Carl von Ossietzky University Oldenburg Department of Biology and Environmental Sciences “Diplomstudiengang Landschaftsökologie”
Diploma thesis:
RIPARIAN MANAGEMENT IN TARANAKI – A SUCCESS FOR NATIVE BIODIVERSITY?
By: Susanne Krejcek
First supervisor: Prof. Dr. Rainer Buchwald
Second supervisor: Dr. Julia Stahl
Oldenburg, March 2009
Diploma thesis
DECLARATION
I hereby declare that this thesis is my own work and that to the best of my knowledge and belief, it neither contains material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma of the university or other institutes of higher learning, except where due to acknowledgement it has been made clear in the text.
Date: 15th of March, 2009
Signature: Susanne Krejcek
Riparian management in Taranaki – A success for native biodiversity?
ACKNOWLEDGEMENTS
First of all I want to thank my family; especially my parents to whom I dedicate my thesis. My studies of Landscape Ecology and my thesis with its research based in New Zealand were only possible with your constant emotional and financial support.
I am especially grateful for the excellent supervision and support I received during my fieldwork and the process of writing my thesis from my supervisors Prof. Dr. Rainer Buchwald and Dr. Julia Stahl. I really appreciate the open ear both of you always had for my questions and the valuable comments you made and the discussions we had.
Furthermore, I am especially thankful for the employment at the Taranaki Regional council. I owe many thanks to Don Shearman who was my first contact at the Taranaki Regional Council and who later did an excellent job as my supervisor in New Zealand, for having an open ear to my questions and contributing to my knowledge about riparian margins in New Zealand. I also thank Basil Chamberlain who accepted my research proposal and thus employed me. Special thanks are directed to Shay Dean, who worked closely together with me on the realization of the research project. Thereby, I am especially thankful for her advice and help with field site choice, the provision of farmer consents, and for introducing me to New Zealand’s beautiful flora and fauna, as well as her assistance in the field. Furthermore, I thank Barbara Hammonds, who assisted in the field and shared her passion for botany and her botanical knowledge with me. I further want to thank Jane Bowden, Stephen Ellis, Chris Fowles, Ray Harris, Fioana Jansma, Chris Lambert, Lisa Mahony, Rosemary Miller, Brent Nicol, Katrina Spencer, Lou Rata, Eileen Pattinson and all other colleagues from the Taranaki Regional Council for their support and the good times I had while working with them. I thank Ines Schönberger from Landcare Research for helping with the identification of some plant species. I thank Victoria Froude for the development of the methodology used for the vegetation and bird surveys. Furthermore, I thank all farmers who are contributing to New Zealand’s native biodiversity with their riparian management and were kindly allowing me access to their property, answered my questions and thus made this study possible.
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I am very grateful for the support of my kiwi-friends while working in New Zealand and the good times we shared.
I owe many special thanks to my friend Nicole Schneider who gave valuable conceptual hints, suggestions and comments on the manuscript and whose emotional support and friendship I very highly value.
Furthermore I thank Vanessa Farley and Alex Ross for correcting my English.
Last, but not least, I thank the DAAD for the scholarship I received for covering my flight costs to New Zealand.
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Riparian management in Taranaki – A success for native biodiversity?
ABSTRACT
Although riparian margins are internationally recognized as areas of high natural biodiversity, they have been widely degraded by land development and urbanization. New Zealand is a typical example thereof. Riparian restoration in New Zealand is mainly aimed for water quality improvements and thus benefits for terrestrial biodiversity have been largely neglected by research approaches in the past. With my study I aimed to investigate the restoration success of managed lowland riparian margins for native terrestrial biodiversity in Taranaki. I therefore compared five different management categories (unfenced, fenced (1-4 years, no plantings), medium aged (4-7 years with plantings), old aged (8-12 years) and as a baseline regenerated field sites (fenced more >20 years)) by mapping vegetation and conducting five minute bird counts. My results have demonstrated the good, succession promoting development of riparian plantings in Taranaki with increases in native plant species richness (i. e. especially ferns and vines), vegetation cover diversity and structural complexity. A further improvement of weed control was identified as a highly recommendable management action with a focus on targeting wandering willie (Tradescantia fluminensis) and blackberry (Rubus fruticosus agg.). Fantails (Rhipidura fuliginosa), waxeyes (Zosterops lateralis) and grey warblers (Gerygone igata) were the only native bird species which profited from riparian management with field site age and were thus positively correlated with the number of tiers above two metres height and the increase in tree and shrub cover. Although riparian margins develop well, not all ecosystem functions seem to be restored, as I did not record any threatened or habitat sensitive plant or bird species. This is possibly due to evident edge-effects caused by too narrow riparian margins. Consequently, allowing for wider riparian margins would be highly recommendable.
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ZUSAMMENFASSUNG
Obwohl Fluss- und Bachauen international als Lebensräume mit natürlich hoher Biodiversität anerkannt sind, wurden sie durch Landentwicklung und Urbanisierung weiträumig modifiziert. Dies ist auch in Neuseeland der Fall, wo anschließende Renaturierungsmaßnahmen hauptsächlich die Verbesserung der Wasserqualität durch Wiederaufforstungsprogramme zum Ziel hatten. Aus diesem Grund sind die Vorteile dieser Programme für die terrestrische Biodiversität wenig bekannt. Mit meiner Studie möchte ich dazu beitragen, diese Lücke zu schließen und habe folglich die Auswirkungen von Taranakis Uferrandstreifen-Renaturierungsprogramm auf die Entwicklung der indigenen Vegetation und Avifauna untersucht. Dazu habe ich fünf verschiedene Untersuchungsgebietskategorien („beweidet“, „ausgezäunt“ (seit 1-4 Jahren), „mittelalt“ (Anpflanzungen sind 4-7 Jahre alt) und „alt“ (Anpflanzungen 8-12 Jahre alt), sowie als Vergleichskategorie natürlich „regenerierte“ Uferrandstreifen (seit mehr als 20 Jahren aus der Beweidung genommen und ausgezäunt)) miteinander verglichen und Vegetationsaufnahmen sowie Vogelkartierungen vorgenommen. Meine Ergebnisse zeigen, dass sich die angepflanzten Arten sowohl gut etabliert haben als auch die Sukzession sich weiter beschleunigt hat. Ein Anstieg des Artenreichtums der Pflanzen, (insbesondere von Farnen und Lianen), sowie Veränderungen bezüglich der Deckungsgrade und der Steigerung der strukturellen Vielfalt konnten nachgewiesen werden. Zudem wurden Brombeeren (Rubus fruticosus agg.) und Wandering Willies (Tradescantia fluminensis) als Problemarten, die weitere Kontrollmaßnahmen benötigen, identifiziert. Die einzigen indigenen Vogelarten, die vom Renaturierungsprogramm mit voranschreitender Sukzession profitierten, waren Fantails (Rhipidura fuliginosa), Waxeyes (Zosterops lateralis) und Grey Warblers (Gerygone igata). Diese Arten waren positiv mit der Anzahl der Vegetationsschichten und der Bewuchsdichte von Bäumen und Sträuchern korreliert. Obwohl sich die Uferrandstreifen gut entwickelt haben, scheinen nicht alle Ökosystemsfunktionen rehabilitiert worden zu sein, da ich weder bedrohte Arten noch Arten mit besonderen Habitatsansprüchen nachweisen konnte. Dies ist vermutlich auf die sichtbaren Randeffekte (nur schmale Uferrandstreifen) zurückzuführen. Dementsprechend ist eine Verbreiterung der Uferrandstreifen für künftige Uferrandstreifen-Renaturierungen sehr empfehlenswert.
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Riparian management in Taranaki – A success for native biodiversity?
CONTENTS
DECLARATION ...... i ACKNOWLEDGEMENTS...... ii ABSTRACT ...... iv ZUSAMMENFASSUNG ...... v LIST OF FIGURES ...... viii
LIST OF TABLES ...... ix LIST OF PLATES ...... x GLOSSARY ...... xi 1 INTRODUCTION ...... 1 2 NATURAL PROPERTIES OF THE INVESTIGATED AREA ...... 5 2.1 Abiotic characteristics ...... 6 2.1.1 Climate ...... 6 2.1.2 Geology and soil ...... 8 2.1.3 Hydrology ...... 9 2.2 Biotic characteristics ...... 10 2.2.1 Vegetation ...... 10 2.2.2 Avifauna ...... 12 3 MATERIAL AND METHODS ...... 13 3.1 Selection of field sites ...... 13 3.2 Data collection vegetation...... 16 3.2.1 Species richness ...... 18 3.2.2 Regeneration ...... 19 3.2.3 Vegetation structure ...... 20 3.3 Data collection avifauna ...... 21 3.4 Statistical analysis ...... 22 3.4.1 Vegetation ...... 22 3.4.2 Avifauna ...... 23 4 Results ...... 25 4.1. Field sites ...... 25
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4.1.1 Pasture management ...... 25 4.1.2 Fertilizers and pest control on riparian margins ...... 25 4.2 Vegetation ...... 27 4.2.1 Species richness ...... 27 4.2.2 Species richness and abundance for vines, ferns and pest plants ...... 28 4.2.2.1 Vines and Ferns ...... 28 4.2.3 Similarity of field sites ...... 33 4.2.4 Regeneration ...... 35 4.2.5 Vegetation structure ...... 37 4.3 Avifauna ...... 58 4.3.1 Species richness ...... 58 4.3.2 Alien bird relative abundance ...... 61 4.4 Vegetation and avifauna ...... 65 4.4.1 The influence of vegetation on bird species richness ...... 65 4.4.2 The influence of vegetation on bird occurrences...... 67 5 DISCUSSION ...... 71 5.1 Vegetation ...... 71 5.2 Avifauna ...... 79 5.3 Vegetation and avifauna ...... 81 5.4 Are plantings necessary to achieve these results? ...... 83 5.5 The value of restored riparian margins for conservation ...... 85 5.6 Potential management conflicts ...... 88 6 CONCLUSIONS AND RECOMMENDATIONS ...... 89 6.1 Conclusions: Riparian management in Taranaki –A success for native biodiversity? ...... 89 6.2 Recommendations ...... 91 6.2.1 Recommendations for management ...... 91 6.2.2 Recommendations for future studies ...... 92 7 REFERENCES...... 94
8 APPENDIX ...... 108
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Riparian management in Taranaki – A success for native biodiversity?
LIST OF FIGURES
Figure 1 : Investigated area 5
Figure 2 : Soil moisture and temperature in Taranaki 7
Figure 3 : Rainfall in Taranaki 7
Figure 4 : Rainfall zones in Taranaki 7
Figure 5 : Location of field sites 15
Figure 6 : Schematic drawing of vegetation mapping 17
Figure 7 : Alien plant species richness 27
Figure 8 : Native plant species richness 27
Figure 9 : Alien vine species richness 28
Figure 10 : Native vine species richness 28
Figure 11 : Native fern species richness 30
Figure 12 : Pest plant species richness and abundance 32
Figure 13 : Similarity in alien plant composition 33
Figure 14 : Similarity in native plant composition 34
Figure 15 : Vegetation height 37
Figure 16 : Ground cover 39
Figure 17 : Number of ground cover groups 40
Figure 18 : Cumulative ground cover values for alien, native and abiotics and litter 41
Figure 19 : Alien and native vine ground cover in comparison 42
Figure 20 : Fern ground cover 43
Figure 21 : Midview cover 45
Figure 22 : Number of midview cover groups 46
Figure 23 : Cumulative midview cover values for alien, native and abiotics and litter 47
Figure 24 : Alien and native vine midview cover in comparison 48
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Figure 25 : Midview fern cover 49
Figure 26 : Cover above two metres height 50
Figure 27 : Top tier plant groups 54
Figure 28 : Alien bird species richness 58
Figure 29 : Native bird species richness 58
Figure 30 : Relative bird abundance per ha 62
Figure 31 : Alien and native bird relative abundances in comparison 63
Figure 32 : Influence of vegetation on single bird species occurrences 68
LIST OF TABLES
Table 1 : Alien plant species 107
Table 2 : Native plant species 110
Table 3 : Native fern species 31
Table 4 : Seedlings 36
Table 5 : Vegetation above two metres 52
Table 6 : Bird species and conservation 60
Table 7 : Comparison of single bird species relative abundances 64
Table 8 : Vegetation and alien bird species richness 65
Table 9 : Vegetation and native bird species richness 66
Table 10 : Significant vegetation variables for CCA 67
Table 11 : Correlations between single bird species and vegetation
variables 70
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Riparian management in Taranaki – A success for native biodiversity?
LIST OF PLATES
Plate 1 : Photos of field sites 14
Plate 2 : Vegetation structure composition 57
Plate 3 : Aerials of unfenced field sites 113
Plate 4 : Aerials of fenced field sites 115
Plate 5 : Aerials of medium field sites 117
Plate 6 : Aerials of old field sites 119
Plate 7 : Aerials of regenerated field sites 121
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GLOSSARY
ACR: Auckland Regional Council
Alien: Species which are or were introduced in New Zealand since first human contact.
Biodiversity: Usually this term refers to the variability among organisms in terms of their genetic diversity, species diversity and ecosystm diversity. My study, however, focuses on species and ecosystem diversity.
DOC: Department of Conservation
Native: A species is native to New Zealand when its natural geographical distribution includes New Zealand; also species which have self established in New Zealand without human support (e.g. waxeyes) are regarded as native.
Pest: Plants or animals which are known to invade native ecosystems and pose a threat to New Zealand’s economy and are thus by law forbidden to be sold or reproduced (based on the Biosecurity Act 1993).
Restoration: The rehabilitation of a former (anthropogenic) degraded area in terms of their ecological functions and species composition, towards a natural state.
Riparian margin: The area between the watercourse of a stream and the top of the outer bank, including the floodplain.
RMA: The Resource Management Act 1991 is the legal framework for riparian management programmes and gives authority to regional councils to develop riparian management programmes.
SER: Society for Ecological Restoration
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Riparian management in Taranaki – A success for native biodiversity?
TRC: Taranaki Regional Council
Weed: Weeds are unfavoured plants, which do not contribute to the national economy in a positive way and thus impede agricultural efforts.
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Riparian management in Taranaki – A success for native biodiversity?
1 INTRODUCTION
Riparian margins are internationally recognized as highly dynamic areas with high natural species diversity (Pollock et al., 1998; Naiman et al., 1993; Gregory et al., 1991), which serve important ecological functions within the landscape (Townsend et al., 2003; Ward, et al., 2002). Riparian margins act as a filter system for stream water quality and protect water courses from high temperatures and insolation; resulting in the dependency of instream organisms on riparian margin vegetation (Rutherford et al., 1997). Furthermore, organic matter from leafs falling into streams are a nutrient source and many instream invertebrates have stages in their lifecycles where they are dependent on suitable terrestrial habitats for their survival (Jackson and Resh, 1998; Hicks, 1997). Natural flooding events disperse plant propagules and continuously create microhabitats for plant establishment leading to rich complex terrestrial habitat structures in riparian margins (Miller, 2006). Consequently, terrestrial fauna finds rich feeding sources in riparian margins due to high biomass production (Chan et al., 2008).
Despite their ecosystem values riparian margins have undergone dramatic changes with human development (Decamps, 1993). Riparian margins in New Zealand are a typical example of riparian habitat modification: The arrival of European settlers approximately 150 years ago led to wide scale forest depletion in New Zealand (Quinn, 2000). With progressing urbanization and land development most lowland forests were cleared (Wardle, 1991), leaving many streams unprotected to sun exposure and eutrophication (Boothroyd et al., 2004; Ministry of the environment, 2001). Declining water quality was accompanied by a shift in species composition which excluded many of the original, more sensitive aquatic species (Boulton et al., 1997; Quinn et al., 1993). Recently, however, increasing public awareness of the relationship between riparian margins and water quality has led to the development of regional Riparian Management Programmes (e.g. Ministry of the environment, 2001; Smith, 1993; TRC, 1992). These were implemented nationwide from the early 1990s; following the Resource Management Act 1991 (RMA) as legal framework (Resource Management Act, 1991).
In the Taranaki region most of the lowland forests were cleared for dairy farming, resulting in the same water quality problem as recognized nationwide (TRC, 1992).
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1 Introduction
Taranaki’s regional riparian management programme is promoted by the Taranaki Regional Council (TRC, 2001b). The council hereby provides farmers with individual Riparian Management Plans (TRC, 1993) at no cost to the farmer, which provide details on fencing off riparian margins and enhancing existing vegetation (alien pasture grasses and herbs) with early seral (native) plant species (TRC, 2002). Plant species are attributed to different units/zones within the riparian margin (TRC, 2001b), with most known for their attractiveness to native birds as feeding sources in addition to stabilizing banks, providing shade and filtering nutrients (Collier et al., 1995).
Improvements in water quality have been demonstrated following riparian management, given that the length of protected riparian margins is sufficient (Collier et al., 2000). Positive effects on instream habitat quality have been primarily attributed to temperature decreases caused by canopy closure in riparian margins (Parkyn et al., 2003) and not so much with nutrient filtration, which would require mostly open vegetation for efficient filtration (Quinn et al., 1993).
International studies have shown the benefits of riparian habitat rehabilitation for terrestrial biodiversity (i.e. avifauna and floristic diversity) additionally to water quality improvements (Bryce et al., 2002; Groom and Grubb, 2002). However, within the New Zealand context, the value of the terrestrial component of riparian margins has mostly been considered with respect to water quality management (Parkyn et al., 2003; Howard- Williams and Pickmere, 1999; Storey. and Cowley, 1997). Consequently, little is known about the effects of New Zealand’s riparian management programmes on native terrestrial biodiversity. Only a few studies have investigated succession patterns and avian diversity in New Zealand’s riparian margins after their conversion into pasture or linked riparian vegetation types. These studies were either purely descriptive (Howard-Williams and Pickmere, 1999), where one stream has been monitored over time; or the vegetation types were very broadly defined as in the Wairoa catchment study where categories such as ‘native forest’ and ‘exotic forest’ were compared to each other among other variables in terms of avian diversity (Boffa Miskell limited, 2000). Although these studies provided interesting insights and gave reason to expect benefits of riparian management regimes on terrestrial biodiversity a further detailed quantitative assessment was needed.
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Riparian management in Taranaki – A success for native biodiversity?
This study is a pilot project within a wider research approach and aims to investigate and quantify the benefits of riparian management on native terrestrial biodiversity in Taranaki (Froude, 2008a). In analogy to international studies monitoring riparian habitat restoration birds were chosen as a focal faunistic group due to their well recognized value as indicator species in New Zealand (Froude, 2003; Froude, 1998). No previously used standard method addressed the particularities of terrestrial biodiversity assessments within the relatively narrow revegetated riparian margins in New Zealand. For this study however, a new method designed for riparian margins, was applied (Froude, 2008a).
