STUDYING SHORT-TIME DYNAMICS OF VEGETATION AND SOIL ORGANIC CARBON IN A SEMI-ARID RANGELAND (CASE STUDY: ZHARF, KHORASAN PROVINCE, IRAN)

Abstract. Rangeland vegetation dynamics encompass all processes of changes in vegetation composition and structure over time. Investigating the rangeland ecosystem dynamics makes it possible to determine the effects of climatic and management conditions on qualitative and quantitative changes of the vegetation in a specific period of time. Accordingly, data collection and measurements for evaluating vegetation dynamics in rangeland ecosystems of Zharf region in Khorasan province, Iran were conducted from 2009 to 2013. Vegetation variables were measured by the means of 3 transects with the length of 500m and sampling plots. Meanwhile, at the location of each plot, soil moisture content was measured at two depths of 0-15 and 15-30 cm using a Time-Domain Reflectometer (TDR) instrument. At the same locations, soil samples from topsoil layer (up to 15 cm depth) were collected to measure organic carbon. Results showed that at a four-year period, depending on inter-annual changes in rainfall and other climatic parameters and under local management practices, more or less changes occurred in some major vegetation factors such as species and total canopy cover. Changes were more prominent in canopy cover of annual plants, perennial forbs and to some extent in perennial grasses. Changes in soil organic carbon showed a very slow trend. Based on soil texture and variations of seasonal and annual rainfall, soil moisture caused variations in vegetation factors. In the study site, considering the relative stability of soil cover by stones, gravels and plant litter, total soil cover changes were a function of changes in total canopy cover of plants. The results of this study could be considered for proper adjustment of rangeland management in Zharf region.