Tree planting choices mediate wildfire damage to tropical forest restoration in eastern Madagascar

Wildfires threaten tropical rainforest conservation and restoration around the world, and they pose a particular risk to the unique species assemblages in eastern Madagascar. Following an intense period of wildfires in 2020–2022 that impacted 33% of 46 tropical forest restoration sites installed by the non-profit organization Green Again Madagascar along Madagascar's central east coast, we compared fire intensity, fire severity, and native tree mortality in a subset of 11 experimental plantings to learn how tree planting choices impacted wildfire risk. Each restored site contained four 25 × 25 m treatment plots, which varied in tree planting size (81 vs. 625 m²), density (123 vs. 1111 trees/ha), and species composition (fire-vulnerable vs. fire-resilient species planted on plot edges). Seventy-five percent of 2772 trees were killed, with strong differences in mortality (41–100%) among 27 native species. The strongest treatment effect was species composition; plantings that included fire-resilient tree species reduced overall mortality by 72%. Other tree planting choices (size, density, and position) had little or no impact on fire behavior or tree mortality. We conclude that wildfires impose a strong environmental filter on native Malagasy trees, selecting for species capable of resisting burning or resprouting following fire. Including these species in restoration plantings will increase the resilience of restored rainforests to wildfires but is unlikely to offer protection to the many endemic trees that are vulnerable to fire mortality.