The planets forests are changing: more and more weak and less resistant species

Forests around the world are quietly being transformed, and not for the better. A global analysis of thousands of different tree species has shown that forests are becoming more uniform, increasingly dominated by fast-growing trees, while slow-growing, long-lived species are disappearing. It is precisely these slower species that act as the backbone of forest ecosystems, storing carbon, stabilizing environments and supporting complex networks of life, especially in tropical regions, where biodiversity is greatest. Trees are essential for life on Earth. They absorb and store CO2, are home to animals, fungi and insects, prevent soil erosion, manage water cycles and provide people with vital resources such as wood, food and shade during hot seasons. But despite their importance, forests around the world are undergoing a major transformation. Recent research shows that many forest ecosystems are becoming more uniform, losing biodiversity and therefore becoming less resilient. These findings come from a large international study published in the journal Nature Plants.By examining more than 31,000 tree species around the world, scientists were able to establish a forecast of how the planets forests may change in the coming decades.More and more fast-growing speciesThe research revealed something worrying: fast-growing tree species are increasingly dominant, often driven (but not only) by the timber industry that is interested in abundant production in a short time. At the same time, slower-growing trees with specialized characteristics are at increasing risk of decline or even extinction. Jens-Christian Svenning, from the Danish National Research Foundation, Aarhus University, and lead author of the study, says that this trend is deeply worrying. The professor warns above all of the danger faced by tree species that only exist in small isolated regions of the world, as they are especially sensitive to possible extinction. "We are talking about extremely unique species, especially concentrated in tropical and subtropical regions, where biodiversity is high and ecosystems are closely interconnected. When specialized native species disappear, they leave gaps in ecosystems that exotic species rarely fill, even if these species are fast growing and highly dispersive," says Jens-Christian Svenning. The trees that support forests are in danger. The most endangered species are slow-growing trees that grow in stable environments. According to Svenning, these species typically have thick leaves, dense wood and a long lifespan, and are especially common in humid tropical and subtropical forests. They form the backbone of forest ecosystems and contribute to stability, carbon storage and resilience to change, says Jens-Christian Svenning. If climate change and logging continue at current levels, forests are likely to favor fast-growing trees with lighter leaves and lower wood density. These characteristics allow rapid growth in short periods. Common examples include species of acacia, eucalyptus, poplar, and some pines. Although these species establish and grow well, they are more vulnerable to droughts, storms, pests, and climate disturbances. This makes forests less stable and less effective at storing carbon in the long term, says Jens-Christian Svenning. Why are non-native trees spreading? The research also highlights the growing role of naturalized tree species, that is, trees native to other places but now growing wild in new regions. Almost 41% of these species share characteristics such as rapid growth and small leaves, which help them survive in disturbed environments. However, Svenning points out that these trees rarely replace the ecological functions of native species. Furthermore, in landscapes affected by current and future disturbances, naturalized species can make the survival of native trees even more difficult, as competition for light, water and nutrients intensifies, he adds. Tropical forests suffer the greatest losses. The study shows that tropical regions and Subtropical regions are likely to experience the most serious impacts of forest homogenization facing the planet. These areas are expected to experience the highest risks of tree species extinction. This is where many slow-growing tree species with naturally small ranges are found. Being confined to very limited areas, these species are especially vulnerable and at risk of disappearing completely if their habitats are destroyed or invaded by fast-growing species, explains the studys first author, Wen-Yong Guo, of the School of Ecological and Environmental Sciences at East China Normal University, Shandong. Guo also notes that fast-growing, naturalized species are expected to continue to spread around the world as current environmental disturbances increase. Therefore, in the colder areas of the northern hemisphere, the dominant dynamic is likely to be the invasion of these species, says Wen-Yong Guo. Human activity drives forest change According to the researchers, human actions are the main driving force of these changes in forest composition. Human-caused climate change, deforestation for infrastructure, intensive forestry, logging and the global trade in tree species play a role. Fast-growing trees are often actively promoted because they produce wood or biomass quickly. However, ecologically, they are often fragile and more prone to disease, explains Wen-Yong Guo.