火干扰因素对藏南地区高山松径向生长及气候响应特征的影响

Effects of fire disturbance factors on Pinus densata growth and climate response characteristics in southern Xizang

森林火灾在二十一世纪内的发生频率逐步升高。大量研究发现森林火灾与树木生长之间存在有紧密的相关性。因此探究森林火灾对于树木生长的影响,分析火灾的不同强度对于树木径向生长是否有着显著的差异,将对于评估森林保护指标有着重要的实际意义。实验基于树木年轮学的研究方法,探究西藏林芝市本日山及九五六两场森林火灾对高山松径向生长的影响,分析在火灾前后高山松径向生长与气温及降水之间的响应关系。基于林芝市比日山及九五六两个火烧区域,建立了受轻度火影响和受中度火影响的高山松样地。利用树木年代学的方法,对年轮宽度指数与1961—2020年气温及降水分别进行相关分析,同时结合火灾的发生时间,将时间序列划分为:1961—2006年火灾前和2007—2021年火灾后。结果显示,轻度火影响的高山松径向生长对气温和降水敏感,特别是在3—8月最高气温上呈现出显著性的增加。中度火影响的高山松径向生长则显著降低。火灾干扰明显抑制了高山松的径向生长,特别是火因子在平均气温和最高气温的干扰上对其径向生长具有明显抑制作用。受到轻度火影响的高山松径向生长在短期内有较为明显的增加趋势,但长期并不显著;而中度火影响的树木径向生长则在短期内不明显下降,但长期显著。受到轻度火影响的高山松中,其径向生长与最低气温之间呈显著的负相关,且使得高山松对外界环境的响应更为敏感,而中度火影响的高山松则并未表现出这种显著的响应状态。因此对于在高海拔地区而言,森林火灾对于树木径向生长有着显著的干扰的同时也提升树木与外界环境的响应程度。

Forest fires have been increasingly frequent in the 21st century and have been shown to be closely related to tree growth.Therefore,studying the impact of forest fires on tree growth and the effects of different fire intensities on tree response is essential for forest protection.In this study,tree⁃ring analysis was used to investigate the effects of two forest fires in Nyingchi,Xizang,on the radial growth of Pinus densata and the relationship between its growth and temperature and precipitation before and after the fires.Sample plots of Pinus densata were established in areas affected by mild and moderate fires in Biri and 956,respectively.Using tree⁃ring analysis and statistical methods,the tree⁃ring width index was correlated with temperature and precipitation data from 1961 to 2020,and the time series were divided into the pre⁃fire period(1961—2006)and post⁃fire period(2007—2021).The results showed that the radial growth of Pinus densata affected by mild fires was sensitive to temperature and precipitation,especially the maximum temperature from March to August,which significantly increased.The radial growth of Pinus densata affected by moderate fires was significantly reduced.Forest fires clearly inhibited the radial growth of Pinus densata,particularly with an inhibitory effect on average and maximum temperatures.The radial growth of Pinus densata affected by mild fires showed a short⁃term increase but a long⁃term reduction,while that of trees affected by moderate fires showed a short⁃term decrease but a long⁃term increase.In Pinus densata affected by mild fires,there was a significant negative correlation between radial growth and the minimum temperature.Pinus densata affected by mild fires were more sensitive to changes in external environmental factors,while those affected by moderate fires gradually weakened their response.In summary,forest fires had a significant impact on the radial growth of Pinus densata,while also increasing its response to external environmental factors.These findings are crucial for forest protection in high altitude areas.