Grazing Exclusion Research Articles

Changes in climate, grazing pressure and nutrient inputs affect the structural integrity and functioning of Andean shrublands

ABSTRACT Background Changes in climate and the intensity of agriculture expansion can alter plant population dynamics and community composition and structure of dry shrublands. Aims We tested how temperature and moisture along an elevation gradient, grazing, and nutrient addition in soil affected demographic attributes of Croton shrubs and the composition and structure of plant species in an inter-Andean dry shrubland. Methods At three elevations, we installed grazing and exclusion plots, combined with four nutrient treatments: control, and addition of nitrogen (N), phosphorous (P) alone and in combination. We measured recruitment and survival of Croton seedlings, as well as survival, growth, fruiting of adult Croton and the composition and structure of neighbouring plants. Results Grazing exclusion improved adult survival of Croton at all three elevations. Grazing exclusion and addition of N and P increased adult growth of Croton at low and medium elevations. Croton seedling recruitment and survival decreased with distance to adult plants. The cover of Croton had a positive relationship with plant abundance and diversity. Conclusions Temperature, moisture, grazing and nutrient addition can alter the demography and cover of Croton, as well as the composition and structure of its neighbouring plants threatening the functioning of the inter-Andean dry shrubland.

Grazing exclusion altered the pattern of the soil seed bank but not the aboveground vegetation along an altitudinal gradient in alpine grassland

AbstractGrazing exclusion by fencing is the principal option to restore degraded grassland, but its effects on recovery and succession of vegetation are not clear, especially in high mountain areas. In this study, we aimed to fill this gap by assessing the effect of seven‐year grazing exclusion on vegetation and soil seed bank along an altitudinal gradient in northern Tibet, China. Species richness, Shannon‐Wiener index and Simpson's diversity index of vegetation and soil seed bank, seed density, and the Sørensen index all displayed a mid‐domain (hump‐shaped) pattern with increasing altitude, except for the Shannon‐Wiener and Pielou indices of soil seed bank in fenced grasslands. These results demonstrated that the impact of grazing exclusion on the patterns of vegetation and soil seed bank change with altitude but are not synchronous. Grazing exclusion increased vegetation coverage but decreased soil seed bank density, and species diversity of vegetation and soil seed bank. The Sørensen index (0.03–0.2) and non‐metric multidimensional scaling (NMDS) analysis indicated that the species composition differed between vegetation and soil seed bank, but no difference was found between fenced and grazed grasslands. The low similarity suggests that the soil seed bank contributes little to vegetation recovery in alpine grassland. Seven‐year grazing exclusion had no effect on either vegetation succession or species composition of soil seed bank in alpine grassland. Overall, our findings suggest reconsidering the use of long‐term grazing exclusion to restore degraded grassland at high altitudes (above 4400 m above sea level) on the Tibetan Plateau.

Grazing Effects on Fuels Vary by Community State in Wyoming Big Sagebrush Steppe

Limiting fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe is often a management priority as fires threatens its ecological integrity and rural economies that depend on it. However, the Wyoming big sagebrush steppe is vast and occurs in different community states from intact (sagebrush-bunchgrass dominated) to exotic annual grass dominated. Grazing has been suggested as the only tool that is likely feasible to apply across such large landscapes to manage fine fuels, but there is concern that over time grazing may induce undesirable shifts in plant community composition (e.g., increases in exotic annuals) that increase fire risk. Therefore, we evaluated the longer-term (+10 yr) effects of contemporary, moderate grazing by cattle compared with grazing exclusion on fuel characteristics in three community states: intact, degraded, and exotic annual grass states. We accomplished this by measuring fuel characteristics in five grazed and ungrazed areas in each community state in 2020 and 2021. Grazing generally decreased fine fuel continuity and biomass and increased the live-to-dead ratio. These fuel alterations are consistent with decreasing the probability of fire ignition and, if ignited, producing a slower spreading fire with shorter flame lengths. The response of several fine fuel characteristics to grazing varied by community state. Fine fuel characteristics also commonly varied among community states and between years. These results suggest that fuel management plans need to recognize that grazing effects will vary by community state and be flexible because fuel characteristics vary spatially and temporally. Overall, our results suggest that contemporary grazing in the Wyoming big sagebrush steppe reduces the probability of wildfire and likely increases the effectiveness and safety of fire suppression. Consequently, grazing exclusion in these communities increases the probability of frequent, large wildfires that are difficult and dangerous to suppress.

