The changes of microtopography along grazing gradient

Desert grasslands are characterized by microtopography that appears to be the result of a long-term accumulation of soil around grass tussocks. Microtopography (or micro roughness) describes variations in soil surface elevation (mm or cm) for a scale of a few meters of horizontal distance and it can contain the depression or mound of the soil surface. If the microtopographgy is flattened, microcatchments are lost and water runoff transports sediments and organic materials off site. Factors that affect this fine-scale patchiness are hypothesized to be the precursor of coarse scale changes leading to desertification. Livestock have the most effect on soil microtopography and this effect will decrease with the increase of distance from critical point. Present research has considered studying microtopography fluctuations of soil surface (maximum depth between two consecutive vegetation patches) along grazing gradient and its comparison with enclosure in salt grasslands of Incheh Boroun, aimed at investigation on stability state of ecosystem. To accomplish this goal, height fluctuations of soil surface were measured through running transects away from the critical point. Grazing zones were defined using dung count method along transects. Results obtained show that depth of micro depressions around critical point is more than the depth of microdepressions in the zone of constant grazing as well as enclosure site. It seems that reduction of vegetation cover and the expansion of bare soil have happened as the result of intense and long term grazing in the area. Micromounds of soil surface have also been flattened because of livestock trampling. The continuation of intensive grazing has exacerbated the effect of erosive factors such as water or wind that cause soil surface to be eroded and microdepressions to appear on the soil surface. The rate of depression has increased or decreased in different regions of the area proportional to rate of grazing; therefore, we can state that elevation of surface microdepressions can be considered as an indicator of utilization of the ecosystem and its stability state.