Time to burn: Landscape drivers of fuel trait variability and fire
regime in savanna ecosystems
Abstract
Fire is a key driver of the structure of plant communities. Fuel traits
are important determinants of fire behavior in tropical savannas and,
thus, of the effects of fire. However, whether these traits are
predictable and how they are influenced by biotic and abiotic drivers
remain to be rigorously evaluated. We tested the hypothesis that fuel
traits are mutually correlated and change in response to abiotic factors
and fire history. We sampled 31 plots in Serra da Canastra National Park
(Brazil) distributed in five soil classes and measured the following
fuel traits: fuel loads, height, continuity, bulk density, and bed
flammability. We determined soil clay content, fire history, climate,
canopy cover and elevation. We also obtained data on future fire
frequency. To test for correlations among fuel traits, we used Pearson
correlation tests and a principal component analysis. For the effect of
abiotic factors on the traits and principal component axes, and for the
effect of fuel traits on future fire regime, we used generalized linear
models. We found two leading axis of fuel trait variability. The first
was positively correlated to fuel height, continuity, loads, bed
flammability, and grass cover, and was predicted positively by time
since last fire. The second axis was positively correlated to fuel bulk
density and continuity, shrub and litter cover, negatively to fuel bed
flammability, and was predicted by canopy cover and soil clay content
(positive associations). Grass fuel loads were the best predictor of
future fire frequency and were negatively correlated to canopy cover and
positively to time since last fire. Our results suggest that fuel traits
change predictably in space and time, that canopy cover and time since
last fire are the main factors controlling community flammability, and
that grass fuel cover is a key predictor of fire frequency in savannas.