The Effects Of Grazing On The Community Structure And Productivity Of Inner Mongolia Grassland

Grazing has important influence on the community structure and ecosystem function for grasslands.At present,grasslands worldwide now suffer from overgrazing,which can greatly alter community structure and productivity.Under the background,this text further studies the effects of grazing on the community structure and productivity at spatial and temporal scales.To address the degradation of grassland,it is very important for the restoration of degraded grassland ecosystems and for grassland protection and sustainable development.Therefore,based on the Inner Mongolia project which aims to return grazing land to grassland project,during 201 1-2013,we investigated community structure(cover,height,and species richness)and productivity(aboveground biomass:AGB)of 250 paired field sites(grazed vs.fenced)across three vegetation types(meadow,typical,and desert steppe)on the Inner Mongolian Plateau to further analyze the influence that grazing on community structure and productivity in Inner Mongolia grasslands.Also we analyzed the patterns and determinations of different vegetation types NPP and grazing capacity at spatial and temporal scales.The findings of this study will provide reference data for grassland pasture management.The main results of this research are as following:(1)Grazing,vegetation type,and year all had significant effects on cover,height,species richness,and AGB(p<0.05),although the primary factor influencing variations in these variables was vegetation type.Spatially,grazing significantly reduced the measured variables in meadow and typical steppes(p<0.05),whereas no changes were observed in desert steppe(p>0.05).Temporally,for a given vegetation type,there was no significant variation in the RRs(response ratios)of cover,height,species richness,and AGB during the years 2011 to 2013(p>0.05).Both linear and quadratic relationships were detected between growing season precipitation and cover,height,richness,or AGB,although specific relationships varied among observation years and grazing treatments.In each vegetation type,the observed community properties were significantly correlated with each other,and the shape of the relationship was unaffected by grazing treatment(p<0.0001).The variations in aboveground biomass in these vegetation types were commonly and dominantly influenced by community cover,height and richness,the mechanisms influencing them varied for different vegetation types.Particularly,variations in AGB in meadow steppe and typical steppe were mainly explained by vegetation height,while in desert steppe those variations were primarily explained by cover.(2)Distribution of NPP shows gradually decreased from the east to west.Different vegetation types had obviously different NPP,the meadow steppe is the highest(122 g·m-2·a-1),the typical steppe is the second(116.17 g·m-2·a-1)and the desert steppe is the least(39.3 g·m-2·a-1).From 2011 to 2013,the average NPP of meadow steppe,typical steppe,and desert steppe in Inner Mongolia were 122.0,116.2 and 39.3 g·m-2·a-1,respectively.NPP increased from 2011 to 2013,and it shows a common feature with regard to time and space aspects that the more precipitation becomes,the larger NPP becomes.The CASA model has a good correlation with the aboveground biomass of the fenced plots((2011:R2=0.53;2012:R2=0.58;2013:R2=0.60;P<0.0001),and has a low correlation with the aboveground biomass of the grazing plots.We also confirmed that NDVI,precipitation,and temperature are the most important determinations on NPP based on CASA model.(3)From 2011 to 2013,the grassland utilization rates for meadow steppe,typical steppe,and desert steppe were 41.28%,40.38%and 38.05%,respectively.In 2011,all three types of grasslands were overgrazed,and the desert steppe in 2012 and 2013 were overgrazed,and some types of grasslands still had surplus grass in 2012 and 2013 based on the CASA model.The livestock carrying capacity of the meadow steppe and typical steppe from 2011 to 2013,changed from severe overloading to not overloading,and overloading rate of desert grassland is still severe.According to actual aboveground biomass,the livestock carrying capacity of all the vegetation types were overloaded during 201 1-2013,and along with the time process,the situation of overloading was gradually reduced.The aboveground biomass in grazed sites was mainly influenced by grazing intensity and the aboveground biomass in fenced sites was mainly influenced by precipitation.Overall,grazing is one of the primary reasons for the decrease in grassland production and overall degradation of grassland in Inner Mongolia.We suggest that when severe grazing disturbance occurs in desert steppe,because limited moisture is available,long-term fencing of grassland should be strictly implemented to allow degraded grassland to recover.For meadow and typical steppe,rotational grazing should be practiced using a short-term rotation in fenced areas to enhance both animal production and to alleviate the degradation of grassland.