With this study I want to answer how floristic and avian diversity as well as vegetation structure develops with progressing succession by comparing different aged planted margins (medium aged (4-7 years) and old (8-12 years)) with riparian margins still in use as pastures and recently fenced margins (1-4 years). Regenerated field sites (at least 20 years old) hereby are the best available example of well developed narrow riparian margins in the region and are thus used as a baseline for the evaluation of planting development. Furthermore, I want to investigate whether any vegetation variables can be identified as important factors for native bird diversity and abundance. As part of my study I aim to answer the following detailed research questions:
Vegetation:
1. Do riparian management practices decrease the number of alien species with field site age, especially pest plant species richness?
2. Does native species richness as well as the proportion of non planted species (e.g. all ferns and vines) increase with field site age?
3. How does plant cover diversity develop with field site age? I hereby hypothesize an increase in the number of plant cover groups with field site age. Furthermore, I expect alien cover to be largest on the ground layer compared to cover at midview (breast height; i.e.1,35m) and skyview (cover above 2m height), with alien herbs as the main contributor.
4. Does the number of seedlings increase with field site age?
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1 Introduction
5. How does vegetation structure gain in complexity with field site age? I hypothesize an increase in vegetation height, the number of tiers and the presence of epiphytic plants with field site age.
Birds:
1. Is an increase in native bird species richness accompanied by a decrease in alien bird species richness?
2. Does native bird species richness increase with field site age?
3. Are the relative abundances of native bird species positively linked with field site age?
Vegetation and birds: 1. Do positive correlations between bird species diversity and gains in structural vegetation development complexity exist between the differently aged field sites?
2. Is the occurrence and relative abundance of single bird species correlated with structural vegetation diversity?
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Riparian management in Taranaki – A success for native biodiversity?
2 NATURAL PROPERTIES OF THE INVESTIGATED AREA
The following chapter will provide background information of the natural properties (abiotic and biotic features) of the investigated area. Within the abiotic section climate, geology and soil as well as hydrology are considered. In the biotic section the vegetation subsection and the avifaunistic subsection combine species information with land use practices and history.
The study was conducted in Western Taranaki within the Egmont Ecological District (TRC, 2004) for the Taranaki Regional Council, based in Stratford/Taranaki, on the west coast of the North Island of New Zealand (Fig. 1).
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Figure 1: The North and South Island of New Zealand (left picture), source: Google Earth (2009) and a close-up of Taranaki (right picture) including a photo of Mt. Taranaki are shown (Taranaki Regional Explorer, 2008).
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2 Natural properties of the investigated area
2.1 ABIOTIC CHARACTERISTICS
2.1.1 CLIMATE
New Zealand is located within the zone of mid-latitude westerlies and therefore weather patterns are determined by successive east-moving anticyclones and depressions with their associated fronts (Wardle, 1991). Taranaki’s temperate maritime climate with moderate seasonal variations (McGlone and Neall, 1994) is strongly influenced by its westerly position (Baldinger and Salinger, 2008). Sunshine hours in Taranaki are average to high compared to other regions in New Zealand (Statistics New Zealand, 1999). Mt Taranaki (2518m) dominates not only the landscape but also alters the regional climate in Taranaki: Wind patterns are influenced by flow over Mt Taranaki’s peak i.e. orographic winds (Burgess et al., 2007).
Precipitation varies considerably within Taranaki, and is generally higher in close proximity to the mountain (Fig. 4). Rainfall data (TRC, 2008) for Kaupokonui at Glenn Rd/Taranaki shows the high rainfall variability (February and October in particular) where sometimes (severe) droughts but also heavy rainfalls with flooding events occur (Fig. 3). However, mean rainfall precipitation is highest during the cooler months (Fig. 2).
Taranaki’s inland areas experience a lower minimum temperature than coastal areas due to elevation and distance to the moderating influence of the sea. Additionally, sheltered inland locations have higher ranges between minimum and maximum temperatures (TRC, 2003). Figure 2: (data: TRC, 2008) shows the minimum, mean and maximum monthly temperatures for Kaupokonui at Glenn Rd/Taranaki. The lowest mean monthly temperatures are recorded for July with 9.05 °C and the highest with 19.37 °C for February. Soil moisture (Fig. 2) is lowest with a mean of 12.06 % in March and highest with 27.10 % in July.
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Riparian management in Taranaki – A success for native biodiversity?
80 25 Mean soil moisture (%) 70 20 60 Mean temperature 50 15 (°C) 40 Min. 30 10 temperature
Percent (°C) 20 Degree Celsius 5 Max. 10 temperatureCelsius Degree 0 0 (°C) Jul Sep Nov Jan Mar May
Figure 2: Soil moisture and temperature for Kaupokonui at Glenn Rd/Taranaki. Mean monthly values for soil moisture in % are illustrated. Mean monthly temperature as well as maximum and minimum temperature are shown.
350
300
250
200
150 Millimetres 100
50
0 Jul Sep Nov Jan Mar May
Min. rainfall Mean rainfall Max. rainfall
Figure 3 (left) and 4 (right): Rainfall for Kauponkonui at Glenn Rd/Taranaki (left graph): Monthly mean, minimum and maximum rainfall in millimetres are shown. Annual rainfall in Taranaki (right figure): Zones in Taranaki for annual precipitation in millimetres are shown (TRC, 2003).
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2 Natural properties of the investigated area
2.1.2 GEOLOGY AND SOIL
The following geological information is largely based on (Molloy and Christie, 1998): Taranaki’s landscape was formed by volcanic activity (McGlone and Neall, 1994). Even today, remnants of past volcanoes are still visible in Taranaki’s coastal area with Paritutu and the Sugarloaf Islands as well known examples. The volcanic activity moved south- east approximately 250 000 years ago. Like the previous volcanoes in this region, the landscape dominating 70 000 year old cone of Mt Taranaki was formed by successive eruptions. Natural erosions redistributed Mt Taranaki’s volcanic debris around its base, known by the term ring plain today. Additionally to tephra deposits avalanches also distributed cold volcanic debris. For the last 50 000 years intermittent collapses of Mt Taranaki’s cone caused lahars to sweep down the mountain. Lahars thereby even reached the sea on the western slopes. Over the last 100 000 years up to 30m of tephra accumulated from many small eruptions in Taranaki. Mt. Taranaki is considered to be dormant, not extinct with the last eruption recorded about 1750 A.D. (TRC, 2003). The soils of the investigated area (on the ring plain) are mostly deep, free-draining, fertile, volcanic ash soils. These soils are known as yellow-brown loams and support intensive dairy farming (TRC, 2003). Taranaki’s ring plain soils are generally in good condition and only a low rate of erosion and structural vulnerability rating are documented (TRC, 2001a). However, 3% of Taranakis soils, mainly alluvial soils next to or on riparian margins, are rated as highly or very highly structural vulnerable. Although fertilizers and agrichemicals are used in Taranaki, residual soil contamination is among the lowest in New Zealand (TRC, 2001a).
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Riparian management in Taranaki – A success for native biodiversity?
2.1.3 HYDROLOGY
More than 300 river and streams flow from Mt Taranaki’s flanks in a characteristic radial pattern (TRC, 2003). According to the Taranaki Regional Council (2005) streams within Taranaki can be characterized as short, narrow and deeply carved into the volcanic ash and debris flow material of Mt Taranaki. They are supplied with water coming from Mt Taranaki. Egmont National Park functions as a reservoir, able to sustain the supply of streams and catchments even in prolonged droughts.
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2 Natural properties of the investigated area
2.2 BIOTIC CHARACTERISTICS
2.2.1 VEGETATION
Originally, Taranaki was covered up to the tree limit with dense conniver/broad leaved forest (McGlone and Neall, 1994). The vegetation consisted mainly of conifers (predominately of the Podocarpaceae-family), with herbaceous and woody flowering plants and ferns (Wardle, 1991; Dawson, 1993). Today, the total area of Taranaki (723,610 ha) contains 57 % pastoral land (414,400 ha) (TRC, 2004). Most of Taranaki’s native forest and native shrub land (a total of 290,000 ha (40%)) is located within the boundaries of Egmont National Park and on the steep slopes of Taranaki’s eastern hill country.
Early Maori settlements (first documented for Taranaki around 1300 AD) used the ring plain as a cultivation area for bracken fern (Pteridium esculentum) (rhizomes are eatable) (Walton, 2000). Therefore forest stripes (mostly in Taranakis’ coastal areas) were cleared by fire for bracken ferns, which are a natural pioneer species after fire events (Brownsey and Smith-Dodsworth, 1989). The arrival of European settlers about 150 years ago led to wide scale forest replacement and its conversion into pasture. Today only small patchy remnants of lowland forest exist outside the boundaries of Egmont National Park (TRC, 2003). Thus information on the original species composition of lowland forests not subject to anthropogenic induced edge effects below 450mNN is incomplete (McGlone, 1982).
However, lowland forests in Egmont National Park show Dacrydium cupressinum- Metrosideros robusta (epiphytic origin)/Weinmannia racemosa forest as the main forest type. Furthermore, Dacrydium cupressinum - Metrosideros robusta - Melicytus ramiflorus - Weinmannia racemosa are represented forest types. Kohkohe (Dysoxylum spectabile), which dominates semi-coastal bush cover occurs on the Kaitake Range up to 240mNN. Between 240mNN and 400mNN tawa (Beilschmiedia tawa) is the dominating tree species within the Kaitake Ranges (Clarkson; 1985). The influence of past volcanic eruptions in debris distribution is still apparent by the dominance of either Weinmannia racemosa or Melicytus ramiflorus as tree species (McGlone, 1982).
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Riparian management in Taranaki – A success for native biodiversity?
Taranaki is one of the most important dairy regions in New Zealand (Statistics New Zealand, 1999). Stocking rates have increased to 2.8 cows on average per ha (Ministry of Agriculture and Forestry, 2008). Cattle graze on pastures consisting of a mixture of introduced grasses and legumes, typically ryegrass and clover species. Taranaki`s farmer also use tall fescue (Festuca arundinacea Schreb) as pasture species (Milne et al., 1997). Additionally to favoured pasture species (pasture)-weeds are a constant issue for pasture management (Wardle et al., 1995).
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2 Natural properties of the investigated area
2.2.2 AVIFAUNA
Except for two native bat species, New Zealand’s native fauna is mammal free and the largest vertebrate diversity is found in birds (DOC, 2000). Due to New Zealand’s island- situation, many birds are flightless and were not adapted to predation by mammals. Thus with human settlement many species became extinct (McGlone, 1989).
The earliest evidence for human settlements in Taranaki dates back to 1300 AD. At that time Taranaki supported large avifaunistic diversity: Nine moa species were found in the Taranaki/Whanganui region along with other species such as the giant rail, goshawk and crow (Walton, 2000). These birds were hunted by Maoris for food (Wilmshurst et al., 2004).
Today, Taranaki supports a rich coastal avifauna (TRC, 2003). However, most diverse inland regions are confined to Egmont National Park, where several endangered species such as the brown kiwi are retreating (Henderson, 2006). A total of 53 native and 23 introduced birds are found in Taranaki, of which 14 native species (e.g.: North Island kokako, kereru) are threatened (TRC, 2004).
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Riparian management in Taranaki – A success for native biodiversity?
3 MATERIAL AND METHODS
3.1 SELECTION OF FIELD SITES
The effects of riparian management in Taranaki on native biodiversity, especially on vegetation and avian species assemblages were investigated. Therefore, I selected together with my colleagues from the TRC five different field site categories based on the recommendations of Froude (2008a), each resulting in four field sites per category (Plate 1):
1. Unfenced sites (U): Cattle have access to streams and riparian margins are unfenced.
2. Fenced sites (F): Alien pasture grasses form the dominating vegetation. Cattle have been excluded with fencing for the last 1-4 years. One fenced field site investigated in this study had a few small native plantings in very poor condition (uncertain survival of plantings), but overall site conditions were unaffected by these plantings. However, due to difficulties in field site availability this field site was not dismissed.
3. Medium aged planted sites (M): Plants (native) were planted 4-7 years ago. Plant species choice was mainly based on the individual riparian management plan developed for the property. Cattle are denied access by fences.
4. Old aged plantings (O): Plants (native) were planted 8-12 years ago. With the start of plantings cattle was excluded with fences from riparian margins.
5. Naturally regenerated sites (R): Vegetation has naturally regenerated. Riparian margins have been set aside from pastures by excluding cattle by fencing for at least 20 years.
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3 Material and methods
U F
M
O R
Plate 1: Every photo shows one typical example of a field site of the management category: U = unfenced, F = fenced, M = medium, O = old and R = regenerated.
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Riparian management in Taranaki – A success for native biodiversity?
A field site is defined as the area between the fences of riparian margins, including the watercourse. The monitoring of birds required a minimum length of 400m for each field site (Froude, 2008b). For appropriate vegetation mapping a minimum of four metres riparian margin width is needed (Froude, 2008a). A minimum distance of 200m was kept between field sites to avoid repetitive recording of individual birds (Froude 2008, pers. com.). A 4km distance to Egmont National Park, which is well recognized as an important area of retreat for native avifauna (Hernderson, 2006), was kept to avoid artificial high species numbers on field sites in close proximity to these areas. One regenerated field site is located north of Mt. Taranaki (Fig. 5); the other field sites are predominately southbound of the mountain, ranging from the western end of Opunake Road (close to Te Kiri) to just east of Stratford’s town boundaries.
Figure 5: Location of field sites. All field sites of the study are shown GPS-referenced on a topographical map showing the main rivers and Mt. Taranaki (middle of the figure). Black dots indicate unfenced field sites, with the letter U.. Yellow dots indicate fenced field sites, coded with letter F. Purple dots indicate medium field sites, coded with the letter M. Pink dots indicate old field sites, coded with the letter O. Blue dots indicate regenerated field sites, coded with the letter R.
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3 Material and methods
3.2 DATA COLLECTION VEGETATION
Managed riparian margins in New Zealand are usually narrow with an average width between four to ten metres (pers. observation) compared to studies elsewhere with a riparian margin/riparian zone of 50m width and more (e.g. Peak and Thompson, 2006; Fischer and Martin, 1999; Spackman and Hughes, 1995). This is due to a management approach which mainly aims for water quality improvements (TRC, 1992).
Given that vines and epiphytes form an important part of New Zealand’s forest plant diversity (Dawson, 1993), a sampling strategy which would address their occurrence and abundance was sought. Due to this unique situation standard methods did not provide adequate sampling strategies. Froude (2008a) modified the standard vegetation mapping methods with regards to the particularities of New Zealand riparian margins in order to develop a standard sampling methodology for New Zealand. Vegetation mapping was conducted using transects according to Froude (2008a):
On each field site a 30m long stripe of representative, preferably homogenous vegetation parallel to the watercourse was chosen for the placement of a vegetation transect. On each plot (i.e. the area from the stream to the fence with 30m length parallel to the stream) the coordinates of the transects starting and end-point were recorded with a handheld GPS for prospective monitoring projects and for the creation of an accurate map showing the field site locations (Fig. 5), as well as for area calculations.
Fertilizers, weed control and pest management are important variables for the development of riparian vegetation (Froude, 2008a). Consequently, I developed a questionnaire for the participating farmers and interrogated them about their pest management regimes and the history of land use on their properties, including fertilizer use and planting species selection for the riparian margins.
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Riparian management in Taranaki – A success for nativenati biodiversity?
Figure 6: Schematic drawing of vegegetation mapping: In two metres distance to the watercocourse one transect with 30m length was laid. Every fullful metre one 50cm edge length quadrate was laid and vegetationv within an ashlar with 45cm height was recocorded. At breast height, which was defined as 1.35m aboveab ground (also referred to as “midview”) the quadradrate was held and vegetation 25cm above and beneath waswa estimated. For cover above 2m height a canopy scopesc was used. On field sites with an average riparianan margin width > than 6m, a second transect was plalaced in 2m distance inwards from the fence line, wherere measurements were conducted as outlined for the firstfi transect
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3 Material and methods
3.2.1 SPECIES RICHNESS
A general species list was developed for all plants which were at least partly rooted in the plot. The recording of alien species and native species was conducted using different abundance and distribution classes as defined in Froude (2008a):
Alien species richness Alien species, including pest plants, were recorded noting their highest tier of occurrence (i.e. ground, understory, sub canopy, and canopy). Furthermore, an distribution estimate ranging from widespread, patchy and localized was recorded together with an estimated abundance score ranging from 1 (i.e. species present) to 10 (i.e. species is occupying all its potential available space based on its ecological requirements). Species were identified to species level, with the exception of alien grasses. Where this was not possible the specimen’s genus or family name was recorded.
Native species Native species were recorded in the same manner as alien species with the following differences: No species distribution estimates were made. Abundance estimates were only recorded for three classes: Rare (only a few individuals), common (many individuals) and abundant (species is using all its possible space).
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Riparian management in Taranaki – A success for native biodiversity?
3.2.2 REGENERATION
A seedling tally was recorded to investigate regeneration of native tree seedlings. For each native species three seedling categories were recorded within the plots: Small seedlings between 16-45cm height, medium seedlings with a height range between 45- 135cm and saplings with a height >135cm but less than 3cm dbh (diameter at breast height). These height class intervals follow those used in the Forest Measurement and Assessment Kit (Formak, 2004) and Allen (1993) and were thus recommended in Froude (2008a).
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3 Material and methods
3.2.3 VEGETATION STRUCTURE
A vegetation transect was laid parallel, in two metres distance to the stream of each field site (Froude, 2008a). On field sites with a vegetation width larger than six metres, a second transect was recorded in two metres distance to the fence. Due to only marginal differences in species composition throughout the plots from field sites of the categories “unfenced” and “fenced” only one transect was incorporated. The geomorphologic features of the transect area were recorded (i.e. location of transect e.g. inner bank). Starting with the first full metre, 30 vegetation intercept points were recorded according to Froude (2008a): Every metre a flexible 50cm edge length quadrate (joints were flexible in order to be put around tree trunks where necessary and to facilitate quadrate placement in dense vegetation) was placed to conduct cover estimates. At each vegetation census point the vegetation height and the highest species were recorded. The number of tiers above two metres height and the species in the tier were recorded. A tier within this context is a layer of vegetation above two metres in height (e.g. 5m high mahoe above 3m high lemonwood would be: Mahoe = top tier, lemonwood = second tier). The ground species were also recorded in the corner where the canopy scope was placed to estimate ‘skyview cover’ (i.e. cover above 2m height). For the estimation of skyview I distinguished between native, alien and naturally occurring plants as well as clearly planted ones. Where it was unclear whether a specimen was planted or not it was recorded as non-planted. All cover values were noted on a percentage scale totaling 100%. For the ground all plant coverage under 45cm height inside the quadrate was estimated. Thereby, the plants were put into semi functional/botanical groups in regards of the promoted zones for plantings (Ministry of the environment, 2001; recommendations by Froude and Dean, 2008 pers.com). These groups were: Mosses, ferns, grasses, sedge/rush/reeds (including flax due to its growth zone on riparian margins), vines, seedlings, other angiosperms (herbs). Trees and shrubs were recorded on species level. Only on two field sites rocks were found (only small area) and thus soil and rocks were both recorded in one group (abiotics and litter). The total of all groundcover groups was 100%. For each vegetation census point the quadrate was regarded as an ashlar with 50cm edge length and 45cm height. In accordance to ground cover mapping I estimated the midview cover. Therefore I placed the quadrate at breast height (1,35m
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Riparian management in Taranaki – A success for native biodiversity?
above ground) and considered 25cm above and underneath the quadrate as estimation borders. Thereby vegetation cover did not reach 100% because volume percentages were estimated.
