فصلنامه تحقیقات مرتع و بیابان ایران
سال بیست و هفتم شماره 3 (پیاپی 80، پاییز 1399)

Research on the environmental controllers in plant communities is one of the research fields for many ecologists. Identifying the factors affecting the vegetation cover in the arid regions is the first step to recognize the destructive factors, which inhibit the growth and development of vegetation. In the current study, using the structural equation modeling method and Partial Least Square – Structural Equation Modeling (PLS-SEM), climatic and pedological variables that affecting the vegetation cover in steppe rangelands of Zayandehrood basin of Isfahan province were identified and modeled. According to the results, soil clay content, maximum runoff height on the soil, temperature, and dryness of the environment are the most important variables affecting the quantity and quality of vegetation in the rangelands of the Zayandehrud basin. Besides, the role of climatic factors is more than soil factors in the distribution of vegetation in the region. The model presented in this research has good accuracy and high flexibility for modeling ecological phenomena.

Utilization of saline lands with the aim of producing lignocellulosic biomass, which has no nutritional value and can be converted to ethanol and at the same time has no effect on human food production, seems necessary. Halophytes and salt-tolerant plants that produce high biomass using saline resources (saline water and soil) can be considered as an important alternative in this regard. For this purpose, this study with the aim of investigation of ethanol producing potential of five species of Auluropus lagopoides, Atriplex leucoclada, Desmostachya bipinata, Halopyrum mucronatum and Halocnemum strobilaceum was conducted in Hormozgan province in 2016. Plant samples were collected at three phenological (vegetative, flowering and seeding) stages from two saline lands in Zaminsang and Sirik, Hormozgan province and three parameters of lignin, hemicellulose and cellulose were measured. Data analysis of variance was performed as a factorial experiment  based on the completely randomized design with three replications and comparison of means with Duncan's multiple range test in SPSS-14 software. The results showed that Halopyrum mucronatum had the potential to produce ethanol in all three vegetative stages. Halocnemum strobilaceum had the potential for ethanol production only at the vegetative growth stage and Aeluropus lagopoides and Desmostachya bipinata had the potential for ethanol production only at the seed ripening stage.

In the present study, the Miqan sub-basin of the Arak region was quantitatively investigated to find out the temporal and spatial variations of groundwater level in the nine Qanats (subterranean canals).  The methodology to evaluate the spatial and temporal changes of groundwater level,  the  26 years data of changes in underground water (1365 -1390) produced by the Water Authority Bureau of Arak city for the Miqan-sub-catchment were collected and analyzed using GIS software and time series methodology processing of data. In this methodology, firstly the mean of water discharge and withdrawals of qanats water for daily, monthly and annually were analyzed and monitored.  Then the trend of changes in the water level of all investigated wells for the 26 years data was graphically determined for those time series respectively. Secondly, a group of hydrograph for this sub-catchment were presented in figures and compared for all-time series based on daily, monthly, seasonally and annually respectively mentioned in the paper. Linear regression (simple linear) and Mann-Kendall statistics method were used to test the significant trend of changes in the underground level for all the periods' mentioned above. In the last stage, to produce the sub-catchment maps for showing the groundwater hydrograph of the plain, interpolation on maps was performed using ARC GIS software. The results indicated that according to the hydrograph of the 26 years of groundwater level has decreased drastically. Available hydrogeological data also show a sharp drop in aquifer water levels in recent years. The maximum rate of decline has been observed in the central parts, located below the Miqan basin. The most important reasons in increasing the rate of groundwater level are the mismanagement and uncontrolled withdrawal of groundwater resources by resident farmers and also the frequent reduction of precipitation

