近30年来白洋淀湿地景观格局变化及其驱动机制

湿地是水陆相互作用形成的独特生态系统,其景观格局极易受到气候变化和人类活动的影响。利用1984—2014年的11期遥感影像数据,综合运用GIS技术和景观格局指数方法,对白洋淀湿地景观格局变化特征及其驱动力机制进行了分析。结果表明,1984—2014年期间,挺水植物和沉水植物呈减少趋势,农田和居民点持续快速增长,纯水体为"增加—减少—再增加"的趋势,林地和裸土地变化幅度不大。其中挺水植物一直是白洋淀最主要的景观类型,占研究区总面积比例达到37%—61%。农田的平均斑块面积最大,挺水植物的最大斑块指数和分维度指数最高,挺水植物和农田的聚集度指数最大,居民点、林地和裸土地空间分布离散,破碎化程度高,连通性差。1989—2004年白洋淀景观多样性指数呈减少趋势,景观格局趋于不稳定,同期聚集度指数上升,湿地连通性增加;1984—1989年和2004—2014年期间白洋淀多样性指数上涨,聚集度指数逐年下降,景观异质性增加。人口和社会经济发展是影响白洋淀景观格局变化的主要因素。

Landscape pattern change and the driving forces in Baiyangdian wetland from 1984 to 2014

Wetlands, unique ecosystems formed by the interaction of land and water, are susceptible to climate change and human activity. Landscape developmental processes are an important subject in the fields of geography and ecology. Landscape pattern index is an indicator of landscape structure, composition, and spatial configuration. In this paper, we discuss changes in landscape patterns in Baiyangdian wetland during 1984-2014, and the driving forces behind these changes, based on Landsat Thematic Mapper (TM) and GF-1 remote sensing images. A landscape classification system was formulated, and landscape pattern indices were selected at the landscape and class levels to reflect patterns in structural composition and spatial configuration and to analyze the evolution of the landscape. Our results showed that the area of emergent and submerged plants had decreased, and farmland and residential areas increased rapidly. Open water showed an "increasing-decreasing-increasing" tendency, while forest and bare land area did not change significantly in the study period. The wetland area (emergent plants + submerged plants + open water) decreased from 1984 to 2014, with an average area of 25008 hm² before 1998 and 21573 hm² after 1998. Emergent plants were the main cover type in Baiyangdian, covering 37%-61% of the total study area, followed by farmland, submerged plants, and open water. Interconversion among emergent plants, submerged plants, and open water occurred with changes in the hydrologic regime. Over the past three decades, farmland has had the largest average patch area, followed by emergent plants. Emergent plants had the highest patch area index and dimension index, indicating that this was a dominant cover type in the study area. In addition, the cohesion indices of farmland and emergent plants were highest and showed a smoothing trend, while residential areas, forestland, and bare land showed a discrete distribution, high degree of fragmentation, and inferior connectivity. Shannon''s diversity indices showed a decreasing trend in Baiyangdian from 1989 to 2004, during which the landscape pattern tended to be unstable, and cohesion indices and wetland connectivity increased. Shannon''s diversity indices, cohesion indices, and landscape heterogeneity increased between 1984 and 1989 and between 2004 and 2014. Population and economic development are major factors affecting changes in landscape patterns in Baiyangdian.