Vegetation restoration constrained by nitrogen availability in temperate grasslands in northern China

AbstractGrazing exclusion using fencing has been considered an effective means of vegetation restoration in degraded grasslands. Increased plant growth during recovery requires more nitrogen (N), which is a major limiting factor in northern China. It remains unclear whether soil N supply in this region can support long-term vegetation restoration. In this study, a field inventory was conducted in seven temperate grasslands in northern China. At each site, grassland outside of the fencing experienced continuous grazing, whereas that within the fencing was protected. Results showed that grazing exclusion significantly increased aboveground biomass, species richness and the Shannon–Wiener diversity index by 126.2%, 42.6% and 18.8%, respectively. Grazing exclusion reduced the concentrations of nitrate and total inorganic N by 51.9% and 21.0%, respectively, suggesting that there may be a mismatch between N supply and plant demand during the growing season. The aboveground biomass, species richness and Shannon–Wiener diversity index in the restored grasslands were positively correlated with legume dominance within the community. These results indicate that the vegetation restoration in temperate grasslands could be constrained by soil N availability, which may be supplemented through biological N fixation.

The effect of sheep grazing abandonment on soil bacterial communities in productive mountain grasslands

Livestock grazing abandonment entails important shifts on the overall ecosystem function, but the effects of this land-use change on specific bacterial taxa remain poorly understood in mountain grasslands. Moreover, we currently lack knowledge about the feedbacks between changes in ecosystem functions affected by livestock abandonment in mountain grasslands and the soil bacterial communities. Here, we evaluated the behavior of bacterial communities' structure and composition at taxa level as a function of short (1-year) and long-term (15-years) grazing abandonment in a mountain grassland. We also linked the observed responses in the bacterial communities to changes in several ecosystem functions (i.e. primary production, plant species biodiversity, carbon stocks and soil fertility). The alpha diversity of the bacterial communities did not show a significant response as a consequence of grazing abandonment. However, we identified significant changes on the overall composition of soil bacterial communities between the long-term abandoned grassland areas and grazed or abandoned areas in the short term. We also evidenced a balance between the number of operational taxonomic units (OTUs) whose relative abundance is favored by livestock grazing (19.51 %) and those with higher relative abundances in long-term grazing exclusion areas (20.23 %) that could behave as indicators of grazing abandonment. Structural Equation Modeling analyses proved that several bacterial taxa associated with relevant ecosystem functions, such as Rhodospirillales order within Alphaproteobacteria phylum, featured significant changes in their relative abundance between grazing treatments. The direct and indirect effects of grazing exclusion on woody species encroachment and soil organic carbon were strongly linked to the changes in the abundance of bacterial taxa indicators. The assessment of the bacterial community response to livestock abandonment in mountain grasslands may thus provide early warning signs before subtle changes in ecosystem functions occur.

Effects of long-term enclosing on distributions of carbon and nitrogen in semia-arid grassland of Inner Mongolia

The effects of long-term grazing exclusion on Carbon (C) and Nitrogen (N) partitioning in the green-plant–litter–root–soil system of grassland are unknown. As such, in this study, we evaluated the C and N contents, stocks, and ecological stoichiometry in Inner Mongolian grasslands by enclosing them for 18 and 39 years inside a fence (F18 and F39, respectively), in comparison with those outside the fence (F0), an area that was under long-term grazing. In F18 and F39, C and N stocks were higher in green plants and litter (undecomposed, incompletely decomposed, and completely decomposed litter), but C and N stocks were lower in the roots and soil (P < 0.05). The N stocks in F39 in incompletely and completely decomposed litter were lower (P < 0.05) compared with those in F18. The C contents in green plants and soil were 5% higher in F39 than in F18, whereas the N contents of litter and soil were 17.13%–37.92% lower. The C/N ratio in green plants and litter substantially increased after long-term enclosure, but decreased in roots and soil. The C/N ratio in litter and soil in F39 was 6.5%–36% higher than at F18, but 1.2%–8.2% lower in green plants and roots. Finally, following long-term enclosure, C and N were primarily transported from the soil and roots to green plants and litter. After 39 years of enclosing, C primarily moved from the litter to soil, while N primarily transferred from the soil to roots, compared with 18 years of enclosing. Our results indicated that the duration of enclosure has different effects on C and N distribution in the green-plant–litter–root–soil system. In conclusion, long-term grazing exclusion is not beneficial for soil C and N sequestration in the grasslands of Inner Mongolia.

