The dynamics and characteristics of population patterns in the vegetation succession process are rarely explored. Scale, pattern and process of ecological succession are three intertwined concepts in modern ecology. Succession research will inevitably involve scale and pattern analyses. Species spatial patterns and interspecific associations at any scale can be analyzed based on point pattern analysis with spatial mapped points of individuals' distribution.Therefore, it is suitable to discuss the relationships between species pattern in the vegetation succession process which have attracted much attention from ecologists. The aim of the present work is to study the spatial pattern formation and relative importance of intra and interspecific competition in dominant tree species of cold temperate coniferous forest in the vegetation succession process in the Pangquangou Nature Reserve. The selected forest communities were treated as a time series of successional stages for the traditional space-for-time succession approach by applying the point pattern analysis.
Pangquangou Nature Reserve is located in the midst of Luliang Mountain range, at 37°45'-37°55' N, 111°22'-111°33' E. It was established for the conservation of the first-class nationally protected bird, Crossoptilon mantchuricum, and the cold-temperate coniferous forest. Cold temperate coniferous forest dominated by Larix principis-rupprechtii and Picea wilsonii is an important vegetation formation and has a large distribution area in Pangquangou Nature Reserve. It plays significant role in water conservation, eco-tourism, biodiversity maintaining etc. in the Pangquangou Nature Reserve. Many research have been conducted, however few of them concerning the distribution patterns of dominant species in the succession process. In the present research, two time series of ecological succession of cold-temperate coniferous forest in the Pangquangou Nature Reserve were established through spatially-sampled data substitution. The first time series reflected the stable development process of Larix principis-rupprechtii as the monodominant community; the second ones reflected the process from Larix principis-rupprechtii as the monodominant community to Larix principis-rupprechtii and Picea wilsonii as the co-dominant communities and then to Picea wilsonii as the monodominant community. Point pattern analysis and Monte-Carlo simulation test were used to analyze the spatial pattern of the two dominant species and their interaction relationship.
The following conclusions were drawn. 1) During the stable development process of Larix principis-rupprechtii reflected by the first time series, the spatial pattern of the species changed from clumped to nearly random distribution and even to uniform distribution at 0-2.5 m scale, which was driven by the intraspecific competition caused by the self-thinning effects; during the process from Larix principis-rupprechtii to Picea wilsonii as the monodominant community reflected by the second time series, the spatial pattern of Larix principis-rupprechtii also gradually changed from clumped to nearly random distribution, which was mainly caused by the colonization and expansion of Picea wilsonii and the resulted interspecific competition. Besides, the spatial scale of Picea wilsonii community gradually increased, with the species colonization and intraspecific competition as the major causes. 2) In terms of the interspecific competition between the two species, no obvious relationship was found when Larix principis-rupprechtii acted as the monodominant community, significant positive relationship was identified at 0-6.5 m scale at the co-dominant stage, and no obvious relationship was found at 0-2.5 m scale when Picea wilsonii became the dominant species. The change of relationship between the two species was mainly driven by the intraspecific and interspecific competition for residual resources.