D3386: Fire regime shapes butterfly communities through changes in nectar resources in an Australian tropical savanna

Fire-dependent savanna provides key habitat for butterflies, yet little is known about how fire regimes, including fire frequency and season, affect them. Such effects are likely to be primarily indirect. We examined the relationships among fire regime, butterfly abundance and diversity, and vegetation structure and floral resources at a long-term fire experiment near Darwin, northern Australia. This region of Australia contains the world’s largest intact tropical savanna and is a major biodiversity hotspot for butterflies. We found that butterfly diversity was strongly related to fire regime, especially through its effects on floral resources. Butterfly abundance was highest in early-season fire treatment plots (mean = 11.9) compared with late-season (mean = 6.7) and unburned (mean = 5.3) plots, and this was correlated with the abundance of floral resources. Butterfly species richness was higher in early-season (mean = 6.8) compared to unburned (mean = 3.3) fire treatment plots but did not differ between early- and late-season (mean = 4.7) plots. Butterfly and floral diversity were similar across fire frequencies in early-season fire treatments all burned in 2019, pointing to a key effect of time-since-fire. Our findings suggest that early-season burning promotes butterfly diversity and abundance, likely by increasing the supply of nectar resources, which has important implications for biodiversity management, given that nectar is a critical resource for many animal taxa.