جستجوی مقالات مرتبط با کلیدواژه « vegetation » در نشریات گروه « منابع طبیعی »

Improving decisions in fire management requires a complete understanding of the spatio-temporal relationships between droughts and fires. To achieve this, the natural areas of Lorestan province were selected as the research site. The fire data from MODIS satellite products and monthly rainfall data of the province were extracted to estimate SPI drought index for the statistical period of 2000 to 2022. The spatial and temporal relationship between the frequency of fire occurrences and the spatial and temporal distribution of droughts in terms of annual and monthly scales was investigated with the Pearson correlation model in the province. The results showed that the trend of fires in the region is increasing. The months of June and July have experienced the highest frequency of fires in the natural areas of the province. Poldokhtar city has had the most frequent fires in natural areas. The whole region has tended to be dry, but the eastern parts mostly included classes with higher degrees of drought. The results of the correlation matrix showed that only the drought events in spring to summer had a significant but moderate negative correlation with the fire events in spring and summer. Despite the obtained results, this study emphasizes that the connection between fires with drought needs more studies and it is not possible to prove the real relationship between the two phenomena with just one calculation index.

 The degradation of resources in many parts of the world is a serious threat to humanity due to its growing trend. Desertification, which is one of the manifestations of this degradation, has affected most countries and has been introduced as the third challenge of the 21st century after the two challenges of climate change and freshwater scarcity. Desertification is the degradation of land in arid, semi-arid, and semi-humid areas. This situation is caused by a series of important processes, the most important of which are the two factors of human activity and climate change. Several methods have been developed to determine the process of desertification, one of which is widely used, the Medalus method. Assessing the status of desertification processes (land degradation) in a village, region or country is important because it provides the opportunity to make informed decisions about the financial dimension and the amount of investment needed to control it. Considering the development of the desertification phenomenon in the Sefiddasht-Borujen region and the need to pay attention to the importance of the results of this destructive phenomenon in the future. The purpose of this study is to evaluate desertification using the Madalus model in the Sefiddasht-Borujen watershed with an area of 92565 hectares, located in Chaharmahal and Bakhtiari province.

 Land use changes were investigated and detected using the distance measurement model. For this purpose, the images of 1998, 2009, and 2018 were used. The amount of changes during this period was determined, and the points where the most changes occurred were selected. Then using these points, in the Medalus model, the factors affecting desertification and its current situation were considered. Then, the effective parameters in desertification were studied in these points separately and the Medalus model was implemented in them. According to the Medalus method, effective factors in the desertification of the region were identified and each factor including climate, vegetation, soil, groundwater, and management and policy was considered as a criterion. Then, the characteristics of the mentioned criteria that were effective in the desertification of this region were considered as indicators. After each indicator received weight in relation to its impact on desertification and by evaluating them, their impact of them on the desertification process was determined. Finally, using the indicators of these criteria, the criteria map and finally, the desertification map were obtained from their geometric mean n order to study the climate criteria, three indices of rainfall, direction, and drought index were considered. The study of the climate was evaluated from 3 sample points in the meteorological and water weight stations of the province, which are harvested as points. To evaluate the soil condition, some physical and chemical properties such as soil texture, acidity, electrical conductivity, and the amount of organic matter were selected. To determine the soil properties, the first 170 sampling points were identified in the study area, and from 0 to 20 cm soil level, sampling was performed and transferred to the laboratory.

The results showed a score of climatic criteria calculated at 1.80 was determined in two classes and had the most role in desertification in the region. The score of management and policy, vegetation, and soil criteria respectively were calculated at 1.76, 1.71, and 1.55 and was determined into two classes severe and very severe. Also, water criteria were calculated at 1.33 and were determined in the middle class. Based on the Medalus model, the current desertification score was estimated to be 1.63. According to this map, the desertification situation of the region was divided into two classes, severe and very severe. Finally, it was calculated that 56% of this area is faced with severe and 44% of it very severe desertification. The result showed that the northern part of the study area is highly vulnerable, while the southern part of the region is less vulnerable to desertification. However, this region has high desertification intensity. The foretold sensitivity of this region to the phenomenon of desertification was consistent. In this model, climate, soil, vegetation, groundwater, management, and policy criteria were selected. According to the results, climate, management, policy, vegetation, soil, and groundwater criteria, respectively, had the greatest impact on desertification of this region due to the low precipitation, drought in recent years, illegal excavation of wells, and uncontrolled extractions more than the capacity of groundwater aquifers in Sefiddasht has caused the drying of most wells in this area. Also, the drying of Dehno Wetland is another reason for the intensity of desertification in the study area.

