The ecology of sprouting in South African forests, savannas and fynbos

Kruger, Laurence

The ecology of sprouting in South African forests, savannas and fynbos

Doctoral Thesis

2005

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

Sprouting has only recently received attention as a key life history strategy, especially in less disturbance prone environments. The aims of this thesis were to explore the ecological role of sprouting in selected South African biomes. In particular, to explore the biogeographic, community and individual level consequences of adopting sprouting as a life history strategy. The thesis is broadly divided into 4 sections. The first three dealing with the ecology of sprouting in forests, fynbos and savannas respectively; and the fourth undertakes to determine whether sprouting is considered in plant ecological strategy schemes. Chapter 1 and 2 deals with the role of sprouting in forests in relation to reseeding as key regeneration strategies in southern Cape forests. Sprouting has been largely been ignored as a regeneration strategy in favour of reseeding in southern African forests. I found that tall forests are dominated by reseeding species, while sprouting species dominate shorter canopied forests. The relative dominance of sprouters has an effect on forest canopy species richness: as sprouter abundance increases, with decreasing canopy height, canopy species richness decreases. Sprouters are able to retain their in situ position in the forests for longer periods of time than do reseeders, which reduces individual and species turnover, and hence canopy species richness. In Chapter 3 and 4, I explore Proteaceae Life History strategies in relation to fire. Sprouting ability and bark thickness are used as key traits in defining Proteaceae life history strategies. Five functional groups are described and are broadly divided into two categories resisters and non-resisters. Resisters include thick barked fire resisting and epicormic sprouting species and non-resisters basal sprouting and thin barked non-resistant species. Sprouting strategy and bark thickness were also found to influence plant architecture and hence individual and stand flammability. Non-resisting species tend to display a more ramified architecture, resulting in a more flammable state. Conversely, thick barked species tend to display a less ramified and therefore more fire resistance architecture. In Chapter 5 I explore how changes in disturbance regime affect Acacia life history strategies in Hluhluwe-Umfolozi Park, KwaZulu Natal, South Africa. Four functional groups are defined based on sprouting ability, bark thickness, seed mass, plant height and wood density. The functional groups are seen to reflect local disturbance regimes: Acacia species found in mesic, frequently burnt portions of the park sprout strongly as adults and/or are fire resistant, but are poorly defended against herbivory. Conversely, species found in more xeric portions, where fire frequency is lower, and herbivore densities higher, are fire-sensitive, well defended against herbivory and sprout weakly as adults. Chapter 6 addresses whether plant ecological strategy schemes take sprouting into account as a key life history strategy. Westoby's LHS scheme, which comprises specific leaf area (SLA), plant height and seed mass, is of the more practicable existing plant ecological strategy schemes. I show that the LHS scheme does not consistently identify sprouting across genera or families. In general, basal sprouters tended to be shorter than congeneric reseeders, but there were no consistent patterns for SLA or seed mass. The results suggest that sprouting ability is mostly orthogonal to other life history traits and should be therefore considered as a separate attribute. A published paper, which is ancillary to the main themes of the thesis, has been included as an appendix.

Keywords

Botany

Reference:

Collections

PhD / Doctoral

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