3.3 DATA COLLECTION AVIFAUNA
Standard bird mapping techniques required adjustments to adapt them to the field site dimensions and particularities of the investigated riparian margins. Therefore, birds were monitored according to Froude (2008a). Birds were recorded according to the five minute bird count method (Dawson and Bull, 1975) on predefined GPS-mapped bird count stations. Due to the special situation on riparian margins background noise had to be accounted for. Therefore I adjusted the recommended distance between bird count stations dependent on the background noise level. A distance of 100m was kept to field site ends to avoid edge effects (as recommended by Froude; 2008a). Depending on field site length in relation to background noise, each field site consisted of two to three bird count stations. I avoided choosing bird count stations close to effluent ponds to reduce the interference with water birds which prefer standing waters. Three bird count repetitions, which are within the recommended range to provide secure results for five minute bird count point transects (Sutherland et al., 2004), were carried out per field site. One field site out of each category was investigated per day. Birds were recorded between 9 am and 3 pm, a timeframe also used by Dawson and Bull (1975). The day and time each field site was surveyed was randomized to avoid artifacts and differences in species composition caused by different activity levels throughout the day. Birds were only recorded under suitable weather conditions (i.e. no winds, no precipitation) within one month (between the 16th of April and the 16th of May 2008) to minimize seasonal differences. All birds seen and heard on field sites were recorded. Bird species were identified according to Heather and Robertson (2005).
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3.4 STATISTICAL ANALYSIS
All ANOVAS and Spearman correlation coefficients were performed with SPSS 16. Tests for normal distribution and regression analysis were conducted with Minitab 15. Canonical Correspondance Analysis and Detrended Correspondence Analysis were performed using Canoco 4.5.
3.4.1 VEGETATION
Five management categories had to be tested against each other for statistical differences. The management categories represent different time steps in succession. Parametric tests were the statistical method of choice to determine differences for the investigated management categories in terms of species richness, vegetation height and vegetation plant cover variables. Thirty vegetation intercept points per field site were included in the analysis. Thus, 30 vegetation intercept points were randomly chosen for field sites with more than one transect (i.e. 60 vegetation intercept points). Before parametrical tests were performed, the data was tested for normal distribution with the Ryan Joiner test. Where data did not meet criteria of normal distribution transformations were conducted. All percentage cover values were transformed (i.e. all ground cover; midview cover and skyview cover estimates) using arsine transformations (Fowler et al., 2008). General linear model-based univariate ANOVAs were performed using the measured vegetation variables as dependent variable and management category as a fixed factor. Significant differences were confirmed through the Tukey B post hoc test. Similarity in floristic composition of field sites was analysed using a unimodal DCA (Detrended Correspondence Analysis: Hill and Gauch, 1980). For the similarity in alien plant species composition, abundance scores were incorporated in a unimodal DCA, detrended by segments. Rare species were downweighted and results are shown as a biplot scatter plots using chi-square distances. Similarity of native plant species composition was analysed in the same way as alien species with the difference that only presence-absence data was used, since abundance scores for native species were not differentiated enough for further statistical analysis. For both analyses gradient lengths were used to determine the degree of heterogeneity.
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Riparian management in Taranaki – A success for native biodiversity?
3.4.2 AVIFAUNA
Bird data was calculated per hectare to facilitate comparison between management categories, since neither field site areas nor radiuses of bird count stations were identical for each field site.
Differences in alien species richness and native species richness for the different management categories were investigated using a general linear model (GLM) based univariate ANOVA. Alien species richness and native species richness were each used as dependent variable with management as a fixed factor.
Relative alien and native bird abundances were each tested for differences between the five management categories using GLM based univariate ANOVAs. I tested for differences in single bird species relative abundance for the investigated management categories using a GLM-based univariate ANOVA. Prior to the analysis all bird species abundances (i.e. blackbird, chaffinch, dunnock, goldfinch, greenfinch, house sparrow, skylark, starling, thrush, yellowhammer, fantail, grey warbler, harrier, kingfisher, pipit, pukeko, tomtit, waxeye and welcome swallow) were tested for normal distribution with the Ryan Joiner test of normal distribution. Where data did not meet criteria of normal distribution arcsinh-transformations were conducted for count data (Fowler et al., 2008). However, data on some bird species could not be normalized sufficiently through transformations to perform ANOVAs and were thus not further analysed.
I analysed the effects of vegetation variables on native and alien bird species richness using linear multiple regression models. To select for the explanatory vegetation variables to be integrated into the models I assessed their degree of correlation and selected only non-correlated variables for the analysis (correlations > 0.5). For native and alien species richness I tested the effects of shrub and tree cover at midview, the number of tiers, midview cover, alien grasses, alien herbaceous plants as well as plant species richness. Consequently, I backward eliminated all those variables from the model that did not affect its explanatory power (α = 0.05). The values for non-significant terms were afterwards attained by adding each non-significant term to the final model that contained all significant terms.
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3 Material and methods
I analysed the effects of vegetation on single bird species relative abundance at field site level performing a CCA (Canonical Correspondence Analysis). Patterns in bird species composition associated with vegetation variables (see below) and in the distribution of single bird species along each vegetation variable are possible to incorporate when using a CCA (Ter Braak, 1986). Bird species with low overall abundance scores were eliminated to give greater weight to bird species with higher abundance scores. Out of the set of vegetation variables (i.e. midview cover, plant species richness, vegetation height, percentage of sky cover, alien herbaceous plants, alien grasses, shrubs and tree midview cover), I removed the ones that were not significantly explanatory for bird species occurrence according to a Monte Carlo permutation test with 499 permutations. After the determination of significant vegetation variables I assessed the correlations between each bird species investigated in the CCA to determine the power of the correlation with the vegetation variable. Therefore I used Spearman’s correlation coefficients. The power of the calculated correlations was classified according to Fowler et al. (2008).
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Riparian management in Taranaki – A success for native biodiversity?
4 RESULTS
In the following chapter I will present the results of data collected for this study in Taranaki/New Zealand. I start with demonstrating the results of my farmer-questionnaire regarding the investigated field sites. Vegetation results are demonstrated before bird count data results. Consequently, the results of interaction and correlations between vegetation and avifauna are displayed in the last section.
4.1. FIELD SITES
The questionnaire was returned for 14 field sites out of 20.
4.1.1 PASTURE MANAGEMENT
Stocking rates for pastures adjacent to field sites irrespective of management regimes on riparian margins increased over the last 15 years. While stocking rates 15 years ago ranged between 1,8 and 3,0 cows per ha with a mean of 2,3 ± 0,1 (SE) they increased to a range between 2,0 and 3,5 cows per ha with a mean of 2,5 ± 0,2 (SE) ten years ago. Stocking rates for the last five years ranged between 2,0 and 3,8 cows per ha with a mean of 2,6 cows per ha ± 0,2 (SE). Pastures adjacent to riparian margins were not subject to cut and carry.
4.1.2 FERTILIZERS AND PEST CONTROL ON RIPARIAN MARGINS
Fertilizers were used by three farmers prior to fencing and planting on riparian margins. Thereby potassium (potash), phosphate (phosphate mixes and products such as Super phosphate) and nitrogen fertilizers (urea (crystalline nitrogen fertilizer)) were applied. Additionally, lime was used to prevent soil acidity. The majority of farmers with a planting management regime on riparian margins cleared weeds chemically before commencing with plantings. For the ongoing weed control Round up is the most widely used overall pesticide. Escort, brushkiller, Tonden, Simazine and Glyphosate are also used. Species targeted with weed control are: blackberry (Rubus fruticosus agg.), gorse (Ulex europaeus), pampas grass (Cortaderia selloana), barberry (Berberis glaucarpa),
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4 Results
ragwort (Senecio jacobea), thistles (Asteraceae), old man’s beart (Clematis vitalba) and foxglove (Digitalis purpurea).
Brushtail possums (Trichosurus vulpecula) are ongoing controlled on all riparian margins except for one without plantings. Methods for control are: Poisoning with cyanide+phosphorus, ferotox+cyanide, shooting and trapping. Possum densities were low at the time of asking according to participating farmers. Only on one site mustelid control is in place. Rodent densities are low to medium according to farmers. Rabbits are poisoned by one farmer; the majority of the other farmers shoot rabbits regularly.
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Riparian management in Taranaki – A success for native biodiversity?
4.2 VEGETATION
4.2.1 SPECIES RICHNESS
Alien species A total of 63 alien plant species was recorded. For a complete species list refer to Table 1 (Appendix). Alien species richness per plot ranged from zero to 21 species (Fig. 7). Regenerated field sites showed lowest alien species richness which was significantly different from all other management types. Species richness was intermediate for medium field sites and did not differ between the other management types (univariate ANOVA and Tukey b post hoc test: df = 4; F = 4,410 and p < 0,001).
Figure 7 (left) and 8 (right): Alien species (left graph) and native species (right graph) numbers found on each management category (U = unfenced, F = fenced, M = medium, O = old and R = regenerated, n = 4). Letters indicate significant differences (univariate ANOVA and Tukey B post hoc test. For alien species df = 4; F = 4,410 and p < 0,001. For native species df = 4; F = 50,560 and p < 0,001).
Native species Native species richness per plot ranged from zero to 36 species with a total of 83 species recorded. For a complete species list refer to Table 2 (Appendix). No significant difference in native species richness was found between unfenced and fenced field sites (Fig. 8). Medium field sites, on the contrary, showed a significant higher native species richness compared to unfenced and fenced field sites. The highest number of native species was recorded on old field sites, which formed together with regenerated field sites the two management categories with the highest native plant species richness (univariate ANOVA and Tukey b post hoc test with df = 4; F = 50, 560 and p < 0,001).
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4.2.2 SPECIES RICHNESS AND ABUNDANCE FOR VINES, FERNS AND PEST PLANTS
4.2.2.1 Vines and Ferns
Vines
Alien Five alien vine species were recorded, i.e. old man’s beard (Clematis vitalba), large bindweed (Calystegia sepium), great bindweed (Calystegia silvatica), convolvulus (Convolvulus arvensis) and blackberry (Rubus fruticosus agg.). Alien vine species richness per plot ranged from zero to three species (Fig. 9). A comparison between different management regimes showed the lowest alien vine species richness on unfenced field sites, and the highest on medium field sites (Fig. 9). Alien vine species richness on fenced, old and regenerated field sites showed intermediate values as compared to unfenced and medium field sites (univariate ANOVA and Tukey b post hoc test: df = 4; F = 3,237 and p = 0,042).
Figure 9 (left) and 10 (right): Alien vine (left graph) and native vine species richness (right graph) for management categories (U = unfenced; F = fenced; M = medium; O = old; R = regenerated; n = 4). Letters indicate significant differences (univariate ANOVA and Tukey B post hoc test for alien vines: df = 4; F = 3.327 and p = 0,042. For native vines: df = 4; F = 33,316 and p < 0,001).
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Riparian management in Taranaki – A success for native biodiversity?
Native A total of five native vine species were recorded: White rata (Metrosideros diffusa), Metrosideros spec., larged-leaved muehlenbeckia (Muehlenbeckia australis), New Zealand jasmine (Parsonsia heterophylla) and supplejack (Ripogonium scandens). Native vine species richness ranged between zero and four species per plot. Vine species richness showed a higher value for old field sites (Fig. 10) compared to younger management types, but no statistical differentiation could be demonstrated yet (univariate ANOVA and Tukey b post hoc test with df = 4; F = 33,316 and p < 0,001). Regenerated sites showed a significant higher, around twofold, number of vine species compared to unfenced, fenced and medium field sites (Fig. 10).
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Ferns
Alien No alien fern species have been recorded on plots of any of the management categories.
Native A total of 26 fern species out of ten families with varying growth forms have been recorded on plots of riparian margins of this study (Tab. 3). Four species of tree ferns were found. Eight fern species were predominantly epiphytic and the remaining fourteen ferns were ground species. Native fern species richness ranged between zero and 16 species per plot. Albeit fern species richness is visibly higher for old field sites compared to younger management categories (Fig. 11) it was not statistical significant. Only regenerated field sites, which had the highest fern species richness, were significantly different from the other management categories (univariate ANOVA and Tukey b post hoc test with df = 4; F = 11,704 and p < 0,001).
Figure 11: Fern species number found within each management category (U = unfenced, F = fenced, M = medium, O = old and R = regenerated, n = 4). Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4; F = 11,704 and p < 0,001).
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Riparian management in Taranaki – A success for native biodiversity?
Table 3: All fern species found on plots of this study listed alphabetical by fern families. MGF = main growth form (G = ground; E = epiphytic, T = treefern, C = creeping). Cons. = conservation status (NTE = not threatened endemic, NTN = not threatened native, VCE = very common endemic, n.a. = not available). Information for species of this table: Brownsey and Smith-Dodsworth (1989); New Zealand Plant Conservation Network (2005).
Family No. Scientific name common name MGF Cons......
Aspleniaceae 1 Asplenium bulbiferum hen and chicken fern G NTE 2 Asplenium flaccidum hanging spleenwort E NTN 3 Asplenium hookerianum spleenwort G NTE var. Colensoicolensos 4 Asplenium oblongifolium shining spleenwort G, E NTE 5 Asplenium spec. n.a. G n.a. Blechnaceae 6 Blechnum chambersii nini G NTN 7 Blechnum filiforme thread fern G, E (C) NTE 8 Blechnum fluviatile kiwakiwa G NTN 9 Blechnum novae-zealandiae kiokio G VCE Cyatheaceae 10 Cyathea smithii ponga T NTE 11 Cyathia cunninghamii gully tree fern T NTN 12 Cyathia medullaris mamaku T NTN
Dennstaedtiaceae 13 Histiopteris incisa water fern G NTN 14 Paesia scaberula ring fern G NTE Pteridium exculentum rahurahu G Dicksoniaceae 15 Dicksonia squarrosa wheki T AE Dryopteridaceae 16 Lastreopsis glabella smooth shield fern G NTE 17 Lastreopsis hispida hairy fern G NTN 18 Polystichum vestitum prickly shield fern G NTE Hymenophyllaceae 19 Hymenophyllum spec. n.a. E n.a. 20 Trichomanes spec. n.a. E n.a. 21 Trichomanes venosum veined filmy fern E NTN Polypodiaceae 22 Microsorum pustulatum hound's tongue E NTN subsp. pustulatum
23 Microsorum scandens fragrant fern E (C) NTN 24 Pyrrosia eleagnifolia pyrrosia NTE Pteridaceae 25 Pteris macilenta sweet fern G NTE Thelypteridaceae 26 Pneumatopteris pennigera gully fern G NTN
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4.2.2.2 Pest plants
Alien plant species data was compared with the annually published National Pest Plant accord (DOC, 2007), where unwanted plants are acknowledged as pest plants according to the Biosecurity Act 1993 (regulates weed management and weed border control in New Zealand).
Six pest plant species (DOC, 2007b) have been recorded on riparian margin plots, i.e. old man’s beard (Clematis vitalba), hawkweed (Hieracium spec.), wandering jew (Tradescantia fluminensis), crack willow (Salix fragilis), African club moss (Selginella krausiana) and gorse (Ulex europaeus). Figure 12 shows a peak of pest plant species richness and abundance for old field sites. Regenerated field sites showed the lowest abundance of pest plants followed by fenced, unfenced and medium field sites. Although not recorded within plots, the following additional pest plants have been registered on riparian margins of this study: Chilean rhubarb (Gunnera tinctoria), pampas grass (Cortaderia sellona) and Himalayan balsam (Impatiens glandulifera).
Figure 12: Pest plant species and abundance for every field site (numbers on x-axis). To facilitate interpretation, management categories are circled in grey (U = unfenced, F = fenced, M = medium, O = old, R = regenerated). Species abbreviations: Cle vit = Clematis vitalba, SAL fra = Salix fragilis, SEL kra = Selginella krausiana, TRA flu = Tradescantia fluminensis, ULE eur = Ulex europaeus. Abundance scores = rank scale from 1-10.
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Riparian management in Taranaki – A success for native biodiversity?
4.2.3 SIMILARITY OF FIELD SITES
Alien species
Although management categories for unfenced and fenced field sites were visually separated by the application of a DCA (Detrended Correspondence Analysis) intermixing could be observed between medium, old and regenerated field sites (Fig. 13). Field site alien species composition was relatively heterogenic with a gradient length of 5,321. Field site 10 and 11 are outliers and differed in alien species composition from other field sites.
Figure 13: Dissimilarity of alien plant composition and abundance is shown by chi-square distances between field sites (Detrended Correspondence Analysis with a gradient length of 5,321 for first axis). Field sites 1-4 are unfenced; 5-8 fenced; 9-12 medium; 13-16 old and 17-20 regenerated.
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Native species
Regenerated field sites are more similar to each other in native species composition (especially in fern and native vine composition) than other management categories and therefore located in close proximity to each other (Fig. 14). The only unfenced field site with native species occurrence was field site 1, with palm leaf fern (Blechnum novae- zealandiae); this species was also recorded on the two fenced field sites (7 and 8) located very close to field site 1. On field site 5 bracken fern (Pteridium esculentum) was the only native species on this field site. Overall field sites are very heterogenic in native species composition with a gradient length of 7,907 for the first axis.
Figure 14: Dissimilarity of native plant composition and abundance is shown by chi-square distances between field sites (Detrended Correspondence Analysis) with a gradient length of 7,907 for the first axis. Field sites 1-4 are unfenced, 5-8 fenced, 9-12 medium, 13-16 old and 17-20 regenerated.
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Riparian management in Taranaki – A success for native biodiversity?
4.2.4 REGENERATION
Regeneration was measured on species level for plots. However, other vegetation structure variables were recorded only within transects for (mainly) functional groups. Therefore regeneration results, although a component of vegetation structure diversity, are displayed here separately.
Unfenced field sites: No seedlings have been recorded (Tab. 4).
