Data from: Determinants of flammability in savanna grass species

1. Tropical grasses fuel the majority of fires on Earth. In fire-prone
landscapes, enhanced flammability may be adaptive for grasses via the
maintenance of an open canopy and an increase in spatiotemporal
opportunities for recruitment and regeneration. In addition, by burning
intensely but briefly, high flammability may protect resprouting buds from
lethal temperatures. Despite these potential benefits of high flammability
to fire-prone grasses, variation in flammability among grass species, and
how trait differences underpin this variation, remains unknown. 2. By
burning leaves and plant parts, we experimentally determined how five
plant traits (biomass quantity, biomass density, biomass moisture content,
leaf surface-area-to-volume ratio and leaf effective heat of combustion)
combined to determine the three components of flammability (ignitability,
sustainability and combustibility) at the leaf and plant scales in 25
grass species of fire-prone South African grasslands at a time of peak
fire occurrence. The influence of evolutionary history on flammability was
assessed based on a phylogeny built here for the study species. 3. Grass
species differed significantly in all components of flammability.
Accounting for evolutionary history helped to explain patterns in
leaf-scale combustibility and sustainability. The five measured plant
traits predicted components of flammability, particularly leaf
ignitability and plant combustibility in which 70% and 58% of variation,
respectively, could be explained by a combination of the traits. Total
above-ground biomass was a key driver of combustibility and sustainability
with high biomass species burning more intensely and for longer, and
producing the highest predicted fire spread rates. Moisture content was
the main influence on ignitability, where species with higher moisture
contents took longer to ignite and once alight burnt at a slower rate.
Biomass density, leaf surface-area-to-volume ratio and leaf effective heat
of combustion were weaker predictors of flammability components. 4.
Synthesis. We demonstrate that grass flammability is predicted from easily
measurable plant functional traits and is influenced by evolutionary
history with some components showing phylogenetic signal. Grasses are not
homogenous fuels to fire. Rather, species differ in functional traits that
in turn demonstrably influence flammability. This diversity is consistent
with the idea that flammability may be an adaptive trait for grasses of
fire-prone ecosystems.