Higher tree diversity is associated with higher tree mortality probabilities in the boreal and temperate forests of North America according to a recent publication in Proceedings of the National Academy of Sciences (PNAS), led by two UQAM researchers Eric Searle and Alain Paquette. While there has been a huge amount of research into the impacts of tree diversity on productivity and standing biomass, investigations into the relationship between tree diversity and mortality have been lacking. The study uses permanent sample plot networks from across Canada and the United States to show that higher tree diversity is directly associated with higher tree mortality probabilities. This link is stronger in temperate than boreal forests and becomes even more pronounced when tree diversity effects are modelled holistically; in particular more diverse stands have higher stand densities which drives further increases in tree mortality. Higher probabilities of mortality in diverse stands did not negate previous results: diversity was still beneficial to productivity. The research calls for more investigation into the impact of biodiversity on forest dynamics and particularly on the role of mortality through holistic modelling frameworks.