نشریه مهندسی اکوسیستم بیابان
پیاپی 9 (زمستان 1394)

Salinity stress is considered as one of the major factors that reduce plant growth in many regions in the world. Agropyron pectiniforme and Agropyron trichophorum species are perennial grasses species that product valuable forage and grazing material in pasture and rangelands of Iran. The aim of this study was determining effect of salinity stress with NaCl on seed germination traits of Ag. pectiniforme and Ag. trichophorum species. The experimental design was a two factorial (species treatments and salinity levels or salt stress 0, 50, 150, 250 mM NaCl) arranged in a completely randomized design with three replicates and 50 seeds per replicate. The data were statistically analysed by the MSTAT-C, computer program. The difference between the means was compared using Duncan test (P

Desertification process has always been led to destruction of vegetation cover and soil and water resources that can occur in different climatic conditions, the intensity of which depends on the natural conditions of the region. Due to the increase in destruction of vegetation as one of the most important consequences of desertification, monitoring the changes and assessment of their trends are essential for planning and resources management. Therefore, the aims of this study were to map the vegetation cover of Navah-Kooh semiarid forests in Sarpol-e-Zahab, and asseying the type and trend of changes using multi-temporal images of MSS, TM, ETM and OLI sensors during a 40-year period (1975-2015). In this regard, the NDVI and classification method were used to enhance the images. Also, the images difference and calculating the area of changes classes were used to determine the type and trend of changes. The results indicate that there are the greatest increasing changes in the rare to normal vegetation class (with area 13.881 km2) in the periods 1984-1987, and also in the non-vegetation to rare vegetation class (with area 10.789 km2) in the periods 1975-1984. Whiles, the maximum of decreasing changes were observed in the normal to non-vegetation class (with area 6.944 km2) in the periods 1992-1998, and also in the normal to rare vegetation class (with area 5.592 km2) in the periods 1987-1990. Overall, the results of changes detection have shown a decreasing trend in vegetation cover of the study area that could be said the main reasons of the destruction are the forests dryness by oak, droughts duration and road construction.

Above 80 percent of Iran is currently located in arid and semi-arid to dry and sub-humid climates and they have sensitive conditions given the climatic conditions and natural characteristics of these regions and improper utilization methods, hence they are potentially and actually subject to the phenomenon of desertification. In this research, the sensitivity of the lands of Masjedsoleiman Area to desertification is evaluated by using IMDPA model, which is one of the methods of desertification assessment in arid and semi-arid regions. For this purpose, after initial assessments 3 criteria, including Climate, Soil and Water, were selected as the effective criteria in desertification of the region with different indices. By using the above-stated method, the scales of each index was obtained in the related criterion and the value of each criterion was calculated using geometric average of the scales of the indices. Then each criterion was elaborated in ArcGIS as database layers. By integrating raster layers of the stated criteria, calculating geometric average of the criteria and analyzing them by using the mentioned model, desertification intensity map of the studied regions was obtained. The results showed that about 2774 square kilometers of the studied area was found to be in medium class of desertification and about 23 square kilometer of the region was in two classes of low and high desertification. Climate with the numerical value of 2.46 and Water with the numerical value of 1.25 had respectively the highest and lowest effects in desertification of the region. Soil, with the numerical value of 2.13, shows the medium desertification intensity.

At this research, the effect of the grazing intensity on the features of the soil seed bank in shrub lands in arid zones in Semnan province was studied. The sampling area (500 hectares) was determined including no-grazing area (un-grazed 15 years), the moderate grazing intensity and the high grazing intensity area near the close of interval each other. In each treatment of soil sampling, systematic sampling was done within the 20 plots of 1 × 1 m intervals along 4 transect of 50 meters and a length of 200 m. Soil samples from each plot at depths of 0-5 and 5-10 cm and radius 3 cm was done by Auger. In each treatment, a total of 20 samples and finally 60 soil samples were collected and transferred to the greenhouse environment. Soil samples were planted with dimensions of 40 x 40 cm sieve containers. After finishing the greenhouse cultivation, seed density per unit area in terms of number of species per square meter was calculated. Considering the density of seeds per square meter, the ratio of frequency of each species to all species was calculated. One-way ANOVA was used to compare the data. Independent student t -test used to compare characteristics of the seed bank was also studied in tow depths. Results show a significant effect because the intensity and depth of seeding is. Both moderate and heavy grazing treatments were created impact on soil seed bank density per unit area. The highest and lowest seed density fluctuations due to the increased depth of the treatments no-grazing (43.5%) and heavy grazing (21.9%) was estimated. The average grazing intensity not changes significantly in the soil seed bank diversity than Un-grazed areas in different layers. But in the heavy grazing, soil seed bank diversity was significantly decreased in the first depth (39.5%) and the second depth (51%).

This study aimed to investigate the effect of canopy cover of individual woody patches on soil seed bank characteristics viz. density, richness and the similarity between soil seed bank and above ground vegetation. The study was conducted in Mazayjan, Zarindasht, south of Fars province in 2013. Therefore, 40 4m2 plots beneath and outside of Ziziphus spina-christi (dominant woody species) were established. Soil samples were collected within two depths (0-5 and 5-10 cm) in each plots by augur to test the germination of the seeds buried in the soil in the greenhouse. Above ground vegetation was also estimated at the growth season. Paired t-test was used to compared soil seed bank characteristics between the two depths, and between inside and outside of the Z. spina-christi canopy cover. The results showed that seed bank density, richness and its similarity with above ground vegetation were significantly higher inside the patches than bare soil. Seed density and richness were significantly higher in the upper than lower layer of soil. As a result, in the dry region, the cover of woody plants is important in conservation of soil seed bank particular for herb species e.g. Asphodelus albus, Antigonon sp., Stipa capensis, Plantago stokessi and Geranium sp.