Fenced field sites: Five species of seedlings have been recorded (Tab. 4). Total seedling abundance was second lowest after unfenced sites with a mean of 3,25 ± 3,25 (SE) seedlings per field site. All seedlings recorded on fenced field sites were presumably planted (refer to methods for explanation).
Medium field sites: Seven species of seedlings have been recorded (Tab. 4) All seedling height classes were represented on medium field sites. Total seedling abundance was intermediate compared as to fenced and old field sites with a mean of 9,25 ± 8,60 (SE) seedlings per field site. Most seedlings were probably planted.
Old field sites: Seedling species richness was more than twofold higher with 17 species on old field sites compared to medium field sites and the highest among the management types investigated. Total seedling abundance was second highest with a mean of 37,5 ± 29,3 (SE) seedlings per field site. Important regeneration species were: Coprosma spp., Pittosporum spp, Geniostoma rupestre and Melicytus ramiflorus. Many seedlings on field sites were presumably offspring from trees and shrubs within the plot (Tab. 4).
Regenrated field sites: Seedling species richness was third lowest with a total of eight species (Tab. 4). Total seedling abundance was the highest within investigated management categories with a mean of 96,5 ± 36,5 (SE) seedlings per field site. Most seedlings were presumably offspring of trees and shrubs within plots. Important species were: Hedycarya arborea, Geniostoma rupestre, Coprosma grandulifolia and Melicytus ramiflorus. Some seedlings established without a propagule source within the plot.
Table 4: (Next page) Mean ± SE seedling numbers are shown for all management categories: U = unfenced, F = fenced, M = medium, O = old, R = regenerated. S = seedling categories with 1 = 16-45cm, 2 = 45-135cm and 3 = >135cm but less than 3 cm diameter at breast height. D = Dispersal; with * = propagule source within plot, x = no propagule source within plot, ? = unclear whether propagules could potentially come from within plot boundaries or not, P = seedling was presumably planted.
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Family Species S U±SE D F±SE D M±SE D O±SE D R±SE D
Araliaceae Pseudopanax arboreus 1 0 0 0,3 ± 0,3 P 0 0 Schefflera digitata 1 0 0 0 0,3 ± 0,3? 2,3 ± 1,3 * 2 0 0 0 0,5 ± 0,6x 7,3 ± 5,3 * 3 0 0 0 0 5,3 ± 3.5 * Asteraceae Brachyglottis repanda 1 0 0 0 0,3 ± 0,3 x 0,3 ± 0,3x 2 0 0 0 1,8 ± 2,0x 0 3 0 0 0 0,3 ± 0,3 x 0,3 ± 0,3x Olearia paniculata 2 0 0 0,3 ± 0,3 P 0 0 3 0 0 0,5 ± 0,6 P 0 0 Coriariaceae Coriaria arborea 2 0 0 0 0,5 ± 0,6x 0 Cornaceae Corokia macrocarpa 1 0 0 0 0 0 Loganiaceae Geniostoma rupestre 1 0 0 0 3,0 ± 3,5? 2,8 ±2,4*x 2 0 0 0 3,8 ± 4,3? 4,5 ± 4,1* 3 0 0 0 0,8 ± 0,9? 1,0 ± 1,2x Malvaceae Hoheria populnea 2 0 0 0,3 ± 0,3 P 0 0 3 0 0 0,8 ± 0,9 P 0 0 Hoheria sexstylosa 2 0 0,8± 1,2 P 0 0 0 Plagianthus regius 1 0 0 0 0 0,5 ± 0,6x 2 0 0,2 ± 0,3 P 0 0 1,8 ± 1,2x 3 0 0 0 0 0,8 ± 0,6x Monimiaceae Hedycarya arborea 1 0 0 0 0 9,8 ± 9,1* 2 0 0 0 0 10,0 ± 7,2* 3 0 0 0 0 2,5 ±2,9* Myrtaceae Aristotelia serrata 2 0 0 0 0,3 ± 0,3* 0 3 0 0 0 0,3 ± 0,3* 0 Arecaceae Rhopalostylis sapida 1 0 0 0 0,3 ± 0,3x 0,3 ±0,3x Fabaceae Sophora microphylla 3 0 0 0,3 ± 0,3 P 0,3 ± 0,3P 0 Pittosporaceae Pittosporum crassifolium 2 0 0 0 0,8 ± 0,9* 0 Pittosporum eugenioides 1 0 1,2 ± 1,7 P 0 3,5 ± 3,0* 0 2 0 0 0 2,5 ± 2,9* 0 Pittosporum tenuifolium 1 0 0,2 ± 0,3 P 0 0,3 ± 0,3* 0 2 0 0 0,6 ± 0,6* 0,8 ± 0,9* 0 Podocarpaceae Podocarpus totara n.a. 0 0 0 0,3 ± 0,3 P 0 Rubiaceae Coprosma grandifolia 1 0 0 0 3,0 ± 2,7* 8,0 ± 5,1* 2 0 0,2 ± 0,3 0 3,8 ± 4,3* 8,0 ± 3,2* 3 0 0 0 0,8 ± 0,6* 17,0 ± 9,8* Coprosma robusta 1 0 0 0 1,8 ± 1,4*x 0 2 0 0 0,5 ± 0,3 P 0,5 ± 0,4 * 0 3 0 0 0 0,3 ± 0,3 * 0 Coprosma repens 3 0 0 0 0,3 ± 0,3 * 0 Scrophulariaceae Hebe salicifolia 3 0 0 0 0,8 ± 0,9P 0 Hebe stricta 1 0 0 0,3 ± 0,3P 0 0 3 0 0 0,8 ± 0,9P 0 0 Solanaceae Solanum aviculare 1 0 0 0 0,3 ± 0,3 ? 0 3 0 0 0 0,3 ± 0,3 ? 0 Violaceae Melicytus ramiflorus 1 0 0 0 2,0 ± 2,3* 5,8 ± 6,6* 2 0 0 0 3,0 ± 2,4* 6,8 ± 7,4* 3 0 0 0 0,8 ± 0,6* 2,0 ± 1,6* Sum of species per management category 0 5 7 17 8
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Riparian management in Taranaki – A success for native biodiversity?
4.2.5 VEGETATION STRUCTURE
4.2.5.1 Vegetation height
Vegetation heights for all management regimes were tested against each other (univariate ANOVA and Tukey b post hoc test with df = 4; F = 191,069 and p < 0,001). Medium field site vegetation height was intermediate compared to vegetation height for fenced and old field sites. Vegetation height was significantly higher on old field sites compared to all other field sites with the exception of regenerated field sites which showed the highest overall vegetation height (Fig. 15).
Figure 15: Vegetation height in metres is shown for all management categories (U = unfenced, F = fenced; M = medium, O = old; R = regenerated; n = 120). Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4; F = 191,069 and p < 0,001).
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4.2.5.2 Ground cover
Ground cover plant group composition showed a trend towards diversification with succession age, represented by management categories.
Percentages for abiotics and litter recorded for unfenced and fenced field sites are similar (Fig. 16). Abiotics and litter groundcover was lower compared to unfenced and fenced field sites on medium field sites. For old field sites the cover percentage of abiotics and litter was more than twofold higher than for medium field sites. Highest percentages for abiotics and litter were recorded for regenerated field sites.
Alien OA (this group includes all alien herbaceous plants other than monocotyl bulbs) showed lower cover percentages from unfenced to regenerated sites (Fig. 16).
Alien grasses/sedges/reeds were most abundant on field sites in the following order: Fenced > unfenced > medium > old > regenerated. Thereby noticeable is the more than six fold lower percentage of cover for regenerated field sites compared to old field sites (Fig. 16).
Alien vine ground cover showed a maximum for medium field sites closely followed by old field sites (Fig. 16).
Native grasses/sedges/reeds/flax cover was not recorded on unfenced, fenced and regenerated field sites. However, ground cover for native grasses/sedges/reeds/flax peaked on medium field sites and was lower on old field sites compared to medium field sites (Fig. 16).
Alien woody plant (alien trees and shrubs and planted alien trees and shrubs) species cover was lower on old field sites compared to regenerated field sites (Fig. 16).
Native woody species ground cover increased on field sites with field site age: medium > old > regenerated (Fig.16). Thereby planted native trees and shrubs ground cover decreased on field sites with field site age: fenced (see methods) > medium > old.
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Riparian management in Taranaki – A success for native biodiversity?
100% Native planted trees and shrubs Native trees and shrubs 90% Native seedlings
80% Native vines
Planted native 70% sedges/reeds/flax Native grasses/sedges/reed/flax 60% Native OA
50% Native ferns Alien vines
40% Alien seedlings Ground cover Ground 30% Alien planted BAN int Alien trees and shrubs
20% Alien grasses/sedges/reeds 10% Alien Monocot bulbs Alien OA 0% Alien moss (SELkra)
U F M O R Mosses/Lichens/Liverworts
Management Alien root/stem
Figure 16: Mean ground cover values for all functional plant groups are displayed for all management categories. U = unfenced (n = 120); F = fenced (n = 120); M = medium (n = 210); O = old (n = 240); R = regenerated (n = 240). Native planted trees and shrubs = all native trees and shrubs which are clear to have been planted; Native seedlings = seedlings of native trees and shrubs; native vines = native vine species including juvenile forms of rata; Planted native sedges/grasses/reed/flax: all native sedges, grasses, reed and flax which have been subject to planting (mainly Carex secta and Phormium tenax); Native OA = native herbaceous plants; Native ferns = ground cover of all native ferns, including tree ferns; alien seedlings = groundcover of all alien shrub or tree seedlings; alien planted BAN int (Banksia integrifolia) = the only alien species which was recorded as ground cover; alien trees and shrubs = all alien trees and shrubs which have naturally invaded the riparian margin; Alien sedges/grasses/reeds = all alien sedges, rushes and reeds,; Alien monocaot bulbs = montbretia (Crocosmia x crocosmiflora); Alien OA = alien herbaceous plants; Alien moss (SEL kra) = only selginella (Selginella krausiana) was recorded as alien moss on riparian margins; Planted rootstem = roots and/or stems of clearly planted native shrubs and trees; abiotics and litter = rocks and natural debris.
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4 Results
Number of groups
The trend of diversification notable in Fig. 16 is supported in Figure 17, where the number of recorded ground cover groups is shown for all management categories. The number of groups hereby was higher from unfenced to old field sites, where they reached their maximum. A lower number of groups could be observed for regenerated field sites compared to old field sites (Fig. 17).
Figure 17: Number of groups are shown for ground cover groups (from Fig. 15) in dependence of management categories (U = unfenced, n = 120, F = fenced, n = 120, M = medium, n = 210, O = Old, n = 240 and R = regenerated, n= 240).
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Riparian management in Taranaki – A success for native biodiversity?
Comparison of alien plants, native plants and litter
No significant differences for cumulative alien plant, native plant and litter ground cover were found between unfenced and fenced field sites (univariate ANOVA and Tukey b post hoc test with df = 4; F = 108,638 and p < 0,001 for alien plant cover; df = 4, F = 86,020 and p < 0,001 for native plant cover; df = 4, F = 116,935 and p < 0,001 for abiotics and litter). A significant lower percentage of cumulative alien plant ground cover was found for medium field sites and even lower values for old sites could be proven (Fig. 18). Regenerated field sites had the lowest alien plant cover.
Unfenced and fenced field sites showed the lowest native cumulative plant cover (Fig. 18). Medium field sites showed significantly higher native plant cover compared to old field sites, but a lower coverage than regenerated sites (Fig. 18). No differences could be validated for unfenced, fenced and medium sites for abiotics and litter, although a slightly lower cover of abiotics and litter is visible for medium field sites (Fig. 18). Old field sites on the contrary showed a more than twofold higher cover percentage for abiotics and litter compared to medium field sites (Fig. 18). The highest cover for abiotics and litter was found on regenerated field sites. Alien ground cover decreased steadily with field site age. Native plant ground cover was only higher than alien cover on regenerated field sites.
Figure 18: Cumulative values for alien plant, native plant ground cover and for abiotics and litter are shown for all management categories (U = unfenced, F = fenced, M = medium, O = old, R = regenerated; n = 120). Letters indicate statistical differences (univariate ANOVA and Tukey B post hoc test with df = 4, F = 108,683 and p < 0,001 for alien plant cover; df = 4, F = 86,020 and p < 0,001 for native plant cover and df = 4, F = 116,935 and p < 0,001).
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Vine and fern ground cover
Vines No significant differences for alien vine ground cover were found on unfenced and fenced field sites, although a marginal absolute higher value is evident for fenced field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 26,046 and p < 0,001). Alien vine ground cover peaked on medium and old field sites (Fig. 19). Alien vine ground cover was more than threefold lower on regenerated sites compared to on medium and old field sites. Furthermore, no significant differences could be found between alien vine cover on regenerated field sites compared to unfenced and fenced field sites. Native vines ground cover was not recorded on unfenced, fenced and medium field sites (Fig. 19). Although a very small coverage (below 1%) could be recorded for old field sites, this was not significantly higher than on the younger management categories (univariate ANOVA and Tukey B post hoc test with df = 4, F = 58,304 and p < 0,001). No significant difference could be found on management categories with the exception of regenerated sites, where native vine ground cover peaked (Fig. 19). Alien vine ground cover compared to native vine cover showed a conspicuous higher cover than native vines for all management regimes except for regenerated field sites, where native vine ground cover was higher than alien vine ground cover.
Figure 19: Mean alien and native vine ground cover in percent are shown for all management categories (U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 120). Letters indicate significant differences (univariate ANOVA and Tukey B post hoc test with df = 4, F = 26,046 and p < 0,001 for alien vines and df = 4, F = 58,304 and p < 0,001).
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Riparian management in Taranaki – A success for native biodiversity?
Ferns Data showed small percentages (below 1%) for unfenced, fenced and medium field sites (Fig. 19). Although medium field site fern ground cover is marginal higher than on unfenced and fenced field sites (Fig. 20), no significant differences were found (univariate ANOVA and Tukey b post hoc test with df = 4, F = 91,281 and p < 0,001). Old field sites showed a significant higher fern ground cover compared to unfenced, fenced and medium field sites (Fig. 20). However, old field site fern ground cover remained significantly lower compared to fern ground cover for regenerated sites (Fig. 20).
Figure 20: Mean native fern ground cover values (%) are shown for all management categories (U = unfenced, F = fenced, M = medium, O = old, and R = regenerated. N = 120). Whiskers indicate ± SE. Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4, F = 91,281 and p < 0,001).
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4.2.5.3 Midview cover
Midview cover showed a trend towards diversification with increasing field site vegetation age (Fig. 21). However, total cover was below 1% for unfenced field sites and was marginally higher for fenced field sites. A peak for midview cover was found for medium field sites, where the dominating plant group consisted of native grasses/sedges/reeds/flax (Fig. 21).
Native grasses/sedges/reeds/flax midview cover was lower on old field sites compared to medium field sites and no cover was recorded on regenerated field sites. Alien grass midview cover was low on unfenced field sites compared to fenced field sites (Fig. 21) and was lower for the other management categories: medium > old > regenerated.
Although lower overall plant coverage was recorded for old field sites compared to medium field sites, the number of plant groups was higher compared to all other management categories. Old field sites also showed the largest number of alien shrubs and trees. Native woody species cover (planted and native trees and shrubs) was lower on medium than on old field sites. Native vine and fern midview cover was highest on regenerated field sites (Fig. 21).
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Riparian management in Taranaki – A success for native biodiversity?
18 Planted native trees
16 Planted BAN int Native planted sedges/rushes/reed 14 Native shrubs and trees
12 Native OA Native vines 10 Alien shrubs and trees 8 Alien vines Cover in % Native sedges/rushes/reed 6 Alien grasses
4 Alien bulbs
Alien OA 2 Ferns
0 Moss/Lichen/Liverworts
UFMOR Root/stem live
Management Abiotics/litter
Figure 21: Mean midview cover estimates (%) for semi-botanical-functional plant groups on all management categories. Planted native trees = all native trees clearly planted, Planted BAN int = Banksia integrifolia - the only alien planted tree recorded, Native planted sedges/rushes/reeds = all clearly planted native sedges/rushes and reeds, additionally flax (Phormium tenax) is also part of this functional group, Native OA = native herbaceous plants, Ferns = native ferns, Root/stem live = all roots or stems, Abiotics/litter = rocks and litter. U = unfenced, F = fenced, M = medium, O = old and R = regenerated.
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Number of groups
The trend of diversification notable in Figure 21 was also supported by Figure 22, where the number of recorded midview cover groups is shown for all management categories. The number of groups was hereby higher from unfenced to old field sites, where they reached their maximum. A lower number of ground cover groups could be observed for regenerated field sites compared to old field sites (Fig. 22).
Figure 22: Number of midview cover groups (which were shown in Figure 20) for all management categories: U = unfenced, n = 120; F = fenced, n = 120; M = medium, n = 210; O = old, n = 240 and R = regenerated, n = 240.
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Riparian management in Taranaki – A success for native biodiversity?
Comparison of alien plants, native plants and abiotics and litter
Cumulative values for alien plants, native plants, abiotics and litter and were tested for differences between management regimes (univariate ANOVA and Tukey b post hoc test with df = 4, F = 8,920 p < 0,001 for alien plants; df = 4, F = 54,973 and p < 0,001 for native plants and df = 4, F = 2,702 and p = 0,30 for abiotics and litter). No significant differences in native midview cover were found for unfenced and fenced field sites (Fig. 23). However, medium, old and regenerated field sites showed significantly higher cover values for native vegetation compared to unfenced and fenced field sites. Although differences between medium, old and regenerated sites for native plant midview cover were not significant, the largest midview cover for native plants was found on medium field sites. Alien plant midview cover was lowest for unfenced sites and second lowest for medium field sites (Fig. 23). Significantly lower values for alien plant midview cover were recorded on regenerated sites compared to old field sites, where alien plant cover peaked. Abiotics and litter cover showed a maximum for regenerated sites (Fig. 23). No significant differences for abiotics and litter cover were found between unfenced and medium field sites and between fenced and old field sites. However, regenerated field sites showed the significantly highest values for abiotics and litter midview cover. Native cover was higher than alien cover on medium, old and regenerated sites (Fig. 23).
Figure 23: Cumulative values (%) of alien and native plant cover and abiotics and litter for all management categories (U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 120). Letters indicate statistical differences (univariate ANOVA with Tukey B post hoc test with df = 4, F = 8,920 and p < 0,001 for alien plants; df = 4, F = 54,973 for native plants and df = 4, F = 2,702 and p = 0,30 for abiotics and litter).
