A native C3 grass alters fuels and fire spread in montane grassland of South Africa

Abstract

Although most fire research in plant ecology focuses on vegetation responses to burning, shifts in plant community composition wrought by climate change can change wildland fuelbeds and affect fire behaviour such that the nature of fire in these systems is altered. Changes that introduce substantially different fuel types can alter the spatial extent of fire, with potential impacts on community succession and biodiversity. Montane grasslands of sub-Saharan Africa are threatened by climate change because species distributions can shift with climatically determined ranges. We studied the impact of patches of the temperate C3 grass Festuca costata in C4-dominated grassland at the transition between their subalpine ranges in South Africa’s Drakensberg. We used empirical data on fuel moisture and fuel load across F. costata-dominated patches in a C4-dominated matrix in fire spread models to predict the effect of larger, higher-moisture F. costata patches on the spatial extent of fire. Results indicate F. costata reduces fire spread and burn probability in F. costata patches, and the effect increases as live fuel moisture increases and patches get larger. However, as a native species, F. costata does not appear to have the extreme, fire-suppressing effect of non-native C3 grasses in other C4 grasslands. Instead, F. costata patches likely increase variability in the spatial extent of fire in this C4-dominated grassland, which likely translates to spatial variability on vegetation succession.