-122.

DSE (2006a) Logging History Data Capture Guidelines. Department of Sustainability and Environment, Victoria.

DSE (2006b) Sustainability Charter for Victoria’s State forests. Department of Sustainability and Environment, Victoria.

DSE (2007a) Code of Practices for Timber Production. Department of Sustainability and Environment, Victoria.

DSE (2007b) Management Procedures for Timber Harvesting Operations and Associated Activities in State Forests in Victoria. Department of Sustainability and Environment, Victoria.

DSE (2008a) Forest Management Plan, Bendigo Forest Management Area. Department of Sustainability and Environment, Victoria.

DSE (2008b) Timber Harvesting Operators’ Procedures. Natural Resources Division, Department of Sustainability and Environment, Victoria.

DSE (2008c) Thinning in State Forests. Policy Statement Department of Sustainability and Environment, Victoria.

ECC (2001) Box-Ironbark Forests and Woodlands Investigation. Final Report. Environment Conservation Council, East Melbourne.

Fagg, P.C. and Roberts. E.R. (1987) Non-commercial thinning using herbicide injection. Thinning Systems Report No.3, the Young Eucalypt Program, CSIRO, Canberra.

Fagg, P. C. (1997) Mistletoe in forest management in Victoria. Victorian Naturalist 114(3):112-115.

Incoll, W.D. (1978) Productivity of alternate methods of non-commercial thinning. Research Branch Report No. 108, Forests Commission Victoria, Melbourne (unpubl.)

Kellas, J.D. (1991) Management of the dry sclerophyll forests in Victoria 2. Box-Ironbark Forests. Chap.9 in Forest Management in Australia, Eds, McKinnell, Hopkins & Fox, Surrey Beatty & Sons Pty Ltd, Chipping Norton, NSW.

Kellas, J. D., Owen, J.V. and Squire, R.O. (1982) Response of Eucalyptus sideroxylon to release from competition in an irregular stand. Forestry Technical Notes 29:33-36, Forests Commission Victoria.

Kerruish, C.M. and Rawlins, W.H.M. (Eds) (1991) The Young Eucalypt Report: some management options for Australia’s regrowth forests. CSIRO, Melbourne.

Murphy, S. and Forrester, D. (2008) Growth responses to thinning in Red Ironbark. Forest Research Report, School of Forest and Science, University of Melbourne (in prep.).

Newman, L.A. (1961) The Box-Ironbark Forests of Victoria, Australia. Bulletin No.14, Forests Commission of Victoria, Melbourne.

NRE (1998) Box-Ironbark Assessment Project (Bendigo Forest Management Area and Pyrenees Ranges). Forests Service Technical Report 98-3. Department of Natural Resources and Environment, Melbourne.

Perrin, G.S. (1891) Report of the Conservator of State forests. In 1981 Annual Report of the Secretary of Mines. Parliamentary Papers, Govt Printer, Melbourne, pp.19-25.

24 Native Forest Silviculture Guideline No. 15

Roberts, E. and McCormack, R. (1986) Non-commercial thinning using clearing saws. Thinning Systems Report No.2, the Young Eucalypt Program, CSIRO, Canberra.

Roberts, E. R. and McCormack, R. J.(1991) Thinning Technologies. In The Young Eucalypt Report, Chapter 4, Eds. Kerruish, C.M. & Rawlins, W.H.M. CSIRO, Melbourne.

Sebire, I. D. and Fagg, P. C. (1997) Thinning of Mixed Species Regrowth. Native Forest Silviculture Guideline No. 14, Forests Service, Department of Natural Resources and Environment, Melbourne.

Sebire, I. D. (2002) Planning for commercial thinning operations. In Proc. of the State-wide Thinning Workshop, Colac, Dec. 2002, Forestry Victoria, Department of Sustainability and Environment, Melbourne.

Shurvell, I. (1999) Thinning coppice by herbicide injection. Silviculture News 10:2-4, Commercial Forestry Branch, Department of Natural Resources and Environment, Melbourne.

Vearing, L. (2002) Report on thinning in the Bendigo FMA. Statewide Thinning Workshop, Colac 2002, Department of Sustainability and Environment, Melbourne.

Webb, A. W. F, (1966) The effect of thinning mountain ash in Victoria. M.Sc. (For.) Thesis. University of Melbourne.

