بررسی تاثیر قرق در وضعیت و گرایش مراتع طبیعی مناطق مختلف اکولوژیکی استان یزد

Long-term studies of vegetation cover changes in rangelands under protected and grazed areas is important in rangelands rehabilitation and management. This study conducted in nine hectare ofNodushan steppes rangelands with 132.8 mm annual precipitation in Yazd province for ten years (1996-2005). Canopy cover, forage .production and regeneration of each species were estimated in inside and outside of exclosure each year and range condition determined. Results showed that total canopy cover increased inside and decreased outside in final year compared with first year of study, but these changes were not statically significant. There was not significant difference in canopy cover of inside and outside in the end of study, too. Shrubs decreased inside and outside but grasses and forbs increased, in the study, compared with first year. These changes that related mainly to Stipa barbata's canopy cover were statically significant only in grasses inside and outside of exclosure. There were not significant differences in grasses inside and outside canopy cover, in the end of study. Most of canopy cover of inside and outside belonged to shrubs and decreasers that mainly related to presence Artemisia sieberi. Low palatability ofthis species in growth stages caused the high stability for that even outside of exclosure. Other important species of shrubs was Eurotia ceratoides. This species which known as a palatable in many steppe and semi-steppe rangelands, deformed Because of high grazing pressure. Canopy cover of tow grasses of Stipa barbata and Stipa arabica, were a little more inside than outside but there were not statistically significant. Plant growth was affected with precipitation influences but there were not significant relationship between species canopy cover and precipitation. Inside forage production increased the end of study, compared with first year that belonged mostly to decreaseres. Forage production affected with precipitation too, but it was not significant relationship between them. The rangeland status was transformed from poor to medium condition inside the boundary; whereas the condition was transformed from poor to very poor outside the boundary during the study years. Consequently, differences between vegetation cover percentage and forage production was negligible inside and outside of the enclosed area. Therefore the effect of preservation activities on rangeland status would be very slow during the time in arid and semi-arid pastures. The conclusion has been certificated by other literature cited in this field.