基于景观功能连通度的鄱阳湖草洲生境斑块重要性评价

Evaluating the importance of habitat patches using landscape functional connectivity for grassland in Poyang Lake

以鄱阳湖草洲为研究对象,综合考虑水位变化与物种扩散生态过程,在识别不同水位梯度下草洲生境范围和斑块组成的基础上,通过基于图论的景观连通度方法分析不同水位梯度和不同扩散距离下草洲景观功能连通度的变化特征,分别运用可能连通度指数的相对值(dPC)和中介度指数(BC)识别重要草洲斑块和关键草洲节点.结果表明,鄱阳湖草洲呈现“水落滩出、水进草退”的景观特征,草洲生境同时面临水体的淹没效应和分割效应.随着水位的增加,草洲分布范围不断缩小,从7.54m水位下的1813.61km^(2)减小到17.17m水位下的182.36km^(2),大斑块破碎与小斑块消失并存.从水位变化过程来看,随着水位的增加,草洲斑块在生态功能上的链接数减少、难以连接的独立组分增加、连接的可能性降低,草洲景观功能连通度逐渐降低.从物种扩散过程来看,物种扩散距离对草洲景观功能连通度具有绝对正向作用,随着扩散距离的增加,草洲景观功能连通度显著增加.共识别出重要草洲斑块124个,这些斑块一般面积较大,主要分布在鄱阳湖中部,集中分布在两个国家级自然保护区内.共识别出关键草洲节点16个,这些节点主要由小型斑块构成且主要分布在鄱阳湖中部和南部的边缘地带.巨型斑块和大型斑块对于维持草洲景观功能连通度有着极其重要的作用,但处于关键节点位置的小型斑块作为脚踏石或连接要素的作用也不可忽视.

Taking the grassland of Poyang Lake as a case,and comprehensively considering the ecological processes of water level change and species dispersal,this study firstly identified the range and patch composition of grassland under different water levels.Then,the graph theoretical approach was applied to analyze the dynamics of functional connectivity of grassland with different water levels and dispersal distances.Finally,the delta value for probability of connectivity(dPC)and betweenness connectivity(BC)were respectively used to identify the important grassland patches and key grassland nodes.The grassland presented the characteristics of"expanding when water falls while shrinking when water rises".The grassland patches faced both the segmentation effect and the inundation effect of water.With the increase of water level,the distribution of grassland decreased from 1813.61km^(2)at the water level of 7.54m to 182.36km^(2)at the water level of 17.17m,and the fragmentation of large patches and the disappearance of small patches coexisted.From the perspective of water level change,with the increase of water level,the number of links in ecological function between patches decreased,the number of independent components increased,the probability of connectivity decreased,and then the functional connectivity of grassland has progressively decreased.From the perspective of species dispersal,the species dispersal distance had an absolutely positive impact on landscape connectivity.With the increase of dispersal distance,the functional connectivity of grassland increased dramatically.The 124 important grassland patches were identified and mapped.They were all consistently large and primarily distributed in the center of Poyang Lake,especially concentrated in the two national nature reserves.The 16 key grassland nodes were determined and mapped.They were very small in size and mainly scattered in the central and southern margin of Poyang Lake.Giant patches and large patches play an extremely vital role in maintaining the functional connectivity of grassland.However,small patches in a pivotal location can not be ignored as stepping stones or connecting elements.