 According to the obtained results, the phenomenon of desertification in this region is accelerating and would cause a destructive consequence. The study area, according to the proposed definition of desertification, has both natural and human desertification conditions. Natural factors such as unfavorable climatic conditions such as lack of rainfall, successive droughts, limited water resources, on the one hand, and destructive human factors such as traditional agricultural system, overgrazing, overexploitation of groundwater, conversion of pastures to land Agriculture, industries, mines and facilities, destruction of vegetation and shrubs, on the other hand, have led to the destruction of pastures and natural resources and accelerated desertification in the region. Evidence shows that in this region water table is lower than in other areas and as a consequence desertification is accelerated. Among the ways to deal with desertification in the region, it is possible to use the pastures and pastures in principle, according to their capacity at the right time, to permanently enclose the region under biological and mechanical desertification activities, proper exploitation of groundwater and prevents land use change.

Shadegan International Wetland is one of the most important environmental assets of the country due to its very high biodiversity and diverse functions. Awareness of wetland changes is one of the basic needs in the proper management and exploitation of this valuable ecosystem. In this regard, remote sensing methods are a useful tool to study and detect changes in wetlands. Therefore, in this study, with the aim of investigating the trend and revealing the changes in Shadegan wetland, Landsat TM, ETM + and OLI satellite images of 1988-1998-2007 and 2017 were used. Three stages of preprocessing, processing and post-processing were performed on the images, Supervised vector classification (SVM) was used and the images were classified into three classes of water, vegetation and without cover or soil. Classification accuracy for images was calculated using two indicators, overall accuracy and kappa. In order to reveal these classes, changes in 9 classes were analyzed. To show the changes, the graph revealing the changes of uses in three time periods was used. The results showed that in the period 1988 to 1998, water area increased by 1.5% in 1998 and vegetation increased by 5% and soil or uncovered area decreased by approximately 7%. Between 1998 and 2007, water area increased by 4% and vegetation decreased by 20%, and soil or uncovered area increased by approximately 15%. In 2017, there was a 7% decrease in water, a 36% decrease in vegetation, and a 30% increase in soil or uncovered area. This study demonstrates the need for immediate attention to the conservation of wetland residual resources for sustainable use for the next generation.

Rapid development of cities due to extensive changes in land use and land cover has had negative effects on global environmental quality. Land cover and  land use changes, and the development of urban and agricultural regions and deforestation are changing the regional and local temperature regime. Knowing the land surface temperature degrees contribute significantly to a wide range of issues relating to the Earth science such as urban climate, global environmental changes, and the study of the interaction of human and the environment. The lack of sufficient meteorological stations to be aware of temperature values in regions lacking a station is considered as a major flaw in monitoring the land surface temperature. Due to the information limitations, collecting data especially to a large extent,  is associated with many problems and obstacles, and the real-time access is difficult or impossible. Therefore, the need to use remote sensing technology with time conditions along with the feature of continuity and data collection in wide ranges can be very effective. The purpose of this study is to investigate the land surface temperature of Namin county in a period of 28 years and to compare the obtained results with land use and vegetation changes.

