Tree evenness sustains multiple ecosystem services in boreal–temperate ecotone

Boreal forests are crucial for carbon sequestration and vulnerable to climate change. Under ongoing warming, these forests would transform into boreal–temperate ecotones, altering their structure and the ecosystem services they provide. However, the roles of tree diversity and forest structure in sustaining multiple ecosystem services within boreal–temperate ecotones remain poorly understood. Here, we conducted a field survey across a large boreal–temperate ecotone in eastern Asia to assess how tree richness, evenness, and key tree species affect multiple ecosystem services, including carbon stock, nutrient cycling, wood production, organic matter decomposition, water regulation, and microbial habitats. We found that tree richness decreased with latitude, reflecting community restructuring across the ecotone. Tree evenness and key species were integral to explaining ecosystem multiservices, with evenness being positively correlated with multiservices. Furthermore, the relationship between tree richness and ecosystem multiservices shifted from negative to positive with increasing tree evenness. These results highlight the critical role of tree evenness and key species, beyond richness, in supporting multiple ecosystem services under climate change, providing valuable insights for managing the ecosystem services of boreal–temperate ecotones.