Effects of long-term grazing exclusion on vegetation structure,soil water holding capacity,carbon and nitrogen sequestration capacity in an alpine meadow on the Tibetan Plateau

Grazing exclusion is one of the primary management practices used to restore degraded grasslands on the Tibetan Plateau.However,to date,the effects of long-term grazing exclusion measures on the process of restoring degraded alpine meadows have not been evaluated.In this study,moderately degraded plots,in which the vegetation coverage was approximately 65%and the dominant plant species was Potentilla anserina L,with grazing exclusion for 2 to 23 years,were selected in alpine meadows of Haibei in Qinghai-Tibet Plateau.Plant coverage,plant height,biomass,soil bulk density,saturated water content,soil organic carbon(SOC)and total nitrogen(TN)were evaluated.The results were as follows:(1)With aboveground biomass and total saturated water content at 0-40 cm depth,the average SOC and TN contents in moderately degraded alpine meadows increased as a power function,and the plant height increased as a log function.(2)The average soil bulk density at 0-40 cm depth first decreased and then increased with increasing grazing exclusion duration,and the minimum value of 0.90 g·cm^(-3) was reached at 15.23 years.The plant coverage,total belowground biomass at 0-40 cm depth,total aboveground and belowground biomass first increased and then decreased,their maximum values(80.49%,2452.92g·m^(-2),2891.06 g·m^(-2))were reached at 9.41,9.46 and 10.25 years,respectively.Long-term grazing exclusion is apparently harmful for the sustainable restoration of degraded alpine meadows.The optimal duration of grazing exclusion for the restoration of moderately degraded alpine meadows was 10 years.This research suggests that moderate disturbance should be allowed in moderately degraded alpine meadows after 10years of grazing exclusion.

Effects of Grazing Exclusion on Soil Carbon and Nitrogen Storage in Semi-arid Grassland in Inner Mongolia, China

The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—′Returning Grazing Lands to Grasslands(RGLG)′ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.

Long-term grazing exclusion influences arbuscular mycorrhizal fungi and their association with vegetation in typical steppe of Inner Mongolia,China

It is not certain that long-term grazing exclusion influences arbuscular mycorrhizal （AM） fungi and their association with steppe vegetation. In this study, soil and plant samples were collected from two sites of grazing exclusion since 1983 （E83） and 1996 （E96）, and one site of free-grazing （FG） in the typical steppe of Xilinguole League, Inner Mongolia, China, and assayed for soil basic physicochemical properties, AM fungal parameters, aboveground biomass and shoot phosphorus （P） uptake as well. The results showed that long-term grazing exclusion of E83 and E96 led to less drastic seasonal changes and significant increases in spore density, hyphal length density and root colonization intensity of AM fungi and even soil alkaline phosphatase activity, by up to 300, 168, 110 and 102％, respectively, compared with those of FG site. In addition, the total aboveground biomass and shoot P uptake of E83 and E96 were 75-992％ and 58-645％, respectively, higher than those of FG. Generally, the root colonization intensity, spore density, and hyphal length density of AM fungi were all positively correlated with the aboveground biomass and even shoot P uptake of plant. These results may imply that grazing exclusion play a critical role in increasing the growth of AM fungi, and subsequently, may increase plant P uptake and aboveground biomass production. Moreover, the spore density could sensitively reflect the impacts of long-term grazing exclusion on AM fungi since survival strategy of spores in soil.

Species Richness and Diversity of Alpine Grasslands on the Northern Tibetan Plateau:Effects of Grazing Exclusion and Growing Season Precipitation

Species richness and diversity indices （Shannon-Wiener index, Simpson dominance index and Pielou evenness index） in alpine grassland ecosystems （alpine meadow, alpine steppe and desert steppe） under grazing-excluded and freely grazed sites were investigated along the Northern Tibetan Plateau Alpine Grassland Transect during summer 2009 and 2010. We found that species richness and diversity have not been significantly altered by short-term grazing exclusion since 2006 at vegetation and regional scales. Species richness and diversity were mainly driven by growing season precipitation （GSP）, which accounted for over 87 % of the total variation observed, Species richness and diversity at grazing- excluded and freely grazed sites appear to respond to growing season precipitation in parallel. Species richness exponentially increased with GSP while diversity indices showed positively linear relationships with GSP. This indicates that GSP on the Northern Tibetan Plateau is crucial in regulating species richness and diversity and should be taken into account in future studies on alpine grassland conservation.

