Mutual feeding mechanism of soil moisture and plantation in Beijing and Tianjin（NO.2017ZY02）、National Natural Science Foundation of China (41877539)
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.