Climate change effects on tree mortality is stronger in young than old-growth forests

Background/Question/Methods

Tree mortality has been reported to increase in recently decades in North American old-growth forests as a result of change of exogenous factors such as regional warming. However, climate change effects on tree mortality in young forests are not understood. This understanding is especially essential for disturbance-driven forests such as fire-driven boreal forests, because the forests contain larger proportion of young forests than old-growth ones, and possibly will increase the proportion for young forests with continuous warming. To investigate how climate changes affect the forests across different stand developmental stages, we conducted the individual tree mortality models for five major boreal tree species, based on long-term measurement data between 1950s and 2000s in Alberta and Saskatchewan, Canada.

Results/Conclusions

We showed that the overall annual mortality probability increased during the study period for all study species. However, the mortality probability increased faster in young forests than that in old-growth forests. The increased mortality probability was also higher in more crowded and pure forests. The further anslyses revealed that the higher increases of mortality probability in younger forests may be the result of higher mortality sensitivity to recent regional warming and its negative effect on water availability in forests at early developmental stages.