نوع مقاله : مقاله کامل علمی پژوهشی
1 کرج- پردیس کشاورزی و منابع طبیعی
2 استاد-دانشگاه تهران
عنوان مقاله [English]
Background and objectives: Getting informed about of land uses patterns and knowing the changes of each land use, during the time is the one of the prerequisites for the correct uses of land. During the last decades many methods of this regard have been developed. One of these methods is the use of landscape metrics. Landscape metrics are quantitative indices that describe compositional and spatial aspects of landscape. The most important impose on these studies is that changes into landscape patterns strongly affected landscape function. Due to the special ecological position of the Arasbaran biosphere, and some destructive factors such as over-grazing, high acreage of agricultural fields and encroachment of human-made structures into natural ecosystems, the area has witnessed a noticeable rate of land degradation during the last decades. For this reason the main objective of this study was analysis of land use and land cover changes using ecological landscape metrics.
Materials and methods: At first, the multi temporal Landsat images dated 1990, 2002 and 2014 were provided. Based on former knowledge from study area and study aim, satellite images were classified in seven classes including high forest, low forest, agriculture, grassland, barren land, water and urban area. For quantitative landscape metrics for each land use map, we used Fragstate software. Selected metrics included CA, PLAND, NP, LPI, MN_SHAPE, ENN, IJI, DIVISION and SHDI.
Results: The result of calculating CA, PLAND and NP metrics showed that forests were degraded and urban area and barren land were extended. Decreasing the index of the largest patch (LPI) and increasing indexes of contagion-interspersion (IJI), ENN and DIVISION for forest area indicates the destruction and disintegration of these lands. In landscape level the number of patches has increased over the time, which represents the intensity of negative and defamatory change during the study. Also, the increasing of Shannon's diversity index confirms the increasing diversity of patches in the regions as a result of increasing patch numbers and changes in landscape. Contribution of each category in altering other LULC categories was also calculated to provide an improved understanding regarding current LULC change processes in the area. Grassland is the most invasive category against low-density forest such that it occupies this category for 815 and 1,219 hectares during both time intervals, respectively.
Conclusion: The result of calculating metrics and change detection showed the changes in the second period (2002-2014) were more intense than the first period (1990-2002). Based on the results can be mentioned that during of study the landscape in Arasbaran region completely fragmented. Also consider spatial diversity and dispersion of land uses, there is a possibility of degradation and land use change in the future. Accordingly, there is a need to develop a suitable program to prevent unwanted changes in the landscape and maintain its spatial continuity. Development in the future should be programmed based on sustainable development principles and attention be pay to protection, maintenance and ecosystem management.