Search

Wulu Mountain Nature Reserve is located between the western margin of the North China Plain and the eastern margin of the Loess Plateau,and shows distinct transitional vegetation types and high species richness.Thus the reserve has an important role to play in plant biodiversity research.In the present study we investigated the plant species distribution along an altitudinal gradient in the Wulu Mountain Nature Reserve in October,2010.The vegetation zones and dominant species in each community changed with increasing elevation,and a combination of rainfall and temperature determined the major communities in the forests.The plant communities were classified as Robinia pseudoacacia forest,Pinus bungeana forest,mixed conifer-broadleaf forest,and Quercus liaotungensis forest.We investigated the species composition of plant communities in different plots to discern patterns of species diversity and distribution along the altitudinal gradient.We calculated α-diversity,β-diversity and γ-diversity using the data collected from the study plots and analyzed with a generalized additive model to examine the following relationships: 1) changes in the total number of trunks and diameter at breast height in all forest plots along the altitudinal gradient;2) species richness in the tree,shrub and herbaceous layers with altitude;3) the Shannon-Wiener diversity index for the tree,shrub and herbaceous layers with altitude;4) Pielou′s evenness index for the tree,shrub and herbaceous layers with altitude;5) β-diversity for the tree,shrub and herbaceous layers with altitude;6) γ-diversity with altitude;and 7) the relationships of grass species richness with total number of trunks and diameter at breast height in all forest plots.The results showed that total number of trunks and diameter at breast height in all forest plots increased with the increase in elevation.Species richness,the Shannon-Wiener diversity index and Pielou′s evenness index for the tree layer were significantly higher in mixed conifer-broadleaf forest at middle elevations(P0.01).Species richness and the Shannon-Wiener diversity index of the shrub layer both peaked at 1507 m but were also relatively high at 1160 and 1260 m,whereas Pielou′s evenness index of the shrub layer increased with the increase in elevation(P0.05).In contrast,species richness and the Shannon-Wiener diversity index of the herbaceous layer decreased with the increase in elevation except at lower elevations,owing to the significant influence of forest canopy cover,whereas no differences in species richness and the Shannon-Wiener diversity index of the herbaceous layer were observed at higher elevations.Pielou′s evenness index of the herbaceous layer increased with the increase in elevation.The Shannon-Wiener diversity index over the entire altitudinal gradient showed the rank order: herbaceous layershrub layertree layer.Beta-diversity showed peaks at middle and high elevations.Gamma-diversity was highest at 1400—1500 m altitude.Aridity at low altitudes and low temperature at high altitudes limited species survival,and only middle elevations experienced favorable precipitation and temperatures to support high plant species diversity.The species richness of grasses decreased with the increase in total number of trunks and diameter at breast height in all forest plots.

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.