Flammability traits of Cape shrubland species with different post-fire recruitment strategies

Abstract

Wild fire is an important disturbance that shapes global biome distributions and maintains the structure, function and biological diversity of plant communities in fire-prone environments. Physical, chemical and architectural properties of plants are known to affect flammability. We wished to explore how these traits contribute to fire properties at the individual species level and how flammability varies with other plant traits, including recruitment strategy. We studied flammability and traits that contribute to it in 29 woody species occurring in fynbos and renosterveld shrublands in the Cape region of South Africa. Fifteen of the species had fire-stimulated recruitment and 14 recruit in unburnt, older vegetation. Flammability was measured on whole plants or large shoots with intact architecture. Results across all species were consistent with other studies in finding that the proportions of dead and fine fuel are good predictors of flammability. Significantly higher flame temperatures and proportions of sample units burnt were recorded for fire-stimulated vs. non-fire-stimulated recruiters. These differences were associated with significant differences in the dead fuel proportion and fuel bed porosity between recruitment strategies. This is consistent with the hypothesis that flammability is most likely to be selected for in species that are the first to occupy post-burn gaps, where a combination of increased flammability and recruitment success enhances their fitness in the fire-prone environment.