The Future of South African grassland communities: An experimental analysis on plant trait responses to fire frequencies and warming. In collaboration with University of KwaZulu-Natal, Pietermaritzburg, South Africa.

Abstract

Fire has historically been an important natural disturbance factor structuring African mesic grasslands and is nowadays a widely used management tool for preserving soils and maintaining grassland structure. With predicted climatic changes ahead of us, increased temperatures and more frequent and intensified wildfires will affect vegetation communities, especially in grasslands that are vulnerable to shifts in disturbance regimes. A major challenge lies in the understanding of plant responses to the climatic and human-induced disturbance changes in order to conserve biodiversity and secure ecosystem functioning. This study investigates the effect of fire frequencies and warming on African grasslands communities, using a trait-based approach. Data on plant functional traits was gathered at two study locations in South Africa which are home to long-term fire and warming experiments using open top warming chambers: Ukulinga Research Farm (altitude: 840m) and Brotherton Research Trail (altitude: 1890m). Comparisons were made between trait data from plots that experienced different disturbance treatments (different frequencies of burning and the presence or absence of passive warming) to study patterns of variation (both communal and species-specific) of six growth-related traits (leaf table height, specific leaf area, leaf dry matter content, culm height, biomass-ratio and number of inflorescences). Results indicate that fire affects plant traits to a greater extent than warming, selecting for slow-growing and tall grass species with the decrease of fire disturbance. Increase in leaf table height was both the result of compositional changes as species-specific changes with less frequent burns, whereas specific leaf area decreases were found to be the result of solely compositional changes. Different responses of community and species-specific leaf dry matter content to fire were found between study locations and an interactive effect for fire and warming was only found for community leaf dry matter content at Brotherton. Results of this study help to understand vegetative changes due to fire disturbances, either natural or human induced, and climatic changes and are valuable for successful conservation strategies.