梵净山自然保护区珙桐天然种群生命表与生存分析

以种群生命表和生存分析理论为基础,采用空间代替时间法和分段匀滑技术,编制梵净山自然保护区珙桐天然种群特定时间生命表,绘制其死亡率曲线、消失率曲线、存活曲线和生存函数曲线,分析种群数量动态变化。结果表明:珙桐种群结构存在波动性,趋于DeeveyⅢ型,其幼年阶段的个体较丰富;珙桐种群死亡率和消失率曲线变化趋势基本一致,在这一发育过程中有两个死亡高峰,一个出现在幼苗向幼树的过渡期(Ⅰ龄级→Ⅱ龄级),另一个出现在从中龄向老龄过渡的阶段(Ⅷ龄级→Ⅸ龄级);种群生存分析表明,珙桐种群的生存率单调下降,累计死亡率单调上升,Ⅷ龄级后,种群生存率小于8%,累计死亡率大于92%,危险率超过生存率;4个生存函数曲线表明,梵净山珙桐有前期锐减、中期稳定和后期衰退的特点。幼苗和中龄级个体的不足是导致珙桐濒危的重要原因。

Life table and survival analysis of natural Davidia involucrata population in Fanjing Mountain Nature Reserve, Guizhou Province of Southwest China

Based on the population life table and the theory of survival analysis,and by using the age class structure represented by DBH(diameter at breast height) class and the stage-smoothing technique,a specific life table of Davidia involucrata population in Fanjing Mountain Nature Reserve was compiled,and the mortality rate curve,killing power curve,survival rate curve,and survival function curve were analyzed,aimed to reveal the quantitative dynamics of the population.There was a fluctuation in the structure of the D.involucrata population.The survival curve of the population appeared to be of Deevey Ⅲ type,and the individuals at young stage were abundant.The mortality rate curve and disappearance rate curve in the lifespan had similar variation trend,and the population had two distinct peaks of mortality,i.e.,from Ⅰ to Ⅱ age class and from Ⅷ to Ⅸ age class.The survival analysis showed that the population mortality rate was increasing all along,while the survival rate was decreasing all the time.After Ⅷ age class,the mortality rate would exceed 92%,and the survival rate would decrease to below 8%,which indicated that hazard rate surpassed survival rate.The survival functional curve showed that the individual number of the population decreased rapidly in early age period,was stable in middle age period,and declined in old age period.The high mortality of seedlings and the deficiency of middle-age trees could be the main reasons leading to the D.involucrata population becoming endangered.