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Vine and fern midview cover
Vines Alien vine cover values were marginal higher for fenced field sites compared to unfenced field sites (Fig. 24). Thus no significant difference was found (univariate ANOVA and Tukey b post hoc test with df = 4, F = 4,756 and p = 0,001 for alien vines and df = 4, F = 18,481 and p < 0,001 for native vines). Alien vine midview cover of regenerated field sites was intermediate as compared to medium and old field sites, which showed the highest alien vine cover. Unfenced and fenced field sites showed the lowest values recorded for alien vine cover (Fig. 24).
No native vine species were recorded on unfenced, fenced and medium field sites (Fig. 24). Although old field sites had higher mean native vine midview cover values (hence still remaining under 0,5%) the difference to unfenced and fenced field sites was not significant. Regenerated field sites formed the only management category with a significant higher native vine cover compared to all other management categories.
The proportion of native vines to alien vines was only higher for native vines on regenerated field sites (Fig. 24).
Figure 24: Mean alien and native vine midview (1,35m) cover in percent for all management categories (U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 120). Whiskers show ± SE. Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4, F = 4,756 and p = 0,001 for alien vines and df = 4, F = 18,481 and p < 0,001).
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Riparian management in Taranaki – A success for native biodiversity?
Ferns
No midview fern cover was found on unfenced, fenced and medium field sites (Fig. 25). Old field sites showed a significantly higher percentage of fern cover compared to unfenced, fenced and medium field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 30,811 and p < 0,001). Regenerated midview fern cover was significantly higher compared with fern cover for all other management categories (Fig. 25).
Figure 25: Native midview fern cover (%) is shown for all management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 120 per management category. Whiskers show ± SE. Letters indicate significant differences (univariate ANOVA and Tukey B post hoc test with df = 4, F = 30,811 and p < 0,001).
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4.2.5.4 Cover above two metres height
Mean cover values for plant species cover above two metres height showed a clear increase of native plant cover (including native planted) with field site age (Fig. 26). No cover above two metres height was recorded for unfenced and fenced field sites (Fig. 26). Exclusively planted species cover was recorded as occurring vegetation cover for medium field sites while for old field sites native, native planted, alien planted and alien plant cover were recorded. Overall, cover values were highest for regenerated sites, which also showed the highest value for native plant species cover and a lower alien plant species cover as compared to old field sites (Fig. 26).
Sky Native species Planted native species Alien species Alien planted 100 80 60 40
Cover in % in Cover 20 0 UFMOR Management
Figure 26: Mean cover values (%) above two metres height for all management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated. Sky = percentage not covered by plant growth, Planted native species = all clearly planted native species, Alien planted = all clearly planted alien species, Native species = all native species and Alien species = all alien species.
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Riparian management in Taranaki – A success for native biodiversity?
4.2.5.5 Vegetation assigned to tiers
No cover above two metres height was recorded on unfenced and fenced field sites. Therefore all values for all investigated parameters (Tab. 5) are consequently zero for these two management categories.
Medium field sites were the youngest field sites with tiers above two metres present: A mean of 0,2 ± 0,03 (SE) tiers above two metres height was recorded with three species present and a maximum total of two tiers. Old field sites had a mean number of 1,1 ± 0,1 (SE) tiers recorded. Regenerated field sites had the highest overall number of tiers above two metres height with a maximum of four tiers and mean of 1,8 ± 0,1 (SE) tiers recorded (Tab. 5).
Old field sites had a higher species number for top tier and first tier species than regenerated sites. Mean alien and native vine species richness above two metres height was higher on old field sites compared to regenerated sites (Tab. 5). However, the probability for alien vine occurrence showed higher values for old field sites compared to regenerated field sites and vice versa for the probability of occurrence of native vine species.
Epiphytic fern species above two metres height were only recorded for regenerated field sites with a frequency of 38 out of 240 vegetation census points (Tab. 5). Ferns above two metres height were recorded for three out of four regenerated field sites. Only on regenerated field sites other epiphytes than ferns were present with a mean species number of 0,3 ± 0,3 (SE) .
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Table 5: Vegetation cover above two metres height is described for all management categories: U= unfenced (n = 120), F = fenced (n = 120), M = medium (n = 210), O = old (n = 240) and R = regenerated (n = 240).
Management: U F M O R
Number of tiers 0 0 0,2 ± 0,03 1,1 ± 0,1 1,8 ± 0,1 above 2m (mean±SE)
Number of species in 0 0 3,0 ± 0,7 7 ,0 ± 0, 8 5,3 ± 1,4 toptier above 2m (mean ± SE)
Number of species in 0 0 0,3 ± 0,3 6,3 ± 3,3 5,0 ± 0,8 1st tier above 2m (mean ± SE)
Number of species 0 0 0 3,5 ± 2,3 5,6 ± 0,9 in 2nd tier above 2m (mean ± SE)
Number of species 0 0 0 0 0,3 ± 0,3 in 3rd tier above 2m (mean ± SE)
Alien vine species 0 0 0 0,8 ± 0,3 0,5 ± 0,3 per site >2m (mean ± SE)
Native vine species per 0 0 0 3,3 ± 0,6 1,0 ± 0,7 site >2m (mean ±SE) _ _
Probability of occurrence 0 0 0 0,75 0,5 for alien vines >2m (ratio of sites)
Probability of occurrence 0 0 0 0,75 1 for native vines >2m (ratio of sites) _ _
Epiphytic fern species >2m 0 0 0 0 1,3 ± 0,6 (mean ± SE)
Fern frequency within 0/120 0/120 0/210 0/240 38/240 transects (occurrence/number of quadrates) _ _
Probability of fern occurrence 0 0 0 0 0,75 (ratio of sites)
Other epiphyte-species/site 0 0 0 0 0,3 ± 0.3 > 2m (mean ± SE)
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Riparian management in Taranaki – A success for native biodiversity?
4.2.5.6 Top tier plant groups
Unfenced field sites were dominated by the occurrence of alien grasses as top tier species (species with highest growth), followed by herbaceous alien plants (AOA), bare Soil, alien sedges/rushes/reeds and a small proportion of litter (Fig. 27).
Fenced field sites had a slightly higher occurrence of alien grasses as top tier compared to unfenced field sites and a higher number of different plant groups was recorded i.e., AOA, litter, alien trees and shrubs, native trees and shrubs and alien vines (Fig. 27).
Medium field sites top tier plant groups were dominated by alien grasses and flax (Phormium tenax) (Fig. 27). Native trees and shrubs, native sedges/rushes/reeds, AOA, and alien vines also occurred along with a small percentage of alien shrubs and trees as top tier for medium sites.
Old sites had a higher proportion of native trees and shrubs for the top tier than medium field sites but less than regenerated sites (Fig. 27). Top tier occurrence of alien grasses on old field sites was besides its occurrence on regenerated sites the lowest recorded. Alien shrubs and trees however, showed a maximum as top tier plant group on old field sites (Fig. 27). Flax (Phormium tenax) as top tier for old sites was more than three times less often recorded compared to medium field sites. Besides alien vines, AOA, and hFlax (hybrid Phormium tenax) ferns were also recorded for old field sites as a top tier plant group. Ferns only occurred on old and regenerated sites; on the latter they had their highest occurrence out of all management categories.
Native trees and shrubs formed more than three quarters of all top tier plant groups recorded at regenerated field sites. Ferns were more than four times more often represented in the top tier on regenerated field sites than on old field sites. Alien trees and shrubs were slightly less often represented in the top tier of regenerated field sites compared to old field sites (Fig. 27).
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Figure 27: Top tier plant groups and abiotic in proportion to each other for all management categories. U = unfenced, n = 120; F = fenced, n = 120; M = medium, n = 210; O = old, n = 240 and R = regenerated, n = 240. AOA = alien herbaceous plants, Roots/stems = roots and stems of all trees and shrubs recorded, Native sedges/rushes/reeds = all native sedges/rushes/reeds, including planted specimens; Flax = Phormium tenax; hFlax = hybrids of Phormium tenax; Rock = pebbles and rocks and Ferns = native ferns.
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Riparian management in Taranaki – A success for native biodiversity?
4.2.5.7 Characterization of vegetation
Unfenced field sites: Vegetation height was lowest for this management category with a mean of 0,33m ± 0,04 (SE). Vegetation was dominated by alien grasses. Alien herbaceous plants formed the second largest group represented in vegetation composition with ca. 25%. Bare soil was represented with an average value of 5% was also apparent (Plate 2).
Fenced field sites: Vegetation was with a mean of 0,64cm ± 0,04 (SE) higher compared to unfenced field sites. 75% alien grasses and 25% herbaceous plants were the recorded species (Plate 2).
Medium field sites: Vegetation height ranged between 10cm and 3,30m, with a mean of 1,40m ± 0,06 (SE) (Plate 2). Ca. 32% of the top tier vegetation consisted of flax (Phormium tenax). Other important species and plant groups were: Alien grasses (ca.30%), native Cortaderia spp. (ca 7%), alien vines (ca. 5%), akirahu (Olearia paniculata) (ca. 9%) and other native trees (ca. 9%). The remaining top tier vegetation consisted of alien herbaceous plants. In 1,4% of all vegetation census points a second tier existed (mostly Phormium tenax) (Plate 2).
Old field sites: Vegetation height ranged between zero cm and 16m, with a mean height of 4,33 m ± 0,23 (SE) (Plate). Top tier main components were: Alien grasses (ca.12%), holly (Ilex aquifolium) (10%), flax (Phormium tenax) (7%), Salix spp. (ca. 10%), native trees (ca. 32%), other alien trees (20%) and the rest mainly of natives sedges and ferns (Plate 2). A second tier was recorded for 35% of vegetation mapping points, mainly consisting of: kanono (Coprosma grandifolia), mahoe (Melicytus ramiflorus), akirahu (Olearia paniculata), lemonwood (Pittosporum eugenoides) and around 1% alien trees. A third tier was recorded for 10.8% of vegetation census points; mainly consisting of barberry (Berberis glaucarpa), wheki (Dicksonia squarrosa), hangehange (Geniostama rupestre) and akirahu (Olearia paniculata). Important ground species and components were: Alien grasses, litter, blackberry (Rubus fruticosus agg.), wandering willie (Tradescantia fluminensis), native ferns, flax (Phormium tenax) and native Cortaderia spp. (Plate 2).
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Regenerated field sites: Vegetation height ranged between 0,75m-12m, with a mean of 6,00m ± 0,18 (SE). Top tier consisted of: wineberry (Aristotelia serrata) (6.2%), kanono (Coprosma grandifolia) (5%), mamaku (Cyathea medullaris) (8.3%), mahoe (Melicytus ramiflorus) (50.6%), pate (Schefflera digitata) (12%), alien trees (ca.2%) and the rest native trees. A second tier was present for 62% of vegetation census points and consisted mainly of: barberry (Berberis glaucarpa), kanono (Corprosma grandifolia), mahoe (Melicytus ramiflorus), pate (Schefflera digitata) and other native trees and shrubs (Plate 2).
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Riparian management in Taranaki – A success for nativenati biodiversity?
Plate 2: Schematic drawing of vegegetation structures of management categories. ’Unfenceded’ diagram: AG = alien grasses, AOA = alien herbaceoeous plants, S = bare soil. ‘Fenced’ diagram: AG = alienen grasses, AOA = alien herbaceous plants. Medium diagram:di OLE pan = Olearia paniculat, PHO ten = Phorormium tenax; NT = native trees and shrubs, nCORTT spp = native Cortaderia spp. ‘Old’ diagram: 1 = Eucacalyptus spp., 2 = Salix spp., 3 = Melicytus ramiflorurus, 4 = native tree, 5 = Tradescantia fluminensis (groground), 6 = alien grasses, 7 = Dicksonia squarrosa, 8 = Olearia paniculata, 9 = Rubus fruticosus agg., 110 = Pittosporum tenuifolium, 11 = native ferns, 12 = Melicytus ramiflorus, 13 = alien herbaceous plants;; 141 = Phormium tenax and native Cortaderia spp.. ‘R‘Regenerated’ diagram: 1 = Cyathea medullaris, 2 = Schehefflera digitata, 3 = Melicytus ramiflorus, 4 = Copoprosma grandifolia, 5 = native vine, 6 = Melicytuss ramiflorus, 7 = Aristotelia serrata, 8 = alien herbacbaceous plants, 9 = native ground fern, 10 = Geniostomama rupestre, 11 = alien tree, 12 = Dicksonia squarrosasa, 13 = Melicytus ramiflorus.
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4.3 AVIFAUNA
4.3.1 SPECIES RICHNESS
Alien birds
Alien bird species richness ranged from one to nine species per field site out of nine families with a total of eleven alien species recorded (Tab. 6), i.e. Australian magpie (Gymnorhina tibicen), blackbird (Turdus merula), chaffinch (Fringilla coelebs), dunnock (Prunella modularis), goldfinch (Carduelis carduelis), greenfinch (Carduelis chloris), house sparrow (Passer domesticus), skylark (Alauda arvensis), song thrush (Turdus philomelos), starling (Sturnus vulgaris), and yellowhammer (Emberiza citrinella). Alien bird species richness was significant lowest on unfenced field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 3,766 and p = 0,026). Fenced, medium and regenerated sites were intermediate as compared to unfenced and old field sites concerning species richness (Fig. 28). Old field sites showed the significant highest alien bird species numbers (Fig. 28).
Figure 28 and 29: Alien (left chart) and native (right chart) bird species richness for all management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 4. Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4, F = 3,766 and p = 0,026 for alien species and df = 4, F = 4,025 and p = 0,02 for native species).
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Riparian management in Taranaki – A success for native biodiversity?
Native birds
Native species richness, out of nine families (Table 6), ranged between zero and nine species recorded on field sites (Fig. 29) i.e. Australasian harrier (Circus approximans), fantail (Rhipidura fuliginosa), grey warbler (Gerygone igata), kingfisher (Halcyon sancta), pipit (Anthus novaeseelandiae), pukeko (Porphyrio porphyrio), tomtit (Petroica macrocephala), waxeye (Zosterops lateralis), and welcome swallow (Hirundo tahitica). Native bird species richness was significantly highest on old field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 4,025 and p = 0,02). Regenerated fields site were intermediate as compared to the other management categories (Fig. 29). No significant differences were found in native species richness between unfenced, fenced and medium field sites, which showed the lowest native bird species richness compared to the other management categories (Fig. 29).
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Table 6: Conservation status and native plant dispersal ability for bird species recorded on riparian margins according to Heather and Roberston (2005) and Clout and Hay (1989).
Family Scientific name common name conservation dispersal
Alien
FRINGILLIDAE Carduelis carduelis goldfinch / more seed predator than disperser
Fringilla coelebs chaffinch / more seed predator than disperser Carduelis chloris greenfinch / considered minor pest more seed predator than disperser
ALAUDIDAE Alauda arvensis skylark / eat mainly adventives, seed predators
EMBERIZIDAE Emberiza citrinella yellowhammer / n.a.
MUSCICAPIDAE Turdus philomelos song thrush / spread weeds spread some native species
PRUNELLIDAE Prunella modularis dunnock / n.a.
MUSCICAPIDAE Turdus merula blackbird / spread weeds able to spread relatively large seeds
PLOCEIDAE Passer domesticus house sparrow / regarded as pest n.a., mostly seed predators
STURNIDAE Sturnus vulgaris starling / can cause (some natives) damage fruit orchards CRACTICIDAE Gymnorhina tibicen magpie / n.a.
Native
ALCEDINIDAE Halcyon sancta kingfisher protected n.a.
ACCIPITRIDAE Circus approximans harrier protected only carnivorous
MONARCHIDAE Rhipidura fuliginosa fantail protected (some natives)
HIRUNDINIDAE Hirundo tahitica welcome swallow protected only carnivorous
RALLIDAE Porphyrio porphyrio pukeko partially protected n.a.
MOTACILLIDAE Anthus novaeseelandiae pipit protected n.a.
ACANTHIZIDAE Gerygone igata grey warbler protected endemic (some natives)
EOPSALTRIIDAE Petroica macrocephala tomtit protected endemic n.a.
ZOSTEROPIDAE Zosterops lateralis waxeye partially protected important for small seeds
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Riparian management in Taranaki – A success for native biodiversity?
4.3.2 ALIEN BIRD RELATIVE ABUNDANCE
Relative bird abundance was lowest for unfenced and fenced field sites (Fig. 30). Relative bird species abundance then was lower for medium field sites < old field sites < regenerated field sites.
Starling (Sturnus vulgaris) relative abundances were not included in the chart since very high numbers recorded on one medium (55,55 starlings per ha) and on one old field sites (77,04 per ha) were clearly linked to supplementary cow feeding at the time of recording. Starlings were only recorded on medium and old field sites and their relative abundance ranged from zero to 0,55 starlings per ha on the remaining three medium field sites and from zero to 1,82 starlings on the remaining three old field sites (Fig. 30).
House sparrows (Passer domesticus) showed similar high relative abundances for medium and old field sites but were lowest on regenerated field sites. House sparrow relative abundance was slightly higher on unfenced field sites and lower on fenced field sites compared to old and medium field sites (Fig. 30). Relative abundance for chaffinches (Fringilla coelebs) was highest on medium field sites compared to old and regenerated field sites (Fig. 30). Chaffinch relative abundance was lower on regenerated field sites compared to old field sites. Thrushes (Turdus philomelus) were most abundant on old field sites followed by medium field sites. Lowest relative abundance for thrushes was recorded on unfenced, fenced and regenerated field sites (Fig. 30). Relative abundances for fantail (Rhipidura fuliginosa), grey warbler (Gerygone igata), and waxeyes (Zosterops lateralis) increased with field site age (Fig. 30).
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Figure 30: Relative bird abundance per ha for management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated; n = 12. *indicate alien bird species.
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Riparian management in Taranaki – A success for native biodiversity?
Comparison of alien and native bird relative abundance
Alien bird relative abundance was significantly lowest on unfenced and fenced field sites and peaked on old field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 3,596, p = 0,011). Relative alien bird abundance was intermediate on medium and regenerated field site compared to all other management categories (Fig. 31).
Native bird relative abundance was significantly lowest on unfenced and fenced field sites (univariate ANOVA and Tukey b post hoc test with df = 4, F = 33,309 and p < 0,001). No significant difference could be found between medium and old field sites although relative native bird abundance is visibly higher for old field sites (Fig. 31). However, relative native bird abundance was significantly higher on both management categories compared to unfenced and fenced field sites. The significantly highest native bird relative abundance was recorded on regenerated field sites.
Alien relative bird abundance decreased with field site age but remained higher compared to native relative bird abundance for all management categories except for regenerated field sites, where it was almost threefold higher with a mean value of 15,05 native birds per ha ± 1,69 (SE) compared to 5,20 ± 1,26 (SE) alien birds per ha (Fig. 31).
