Afforestation reshapes wildfire activity across global temperate biomes

In temperate ecosystems, afforestation is rapidly expanding as a flagship climate mitigation strategy. Yet its impact on wildfires remains poorly understood, raising concerns that establishing planted forests over nonforest areas may intensify wildfire activity under increasingly fire-prone climatic conditions. Here, we combine land-use change data, fire activity records, climatic and anthropogenic covariates to quantify how afforestation alters fire occurrence and burned area across 67,248 patches distributed throughout global temperate biomes using satellite records starting in 2001. We found that, on average, afforestation increased fire occurrence by 26% and burned area by 23% in global temperate regions. However, these effects differed markedly among biomes. Wildfire responses ranged from a near-threefold increase in fire occurrence in Temperate Conifer Forests and a 38% increase in Mediterranean Woodlands biomes to an 18% reduction in the Temperate Grasslands, Savannas, and Shrublands biome. In Temperate Broadleaf and Mixed Forests, afforestation reduced fire occurrence but increased burned area, indicating a shift toward less frequent but larger wildfires following the conversion to planted forest. These contrasting, biome-specific responses show that the consequences of afforestation on wildfire activity may depend strongly on ecological and regional context. The strong variability at biome-scale questions the premise that tree planting provides consistent climate mitigation benefits across all landscapes, and highlights the need to evaluate afforestation initiatives alongside regional disturbance regimes. Our findings indicate that wildfire risk should be explicitly accounted for when assessing the long-term effectiveness of afforestation as a climate mitigation strategy in a warming world.