Study area
The study was carried out in 2658 ha of desertic arid area in the Abougovair region (extended form 32° 13ʹ 17″ to 32° 16ʹ 56″ N and 47° 43ʹ 16″ to 47° 48ʹ 30″ E), located in Dasht-Abbas town, in southern part of Ilam province, Iran (Fig. 1). In this region, sand dune (1018.6 ha), poor rangeland (1307 ha), non-rain fed (182.9 ha), and rain-fed (149.6 ha) are the main land uses, and agriculture and animal husbandry are the main occupations of the people. The mean annual precipitation, potential evapotranspiration, and temperature were 210 mm, 3857.5 mm, and 26.2 °C, respectively. The altitude in the studied area varied between 60 to 220 m above sea level, and the slope is less than 8%. The soil type in the study area is Inceptisols, based on USA classification.
The desertification in this arid region is mainly due to climatic conditions, improper extraction of groundwater, population growth, degradation of pastures and rangeland, increase in the number of livestock, and expansion of agricultural lands. To combat desertification, with the approval of the Forests, Range and Watershed Management Organization of Iran, it was decided to stabilize an area (about 400 ha) of this region using excess petroleum materials (i.e., oil-mulch). Therefore, in 2018, 8.2 ton/ha oil-mulch was sprayed to stabilize sand dunes and facilitate plant establishment.