Figure 31: Alien and native bird relative abundance per ha for management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated, (n = 12). Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test with df = 4, F = 3,596 and p = 0,11 for alien birds and df = 4, F = 33,309 and p < 0,001 for native birds).
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Comparison of single bird species relative abundances
Only chaffinches (Fringilla coelebs), thrushes (Turdus philomelus) as alien species and fantails (Rhipidura fuliginosa), grey warblers (Gerygone igata) and waxeyes (Zosterops lateralis) as native species met the requirements for univariate ANOVAs and thus showed significant differences for management categories (Tab. 7)
No significant differences for chaffinches were found between unfenced and fenced field sites. Chaffinch relative abundance peaked on medium field sites and was lower for old field sites compared to regenerated field sites. No significant differences were found for thrush relative abundance between unfenced, fenced and regenerated field sites. Thrush relative abundance was highest on old field sites and intermediate on medium field sites compared to all other management categories (Tab. 7).
Grey warbler and fantail relative abundance showed both no significant differences for unfenced, fenced and medium field sites (Tab. 7). Relative abundance was higher on old field sites and peaked on regenerated field sites. Waxeye relative abundance was lowest on unfenced and fenced field sites and no significant differences were found between these two management categories. Relative abundance for waxeyes was second highest on medium and old field sites and showed a significant peak for regenerated field sites.
Table 7: Comparison of single bird species relative abundances for management categories: U = unfenced, F = fenced, M = medium, O = old and R = regenerated (with n = 12). Letters indicate significant differences (univariate ANOVA and Tukey b post hoc test). *= alien bird species.
Species common name U F M O R df F p-value
Gerygone igata grey warbler a a a b c 4 15,765 <0,001 Fringilla coelebs* chaffinch a a c bc ab 4 8,651 < 0,001 Rhipidura fuliginosa fantail a a a b c 4 30,440 <0,001 Turdus philomelos* thrush a a ab b a 4 3,287 0,017 Zosterops lateralis waxeye a a b b c 4 33,699 <0,001
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Riparian management in Taranaki – A success for native biodiversity?
4.4 VEGETATION AND AVIFAUNA
4.4.1 THE INFLUENCE OF VEGETATION ON BIRD SPECIES RICHNESS
Alien bird species richness
Alien bird species richness was higher with denser shrubs and tree cover at midview (1,35m height), vegetation height, and vegetation cover above 2m (Tab. 8). A negative influence of alien OA (alien herbs) (coefficient = -0,029, SE = 0,021, T = 5,262 and p= 0,063) is apparent for alien bird species richness. Results were obtained by performing multiple linear regressions with backward elimination. Thereby, the following variables were eliminated (with α = 0,05): Midview (vegetation cover at 1,35m), alien grasses, number of tiers, plant species richness.
Table 8: Vegetation variables with a significant influence on alien bird species richness. Results obtained by multiple linear regressions with backward elimination of the following variables: midview, shrub and trees (cover at breast height (1,35m), alien grasses, alien OA (alien herbs cover (mostly ground),vegetation height, cover above 2m, number of tiers, plant species richness.
Veg.variables coefficient SE std. coefficient T p
Shrubs and trees 0,109 0,021 0,588 5,262 0,000 Alien OA -0,029 0,015 -0,205 -1,896 0,063 Vegetation height 1,068 0,239 1,489 4,465 0,000 Cover above 2m 0,091 0,018 1,688 4,938 0,000
Native bird species richness
Native bird species richness was higher with denser shrubs and tree cover at midview (1,35m height) and negatively influenced by alien OA (alien herb cover (mostly on the ground)) and alien grasses (cover (mostly on the ground)) (Tab. 9). Results were obtained by performing multiple linear regressions with backward elimination. Thereby the following variables were eliminated (with α = 0,05): Midview (vegetation cover at 1,35m), number of tiers, and plant species richness.
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Table 9: Vegetation variables with a significant influence on native bird species richness. Results were obtained by multiple linear regressions with backward elimination of the following variables: midview, shrub and trees, alien grasses, alien OA (alien herbs), height, cover above 2m, number of tiers, plant species richness.
Veg.variables coefficient SE std. coefficient T p
Alien grasses -0,020 0,006 -0,355 -3,293 0,002 Alien OA -0,028 0,012 -0,252 -2,433 0,018 shrubs and trees 0,046 0,016 0,310 2,775 0,007
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Riparian management in Taranaki – A success for native biodiversity?
4.4.2 THE INFLUENCE OF VEGETATION ON BIRD OCCURRENCES
Cover of alien grasses, alien herbaceous plants, shrubs and trees (regardless whether native or alien) and the number of tiers were identified as vegetation variables with the greatest influence on bird species occurrence and abundance (Monte Carlo permutation test with 499 permutations) (Tab. 10). Other variables tested were: midview cover; species richness, vegetation height and percentage of sky cover (vegetation cover above two metres height). All these variables were non-significant with a p-value > 0,05 and were therefore not included in the Canonical Correspondence Analysis.
Table 10: Vegetation variables with significant results of Monte Carlo permutation test (p < 0,05) for CCA (Canonical Correspondence Analysis). No. of p. = number of permutations used for the performance of Monte Carlo’s permutation test.
Veg. variable No. of p. F-value p-value explains out of 0,756
Tiers 499 10,851 0,002 0,339 Alien grasses 499 2,153 0,050 0,064 Shrubs and trees 499 2,216 0,032 0,066 Alien herbs 499 2,128 0,034 0,062
The results of the Canonical Correspondence Analysis (CCA) on the bird communities at point survey locations are shown as a biplot of the species along the first two axes of the ordination in Fig. (32). The first canonical axis explained 19,8% of variance of the dataset and the second axis 5,5%. The vectors for the species scores and vegetation variables collectively explained 71,8% of the variance in the species-environment relationship on the first axis and 19,9% along the second axis. Therefore both axes explained a total variance of 91,7%. Species-vegetation correlation coefficients were 0,873 for the first and 0,556 for the second axis, which further confirmed the power of the selected variables. Arrow length in Figure 32 indicates both: Importance and variance of the illustrated variable within the ordination diagram (Te Braak, 1986). Waxeyes, grey warblers, fantails and blackbird occurrence was mainly influenced by the occurrence of shrubs and trees and the number of tiers present on riparian margins (CCA).
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The occurrence of house sparrows, welcome swallows and chaffinches was more positively correlated with alien herbs and alien grasses ground cover than with the number of tiers and the cover of shrubs and trees (Fig. 32). For all other bird species vegetation variables only explain marginal tendencies of dependence.
Figure 32: Canonical correspondence analysis ordination diagram for bird species at bird count level. Triangles indicate the scores for the individual bird species as a function of the axes, which represent linear combinations of vegetation variables (AG = alien grasses; AOA = alien herbaceous plants). Arrows indicate the vegetation variables included into the model. Arrow length shows the relative importance of the variable. The direction of each arrow in relation to the axes indicates how well it is correlated with it. Locations of the individual bird species relative to the arrows display the vegetation structure and combination associated with the occurrence of the species.
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Riparian management in Taranaki – A success for native biodiversity?
Correlations between vegetation and single bird species abundances
Alien birds A strong positive correlation was found for the relative abundances of blackbirds with the number of tiers (0,720**) and a modest correlation with the cover of trees and shrubs at midview. Blackbirds were modest negatively correlated with alien grasses and weak negatively correlated with alien herbs (Tab. 11). Chaffinches were the only other alien bird which showed a modest correlation with the vegetation variables tested: A positive modest correlation was found between chaffinches and the cover of trees and shrubs (0,406**). All other correlations between alien bird species were either only weak or not significant (Tab. 11).
Native birds Fantails were found to have a strong positive correlation with tier number (0,853**) and a modest correlation with trees and shrub cover at midview (0,674**). Fantails were modest negatively correlated with alien grasses and alien herbs (Tab. 11). Grey warblers were modest positively correlated with the number of tiers (0,613**) and tree and shrub cover at midview (0,447**). A modest negative correlation was found between grey warblers and alien grasses as well as with alien herbs (Tab. 11). Waxeyes showed a strong positive correlation with the number of tiers (0,821**) as well as with tree and shrub cover at midview (0,725**). All other correlations between native birds and tested vegetation variables were either only weak or not significant (Tab. 11).
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Table 11: Correlations between single bird species and vegetation variables identified in Table (10). Values for correlations are Spearman Rank correlation coefficients; * indicates significant correlations with p < 0,05 and ** indicates very significant correlations with p < 0,001. I = invertebrates; F = fruit, S = seeds, P = plants, N = nectar and V = vertebrates. + = main food source, - = food partly consisting of, Tiers = number of tiers, trees = cover of all trees and shrubs at midview (1,35m height), AG = alien grasses, AOA = alien herbaceous plants (O’Donnell et al., 1994).
Species food foraging tiers trees AG AOA
Alien
blackbird I+F flicking leaves on ground 0,720** 0,665** -0,598** -0,384** chaffinch S, I, F gleaning 0,377** 0,406** n.s. n.s. dunnock I picking on ground n.s. n.s. n.s. n.s. goldfinch S+; I- gleaning n.s. 0,258* n.s. n.s. greenfinch S+; F- gleaning n.s. 0,283* n.s. n.s. house sparrow S+; I-; F-; N- gleaning n.s. n.s. 0,242* n.s. skylark S, P, I gleaning n.s. n.s. n.s. n.s. starling I; F; N- hawking for insects n.s. 0,356** n.s. n.s. thrush I; F picking on ground 0,218* 0,323** n.s. n.s. yellowhammer S, I, F gleaning n.s. n.s. 0,302** n.s.
Native
fantail I hovering/hawking 0,853** 0,674** -0,695** -0,583** grey warbler I gleaning and hovering 0,613** 0,447** -0,545** -0,521** harrier V hovering n.s. n.s. n.s. n.s. kingfisher I+; V swooping n.s. n.s. n.s. -0,226* pipit I picking on ground n.s. n.s. n.s. n.s. pukeko P+; I-; V- picking on ground n.s. 0,306** n.s. n.s. tomtit I gleaning and hovering n.s. n.s. n.s. n.s. waxeye I; F; N- gleaning 0,821** 0,725** -0,612** -0,524** welcome swallow I hawking -0,280* -0,373** 0,242* n.s.
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Riparian management in Taranaki – A success for native biodiversity?
5 DISCUSSION
For all variables investigated, unfenced and fenced field sites showed lowest values for native biodiversity and a significant distinction between these two management categories was in most cases not possible. Native plant species richness increased with field site age, while alien species richness did decrease with the exception of old field sites, where also highest pest plant species richness and abundance were found. A trend in diversification for native vines and ferns and an increase in cover were visible for old field sites compared to younger field sites. Thus regenerated field sites showed the highest diversification. Alien plant species cover was highest for groundcover compared to midview and sky cover, where native species cover dominated. Structural diversification increased with field site age. Bird species richness showed an increase for alien birds with field site age with the exception of regenerated field sites. Native bird species richness however showed no clear dependencies on the management regime. However, overall field site use increased with field site age. Alien bird species hereby dominated compared to native bird species with the exception of regenerated field sites, where native bird relative abundance was higher. Three native bird species increased in their relative abundance with field site age; these were fantails, grey warblers and waxeyes. These birds also corresponded positively to shrub and tree cover and structural vegetation diversity.
5.1 VEGETATION
Alien species
Riparian margins are prone to alien plant invasion due to constant creation of new microhabitat on floodplains and hydrochoric propagule dispersal (Hulme, 2006; Hood and Naiman, 2000; Planty-Tabacchi et al., 2002). Generally habitats with high edge to core ratios, as it is the case for Taranaki’s managed riparian margins, are more susceptible to weed invasions compared to areas with higher interior habitat proportion (Honnay et al., 2002; Timmins and Williams, 1991). I assumed that a successful management of
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riparian margins would be accompanied by a replacement of the existing vegetation which almost entirely consisted of alien herbs and grasses prior to the planting of native species. Thus, I anticipated a relative decrease of alien species richness with progressing successful succession of riparian plantings towards natural conditions. In contrast to my expectations, medium field site’s alien species richness was lower than on old field sites. One explanation for the high alien species richness on old field sites could be the high native species richness on these sites. High native species richness in riparian areas can be accompanied by high alien species numbers due to constant disturbance and microhabitat creation (Planty-Tabbacchi et al. 2002). This is contrasting to the believe that species rich communities are more difficult to invade (Elton, 1958).
However, the history of riparian planting regimes suggests that high alien species richness on old field sites could additionally be due to insufficient weed control, and at least partly be attributed to the planting of alien species on old field sites or upstream of old field sites with subsequent uncontrolled establishment. At the time of planting for old field sites (late 1990s), alien species were promoted for bank stabilization (Hayes, 2004; Wilkinson, 1999). Especially willows, poplars, and eucalypts were planted at that time. Particularly willows (Salix spp.) are now known to replace native species in riparian areas (Craw, 2000; van Kraayenwoord and Hathaway, 1986) and to have adverse effects on instream fauna due to their deciduous nature (Lester et al., 1994; Winterbourn et al., 1981). Thus willows block streams with organic leaf matter in autumn, contrasting to the mostly evergreen native riparian species (Wardle, 1991). Although there is still a controversy since no single native species is as good in stabilizing banks as willows are (Czernin and Phillips, 2005), the Taranaki Regional Council promotes predominantly native species compositions, which were identified as equivalents and are planted instead (eg. flax (Phormium tenax) together with cabbage trees (Cordyline australis); Czernin and Phillips, 2005). Due to different planting histories and initial weed controls different outcomes can be anticipated for today’s medium aged field sites in terms of alien species richness, given that weed control efficiency is further improved. However, it seems that willows also had some positive effects on birds in riparian margins as they attracted both native and alien species (pers. observations). Hayes (2004) found lower species diversity and abundances of invertebrates associated with willows in New Zealand and concluded
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Riparian management in Taranaki – A success for native biodiversity?
that willows were mainly used by alien birds, but also to a lesser extent by natives as perching posts. I could not confirm whether this was also the case for the investigated field sites or if high bird abundances were coincidental observations. However, willows were the only woody species present for substantial parts of some younger field sites (unfenced and fenced). For some old field sites willows were the highest trees, which would make them suitable as perching posts.
Additionally to alien species richness I was interested in the occurrence of pest plants and other ‘problem-weeds’. Howard-Williams and Pickmere (1999) as well as Warr (2004) demonstrated evidence for wandering willie (Tradescantia fluminensis) and blackberries (Rubus fruticosus agg.) additional to Salix spp. to be problem weeds in riparian margins. In the case of wandering willie, crack willow (Salix fragillis,) and grey willow (Salix cincerea), these species are nationwide acknowledged as pest plants (Biosecurity New Zealand, 2006). My study further supports the invasive traits of wandering willie and blackberries in the riparian context. Furthermore, I could confirm the regeneration hindering effects of wandering willie on riparian margins, which has been described by numerous studies (e.g. Standish et al., 2001; Kelly and Skipworth, 1984). In the majority of vegetation intercept points within one old field site plot wandering willie showed comprehensive cover and suppressed seedling growth, although seedling growth was observed adjacent to wandering willie cover. Even where shading from the above vegetation was relatively large (with ca. 80% vegetation cover on average and some intercept points with 95% of vegetation cover and no obvious clearings in close proximity) wandering willie was abundant and showed no signs of light deficiency. Wandering willie has been described by Standish et al. (2001) and Maule et al. (1995) as limited in growth by light availability off less than 1% of total insolation with shading as a recommendable management action. Despite these research findings it seems not reasonable to wait for sufficient shading as a management tool for riparian margins in Taranaki, as the spots with wandering willie infestations had similar canopy vegetation cover compared to regenerated field sites. Thus no further decrease in wandering willie through shading might occur within the next decade. Solar insolation from edges might further impede management through shading. Additionally, the dynamic nature of riparian areas might create clearings and thus impede management efforts. Notably no
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5 Discussion
weed control of participating farmers specifically targets (the often inconspicuous) wandering willie. Blackberry was the foremost important alien vine species on managed riparian margins with observed negative effects (smothering and replacement) on native flora, with highest abundances recorded on medium aged field sites. This is in accordance with Froude (2008b) and Webb et al. (1988) who acknowledged the sometimes rampant invasion characteristics of blackberry on riparian margins. Potential benefits for native biodiversity could be the berries of blackberry (Rubus fruticosus agg), which are known to be at least eaten by waxeyes (were also recorded on riparian margins) in New Zealand (Williams and Karl, 1996; Burrows, 1994).
Native species
I expected native species richness to increase with field site age if restoration efforts were successful. I hereby measured overall native plant species richness but focused in particular on vines and ferns as these were not planted and thus indicate natural succession dynamics. The value of vines and ferns as an important part of New Zealand’s forest flora is well recognized (Burns and Dawson, 2005; Dawson, 1993; Wardle, 1991). Particularly the management expectations of natural fern establishment (ARC, 2005) inspired me to research if these management goals are achieved in Taranaki with current management practices.
The increase of native species richness with field site age demonstrated for Taranaki’s riparian margins supports the results of the Whangamata stream recovery study (Howard- Williams and Pickmere, 1999), where an increase in native species richness was also positively correlated with field site age. Most species recorded on riparian margins in Taranaki were also found on other riparian margin vegetation surveys (Langer et al., 2008; Howard-Williams and Pickmere 1999). Thereby, species numbers could not be directly compared as methods differed considerably. Albeit my approach was to choose a representative riparian margin stripe for the location of plots, I probably found less species compared to methods which take longer transects into account due to the high variability on riparian margins. Nevertheless, the analogies in species composition indicate a good development of riparian margins in Taranaki.
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Riparian management in Taranaki – A success for native biodiversity?
The native vine species recorded on old and regenerated margins are typical regional species which require a high light intensity for growth, with the exception of native jasmine (Parsonsia heterophylla), which was described by Baars and Kelly (1996) as more shade tolerant than large-leaved muehlenbeckia (Muehlenbeckia australies). Baars et al. (1998) described large-leaved muehlenbeckia as liana of mid succession stages in disturbed areas such as forest margins, while supplejack (Ripogonium scandens), bush laywer (Rubus cissoides) and rata spp. (Metrosideros spp.) were associated with later succession stages. These species all occurred on regenerated riparian margins of my study and suggest a development of different succession stages in close proximity to each other as typical for riparian margins (Naiman et al., 2005) (including later succession species, which were not recorded on younger field sites).
Schnitzer and Bongers (2002) described vines and their comprehensive cover on the edges of vegetation. The microclimate creation by vines through comprehensive cover on edges could be beneficial for riparian margins, as the development of regenerated sites suggests with filmy fern (Hymenophyllaceae) establishment. However, large leaved muehlenbeckia has been found to smother native canopy species similar to the smothering of introduced vines such as Clematis vitalba (Baars and Kelly (1996). Although I did not find evidence for lethal smothering on the investigated plots, one farmer actively manages this species and emphasized the threat he attributes to large-leaved muehlenbeckia on the favored natives on his riparian margins (pers. comm., 2008).
