近40年河北坝上地区杨树人工林径向生长对气候变化的响应差异

运用树木年轮气候学方法，研究近40年河北坝上地区健康和衰退小叶杨人工林径向生长对气候响应敏感性差异，揭示健康和衰退杨树生长与气候关系的时间变异规律。结果表明：（1）衰退杨树径向生长对温度、降水等气候因素响应较健康杨树敏感。衰退杨树年表中的气候信号较强，与当年生长季（4、8-10月）的气温因素呈显著负相关，与上一年休眠期（9月-当年1月）和当年生长季（7月）的降水和相对湿度呈显著正相关。健康杨树年表中气候信号较弱，主要与上一年冬季（12月）和当年生长季（4月）的气温因素呈显著负相关，与上一年生长末期（8-11月）降水和相对湿度呈显著正相关。（2）从各年表与帕默尔干旱指数（PDSI）的响应强度来看，衰退杨树生长更易受夏季干旱胁迫影响。衰退杨树年表与上一年9月-当年3月、6-10月的PDSI呈显著正相关，而健康杨树径向生长与PDSI呈弱的正相关。（3）1975-2017年间，随气温升高，健康和衰退杨树生长对温度的敏感性下降；健康杨树生长对降水和PDSI的敏感性较为稳定，适应能力强，而衰退杨树生长对降水和PDSI的敏感性增强，适应能力变弱。综上所述，干旱胁迫是限制衰退杨树生长的主要因素，而健康杨树生长受气候影响较弱，能适应当地气候条件。衰退杨树对气候变化响应较健康杨树明显，在气候变暖背景下，衰退杨树生长的气候限制因子由温度转变为水分，导致河北坝上地区遭受干旱灾害时发生退化的趋势更加明显。

Climate effect on the radial growth of Populus simonii in Northwest of Hebei for last four decades

Dendroclimatic methods have been used to establish standard chronologies for the healthy and the declining trees of the Populus simonii artificial forest in northwest of Hebei Province over the past four decades. Correlation analyses were conducted between these chronologies and local climatic factors to establish the temporal variations of the growth-climate relationship for the the healthy and the declining trees of the Populus simonii forest. The results showed that (1) the tree-ring growth of the declining trees was more sensitive to meteorological factors than that of the healthy trees. The series of tree-ring widths of the declining trees exhibited significantly negative correlations with the temperature factors in April and from August to October of the current year; meanwhile, it yielded positive correlations with total precipitation and relative humidity from September of the previous year to January and for July of the current year. For the healthy trees, the series was significantly negatively correlated with the temperature factors for December of the previous year and April of the current year and positively correlated with the total precipitation and relative humidity from August to November of the previous year. (2) From the chronological response to the Palmer Drought Index (PDSI), the declining trees were more susceptible to summer drought stress. The tree-ring width series of the declining trees had a strongly positive correlations with the PDSI from September of the previous year to March of the current year, whereas from June to October of the current year, while the healthy trees were weakly affected by drought. (3) As the temperature rose from 1975, the temperature sensitivity of the healthy and the declining trees decreased, and the PDSI and total precipitation sensitivity of the declining trees increased; meanwhile, the healthy trees were stable. In summary, drought stress was the main factor limiting the growth of the declining trees, whereas the healthy trees were less affected by climate and could adapt to local climatic conditions. The declining trees were more sensitive to climate change than the healthy trees. With the warming and drying, the climatic limiting factor of the declining trees will change from temperature to moisture, which leads to a more pronounced trend of degradation during drought stress.