人工管理和自然驱动下盐城海滨湿地互花米草沼泽演变及空间差异

Spatiotemporal characteristics of Spartina alterniflora marsh change in the coastal wetlands of Yancheng caused by natural processes and human activities

将盐城国家级自然保护区核心区划分为人工管理区和自然湿地区两种模式,根据2000年、2006年、2011年3个时相的ETM+影像,运用RS、GIS技术和景观生态学方法,分析不同驱动力下互花米草沼泽景观变化的差异。结果表明:(1)人工管理区,2000—2011年,互花米草沼泽面积由272hm2增加到781hm2;平均分维数呈下降的趋势,聚合度指数呈上升的趋势,表明互花米草沼泽在空间上趋于聚集,在形状上趋于规则;从互花米草沼泽增长速率看,2000—2011年,呈现先快后慢的特征。在景观空间演变上,互花米草沼泽的平均宽度从598.679m增加到1719.002m,表现出向海陆两个方向扩张的特征。(2)自然湿地区,2000—2011年互花米草沼泽面积由2023hm2增加到3974hm2;平均分维数和聚合度指数呈先上升后下降的趋势;米草沼泽增长稳定,年增长约160—180 hm2/a,单位长度岸线年增长面积约为15hm.2km-.1a-1左右;比较发现,自然湿地区互花米草沼泽的增长速度高于人工管理区的增长速度。在景观空间演变上,互花米草沼泽平均宽度从1625.586m增加到3193.317m,2000—2006年表现出向海洋单方向扩张的特征,2006—2011年表现出向海陆两个方向扩张的性质。(3)在自然条件下互花米草沼泽扩张受到气候、地貌过程、水文过程、植被类型及种间竞争的影响,表现出明显的带状特征。在人工管理下,通过建设拦水堤坝等,阻止了潮汐作用下海水的扩散能力,生态过程发生改变,致使生态系统类型向淡水湿地方向演变,抑制了互花米草沼泽的扩张,表现出一定的镶嵌格局。

As Landscape changes have been the most significant feature of the coastal wetland, we focused on the core area of Yancheng Nature Reserve in the research. Basing on the type of landscape change, we divided this area into two parts： change in the northern area which was characterized as from human activities, and that in the southern area characterized as from natural causes. Using remote sensing digitized data from 2000, 2006 and 2011, and applying GIS techniques and methods of landscape ecology, we analyzed the differences between the temporal and spatial changes in landscape pattern caused by natural and artificial reasons. The result showed us that from the following three aspects. Firstly, in the District by human activities, from the year 2000 to 2011, the area of S.alterniflora marsh increased from 272hm2 to 781hm2; the average dimension tended to decline while the polymerization index showed an increasing tendency, which means the S.alterniflora marsh tended to gather in space and to be regular in pattern form; the growth rate of S.alterniflora marsh first appeared quick and then slow. In terms of spatial landscape evolution, the S.alterniflora marsh extended in both seaside and landside, with its width increasing from 598.679m to 1719.002m. Secondly, in the District by natural processes, from 2000 to 2011, on one hand, the area of S.alterniflora marsh increased from 20230hm2 to 39740hm2. On the other hand, the average dimension and polymerization index appeared a decline trend after initial ascent. And thus, the growth rate of S.alterniflora marsh was stable at the speed of 160-180 hm2/a annually while the coastline increased 15hm2·km-1·a-1 per unit length annually. By comparison, during 2000 to 2011, the growth rate of S.alterniflora marsh in natural wetland district was higher than that in the manual management district. In terms of spatial landscape evolution, the width of S.alterniflora marsh increased from 1625.586m to 3193.317m, as it extended to seaside direction from 2000 to 2006 while in both seaside and landside directions from 2006 to 2011. Thirdly, by natural processes, the expansion of S.alterniflora marsh was influenced by the climate, geomorphic processes, hydrological processes, vegetation pattern and competition between species, as a result, it appeared strong zonal characteristic. By human activities, the ecological process changed as the expansion power of seawater was affected,with the dam being blocked.Consequently, the ecological system evolved towards the freshwater wetland and furthermore it restrained the expansion of S.alterniflora marsh, which present inlay pattern to a certain degree.