Ferns were not planted as they are expected to self-establish with progressing microclimate improvement through planting induced succession (ARC, 2005). To determine whether or not this management goal was achieved I focused additionally on fern species richness, composition and abundance. My findings suggest a good development towards a natural range with the presence common ground ferns (e.g. hen and chicken fern (Asplenium bulbiferum) and hairy fern (Lastreopsis hispida)) and tree ferns (e.g. mamaku (Cyathea medullaris), wheki (Dicksonia squarrosa)) as typical examples of fern species in natural forests and also common species in secondary forest succession (Wardle, 1991). Most fern species recorded on riparian margins were typical species of stream sides (e.g. smooth shield fern (Lastreopsis glabella), nini (Blechnum chambersii), kiwakiwa (Blechnum fluvatile)) and/or require damp shady conditions (e.g.
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gully fern (Pneumatopteris pennigera), sweet fern (Pteris macilenta); Brownsey and Smith-Dodsworth, 1989). Most fern species need to have a shelter from direct sun exposure to minimize desiccation (Hennessey, 2006). I could support this with my study, as fern species richness and abundance were clearly linked to canopy closure and thus only sites with a closed canopy supported a variety of fern species. The only exceptions were the presence of the natural pioneer species braken fern (Pteridium esculentum) at the edges of an old and a regenerated riparian margin as well as on one fenced field site and the coincidental occurrence of a palm leaf fern (Blechnum novae-zealandiae) specimen recorded on the eroded bank of an unfenced site. Albeit van Davies-Colley et al. (2000) found filmy ferns (Hymenophyllaceae) not at forest edges due to microclimatic changes regenerated field sites show the potential of narrow riparian margins to develop vegetated strips suitable for filmy fern establishment. Filmy ferns are known to require a moist microhabitat (Dawson, 1993) and are described as a characteristic component of Taranaki’s forests (Clarkson, 1985), which further indicates a good development of the riparian margins in Taranaki.
A comparison with the national and the regional thread list for plants showed no analogies for unplanted species recorded on field sites (DOC, 2007; TRC, 2004).
A comparison with Wardle (1991), who describes forest succession in New Zealand, showed that most species found on the investigated margins are region-typical seral species. The only mature forest species found were totara (Podocarpus totara) and rimu (Dacrydium cupressinum), but these species were just recently planted and thus cannot be used as indicators for a natural development towards mature forest species establishment.
Additional to species diversity the ability to sustain the attained biodiversity is very important when monitoring restoration success. Thereby, seedling regrowth was described as an indicator of biodiversity regeneration within ecosystems and an important measure for the estimation of future developments (SER, 2005). Native seedlings were found to increase in numbers with field site age on riparian margins, given they were not smothered by weed infestations, and thus suggest riparian margin sustainability if weed control is further improved.
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Vegetation cover
A diversification in plant cover is characteristic for a well progressing restoration (Wilkins et al., 2003). Thus we expected a diversification of plant cover with field site age. As anticipated, the number of vegetation groups increased for every investigated height (i.e. ground, midview (1,35m) and skyview (above 2m)) with field site age. Due to the previous land use most alien species were composed of alien herbs, derived from previous pasture. Alien herbs have been shown to decrease with canopy closure (Schütz, 2004; DeFerrari and Naiman, 1994), which supports my results, as I found most alien herbs replaced with canopy closure by native ground ferns and litter cover on regenerated field sites. Hence, I expect a further decrease of alien herb cover for today’s medium and old field sites. Jansen et al. (2004) also defined an increase in litter cover for riparian margins as a good sign of a transformation to more natural conditions and the ability to perform ecosystem functions such as providing habitat for fauna and the ability to retain plant propagules. A comparison of litter cover with field site age shows the trend towards natural conditions and therefore a trend towards natural development (Jansen et al., 2004).
Structural diversity on riparian margins in Taranaki
A diversification of vegetation structure is widely acknowledged as an indicator of succession patterns, especially forest succession (Clebsch and Busing, 1989; Horn, 1974; Clements, 1916). Therefore I expected an increase in structural diversity with field site age. The number of tiers occurring above two meters in height increased with field site age and was accompanied by a general increase in vegetation height. Epiphytes are an important component of New Zealand’s floristic diversity and add to structural diversity (Dawson, 1993). Old field sites were the youngest field sites with epiphytes recorded. Epiphytes thereby remained below two meters in height, while on regenerated sites they also occurred at greater heights. Furthermore, epiphyte occurrence increases with host tree diameter (Burns and Dawson, 2005), which is tree-age related and therefore also positively linked with field site age. My investigated margins show a good development with increasing number and diversity of epiphytes when comparing medium field sites
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(no epiphytes) with old field sites (epiphytes below 2m height) and with regenerated field sites (epiphytes also at heights above two metres).
Difficulties in the distinction between planted and unplanted tree species on old field sites shows how well the gaps between plantings have been filled - thus further indicating a good structural development.
These results suggest that vegetation on the investigated old and regenerated margins resembles successional bush with dense vegetation and an average height below ten metres (Wardle, 1991). My research findings indicate that riparian margins will continue to develop into strips with an array of different native species, composed of different life form strategists and succession stages, forming a mosaic with a species composition determined by disturbance (Richardson et al., 2007; Naiman et al., 2005; Pabst and Spies, 1998).
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5.2 AVIFAUNA
Alien species
Alien bird species richness increased with field site age peaking at old field sites and was lower on regenerated field sites compared to old field sites. Therefore alien bird species richness rather resembled the species richness pattern found for native birds than a linkage between an increase in native species richness accompanied by a decrease in alien species richness. My results support Diamond and Veith (1981), who found evidence for coexistence rather than direct competition for food between alien and native bird species. This is attributed to New Zealand’s paucity in avian species richness and the lack of co- evolution on species level between food sources and bird species (O’Donnell and Dilk, 1994) and habitat modification which supports alien bird species more than native birds (Diamond and Veitch, 1981). Alien bird species found at riparian margins were mostly opportunistic generalists such as house sparrows, which are ranked as one of the top ten of the most common species in New Zealand and have a broad habitat range (Spurr, 2008). Furthermore, the proportion of granivorous birds amongst alien birds was higher compared to native birds. Hence, one reason for the recording of these species could be the seeding of several weeds at the time of the bird counts (e.g. alien thistles). Additionally, alien bird species such as starlings, yellowhammer, greenfinches and house sparrows seemed to profit from supplementary cow-feedings adjacent to field sites. Some of the alien bird species recorded on riparian margins are known for dispersing weeds and native plants (e.g. blackbirds (Turdus merula) and starlings (Sturnus vulgaris); Williams, 2006). Greenfinches (Carduelis chloris) are acknowledged as a minor pest and house sparrows (Passer domesticus) are regarded as a pest species (Heather and Roberston, 2005) but are not managed on the investigated farms. Deschenes et al. (2003) found evidence that farmland field strips do not accelerate the abundances of field and crop damaging birds. Relative abundances of sparrows and greenfinches were not alarmingly high on Taranaki’s riparian margins and thus support Deschenes et al, (2003).
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Native species
Native bird species richness followed the pattern of alien bird species diversity and increased with field site age, peaked at old field sites, where also the highest overall plant species richness was found, but was lower on regenerated sites compared as to old field sites. My study supports the finding that (native) bird numbers increase throughout succession (Howard-Williams and Pickmere, 1999; Robertson and Hackwell, 1995), as the abundances of native birds increased with field site age. Although species richness was lower on regenerated field sites compared to old field sites relative native bird abundance clearly dominated. In New Zealand’s biodiversity strategy (DOC, 2000) the increase of native birds (including common species such as fantails) is set as an important target for riparian management as these species require habitat structures with sufficient abundances of (native) insects for their survival, as in the case of fantails and grey warblers (Day, 1995), and are known for their excellent capability to spread native plants as for waxeyes (Clout and Hay, 1989). Furthermore, an increase demonstrated of these three species with native vegetation cover has been demonstrated (Boffa Miskell limited, 2000). Except for the tomtit (singular observation on an old field site) which is known to have responded sensitively to lowland habitat modification and destruction in the past (Heather and Robertson, 2005), I could not find evidence for any threatened or sensitive species on riparian margins. Farmer observations indicate the occurrence of tuis and bell birds on regenerated field sites. I did not record these species, albeit they should be able to find suitable food on riparian margins, with flax (Phormium tenax) and kowhai (Sophora microphylla) planted to attract these species (Ministry for the environment, 2001; Craig and Stewart, 1988). As I, however, only counted birds in late summer/early autumn other species might occur at other times of the year, as many species in New Zealand are known to seasonally migrate for opportunistic feeding sources (Dawson et al., 1978).
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5.3 VEGETATION AND AVIFAUNA
Birds are known to be attracted to vegetation structures but also to shape vegetation by dispersing seeds (e.g. Ferguson and Drake 1999). This is particularly the case in New Zealand, where ornithochore dispersal is one of the main dispersal strategies of native plants (Clout and Hay, 1989) Due to incomplete information on individual farmer’s planting choices (especially for old field sites), I could not evaluate which woody species established though bird dispersal.
Vegetation components having a significant influence on bird species occurrence on Taranaki’s riparian margins are related to structural vegetation diversity. It has long been acknowledged that birds are attracted to structural diversity in landscapes such as hedges or woodlands (e.g. Cody, 1981; Willson, 1974; MacArthur, 1964; MacArthur and MacArthur, 1961). My study supports these results as a correspondence analysis revealed vegetation structures such as the density of trees and shrubs, and the number of tiers to be important for species occurrence. Bird species richness was positively related to vegetation height and the vegetation cover (skycover) above two metres and negatively influenced by the occurrences of alien ruderal plants. For some species with relatively clear habitat preferences, I could link riparian margins with relative abundances. Chaffinches and blackbirds are known to be attracted to structural vegetation features, but prefer those to be relatively open structured (Wittingham, 2001; Hatchwell et al., 1995). This is supported by my results, as chaffinches were more abundant on medium field sites compared to old field sites and even less on regenerated field sites. This supports international research findings from riparian margins, where species richness and abundances were positively linked with the development of a riparian forest (Jansen and Robertson, 2001; Naiman and Decamps, 1997; Triquet et al., 1990). Overseas studies also recognize the influence of riparian margin width and recommend wider margins than implemented in New Zealand (Pearson and Manuwal, 2001; Spackman and Hughes, 1995. According to Peak and Thompson (2006) habitat preferences of forest area sensitive species are linked with habitat size, thereby not only the total area but also the width of the habitat is of importance. This has been supported by research on corridor use within fragmented habitats, where only corridors of a certain width are used as stepping
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stones to other habitats (Lindenmayer and Nix, 1993). Within Taranaki lowland forest remnants are scarce over large areas and the current vegetation consists of less than 10% native vegetation on the ring plain (TRC, 2004). For a successful corridor use of riparian margins as linkages between habitats there is also a need to establish suitable habitats, since they might not be sufficiently wide to fully support more sensitive species territory requirements. Additionally to habitat size and shape plant species choice is an important management tool in bird conservation and thus people are encouraged to plant adequate species in their gardens (DOC, 2007; Collier et al., 1995). Plant species for riparian margin restoration were also chosen by their ability to attract native birdlife (NIWA, 1995). Sometimes alien plant species might be more attractive to native bird life as feeding sources (Medway, 2008; DOC, 2000) and thus can pose a difficult trade-off between bird conservation and the conservation of native flora.
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5.4 ARE PLANTINGS NECESSARY TO ACHIEVE THESE RESULTS?
Plantings are usually the method of choice when the desired ecological rehabilitation or restoration is not feasible within the anticipated timeframe or is not feasible at all without management. This is often the case when seed-banks have been destroyed by land-use practices (Atkinson, 1994). Unfortunately, only little is known about diasporebanks in New Zealand. Ogden (1985) assumes that forest seed-banks are similar to seed banks overseas and found evidence for small seed banks for New Zealand’s early succession species such as wineberry (Aristotelia serrata). The investigated riparian margins could have different diaspore banks due to differing land uses. For example, some riparian margins were lined by barberry hedges (Berberis glaucarpa), which were later replaced by electric fencing, thus potentially influencing soil characteristics and seed-bank features. In other areas seed-banks may have been destroyed through tilting and the application of herbicides when the margins were still utilized as pastures. Even though succession is possible for retired margins without plantings this would probably take considerably longer. Riparian margins which have been fenced off and retired from grazing (i.e. fenced field sites) did not show considerable differences in native species composition and vegetation structure compared to unfenced field sites. Examples for the succession hindering effect of dense pasture grass root structures have been demonstrated in various international (D’Antonio and Vitousek, 1992; Schultz et al., 1955) and national studies (Howard-Williams and Pickmere, 1999), where some parts of the riparian margins still showed the same species composition with alien grasses as at the start of the project 30 years earlier. Furthermore, the Ministry for the Environment (2001) highlighted the succession hindering effects of productive alien grasses in New Zealand. Consequently, the TRC started to promote plantings rather than passive restoration (TRC, 2002). As already emphasized by Howard (1964) New Zealand’s native species are not adapted to intensive grazing by cattle and are therefore also less adapted situations where diaspores have to out-compete alien grasses. In some cases pest plants can invade the ecological niches of retired sites and induce an (alien) plant succession (Williams, 1983). Gorse is known for its comprehensive coverage and is therefore one of the managed pest plants (Biosecurity New Zealand, 2006). Although over the long term positive effects for a
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nursery of native vegetation has been demonstrated in New Zealand (Barker, 2008), gorse is also acknowledged as a problem weed in riparian areas (TRC, 2007). Weed control has taken place on the regenerated field sites of my study. Therefore it seems feasible to conclude that natural succession is probably considerably slower than an anthropogenic induced one and thus requires intensive weed control. Furthermore, on some retired riparian margins an establishment of native species and a succession towards the anticipated sheltering riparian margin might not be foreseeable within the required timeframe for water quality improvements without any initial plantings or other forms of facilitation for favoured species (Ministry for the environment, 2001), and in some cases might not be foreseeable at all (Howard-Williams and Pickmere, 1999).
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5.5 THE VALUE OF RESTORED RIPARIAN MARGINS FOR CONSERVATION
To assess rehabilitation and restoration success it is crucial to know the sites’ potential (Egan and Howell, 2001; Swetnam et al., 1999) and to have realistic management goals for evaluating monitoring efforts (Ehrenfeld, 2000). However, we did not have any true remnant sites with original riparian forests within a continuous forest for comparison and thus cannot fully estimate to what extent the narrow revegetated riparian stripes can perform the original ecosystem functions and support original species diversity. Despite this shortage of a control group, it has been proven that rehabilitated riparian margins in New Zealand have the ability to improve water quality through shading and nutrient filtration (Perrie, 2008; Parkyn et al., 2003; Collier et al., 2000; Storey and Cowley, 1997), which is one of the important ecosystem functions of riparian margins within the landscape (Naiman et al., 2005). My study shows the good development of the terrestrial component of managed riparian margins (given that weed and pest control is sufficient), and their ability to develop into patches of native riparian bush with a species composition typical for secondary succession in the region. That is, if measured on the development of regenerated field sites. Collier (1994) highlighted the importance of realistic goals for riparian management in New Zealand regarding the vegetation development. The dynamics of riparian margins which determine dynamical vegetation succession patterns are of specific importance (Cooper et al., 2003; Naiman and Decamps; 1997). Thereby, floods alter and shape vegetation structures in unpredictable time intervals regardless of the season in New Zealand (Howard-Williams, 1991).
The natural value of areas is often also measured by their ability to provide refuge for endangered species (Primack, 2002; Spellerberg, 1991). I could not find any endangered birds or any endangered plants. One reason for a lack of sensitive bird species could be edge related predation effects, as predator intensity has been shown to increase with edge creation (e.g. Haegen and Degraaf, 1996; Murcia, 1995; Andren and Angelstam, 1988). Thus predation could be a problem on the investigated margins due to their linear, narrow structure. The harming effects on native birdlife by introduced mustelids (mustelidae) and brushtail possums (Trichosurus vulpecula) in New Zealand is well documented (Brown, 1997; O’Donnell, 1996). Brushtail possums are controlled on riparian margins and I did
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not observe possum related vegetation browsing damage and thus conclude that management efforts are sufficient. Coincidental observations of mustelid activity on riparian margins however, could be a sign for high mustelids numbers and thus be a threat to native birdlife. This could be explained by the absence of specific mustelid control (only one farmer controlled them). More research at different times of the year is needed to investigate the potential value as breeding sites for native birds and to investigate whether at other times of the year birds use revegetated riparian margins as feeding sources.
International studies (Naiman et al., 2005) as well as national ones (Perrie, 2008) have shown that narrow riparian margins are not enough to fully restore all ecosystem functions and to mitigate edge effects. Therefore Hanowski et al. (2001) promote a riparian landscape approach for buffer width determination. In Taranaki only riparian margins are restored. Although riparian margin width for retirement is supposably determined on a case to case base, it is also linked with stream width and therefore sometimes very narrow (TRC, 1992). Contrasting to current management practices wider riparian margins (40m) are recommended to minimize edge effects within the New Zealand context (van Davies-Colley et al., 2000). This is supported by international studies which promote a minimum riparian buffer zone between 25-50m (e.g.Pearson and Manuwal, 2001; Wenger, 1999). Within New Zealand, Miller (2006) found a gradual decline in plant species diversity away from riparian margins. How much the natural floristic and faunistic species diversity adjacent to streams is dependent on a continuous forest is, however, not fully understood, as information about natural riparian margins within continuous forests is scarce in New Zealand. Rehabilitation and maintenance of modified natural areas for native biodiversity within high productive landscapes with little or no native vegetation is one of the key objectives of New Zealand’s biodiversity strategy (DOC, 2000). Rehabilitated riparian margins could be classified as modified natural areas due to their narrowness and their susceptibility to adjacent land use practices. Restored riparian margins are expected to function as local key sites for a development towards higher biodiversity on a regional scale and as corridors for native wildlife (TRC, 2004, Norton and Miller, 2000). Whether the creation of riparian margins really leads to a higher biodiversity for the region has to be evaluated once the majority of
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riparian margins are rehabilitated, as the current implementation rate of Riparian Management Plans is very low with only 7% (Froude, 2008a). In times with growing concern for climate change and carbon emissions, restored riparian margins provide an opportunity to fix some CO2 from cattle faeces within woody plantings and thus contribute to climate conservation additionally to contributing to biodiversity and enhancing the aesthetics of the landscape.
