Management of Critically Endangered renosterveld fragments in the Overberg, South Africa Odette Elisabeth Curtis Thesis presented for the degree of Doctor of Philosophy Department of Biological Sciences University of Cape Town April 2013 Supervisor: Prof. William Bond Co-supervisor: Simon Todd PLAGIARISM DECLARATION By submitting this thesis, I acknowledge that I know the meaning of plagiarism and declare that all the work in the thesis, save for that which is properly acknowledged, is my own. _______________________________________ Odette Curtis 2nd April 2013 DECLARATION OF FREE LICENSE I hereby: a) grant the University of Cape Town free license to reproduce the above thesis in whole or in part, for the purpose of research; b) declare that: i) the above thesis is my own unaided work, both in conception and execution, and that apart from the normal guidance from my supervisors, I have received no assistance except as stated below; ii) neither the substance nor any part of this thesis has been submitted in the past, or is being, or is to be submitted for a degree at this University or at any other University. I am now presenting the thesis for examination for the Degree of PhD. _______________________________________ Odette Curtis 2nd April 2013 Copyright © University of Cape Town All Rights Reserved DEDICATION This thesis is dedicated to Philip Anthony Hockey (1956 – 2013), who helped me develop the platform on which I have built my academic career, and whose friendship is sorely missed. Drawing by Chris van Rooyen ACKNOWLEDGEMENTS Thank you to my supervisor, Prof. William Bond, for guidance and patience and time in the field. For believing in me and for moral support when I needed it, particularly at the end. For a willingness to experience renosterveld, while teaching me to love renosterbos! To my co-supervisor, Simon Todd, for ordinations and analyses, for long discussions, for a shared passion for renosterveld, for guideance and for patience and support through the entire project. This work was made possible by funding provided by the Table Mountain Fund, WWF-SA from 2007- 2011 and through NRF funding during 2011 and 2012 (through Prof. William Bond). Thank you. And to David Roby in the USA, for philanthropic funding in support of renosterveld conservation. To colleagues who advised and guided, who commented on chapters: Prof. Sue Milton and Dr. Ian Newton. Thank you to Tracey Nowell for sifting through soil samples, locating ‘missing’ samples and giving me peace-of-mind by being a reliable support system. I am indebted to the Board of the Overberg Lowlands Conservation Trust: Dirk van Papendorp (Chairperson), Alan Jeftha, Lesley Richardson, Sean Privett and Prof. Charles Stirton. I am priveledged to have you onboard. Thanks to all of you for what we are doing and what we have to look forward to. For allowing me the time to finish this. And to Dr. Rob Brett and David Houghton, for their support on the OLCT’s activities from afar. A sincere thank you to Chris Martens (CapeNature) for early discussions, management of risky control burns and assistance with setting up experiments. And to the landowners (Valerian van der Byl, Ian le Roux, Albert Bester, Tom and Trevenen Barry and Dirk van Papendorp), who made sure that burning treatments were carried out, who protected burning exclosure plots, for managing fencing of grazing exclosures and for allowing me constant access to their properties. To all the other landowners whose properties I have had the priveledge of exploring. Thank you for your openness and willingness to listen. Thanks in particular to Keith and Michelle Moddie and Neels and Annelize Uys for accommodation in the field and a willingness to see more and to conserve renosterveld. To Charlie Stirton, for late-night discussions, lots of laughs, wonderful times in the field, moral support, academic collaboration, friendship and Polhillia curtisiae and Otholobium curtisiae. And Muthama Muasya, for collaborations and fun field trips – looking forward to many more! Cameron and Rhoda McMaster for teaching me bulbs, for days spent on our kness collecing data, for friendship and constant support. Flora Cameron, for her passion and compansionship, for days in the field with flowers. My dear friends, Dee and Neal Robinson, for delivered dinners in the last weeks of writing, for listening to rants, for understanding. And to a few special friends: Sarah Foyle, Samantha Peterson, Emma Sexton, Lucy Olden, Phoebe Barnard, and Julian and Madelain Reid, for their friendship and moral support through it all. Special thanks to Heather D’Alton for sushi evenings and checking references at the end. And to Samantha Hockey for seeing the final night through with me, for meticulous reference checks, extra paper for printing