IRANIAN JOURNAL OF RANGE AND DESERT RESEARCH
Year:2004 | Volume:11 | Issue:3|Papers Count:7

Nowadays numerous approaches are developed to predict soil loss, which some of them are process-based models and others are empirical. Soil erodibility parameter is one of the intrinsic characteristics of soil used in erosion models to estimate soil loss. Many researchers have attempted to find the relationship between soil characteristics and erodibility factors to show which soil properties are represented for soil erodibility indices. Since water-stable aggregates are most likely responsible for the most of physiochemical characteristics of soil, in this study we tried to investigate the relationship between soil erodibility factors and some soil characteristics indices, such as MWD and WSA to represent the soil sensitivity to erosion. This paper reports the study carried out in the Research Institute of Forests and Rangelands Erosion Lab. The aim of the paper is to compare aggregate stability indices with conventional erodibility factors used both in empirical and process-based models of soil erosion, using small scale flume and rainfall simulator. Two different models of soil erosion such as GUEST and USLE were selected for this study. The first model is a process-based model and the second one is an empirical equation. A laboratory rainfall simulator that produced rain 'with drop sizes and velocities similar to natural rainfall was used to apply rainfall to soil bed in the I by 1 meter tilting flume. Four contrasting soil types at 5 slopes and 4 different intensities were conducted to generate sediment. Runoff samples for sediment concentration. Were collected every 20 to 60 minutes due to soil sensitivity to erosion. Water stable aggregate (WSA) and mean weight diameter of sediment particles (MWD) were determined using the wet sieving method. Erosion data were obtained from 80 runs and erodibiliy factors both for GUEST and USLE models were then calculated. The results of this experiment indicated strong relation between MWD and the erodibility parameter (B), as described by the GUEST model, but not a good indicator for USLE. In addition the water stable aggregate index WSA>0.125 mm showed a significant correlation with erodibility parameter both for GUEST and USLE models.

The case studies concerning the rate of soil movement by wind in flat areas in central parts of Iran show that soil erosion in these areas is more than water erosion in mountainous areas of the some parts. The sand dune fixation and combat desertification office is responsible for combating wind erosion and the reduction of desertification effects. As a result of some requests from desert provinces some proposals have been approved and also some projects have been performed but, in fact, due to financial limitations in our country, they are not perfectly practical. The studies which was done in desert areas show that the best time for combating wind erosion is the off - take stage, because it involves lower expense and more success. However, in some sedimentation areas, it is necessary to perform some projects to reduce the losses resulting from erosion. Therefore, through a national program the office took action to-recognize and classify critical points and loss rate to estimate. In this article, Tehran province eotimate only is under consideration. To recognize critical points of wind erosion in Tehran province, the source finding method of sand dunes has been used (Ekhtesasie-Ahmadi, 1374). In this method, the effective factors in finding these points are considered and through a systematic process, off -take, carrying and sedimentation areas are determined. Through gathering some local information and questionnaires, considering morphological studies on wind deposition, and also studying the eroding wind regime effective on wind erosion, the sand movement direction is determined. Through some researches, it was specified that from among 12 towns of Tehran province which covered 1, 890, 900 hectares, only 101, 725 hectares are considered as critical points. These points are located in Mahdasht region in Karaj town, NajmAbad region in Savojbolagh town and Abardej region in Varamin town. According to intensity of loss rate, Mahdasht is placed at the first rank and Abardej and NajmAbad are placed on the second rank.

Geomorphological deserts are considered of initial primary deserts that have been classified and defined the from viewpoint of morphogenic, structural, litoedafical and composite properties. In this paper morphogenic method has been used as a base for defining and classification of geomorphologial deserts of Tehran province. For this purpose by using geological and topographical maps and combination of their data the geomorphological features individual for desert such as pedimonts, flood plains, nabkhas, salt deserts and salty flats, badlands, salty dome and salty massens and etc..., have been identified. Then by using ETM satellite images, feature boundary has been improved and the features identified and added to it. Finally recognized boundaries have been introduced as deserts boundary of Tehran province. Based on the obtained results, the geomorphological deserts of Tehran province have been extended in its western and south - west boundaries. Its total area has been calculated 30955 ha. That's equal to 16.79 percent of the province total area.

