[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 1, 2 and 3 to protection, and 2, 4 and 4 S. tibetica trees as Class 1, 2 and 3 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.