Leaf dry matter content (LDMC) is an important determinant of plant flammability. Investigating global patterns of LDMC could provide insights into worldwide plant flammability patterns, informing wildfire management. We characterised global patterns of LDMC across 4074 species from 216 families, revealing that phylogenetic and environmental constraints influence LDMC. LDMC varied across growth forms and taxonomic groups, displaying phylogenetic niche conservatism. Temperature, precipitation, aridity index, soil total nitrogen content and wildfire activity affected LDMC, and the effect of wildfire activity was stronger than other environmental factors across species with postfire regeneration abilities. Such species had higher LDMC, and their LDMC was less phylogenetically conserved and more strongly associated with fire activity. Our results suggest that, although LDMC shows phylogenetic niche conservatism, LDMC is determined by environmental factors, especially wildfire activity. Wildfire has likely acted as a selective pressure towards high LDMC across species that persist through fire using postfire regeneration.

Plant flammability is an important driver of wildfires, and flammability itself is determined by several plant functional traits. While many plant traits are influenced by climatic conditions, the interaction between climatic conditions and plant flammability has rarely been investigated. Here, we explored the relationships among climatic conditions, shoot-level flammability components, and flammability-related functional traits for 186 plant species from fire-prone and nonfire-prone habitats. For species originating from nonfire-prone habitats, those from warmer areas tended to have lower shoot moisture content and larger leaves, and had higher shoot flammability with higher ignitibility, combustibility, and sustainability. Plants in wetter areas tended to have lower shoot flammability with lower combustibility and sustainability due to higher shoot moisture contents. In fire-prone habitats, shoot flammability was not significantly related to any climatic factor. Our study suggests that for species originating in nonfire-prone habitats, climatic conditions have influenced plant flammability by shifting flammability-related functional traits, including leaf size and shoot moisture content. Climate does not predict shoot flammability in species from fire-prone habitats; here, fire regimes may have an important role in shaping plant flammability. Understanding these nuances in the determinants of plant flammability is important in an increasingly fire-prone world.