White, D.A. and Kile, G.A. (1991) Thinning damage and defect in regrowth eucalypts. In The Young Eucalypt Report, Chap.6, eds. Kerruish, C.M. & Rawlins, W.H.M., CSIRO, Melbourne. Thinning of Box-Ironbark Forests 25

ACKNOWLEDGEMENTS

The following DSE staff are thanked for contributing their experience and knowledge to improve various drafts of this Guideline:

Jim Allen Kendra Dean Stephen Deed Merv Flett John Hosking Tuesday Phelan

Maps/Photos: Figure 1 (Kate Shanahan), Figures 2 & 4 (Peter Fagg), Figure 3 (John Hosking), Figure 5 (Simon Denby)

26 Native Forest Silviculture Guideline No. 15

GLOSSARY basal area – the sum of the cross-sectional area measured at breast height of the trees in a given stand, usually expressed as square metres per hectare (m2/ha). breast height – 1.3 m above upper ground level; the height at which a tree is measured for diameter and basal area. callus – new, undifferentiated tissue produced at wound margins. Later develops into new wood which grows to cover (occlude) the wound. cambium – thin layer of tissue in tree trunk between the bark and the sapwood from which the new bark and new sapwood are formed. closure – the stage in the life of a stand when the tree crowns (canopy) touch each other. competition – the relative growth of trees (stem and canopy) as a consequence of the limited availability of water, nutrients and light. coupe – an area of forest of variable size, shape and orientation, from which timber is harvested. crop tree – tree that is selected for retention during a thinning operation. crown class – description of the relative position and condition of a tree crown.

dominant – a tree with crowns extending above the general level of the canopy; larger than the average tree in the stand, with a well-developed crown.

co-dominant – tree with a crown forming at the general level of the canopy, with a medium-sized crown.

intermediate – a tree shorter than dominant or co-dominant trees, with small crowns extending into the canopy.

suppressed – a tree with a crown entirely below the general level of the canopy. dbh(ob) – diameter of a tree at breast height (over bark). debarking – the removal of bark from a tree or log. defect – (in sawmilling context) that part of the volume of a log that cannot be used due to fungal decay, insect attack, excessive knots, etc. dominant – a tree that dominates others in terms of height and diameter. dominant height – mean height of the dominant or largest trees in a stand. early spacing – see pre-commercial thinning. epicormics – shoots arising from dormant buds in the trunk or branch of a woody plant, often following exposure to increased light levels or fire.

Thinning of Box-Ironbark Forests 27 even-aged – a forest or stand of predominantly the one age. extraction track – the track along which logs are removed from the forest to the roadside or landing. feller-buncher – a harvesting machine that fells trees (by shearing or sawing) and then places them into heaps (bunches) on the ground. felling head – a mechanical, hydraulically-operated device attached to the end of an articulated crane, use to fell trees. They may be ‘single tree’ or ‘accumulating’ heads, or ‘fixed’ and ‘floppy’ heads. fixed-grapple loader – an excavator-based machine with two pairs of opposing forks, used for debarking and/or loading at a landing; often termed a ‘crab-grab’. A shearing blade or chainsaw may be incorporated to cross-cut trees. flash-back – the translocation ( via root grafts) of herbicide from the root system of a treated tree or stump to the root system of adjoining untreated trees, leading to injury to the untreated tree(s). form – the taper and general shape of a tree, particularly its trunk. grapple harvester – a harvesting machine with the head capable of felling, debarking and /or delimbing, and cross-cutting. habitat tree – a tree identified and protected from harvesting to provide habitat or future habitat. herbicide – a chemical used to poison plants, including trees. increment – the increase in volume, diameter, height or other measure of individual trees or stands during a given period. Mean annual increment (MAI) – the total increment up to a given age divided by that age. kino – reddish-black coloured phenolic substance found in veins or pockets in wood of some eucalypt species as a response to damage or stress. landing – a place where trees or parts of trees are sorted, processed and/or loaded for transport from the forest. mean annual increment – see increment. outrow & bay method – a methodical thinning practice aimed at minimising damage to retained trees and ensuring access to the whole coupe. The outrows are narrow, parallel tracks cut by the harvesting machinery to obtain access into the stand; the bays are the retained strips between the outrows. overwood – all trees over 60 cm dbhob, all other habitat trees, and current sawlog trees. pre-commercial thinning –- the manual or mechanical thinning of a young dense stand in which the trees removed are not merchantable. Also known as ‘early spacing’. processing – any or all of the operations of debarking, de- or cross-cutting, but not including felling. regrowth –- any trees or forest in which the majority of trees are less than 60 years old.