and for keeping me calm in the last few hours. To my parents, Philip and Liesbeth Curtis, who have always given me the freedom to choose what I wanted and the support when I chose it. For patience and understanding, for consistency and for never doubting me. TABLE OF CONTENTS Subject Page # Thesis summary (abstract) 1 Chapter 1: General Introductory chapter 3 Chapter 2: Site description chapter 25 Chapter 3: Renosterveld: shrubby grassland or grassy shrubland? Introduction 32 Study area and methods 38 Results and discussion 39 Conclusions 45 Chapter 4: Is renosterveld a fire-stimulated system? Introduction 50 Study area and methods 52 Results and discussion 55 Conclusions 62 Chapter 5: Diversity in renosterveld Introduction 69 Study area and methods 72 Results and discussion 74 Conclusions 84 Chapter 6: Predicting species extinction risk in renosterveld using simple models Introduction 92 Study area and methods 95 Results and discussion 98 Conclusions 105 Chapter 7: Fire and grazing in renosterveld: testing responses using experimental plots Introduction 112 Study area and methods 118 Results 122 Discussion and conclusions 150 Chapter 8: Synthesis 163 Appendices 181 THESIS SUMMARY Lowland renosterveld is a relatively fertile, shale-derived vegetation type found within the Fynbos Biome of South Africa, a biome which is recognized as one of the world’s smallest, yet richest plant kingdoms. Due to the fact that renosterveld tends to be dominated by a handful of small-leaved asteraceous shrub species, it creates the illusion that it is a homogeneous habitat with low levels of alpha diversity and species turnover. This is exacerbated by the widely accepted, although not proven, hypothesis which states that current-day renosterveld is derived from a pristine C4 grassland and that the dominance of asteraceous shrubs is solely due to more than 300 years of mismanagement in the form of overgrazing. This process of degradation is believed to have started with the arrival of the European settlers who exterminated the large herds of free-roaming ungulates and replaced them with livestock (sheep and cattle), which, through their selective feeding habits and their sedentary manner of grazing, altered the system from a grassland to a shrubland. The debate over what renosterveld actually is, combined with a dearth of knowledge as to its ecological functioning, has meant that management recommendations are largely based on a combination of guess-work and inferences from studies in adjacent and similar fynbos and karoo habitats. Additionally, renosterveld has been severely transformed for agricultural development, rendering it a Critically Endangered vegetation type, with 4- 10 % of the oringial extent remaining. In this thesis, I focus on lowland renosterveld in the Overberg (also referred to as South Coast Renosterveld), Western Cape, South Africa. I investigate, through the use of soil carbon-isotope analyses, the grassy-shrubland vs. shrubby grassland debate and assess whether or not the theory that renosterveld is merely a degraded grassland has merit. I evaluate diversity levels at the alpha, beta and gamma scales and contrast these with comparable Mediterranean-climate vegetation types, while considering the implications for conservation planning for renosterveld in the Overberg. Through the use of a simple model, I investigate whether it is possible to predict species extinction rates at the local (patch) level. I then assess responses to grazing and fire, through a combination of controlled experiments and random surveys, in order to assess management requirements. I found that South Coast Renosterveld was more-than-likely always a grassy-shrubland, and that although data suggest slightly higher C4 inputs historically, rensoterveld was never a pure C4 grassland. Alpha diversity was on a par, if not higher, than that of any other studied fynbos habitats and is comparable, if not richer, than its other Mediterranean-climate shrubland counterparts. Similarly, species turnover across habitat and landscape gradients was high, suggesting that multiple renosterveld Page | 1 reserves will be crucial for the long-term preservation of this habitat and associated ecological processes. Renosterveld in the Overberg responds positively to fire, through a significant increase in flowering and germination in post-burn vegetation, while older renosterveld is less productive. However, I also demonstrate that regular short burning intervals are not advisable for this relatively dry shrubland, which is better suited to fire frequencies similar to, or lower than, those in comparable fynbos habitats. Grazing impacts did not manifest on plant diversity or cover, but did affect size and productivity of species favored by livestock, suggesting