جستجوی مقالات مرتبط با کلیدواژه « درصد پوشش گیاهی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Different rangeland management measures such as fencing and improvement can provide the potential for their restoration. This study aimed to investigate the effect of a range of rangeland management measures including fencing, remediation, and grazing on some soil properties in the rangelands of Kurdistan province. We established 25 plots of 1×1 m2 each along two transects with 240 m length (120 m perpendicular to the slope and 120 m parallel to the slope). At each plot center, soil samples (0-15 cm depth) were taken, together with other attributes comprising litter, vegetation, bare soil, and gravel percentages. This resulted in 75 soil samples from three study areas. Furthermore, some chemical soil properties were analyzed in the laboratory after drying and preparing the soil samples. We used one-way analysis of variance (ANOVA) to analyze the data, as well as Pearson correlation to study the relationship between the parameters. Results revealed statistically significant differences in some soil properties amongst the study areas. In addition, the amount of soil carbon (1.94%), nitrogen (0.205%), C/N ratio (9.48), phosphorus (288mg/kg) and potassium (129 mg/kg) showed the highest rates in the improvement area, whereas all those parameters including carbon (1.25%), nitrogen (0.179%), C/N ratio (7), phosphorus (170mg/kg) and potassium (75 mg/kg) showed the lowest rate across the grazing rangeland. Further, pH (8.27) and EC (174 µs/cm) showed the highest levels in the grazing area. The results of the Pearson correlation showed that the percentage of vegetation was significantly and positively related to all soil properties except pH and Ec. In addition, bare soil and gravel percentages indicated a significant negative relationship with soil carbon, nitrogen, phosphorus, and potassium. We conclude that fencing and rangeland remediation treatments can enable significant positive effects on soil nutrients that are essential for plants.

Measuring the diversity and identifying plant vegetation traits and functional groups and classifying them, in addition to helping to accurately identify the vegetative capacity of the area, helps us to understand the vegetation response of the area to disturbances and presence. Potentially resistant species with similar or invasive traits help. The purpose of this study was to investigate and evaluate the vegetative status of the region, the trend of changes and evaluation of the second sequence of dust centers in Khuzestan after planting seedlings in different ways. Functional groups (PFTs) were used. To evaluate the changes in the vegetation of the area by field survey, 15 transects of 100 meters with distances of 50 meters were systematically randomly selected (the first transect was randomly selected and the rest with a defined distance of 50 meters). Due to the uniformity of plant species composition and the absence of environmental effects, a total of 180 fixed plots with dimensions of 1 square meter (location recording with GPS device) were installed. The results of a recent study in three areas of the dust center in the southeast of Ahvaz showed that in selected areas, various irrigation methods along with rainfall will cause significant changes in the percentage of cover (frequency) and the number of species from 2017 to 2020. Functional groups in the Tovayel region with surface irrigation (Faro) In 2020, nine groups were identified, in Bagan region with tanker irrigation and hole digging with seven excavators, and in Hanitieh region with tanker irrigation and hole digging seven functional groups. The results of T-test analysis also showed that there is a significant difference between the average of the two values of all indicators, including the diversity of Shannon and Simpson in March 2017 and March 2020 for all three regions so diversity indicators raised since number of species and cover increased.

The study of vegetation and the measurement of diversity indices are suitable tools for studying the status of forests and rangelands and evaluating them. The purpose of this study is to evaluate the trend of vegetation changes during four consecutive years and in two seasons in the Bagan region. For this purpose, 5 transects of 100 meters with distances of 50 meters in the study area were considered systematically randomly. A total of 30 plots of one fixed square meter were installed along the transects. In two growing seasons, spring and fall, from 2017 to 2020, the type and percentage of cover of native species were harvested. Dominance, uniformity and diversity of Simpson, Shannon and Hill species were measured using PAST and R software. The results of one-way analysis of variance (ANOVA) showed that there is a significant difference between the mean of dominance, Shannon and Simpson indices, percentage of cover, and the number of species in the spring of different harvest years. In fall, except for the dominance index in other indices during July 2019 compared to 2018, there was a significant difference. From the results, it can be concluded that despite the return of some annual or short-lived species such as Bienertia cycloptera Bunge and Salsola jordanicola Eig. following irrigation of cultivated seedlings and rainfall, the study area is still sensitive and fragile and needs to be managed and confined until proper rehabilitation.

