生境片断化对濒危植物景东翅子树种群结构与动态的影响

Effects of habitat fragmentation on population structure and dynamics of the endangered plant Pterospermum kingtungense

生境的破坏及其片断化是生物多样性丧失的主要原因,了解生境片断化对植物种群动态的影响十分必要。本文比较分析了不同大小生境片断(5 ha和15 ha)和连续森林中濒危植物景东翅子树(Pterospermum kingtungense)种群的结构与动态,目的是明确影响景东翅子树种群动态的关键生活史阶段及其种群保护的目标,为濒危植物种群保护和管理策略的制定提供科学依据。在上述3种生境中分别设立3个50 m×100 m的1.5 ha固定样地,调查景东翅子树所有个体的胸径(其中幼苗和幼树为地径)和高度、个体的存活及幼苗的补充情况。基于上述统计参数,建立预测种群动态的Lefkovitch矩阵模型,同时应用矩阵模型的弹性分析方法量化种群统计参数对种群增长率的相对贡献。结果表明:(1)在5 ha和15 ha生境片断及连续森林各1.5 ha的样地中,2018年首次调查到景东翅子树的个体数分别为34、82和88株,2019年复查时的个体数分别为33、82和87株。3种生境中景东翅子树种群的年龄结构均以幼树为主,但5ha生境片断森林缺乏幼苗和大树(包括成树和亚成树),而15ha生境片断森林幼苗较丰富。(2)在3种生境中景东翅子树种群的增长率等于1(15 ha生境片断)或趋近于1(5 ha生境片断和连续森林),说明不同生境中的景东翅子树种群比较稳定,这主要是因为其各生活史阶段的存活率均较高。(3)景东翅子树成树和亚成树阶段的存活率对种群增长率的贡献最大,是影响其种群动态的关键生活史阶段。因此对于大树(包括成树和亚成树)的保护是极度濒危植物景东翅子树种群维持的关键。研究结果揭示小生境片断降低了景东翅子树种群的数量,改变了种群的结构,但对种群动态的影响效应尚未显现。因此对于这些小生境片断中濒危植物种群的保护和恢复是可行的,也是有价值的。

Aims:Habitat destruction and fragmentation are the leading cause of biodiversity loss.Therefore,it is necessary to understand the effect of fragmentation on plant population dynamics.The present study compared the population structure and dynamics of the endangered plant Pterospermum kingtungense in fragmented habitats of different sizes(5-ha and 15-ha)and continuous forests.We sought to identify the key life history stages that affect the population dynamics of P.kingtungense,with the goal of the providing a scientific basis for the formulation of endangered plant protection and management strategies.Methods:Censuses were conducted over a one-year(2018–2019)period in three 50 m×100 m sampling plots in each of the three habitats.All P.kingtungense plants were measured for DBH(diameter at breast height,but ground diameter for seedlings and saplings),height,survival,and seedling replenishment.Based on the investigated demographic parameters,annual transition matrices were established for each habitat to predict the population dynamics,and the relative contribution of the population demographic parameters to the population growth rate was quantified by the elastic analysis method of the matrix model.Results:Across the two years,we recorded an average of 33.5,82 and 87.5 P.kingtungense individuals in the 5-ha fragment,15-ha fragment and continuous forest plots,respectively.Saplings dominated in the three habitats,but seedlings and big trees(comprising subadult and adult)are scarce in the 5-ha forest fragment,while seedlings are abundant in the 15-ha forest fragment.The population growth rate of P.kingtungense was equal to(15-ha fragment)or approaching(5-ha fragment and continuous forests)one,suggesting that P.kingtungense populations were stable in different size fragments and continuous forests.This stability is mainly due to the high survival rates of the populations in each life cycle stages.The survival rates of adult and subadult stages contribute substantially to the population growth rate,and these are the key life cycle stages affecting population dynamics in this species.Thus the protection of large trees(i.e.,adults and subadults)is key to maintaining populations of the endangered plant P.kingtungense.Conclusion:Our findings reveal that the population size of P.kingtungense decreased and its population structure altered in the small fragmented habitat,but the effect on the population dynamics may not yet have shown themselves.Therefore,it is feasible and valuable to protect and restore the endangered plant populations even in small,fragmented habitats.