Natural Resources Canada, Canadian Forest Service, Edmonton, AB, Canada.
Alberta Agriculture and Forestry, Forest Health and Adaptation, Edmonton, AB, Canada.
Glob Chang Biol. 2017 Dec;23(12):5297-5308. doi: 10.1111/gcb.13795. Epub 2017 Jul 17.
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 boreal tree species. Allometric equations were used to calculate annual growth in aboveground tree biomass (G ) from ring width measurements. Results showed an increasing trend in G 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 G from the predrought decade of 1991-2000 to the subsequent decade of 2001-2010. The remaining 57 stands exhibited a decline in mean G 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 decadal mean G and the change in decadal mean values of a climate moisture index from 1991-2000 to 2001-2010. Subsequent analyses of boreal stands 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 G 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 towards more frequent, severe drought continues in the region.
自 2001 年以来，加拿大西部内陆地区的大部分地区气候明显比正常情况干燥，这对该地区的森林造成了广泛影响。考虑到气候变化预测持续变暖变干，这对未来构成了重大担忧。我们对艾伯塔省和萨斯喀彻温省中西部的 75 个纯白云杉（Picea glauca）林分进行了树木年轮分析，以研究最近气候干燥对这种重要的北方树种生长的影响。我们使用了树木年轮分析方法来从年轮宽度测量中计算地上树木生物量（G）的年生长量。结果表明，从 20 世纪 60 年代到 90 年代，G 呈增长趋势，随后在 2001-2002 年的严重干旱期间急剧下降。在这 75 个林分中，只有 18 个林分恢复得足够好，使得从 1991-2000 年的干旱前十年到随后的 2001-2010 年，平均 G 有所增加。其余 57 个林分的平均 G 在这两个十年之间有所下降。气候干燥是生长下降的主要原因，从十年平均 G 的百分变化与 1991-2000 年至 2001-2010 年的气候湿度指数十年平均值变化之间的显著林分水平关系可以看出这一点。对 2015 年在艾伯塔省采样的北方林分的进一步分析表明，随着 2014-2015 年干旱情况加剧，白云杉的生长进一步下降。总体而言，1997 年至 2015 年期间，平均 G 下降了 38%，但令人惊讶的是，年轻、生产力高的林分与年老、生产力较低的林分相比，其下降幅度百分比没有显著差异。因此，林分老化不能解释过去四分之一个世纪白云杉生长的下降，这表明如果该地区频繁发生严重干旱的趋势持续下去，这些森林将面临风险。
