Bird Community Structure and Convergence in Afromontane Forest Patches ofthe Karkloof/ Balgowan Range, KwaZulu-Natal Robyn Wethered 2001 Bird Community Structure and Convergence in Afromontane Forest Patches ofthe Karkloof/ Balgowan Range, KwaZulu-Natal. Robyn Wethered Submitted infulfilment ofthe academic requirements for the degree of Master ofScience in the School ofBotany and Zoology Department ofZoology and Entomology University ofNatal Pietermaritzburg May 2001 Mom and Dad, thanks for everything - this is for you! 11 Preface This study was carried out in the School of Botany and Zoology, Forest Biodiversity Programme, University of Natal, Pietermaritzburg, from December 1998 to May 2001, under the Supervision ofProf M. 1. Lawes. The study represents original work by the author and has not been submitted in any form to another University. Where use was made of the work of others, it has been acknowledged in the text. The chapters of the thesis are written in accordance with the required format for submission to the journal Biodiversity and Conservation. The chapters depart from this format in the following areas: 1) tables and figures appear in the text and not on separate sheets at the end of each chapter, 2) one acknowledgements section, and 3) one summary with information on all the chapters, is provided at the beginning ofthe thesis. SIGNED" ,~.v,.I.,-,fl)~.. - R. Wethered 111 Acknowledgements There are a number ofpeople that must be thanked for their assistance with this study: Prof M. 1. Lawes for his enthusiasm, guidance, and ruthless pursuit of perfection throughout the duration of this project. Prof S. E. Piper for his guidance and much needed help with generalised linear models. Prof M. Perrin for his guidance and input of ideas, and Dr H. Eeley for her contribution ofideas and proofreading. To Sven Bourquin for showing me the ropes in the field and to Sharon Lemos, Dave Thompson, Fabienne Field, and Connor Cahill for their valuable assistance in the field. A special thank you to David Phillips for moral support and encouragement, and who so willingly gave up valuable workdays to assist me in the field. A special thank you to Myles Hunt for his continued support and encouragement, and for allowing fieldwork to be conducted at Leopards Bush. To Mr and Mrs Kimber for their kindness and hospitality and for accommodating me at Maritzdaal. Also a special thank you to Sheelagh for her kindness and hospitality and for accommodating me at Irish Mist Farm. Thank you to the following land owners for allowing me to conduct fieldwork on their land: Mr C. Brown, Mr L. Growe, Mr R. Dales, Mr and Mrs Shuttleworth at Shuttleworth Weaving, Mr and Mrs Peacock at Lythwood Lodge, Jenny Geekie at Benvie, the Sinclair family, the Griffin family and the McKenzie family. I also acknowledge Mondi Paper for allowing fieldwork to be conducted on the Gilboa forestry estate; and CCWR for supplying climate data. Last but not least, a very special thanks to my parents for their continued financial support and encouragement. IV Forest fragmentation is caused by the clearing of patches of indigenous vegetation for agriculture, urban development, and other human land uses. Such action results in patches of remnant natural vegetation being surrounded by altered vegetation. I investigate the effects of forest fragmentation and matrix type on avian diversity and assemblage structure in forest patches ofthe historically fragmented Karkloof / Balgowan forest range, KwaZulu-Natal, South Africa. This study compares the bird assemblage diversity and composition of indigenous forest patches surrounded by commercial forestry (Gilboa complex) with that surrounded by natural grassland matrix (Balgowan complex). Insularisation of Afromontane Mistbelt forest in KwaZulu-Natal has led to loss of species where forest fragments support fewer bird species than comparably sized patches of mainland forest. Small fragments within natural grassland have fewer bird species per unit area than larger fragments. Forest patch area-dependent density compensation is evident and bird assemblages appear saturated. Bird assemblages are characterised by a non-random species distribution pattern where area-dependent processes are dominant, and the loss of species from fragments follows a deterministic sequence. In forests in the plantation-dominated matrix no island-effect is detectable and it appears that forest patches are converging on the same bird species richness, regardless of forest size. No density compensation is evident and bird assemblages are not saturated. The sequence of species loss from forest patches is not as predictable, where a random yet prominent colonisation process exists. As commercial plantations provide suitable habitat cover for movement