Retracted: Distributions of trace elements with long‐term grazing exclusion in a semi‐arid grassland of inner Mongolia

AbstractWe still know little about the distributions of trace elements in grassland with long‐term grazing exclusion. The contents, stocks, and proportions of iron (Fe), aluminum (Al), manganese (Mn), and boron (B) in green plant–litter–root–soil were evaluated by enclosing for 18‐, and 39 years inside the fence (F18 and F39) and grazing outside the fence (F0) in Mongolia grassland. Results showed that F18 and F39 decreased the stocks of Fe, Al, and Mn in green plant and root compared with F0 (p &lt; .05), while increased the stocks of them in litter (p &lt; .05). The F18 obviously increased the stocks of Fe and Mn in soil, especially B (p &lt; .05). The stock of Fe, Al, and Mn in green plant at F39 was 28.6%, 13.9%, and 39.2% higher than that at F18. The stocks of trace elements in undecomposed litter at F39 were increased by 12.7%–52.2% compared with F18, while the stocks of them in complete decomposed litter were decreased by 32.2%–42.5%. The stocks of trace elements in soil at F39 were 9.1%–28.0% lower than that at F18, especially B (p &lt; .05). In conclusion, the trace elements were mainly shifted from green plant and root to soil and complete decomposed litter with 18‐year grazing exclusion. The trace elements were shifted from complete decomposed litter and soil to root with 39‐year grazing exclusion compared with 18‐year grazing exclusion.

Small effects of livestock grazing intensification on diversity, abundance, and composition in a dryland plant community.

Livestock grazing is a globally important land use and has the potential to significantly influence plant community structure and ecosystem function, yet several critical knowledge gaps remain on the direction and magnitude of grazing impacts. Furthermore, much of our understanding of the long-term effects on plant community composition and structure are based on grazer exclusion experiments, which explicitly avoid characterizing effects along grazing intensity gradients. We sampled big sagebrush plant communities using 68 plots located along grazing intensity gradients to determine how grazing intensity influences multiple aspects of plant community structure over time. This was accomplished by sampling plant communities at different distances from 17 artificial watering sources, using distance from water and cow dung density as proxies for grazing intensity at individual plots. Total vegetation cover and total grass cover were negatively related to grazing intensity, and cover of annual forbs, exotic cover, and exotic richness were positively related to grazing intensity. In contrast, species richness and composition, bunchgrass biomass, shrub density and size, percentage cover of bare ground, litter, and biological soil crusts did not vary along our grazing intensity gradients, in spite of our expectations to the contrary. Our results suggest that the effects of livestock grazing over multiple decades (mean=46 years) in our sites are relatively small, especially for native perennial species, and that the big sagebrush plant communities we sampled are somewhat resistant to livestock grazing. Collectively, our findings are consistent with existing evidence that indicates the stability of the big sagebrush plant functional type composition under current grazing management regimes.

Plant Community Traits Respond to Grazing Exclusion Duration in Alpine Meadow and Alpine Steppe on the Tibetan Plateau.

Grazing exclusion has been a primary ecological restoration practice since the implement of “Returning Grazing Land to Grassland” program in China. However, the debates on the effectiveness of grazing exclusion have kept for decades. To date, there has been still a poor understand of vegetation restoration with grazing exclusion duration in alpine meadows and alpine steppes, limiting the sustainable management of grasslands on the Tibetan Plateau. We collected data from previous studies and field surveys and conducted a meta-analysis to explore vegetation restoration with grazing exclusion durations in alpine meadows and alpine steppes. Our results showed that aboveground biomass significantly increased with short-term grazing exclusion (1–4 years) in alpine meadows, while medium-term grazing exclusion (5–8 years) in alpine steppes (P < 0.05). By contrast, belowground biomass significantly increased with medium-term grazing exclusion in alpine meadows, while short-term grazing exclusion in alpine steppes (P < 0.05). Long-term grazing exclusion significantly increased belowground biomass in both alpine meadows and alpine steppes. medium-tern, and long-term grazing exclusion (> 8 years) significantly increased species richness in alpine meadows (P < 0.05). Only long-term GE significantly increased Shannon-Wiener index in plant communities of alpine steppes. The efficiency of vegetation restoration in terms of productivity and diversity gradually decreased with increasing grazing exclusion duration. Precipitation significantly positively affected plant productivity restoration, suggesting that precipitation may be an important factor driving the differential responses of vegetation to grazing exclusion duration in alpine meadows and alpine steppes. Considering the effectiveness and efficiency of grazing exclusion for vegetation restoration, medium-term grazing exclusion are recommended for alpine meadows and alpine steppes.

