نشریه مهندسی اکوسیستم بیابان
پیاپی 12 (پاییز 1395)

Due to the harsh environmental conditions in arid and semi-arid area of country, it is essential to assess the factors affecting the vegetation in such areas. This study aimed to investigate the effect of some soil physicochemical properties (including texture, bulk density, moisture, organic matter, carbon, nitrogen, potassium, lime, sodium, electrical conductivity and pH) on Haloxylon persicum canopy cover in Yanesy region, north Gonabad. After field assessments, two adjacent areas including natural and planted stands of Haloxylon persicum were selected for sampling. Randomly located quadrats along transects were used for vegetation sampling. Soil samples were taken from each quadrats at 0-10 and 10-50 cm depths. After transferring the samples to the laboratory, soil texture, bulk density, humidity, organic matter, carbon, nitrogen, potassium, lime, sodium, EC and pH were determined. The results showed that there is significant relationships between Haloxylon persicum canopy cover and some soil properties, so that in planted stand, canopy increase was positively correlated with increasing in sodium, electrical conductivity, potassium, nitrogen, organic matter (at superficial soil) and decreasing in humidity. In natural stand, canopy cover was increased with increase in soil moisture, silt, nitrogen, clay, carbon and organic matter and was decreased with increased sodium, potassium, salt and sand. There were no significant relationships between the amount of lime, pH and bulk density with canopy cover of Haloxylon persicum. Therefore it could be stated that increase of Haloxylon persicum cover has different effects on the soil properties of two sites, so that the negative effects of planted site can be related to high plantation density.

A standardized sampling technique for measuring plant diversity is needed to assist in resource inventories and for monitoring long-term trends in vascular plant species richness.With considering to the estimated richness amount (via different methods) are changing influenced by interaction of plot distance and shape, and also, presenting of a plot design (that can be near to reality) is important due to the studing of species richness in ecological concepts. In this research, we compared the two sampling methods, Whittaker plot and Modified Whittaker plot in grassland and shrubland vegetation types in Taleghan rangeland of Iran. The result of this study showed that there is a significant difference between the two methods in determining species richness for grassland and shrubland vegetation types in Taleghan rangelands. The Modefied Whittaker design often returned significantly higher (P

This study aimed to estimate of spatial distribution scope of plant species and preparation of predictive distribution maps of plant species using Artificial Neural Network (ANN) in Taftan west rangelands of Khash city. To this end, vegetation sampling was carried out by random-systematic method after identification and separation of plant species habitats. In order to sample the soil at each habitat, eight holes was drilled and samples were taken from 0-30 and 30-60 cm depths. Habitats distribution of plant species was modeled using multilayer perceptron after measurement of soil characteristic in the lab and providing of environmental variable maps including physiographic characteristic (slope, aspect and elevation), geological formation and soil physical and chemical properties using GIS and Geostatistics. Simulation of presence and absence probability was conducted after selection of optimal predictive model for each plant species. Then the optimal threshold was determined using equal sensitivity and specificity method and were examined the compliance between predicted and actual maps by calculating kappa index. Based on Kappa value, the agreement of predicted and actual map was very good for the habitats of Haloxylon persicum .Moreover, predictive maps of Artemisia aucheri, Artemisia sieberi and Amygdalus scoparia habitats have good agreement with actual maps of these species. As well as, correspondence of predictive and actual map of Zygophyllum eurypterum was assessed at moderate level. These results indicate that multilayer perceptron method (MLP) is capable to provide precise prediction models through data mining rules and modeling of nonlinear processes. Besides cost and time saving of research, this can lead to precise prediction of geographic scope of plant habitat distribution, as a result will increase success possibility of rehabilitation plans in the rangelands.

