Moslem Rostampour; Mohammad Saghari
Abstract
Introduction: Each of the different exploitation and management methods in rangelands have different effects on the rangeland ecosystem functions. Incorrect and inappropriate ways of rangeland use, especially in the last few decades, have caused severe damage to natural resources. There is a few research ...
Read More
Introduction: Each of the different exploitation and management methods in rangelands have different effects on the rangeland ecosystem functions. Incorrect and inappropriate ways of rangeland use, especially in the last few decades, have caused severe damage to natural resources. There is a few research on the effects of grazing on sand habitats of desert areas. The aim of the current research is to investigate the effect of different methods of rangeland utilization on ecological characteristics, including the percentage of vegetation cover, plant density, species richness, diversity, evenness and dominance, and species similarity in the studied rangelands.Material and methods: This research was conducted in the outskirt, seminomadic, settled nomadic and enclosure in Zirkouh, South Khorasan province. In each rangeland, the list of plant species, density and vegetation cover of each species was determined separately. Also, the range condition was evaluated by the modified four-factors method. In addition to numerical indices, the ranking of species diversity was investigated using the Renyi diversity ordering curve. In order to check the species similarity between the four studied rangelands, Jaccard's similarity index was used, and hierarchical cluster analysis (Euclidean distance and Ward's method) was used to better display the species similarity. Finally, the relationship between vegetation cover and the number of species and biodiversity indices was tested by Pearson's correlation coefficient.Results and discussion: Based on the modified four factors method, the condition of outskirt and seminomadic rangelands were moderate and settled nomadic rangeland was poor and enclosure rangeland, has been evaluated as good. The results of ANOVA showed that the effect of grazing methods on the vegetation cover (at the 0.05 level) and the total and average species richness (at the 0.01 level) were significant. Enclosure rangeland had the highest plant cover percentage and plant density (54.73% and 80, respectively) and the settled nomadic rangeland had the lowest plant cover percentage and plant density (15% and 5, respectively). The highest species richness belonged to enclosure rangeland and there was no difference between other rangelands. Compared to other rangelands, the seminomadic rangeland had the highest proportion of native plants and the lowest proportion of increaser plants in the plant composition of total richness. The highest proportion of increaser plants was observed in settled nomadic rangelands. In terms of species diversity, enclosure rangeland had the highest Shannon-Wiener diversity index (2.03) and Simpson diversity index (0.80) compared to other rangelands. The results of the correlation coefficients of vegetation cover and the number of species and species diversity indices showed that, in general, there is a significant positive correlation between the diversity indices and vegetation cover and the number of species. In addition, there is a significant negative correlation between the species evenness and dominance indices, as well as vegetation cover and the number of species. The results of the Jaccuard similarity index show that the highest degree of species similarity is observed between the outskirt and the settled nomadic rangelands (62%).Conclusion: The results showed that the overgrazing around the livestock pen in the settled nomadic rangeland is clearly visible and it has led to a significant decrease in vegetation cover, plant density and species diversity. Resting in rangelands (in the enclosure) and delaying grazing (in seminomadic rangeland) can also enhance vegetation and biodiversity. In terms of the percentage of vegetation cover, density and plant composition, the seminomadic rangeland is located next to the enclosure. The most proportion of forage species was observed in the plant composition of the seminomadic rangeland. If we accept the hypothesis that range enclosure causes the plant succession towards the climax stage and in range management, the sub-climax stage is always better than the climax stage, in this case, in terms of livestock and range management, the temporary settlement of nomads will be more beneficial than range enclosure.
Asad Eyni; Mohsen Taban
Abstract
Introduction: Nowadays, cities are facing problems such as overheating caused by urban congestion, causing thermal islands and environmental problems, which make life difficult in some places. The wind flow in the urban environment is an important factor affecting the exchange of heat and moisture, particle ...
Read More
Introduction: Nowadays, cities are facing problems such as overheating caused by urban congestion, causing thermal islands and environmental problems, which make life difficult in some places. The wind flow in the urban environment is an important factor affecting the exchange of heat and moisture, particle transport, and urban ventilation. Studies show that physical factors such as enclosure change, the elevation of buildings, and different orientations of passageways in urban texture affect the speed and direction of the wind flow. The purpose of this study was to analyze climate data related to wind flow in two urban areas of Dezful and investigate the effect of enclosure of passages on the wind flow. Material and methods: In order to carry out the study, two areas of Siah-Pushan and Gozare-Shahi in the range of historical texture of Dezful, with similar and different physical factors, were selected for the analysis of physical conditions by comparing climate data. Data on the intensity of the wind and the ambient temperature of both areas in five periods of 9 -11 am, 11am-1 pm, 2-4 pm, 4-6 pm, and 6-8 pm, and in two seasons, winter and summer, were selected. Then, the enclosure of the collected points was calculated and using the linear regression analysis, the relationship between enclosure and wind speed was assessed. Results and discussion: The results showed that the velocity of the southwest-northeast wind flow was more than other orientations. Also, surveys showed that increasing the specific enclosure can increase the wind speed by a certain magnitude. In Gozare-Shahi, the results of the regression diagrams in the winter indicated that a direct relationship exists between the enclosure of the cross-sections and the velocity of the wind. With the minimum enclosure (0.35) increasing 1.5 to 3 times, the initial velocity of wind increased up to 31- 121 percent. The results of the linear regression diagrams in Siah-Pushan indicated that with 2 to 6 times increase in the enclosure, the wind speed increases up to 1.1 to 1.8 times. The results obtained from the linear regression diagrams in Gozare-Shahi passage showed that the enclosure of passways and the velocity of the wind flow are directly correlated. With the minimum enclosure (0.35) increasing 1.5 to 3 fold, the initial velocity of the wind increased 10 to 40 percent. In Siah-Pushan range, the enclosure of transitions was directly correlated with the wind. Also, the results showed that by increasing the enclosure up to 2 to 6 times, the velocity of the wind increased 1.03 to 1.20 times. Conclusion: Increasing the velocity of the wind led to better ventilation in the urban environment. On the other hand, increasing the enclosure increased the velocity. Uniform buildings, as well as regular enclosures with the least changes, will increase the velocity of the wind stream, as well as less turbulence. Thus, increasing enclosure, as well as regular buildings, can ultimately lead to better urban environments.