Mining is one of the most effective human activities to change the situation in the region, particularly in arid area. The human demand for minerals and energy resources under the ground has made mining and exploration operations inevitable. Mining is one of the common human behaviors with numerous outcomes for the ecosystem along with serious environmental and ecological consequences in natural ecosystems such as desert areas, leading to positive and negative changes in these areas.

In this study, it has been sought to assess the ecological vulnerability of mining areas of Tabas using environmental degradation model. The current applied research methodology is based on spatial data analysis and spatial analysis tools in ArcGIS software environment. In this regard, altitude, direction and slope maps were extracted from ASTER, while NDVI map was extracted from MODIS to determine vegetation vulnerability. In the next step, necessary corrections, drawings and analyses were performed. Isothermal maps were used to produce climatic maps for the temperature factor and the border and coastal zone stations were considered for the precipitation factor. Soil maps were obtained from soil map files, while geological maps were taken from geological map files at a scale of 1:100000 and groundwater maps were used from baseline data of regional water stations. To quantify environmental degradation phenomena, severity and degree of ecosystem vulnerability, an environmental degradation model is developed. This model is one of the methods of modeling system analysis, introduced for the conditions of Iran.

The results of the analysis and summarization of the data from the study area elevation map show that the highest level is related to Class 1 and less than 1000 m (66%) and the second level is Class 2 with 28.77% of the study area is located. As more than 94% of the area is covered by one or two vulnerabilities. Therefore, the ecological factor of elevation in the region is not very sensitive. While regarding the factor of slope, 45.69% of the area was in the vulnerability codes of 2 and 3. Moreover, considering the geographic direction, over 47% of the area had high ecologic vulnerability and was placed in code of 3, while 86.55% of the area with a depth of less than 10 cm was in code5 regarding the factor of soil. In addition, 71.71% of the area was in vulnerability codes of 3, 4 and 5 regarding geological factors and 100% of the area was put in vulnerability code of 1 with average annual temperature of over 15 degrees Celsius for the factor of temperature. Regarding precipitation, 99.47% of the area had the vulnerability code of 8, while vegetation and low NDVI indicator of the area led to a vulnerability code of 4. Most of the area is located in the first class of EC (387-771 microseconds) with a vulnerability code 1. This code covers about half of the area. Finally, 99% and 98% of the area were assigned vulnerability codes of1, 2 and 3 considering the depth and quality of underground water, respectively. The scope of ecologic vulnerability in the overall area under study, 62.21% of the area was in vulnerability code of 2, and 30.36% in vulnerability code of 3. Accordingly, 11.6% of the area under study which covered 679579.9 acres was exploited for mining, out of which 658047.6 acres were located in vulnerable and semi-vulnerable ecologic areas with vulnerability codes of 2 and 3.

In the present study, soil and geological factors have the most ecological limitations. In this area, due to the high sensitivity of the soil, the possibility of erosion is high and special attention should be paid to soil erosion during the environmental management process. Particularly in areas with low vegetation or barren land, there is a wide range of restrictions. In addition, the vulnerability of these areas increases with decreasing vegetation density. The percentage of vegetation in the eastern and southwestern districts of Tabas is higher and with a sensitive vulnerability class. The southern areas of the city are more resistant than the north, but are scattered and scattered. So, ecological restrictions are expected to increase in the western and central parts of Tabas County due to the low density of vegetation. So there will be more destruction and erosion. Obviously, urgent decisions to protect sensitive areas to prevent damage to land during extraction and operation are essential. Therefore, the mining areas in Tabas County need special management attention. The mine exploitation area comprises 62% of the study area, most of which is located in sensitive and semi-sensitive classes with vulnerability codes 2 and 3. Also, soil and geological factors with the highest ecological limitation are more diverse than other factors in the region. Therefore, due to the high sensitivity of the soil and the possibility of erosion, especially in areas with low vegetation cover or desolate areas (eastern and southwestern areas) as if are most vulnerable, special attention should be paid to erosion during the mining process.

