毛乌素沙地天然臭柏种群生命表分析

 为了探讨毛乌素沙地天然臭柏种群动态，在图克臭柏保护区内，进行了样方调查，用WinDENDROTM年轮分析系统测定臭柏树盘的年龄。调查数据经均滑技术处理后，以种群生命表及生存分析理论为基础，编制臭柏种群特定时间生命表，分析臭柏的死亡率、消失率、平均生命期望、存活曲线及生存函数曲线。结果表明：臭柏种群有两个死亡高峰期，第一个高峰期为Ⅰ龄级，属幼龄期，死亡率达94%;第二个高峰期从Ⅵ龄级开始，死亡率在27%～47%之间。臭柏种群的消失率与死亡率的变化趋势基本一致。平均生命期望在Ⅰ龄级时为0.82 a,Ⅱ龄级达到最大，为4.67 a, 说明这个时期臭柏的生命活动最旺盛，之后开始逐渐下降，最后降低为零。经指数函数方程Nx=Noe-bx和幂函数方程Nx=Nox-b对臭柏种群存活曲线做相关性检验,结果表明，其存活曲线更趋近于DeeveyⅢ型，种群的生长趋势属增长种群，即臭柏种群幼龄期死亡率高，之后的死亡率降低，而且在一定的水平下趋于稳定。臭柏种群的生存率单调下降，积累死亡率单调上升。死亡密度函数曲线的凸点与平均生命期望曲线的凹点相对应，二者呈互补形式。危险率与死亡率的变化趋势相吻合。说明引入生命表中的4个生存函数能较好地显示种群的动态变化，生存分析理论和生命表相结合能更好、更真实地反映种群的生存状况。

Analysis on Life Table of Natural Sabina Vulgaris Population in MU Us Sandy Land

In order to study the dynamics of natural Sabina vulgaris population, the quadrat method was used in Tuke protective area in Mu Us sandy land. Individual ages were determined using WinDENDROTM tree-ring analysis system. Time-specific life table were made by accounting the investigated data with smoothing technique and according as the theory of life table and survival analysis. The curves of mortality rate, vanish rate, life expectancy, survival and survival function of the S. vulgaris were made for analysis based on time-specific life table. The results showed that: there existed two peaks of mortality rate in the lifespan, one was in Ⅰ age class which belongs to young trees, mortality rate reach to 94%, and the other started at Ⅵ age class, mortality rate between 27% and 47%. Vanish rate had the similar fluctuation as the mortality rate. The life expectancy value was 0.82 year in Ⅰ age class, the value reach to 4.67 year in Ⅱ age class which was the maximal value in the lifespan, this indicated that S. vulgaris population had the most active physiological movement in this stage, then the value declined with the increased age classes, at last it became zero. The survival curve of S. vulgaris population conformed to the type of DeeveyⅢ verified the relativity by a index function and a power function. This means S. vulgaris population should be an increscent population, and high mortality rate of S. vulgaris population appeared in young tree stage, then it was low and keeping in a steady level. The survival rate monotony downtrend and the cumulative mortality rate monotony rise. The death density function had the opposite exhibition compared with the life expectancy. The hazard rate had the same variation trend as the mortality rate. The four survival functions used in time-specific life table could well explain the dynamics of S. vulgaris population, the theory of survival analysis and life table were combined could reflect the survival conditions of S. vulgaris population more truly.