宁夏黄河流域景观破碎化时空变化特征

基于RS和GIS技术,以土地利用数据为基础,采用有效粒度尺寸对宁夏黄河流域1985年和2010年的景观破碎化进行时空变化分析。结果显示:流域整体的有效粒度尺寸(meff)从1985年的6326.62 km2下降到2010年的2974.32 km2,破碎化程度呈显著加剧变化;从流域内部来看,景观破碎化程度最大的是黄左区间,破碎化程度最小的是苦水河和红柳沟;除引黄区间外,其余分区景观破碎化程度在25年间均有所加剧。特征尺度分析结果显示研究区景观破碎化空间变异分析的合适尺度为4500 m;景观破碎化指数的空间变异结果表明破碎化程度较大的区域面积明显多于破碎化程度弱的区域,景观破碎化空间异质性在25年间表现出明显的上升趋势。在海拔背景条件下,2400 m以下区域的景观破碎化程度较高,2400m以上区域破碎化程度较低,且随海拔的升高有降低的趋势;流域景观破碎化受人为干扰影响强烈,在人为干扰较强的1000—1500 m区段的景观破碎化程度最大;景观破碎化在时间上的变化受人为干扰影响产生的变化最为显著,由自然条件改变产生的影响有限。研究结果可为西北地区景观格局及景观破碎化的研究提供参考,并为区域景观格局优化和土地的有效管理提供依据。

Analysis of spatial-temporal changes in landscape fragmentation in the Ningxia Yellow River Valley

Landscape fragmentation is the result of the transformation of large habitat patches into smaller and more isolated fragments. Fragmentation greatly affects the structure and function of the landscape ecosystem. It is necessary to quantify the degree of landscape fragmentation to optimize regional development planning and decision-making in an ecological manner. Effective mesh size (m_eff), which is based on the probability that two points chosen randomly in a region are connected (i.e., located in the same patch), can be used to quantify landscape fragmentation. The Ningxia Yellow River Valley, located in arid and semi-arid regions, accounts for most of the Ningxia Hui Autonomous Region, and its fragmentation may have great significance to the eco-environmental safety of Northwest China. We investigated landscape fragmentation based on Remote Sensing and Geographic Information System techniques using m_eff and multi-temporal land use data. Quantitative analysis revealed that the degree of landscape fragmentation of the entire Ningxia Yellow River Valley was higher in 2010 than in 1985, corresponding to a decline in the m_eff from 6326.62 km² in 1985 to 2974.32 km² in 2010. The m_eff of seven sub-basins in the Ningxia Yellow River Valley indicated that the Huangzuo area had the highest degree of fragmentation in both 1985 and 2010. Furthermore, the degree of landscape fragmentation in all sub-basins increased from 1985 to 2010, except in the Yellow River Water Irrigation Area. The expansion of the built-up areas and farmland in the Yellow River Water Irrigation Area simplified the landscape in contrast with the more complex landscapes in other sub-basins. Based on the semi-variable function and moving window method, the characteristic scale for analyzing landscape fragmentation heterogeneity in the Ningxia Yellow River Valley was 4500 m. The spatial heterogeneity of landscape fragmentation indicated that the area with high fragmentation values was larger than the area with low fragmentation values both in 1985 and 2010. The area with high landscape fragmentation values was mostly distributed in the south and mid-east of the Ningxia Yellow River Valley. The spatial variation of highly fragmented areas was higher in scope and degree in 2010 than in 1985, and spatial heterogeneity exhibited a similar change. In terms of elevation, landscape fragmentation below 2400 m was greater than that of areas higher than 2400 m above sea level. Moreover, the degree of landscape fragmentation decreased with increase in elevation above 2400 m. In addition, landscape fragmentation heterogeneity was related to anthropogenic disturbance-the zone 1000-1500 m away from buildings had the highest degree of fragmentation. The change in landscape fragmentation from 1985 to 2010 was mostly affected by human activities. The results provide valuable guidance for further studies on landscape pattern optimization and efficient management of land use in Northwest China.