Application of GIS to Measure and Evaluate Landscape Changes
Chi-Chuan Cheng (Taiwan)
Deputy Director, Taiwan Forestry Research Institute
53, Nanhai Road, Taipei 100, Taiwan
Telephone: +886-2-23039978 Facsimile: +886-2-23757469
E-mail: cccheng@serv.tfri.gov.tw
Jihn-Fa Jan (Taiwan)
Assistant Professor, Department of Geography
National Changhua University of Education
1, Jinn Der Road, Changhua 500, Taiwan
Telephone: +886-4-7232105 ext. 2825 Facsimile: +886-4-7211186
E-mail: jfjan@cc.ncue.edu.tw
Key words: GIS, landscape ecology, landscape diversity.
Abstract: This study used the 'Liukuei ecosystem management area' of the Taiwan Forestry Research Institute as the study area. Geographic information systems were used to integrate indices of landscape structures to investigate the effects of management activities on the landscape. Forest type maps of the area in 1988 and 1996 were derived using digital photogrammetry and GIS. To analyze the effects of cutting and forest road building on the landscape, indices of landscape structure referring to landscape composition and landscape configuration were calculated. The results show that cutting and forest road building increased the numbers and types of patches. They not only directly altered the variety and abundance of the patches, but also indirectly affected landscape structure properties such as landscape diversity, evenness, and interspersion and juxtaposition. Several indices were compared, and it was found that the Shannon diversity performed better in distinguishing landscape changes. In addition, the effects of cutting and forest road building on the landscape were not significant based on the t-test result of the Shannon diversity index. This study reveals that integration of GIS and quantitative indices of landscape structure is a feasible and efficient approach for evaluating the effects of management activities on landscape.
1. Introduction
Landscape monitoring is a basis for studying forest landscape changes and validating theories of landscape ecology. Landscape ecology is a science that studies the relationships and mechanisms among landscape patches, i.e. a research focuses on the structure, function, and change of the landscape. However, to understand the function and change of the landscape, it is a prerequisite to quantify the landscape structure (O'Neill et al., 1988; Li, 1990; Turner, 1990; Turner and Gardner, 1991). Early studies on the quantification of landscape structure were mostly for special purpose or lack of analysis tools, thereby the results were limited (Turner, 1990). In recent years, the development of geographic information system (GIS) makes timely temporal and spatial information accessible. Moreover, its capability of spatial analysis and presentation makes it a useful tool for studying landscape spatial structure and landscape change analysis. Publications on the application of GIS in landscape research include: Burrough (1986), Cola (1989), Lam (1990), Rex and Malason (1990), and Olsen et al. (1993).
Integration of landscape ecology and GIS in landscape monitoring for forest management in Taiwan has become the main focus of researches recently. Wang (1998) and Cheng el al. (1999) used GIS and fractal dimension to monitor spatial variation of forest landscape. Huang (1997) used Shannon index to monitor landscape diversity. However, publication concerning application of landscape index to evaluate the effects of cutting and forest road building on landscape structure and landscape changes has not been seen. Therefore, this study used digital photogrammetric technique to produce 1/5000 scale forest type maps of the 'Liukuei ecosystem management area' in 1988 and 1996. The objective was to apply GIS and quantitative indices of landscape structure to investigate the effects of cutting and forest roads building on landscape changes in the study site.
2. Materials and Methods
2.1 Study area and materials
The 'Liukuei ecosystem management area' occupies about 2440 hectares. Approximately 75% of the area is covered with natural hardwood forest, whereas only a small portion of the area is plantation, within which Taiwania cryptomerioides is the most commonly planted species.
Two forest type maps (scale 1/5000) of 1988 and 1996 were produced using digital photogrammetric technique (as shown in Figure 1). A GIS database was established for quantitative analysis of the landscape structure. The software and hardware used in the study included a digital photogrammetric workstation, personal computers, ARC/INFO, ArcView GIS, and ERDAS IMAGINE.
2.2 Analysis methods
Quantification of landscape structure is a key element for studying landscape functions and changes. Therefore, this study applied GIS to calculate indices of the landscape structure using the forest type maps for 1988 and 1996, respectively. These indices were then used to analyze the landscape changes in the study area.
2.2.1 Quantification of landscape structure
A landscape can be characterized by its composition and configuration (Dunning et al., 1992). Landscape composition refers to the variety and abundance of patch types within a landscape. Landscape configuration refers to the placement or spatial character of patches within a landscape. These two aspects can independently or jointly affect the ecological processes. This study followed the approach proposed by McGarigal and Marks (1994) to quantify the landscape structure. Several quantitative indices were used to measure landscape composition and landscape configuration for analyzing the effects of landscape changes.
Three indices were used to characterize the landscape composition, that is, landscape diversity, patch richness, and landscape evenness. The landscape diversity is often represented by three indices, which include Shannon diversity index (SHDI), Simpson diversity index (SIDI), and modified Simpson diversity index (MSIDI). Patch richness (PR) is simply the number of patch types. The landscape evenness is further described by Shannon evenness index (SHEI), Simpson evenness index (SIEI), and modified Simpson evenness index (MSIEI). For landscape configuration, this study used the interspersion and juxtaposition index (IJI) to illustrate the distribution characteristics of the landscape patches. Detailed definitions of these indices can be referred to McGarigal and Marks (1994).
2.2.2 Monitoring of landscape changes
Figure 1. (a) Forest type map of 1988, (b) forest type map of 1996.
2.2.2.1 Analysis of landscape changes
Figure 1 illustrates the distribution of each forest type in1988 and 1996. The landscape is mostly composed of natural mixed hardwood forests, which can be regarded as the matrix of landscape. Resulting from human disturbances, plantations and forest roads can be treated as patches and corridors. From 1988 to 1996, it is apparent that management activities (e.g. plantations replanted after cutting and forest road building) were two major landscape changes. Therefore, this study used the aforementioned eight quantitative landscape structure indices to analyze the effects of cutting and forest road building on landscape changes.
