长白山北坡植物群落间物种共有度的海拔梯度变化

群落同各生活植物及种所有植物种的共有度，一定程度上反映了群落间的相关性及沿环境梯度的物种替代关系。应用梯度格局法在长白山北坡海拔700－2600m之间，海拔每上升100m设置一块样地，共计20块样地，应用Jaccard指数，对各海拔植物群落间物种共有度的海拔梯度变化进行了分析，不同海拔群落间物种的共有度，无论以哪一层次的植物来表达，基本都以与其最相邻海拔的群落之间为最高；如相邻海拔的两个群落属于不同植被类型，其共有度较低。群落间物种共有度的峰值与谷点反映了群落类型随海拔具有间断性变化，乔、灌、草各生活型物种的共有度以及所有植物物的共有度，在同一海拔差群落间的数值都非常接近，并均随着海拔的增加呈明显的下降趋势，表明群落各层次物种的构成有很大的相关性以及物种之间的共存性。

Co-occurrence of plant species among communities with changes in altitudes on the northern slope of Changbai Mountain

The Co occurrence of species among communities at different altitudes may reflect the relationships among communities, coexistence and the replacement of species along the altitude gradient at some extent. Continuous or disjunctive distribution of different species along altitude gradient not only reflected the environment variation at altitude gradient, but also the biological and ecological spatiality as well as the adaptability of species. The northern slope of Changbai Mountain where there is not only a high diversity in vegetation types and species, but also high variation of diversity pattern along the altitude gradient. It is a perfect transect for the research of biodiversity and gradient patterns. From 700 m to 2600m on the northern slope of Changbai Mountain, twenty plots were investigated with an interval of 100m in altitude. By using Jaccard index, co occurrence of plant species among communities at different altitudes was analyzed. For species of different life forms or all the species as a whole, co occurrence of plant species between neighboring communities was the highest except for that between different vegetation types. The peak values and valley values of co occurrence of plant species among communities along altitude gradient were matched with vegetation gradient patterns. co occurrence of plant species at different layers or all the plant species among communities with the same altitude difference were nearly the same, and decreased as the increase of altitude difference. These results showed that plant species compositions at different layers of the communities were highly related. It is suggested that these well developed and also well protected communities have consistent relationship between canopy species and understory species. It was impossible to have communities with high co occurrence of plant species as canopy species at the same time low co occurrence of plant species as understories.