Fire frequency filters species by bark traits in a savanna-forest mosaic

Aims: Savanna and forest biomes co-occur across many subtropical landscapes in Africa, and can be differentiated by their fire regime: fires are more frequent in savannas compared to forests. Bark thickness is a key trait of savanna trees, promoting their survival in this context. The rate of bark production should therefore be critical for determining how quickly a developing sapling would be protected or bark could regenerate between two fires. Despite this, the rate of bark production has seldom been measured in studies of fire-tolerant vs fire-intolerant species. Location: Hluhluwe-iMfolozi Game reserve, South Africa. Methods: We examined the distribution of woody species in a South African park over 253 sites, stratified by biome. We described the bark traits of the 63 most abundant species and related them to the fire frequencies of the sites where they occur. Results: Bark growth rate was a good predictor of woody plant persistence in fire-prone savanna ecosystems. A key exception was root-suckering species, which have their structure physically protected underground and can thus survive frequent fires while producing little bark. Conclusion: Species of different forest types and savanna have different bark characteristics, highlighting the important role played by fire in shaping biome distribution.