Organic Carbon Stored in the Aerial Phytomass of Fire-threatened Andean Grassland Species

The practice of burning Andean grasslands in uncontrolled conditions and dry seasonal periods affects the sustainability of the ecosystem with the loss of native grasslands species with superficial roots, the volatilization of organic matter and superficial soil nitrogen, and greater susceptibility to wind and rain erosion, which affects the forage supply of grazing areas that affect the economy of the cattle rancher in addition to emitting abundant CO₂ into the atmosphere. The objective was to quantify the loss of organic carbon contained in the aerial phytomass of burned grasslands and the dynamics of recovery of their shoots, for which seven grasslands with different dominant species and the exclusion of grazing were chosen from five plots of 900 m² with five subplots of 64 m², whose aerial phytomass was harvested, and the shoots were measured in their leaf height for nine months. As a result, variable amounts of carbon were obtained according to dominant grassland species for p: 0.001 from 5.02±1.05 to 20.02±0.95 t/ha, equivalent from 22.09 to 73.47 t.CO₂/ha. The recovery of shoot phytomass barely reached 37.32% to 55.94% concerning the initial amount obtained in the mother plants. It was concluded that each grassland has its performance of storage and recovery of stored carbon and the findings should be cause for reflection and be the basis for public policies to promote the protection of grasslands.

Functional imbalance not functional evenness is the third component of community structure

It is generally assumed that functional richness, diversity and evenness are complementary and, taken together, describe different facets of the distribution of species and their abundances in functional space. However, although these three primary components of community structure are commonly accepted by most community ecologists, measures of functional evenness usually fail to properly capture the regularity of species abundances in functional space. In this paper we will use an underexplored decomposition of Rao’s index of functional diversity to introduce the notion of functional imbalance, an indicator of the strength of interaction between species abundances and their functional dissimilarities. Functional diversity always increases with increasing functional imbalance. Therefore, functional imbalance seems a more appropriate indicator of this facet of community structure than functional evenness. A worked example aimed at evaluating the influence of grazing on plant community structure showed that all proposed measures of functional imbalance were able to highlight the main functional changes of a dry calcareous grassland in Tuscany (Italy) following grazing exclusion.

Grazing Changed Plant Community Composition and Reduced Stochasticity of Soil Microbial Community Assembly of Alpine Grasslands on the Qinghai-Tibetan Plateau.

Grazing is a substantial threat to the sustainability of grassland ecosystems, while it is uncertain about the variety of plant and soil microbial community and the linkages between them limit the comprehensive understanding of grazing ecology. We conducted an experiment on the effects of the grazing regimes rotational grazing (RG), continuous grazing (CG), and grazing exclusion (GE) on an alpine meadow in Qinghai-Tibetan Plateau. The differences of plant community composition, soil microbial community assembly mechanism, and taxonomic and functional composition between grazing regimes were examined, and the relationship between plant species and the soil microbes was assessed by constructing a co-occurrence network. The results showed that the plant community composition varied with the grazing regimes, while the soil microbial community composition did not vary with the grazing regimes. The soil bacterial functional composition was similar under RG and CG, while the soil fungal functional composition was similar under GE and RG. The soil microbial community under all grazing regimes was assembled mainly according to stochastic rather than deterministic mechanisms, and RG and CG reduced the relative importance of the stochastic ratio. At the microbial phylum level, CG and GE increased the relative abundance of Acidobacteria and Armatimonadetes and CG and RG increased the relative abundance of Elusimicrobia. In the network of plant species and soil microbial classes, plants and bacteria themselves were mainly positively linked (symbiosis and promotion), while plants and soil microbes were mainly negatively linked (competition). There were five microbial generalists in the network, which connected with many microbes, and four showed no difference in their abundance among the grazing regimes. Overall, the stable key microbes in the network and the fact that many of the plants are unconnected with microbes weakened the impact of grazing-induced changes in the plant community on soil microbes, probably resulting in the stable soil microbial community composition. Moreover, there was still a dominant and tolerant plant species, Kobresia pygmaea, that connected the plant and microbial communities, implying that the dominant plant species not only played a crucial role in the plant community but also acted as a bridge between the plants and soil microbes; thus, its tolerance and dominance might stabilize the soil microbial community.

