The Edge Effect Of Community Patch In A Marsh In Sanjiang Plain

Habitat fragmentation is a major characteristic of the landscape in the marsh in Sanjiang Plain in northeastern China.Whether exist edge effects and the effect on species diversity is a problem that wetland biodiversity research area concerns. Based on Quick Bird satellite image data, the present study examined herbaceous community patches in the marsh of the Sanjiang Plain. The vascular plant species and plant life forms were recorded using transect method and quadrat (1m×1m) method. Four indices were selected to describe plant diversity of the community patches: Species number (S), Margalef richness index (R), Simpson index (D) and Shannon-Wiener index (H′), plant species number, plant life forms and soil moisture were compared among different sample circles, and based on these data to determine the depth of edge effects and analyze the reasons leading to edge effects and the relationship between of edge effects and species diversity.The result showed that the plant species number had a decreasing trend in unit length of the segment of sample gradually from edge to center of patch. Species number-distance curve y=-1.3464㏑(x) + 6.7628 (R2=0.9551). By hierarchical cluster analysis, based on the number of plant species, three groups 1 to 4, 5 to 8 and 9 to 17 were set in 17 segments of sample from the edge to the center, a significant difference on the number of species among groups (p=0.000). The indices S,D,H′,R between edge zone and core zone showed significant difference(p= 0.000). The plant life forms appeared disciplinarian variety from edge to core of the patches, annual plants and weeds of edge zone were higher than core zone obviously, however, aquicolous plant had a contrary result. Soil moisture of different circles showed significant difference from edge zone to core zone(p=0.003). The indices S,D,H′,R of different circles correlation with soil moisture(r=-0.941,p=0.017;r=-0.883,p=0.047;r=-0.912,p=0.031;r=-0.950,p=0.013).Species number, diversity indices analysis, plant life form analysis, as well as soil moisture analysis have demonstrated the existence of edge effects in patch herbaceous community in the marsh in Sanjiang Plain. Habitat heterogeneity of patch, especially difference of space gradient in water condition is an important reason lead to edge effects. Through Species number-distance curve, hierarchical cluster analysis of species number in segments of sample and significant of difference comparation, integrated determine the depth of edge effect in patch herbaceous community in a marsh in Sanjiang Plain is 0m～9m ring regional from edge zone to core zone. Edge effect took on positive effect in patch herbaceous community in the marsh in Sanjiang Plain. A total of 163 kinds of species were recorded, which represents 9.2% of the vascular flora in Heilongjiang province. 163 species of edge zone and 78 species of core zone were recorded. Some weeds form the regional farmlands were also found in every patch.In the context of landscape fragmentation, edge effect plays an important role in the preserving plant diversity in the local area.