the study of biological soil crust (mosses) roles in protection of surface soil in front of water erosion (case study: rangelands around torogh dam in khorasan razavi province)

soil erosion is a main hazard in most area of the country specially in arid and semi-arid regions and itis very important because of sedimentation, pollution, increased flooding and its negative effects onsoil productivity. one of the features of arid and semi-arid areas is the presence of low cover ofvascular plants. these empty spaces are usually good niches for biological soil crusts or cryptogamslike mosses. these crusts contribute to a variety of ecological functions and have different effects onsoil features and vascular plants. the present study was carried out in the rangelands of torogh dambasin of khorasan- razavi province in order to find the effects of such kind of plants (mosses) onwater erosion. for this purpose, artificial runoff streams in plots with two intensity (low and high) for30 minutes. in order to study the effects of different amount of mosses on sedimentation and specificerosion, four different density of mosses in the same experimental situation were studied: high (60-75% of plot), medium (35-50% of plot), low (10-20% of plot) and control (0%). the results ofanalysis of variance and tukey method by the use of minitab software showed a significant differencein 95% level between the four considered density of mosses and the two intensity of water. as mossesdensity decrease, sedimentation and specific erosion increased consequently. but there were nosignificant differences in infiltration between the different treatments.