A major global study published in Nature Plants reveals that the world's forests are undergoing a rapid transformation. The research shows that fast-growing tree species are taking over, while the slow-growing, long-lived trees that serve as the backbone of natural ecosystems are in decline. This shift is making forests more uniform and less capable of recovering from stress. Driven by human activity, these changes are most extreme in tropical and subtropical regions. Scientists warn that protecting slow-growing species is now an urgent matter, and they suggest that forest management must prioritize these trees to ensure diversity and long-term stability.