Non-additive effects on plant mixtures flammability in a tropical mountain ecosystem

Background Consumability, a component of flammability, describes how well plants burn and may be influenced by species traits and climate change. However, knowledge gaps remain regarding how species mixtures interact and whether non-additive effects are mediated by functional traits and diversity. Aims This study examined the consumability of species mixtures in Brazil’s tropical montane grasslands (campos de altitude), focusing on traits and species interactions. Methods Laboratory tests measured remaining biomass (a proxy for consumability) in monospecific and three-species mixtures for seven species. Traits like specific leaf area (SLA), leaf dry matter content (LDMC), fuel moisture at ignition (FMCig) and maximum combustion rate (MCR) were assessed, along with functional diversity, to understand their influence on consumability. Results Consumability in species mixtures differed from predictions based on individual species values, indicating non-additive effects. Leptostelma maximum, Pleroma hospita and Chusquea pinifolia, despite low or medium individual consumability, contributed most to mixture consumability. Higher SLA reduced consumability, whereas higher MCR, LDMC and functional index FRich increased it. Conclusions Our results suggest that low-consumability species like L. maximum may reduce fire severity, offering opportunities for fire management in the campos de altitude. Implications These findings highlight the importance of considering species interactions in mixtures and identifying traits that shape plant community flammability.