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.
Summary
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.