of forest birds, colonisation of both distant and small indigenous forest patches has been possible, reducing the effects of area-dependent extinction in the forest patches but also resulting in lower species richness in larger patches. Bird species of the Karkloof / Balgowan forest range appear to be fragmentation adapted, and most species are resilient to further landscape change. Certain species are however more prone to local extinction than others. The major predictors of extinction risk are body size, abundance status, and feeding guild. Patch area is the dominant force governing traits in the natural Balgowan complex where larger species with low natural abundance and an insectivorous diet are most prone to local extinction. In the Gilboa complex the nature of the plantation matrix appears to be masking the species natural responses to fragmentation making it difficult to predict which species are most at risk. In order to preserve maximum bird diversity, including high-risk species, the largest intact forest units (::::302ha) must be conserved. Evidently, the nature ofthe matrix affects avifaunal diversity and distribution in forest patches, and plantations have the capacity to significantly alter bird assemblage structure and composition in indigenous forest patches. Forest fragments must be considered as integrated parts of a complex landscape mosaic, and this study emphasises the importance of understanding landscape-scale processes. Knowledge of ecological and life history traits proves valuable for predicting community level response to landscape change. Keywords: Afromontane forest; fragmentation; forest birds; landscape change; assemblage structure; diversity; species-area; minimum critical patch size; nested subsets; community convereence: incidence functions; lift history traits; extinction proneness; extinction filtering; South Africa. b ' v Table of Contents Page Number Preface .ii Acknowledgements .iii Abstract .iv Table ofContents v CHAPTER 1 Introduction 1-22 1.2 Landscape andhabitatfragmentation 2 1.3 The history ofAfromontaneforestfragmentation andExtinctionfiltering 4 1.4 Species-area effects 5 1.5 Non-equilibrium theories ofcommunity composition: Community convergence andnestedsubset theory 6 1.6 Matrix transformation: species' response to landscape change 9 1.7 Conservation andmanagement 11 1.8 Summary 12 1.9 References 13 CHAPTER 2 Insular Effects on Forest BirdDiversity: Species-Area Relationships in a FragmentedForest Landscape 23-60 2.1 Introduction : 23 2.2 Methods 2.2.1 Study area 25 2.2.2 Forestpatches sampled 27 2.2.3 Birdcensus methods 27 2.2.4 Data analysis 29 2.2.5 Species diversity 29 2.2.6 Rarefaction 30 2.2.7 Area, isolation, andhabitat diversity 30 2.2.8 Species-area analysis i. Species-area curves 31 ii. Minimum criticalpatch size 31 2.3 Results 2.3.1 Birdspecies richness anddiversity 32 2.3.2 Population density 34 2.3.3 Is density compensation occurring in these forests? 35 2.3.4 Area, isolation andhabitat diversity 37 2.3.5 Species-area analysis i. Species-area curves 37 ii. Minimum criticalpatch size 38 2.4 Discussion 41 VI 2.5 Conclusion 46 2.6 References 47 Appendix 2.1 58 Appendix 2.2 59 Appendix 2.3 60 CHAPTER 3 Nestedness ofForest Bird Communities in a Fragmented Landscape: Selective Immigration or Extinction? 61-85 3.1 Introduction 61 3.2 Methods 3.2.1 Study area 64 3.2.2 Birdcensus methods 65 3.2.3 Cluster analysis 65 3.2.4 Correspondenceanalysis 65 3.2.5 Nested subset analysis 66 3.2.6 Mechanisms ofnestedness 67 3.2.7 Predictability ofextinction 68 3.3 Results 3.3.1 Cluster analysis - how similar are the bird assemblages among patches? 68 3.3.2 Correspondenceanalysis - how variable are the bird assemblages among patches? 69 3.3.3 Nested subset analysis i. All bird species 70 ii. Forest dependent species 71 3.3.4 Mechanisms ofnestedness: selective extinction or colonisation? 72 3.3.5 Predictability ofextinction 72 3.4 Discussion 73 3.5 Conclusion 77 3.6 References 78 Appendix 3.1 84 Appendix 3.2 85 CHAPTER 4 Species Viability in a Disturbed andFragmented Forest Landscape - Ecological and Life History Traits 86-124 4.1 Introduction 86 4.2 Methods 4.2.1 Study area 89 4.2.2 Bird census methods 90 4238... .pectesresponse. tofr agmentation . 90 4.2.4 Ecological andlife history traits ofbird species 91 4.2.5 Predictors oflocal extinctionproneness 94 vu 4.3 Results 4.3.1 Species response tofragmentation i. Area effects 94 ii. Effect ofthe matrix: Balgowan / Gilboa comparison 95 4.3.2 Predictors oflocal extinction proneness 97 4.4 Discussion 102 4.5 Conclusion 106 4.6 References 107 Appendix 4.1 117 Appendix 4.2 120 Appendix 4.3 122 Appendix 4.4 124 CHAPTERS Summary: Conservation andManagement 125-128 5.1 Implicationsfor conservation: importantfindings 125 5.2 Management