A comprehensive study of over 31,000 tree species worldwide indicates that forests are becoming more uniform, with fast-growing trees gaining dominance while slow-growing, long-lived species decline. This transformation threatens ecosystem stability, carbon storage, and biodiversity, particularly in tropical regions. Scientists urge changes in forest management to protect vulnerable native trees.
Forests worldwide are undergoing a profound change, as revealed by an international study published in Nature Plants. Researchers analyzed more than 31,000 tree species to predict shifts in forest composition over coming decades. The findings show a clear trend: fast-growing species, often with lighter leaves and lower wood density, are proliferating, while slower-growing trees with dense wood and thick leaves are at risk of decline or extinction.
These slow-growing species, prevalent in moist tropical and subtropical forests, serve as the ecosystem's backbone. They enhance stability, store carbon effectively, and support diverse life forms. Jens-Christian Svenning, a senior author from Aarhus University, highlighted the peril to unique species in isolated regions: "We are talking about highly unique species, especially concentrated in tropical and subtropical regions, where biodiversity is high and ecosystems are tightly interconnected. When specialized, native species disappear, they leave gaps in ecosystems that alien species rarely fill, even if those species are fast-growing and highly dispersive."
Human activities, including climate change, deforestation, logging, and global trade, drive this homogenization. Fast-growing trees like acacia, eucalyptus, poplar, and pine are promoted for quick timber production but prove vulnerable to droughts, storms, pests, and climatic shocks. Svenning noted: "Although these species establish and grow well, they are more vulnerable to drought, storms, pests, and climatic shocks. This makes forests less stable and less effective at storing carbon over the long term."
Tropical areas face the severest impacts, with rising endangerment of slow-growing species confined to small ranges. First author Wen-Yong Guo from East China Normal University explained: "This is where many slow-growing tree species with naturally small ranges occur. Because they are confined to very limited areas, these species are especially vulnerable and risk disappearing entirely if their habitats are destroyed or taken over by fast-growing species."
Naturalized species, originating elsewhere but thriving in new areas, exacerbate the issue. Nearly 41 percent of them exhibit rapid-growth traits suited to disturbed environments, yet they fail to replicate native ecological roles and intensify competition. Guo added that in northern regions, invasions by such species are likely to dominate.
The study calls for urgent action in forest management. Svenning advocated prioritizing slow-growing and rare species in restoration: "When establishing new forests, far more emphasis should be placed on slow-growing and rare tree species. This would make forests more diverse and resilient." By modeling future scenarios, researchers predict further dominance of naturalized fast-growers unless interventions occur.