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5.6 POTENTIAL MANAGEMENT CONFLICTS
While native bird species occurrence could be correlated with the development of a riparian forest, this might not necessarily be beneficial if nutrient filtration is the main management objective (Quinn et al., 1993). Therefore a wide spaced planting regime has been described as beneficial; and deciduous trees have been promoted for this purpose (TRC, 1992). This however, if implemented, could be very disadvantageous for native terrestrial biodiversity, depending on the ability of plants to self-establish between these planting gaps. The microhabitat developing with canopy closure was one of the foremost important succession patterns I found. A prevention of canopy closure would be disadvantageous for native terrestrial biodiversity, especially for moisture sensitive species (Wardle, 1991).
However, New Zealand’s instream fauna is very sensitive to temperature increases (Perrie, 2008), and therefore needs sufficient shading as management action. This can be achieved with the restoration of riparian margins (Parkyn et al., 2003). Economic interests might impede conservation objectives, as financial losses are expected by farmers with the implementation of wide riparian margins and thus the retirement of high productivity dairy land. However, Langer et al. (2008) have shown the potential of alien riparian pine plantation buffer in New Zealand for native vegetation and Norton and Miller (2000) suggested a connection between forest remnants via forests for timber production. Further research should be targeted to investigate whether such combined management regimes could be financially and ecologically sustainable in the riparian context, buffering a native riparian margin with a commercial forest buffer.
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6 CONCLUSIONS AND RECOMMENDATIONS
6.1 CONCLUSIONS: RIPARIAN MANAGEMENT IN TARANAKI –A SUCCESS FOR NATIVE BIODIVERSITY?
The evaluation of Taranaki’s riparian management program for benefits of terrestrial biodiversity was the focus of my study. The research results have demonstrated that riparian margin plantings in Taranaki develop well and hasten natural secondary succession with native plant species, which might not be possible without initial plantings. Native plant species richness increased with field site age, but was not accompanied with a clear decrease of alien plant species, which could be at least partly explained by the differing planting history for old field sites compared to medium field sites and the invasion of alien plant species which are yet not targeted by weed control. Seedling numbers increased on riparian margins with field site age, thus indicating a persistence of the present vegetation if weed control is efficient. Overall plant cover diversity increased as well as vegetation structure with field site age. Alien species thereby mainly consisted of alien herbs, as hypothesized, and a further decrease for most species can be expected with progressing canopy closure. This further supports the assumption that riparian margins are developing well and towards a natural stage.
For bird species richness the trend was not as clear towards an increase in native species richness and a decrease in alien species richness as anticipated. One possible explanation for this could be the surrounding land use and edge-related predation by pest animals such as mustelids. Overall, bird abundances increased for native birds as expected and regenerated field sites showed that an out-competition of alien species abundances is possible and a feasible management target. Fantails (Rhipidura fuliginosa), grey warblers (Gerygone igata) and waxeyes (Zosterops lateralis) profited from Taranaki’s riparian management program practices. Despite these positive outcomes my study also shows that there are limits to what riparian management can accomplish on narrow stripes of riparian margins, as I could not evidence any threatened species retreating to riparian margins. Furthermore, not all ecosystem-functions might be restored with current riparian
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management practices as we found evidence for edge effects. Nevertheless, it is a very valuable tool for the enhancement of terrestrial biodiversity within the highly modified farm landscape. Riparian margins thereby contribute the main proportion of more natural, but still modified, habitats for native terrestrial biodiversity contrasting to adjacent lands with high productive alien grasslands.
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6.2 RECOMMENDATIONS
6.2.1 RECOMMENDATIONS FOR MANAGEMENT
My study has demonstrated the importance of plant choice for initial plantings and of efficient weed control. Future farmers participating in the riparian management programme should be informed more thoroughly about specific problem weeds in riparian margins (e.g. blackberry, willow and wandering willie). Especially wandering willie was not yet targeted by specific weed control, but should be eradicated whenever possible. Blackberry should be more vigorously managed, as comprehensive cover seemed to smother native vegetation in some areas. However, it is important to concentrate eradication and weed control efforts on upper reaches of the stream before conducting weed control downstream. That is to prevent management failure induced by hydrochore weed dispersal. Animal pests such as brushtail possums (Trichosurus vulpecula) and in some cases hares and rabbits are controlled on riparian margins but mustelids, which are known to prey on birds (Roser and Lavers), are to date not specifically targeted as a controlled species (with one farmer as exception). Hence, more information is needed to investigate whether high mustelid numbers are present on planted riparian margins and, if so, whether they reduce native bird diversity and abundances on riparian margins (which is expectable). Consequent management should be applied if mustelids are a serious threat on riparian margins. According to research overseas (e.g. Pearson and Manuwal, 2001; Wenger, 1991) and within New Zealand (Miller, 2006; van Davies-Colley et al., 2000), native biodiversity would profit from wider riparian buffer zones; recommendations proclaim a width of 40m for New Zealand riparian buffers (van Davies-Colley et al., 2000). This might financially not be feasible and thus options with timber production efforts adjacent to native riparian margins should be further investigated.
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6.2.2 RECOMMENDATIONS FOR FUTURE STUDIES
I could not distinguish between planted and unplanted species and specimens and therefore used vines and ferns as indicator plant groups for naturalness. However, more specific results and a quantification of self-established plant species would give valuable insights for management and reveal more information about succession dynamics. Therefore a digitalized databank for riparian margin planting regimes needs to be established to facilitate field site choice and analysis for future monitoring projects. Even though I do not expect many differences in plant species seasonal conspicuousness for the investigated riparian margins, most studies record vegetation at different times of the year (Spellerberg, 1991) and some species missed in my study might be found during multi-seasonal samplings,. For a fully comprehensive investigation of riparian plants in New Zealand I recommend a detailed analysis on species cover level. This would facilitate the interpretation of habitat characteristics and enable the possibility to analyse more specific functional plant groups in terms of their life strategies and succession patterns. More information on species compositions would be particularly interesting, since only little information is available on terrestrial riparian margin plant diversity in New Zealand. Thereby all vascular plant species should be attributed with individual cover values, including identifying root stems on species level. Since a more detailed estimation for abundance was not possible for native species, due to their presence throughout the various tiers and the occurrence of epiphytes, a frequency analysis could reveal more information. Further proclaiming a species based approach for cover estimation. To facilitate the recommendation of weed management actions a seedling tally for alien species should be incorporated in the sampling protocol.
Bird monitoring took place in early autumn and thus bird counts during other seasons, such as spring, would be recommendable to investigate whether riparian margins are used as breeding and feeding habitats at other times of the year. Furthermore, it would be highly valuable for the evaluation of riparian margin rehabilitation to investigate more natural settings e.g. to compare the various management regimes to riparian margins within continuous forest.
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Due to varying distances between bird count stations caused by high background noise levels and differing riparian margins widths bird count results should be analysed per hectare to facilitate interpretation and to ensure comparability.
Despite the well acknowledged indicator value of birds for landscapes (Gregory et al. 2005), it would be valuable to investigate whether and, if so, to what extent other faunistic groups profit from riparian planting regimes. As New Zealand’s main faunistic biodiversity is found within invertebrates (Hutcheson et al., 1999), it would be interesting to conduct research on benefits of riparian management on these taxa. Hutcheson et al. (1999) emphasized that beetles in general, but carabidae in particular, could be an overlooked indicator group with value for conservation within New Zealand.
Once more research has been conducted about riparian margin restoration a scoring evaluation system in analogy to overseas riparian monitoring programmes (e.g. Jansen et al., 2004) could be developed to compare restoration success throughout New Zealand. If modified for scientific evaluation and combined with overseas scoring systems, the cultural health index (Tipa and Teirney, 2003) could give valuable conceptual hints for the development of a scoring system in New Zealand.
I investigated the most important management categories of Taranaki’s riparian management programme. Thereby my study has shown how important the combination between pasture retirement (by fencing) and initial plantings is for native biodiversity. In many cases of land use history, however, remnant vegetation is present despite cattle grazing and it is expected that cattle exclusion combined with enhancement plantings can provide very positive results in such situations (ARC, 2005). Consequently, more types of riparian management should be investigated (e.g. enhancement plantings and only fenced margins over longer periods of time) as highlighted by the TRC and thus recommended by Froude (2008a). Further studies of the management regimes targeted with this study should be conducted to support my findings.
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8 APPENDIX
Table 1: Complete alien plant species list for all management categories. ncy = not yet classified (New Zealand Plant Conservation Network, 2005). Grasses were not identified to species level and are thus not included in the list.
Family No. Scientific name common name Classification
Aceraceae 1 Acer spp. maple ncy Apiaceae
2 Conium maculatum hemlock ncy Aquifoliaceae
3 Ilex aquifolium holly ncy Asteraceae
4 Achillea millefolium yarrow ncy 5 Asteraceae spp. n.a. n.a. 6 Bellis perennis bellis daisy ncy 7 Cirsium arvense Californian thistle ncy 8 Cirsium vulgare Scotch thistle ncy 9 Conyza albida broad leaf fleabean ncy 10 Conyza canadensis Canadian fleabean ncy 10 Crepis capillaris hawksbeard ncy 11 Hieracium spp. n.a. unwanted, pest plant 12 Hypochaeris radicata catsear ncy 13 Leontodon taraxacoides hawkbit ncy 14 Leucanthemum vulgare oxeye daisy ncy 15 Senecio jacobea ragwort ncy 16 Sonchus arvensis perennial sow thistle ncy 16 Taraxum officinalis dandelion ncy Berberidaceae
17 Berberis glaucocarpa barberry ncy Boraginaceae Myosotis laxa subsp. 18 caespitosa field forgot-me-not ncy Caryophyllaceae
19 Cerastium fontanum mouse ear chicksweed ncy 20 Stellaria spp. n.a. n.a.
Commelinaceae
21 Tradescantia fluminensis wandering jew unwanted; pest plant Convolvulaceae
22 Calystegia silvatica great bindweed ncy 23 Convolvulus arvensis convolvulus ncy
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8 Appendix
Table 1 continued
Family No. Scientific name common name Classification
Fabaceae
24 Fabaceae spp. n.a. n.a. 25 Lotus major birdsfoot trefoil n.a. 26 Lotus pedunculatus lotus ncy 27 Lotus spp. n.a. n.a. 28 Lupinus arboreus tree lupine
29 Trifolium arvense haresfoot trefoil ncy 30 Vicia spec. n.a. n.a. 31 Trifolium pratense red clover ncy 32 Trifolium repens white clover ncy 33 Trifolium spp. n.a. n.a. 34 Ulex europaeus gorse unwanted, pest plant 35 Castanea sativa European chestnut ncy Iridaceae
36 Crocosmia x crocosmiiflora montbretia ncy Juncaceae
37 Juncus effusus leafless rush ncy 38 Juncus spp. n.a. n.a.
Lamiaceae
39 Prunella vulgaris self heal ncy 40 Prunella vulgaris self heal ncy
41 Stachys sylvatica hedge woundwort ncy
Myrtaceae
42 Eucalyptus spp. n.a. n.a. Phrymaceae
43 Mimulus guttatus monkey musk ncy
Phytolaccaceae
44 Phytolacca octandra inkweed ncy Plantaginaceae
45 Plantago lancelota narrow-leaved plantain ncy 46 Plantago major broad-leaved plantain ncy
47 Plantago spp. n.a. n.a.
Polygonaceae
48 Persicaria hydropiper water pepper ncy 49 Rumex acetosa sorrel ncy
50 Rumex obtusifolius broad-leaved dock ncy
Primulaceae Anagallis arvensis subsp. pimpernel 51 arvensis ncy
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Table 1 continued:
Family No. Scientific name common name Classification
Proteaceae
52 Banksia integrifolia banksia ncy Ranunculaceae
53 Clematis vitalba old mans beard unwanted; pest plant 54 Ranunculus acris giant buttercup ncy
55 Ranunculus repens buttercup ncy
Rosaceae
56 Rubus fruticosus agg. blackberry ncy Rubiaceae
57 Galium aparine cleavers ncy Salicaceae
58 Populus spp. poplar n.a. 59 Salix fragillis crack willow unwanted; pest plant
60 Salix spec. willow ncy
Scrophulariaceae
61 Digitalis purpurea foxglove ncy Selaginellaceae
62 Selaginella kraussiana selaginella unwanted; pest plant Solanaceae
63 Solanum nigrum black nightshade ncy
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Table 2: Complete species list of native plants for all management categories. Plant species with range restriction or status according to the National threat list (DOC, 2005) were planted.
Family No. Scientific name common name conservation
Agavaceae 1 Cordyline australis cabbage tree abundant endemic Apocynaceae 2 Parsonsia heterophylla New Zealand jasmine not threatened endemic Araliaceae 3 Araliaceae spec. family not endemic 4 Pseudapanax arboreus whauwhaupaku not threatened endemic 5 Pseudapanax colensoi three finger not threatened endemic 6 Schefflera digitata pate not threatened endemic Arecaceae 7 Rhopalostylis sapida nikau palm not threatened endemic Argophyllaceae 8 Corokia macrocarpa whakataka range ristricted Aspleniaceae 9 Asplenium bulbiferum hen and chicken fern not threatened endemic 10 Asplenium flaccidum hanging spleenwort not threatened native 11 Asplenium hookerianum spleenwort not threatened endemic var. colensoicolensos 12 Asplenium oblongifolium shining spleenwort not threatened endemic 13 Asplenium spec. n.a. n.a. Asteraceae 14 Brachyglottis repanda rangiora not threatened endemic 15 Olearia lineata n.a. threatlist: 6 (sparse), endemic 16 Oleria paniculata akiraho not threatened endemic Blechnaceae 17 Blechnum chambersii nini not threatened native 18 Blechnum filiforme thread fern not threatened endemic 19 Blechnum fluviatile kiwakiwa not threatened native 20 Blechnum novae-zealandiae kiokio very common endemic Coriariaceae 21 Coriaria arborea tutu not threatened endemic Cyatheaceae 22 Cyathea smithii ponga not threatened endemic 23 Cyathia cunninghamii gully tree fern not threatened native 24 Cyathia medullaris mamaku not threatened native 25 Carex coriacea cutty grass not threatened endemic 26 Carex secta pukio not thretened endemic Dennstaedtiaceae 27 Dennstaedtiaceae spec. n.a. n.a. 28 Dennstaedtiaceae spec. n.a. n.a. 29 Histiopteris incisa water fern not threatened native 30 Paesia scaberula ring fern not threatened endemic Pteridium exculentum Rahurahu Dicksoniaceae 31 Dicksonia squarrosa wheki abundant endemic Dryopteridaceae 32 Lastreopsis glabella smooth shield fern not threatened endemic 33 Lastreopsis hispida hairy fern not threatened native 34 Polystichum vestitum prickly shield fern not threatened endemic Elaeocarpaceae 35 Aristotelia serrata wineberry not threatened endemic Fabaceae 36 Sophora microphylla kowhai not threatened endemic Griseliniaceae 37 Griselinia littoralis broadleaf not threatened endemic 38 Griselinia littoralis hybrid n.a. n.a. Hemerocallidaceae 39 Phormium tenax herakeke not threatenedendemic 40 Phormium tenax hyb. black n.a. n.a. 41 Phormium tenax hyb. yellow n.a. n.a.
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Table 2 continued:
Family No. Scientific name common name conservation
Hymenophyllaceae 42 Hymenophyllum spec. n.a. n.a. 43 Trichomanes spec. n.a. n.a. 44 Trichomanes venosum veined filmy fern not threatened native Loganiaceae 45 Geniostoma rupestre hangehange not threatened endemic Malvaceae 46 Hoheria populnea houhere not threatened endemic 47 Hoheria spec. n.a. endemic genus 48 Plagianthus regius ribbonwood not threatened endemic Monimiaceae 49 Hedycarya arborea pigeonwood not threatened endemic Myrtaceae 50 Leptospermum scoparium manuka not threatened var. scoparium native 51 Metrosideros diffusa white rata not threatened endemic 52 Metrosideros excelsa pohutukawa not threatended endemic 53 Metrosideros spec. n.a. n.a. Onagraceae 54 Fuchsia excortica tree fuchsia not threatened endemic Orchidaceae 55 Earina autumnalis raupeka not threatened endemic Pandanaceae 56 Freycinetia banksii kiekie not threatened endemic Piperaceae 57 Macropiper excelsum kawakawa not threatened endemic Pittosporaceae 58 Pittosporum colensoi n.a. not threatened endemic 59 Pittosporum crassifolium karo not threatened endemic 60 Pittosporum eugenoides lemonwood not threatened endemic 61 Pittosporum ralphii karo not threatened endemic 62 Pittosporum tenuifolium kohukohu not threatened endemic Plantaginaceae 63 Hebe salicifolia koromiko not threatened native 64 Hebe stricta koromiko not threatened endemic Poaceae 65 Cortaderia toetoe toetoe abundant endemic Podocarpaceae 66 Dacrydium cupressinum rimu not threatened endemic 67 Podocarpus totara totara not threatened endemic Polygonaceae 68 Muehlenbeckia australis pohuehue not threatened native 69 Microsorum pustulatum subsp. hound's tongue not threatened native pustulatum 70 Microsorum scandens fragrant fern not threatened native 71 Pyrrosia eleagnifolia pyrrosia not threatened endemic Proteaceae 72 Knightia excelsa rewarewa not threatened endemic Pteridaceae 73 Pteris macilenta sweet fern not threatened endemic Rhamnaceae 74 Pomaderris apetala tainui 1 nationally critical subsp. Maritime Ripogonaceae 75 Ripogonum scandens supplejack not threatened endemic Rosaceae 76 Acaena spec. n.a. n.a.
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Table 2 continued:
Family No. Scientific name common name conservation
Rubiaceae 77 Coprosma grandifolia kanono not threatened endemic 78 Coprosma repens taupata not threatened endemic 79 Coprosma robusta karamu not threatened endemic 80 Coprosma robusta karamu not threatened endemic Solanaceae 81 Solanum aviculare poroporo not threatened native, var. aviculare however declining in parts of the NI Thelypteridaceae 82 Pneumatopteris pennigera gully fern not threatened native
Violaceae 83 Melicytus ramiflorus mahoe not threatened endemic
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Riparian management in Taranaki – A success for native biodiversity?
Field site aerials (Courtesy of the Taranaki Regional Council, 2008):
Plate 3: Unfenced field sites (blue lines = streams, red lines = roads)
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Riparian management in Taranaki – A success for native biodiversity?
Plate 4: Fenced field sites (blue lines = streams, red lines = roads)
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Riparian management in Taranaki – A success for native biodiversity?
Plate 5: Medium field sites (blue lines = streams, red lines = roads)
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Riparian management in Taranaki – A success for native biodiversity?
Plate 6: Old field sites (blue lines = streams, red lines = roads)
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Riparian management in Taranaki – A success for native biodiversity?
Plate 7: Regenerated field sites (blue lines = streams, red lines = roads)
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