Understanding Population Dynamics of Euptelea pleiospermum from Spatial Distribution Characteristics

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.