景观格局-土壤侵蚀研究中景观指数的意义解释及局限性

景观格局分析是景观生态学研究的重要组成部分。景观指数是景观格局分析的有力工具。近年来,景观格局与土壤侵蚀关系的相关研究增多,常规景观格局指数得到应用。但针对土壤侵蚀过程的景观指数意义解释不足,景观指数在刻画景观格局-土壤侵蚀过程关系存在局限。选择了连接性、多样性、边界/斑块密度、形状4个方面的12个常用景观指数,对这些指数在景观格局-土壤侵蚀过程关系研究中的意义进行阐述,对指数应用的局限性及其原因进行了分析。景观数据属性、景观指数本身性质和土壤侵蚀过程的复杂性使得常规景观格局指数在景观格局-土壤侵蚀关系研究中存在不足。这3方面的影响使得常规景观格局指数与土壤侵蚀表征变量之间不存在确定的关系,从而难以通过景观指数来表征景观土壤侵蚀特征。缺乏土壤侵蚀过程基础是常规景观指数在土壤侵蚀研究应用中存在局限的主要原因。因此,构建基于土壤侵蚀过程的景观指数是景观格局-土壤侵蚀关系研究的需要和新的发展方向。

Implication and limitation of landscape metrics in delineating relationship between landscape pattern and soil erosion

Landscape pattern analysis (LPA) is an important topic of landscape ecology. The ultimate goal of LPA is to link spatial patterns of landscape with ecological processes, and detect status of processes using landscape pattern information. By analyzing spatial arrangement of relevant factors about landscape, LPA can obtain information to predict dynamic pattern of ecological processes. Landscape metrics can represent the spatial distribution of landscape and it has been used as a common tool in LPA. In the past decades, with the development of landscape ecology theories and spatial information technology, many types of landscape metrics were developed. Soil erosion is a globally critical material transport process across earth surface. It is inherently impacted by spatial arrangement of source and sink areas, flow paths and impedances of runoff and sediment transport. To account for it, diverse landscape metrics have been widely applied to delineate the relationship between landscape pattern and soil erosion. In general, a perfect landscape metrics should logically reflect soil erosion process and coordinate well with process variables. However, published literatures indicated that many common landscape metrics did not have specific correlation with soil erosion variables. Consequently, there is lack of proper interpretation for most of the common landscape metrics based on mechanism of how landscape pattern affect soil erosion process. Besides, some inherent limitations of landscape metrics exist in linking landscape pattern with soil erosion. In this review, twelve common landscape pattern metrics concerning landscape connectivity, diversity, edge/patch density and shape characteristics were presented. Their implications and limitations in linking landscape pattern with soil erosion process and indicating soil erosion status were explicitly elaborated. As most of landscape metrics were not developed on the basis of soil erosion mechanism, there were lack of specific relationship between landscape metrics and variables expressing soil erosion status. The properties of landscape data, inherence of metrics and complexity of soil erosion process across different scale caused limitations of applying landscape metrics in soil erosion research. The commonly used landscape analysis data only focused on land cover or land use type, but ignored spatial arrangement of different functionally topographical elements in soil erosion. With respect to inherence of landscape metrics, most of them were only statistical expression of geometry characteristics or spatial distribution of land use or land cover units, which lacked of ecological meaning. For those developed based on other ecological processes, they were not perfectly suitable to indicate erosion process. The combination of above three limitations made the uncertainty and inability in using metrics to describe relationship between landscape pattern and soil erosion processes. Therefore, detecting soil erosion status under specific landscape pattern by common landscape metrics was unreliable. In summary, ignorance of physical mechanism of soil erosion process was the main reason for the limitation of employing landscape metrics to evaluate soil erosion probability or risk across landscapes. Development of landscape metrics based on soil erosion process is necessary. It is a new prospect in studying interaction between landscape pattern and soil erosion.