One of the ways of restoration and reclamation of damaged rangeland is to use different methods of rain harvesting such as pitting, counter furrowing, flood spreading, small arc basins system and etc., along with the reduction of runoff, it increases the soil moisture content and thus increases vegetation cover. Biodiversity is most commonly used to describe the number of species. It is studied in 3 levels, including genes, species, and ecosystems. However, species diversity is a major issue of biodiversity on a local and regional scale. Species composition and biodiversity are among the fastest and most important indicators for determining rangeland ecosystems condition. Due to the new construction of this structure in the rangelands of Iran, so far, little research has been done on the effect of small arc basins system on vegetation and forage production. Particularly, there is limited research on the variation of richness and species diversity by Construction of this structure. Abdollahi et al. (2016) investigated the effects of crescent pond structure on vegetation and soil parameters in Saravan rangelands of Sistan and Baluchestan province. The results of their research showed that, significant differences were found for all vegetation parameters between the crescent structure and control treatment, indicating the positive effect of crescent structure on vegetation parameters. The purpose of this study was to investigate the effect of constructing small arc basins system has been investigated on the composition of vegetation and biodiversity in the rangelands of South Khorasan province. Sampling in the rangelands of Sarbisheh, South Khorasan Province, was carried out in small arc basins area. Vegetation sampling was carried out in the rangelands by systematic-random method at the flowering stage of the dominant plant species in the spring of 2014.vegetation characteristics such as density, composition, cover percentage, and species richness indices (Margalef and Menhinick), species diversity indices (Simpson, Shannon - Wiener and Fisher's alpha) and species evenness (Pielou) were investigated in two areas (small arc basins area and the control area).The all biodiversity indices were calculated using PAST software. To compare the vegetation characteristics including density, composition, vegetation percentage, species richness, diversity and evenness, independent samples t-test were used. In general, 30 plant species were identified in two areas (small arc basins area and the control area), which belong to 17 families and 27 genera. The results showed that the number of plant species in the control area is 9 and in the small arc basins area is 30 species. The results of comparing the total vegetation cover percentage in both areas showed that the percentage of total coverage is very significant (p <0.01). The effect of construction of the small arc basins area system on the density of rangeland plants was very significant (p <0.01) and this system has significantly increased the density of rangeland plants., there is a significant difference in species diversity between the two regions in terms of Simpson diversity index and Shannon-Wiener's diversity index, but this difference is not significant in the alpha-Fisher's index. The results of the data on the study of richness indices also show that the Margalaf's richness index shows a very significant difference in the comparison of species richness in the two study areas, but this difference was not significant in terms of the Menhinick's index. Discussion and The results showed that the construction of small arc basins in the study area increased the number of plant species, species density and vegetation percentage compared to the control area, which indicates the positive effect of this structure on improving the ecosystem conditions. Research in this area also confirms this result. The results of this study indicate that the number of annual and perennial species in the control area (totally nine species) from 4 and 5 species in the control area has increased to 15 species for both species (a total of 30 species) in the small arc basins area. As well as, the results indicate that the vegetation cover percentage and frequency of perennial species is more than annual species. Several studies have indicated that species diversity has a significant relationship with soil texture and soil moisture. Since the construction of small arc basins leads to changes in soil moisture content and soil texture. Therefore, it has a significant effect on species diversity. Finally, according to the results of this research as well as previous researches, we can say that the effect of small arc basins system was positive on the ecological characteristics of vegetation in the study small arc basins treatment. Therefore, it can be considered as one of the most effective methods for the restoration of degraded rangelands.

