从空间分布特征认识珍稀植物领春木的种群动态

Understanding Population Dynamics of Euptelea pleiospermum from Spatial Distribution Characteristics

领春木(Euptelea pleiospermum)系第三纪孑遗植物和东亚特有种,目前已被列为国家Ⅲ级重点保护植物。基于空间定位数据以最近邻体距离统计研究了神农架地区领春木的空间分布特征,比较幼苗(DBH≤2.5 cm)、幼树(2.5～7.5 cm)和成树(>7.5 cm)各径级(代表各生活史阶段)形成的时间序列上的空间格局差异,进而探讨空间格局与立苗、补员、种内竞争等种群动态过程的相互关系。结果显示,在邻域尺度上,领春木的空间格局呈聚集态;幼苗(或幼树)的大小与其距离最近幼树(或成树)的远近没有相关性,幼树(或成树)周围一定距离以内出现同等大小个体的概率约等于幼苗(或幼树)出现的概率,且幼树与最近幼苗(或成树与最近幼树)的平均距离与幼树之间(或成树之间)的平均最近邻体距离没有显著差异;任意个体的大小、任意个体与相应最近邻体的大小之和与相应的最近邻体距离均为显著的正相关关系,但幼树间的最近邻体距离并不大于幼苗随机死亡产生的最近邻体距离,成树间最近邻体距离也不大于幼苗+幼树随机死亡产生的最近邻体距离。这些结果表明,领春木的聚集分布可能与种子散布、生境异质性对立苗格局的作用有关;已定植的大个体可能不限制其邻域内小个体的布局与生长,但是长期的补员过程与邻体间的相互作用不无关系;邻体间存在一定程度的竞争作用,但是竞争强度并未充分激化至发生距离依赖的死亡。

Euptelea pleiospermum,a Tertiary relic and East-Asian endemic species,is a rare and threatened species in China,which requires protection.Based on stem mapping data,the spatial characteristics of E.pleiospermum in the Shennongjia Mountains were examined by nearest neighbor distance statistics.Following the pattern differences and changes within and between each life-history stage（represented by size class,seedling ≤2.5 cm,2.5 cm〈sapling≤7.5 cm,adult tree〉7.5 cm in DBH）,the pattern-forming processes such as seedling establishment,recruitment and intra-specific competition were inferred and assessed.Euptelea pleiospermum was overall aggregated at the neighborhood scale.Sizes of small individuals（seedlings or saplings） showed no correlation with distances to nearest larger individuals（saplings or adult trees）.Within a given radius of focal large-size individuals（saplings or adult trees）,the probability of occurrence of size-identical and smaller individuals（seedlings or saplings） were approximately equal.Mean nearest neighbor distance from large-size individuals to nearest individuals in consecutive lower class（sapling vs.nearest seedling,or adult tree vs.nearest sapling） did not differ significantly from that measure within large size classes（within sapling or adult tree classes）.Both summed sizes of nearest neighbor pairs and sizes of focal individuals were significantly correlated with nearest neighbor distances.Mean nearest neighbor distance within sapling class did not differ from the expected one within random-mortality-introduced seedling class,and likewise mean nearest neighbor distance within adult class did not differ from the expected one within random-mortality-introduced juvenile class（seedlings＋saplings）.These results suggest that（1） the aggregated distribution of E.pleiospermum may be due to the effects of seed dispersal and/or habitat heterogeneity on seedling establishment,（2） within their neighborhood established large individuals of E.pleiospermum did not appear to limit the locations and growth of smaller con-specific individuals,but neighbor-interactions may have an effect on long-term recruitment,（3） intra-specific competition existed in the E.pleiospermum population but it was not strong enough to produce distance-dependent mortality.