Recent climatic drying leads to age‐independent growth reductions of white spruce stands in western Canada
2017
Since 2001, climatic conditions have been notably drier than normal across large areas of the western Canadian interior, leading to widespread impacts on the forests of this region. This poses a major concern for the future, given climate change projections for continued warming and drying. We conducted tree-ring analysis in 75 pure stands of white spruce (Picea glauca) across Alberta and west-central Saskatchewan to examine the effects of recent climatic drying on the growth of this important
borealtree species. Allometric equations were used to calculate
annual growthin aboveground tree biomass (GBM) from ring width measurements. Results showed an increasing trend in GBM from the 1960s to the 1990s, followed by a sharp decline during the severe drought of 2001–2002. Of the 75 stands, only 18 recovered sufficiently to cause an increase in mean GBM from the pre-drought
decadeof 1991–2000 to the subsequent
decadeof 2001–2010. The remaining 57 stands exhibited a decline in mean GBM between these
decades. Climatic drying was a major cause of the growth decline, as shown by the significant stand-level relationship between percentage change in
decadalmean GBM and the change in
decadalmean values of a climate moisture index from 1991–2000 to 2001–2010. Subsequent analyses of
borealstands sampled across Alberta during 2015 revealed that white spruce growth had declined even further as drought conditions intensified during 2014–2015. Overall, there was a 38% decrease in mean GBM between 1997 and 2015, but surprisingly, the percentage decrease was not significantly different for young, productive stands compared with older, less productive stands. Thus, stand ageing cannot explain the observed decline in white spruce growth during the past quarter century, suggesting that these forests are at risk if the trend toward more frequent, severe drought continues in the region. This article is protected by copyright. All rights reserved.
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