Divergent responses of Picea crassifolia Kom. in different forest patches to climate change in the northeastern Tibetan Plateau

Global climate changes have significantly affected tree growth and forest structures and functions in some arid and semi-arid regions, which are becoming warmer and wetter. Due to natural factors such as climate and terrain, some tree species may form different forest patches at the edges of their distribution areas. However, how forest patches of various sizes respond to climate change is unclear. In this study, we collected 203 tree cores from six different sizes of forest patches at the edge of the distribution area of Picea crassifolia Kom. in the northeast Tibetan Plateau. And we used the dendrochronology method to study the response of tree growth and resilience in different forest patches to climate change from 1961 to 2020. We simultaneously measured the contents of nonstructural carbohydrates (NSC), total nitrogen and total phosphorus of tree needles. Our results showed that the growth of trees in small- and medium-size forest patches (0.8-18.6 ha) has increased significantly. The early growing season (May-July) minimum temperature was the most important climate factor driving the growth of small- and medium-sized patch trees. The early growing season maximum temperature was the most important climate factor that inhibited the growth of trees in the largest patches (362.8 ha). The growth of individual trees in medium forest patches was better and the correlation with annual minimum temperature, maximum temperature, precipitation, actual evapotranspiration, and palmer drought severity index was stronger. The higher NSC content, stronger photosynthesis, and higher nitrogen utilization efficiency in leaves might be one of the reasons for the better growth of trees in moderate forest patches. In extreme drought years, as the forest patch area increased, the overall trend of tree growth resistance showed a unimodal pattern, with the highest at a forest patch area of 7.1 ha, while the overall trend of tree growth recovery was opposite. Therefore, we should strengthen the management of trees in large forest patches to cope with climate change.