The data used in this study included  Landsat 8 satellite image of the OLI sensor in order to extract land use map and  TIRS sensor image to extract land surface temperature for the year 2015. Moreover, Landsat 5 satellite image of the TM sensor were used to extract land use map by using visible and infrared bands, and also to extract land surface temperature by using thermal bands for the year 1987. Images were taken in late spring and early summer due to the lack of high cloudy and snowy covers , as well as the high intensity of sunlight. The eCognition8.9 software was used for object-based classification. Classification in five classes (dry and irrigated farming, rangeland, forest and residential) and six classes (dry and irrigated farming, rangeland, forest, residential and water bodies) were selected  for the years 1987 and 2015 respectively. To assess the accuracy and comparison of the obtained maps, the error matrix, overall accuracy, and kappa statistics were used. Split-Window method was used to extract the land surface temperature of the study area. Finally, in order to analyze the relationship between land surface temperature with vegetation index, the correlation coefficients between land surface temperature and vegetation index were calculated based on land use types in the years 1987 and 2015.

The highest land use area in the years 1987 and 2015 belongs to the rangeland use with 43781 and 34114 hectares  respectively and the second land use area belongs to dry farming use with 23854 and 33277 hectares respectively. Moreover due to the lack of water use , the lowest land use area in 1987 belongs to residential use with 1301 hectares, while in 2015 with the construction of water structures, water use with an area of 86 hectares has the lowest land use area. The highest land use area increase was in the dry farming with 9423 hectares, which is a significant increase compared to 1987. The highest recorded temperature for Namin county in 1987 and 2015 was related to dry farming use (34°C and 27°C, respectively), indicating the concentration of heat in these regions. This type of land use has the highest temperature due to the factors such as the dryness of the products at this time and the harvest of the products. In 1987, dry farming use had the highest temperature (34°C), but in 2015 it experienced a decrease in temperature (27°C), despite the fact that it had the highest land surface temperature compared to other  types of land uses in 2015. The reason can be attributed to the factor of harvesting crops. Due to the fact that the rainfed crops in the study area are mostly wheat, and at this time of the season, most of the wheat is ripe or harvested, so the transpiration of these products is insignificant. The lowest recorded temperatures in Namin county are related to the uses of water bodies (21°C), forest (21°C) and irrigated farming (22°C), respectively.  Since water has a high heat capacity, it has the greatest effect on reducing the temperature. In forest and irrigated farming land uses, due to the higher vegetation density, the land surface temperature has the lowest value (23°C and 24°C in 1987 and 21°C and 22°C in 2015 respectively) compared to the other land use types. Agricultural land use in this area has the lowest land surface temperature (24°C in 1987 and 21°C in 2015) after forest areas. Due to the fact that the crops cultivated in this area are plants such as potatoes and these plants have more water needs, therefore these plants have a high greenness value at June to early July, which has led to more transpiration in the area where they are cultivated than other areas, thus it has been very effective in keeping the land surface temperature cool. The rangeland use has had high land surface temperatures (27°C and 25°C, respectively) in the two study  years, and there is little difference between the two years. According to the study season which was late June to early July, the high temperature of this land use type is due to the increase in the areas lacking canopy cover or areas having low or scattered vegetation. Due to the fact that in August, most of the leaves and brunches of the existing plants are dry and the transpiration is low, high temperatures are also recorded. The relationship between land surface temperature and vegetation index in rangeland use in the two study years had the highest correlation (0.91 in 1987 and 0.83 in 2015), while the correlation coefficient of the forest use was the lowest (0.46 in 1987 and 0.23 in 2015).

Land use type and land use and vegetation changes have a significant effect on land surface temperature changes. However, areas without vegetation have a higher land surface temperature than the areas with vegetation. The results showed that there was no significant correlation between vegetation cover and land surface temperature, which is mainly due to sufficient vegetation. In general, the results showed that in most areas with lower temperatures, there is high density vegetation indicating an inverse relationship between vegetation index and land surface temperature.

The aim of this study was assessed desertification potential of the Dashte Abbas in the semiarid region of Ilam provience18028.8 hectares by using the Iranian model of desertification potential assessment (IMDPA) on soil and vegetation cover indicators. The geometric average for each index including effective soil depth, soil texture, electrical conductivity of soil, percent of gravel, the operation of the plant, the revitalization of vegetation and vegetation condition was obtained using ArcGIS®9.3 and the status map of each criteria was prepared. Finally, by combining and determination of geometric mean desertification intensity map was obtained. The desertification intensity map based on soil criteria demonstrated that over 4843 hectares (28.86% of the total area) and 13185 hectares (73.13% of the total area) has been taken in low and moderate classes, respectively. Also the obtained results from geometric average of vegetation cover criteria indices showed that 7005.99 hectares (38.86% of the total area) in the lower classes and 407.45 hectares (2.26% of the total area) and 10615.35 hectares (58.88% of the total area) has been taken in moderation and Severe classes, respectively. The results of the assessment the considered Catteries indicating that vegetation cover criteria with values of 2.6 is the most influential criteria in the severity of desertification in the study area. Accordingly, it can be said that the quantitative value of the desertification intensity of the total area has been taken in moderate class.

