واکاوی تغییرات سنجه های سیمای سرزمین در یک دوره 30 ساله (مطالعه موردی: حوزه آبخیز تجن)

Analyzing the changes of land features in a 30-year period (case study: Tajen watershed)

Introduction
In recent years, irrational human use of land due to incorrect exploitation or wrong management in relation to land administration has faced an increasing trend and has led to extensive ecological and social economic effects. Although the improvement in the agricultural sector has greatly increased the amount of production during the last 50 years, it has brought environmental problems, especially the fragmentation of the country's natural lands and changes in the landscape. On the other hand, relying on the past land use situation and using the historical data of land surface changes alone cannot be used in the design of plans and implementation measures. Therefore, a complete understanding of the state of the landscape, its past changes and the prediction of future changes can play an important role in the sustainable management of resources. Therefore, in this research, it is intended to evaluate the changes in the shape and structure of vegetation patches during possible changes in the future of the Tejn watershed in Mazandaran province, and also to consider the potential possibilities of using land surface measurements in the management of the watershed. In addition, by identifying the priority areas, it can provide an important guide in the direction of environmental protection and management of the basin against further destruction and promotion of sustainable development in this area.

Method
In this research, using the land use maps of 2010 and 2040 (Rajaei et al., 2020), the topography measures at the class level were calculated using FRAGSTATS 2.4 software for the two main uses of forest and pasture (Table 1). It is worth mentioning that the investigation of land features at the sub-basin scale is the first step to manage the shape and structure of the land features of the basin (Xin et al., 2022). Measurements were extracted based on the sub-areas separately. To achieve this goal, the land cover map was extracted for each sub-are

Result and Discussion
FRAC index shows slight changes in pasture. The pastures are located in the upstream areas, which have colder weather conditions and a shorter growth period. On the other hand, rural and urban areas are less concentrated there, as a result of human access and destruction of pastures, compared to forest use, less happened. In the use of forest in a number of sub-areas 19, 18, 10, 12 and sub-area 24, it shows a higher trend, which is because in these sub-basins, especially in sub-basin 24, there is a high concentration of villages and the city of Frame. which has caused severe destruction of forest lands and turning them into agricultural lands in this sub-region. In a number of sub-areas, there is also a reduction in FRAC, which can be caused by the digestion of forest patches among man-made covers, especially the consolidation of agricultural lands. On the other hand, the measure of the environment has increased in the area of the forest and pasture class in the future harvest, which is a sign of the increasing fragmentation of the land surface in the studied area (Hui, et al., 2022). In forests, this greatly increases the value of many remaining forest patches for the protection of biodiversity and reduces the destruction of species. The increase of this index leads to the increase of the common border of forest and pasture land use with agricultural land use, as well as increasing access and influence, so agricultural land use will have a greater chance of encroaching on the biodiversity of the area and also transferring the pollution load to water sources. Also, they considered forests as a factor in improving water quality, which prevents soil erosion and the washing of minerals in it due to the presence of suitable vegetation, and by reducing the speed of surface currents, it provides an opportunity for sedimentation and Provides absorption of soluble substances. In general, the more the implementation of management activities causes more continuity of vegetation in the basin, the value of the forest CONNECT index will increase. The connection of the forest in the semi-arid land will lead to the ease of movement and dynamics of animals and plants in isolated habitats, and as a result, it will lead to the survival of the environment (Medeiros et al., 2022). The index of CONNECT has decreased in all sub-areas in the use of forest and pasture in the land use of 2040, with the exception of sub-area 24 in the use of forest and sub-area 16 in the use of pasture. The reason that this index is higher in these two sub-areas is the existence of residential spots and agricultural lands close to each other. If the spots are large and far apart, the spread index will be lower (Wang et al., 2022). Therefore, it is suggested to establish residential development in the areas where its contagion to other spots is less. On the other hand, the normalized shape index is one of the advanced measures in the quantification of the shape of patches, and its values increase between 0 and 1 as the shape of the spot moves away from the square. In all sub-basin in both pasture and forest classes, this index shows an increase, which indicates the increase of irregular forms of pasture and forest utilization patches.Examining the statistical difference of land features at the sub-basin level between the studied period showed that there is no significant difference in the indicators introduced in pasture use between 2010 and 2040, but the changes of these indicators in forest use except for the index Contagion has been significant.
Therefore, according to the obtained results, only the area of land use cannot be the factor describing the situation in the region. In a sub-region, they may have the same characteristics and the same composition of users, but the form of the users is completely different and effective. Also, the results of this study emphasize the importance of reducing changes in land use and management necessary to achieve environmental goals and clearly show the necessity of different strategies for sustainable future management. Therefore, it is suggested to review the watershed vegetation management scenarios with emphasis on the greatest potential in improving the continuity and connection of vegetation patches and reducing the effects of environmental degradation.