泾河流域分县景观格局特征及相关性

景观生态主要是研究生态系统的空间格局。因而很有必要对空间格局进行数量化的分析,在此基础上进行科学管理。应用斑块数、斑块面积、斑块密度、优势度、聚集度和分维数计算了泾河流域31个县景观格局的特征,首次以景观特征值为基础,将研究区域各县景观进行分类,并对不同类型的景观特征及相关性进行分析。结果表明,近年来流域破碎化程度有所增加,各景观指数值在研究区域之间变异很大。优势度和聚集度比较高的区域土地利用较单一,常常是以农用地为主导如咸阳、泾阳和乾县,或以农地和草地共同主导如环县。而优势度和聚集度较低的区域,土地利用较多样化,农地、林地和草地面积比例相近,如泾源、平凉、陇县、宁县和旬邑,这些县位于黄土丘陵沟壑区和黄土高塬沟壑区。高优势度、高聚集度和低分维数的区域为陕西省咸阳市,为泾河流域冲积平原区,土地利用以大面积的农用地为主导。景观指数的相关分析表明,3种主要的土地利用面积比例之间存在极显著负相关,林地面积和优势度、聚集度有极显著负相关,而草地面积和分维数存在极显著正相关,分维数高的县位于泾河流域中游的黄土高原沟壑区,分维数低的县位于下游河谷阶地和关中平原和黄土高原交界处。这种相关性表明了自然地貌及人类活动对景观的影响和干扰作用。

Characters of landscape patterns and correlation in Jinghe watershed

Landscape ecology describes spatial patterns of land uses and ecosystems.In order to manage landscapes sustainably,methods are needed to express spatial patterns in a suitable way.In the present paper six indices that describe spatial patterns are applied,namely patch number,patch area,patch density,dominance index,contagion index and the fractal dimension.These indices have been used for the analysis of the landscape patterns of all 31 counties located in the Jinghe watershed,Northwest China.Applying these indices,the different landscapes of the watershed have been classified into three types of spatial landscape patterns.The counties showed distinct variations in their indices.Agriculture,forest and grassland are the three dominant land use types in the watershed.High values of dominance and contagion indices were found in landscapes with relatively simple land use patterns,both for agricultural and grass land;these areas are mostly located in the lower reaches of the watershed,such as in Xianyang,Jingyang and Qianxian counties.Low values of dominance and contagion indices are typically associated with more diversified land use and with an almost equal share between agriculture,forest and grass land;These areas are mostly found in the loess uplands and in ravines,as well as on the loess plateau such as in Jingyuan,Pingliang,Longxian,Ningxian,and Xunyi counties.A combination of high dominance and contagion indices with a low fractal dimension was observed in Xianyang city,which is located in the relatively large plain loess scalariform areas in the lower reaches of the watershed.The significant positive correlation found between forestland area,dominance and contagion indices,and between grassland and fractal dimension indicate that forest and grassland are normally scattered in the watershed,signifying that the encroachment of agricultural land use into grassland leads to a high degree of fragmentation of land use.This clearly demonstrates the human manipulation of the landscape.The temporal changes of landscape indices observed in the watershed over the last decades have not been significant.The paper concludes that continued research on developing and applying landscape indices are critical for large-scale environmental impact assessment and landscape management.In particular,correlations should be established between index values and the actual ecological processes occurring on the ground.Basic questions to be addressed in further research should be the depiction of changes of the indices over time and how well these changes correspond to the actual ecological changes taking place on the ground.