西藏尼木县古树年龄鉴定及生长历史分析

鉴定老龄树的古树等级并了解其生长历史是国家古树名木普查建档工作的重要内容.本研究利用树木年轮学方法,调查估算了西藏拉萨市尼木县20棵胸径较大的核桃和10棵大果圆柏的树龄,分析其生长历史.结果表明: 20棵核桃树中,一级古树、二级古树及三级古树分别为4、7及9棵;10棵柏树中,有2棵一级古树、4棵二级古树、4棵三级古树.历史上的持续低生长现象在某些时间段内2个树种间表现出明显的同步性,主要集中在20世纪40至80年代,但古树生长在个体间表现出较大的生长差异.古树生长与帕默尔干旱指数(PDSI)表现出显著的正相关关系.研究区古树主要分布于村庄和道路两旁,人类活动频繁.古树的径向生长受到该区域气候调控的同时也受到人类活动的干扰,这导致了古树的径向生长变化在不同树种间表现出空间同步性,而在个体间表现出较大的生长差异.因此,相关部门在制定古树保护措施时应同时考虑气候变化和人类活动对古树生长的影响.

Age investigation and growth history analysis of old trees in Nyemo County of Tibet,China.

Investigating age and growth histories of old trees is important for census and document of old trees in China. In this study, we analyzed the age and growth histories of 20 old trees of Juglans regia and 10 old trees of Sabina tibeticain Nyemo County, Tibet, China, using dendrochronological methods. The results showed that 4, 7 and 9 J. regia trees were identified as Class Ⅰ, Ⅱ and Ⅲ to protection, and 2, 4 and 4 S. tibetica trees as Class Ⅰ, Ⅱ and Ⅲ to protection, respectively. Tree growth of both species was synchronized in the study area, especially during 1940s-1980s. There were substantial differences in the growth among individuals. Significantly positive correlation was found between the ring-width chronologies of the two tree species and Palmer drought severity indices (PDSI). Old trees were mainly distributed in villages and road sides, where human activities were frequent. In addition to the climatic factors, frequent human activities in the study area played an important role in affecting tree radial growth. It caused synchronous radial growth of the old trees between those two species and significant variation among different individuals. Both climate change and human activities should be considered to make the conservation plans for old trees in Nyemo County.