28 Native Forest Silviculture Guideline No. 15 rotation – the planned number of years between the regeneration of a forest stand and its final harvesting. silviculture – the science and practice of managing harvesting, forest establishment, composition and growth, to achieve specified objectives. site quality – the potential of a site to grow trees/timber, which is a function of soil quality, rainfall and aspect. snigging – the towing or winching of a log by a tractor/bulldozer from the stump to a landing. stand – a group of trees in a forest that can be distinguished from other groups on the basis of age, species competition, condition, etc. stem injection – insertion of a herbicide into a cut or notch made in the trunk of a tree in order to stress or kill the tree. stocking – the density of a forest stand, usually expressed in terms of the number of trees per hectare, basal area, or percentage of plots with established seedlings. thinning – the removal of part of a forest stand or crop, with the aims of increasing the growth rate and/or health of retained trees, and in commercial harvesting, obtaining timber from trees that would otherwise eventually die before final harvest. wind-throw – blowing down of a tree or trees by strong winds. Thinning of Box-Ironbark Forests 29

Appendix 1

PRE-THINNING STAND ASSESSMENT PROCEDURES – Commercial Thinning (where timber is to be sold)

1. INTRODUCTION A pre-thinning assessment of each stand/coupe proposed for commercial thinning must be carried out prior to the preparation of the Wood Utilisation Plan:

(i) so that stands which are selected for thinning meet the criteria (see Table 3) and to assist in prioritising stands for thinning; (ii) because the prescribed thinning intensity is based on the unthinned basal area; and (iii) to estimate merchantable volume (where needed).

2. OFFICE PLANNING – potential coupe identification 2.1 From maps of previous stand treatments, and ground knowledge, identify all potential stands for thinning.

2.2 Mark the areas considered potentially suitable for thinning on a map, ready for ground assessment, including year of last harvest if known.

3. FIELD ASSESSMENT The field procedure is easier with two people in the assessment team.

3.1 Equipment needed • stand map (preferably approx. 1:15,000) • hip chain & cotton (optional) • compass or GPS unit • pencil and recording sheets (copy the blank sheet attached, or download from DSE intranet) • basal area string gauge or prism (1 or 2 factor) • diameter tape • clinometer • 30 m tape • coloured tape

3.2 Number, size and location of plots (i) Variable Probability Sampling plots are recommended. These are plots defined by a basal area gauge for estimating basal area and volume. (ii) Plot density should be not less than 1 plot per 3 ha. This is equivalent to a square plot grid of about 170 m x 170 m.

30 Native Forest Silviculture Guideline No. 15

(iii) In the office, systematically, from a random start, locate the required number of plots over the area and mark them on the stand map. Calculate the on-ground distances and bearings between the plots, and from a known point (e.g. track junction) to the nearest plot. A GPS unit may be used where available.

3.3 Recording (i) Traverse to the plot centre using pacing and compass or GPS. Mark the plot centre. (ii) Record the relevant stand and assessment information at the top of the sheet (see attached example). Check site quality estimation, based on adjacent mature stand or overwood. (iii) Record the following information for each plot:

• On a full 360 degree sweep with BA gauge, estimate dbhob class of each tree counted “in”, by species and crown class. Use the diameter tape occasionally to help get your estimations correct; • estimate merchantable height/length (to 10 cm DSE) of trees that would be removed (use 15 cm DSE for residual or class 2 sawlogs if RL only operation); • ht (m) to first green branch on one typical co-dominant tree that would be retained (i.e. clear bole height); • maximum slope; • comments on any significant defect/hollows in the tree(s); and • note any significant variation between plots.

4. FOLLOW-UP OFFICE WORK

4.1 Estimate of timber volume that could be harvested

For each plot, use the formula (only for trees to be removed):

Volume (m3/ha) = average merchantable length (m) x BA/ha x factor (0.6)

For maximum BA removal guidelines - see Section 3.5.1

4.1 Determination of suitability of stand for thinning

If the average of all plots in a particular stand meets all the necessary criteria (see Table 3, p.12), the stand is suitable and may be scheduled for thinning.