Is the bryophyte soil diaspore bank buffered against nutrient enrichment and grazing exclusion?

PurposeSoil diaspore banks of bryophytes are poorly known in tundra grasslands, yet can be important for the maintenance of local bryophyte assemblages. We examined the effects of fertilization and grazing exclusion on above-ground bryophyte assemblages and soil diaspore banks in a tundra grassland.MethodsWe collected soil diaspore samples and recorded the cover of above-ground bryophytes from a full-factorial experiment with NPK fertilization and grazing exclusion treatments (a Nutrient Network site in NW Finland). Soil diaspore samples were germinated on trays in a greenhouse. We analyzed the compositions of diaspore bank assemblages and of above-ground assemblages and assessed their responses to the experimental treatments.ResultsThe diaspore bank contained c. 50% of taxa found in above-ground assemblages; 26 bryophyte taxa germinated from the diaspore bank, while 40 taxa were found in the above-ground assemblages. These communities had distinct species compositions: the diaspore bank was dominated by Pohlia nutans, while above-ground assemblages were dominated by several species. NPK fertilization and grazing exclusion had negative effects on bryophyte richness and cover in above-ground assemblages, and weaker effects on these responses in the diaspore bank.ConclusionSoil diaspore banks comprise about half of the bryophyte taxa encountered in above-ground assemblages. Bryophyte diaspore banks are more buffered against nutrient enrichment and grazing exclusion than above-ground assemblages, suggesting that diaspore banks may enhance persistence and recovery of local bryophyte assemblages from environmental changes.

Transhumant Sheep Grazing Enhances Ecosystem Multifunctionality in Productive Mountain Grasslands: A Case Study in the Cantabrian Mountains

Understanding the effects of traditional livestock grazing abandonment on the ability of mountain grasslands to sustain multiple ecosystem functions (ecosystem multifunctionality; EMF) is crucial for implementing policies that promote grasslands conservation and the delivery of multiple ecosystem services. In this study, we evaluated the effect of short- and long-term transhumant sheep abandonment on EMF through a grazing exclusion experiment in a grassland of the Cantabrian Mountains range (NW Spain), where transhumant sheep flocks graze in summer. We considered four key ecosystem functions, derived from vegetation and soil functional indicators measured in the field: (A) biodiversity function, evaluated from total plant species evenness, diversity and richness indicators; (B) forage production function, evaluated from cover and richness of perennial and annual herbaceous species indicators; (C) carbon sequestration function, evaluated from woody species cover and soil organic carbon indicators; and (D) soil fertility function, evaluated from NH4+-N, NO3–-N, P and K content in the soil. The EMF index was calculated by integrating the four standardized ecosystem functions through an averaging approach. Based on linear mixed modeling we found that grazing exclusion induced significant shifts in the considered individual ecosystem functions and also on EMF. Long-term livestock exclusion significantly hindered biodiversity and forage production functions, but enhanced the carbon sequestration function. Conversely, the soil fertility function was negatively affected by both short- and long-term grazing exclusion. Altogether, grazing exclusion significantly decreased overall EMF, especially in long-term livestock exclusion areas, while the decline in EMF in short-term exclusions with respect to grazed areas was marginally significant. The results of this study support the sustainability of traditional transhumance livestock grazing for promoting the conservation of grasslands and their ecosystem function in mountain regions.

Can grazing by elk and bison stimulate herbaceous plant productivity in semiarid ecosystems?

