Forest productivity decline across region and species composition in western Canadian boreal forests

Background/Question/Methods

Forest productivity has been reported to decline over the past few decades in western boreal forest region, and the declines are attributed to regional warming and drought. By analyzing annual aboveground biomass changes in 871 permanent sampling plots (PSPs) measured from 1958 to 2009, here we addressed: 1) whether the decline varies along a drought gradient in this region and 2) whether the decline differs with forest types. To examine climate change-associated annual biomass changes, we de-trended the effect of stand developmental processes for each of the four forest types: deciduous forests (DEC), early successional conifer forests (ESC), late successional conifer forests (LSC), and mixed forests (MIX).

Results/Conclusions

Our results showed that forest productivity declined from 1958 to 2009  for all the forest types. However, the decline rates in dry area were higher than that in wet area. In addition, forest declines differ among forest types with the strongest decline in late successional conifer forests. Further analyses indicated that the forest declines were strongly associated with regional warming and its negative consequence on water availability. Given the drought gradient between the boreal forest and grasslands, our results suggest that the western boreal forest may have undergone retreat at its south edge over last few decades. Our results also indicated a potential climate change-induced forest compositional change that is independent of forest development.