Analysis of Changes in the Scale of the Watershed Based on the Metrics and Spatial Patterns of the Landscape (Case Study: Anzali Watershed)

Human beings have extremely changed the shape, pattern, and function of nearly all landscapes. The cumulative effects of human activities on the environment have been the impetus for extensive research aimed at identifying guiding metrics to assess the quality of the environment in terms of planning, monitoring, and resource management purposes. In order to control and restrict human impacts scientists, planners, and natural resource managers are looking for holistic approaches to interpret the relation between land use and the quality of the environment. In this regard habitat fragmentation, alteration of the hydrologic system of the watershed, and water quality have attracted the most attention. Landscapes have been studied at different scales and various metrics have been introduced to measure the quality of the environment. In the past years, ecological recognition has introduced a big picture based on the main pattern and landscape ecology principles. The foundation of this big picture is based on the idea that there are indispensables patterns in the landscapes that if they are maintained the important functions are protected. In this regard, some of the ecosystem's attributes are not saved and important natural assets will be protected. A landscape is a mosaic including a mix of ecosystems and land uses that repeat in a similar form. The mosaic pattern of landscape or spatial arrangement of landscape elements determines the movement of material, energy, organisms, and humans between local ecosystems. Also the movement of animals, water, nutrient, and human determine the arrangement of mosaic patterns. Landscape ecologists identified five main ways in which human alter landscape spatially: perforation, dissection, fragmentation, shrinkage, and attrition. These changes result in different spatial patterning of landscape elements that can alter the ecological process and population distribution of plants and animals. So, the purpose of this study was to investigate the landscape pattern change of Anzali watershed in the north of Iran.  

In this study, Landsat satellite imagery for 1994, 2008, and 2018 was used to determine land cover/land use using remote sensing. For landscape analysis, metrics of a number of patches (NP), class area (CA), patch density (PD), percentage of land (PLAND), and large patch index (LPI) were used. Based on how to change landscape metrics, landscape pattern change was examined through patterns of attrition, aggregation, creation, and dissection.  

Findings indicated a 10 percent decrease in forest cover and a 5.8 percent increase in agricultural land use. Also, a large patch index decreased for forest cover. According to landscape pattern change, Attrition was a dominated pattern that occurred mainly in forest cover. The second pattern was Creation that occurred for agriculture land use. Findings indicated decreasing in Anzali watershed integrity and connectivity of the forest patches as the most important patches in the watershed. Forest patches decreased in the area through attrition, aggregation, and dissection. In contrast, agriculture land use developed through aggregation and direct convert of isolated natural patches.

The pattern of land cover changes in the Anzali watershed indicated a shift in the balance towards the development of disturbed land cover, especially agriculture. However, forest cover as the most important land cover in the area has not been fragmented yet (simultaneous increase in the number of patches and drastic reduction of the area). The reason for this is based on the largest patch index of forest class. One of the forest patches alone, covering an area of 2071/34 hectares in 2018. Patterns of attrition, aggregation, creation, and dissection have provided the basis for the occurrence of disruption in forest cover. In this case, forest cover loses many of its capabilities, especially habitat services, water conservation, and decreasing soil erosion.