It is possible that the average of only some of the plots meet all the criteria. In this case, part of the stand (if large enough to make harvesting economically viable) could be thinned.

See next pages for Recording Sheet and Example. Thinning of Box-Ironbark Forests 31

DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT Pre-Thinning Stand Assessment Field sheet

FMA/Block: Est age: Assessors: Compt/Stand: Plot type: Date: Stand area: Page: of

Plot no. Plot no. Plot no. Max. slope Max. slope Max. slope BA BA BA Clean bole ht Clean bole ht Clean bole ht Sp Dbhob Merch Sp Dbhob Merch Sp Dbhob Merch Class* Length# Class* Length# Class* Length# (m) (m) (m)

Mean Mean Mean

Comments Comments Comments

• * DBHOB classes (suggested) : 10-19, 20-29, 30-39, 40-49, 50-59, 60+ cm • # Merchantable lengths of trees that would be removed.

32 Native Forest Silviculture Guideline No. 15

EXAMPLE DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT Pre-thinning Stand Assessment Field Sheet

FMA/Block: Est age: 35 yrs Assessors: AB/CD Compt/Stand: Plot type: BA sweep with 1 Date: 22/2/2009 factor Stand area: 24 ha Page: 2 of 2

Plot no. 4 Plot no. 5 Plot no. 6 Max. slope 3 deg Max. slope Max. slope BA 15 m2 BA BA Clean bole ht 6 m Clean bole ht Clean bole ht Sp Dbhob Merch Sp Dbhob Merch Sp Dbhob Merch Class* Length# Class* Length# class Length# (m) (m) (m) RIB 13 2 “ 29 “ 16 3 “ 19 3 “ 22 3 “ 32 “ 28 “ 20 2 GB 29 GB 34 RIB 17 2 “ 23 “ 27 “ 31 “ 16 2

Mean 2.4 Mean Mean

Comments Comments Comments Potential thinning volume: 2.4 x 7 x 0.6 = 10.1 m3/ha

• DBHOB classes (suggested) : 10-19, 20-29, 30-39, 40-49, 50-59, 60+ cm • # Merchantable lengths of trees that would be removed. Thinning of Box-Ironbark Forests 33

APPENDIX 2

POST-THINNING STAND ASSESSMENT PROCEDURES – Commercial Thinning

1. INTRODUCTION Regular sample assessment of stocking and damage is required to ensure that the thinning operation follows this Guideline and the Management Procedures (DSE 2007b).

Assessments should be carried out, in stages, as soon as practicable after an area of 9-10 ha has been thinned – to enable timely (possibly corrective) feedback to the thinning team.

The assessment method described assumes that uniform thinning (rather than the outrow/bay method) has been used. ‘Plots’ are delineated with a BA gauge at a rate of 1 plot for every 3 hectares thinned, with 3 plots (9 ha) assessed in a group as the thinning progresses.

2. EXPLANATORY NOTES ON PRESCRIPTIONS

2.1 Basal area & stocking (i) The BA is determined as an average based on the assessment procedure outlined below. There will be spots where higher and lower basal areas will occur: a maximum of ± 20% variation around the average would be acceptable. (ii) Note that the retained BA is based on all standing live trees above 10 cm dbhob regardless of crown class because the initial BA includes all such trees.

2.2 Damage (i) The maximum damage limit (10% of retained trees) is an average over 9 ha (3 plots), based on the assessment procedure below. (ii) All retained trees must be assessed for damage, including trees of 'intermediate' crown class if they have been retained to fill gaps. (iii) Damage which cannot be attributed to the current thinning operation is noted, but not included in the calculation of damage %.

3. ASSESSMENT PROCEDURE The procedure is designed so it can be done by one person. Two people could, however, make the job quicker.

3.1 Equipment needed • recording sheets (see p. 35) and pen/pencil • coloured marking tape • BA gauge (1 factor) • coupe map at approximately 1:6,000 scale

34 Native Forest Silviculture Guideline No. 15

3.2 Plot location and delineation (i) Progressively establish BA sweep plots evenly at the rate of 3 plots every 9 ha of thinned area, without bias as to thinning and stand variations. This plot density is equivalent to a plot (square) spacing of about 170 m. (ii) Mark the plot number on plastic tape and tie it to a nearby plant/stem, for re-location later if needed. Mark the plot locations on the coupe map.