Reconsidering the efficiency of grazing exclusion using fences on the Tibetan Plateau

Grazing exclusion using fences is a key policy being applied by the Chinese government to rehabilitate degraded grasslands on the Tibetan Plateau(TP)and elsewhere.However,there is a limited understanding of the effects of grazing exclusion on alpine ecosystem functions and services and its impacts on herders’livelihoods.Our meta-analyses and questionnaire-based surveys revealed that grazing exclusion with fences was effective in promoting aboveground vegetation growth for up to four years in degraded alpine meadows and for up to eight years in the alpine steppes of the TP.Longer-term fencing did not bring any ecological and economic benefits.We also found that fencing hindered wildlife movement,increased grazing pressure in unfenced areas,lowered the satisfaction of herders,and rendered substantial financial costs to both regional and national governments.We recommend that traditional free grazing should be encouraged if applicable,short-term fencing(for 4-8 years)should be adopted in severely degraded grasslands,and fencing should be avoided in key wildlife habitat areas,especially the protected large mammal species.

Impact of Grazing Exclusion on the Surface Heat Balance in North Tibet

The grazing exclusion program used by the Tibetan government to protect the ecological environment has changed the vegetation and impacted the surface heat balance in North Tibet. However, little information is available to describe the in?uences of the current grazing exclusion program on local surface heat balance. This study uses the records of fenced grassland patch locations to identify the impact of grazing exclusion on surface heat balance in North Tibet. The records of fenced grassland patch locations, including the longitude, latitude, and elevation of the vertices of each fenced patch(polygon shapes), were provided by the agriculture and animal husbandry bureaus of the counties where the patches were located. ArcGIS 10.2 was used to create polygon shapes based on patch location records. Based on satellite data and the surface heat balance system determined by the model, values for changes in land surface temperature(LST), albedo and evapotranspiration(ET) induced by grazing exclusion were obtained. All of these can influence surface heat balance and alter the fluctuation of LST in the northern Tibetan Plateau. The LST trends for day and night showed an asymmetric diurnal variation, with a larger magnitude of warming in the day than cooling at night. The maximum decrease in absorbed shortwave of LST(?0.5 ? ?0.4 ℃ per decade) occurred in the central region, while the minimum decrease(?0.2 ? ?0.1 ℃ per decade) occurred in the eastern region. The decreased latent heat lead to the LST increased maximum(>1 ℃ per decade) occurred in the central region, The eastern region increased at a rate of 0.2?0.5 ℃ per decade, while the minimum increase(0?0.1 ℃ per decade) occurred in the northwestern region.

Accumulation of soil organic carbon during natural restoration of desertified grassland in China's Horqin Sandy Land

China＇s Horqin Sandy Land,a formerly lush grassland,has experienced extensive desertification that caused considerable carbon（C） losses from the plant-soil system.Natural restoration through grazing exclusion is a widely suggested option to sequester C and to restore degraded land.In a desertified grassland,we investigated the C accumulation in the total and light fractions of the soil organic matter from 2005 to 2013 during natural restoration.To a depth of 20 cm,the light fraction organic carbon（LFOC） storage increased by 221 g C/m2（84%） and the total soil organic carbon（SOC） storage increased by 435 g C/m2（55%）.The light fraction dry matter content represented a small proportion of the total soil mass（ranging from 0.74% in 2005 to 1.39% in 2013）,but the proportion of total SOC storage accounted for by LFOC was remarkable（ranging from 33% to 40%）.The C sequestration averaged 28 g C/（m2·a） for LFOC and 54 g C/（m2·a） for total SOC.The total SOC was strongly and significantly positively linearly related to the light fraction dry matter content and the proportions of fine sand and silt＋clay.The light fraction organic matter played a major role in total SOC sequestration.Our results suggest that grazing exclusion can restore desertified grassland and has a high potential for sequestering SOC in the semiarid Horqin Sandy Land.