Following the destruction of vegetation and increasing soil water losses in watersheds violators of the last decades due to uncontrolled exploitation and unethical's resources has intensified. This contributed to increased life expectancy and reduced flood sedimentation tanks Dam reservoir lower production and production losses in the national capital. This study aims to assess the impact of some measures of biological functions (forestry, pastoral work) in varazan village in mazandaran kojoor area planted seedling in previous years has been chosen and checked. In thisresearch andhepothese are defined such as :Does the implementation of biological measure is the reason for soil erosion is reduce. How these factors efecton the establishment of vegatation condition will get better with time or not? is conducted on erosion and sediment yield. • .This information is necessary to achieve applicable results before and after project implementation and evaluation of biological placed. • All information on this project as the basis for the study of field work for this study has been Measure implemented after the study is the most important part of the comparison In this study, the relationship of the natural soil is universal formula. Kidneys cases mentioned in the Universal Soil Equation (A = RKLSCP) has been studied. The maps of the study area classified into 14 units (based on the direction and velocity) on the map, we proceed to the grid. Then the plots in a randomized systematic sampling grid based on the purpose of determining the nature of the plot, we would like to implement. Methods based on field sampling and density of vegetation soil profile and other relevant information. To soil erosion and sedimentation. Recognizing the important measure as well as other items used in the Universal Soil equation. Fraction of vegetation cover systemic random line transect method, 44 samples were taken Estimating canopy as well as 14 hidrologycal units (per unit of work) is taken to determine the direction the item was sent to the Laboratory of Soil Science. Precedent canopy and density of 62 percent to 84 percent increase then the result of calculations obtained with the deposition rate of the output area of 5.8 ha to 4.3 tons per hectare This result means that the corrosion rate has decreases with increasing vegetation therfor the hypotesis was accepted.

Grazing management and the balance between domestic animal and rangeland need to complete information about rangeland ecosystems and identification of relation between vegetation and livestock. Thus, this research have been studied on the effect of different utilization intensities on vegetation changes in winter rangelands of Miankaleh. After identifying the utilization units, sampling was done in each area with transect-quadrate and systematicrandom method. Number and size of plot identified by statistical and minimal area method, respectively. Then, canopy cover percentage, Frequency, production and palatability of species was recorded in the plots. At last, data analysis was done with variance analysis and means comparison. The results showed that the Gramineae family had more frequency in different grazing intensities, which shows that the Miankaleh rangelands have high vegetative potential to this family nevertheless changes of grazing intensities and dominant species changes from critical to reference area. Also, the effects of low grazing cause to appearance of Trifolium pratense in reference area.

The recognition of relationship between vegetation and physiographic factors can be useful and effective in estimating the kind and amount of vegetation for the management of various ecological ecosystems of rangelands. For this purpose, the present research deals with studying the effects of physiographic factors on the various vegetative changes of Lasem watershed rangelands. The samples were randomly selected from the vegetatives after the identification of plant types and the determination of the size and number of them. Then, the databases, including the slope, aspect, altitude, and lithology in the area of Arc GIS 9.2 were prepared, and by overlaying them, and after the field controlling, the needed data in each plant type were determined. Finally, the correlation between the physiographic factors with plant types and the means of the properties of the groups were computed with the SNK test. Also, the plant communities were ranked and classified with DCA, CCA and Canoco software, The results showed that shrubs had more correlation with altitude and aspect than grasses, but none of them had any significant relation with the slope. Also, the overgrazing of livestocks decreased the amount of this correlation.