大兴安岭林区南、北部天然樟子松生长对气候变化的响应差异

利用树木年代学方法,建立大兴安岭林区南、北部樟子松(Pinus sylvestris var.mongolica)年轮宽度年表,探讨樟子松径向生长对气候变化的响应差异。结果表明,南部(阿尔山、海拉尔)树轮宽度主要与当年4—9月的平均标准化降水蒸散指数SPEI(Standardized Precipitation Evapotranspiration Index)极显著正相关(r=0.639,P0.01),而北部(漠河、塔河)树轮宽度主要与同时期的平均最低温极显著正相关(r=0.488,P0.01)。说明南部樟子松径向生长主要受当年4—9月的水分限制,北部主要受同期平均最低温调控。两个地区树木生长对降水的响应一致,对当年4—9月(6月除外)的温度响应相反。近几十年来随着温度显著升高(P0.01),南部树木生长对4—9月平均最高温的负响应不断增强,而北部树木对同时段平均最低温的正响应更加明显。同时,南部樟子松生长量快速下降(r=0.612,P0.001),而北部生长量显著增加(r=0.474,P0.001)。研究发现,高温加剧干旱胁迫是南部樟子松生长量下降的主要原因,而北部樟子松生长量增加是受到4—9月平均最低温和降水量的相互作用。如果持续变暖,未来樟子松分布区可能北移。

Different responses of natural Pinus sylvestris var. mongolica growth to climate change in southern and northern forested areas in the Great Xing'an Mountains

The Pinus sylvestris var. mongolica natural forest is mainly distributed in the Great Xing''an Mountains. To investigate different responses of radial growth of P. sylvestris var. mongolica to climate change in the southern and northern regions, we collected tree-ring samples from the southern and northern edges of the natural distribution of the forest. Tree-ring width residual chronology (RES) was developed using dendrochronological methods for each region. The relationship between tree-ring width and climate factors, including monthly mean temperature, monthly mean maximum temperature, monthly mean minimum temperature, monthly precipitation, and standardized precipitation evapotranspiration index (SPEI) from the previous October to September of the current year was analyzed by correlation analysis during the study period (1960-2013). The results indicated that tree-ring width was significantly positively correlated (r=0.639, P < 0.01) with average SPEI in April-September in the southern region (Arxan and Hailar), whereas it was significantly positively correlated (r=0.488, P < 0.01) with mean minimum temperature during the same period in the northern region (Mohe and Tahe). The southern trees suffered from water stress, whereas the northern trees suffered from low temperature stress. Thus, the southern tree radial growth was mainly limited by moisture from April to September, but northern tree growth was affected by the monthly mean minimum temperature of the same period. Radial growth exhibited consistently positive responses to precipitation, but the response was opposite for temperature from April to September (except June) in the two regions. Tree-ring width was basically negatively correlated with temperature in the southern area, and it was mainly positively correlated in the northern area. As temperature increased significantly in recent decades (P < 0.01), the sensitivity of radial growth of P. sylvestris var. mongolica to mean temperature during April to September increased, and tree radial growth showed an increasingly negative response to the mean maximum temperature from April to September in the southern region and an increasingly positive response to the mean minimum temperature in the northern region at 31-year intervals. In addition, temporal changes in growth patterns differed between the two regions over the past 54 years. Radial growth declined rapidly in the southern region (r=0.612, P < 0.001), whereas it increased significantly in the northern region (r=0.474, P < 0.001). The fitted linear regression showed that the rate of decline in basal area increment (BAI) was 0.253cm² /a in the southern area, and the rate of increase was 0.039cm² /a in the northern area. Further study determined that mean maximum temperature for April to September contributed most to southern tree growth variability from 1960 to 2013 (r=-0.681, P < 0.01). Hence, increasing drought stress caused by high temperature was the main reason for growth decline in the southern area. The northern BAI series tracked the standardized mean minimum temperature and precipitation series for April to September well. Rising minimum temperature benefited cambial cell activity and prolonged the tree grow period at high latitudes, and thus, increasing growth of northern trees was affected by both mean minimum temperature and precipitation. The warming climate restrains southern tree growth but promotes northern radial growth. If the warming is sustained, the distribution area of P. sylvestris var. mongolica may move northward in the future.