Thresholds for warming-induced growth decline at elevational tree line in the Yukon Territory, Canada
Thresholds for warming-induced growth decline at elevational tree line in the Yukon Territory, Canada
复制标题
DOI：
10.1029/2004gb002249
复制
发表时间：
2004-09-24
影响因子：
5.2
通讯作者：
Cherubini, P
中科院分区：
文献类型：
--
作者：
D'Arrigo, RD;Kaufmann, RK;Cherubini, P
一些树木年轮研究表明，最近北纬地区的生长速度有所下降。确切的原因还不是很清楚。在这里，我们确定了在加拿大西北部海拔林线上一个公认的温度敏感点的树轮记录中下降的温度阈值。正年轮宽度/温度关系已经减弱，以至于1965年前的线性模型系统地高估了1965至1999年的年轮宽度。一个非线性模型显示了这一年表与夏季气温之间的倒U形关系，根据附近的一个站，7-8月的最佳平均气温为11.3摄氏度。自20世纪60年代以来，这一最佳值一直被超过，同时出现的下降表明，即使在树线上，当温度超过生理阈值时，树木也会受到负面影响。如果继续变暖而有效降水量没有显著增加，近几十年的大规模绿化可能会被大规模的褐变所取代。这种褐变可能会减缓或逆转北方森林的碳吸收。
A few tree ring studies indicate recent growth declines at northern latitudes. The precise causes are not well understood. Here we identify a temperature threshold for decline in a tree ring record from a well-established temperature-sensitive site at elevational tree line in northwestern Canada. The positive ring width/temperature relationship has weakened such that a pre-1965 linear model systematically overpredicts tree ring widths from 1965 to 1999. A nonlinear model shows an inverted U-shaped relationship between this chronology and summer temperatures, with an optimal July-August average temperature of 11.3degreesC based on a nearby station. This optimal value has been consistently exceeded since the 1960s, and the concurrent decline demonstrates that even at tree line, trees can be negatively affected when temperatures warm beyond a physiological threshold. If warming continues without significant gains in effective precipitation, the large-scale greening of recent decades could be replaced by large-scale browning. Such browning could slow or reverse carbon uptake by northern forests.