Linking forest productivity decline to demographic attributes in western Canadian boreal forest

Background/Question/Methods

It is evident that climate change has resulted in temporal decline of forest productivity in western boreal forest region, and the decline varies along a drought gradient and among forest types. However, it is uncertain whether the decline is a result of increased tree mortality, reduced growth of surviving trees, reduced ingrowth, or all of the three demographic attributes. By analyzing 871 permanent sampling plots (PSPs) measured from 1958 to 2009, here, we linked temporal changes of forest productivity to the changes of the three demographic attributes. To examine climate change-associated annual biomass changes and three demographic attributes, 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

Climate change associated biomass loss due to tree mortality increased significantly for all forest types. The highest increase rate was found for LSC, followed by DEC, MIX and ESC. For DEC, while the overall forest productivity declined, the growth of surviving trees and ingrowth increased significantly and partially compensated the biomass loss due to increased mortality. However, for other three forest types, while biomass loss due to mortality increased, growth of surviving trees and ingrowth also decreased. The Pearson’s correlation analysis indicated that, among three demographic variables, biomass loss due to mortality was the primary driver to the temporal decline of forest productivity, followed by reduced growth of surviving trees and ingrowth. We anticipate our analyses to be a starting point for understanding of how individual demographic attributes might contribute to temporal changes in ecosystem productivity under climate change.