摘 要 ：基于Quick Bird影像选择样地区域，采用样方法进行群落学调查。选取丰富度指数（R）、Simpson指数（D）、Shannon-Wiener指数（H′）、Pielou均匀度指数（Jsw）测度多样性水平。结果表明：19个岛状林共记录到维管植物140种，隶属于44科，102属，与相邻的洪河自然保护区内的同类型群落相比较有些物种已经消失。山杨林(Ass. Populus davidiana)、白桦林(Ass. Betula platyphylla)和杨桦林(Ass. P. davidiana+B. platyphylla)3种群落类型多样性指数在灌木层之间差异显著（p<0.05）。岛状林总体3个层次之间的R、D、H′大小顺序均为草本层>灌木层>乔木层，3者之间差异极显著（p<0.01）。岛状林斑块的物种丰富度与斑块面积（r=0.591, p<0.01）、周长（r=0.674 , p<0.01）和形状指数（r=0.584,p<0.01）极显著相关，而D、H′、Jsw与周长、面积和形状指数相关均不显著。受到一定人为干扰的岛状林群落仍具有较高的植物多样性，其中草本层植物多样性占有重要地位。林窗干扰是导致林下植物多样性较高的重要原因。边缘效应可能是引起群落斑块物种丰富度随着斑块面积、周长和形状指数的增大而增加的重要原因。岛状林群落斑块对于维持该地区的植物多样性具有重要意义。
Abstract:Aims Island forest is a major vegetation type of the Sanjiang Plain in northeastern China. However, its species diversity is at risk of decline. Our objectives were to 1) describe the flora, 2) determine the level of plant diversity, and 3) determine relationships between diversity indices and patch characteristics (area, perimeter and shape index). Methods We used Quick Bird satellite image data to identify a 65 km2 study site . The quadrat method was used to investigate community patch characteristics such as area, perimeter and shape index, which were analyzed with Erdas Imagine 8.7. Four indices were selected to describe plant diversity: richness (R), Simpson (D), Shannon-Wiener (H′), and Pielou (Jsw). Important findings The 19 patches of the island forest had 140 species of vascular plants of 44 families and 102 genera dominated by cosmopolitan and temperate genera. Our data suggested that, compared with the neighboring community in the Honghe Nature Reserve, some plant species had disappeared. The diversity indices were significantly different among shrub layers of the Populus davidiana, Betula platyphylla and P. davidiana + B. platyphylla communities (p<0.05). Additionally, R, D and H′indices of different layers were as follows: herb layer > shrub layer > tree layer, with significant differences among them (p<0.01). While statistically significant correlations were observed between the R index and patch area (r=0.591, p<0.01), perimeter (r=0.674, p<0.01) and shape index (r=0.584, p<0.01), no correlations were noted for the D, H′ and Jsw indices. Diversity levels remained relatively high after human disturbance. The greatest difference among patches was noted in herb layers. Our data also suggested that gap disturbance was an important cause of higher understory diversity. Plant species richness increased with patch area, perimeter and shape index, most likely resulting from edge effects. Our results demonstrated that the island forest plays an important role in preserving plant diversity in the region.