Influence Of Enclosing Grazing On Stipa Klemenzii Steppe Community And Soil

Stipa klemenzii Roshev,a typical type of desert-steppe community,was selected as the object of study to find out the influence of enclosure and grazing prohibition on desert-steppe community during the implementation of the grassland reward and subsidy policy.The dynamic change of community during 8-year enclosure,the community characteristics and physical and chemical properties of soil in the 8-year enclosure area,and those in the free grazing area were compared and analyzed,with a view to providing a reference for evaluating actual effect of the reward and subsidy policy.Specific conclusions are made as follows:1.Enclosure to prevent grazing for 7 years didn' t significantly change the quantities of phytocoenosium under the category of Family,Genus and Species.The density of phytocoenosium manifested a trend of decrease in the early period(the 1st-4th year)and increase in later period,for which other perennial plants,bulbiferous plants and annual&biennial plants are three functional groups that contribute the most to the total density change of phytocoenosium;other perennial plants and liliaceous plants are two crucial families that result into total density change;and the main species that affect phytocoenosium density are stipa klemenzii,allium mongo licumregel,and sal sola collina.2.Phytocoenosium biomass demonstrated a trend contrary to the density,i.e.,increase in the early period(the 1st-4th year)and decrease in later period,for which other perennial plants and perennial bunchgrass are main functional groups that result into biomass change;miscellaneous plants,gramineae,liliaceae and compositae are main families that affect biomass change;and stipa klemenzii and sal so la collina are main species that affect biomass change.3.Both diversity index and evenness index manifested a one-peak curve with increase in the middle period.If enclosure to prevent grazing is considered as an interference measure,the variation of diversity index conforms to the theory of "moderate interference".4.From the 4th 5th year since the measure was taken,obvious sand deposition was observed in phytocoenosium,which rapidly accumulate at a speed of 2.lcm/year during the 4th-8th year.Sand deposition is one of the dominant factors that results into phytocoenosium variation.5.As a result of grazing prohibition,for topsoil at depth from Ocm to 10cm,content of soil with grain size>2mm and grain size>2-1mm significantly improved and those with grain size between 0.25-0.125mm significantly reduced;for soil at depth from 10cm to 20cm,content of soil with grain size between 0.5-0.25mm significantly increased and those with grain size between 0.125-0.25mm significantly reduced.6.Enclosure to prevent grazing improved content of organic matter and CaC03 in soil.Soil at depth of 10-30cm contains more organic matter than that in topsoil and soil at depth of 30-40cm.For soil at depth of 0-40cm,content of CaCO3 increased with deepening soil layer,and that in lower layer is significantly higher than that in topsoil.Taking stipaklemenzii grassland as an example,total carbon content is the highest in soil layer at depth of 10-30cm.7.Enclosure to prevent grazing significantly reduced content of readily available nitrogen and readily available phosphorus in soil layer at depth of 0-20cm and changed their original spatial distribution pattern that in free grazing region they exist much more in topsoil at depth of 0-10cm than in lower soil layers,resulting into a homogenization phenomenon in which no obvious variation was observed among different soil layers.8.Enclosure to prevent grazing significantly improved total nitrogen content in soil layer at depth of 0-10cm.9.Eight years of enclosure and grazing prohibition,while greatly improved the number of branches of allium mongolicumregel and the height of stipa klemenzii,also significantly reduced the size of branches,base clump width and clump width of the two kinds of plants.10.Long time fencing enclosure can increase competitive edges of most perennial herbs,enabling them to grow in a clumped distribution;short time fencing enclosure can enhance aggregation of stipa klemenzii,etc.Fencing enclosure proves to be an effective method in controlling population quantity of harmful species in grassland like caltrop and can achieve obvious effect in a short time.With regard to the method to measure distribution pattern of plant species in grassland region,Variance/Mean value method has higher confidence level than clumping degree index method.