山西五鹿山白皮松群落乔灌层的种间分离

Abstract

The Wulu Mountains,a part of the Luliang Mountain Range,are situated at 36°23′45″—36°38′20″N,111°08′—111°18′E in western Shanxi Province,China.This area has a warm-temperate continental monsoon climate with abundant plant resources and high biodiversity.Appropriate conditions for the growth of Pinus bungeana Zucc.ex Endl.are limited within the Wulu Mountains which include only a part of the overall range of P.bungeana.Therefore,building nature reserves in which P.bungeana can be studied systematically is important both ecologically and academically,with the goal of studying this species in its warm temperate north China climate so it can be preserved in natural forests indefinitely. Interspecific relationships are an important factor affecting community composition,structure,function and dynamics.Interspecific segregation refers to the relative distributions of two or more related species.It reflects the degree of mixing of two species based on their interrelationships.For example,the less two species mix,the higher the degree of interspecific segregation exists. The segregation relationship between different species pairs can be helpful in revealing the phenomena of species interactions,community structure and dynamics.This relationship can be used to explore the impacts of environmental differences on species distribution.Practically,such study is the scientific foundation of species conservation,restoration and the reconstruction of degraded ecosystems. We established 55 quadrats within natural P.bungeana communities to study the intraspecific and interspecific competition relationships of nine tree species and patterns of interspecific segregation of all species in the tree and shrub layers of P.bungeana communities.Using ArcView GIS software and the nearest neighbor method,interspecific segregation was studied with an N × N nearest-neighbor contingency table,a 2 × 2 nearest-neighbor contingency sub-table,and Hegyi′s competition index model for the individual tree species. The results indicate:(1) most of the species pairs are randomly segregated(80%),some species pairs are positively segregated(16.19%),and only a few species pairs are negatively segregated(3.81%).(2) There are some differences among different species in the interspecific segregation of all species.The larger individuals representing dominant species in the communities tended to be positively segregated with the other large trees and shrubs,probably because of their stronger competitive vigor.For example,P.bungeana,which is the most common and dominant species of this community,was positively segregated from Platycladus orientalis,Quercus wutaishanica,Ulmus pumila,Syringa pubescens,Cotoneaster multiflorus,Sophora davidii,Viburnum mongolicum,the dominant species of this community.Negative segregation appeared between dominant species and companion species in the communities,such as P.bungeana and Populus davidiana,P.orientalis and F.vulgaris,S.microphylla and Salix wallichiana.This appeared to be caused by the fact the companion species had fewer individuals,lower coverage and similar habitat requirements to the dominant species.Intensive interspecific competition resulted in a mosaic distribution and full competitive exploitation of resources among species,apparently causing them to be more likely to become negatively segregated. The 15 species from the forest plots were divided into three ecological species groups(ESG),based on their niches and relationships between the species,other plants and the environment.(3) The status of interspecific segregation of species has a close relationship to their intraspecific and interspecific competitive relationships and spatial distribution patterns.The larger individuals representing dominant species with more severe intraspecific competition than interspecific competition and appearing to have an aggregating distribution in the communities tended to be positively aggregated with the other large trees and shrubs.Negative aggregation(segregation) appeared between dominant species and companion species which have more severe interspecific competition than intraspecific competition in the communities.The interspecific competition of species within the same ESGs was more intense than in species in different ESGs.(4) The interspecific segregation is related to the heterogeneity in the communities,in that aggregation often occurs between two species which have different habitat requirements;while the segregation often appears between two species which have same or similar environmentally requirements.(5) The results show the 15 species we studied overlapped in distribution and were characterized by overall non-segregation.(6) The intraspecific and interspecific relationships were caused by ecological niches to which the different species are adapted and their biological requirements,and these differences may be the mechanisms which allow these species to stably coexist in the P.bungeana community of the Wulu Mountain Nature Reserve.