关键词: 樟子松, 杨树, 三北防护林, 森林衰退, 生态弹性

Abstract: With global climate warming and the alteration of precipitation regime, the Three-North Shelter Forest in China has been degraded in recent years, which is a primary challenge for shelterbelt construction. Our understan-ding of the physiological mechanisms behind forest decline remains limited. In this study, we employed dendrochronological methods to measure the basal area increment (BAI) and tree-ring width of both healthy and degraded Pinus sylvestris var. mongolica and Populus L. We developed corresponding standardized chronologies (STD) to analyze their responses to climatic factors and ecological resilience during drought periods, and to elucidate the mechanisms of degradation in P. sylvestris var. mongolica and Populus L. under climate change, as well as their differences in drought adaptability. The results showed that radial growth in healthy P. sylvestris var. mongolica had significantly increased since 1978, with higher mean BAI of healthy trees than the degraded trees. They both exhibited a significant positive correlation with the annual palmer drought severity index (PDSI). Healthy P. sylvestris var. mongolica was less sensitive to precipitation and more resistant and resilient during drought periods. Since 1983, there had been no significant trend in radial growth for either healthy or degraded Populus L., though the mean BAI of healthy Populus L. was significantly higher than that of declining trees. Healthy Populus L. trees exhi-bited weaker correlations with precipitation, PDSI, and vapor pressure deficit (VPD) compared to the degraded trees, yet they showed higher resistance and resilience during droughts. P. sylvestris var. mongolica showed signs of decline earlier than Populus L. and demonstrated greater sensitivity to the PDSI. Nevertheless, it exhibited higher resistance and resilience than Populus L. In conclusion, drought and precipitation emerge as the primary climatic factors contributing to the decline of P. sylvestris var. mongolica and Populus L., with degraded trees being more sensitive to climate change. P. sylvestris var. mongolica demonstrated stronger adaptability to cumulative drought than Populus L., making it more likely to survive under future scenarios of increased drought caused by climate warming. This study provided data support and scientific insights for species selection in the Three-North Shelter Forest Project.

Key words: Pinus sylvestris var. mongolica; Populus L.; the Three-North Shelterbelt; forest declining; ecological resilience.