Plant species distribution, composition and diversity in deserts of arid and semi-arid areas, especially saltland; depend on soil physical and chemical gradients. The aim of this research was to investigate changes in the plant species diversity and richness along a soil salinity gradient in the margin rangelands of Petregan Playa. After vegetation zoning in relation to soil salinity, random-systematic sampling within each zone was taken. Within each zone, three stands were selected, then, within each stand, plant vegetation cover, density and species diversity indices were measured. For ordination vegetation along the soil salinity gradient, Detrended Correspondence Analysis (DCA) method was used. The results showed that there were significant differences in the plant total cover, annuals and perennials plant cover between different soil salinity zones. Also, the soil salinity gradient has a significant effect on the species richness and diversity, as the first zone (high salinity) has the lowest species richness and diversity. It can be concluded that, in general, only high salinity level has a significant effect on the plant species diversity.

Using of flood to supply plant water requirement for its growing and decreasing of flood damages is possible by many different methods. By using of water spreading systems, seasonal flood in susceptible land will be spread with different effects on groundwater, plant cover and soil on these lands. In order to measure the effect of water spreading system on changes of vegetation, soil salinity and organic carbon in Miankooh floodwater spreading area, 40 random plots of 2 sq. meter were taken in floodwater spreading area and 20 points were selected outside the floodwater spreading(control areas) and vegetation were changes measured. Meanwhile, to investigate soil salinity and organic carbon changes, 8 profiles were taken from four depths ranges including 0-10, 10-20, 20-30, 40-60 cm in the area affected by flood and sediment and some points were selected in outside floodwater spreading(control areas). The statistical results indicated that floodwater spreading have significant effects on vegetation cover and salinity reduction (in depth=0 to 10cm) while no significant effect on soil organic carbon. Generally floodwater spreading from one hand can reduce soil salinity and consequently increase amount of plant cover in arid and semi-arid regions but on the other hand, high volume of flood and deposition of sediments, reduce the efficiency of water spreading over the time.

GIS and satellite images have widely been used in natural resources assessment and management. Vegetation cover can be measured using remote sensing indices. The objective of present study was to investigate the application of AWiFS satellite images to measure vegetation cover percentage in Semirom- Isfahan province. Vegetation cover percentage was measured in 150 plots with size of 100 m2 each in 2009. Linear regression between field data and remote sensing vegetation indices was used to produce vegetation cover in the study area. Vegetation cover models were produced using different indices. According to the results, SAVI index had the highest correlation with field data (r = 0.74) and it was used to produce vegetation cover percentage map. Study area vegetation cover was classified in four classes: <20%, 20-30%, 30-40% and >40% using SAVI index. The produced vegetation map indicates that most of the region had low vegetation cover (<20% and 20-30%). The correlations of other measured vegetation indices including NDVI, PVI, RVI, TSAVI and MSAVI with vegetation cover percentage were 0.64, 0.69, 0.71, 0.72 and 0.70 respectively.

Measurement and monitoring of vegetation cover fraction is very important in many environmental studies. Although remote sensing techniques have shown successful to estimate the parameter, but still remote sensed measurements of it encounter to special problems in desert areas. In this research has tried, the relationship between reflections in the different bands of LISSIII and TM sensors and percentage of vegetation cover be investigated using field measurements of vegetation cover fraction in a desert area. Accordance with the findings of this research, if we consider the relationship linear, only correlation between the percentage of vegetation and the near-infrared band has shown significant at the 0.05 level (2-tailed). While if we consider it nonlinear, correlation between reflections of all bands and the percentage of vegetation cover have shown significant at the 0.01 level (2-tailed). Also according to the results was determined using a linear multivariate regression equation and using all the bands, it is possible to make the relationship significant at all levels and to improve accuracy of estimations of the model. Even was observed with the change in the type of used regression model and covert it to a non-linear multivariate regression model, it is possible to improve the correlation coefficient and the coefficient of determination between the observed and estimated vegetation cover percentage significantly, In a way that correlation coefficient and the coefficient of determination between the observed and estimated vegetation cover percentage at best condition is calculated 0.917 and 0.841 respectively. Based on the results obtained in this study to increase the accuracy of modeling the nonlinear relationship between percent vegetation cover and the band satellite reflections using artificial neural network is the best way. In this research using artificial neural networks increase the accuracy of modeling significantly, so that the the coefficient of determination was passed 0.9 at best. Also based on neural network modeling hundred repetitions of this research can be refer to a neural network with radial function has better accuracy of modeling than multi-layered neural network to determine the percentage of vegetation using satellite data in drylands.

