Data from: Community-level flammability declines over 25 years of plant invasion in grasslands

1. Exotic plant invasions can alter fire regimes in plant communities.
Invaders often possess traits that differ from native plants in the
community, resulting in increases or declines in community-level
flammability, changing fire regimes, and potentially causing long-term
modifications to plant community composition. Although considering traits
of multiple invaders and native species together is useful to better
understand how invasions change community-level flammability, few studies
have done this. 2 Measured morphological and flammability traits of 51
native and exotic plant species common in tussock grasslands in New
Zealand’s south-eastern South Island to examine relationships between
morphology and whole-plant and shoot-level flammability. Plant community
data from 103 permanent transects in this region measured over a 25 year
period (c. 1982-2007) were used to determine how flammability changed with
increasing levels of plant invasion. 3. Invasion by exotic plants has led
to reduced community-level flammability due to shifts from native tussock
grasses with high flammability and high fuel loads to mat-forming exotic
forbs with low flammability and little fuel. These changes will likely
lead to considerable alterations to the fire regime, resulting in lower
intensity fires that burn more patchily and for shorter amounts of time,
potentially causing further changes in floristic composition. We found
considerable differences in flammability across the wide range of species
and growth forms that we studied, emphasising the importance of
quantifying species-level flammability and the need to avoid treating
grasslands as homogenous in terms of their flammability. Total biomass,
leaf length and leaf area were the traits most positively correlated with
flammability in these tussock grasslands. 4. SYNTHESIS. We show how plant
invasions over decadal timescales have reduced the community-level
flammability of tussock grasslands and, for the first time, demonstrate
how this can be driven by exotic forbs. The total biomass of constituent
species is a useful surrogate for community flammability across a wide
range of species and growth forms in both temperate grasslands and savanna
ecosystems and should be used in dynamic global vegetation models to
assess how flammability varies under various global change scenarios.