The presence of Damghan Erg in West of Damghan Playa indicates high wind activity in this desert region. Due to technological advances and population growth in recent decades, large parts of past land uses have changed. These changes can exacerbate wind erosion and affect lands sedimentation. In this study, first, the land use maps of years 1974 and 2003 were prepared. The comparison of these maps shows that a significant area of rangelands have been converted to agricultural lands. Also, part of the agricultural lands has been converted to residential and industrial lands and a small area of ​​agricultural lands has been dilapidated. The soil or surface sediment were sampled in three treatment as old agricultural lands (that they have preserved their use), new agricultural lands (that they were formerly rangelands) and ranelands (with five replications). Soil particles grading have been studied by sieves of 2000,1180,600,250,150,75 and less than 75 micron based on the weight and frequency percent of each particle size class and indicators of particle (diameter mean, skewness, sorting and elongation) were specified using software GRADISTATE. At last, land sedimentation assessment was identified based on the abundance of particles with a diameter less than 2000 micron (susceptible to erosion). The results have been prepared as 7 maps that they express region sedimentation in each particle size class. Particles dispersion map with diameter larger than 2000 micron indicates stable particle dispersion against wind erosion and other maps show unstable particles dispersion. Comparing the land use map with particles dispersion maps show that the most unstable particles dispersion is in rangelands, the least dispersion of them is in agricultural land and rangelands have more sedimentation than the other treatments.

Climatic characteristics adapted to human comfort are the functions needed for tourists to choose a tourism destination. This parameter has a major role in preparation of tourism calendar. Desert tourism is one of the important destination so Eco-tourist. Iran has unique capabilities in this field because of its geographical- climatic condition. In this article we have tried to provide a tourism calendar proportional to climatic conditions in order to activate this environmental capability. So in this study, tourism comfort climates of 11 provinces which are located in desert regions have been evaluated by using tourism climate index (TCI). In this regard, TCI index was calculated for 72 synoptic stations on a monthly basis and then the results were zoned on GIS software environment through the interpolation method. Ultimately, 12-month tourism climate map of Iran's desert regions were drowning separately. The results showed that in the winter months’ southern regions and provinces of the country have ideal condition. In the summer, in spite of remarkable reduction of quality of tourism climate index of the region, desert provinces which are located in higher latitudes have more suitable condition. Meanwhile in the spring and autumn tourism climate index (TCI) mainly offers very ideal and convenient condition in large part of the area of study. Therefore, according to the results, in terms of tourism climate index, desert regions of the country are considered as valuable potentials in tourism and attracting tourists in cold seasons. Thus, officials and tour guides who are active in field of tourism can plan effectively in order to flourish tourism industry and consequently provide required context toward economic growth and prosperity for the residents of this part of the country.

Soil erosion is considered as one of the most significant indices of land degradation, which once evaluated, a wide gamut of changes in the environment could be evaluated. The aim of this study was to evaluate the risk of soil erosion by the application of the CORINE model, as a suitable means of soil erosion assessment, in the semi-arid western areas of Golestan province. In this study, soil, geology, climate, land cover and slope data were used, accompanied by extensive field reconnaissance. Maps accuracies were determined based on the Chi Square index and Mann-Whitney test. Firstly, soil Erodibility map was prepared from soil physical parameters and Erosivity factor (calculated based on the Fournier moisture index and Bagnouls-Gaussian aridity index). Then by superimposing layers with slope and land cover maps in the GIS environment, soil erosion risk map (potential and actual) was prepared. Results propose that, in view of the potential risk, 23 percent of the region is marked with low potential, 54% with moderate, and 7% with high erosion risk. Also, from the viewpoint of actual erosion risk, 54% of the area is devoted to low risk, 25% with moderate and 2% corresponds with high risk. The differences in the area of risk maps, at 1 % level were significant and In terms of accuracy, maps have great compatibility with ground realities. This study emphasizes on the capabilities of the CORINE model and the GIS technique in the evaluation of soil erosion.

Wetlands as one of the most important and most valuable natural ecosystems in the world play an important role in filtering pollutants and reduce dust, creating a favorable microclimate, biodiversity and genetic and organic materials reservoirs. In central part of Iran, climatic and human factors have created significant differences between dry and wet surfaces of Gavkhooni wetland in recent decades and have provided a background to produce more dust in central part of Iran. This research aims to study and assess important factors that influence the process of changes occurring in wetlands and wetland drying up during the last 22 years by using remote sensing and artificial neural networks. To do so, 21 landsat imagery has been used. After that, Normalized Difference Water Index was calculated and the dry and wet surfaces has been separated. The average rainfall, temperature, flow, evaporation and water table depth for the study area was interpolated using Thiessen method and the trend of these parameters was examined using the Mann - Kendall. Finally, to determine the importance of each factor affecting wetlands drying up, various functions of artificial neural networks were compared and the best model was used to determine the importance of each parameter. The results of Mann - Kendall showed a significant decrease in ground water level and input flow to the wetlands in the period of the study. This study showed that the most important factors that influence the level of the Gavkhuni wetland are flow entering the lagoon, evaporation, drop in groundwater level, temperature and rainfall respectively.