3.3 Recording and plot assessment Record assessment information at the top of the assessment sheet. Fill in the data as required for each plot, as follows:

(i) Basal area. With the gauge, count and record all live trees above 10 cm dbhob, by species. Record dbhob class as per pre-thinning. (ii) Damage. For each tree counted “in”, check all sides of the bole and crown for damage, particularly in the section to 3 m above ground level. Tick the box if a tree is damaged (bole or crown) in the current operation (see definition of “damage” below). For pre- thinning damage, write “old'.

Damage is defined as – • breakage or splitting of the bark-wood bond, of more than 100 cm2, on the main bole, whether bark is removed (‘open’ wound) or not (‘closed’ wound) • breakage or removal of >30% of the original crown.

(iii) Crop tree retention & stump heights. By examination of stumps, check adherence to prescriptions relating to thinning from below, retention of crop trees, species mixture, and stump heights. (iv) Note any issues between plots.

4. FOLLOW-UP ACTION 4.1 Feedback to Thinning Team Leader. As soon as practicable after each group of 3 plots (9 ha) have been assessed, advise the supervisor or Team Leader of the results, giving advice if necessary, on how the operations should be modified in relation to trees taken/not taken, damage, etc. 4.2 Recording. File the recording sheets with the Coupe Plan and update the Coupe Information System (CIS). See next pages for Recording Sheet and Example. Thinning of Box-Ironbark Forests 35

DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT Post-thinning Stand Assessment Field Sheet

Coupe name & address: Period of thinning: Product:

Year & origin of stand: Machinery:

Slope/terrain: Operators:

Pre-thinning BA: Assessor(s):

Plot No. Date: Plot No. Date: Plot No. Date: Damage DBH Damage DBH Damage DBH Crown Crown Crown Species class Species class Species class Class bole crown (cm) Class bole crown (cm) Class bole crown (cm)

Total retained BA 2 2 2 Total retained BA (m /ha) Total retained BA (m /ha) (m /ha)

Damaged trees % Damaged trees % Damaged trees %

(x/n x 100) (x/n x 100) (x/n x 100)

Average of 3 plots (9 ha) 2 2 BA (m /ha) >8 m /ha Damage (%) <10% [prescribed limits in shaded boxes] Comment:

Action taken( if required):

36 Native Forest Silviculture Guideline No. 15

EXAMPLE DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT Post-thinning Stand Assessment Field Sheet

Coupe name & address: Period of thinning: Oct-Dec 2008 Allen Rd, Wellsford SF Product: domestic firewood

Year & origin of stand: Sawlogs cut 1980 Machinery: chainsaws

Slope/terrain: <5 deg Operators: Bendigo DSE (Leader- Bill Smith)

Pre-thinning BA: 18 m2/ha Assessor(s): JA/PB

Plot No. 4 Date: 20/10/08 Plot No. 5 Date: 20/10/08 Plot No. 6 Date: 20/10/08

Damage DBH Damage DBH Damage DBH Crown Crown Crown Species class Species class Species Class Class Class Class bole crown (cm) bole crown (cm) bole crown (cm)

RIB cd YG cd x RIB cd “ d “ cd GB d GB cd x RIB d “ i “ i “ i “ cd “ d YG i RB i RB i GB cd YG cd old “ cd “ d “ cd RIB d RB i GB d “ cd YG cd GB d

Total retained BA 2 Total retained BA 2 9 Total retained BA (m /ha) 8 2 10 (m /ha) (m /ha)

Damaged trees % 11.1 Damaged trees % Damaged trees % 12.5 nil (x/n x 100) (x/n x 100) (x/n x 100)

Average of 3 plots (9 ha) 2 2 [prescribed limits in shaded boxes] BA (m /ha) 9.0 >8 m /ha Damage (%) 7.9 <10%

Comment: Average retained BA (9 m2/ha) is good, and damage is no more than 10%. Species mix OK; stump heights occasionally too high. Action taken( if required): JA advised Bill of good results on 24/10.