Drought is a natural and climatic phenomenon that occurs in world wide areas every year and occurrence becomes an inevitable issue. This phenomenon is impaired in ecosystem. Arid rangeland ecosystems are a significant part of our land that is brittle systems that climatic changes are useful to simply unfounded destruction. Therefore, drought identifying and monitoring valid descriptive statistics indicators is the first step toward managing this phenomenon. Drought monitoring by using traditional systems is difficult. Remote sensing technology, coupled with geographic information systems, their ability in data performance has shown that in time of drought. This study was conducted at rangelands of Yazd Province to monitor of drought. In this study has been trying to research this index NDVI, EVI, NMDI, LST and TCI bands of MODIS images extracted from the data and precipitation data from climatology stations to use the range . Regarding the comparison between drought indices and indicators for climate satellite and satellite set performance indicators , to evaluate the climatic index SPI closest climatology stations to the monthly precipitation statistics for the period 2000-2008 types of rangeland in the study was used . To extract the parameters of satellite imagery resolution bands of MODIS images of 500 meters, the eight -day harvest interval for the period 2000 to 2012 and during the months of February through September, before and after it was prepared. Due to the different periods of precipitation data and satellite imagery, Joint Range Index Comparison between 2000 -2007 was considered. Data from other years was used to verify the accuracy of the results. Indices at intervals of three, six, nine, 12, 18 and 24 months showed that the volatility of short-term drought intervals greater than long-term intervals. But enjoying a bit of persistence. So in short periods of drought month intervals is greater than the other. Regarding the relationship between drought and precipitation, precipitation and meteorological drought index results showed that drought index ranged from three to nine months; with precipitation amounts of one percentage correlations are significant. In other words, changes in the amount of monthly precipitation index SPI is effective in short-term timeframe. Statistical comparison between results of calculation of satellite indicators and meteorological drought index showed that SPI index in short term with heat index and NMDI index has the highest correlation in one percent level.

Now floodwater spreading on aquifers is one of the suitable methods for control and efficient use flood and artificial feed groundwater in arid and semi-arid regions and determine appropriate locations with accuracy and required speed for floodwater spreading it is of utmost importance. In this study, were identified main criteria four, sub criteria eight and indicators 24 Criteria, sub criteria and indicators flood water spreading bolterusing Delphi method and determine their degree and percent importance. For this purpose, a questionnaire experts survey (Delphi questionnaire) containing extracted criteria preparation and was in the hands of specialists. For each criteria, sub criteria and indicators calculated criteria percent importance and importance degree. According to the criteria importance the chart be provided selection possible elected criteria. criteria, sub criteria and indicators Prioritization was determined of the percent importance and importance degree each criterion. Finally GIS help were prepared site selection maps.The results showed that according to questionnaire and the opinions experts and charts in site selection flood water spreading watershed ivar respectively soil infiltration indicators, flooding quality, soil texture, slope, and the presence aqueduct and sub criteria water, aquifer and topography and infiltration and flooding criteria were considered important and appropriate. Region prone to floodwater spreading are located in quaternary units the watercourse and alluvial fans, alluvial terraces up and down terraces that the causes can cited be placed units these in the margins of the main channels, consisted of clay and silt very low, sand and gravel abundant and be at the lower elevations and low slopes.

Nebkhas, which are formed by shrubs, are a common phenomenon in arid and semiarid landscapes and play important roles in preventing soil erosion and nutrient loss. Halocnemum strobilaceum is one of the important indigenous plant species of Mighan playa that can not only protects itself against wind erosion but also reduces sediment removal and can forms Nebkha phenomenon. This study aims at examining the role of Ha strobilaceum in controlling wind erosion (Nebkha formation), and its morphometric relation with the accumulated sand in marginal dune land of Mighan playa, Arak, Iran. This study performed at an area of 1000 square meter. In order to analyze the morphometric characteristics of Nebkhas and the amount of accumulated sand in this Vegetative type, parameters including length, width and height of the Nebkhas and canopy cover of Ha strobilaceum were measured separately. The results reveal that Ha strobilaceum can stabilize 74.1m3h-1 equal to 118/56 ton/ha that average is a remarkable number considering the dimensions of the Nebkhas and can prevent soil erosion. So there are correlation among Nebkha volume and large diameter and canopy area, (r=0.68*). and There was no significant relationship between Nebkha volume and plant height (from the top Nabka).

Soil erodibility is one of the six components affecting water erosion of the universal soil loss equation (USLE). K-factor ýis best obtained from direct measurements on natural plots. This is an infeasible task on large scales. To overcome this ýproblem measured K-factor values have been related to soil properties and the soil classification maps are used. The ýcurrent research examines the ability of the soil maps for calculation of erodibility factor in the watershed scale. This ýsubject was followed by investigation of difference of erodibility components among the soil types of Darabkola ýWatershed. Also, geostatistical technique with Kriging method are used for representation of the spatial distribution of ýK-factor. Results showed that among the K-factor components, percent of silt, structure class and permeability had ýsignificant difference between some of soil types, and other components and K-factor didn’t have significant ýdifference. In conclusion any coincidence seemed between erodibility map and soil types map.