Species distribution models (SDMs) are the basis of informed decisions in vegetation management by quantifying the relationship between species distribution and influential environmental variables. The present study aimed to evaluate the GAM and CART models' performance in estimating the potential habitat distribution as well as recognizing the ecological needs of plant species in the Khezri rangelands of Bayaz plain of southern Khorasan. According to the regional condition and field observation, in an area of about 14500 hectares, vegetation sampling was done using the randomized-systematic method. Eighteen environmental variables including land characteristics, Normalized Difference Vegetation Index (NDVI), and salinity index were used as an estimator to generate maps of predictor variables. After modeling the habitat distribution prediction using CART and GAM methods in R 3.5.2 software, the accuracy of the models was assessed using the subsurface area (AUC) statistics. After determining the threshold by the TSS method, the continuous utility map was converted to the presence/absence map and the degree of conformity of the maps with the kappa index was calculated. Based on the results of the used models, the variables of the base level of the channels network, the vertical distance to the channels network, the depth of the valley, the wetness index, and the relative position of the slope are effective in habitat suitability for species establishment. In general, the GAM method has high accuracy in estimating the habitat distribution range of all species studied (Kappa≥ 0.9). According to the maps obtained from the GAM model, the highest and lowest potential habitats belong to S. rigida and T. serotina species. Therefore, the GAM method can be useful in accurately identifying the ecological needs of plant species and therefore their distribution useful at the local scale. As a result, it is suggested that this method be used as part of a management support system in the protection and restoration of vegetation in the rangelands of the Bayaz plain.

Drought can reduce the sustainable production of natural ecosystems, including rangelands. The main purpose of this study was to expand the vulnerability of rangelands drought in the Pishkuh watershed in Yazd province. In the present study, geographical information systems and multi-criteria decision-making method (AHP) were used. In this regard, the parameters affecting the drought vulnerability of rangelands of the study area, including slope, slope direction, precipitation, soil texture, and evaporation were extracted and converted into information layers with the help of GIS. After weighing the layers in terms of importance in drought vulnerability in the framework of multi-criteria decision making (MCDM), the final combination and drought vulnerability map of the study area was prepared. Also, to control and measure the final map, field studies of the study area were used. Finally, a map of the dominant rangeland vegetation type was prepared and overlapped with the drought vulnerability map of the rangelands of the study area to identify the most resistant and vulnerable rangeland vegetation type. The results showed that the highest weight of the effective parameters in rangeland drought vulnerability was related to the precipitation with a value of 0.54, and the lowest weight was related to the slope with a value of 0.061. Based on the results, the eastern, southeastern, and southern regions of the Pishkuh watershed have the highest rate of rangelands drought vulnerability, and Ar.au-St.ba.Sc.or type is the most vulnerable vegetation type in the study area. It is recommended that more management resources and strategies be implemented in vulnerable rangelands to protect the soil and its vegetation.

Rainwater harvesting is a management technique with many positive results that can be used to supply the water needed by livestock in rangelands. In this study, suitable sites for the construction of rainwater harvesting systems using multi-criteria analysis (MCE) and hydrological model (HM) in the GIS environment were identified in the nomadic ecology of Ab Bahareh at the interval of Bahmaei and Lendeh counties in Kohgiluyeh and Boyer-Ahmad province. For this purpose, appropriate criteria maps to identify sites of rainwater harvesting system including slope, rock type, land use and land cover, runoff depth, and drainage density were provided in the GIS environment. After classifying the suitability map of each criterion, the classified map of the criteria was overlaid into the geographic information system environment and the appropriate sites for the rainwater harvesting system were identified. The results showed that in terms of each of the selected parameters, except for the slope, about 30 to 50 percent of the Ab Bahareh area was very suitable for the construction of rainwater harvesting systems. Due to the mountainous nature of the region, the slope parameter is the main limitation for the construction of rainwater harvesting systems. Based on the combined analysis of all the criteria selected, about 25% of the nomadic ecosystem of Ab Bahareh is highly suitable for the construction of rainwater harvesting systems, especially pits and ponds, rock outcropping catchment, road catchment, and check dams that can be provided during the dry season between rains. In regard to the number of 4000 goats and sheep in 5 villages in the nomadic ecosystem of Ab Bahareh, assuming the daily requirement of each livestock to 4 liters of water and the dry period of 30 days between the main rains, the total catchment area for the 25 mm rainwater harvesting system to meet the needs of livestock in the region is about 2.4 hectares.