Arctic Research Center, Hokkaido University, Sapporo, Japan.
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
Glob Chang Biol. 2018 Sep;24(9):4225-4237. doi: 10.1111/gcb.14135. Epub 2018 Apr 16.
The terrestrial forest ecosystems in the northern high latitude region have been experiencing significant warming rates over several decades. These forests are considered crucial to the climate system and global carbon cycle and are particularly vulnerable to climate change. To obtain an improved estimate of the response of vegetation activity, e.g., forest greenness and tree growth, to climate change, we investigated spatiotemporal variations in two independent data sets containing the dendroecological information for this region over the past 30 years. These indices are the normalized difference vegetation index (NDVI3g) and the tree-ring width index (RWI), both of which showed significant spatial variability in past trends and responses to climate changes. These trends and responses to climate change differed significantly in the ecosystems of the circumarctic (latitude higher than 67°N) and the circumboreal forests (latitude higher and lower than 50°N and 67°N, respectively), but the way in which they differed was relatively similar in the NDVI3g and the RWI. In the circumarctic ecosystem, the climate variables of the current summer were the main climatic drivers for the positive response to the increase in temperatures showed by both the NDVI3g and the RWI indices. On the other hand, in the circumboreal forest ecosystem, the climate variables of the previous year (from summer to winter) were also important climatic drivers for both the NDVI3g and the RWI. Importantly, both indices showed that the temperatures in the previous year negatively affected the ecosystem. Although such negative responses to warming did not necessarily lead to a past negative linear trend in the NDVI3g and the RWI over the past 30 years, future climate warming could potentially cause severe reduction in forest greenness and tree growth in the circumboreal forest ecosystem.
过去 30 年来，高纬度地区的陆地森林生态系统经历了显著的变暖速率。这些森林被认为对气候系统和全球碳循环至关重要，特别容易受到气候变化的影响。为了更准确地估计植被活动（如森林绿色度和树木生长）对气候变化的响应，我们研究了包含该地区过去 30 年树木年代学信息的两个独立数据集的时空变化。这两个指数是归一化差异植被指数（NDVI3g）和树木年轮宽度指数（RWI），它们在过去的趋势和对气候变化的响应方面都表现出显著的空间变异性。这些趋势和对气候变化的响应在环极（纬度高于 67°N）和环北方（纬度高于和低于 50°N 和 67°N）的生态系统中存在显著差异，但它们在 NDVI3g 和 RWI 中的差异方式相对相似。在环极生态系统中，当前夏季的气候变量是 NDVI3g 和 RWI 指数对温度升高呈正响应的主要气候驱动因素。另一方面，在环北方森林生态系统中，前一年（从夏季到冬季）的气候变量也是 NDVI3g 和 RWI 的重要气候驱动因素。重要的是，这两个指数都表明，前一年的温度对生态系统产生了负面影响。尽管这种对变暖的负面响应不一定导致过去 30 年来 NDVI3g 和 RWI 的负线性趋势，但未来气候变暖可能会导致环北方森林生态系统中森林绿色度和树木生长的严重减少。
