CORE Metadata, citation and similar papers at core.ac.uk Provided by Wits Institutional Repository on DSPACE FIRE-MEDIATED SUCCESSION AND REVERSION OF WOODY VEGETATION IN THE KWAZULU-NATAL DRAKENSBERG, SOUTH AFRICA ___________________________________________________________________ Andrew de Villiers School of Animal, Plant and Environmental Sciences Faculty of Science University of the Witwatersrand 2012 Declaration I declare that this dissertation is my own work. It is being submitted for the Degree of Master of Science in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. Signature of candidate 19 October 2012. ii Abstract Long term fire exclusion has been attempted in Catchment IX (CIX) at Cathedral Peak. Baseline vegetation of CIX was sampled in 1952, with follow-up surveys in 1973, 1986 and 2010. These took place at key times in terms of changes in fire history within the catchment. Complete fire exclusion was achieved between 1973 and 1986, but eight accidental fires burnt part of CIX thereafter. The woody component was resurveyed in 2010 after the latest of thirteen unintended fires had swept through CIX in 2007. This fire burnt about 90% of the catchment. The vegetation of the area not burnt was a distinct community and size structure indicating it had not been burnt by other accidental fires. Partial exclusion of fire over 58 years resulted in vegetation transforming from grassland to a grassland-fynbos-scrub forest mosaic. Erica evansii and Leucosidea sericea, a reseeder and resprouter respectively, were the two dominant species in CIX. These displayed expected responses to a single fire, resulting in dominance shifting from E. evansii (92% mortality) to L. sericea (1.6% mortality). The decrease in E. evansii individuals resulted in a relative increase in community contribution of species not affected by fire. Leucosidea sericea’s post-fire dominance in burnt plots was not apparent in fire-protected areas. A successional trend of colonisation of woody species, predominantly E. evansii and L. sericea, into grassland was observed. Despite occasional fires since 1986 vegetation did not revert to grassland. The emergent woody community was not homogenous. This was attributed to a combination of an irregular pattern of accidental burns and environmental variability within the catchment. The mosaic of distinct grassland, woodland, ecotonal and scrub forest communities are predicted to remain as such. iii Acknowledgements Support for this study was provided by the South African Environmental Observation Network, the National Research Foundation and the University of the Witwatersrand. Ezemvelo KZN Wildlife are thanked for providing accommodation and allowing access to the study site. I would like to thank Professor Tim G. O‟ Connor for his mentorship, suggestions and guidance throughout the past two years. He has taught me much. In addition, I would like to thank Dr. Terry M. Everson for her help and assistance when asked for. Special thanks are expressed to Miss Michelle L. Tait and Mrs. Mariette de Villiers with their help in editing preliminary versions of chapters one and two, and to Lisa for her love, support and help throughout the past years. To God be the glory. “The earth is the LORD's, and everything in it, the world, and all who live in it...” Psalm 24:1 iv Contents Abstract ................................................................................................................................ iii Acknowledgements ............................................................................................................ iv List of Figures ................................................................................................................... viii List of Tables ........................................................................................................................ x CHAPTER 1 : Introduction ................................................................................................. 13 1.1 Fire in the natural environment................................................................................ 13 1.2 Catchment IX: An experimental catchment ........................................................... 15 1.3 This study.................................................................................................................... 17 CHAPTER 2 : Literature review ........................................................................................ 18 2.1 Montane vegetation dynamics ................................................................................. 18 2.2 Treelines ..................................................................................................................... 18 2.3 Reason for moist grasslands: Fire .......................................................................... 20 2.4 Characteristics of fire ................................................................................................ 21 2.5 Moist grasslands and succession ........................................................................... 22 2.6 Erica evansii ............................................................................................................... 23 2.7 Leucosidea sericea ................................................................................................... 24 2.8 Moist grasslands and forests: alternate systems ................................................. 24 CHAPTER 3 : Changes in woody vegetation between 1973, 1986 and 2010 as a result of partial fire exclusion in Catchment IX, Cathedral Peak, KwaZulu-Natal Drakensberg, South Africa.................................................................................................. 26 Abstract .............................................................................................................................. 26 3.1 Introduction ................................................................................................................. 27 v 3.2 Material and Methods ............................................................................................... 32 3.2.1 Study site ............................................................................................................. 32 3.2.2 Approach ............................................................................................................. 33 3.2.3 Statistical analyses............................................................................................. 34 3.3 Results......................................................................................................................... 36 3.3.1 Changes in the overall woody community...................................................... 36 3.3.2 Changes in the distribution, density and mean height of the Leucosidea sericea population during periods of contrasting fire regimes............................... 36 3.3.3 Changes in the distribution, density and mean plant height of the Erica evansii population during periods of contrasting fire regimes ............................... 43 3.4 Discussion................................................................................................................... 47 3.4.1 Vegetation changes in fire-protected areas over time.................................. 47 3.4.2 Vegetation changes in fire-prone areas over time ........................................ 48 3.4.3 Successional pattern of change ....................................................................... 50 3.5 Conclusion .................................................................................................................. 51 3.6 Appendix ..................................................................................................................... 53 CHAPTER 4 : Effect of a single fire on woody vegetation in Catchment IX, Cathedral Peak, KwaZulu-Natal Drakensberg, following extended partial exclusion of fire....... 56 Abstract .............................................................................................................................. 56 4.1 Introduction ................................................................................................................. 57 4.2 Material and Methods ............................................................................................... 61 4.2.1 Study site ............................................................................................................. 61 4.2.2 Approach ............................................................................................................. 62 4.2.3 Statistical analyses and assumptions ............................................................. 63 4.3 Results......................................................................................................................... 64 vi 4.4 Discussion................................................................................................................... 77 4.5 Conclusion .................................................................................................................. 80 CHAPTER 5 : Influence of the abiotic environment on the response of woody vegetation to the partial exclusion of fire in Catchment IX, Cathedral Peak, KwaZulu- Natal Drakensberg, South Africa ....................................................................................... 82 Abstract .............................................................................................................................