岷江上游林线附近岷江冷杉种群的生存分析

岷江冷杉 (Abiesfaxoniana) 林是青藏高原东南缘亚高山暗针叶林的主要类型之一, 在岷江上游地区, 岷江冷杉林一般在 2 80 0~ 380 0m之间呈带状分布并且在阴坡形成林线。为了对岷江上游林线地段的岷江冷杉种群进行生存分析, 在岷江上游林线附近弓杠岭 (33°0 2′39″N, 10 3°4 3′11″E) 设置了 10个样地, 使用侧生轮枝计数或WinDENDRO系统对个体年龄进行确定。调查数据经匀滑技术处理, 编制了岷江冷杉种群特定时间生命表, 绘制了岷江冷杉种群的存活曲线、死亡率曲线和消失率曲线。结果表明:1) 岷江上游林线地段岷江冷杉种群存活曲线趋于Deevey_Ⅲ型。 2) 林线地段岷江冷杉种群生存率呈单调下降趋势, 生存率下降趋势前期高于后期, 说明岷江冷杉种群幼苗死亡率高, 种群后期比较稳定。3) 林线地段岷江冷杉林整个生长期中出现了两个死亡高峰期, 一个出现在幼苗向幼树过渡时期 (0~ 4 0年), 另一个出现在中龄时期 (180年) 。岷江上游林线地段岷江冷杉种群幼苗死亡率较高的原因可能和林线地段的温度较低、积雪厚度、风向、水分等环境条件有关。

SURVIVAL ANALYSIS OF ABIES FAXONIANA POPULATIONS NEAR TIMBERLINE ON THE UPPER MINJIANG RIVER

Abies faxoniana forests are one of the major types of sub-alpine dark coniferous forests on the eastern Tibetan Plateau. In the mountainous areas of the upper Minjiang River, it is distributed between altitudes of 2 800-3 800 m a.s.l and usually forms the upper timberline on shaded slopes. To explore the survival status of A. faxoniana populations, ten plots (20 m×20 m) were investigated and analyzed in Gonggangling (33°02′39″ N, 103°43′11″ E). Individual ages were determined using WinDENDRO system or by counting tree branches. Time-specific life tables or vertical life table curves of survival-mortality based and hazard based age structures were drawn. The results showed that: 1) The survival curve of the population conformed to the type of Deevey-Ⅲ; 2) With an increase in the population mortality ratio and a decrease in the survival rate, the mortality ratio greatly increased in ages 0-40 years, reaching 89.7%; 3) There existed two peaks of mortality in the lifespan, one was from seedlings to young trees (0-40 years) and the other in the adult stage (180 years). It is suggested that the mortality rate of A. faxoniana seedlings is impacted most by temperature, wind, snowpack depth, water and other environmental factors.