Estimation of vegetation features from space is a great challenge for agronomist، hydrologist and meteorologist communities. Now، the use of vegetation indices to estimate vegetation characteristics is very popular. They are empirical combinations between Visible (generally Red، R) and Near Infrared (NIR) reflectance that show good correlation with plant growth، vegetation cover، and biomass amount. The main objective of this study was to introduce a suitable model based on satellite images in order to estimate vegetation Fraction in Sade Nahrein basin (Tabas، Yazd، Iran). To do so، IRS-LISIII (2007)، ETM+ (2005) and vegetation fraction measured in fielwork (54 plots) have been used. Making comparable field data and pixel values، the average value of pixels located in the sampling sites was extracted and then 11 different vegetation indices were calculated. In the next step، the 6 output models have been evaluated using linear regression method and fitting the regression line between observations and estimated values in the validation data. The results showed that the model in which MSAVI1 was used has the highest accuracy (R2=0. 866) and therefore is the most suitable model for estimation of vegetation fraction in the study area.

Analysis of vegetation is one of the important factors in appropriate management of rangelands. The current research was conducted to evaluate canopy cover percentage, forage production, and species density in four areas including reference area, personal rangeland, key area and critical area in the region of village. In each area, 5 transects were established on which 10 quadrate 1 m were used with regard to the plant type and distribution of species. The lengths of each transect and the distance between them were determined 100 m and 20 m respectively according to the species density and distribution. Canopy cover percentage, forage production and species density were recorded in all quadrates. Clipping and weighing method was used to estimate forage production. Data analysis was performed using one way ANOVA and Duncan test. Results indicated that there was significant difference in canopy cover percentage (p≤ 0/1), forage production (p≤ 0/05) and species density (p≤ 0/01) among 4 studied areas. The result showed that with moving from reference to critical area, canopy cover percentage, forage production and species density dramatically decreased as palatable species (class I), average palatable species and non palatable and invasive species had the most canopy cover percentage, forage production and density respectively in reference area, personal rangeland and common area between village and critical area. Perennials and palatable grasses such as Bromus tomentellus and Hordeum bolbosum had the highest canopy cover percentage, forage production and density in reference area. With a gradual increase in grazing intensity, percentage of palatable species decreased while non palatable species like Boisseria squarrosa and Centaurea virgata increased. This research revealed that heavy grazing jeopardized the sustainability of the rangeland ecosystem by creating unfavorable changes in vegetation characteristics.

Investigation for adequate sample size is essential for annual yield measurement in each range sites. For this purpose, a key area was selected in the Nir range research station that is indicator of steppic rangelands of Yazd province. One hundred and fifty 2m-1 quadrate plots with 25 m space were systematically located on 5 transects. Forage yield measurements were carried out with clipping and weighting methods in mid-May 2004. Forage yield per hectare were calculated based on 10 until 150 mentioned plots data. Adequate sample size was determined with drawing method. Results showed that total forage yield in the area were assessable with clipping and weighting method by thirty 2m-1 quadrate plots, but separate species yields were analyzed by one hundred 2m-1 quadrate plots data. Forage yield estimation with clipping and weighting in thus sample size is more consumed time and expensive. Thus, the double sampling model with cover were recommended for these rangeland inventory that were measured cover and yield with 100 and 25 plots, respectively.