Convection as a short-term and long-term atmospheric processes that affect the climate and weather system, has been much studied. In this study, different types of parameterizing convection in precipitation field will be assessed in fourth version of the dynamic model of regional climate (RegCM4). The simulations are conducted for 2004 with 60*60 km grid spacing in mother domain, then the North East region of Iran was nested in mother domain with 20*20 km grid spacing. RegCM4 was run four times, keeping all the components of the model and the initial and boundary conditions the same, by each time coupling one the convection schemes (Kou, Grell Arakawa-Schubert, Grell Fritch-Chappell, Emanuel) with the model, then the results were nested. After running the model, results were compared with Aphrodite precipitation data and the statistical criteria, including Root Mean Square Error, Bias, Correlation, Mean Absolut Error and Differences in annual and seasonal observed and simulated precipitation were calculated. According to statistical criteria, the best scheme for this area is Grell Arakawa-Schubert scheme.

Desertification is a global problem in most arid and semiarid countries including Iran are facing with this problem. Desertification causes many restrictions in terms of agriculture, food security, livestock rising, industry and providing service costs. This phenomenon is a process which gradually developed and accelerated and adjustment costs is increasing exponentially, so according to resource constraints and the desert area sensitivity, providing optimal combat desertification alternatives natively is necessary to achieve success in controlling and reducing the effects of this phenomenon among different regions. This paper tries to provide systematic and optimal alternatives in a group decision-making model. At the first in the framework of Multiple Attribute Decision-making (MADM), indices preference was determined using Eigenvector model. Alternatives priority was evaluated by Borda model. The results showed that the alternative of prevention of unsuitable land use changes (A18) is the most important alternative in combat desertification prosess in the study area and alternatives of vegetation cover development and reclamation (A23) and modification of ground water harvesting (A31) were in the next priority, respectively. Therefore, it is suggested that the obtained results and ranking should be considered in projects of controlling and reducing the effects of desertification and rehabilitatyion of degraded lands plans.

It has been paid less attention to effect of environmental factors on species richness and diversity indices in fragile ecosystems around Playa. Therefore this study was conducted to evaluate the effect of geographical directions and distance from Playa salt layer on the composition and species diversity in Sirjan Playa, Kerman Province, Iran. Determination of intervals 10, 1000 and 2000 meters in four main geographical aspects surrounding salt crust (North, South, East and West), were done using GPS positioning and field operation. Along the perpendicular direction, sampling of vegetation in each distanc by relevee (with dimensions equal to minimum level) in early May 2016 with three replications was carried out systematically. After determining the diversity of each unit in the software PAST and BIO-DAP, statistical analysis of data for analysis of variance (ANOVA) and mean comparison with Duncan's multiple range test was performed by SPSS software.The results showed that the main effects and interaction of geographical directions and distance from playa salt layer on all indicators of species diversity and richness were significant. In all directions at intervals of 10 meters of salt crust due to the dominance of one-dimensional of Halocnemum strobilaceum plant species and the absence of other plant species, dominance index and uniformity index of Jaccard were maximum and cotroversially richness (Menhing, Margarf and Fisher) and diversity (Shannon - Wiener, Simpson) were minimal. Due to the presence of other plant species with Halocnemum strobilaceum in 1000 meter of distance of all directions (except for the west), all the richness and diversity on the contrary of dominance and uniformity indicators increased significantly and the situation in most indicators were kept at a distance of 2000 meters. According to the development of a single plant species (Halocnemum strobilaceum) strip with very low species diversity and non-uniformly with increasing distance from center of playa in the west, likely to spread the risk of desertification and land degradation in this direction than in other directions.