AbstractPlant communities in rangeland ecosystems vary widely in the degree to which they can compensate for losses to herbivores. Ecosystem‐level factors have been proposed to affect this compensatory capacity, including timing and intensity of grazing, and availability of soil moisture and nutrients. Arid ecosystems are particularly challenging to predict because of their high degree of temporal variability in moisture inputs. We used a replicated herbivore exclusion experiment to evaluate herbaceous plant responses to grazing by large ungulates to test current theory and identify constraints on plant compensation in a dryland ecosystem. We measured nitrogen (N) yield and herbaceous production in three plant communities: meadows, willow‐associated herbaceous communities, and riparian communities. We implemented grazing exclusion treatments from 2005 to 2008 in areas with elk and bison and areas with only elk. Grazing by large ungulates increased herbaceous production and N yield in herbaceous riparian communities. In willow communities, herbaceous plants displayed equal compensation in response to grazing in total aboveground production and N yield. Our results support the idea that plant compensation in this semiarid system is contingent on soil moisture availability, wherein the most productive sites (that received substantial moisture inputs from subsurface flow) exhibited overcompensation. Although the herbaceous riparian communities we studied are isolated patches of productive grassland in an otherwise shrub‐dominated and minimally productive semiarid landscape, grazing by a combination of bison and elk removed only 44%–53% of aboveground net primary productivity (ANPP) during the growing season, and 25%–38% of production over winter. Consumption by ungulates was a positive linear function of herbaceous production, similar to reported patterns from other temperate and tropical grazing ecosystems. The slope of this relationship was affected by the analytical method used to calculate ANPP and consumption rates, but, regardless of the method, was lower or similar to reported slopes for other intensively grazed systems (Yellowstone, Serengeti, Laikipia) that have sustained high ungulate densities for decades to centuries. Given that the vegetation communities exhibited equal or overcompensation in terms of total herbaceous ANPP in both years, elk and bison population levels during our study period did not appear to occur at densities leading to degradation of herbaceous communities.

Free particulate organic carbon plays critical roles in carbon accumulations during grassland succession since grazing exclusion

Grazing exclusion is proposed as an effective strategy for to recover degraded grasslands and increase carbon accumulation. However, few studies have explored the response of soil organic carbon (SOC) and its components to grazing exclusion during long-term succession. In this study, we collected soils from sites with a chronosequence of ~33 years after grazing exclusion with randomized and replicated experiments in the temperate grasslands of the Loess Plateau, China. The contents of SOC, free particulate organic carbon (fPOC), occluded particulate organic carbon (oPOC), and mineral-associated organic carbon (MOC) and their driving factors in the 0–60 cm soil layer were examined in each grassland. The results showed that fPOC, oPOC, and MOC contents were significantly affected (P < 0.05) by grazing exclusion duration and soil depth. Soil fPOC, oPOC, POC, and MOC contents increased with exclusion time, but decreased with soil depth. SOC content was significantly improved since grazing exclusion for more than 26 years compared with that for active grazing grasslands. The fPOC played critical roles in promoting the SOC formation within the entire soil profile (0–60 cm depth). Across the sampled areas, we found a positive association between the concentrations of SOC and its fractions, and the input of litter to the topsoil (0–40 cm), and soil extracellular enzymes at greater depths (40–60 cm). Our results indicate the potential of grazing exclusion for promoting SOC accumulation in semiarid regions, and highlight the need to understand soil carbon stabilization mechanisms in both top- and subsoil under future climate change scenarios.

Short-Term Grazing Exclusion Alters Soil Bacterial Co-occurrence Patterns Rather Than Community Diversity or Composition in Temperate Grasslands.

Grazing exclusion is one of the most common practices for degraded grassland restoration worldwide. Soil microorganisms are critical components in soil and play important roles in maintaining grassland ecosystem functions. However, the changes of soil bacterial community characteristics during grazing exclusion for different types of grassland remain unclear. In this study, the soil bacterial community diversity and composition as well as the co-occurrence patterns were investigated and compared between grazing exclusion (4 years) and the paired adjacent grazing sites for three types of temperate grasslands (desert steppe, typical steppe, and meadow steppe) in the Hulunbuir grassland of Inner Mongolia. Our results showed that short-term grazing exclusion decreased the complexity and connectivity of bacterial co-occurrence patterns while increasing the network modules in three types of temperate grasslands. The effects of grazing exclusion on soil bacterial α-diversity and composition were not significant in typical steppe and meadow steppe. However, short-term grazing exclusion significantly altered the community composition in desert steppe, indicating that the soil bacteria communities in desert steppe could respond faster than those in other two types of steppes. In addition, the composition of bacterial community is predominantly affected by soil chemical properties, such as soil total carbon and pH, instead of spatial distance. These results indicated that short-term grazing exclusion altered the soil bacterial co-occurrence patterns rather than community diversity or composition in three types of temperate grasslands. Moreover, our study suggested that soil bacterial co-occurrence patterns were more sensitive to grazing exclusion, and the restoration of soil bacterial community might need a long term (>4 years) in our study area.

