树木年轮揭示的东灵山主要树种间干旱耐受性差异

近年来北京地区的森林随极端干旱加剧表现出脆弱性特征,为了解气候变化下不同树种的干旱耐受性,选择北京东灵山森林内3个乔木树种(华北落叶松、油松和辽东栎),利用树木年轮生态学方法分析了径向生长与气候的关系,以及对极端干旱事件的抵抗力和弹性。结果表明: 华北落叶松和油松与5—6月气温呈显著负相关,辽东栎与5月气温呈显著负相关;华北落叶松与6月降水量、5—6月和8—9月相对湿度呈显著正相关,油松与6—8月降水量和相对湿度呈显著正相关,辽东栎与2月和5月降水量、5月相对湿度呈显著正相关;所有树种均与当年5—7月标准化降水蒸散指数(SPEI)呈显著正相关。华北落叶松是干旱耐受性最弱的树种,径向生长在所选极端干旱事件中(1994年、2001—2002年和2007年)下降幅度最大(46.6%～69.6%),抵抗力(0.534、0.304、0.530)和弹性(0.686、0.570、0.753)显著低于辽东栎和油松,辽东栎在2007年抵抗力显著高于油松,弹性无显著差异。生长季持续的高温或降水减少引起的极端干旱是树木径向生长下降的主要原因,树种间各异的生理生态策略是干旱耐受性差异的可能原因。研究结果可为未来造林树种选择和森林管护措施制定提供新依据,以在气候压力持续增加背景下维持森林生态系统功能和服务。

Differences of drought tolerance of the main tree species in Dongling Mountain,Beijing, China as indicated by tree rings

Forests in Beijing exhibit vulnerability to increasing stress of extreme drought in recent years. To investigate the drought tolerance of different tree species, we chose three tree species (Larix principis-rupprechtii, Pinus tabuliformis, and Quercus wutaishanica) from the forest of Dongling Mountain in Beijing and used dendroecological method to analyze the relationship between radial growth and climate, as well as their resistance and resilience to extreme drought events. Our results showed that the radial growth of L. principis-rupprechtii and P. tabuliformis was significantly negatively correlated with monthly mean temperature from May to June, but that of Q. wutaishanica was significantly negatively correlated with monthly mean temperature only in May. The radial growth of L. principis-rupprechtii was significantly positively correlated with monthly mean precipitation in June, monthly mean relative humidity from May to June and August to September. The radial growth of P. tabuliformis was significantly positively correlated with monthly mean precipitation and monthly mean relative humidity from June to August. The radial growth of Q. wutaishanica was significantly positively correlated with monthly mean precipitation in February and May, and monthly mean relative humidity in May. The radial growth of all the three species was significantly positively correlated with monthly mean SPEI (standardized precipitation evapotranspiration index) from May to July. L. principis-rupprechtii was least drought tolerant, as indicated by the greatest growth reduction (46.6%-69.6%), lowest resistance (0.534, 0.304, 0.530) and resilience (0.686, 0.570, 0.753) during the three extreme drought events occurred in the 1994, 2001-2002, and 2007. In contrast, tree growth of Q. wutaishanica showed the highest drought resistance in 2007, whereas no significant differences were observed between other two species. Extreme drought events caused by continuous high temperature and reduced precipitation during the growing season accounted for the reduction in tree radial growth. The various physiological and ecological strategies of tree species were the possible reasons for the difference in drought tolerance. Our results could provide a basis for the selection of suitable afforestation tree species and the formulation of forest protection mea-sures to maintain forest ecosystem functions and services under the background of undergoing climate change.