Both climate change and man-made forest development processes cause increases in tree mortality in young and old forests but higher climate change-associated mortality increases are seen in young forests. This finding, reported a study published in Nature Communications this week, could have implications for the way in which the impact of climate-change on forests is assessed.

Old forests, assumed to be a good representation for regional forests in general, are used to calculate temporal trends in tree mortality. Based on these studies, it has been thought that only climate change, through global warming, drives temporal tree mortality increases in old forests. Yong Luo and Han Chen analysed tree mortality patterns in five boreal tree species in western Canada, and found that the effects of climate change on tree mortality were not the same for young and old forests, and local changes within a forest also plays a part.

This finding, revealing that the causes of tree mortality are more complex than previously thought, suggests a more comprehensive analysis of how forest ecosystems might respond to climate change is needed.