Higher tree diversity is linked to higher tree mortality

Significance Despite a significant amount of recent research describing how tree species diversity improves forest productivity, few studies examine how tree diversity affects tree mortality, which is a key ecosystem function that drives succession, composition, and competition. Using a plot network from across Canada and the United States, here we show that plots with higher tree diversity also experience higher tree mortality. This effect becomes even more prominent when tree diversity effects are modeled holistically; in particular, more-diverse plots have higher stem densities, translating into higher mortality probabilities. We call for the use of integrated model frameworks when examining the response of forest ecosystem functions to diversity, thus ensuring proper accounting of direct and indirect effects.