The effect of altered rainfall seasonality on post-fire recovery of Fynbos and Renosterveld shrublands in the Cape Floristic Region

Doctoral Thesis


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Shifting climate patterns are a cause for concern for natural ecosystems globally. Of particular concern is the effect of climate change on fire-prone, Mediterranean-type shrublands globally because of the heightened sensitivity of post-fire vegetation to environmental conditions. In this thesis, I focused on investigating the relationships between rainfall seasonality patterns and post-fire vegetation processes in neighbouring Fynbos and Renosterveld shrubland communities within the mega-diverse Cape Floristic Region of South Africa. I investigated vegetation sensitivity to moisture availability at multiple levels of detail including 1) productivity and community structure, 2) growth form responses and 3) physiological performance over three years. Post-fire rainfall patterns were manipulated by artificially increasing summer rainfall and reducing winter rainfall over permanent, field sites, thus reducing annual seasonality and creating soil moisture contrasts between control and treatment plots over warm and cool seasonal periods. At all levels of investigation, postfire vegetation processes at the Fynbos site were relatively insensitive to variations in moisture availability relative to the Renosterveld site where vegetation processes and community structure were strongly affected. Nutrient limitation and lower soil tension in coarse, sandstone-derived soils of the Fynbos site could strongly limit the influence of soil moisture patterns on post-fire physiology leading to stable growth, community structure and productivity under a variety of moisture regimes. Soil moisture patterns during the first summer had significant and long-term implications for community structure and productivity patterns in the Renosterveld site, highlighting the sensitivity of vegetation patterns to early post-fire processes. Overall this study demonstrates that post-fire rainfall patterns can have strong effects on vegetation recovery processes but that structurally similar shrublands, which are specialised to differing soil types, could show marked differences in their response to climate change due to the mediation of climate responses by soils.