画稿溪国家级自然保护区珍稀植物桫椤种群结构与更新

Population Structure and Regeneration of the Endangered Tree Fern Alsophila spinulosa in Huagaoxi National Nature Reserve,Southwestern China

根据四川画稿溪国家级自然保护区桫椤(Alsophila spinulosa)种群分布特点,设立4个样地1个样带共44个样方(20 m×20 m),从种群密度、生命表和生境关联(草本层郁闭度和林分受干扰强度)等方面研究了保护区桫椤种群的结构特征。结果表明,每个桫椤种群样方的平均密度为0.088株/m2,幼苗密度为0.049株/m2;桫椤种群的死亡率和消失率曲线变化基本一致,发育过程中出现3个死亡高峰值,分别在第1龄级(H<0.01 m)、第7龄级(3.90 m≤H<4.80 m)和第10龄级(H≥6.60 m)阶段;种群生存率单调下降,累计死亡率单调上升,第7龄级以后,种群生存率小于1%;根据种群生存率函数Si、累计死亡率函数Fti、死亡密度函数fti和危险率函数λti4个生存函数曲线表明,画稿溪桫椤种群具有前期锐减、中期稳定、后期衰退的特点。桫椤各龄级阶段密度与草本层郁闭度均无显著相关(p≥0.18),然而桫椤幼苗(第1龄级)以上的个体密度、第7龄级密度与干扰度之间呈显著负相关(p<0.05)。综合分析表明,画稿溪桫椤种群具有一定的自然更新能力,但人为活动的干扰可能是限制桫椤种群的因素之一。

Population structure and regeneration of the endangered tree fern Alsophila spinulosa in Huagaoxi National Nature Reserve were examined by life table,survival analysis and habitat （ground cover and disturbance intensity） associations. We established 44 plots （20 m × 20 m）,recorded the height （H） of each tree within each plot and grouped them into ten age class：1,H 〈 0.01 m; 2,0.01 m ≤ H 〈 0.60 m; 3,0.60 m ≤ H 〈 1.20 m; 4,1.20 m ≤ H 〈 2.10 m; 5,2.10 m ≤ H 〈 3.00 m,and so on. Results revealed that the mean density of the A. spinulosa plots was 0.088 plants/m2,with a seedling density （class 1） of 0.049 plants/m2. There were three peaks in mortality occurring in the first,seventh and tenth age classes,successively. After the seventh size class,the survival rate declined to less than 1%. Four survival function curves showed that A. spinulosa was characterized by sharp shrinkage in the early ages,stationarity in the intermediate ages and decline in the late ages. Stem density of A. spinulosa was not correlated with ground cover for any size class （p ≥ 0.18）,while densities of all non-seedling individuals and the seventh size class showed a negative correlation with disturbance intensity （p 〈 0.05）. The results suggested that the A. spinulosa population had the capacity for natural regeneration,but human interference might limit its population density.