Study on autecology of range plant species is an essential step to arrange key information for managing rangeland ecosystems. This study was conducted to provide information about some autecological functions of three range plant species namely Artemisia sieberi, stipa hohenackeriana, and Ferultt gumosa in Ghom province of Iran. Some topographic, climatic, and edaphic aspects, as well as the boundaries, of the ecological habitats of these species were delineated. phenological stages, root system, and the way of presence of each of these three species in the vegetation composition were determined. The names of other species that grow in the same ecological habitat of each of these three species were listed. The results show that the ecological habitats of Artemisia sieberi in Ghom province are in an elevation range of 1000-1900m above sea level. In these habitats, average annual precipitation is 100-260 mm; absolute minimum and absolute maximum temperatures are -12 and 49 C, respectively. In study sites, the average of canopy cover, frequency, and density of this plant were 8.12%, 48%, and 8750 plants/ha, respectively.Vegetative growth of this range plant starts in early March and ends in early July. The period of summer dormancy is from early July until early September. Its flowering stage starts in late September, and the seeds ripen in mid November. This species has a taproot system with one primary root and numerous secondary roots. Ecological habitats of Stipa hohenackeriana species in Ghom province were located in some parts of rangeland areas with altitudes of 1000-2700m above sea level and slopes of 2-60%. In these habitats, average annual precipitation is 140-300 mm; absolute minimum and absolute maximum temperatures are -23.5 and 49 Co, respectively. In the study site, the average of canopy cover and frequency of this range plant were %3.3 and %50, respectively. At altitudes below 1900m above sea level, vegetative growth of this plant is in March, and seed ripening stage is in mid May to late June. While, at 2500 m above sea level, vegetative growth starts in mid April, and seeds ripen in mid July. The plant has a fibrous root system with so many fine roots of similar diameter. Mountainous habitats of Ferula gumosa in Ghom province were located in altitude range of 2150-3220 m above sea level, with slopes of 40-60%, and average annual precipitation of 307 mm. Absolute minimum and absolute maximum temperatures in these habitats are -23.5'C and 39'C, respectively. In study sites, the average of canopy cover, frequency, and density of this plant were 14. 2%, 44.5%, and 6400 plants/ha, respectively. Vegetative growth of Ferula gumosa starts in early April, and seeds ripen in mid July. The root system of this range plant is a thickened taproot from which several branch roots arise. The results of this study suggests that considering the autecological characteristics of these three species is highly essential for managing of such rangeland ecosystems.

Sainfoin, (Onobtychis sativa), is recognized as a well adapted species for range improvement in semi arid zones of Iran. Usage of fertilizer and its effect is a commonly asked question. Four levels of Ammonium phosphate i.e. 30, 40, 50 and 60 kg/ha, and three levels of sainfoin seeds, 30, 40, 50 Kg/ha were used in a randomized complete block design with three replication. The study site is located at 20 Kilometers west of Doroud in Lorestan province where rainfed agriculture is a common practice. Dry matter per hectare was recorded and analY71edR. esults show that the highest level of production belongs to combination of 40 Kg/ha.

Today remote sensing has special place in national resources and vegetation studies. In this research vegetation and land use changes in margin of Damghan playa was studied. In this site, sand dune stabilization with use of Haloxylon plant has been done. Using MSS and ETM of 1977 and 2000, positions of sand dune in study site were detected and vegetation on sand dune with help of image processing techniques such as NDVI index alongsid with visual interpretation and field check was studied. Land use of sand dune surrounding areas and groundwater quantities were studied. The results show increase of vegetation on sand dune about 160 hectares, and increase of cultivated lands around of sand dune about 2067 hectares during the studies. Also, the results of ground water show about 45 cm annual decrease. Therefore sand dune stabilization, increase of ground water extraction and cultivated land increase, occasionally cause to increase of economical condition in study site, but decrease of ground water level cause salinization and critical decrease water wells.