Microtopographic heterogeneity mediates the soil respiration response to grazing in an alpine swamp meadow on the Tibetan Plateau

Soil respiration (Rs) is a major component of terrestrial carbon cycling, which varies greatly with spatial heterogeneity or under grazing. There is scant evidence for the interactive effects of microtopography and grazing on Rs, particularly in alpine swamp meadow ecosystems where hummocks and hollows are common microtopographic features. We conducted a grazing exclusion experiment in an alpine swamp meadow on the central Tibetan Plateau. Seasonal variation in Rs and relevant environmental factors were observed between hummocks and hollows in the free grazing plots and grazing exclusion plots. The growing season Rs was significantly higher in the hummocks than that in the hollows. The responses of Rs to grazing varied greatly with microtopographic heterogeneity, with grazing significantly decreasing Rs in the hummocks but greatly increasing Rs in the hollows. The grazing-induced relative changes in aboveground biomass, belowground biomass, soil organic carbon and microbial biomass carbon were positively correlated with the changes in Rs. Grazing and microtopography caused changes in soil temperature and microbial biomass were the major factors that driving the seasonal variation in Rs. This information stresses the importance of hummock-hollow microtopography in regulating carbon cycling in grazed alpine swamp meadows.

Effect of Grazing Exclusion and Rotational Grazing on Soil Aggregate Stability in Typical Grasslands in Inner Mongolia, China

Soil aggregate is extremely important for soil health and sustainable land management. Overgrazing has caused serious degeneration of grassland in the past decades and how to restore the degraded soil through grazing management is urgently needed. In this research, we investigated effects of long-term grazing exclusion and short-term rotational grazing with different grazing intensities on aggregate stability in the upper 10 cm of soil at two grazing sites in Xilinhot, Inner Mongolia. Treatments included long-term (34 years) exclusion, moderate-term (21 years) exclusion, and continuous grazing at adjacent reference plots. In addition, effects of rotational grazing under different grazing intensity [i.e., no grazing (0 days/month), light grazing (3 days/month), moderate grazing (6 days/month) and high grazing (12 days/month)] were investigated after 5 years. Stability of aggregate fractions were determined using wet sieving. Our results showed that the stable aggregates fraction were significantly increased under grazing exclusion for both fine (0.25–1 mm) and coarse (1–2 mm) size fractions. At the rotational grazing site, stability of fine aggregates was significantly enhanced under grazing compared with no grazing, while there was little influence on stability of coarse aggregates. Our results showed that grazing exclusion significantly increased soil aggregate stability and the peak appeared in moderate-term exclusion, meanwhile, rotational grazing had little influence on aggregate stability. We suggest that rotational grazing rather than long-term grazing exclusion is a better way for soil aggregate stability and soil health, and current grazing prohibition policies may need to be adjusted.

Grazing exclusion had greater effects than nitrogen addition on soil and plant community in a desert steppe, Northwest of China

BackgroundThe impacts of increasing nitrogen (N) deposition and overgrazing on terrestrial ecosystems have been continuously hot issues. Grazing exclusion, aimed at restoration of grassland ecosystem function and service, has been extensively applied, and considered a rapid and effective vegetation restoration method. However, the synthetic effects of exclosure and N deposition on plant and community characteristics have rarely been studied. Here, a 4-year field experiment of N addition and exclusion treatment had been conducted in the desert steppe dominated by Alhagi sparsifolia and Lycium ruthenicum in northwest of China, and the responses of soil characteristics, plant nutrition and plant community to the treatments had been analyzed.ResultsThe grazing exclusion significantly increased total N concentration in the surface soil (0-20 cm), and increased plant height, coverage (P < 0.05) and aboveground biomass. Specifically, A. sparsifolia recovered faster both in individual and community levels than L. ruthenicum did after exclusion. There was no difference in response to N addition gradients between the two plants.ConclusionsOur findings suggest that it is exclusion rather than N addition that has greater impacts on soil properties and plant community in desert steppe. Present N deposition level has no effect on plant community of desert steppe based on short-term experimental treatments.