Grazing-induced Changes Research Articles

The influence of grazing intensity on soil organic carbon storage in grassland of China: A meta-analysis

Grazing can potentially affect grassland soil carbon storage through selective feeding, trampling and fecal excretion of livestock. The numerous case studies and a few meta-analyses have focused on grazing-induced changes in soil organic carbon (SOC) storage, but the effects of grazing on SOC in major grassland types of China are not clear. In this study, we performed a comprehensive meta-analysis to identify the impact of grazing on soil carbon in China. We found that the key factors affecting the SOC content of grazing grasslands is grazing intensity. Heavy grazing (HG) significantly decreased the SOC content by 7.5 % in major grassland types of China (95 % confidence interval (CI), −11.43 % to −3.57 %, P < 0.001). The SOC content in temperate desert steppes (7.22 %), temperate meadow-steppes (10.89 %) under heavy grazing (HG) showed significantly (P < 0.05) decreased. HG resulted in significant (P < 0.01) decreases in SOC content (6.91 %) of Kastanoze. Our study highlighted that formulating rational grazing strategies according to grassland and soil types was the key to increasing SOC storage and sequestration under climate change and increased human pressure.

Aboveground Biomass Estimation and Time Series Analyses in Mongolian Grasslands Utilizing PlanetScope Imagery

Mongolia, situated in central Asia and bordered by Russia to the north and China to the south, experiences a semi-arid climate across most of its territory. Grasslands are pivotal in Mongolia’s agricultural sustainability and food security, facing rapid changes in the last two decades that underscore the ongoing need for innovative approaches to assess vegetation conditions. This study aims to evaluate grassland biomass measurement and prediction through the analysis of high-resolution satellite data. By conducting a time series assessment of grazing-induced changes in vegetation dynamics at the long-term monitoring sites of the Botanic Garden and Research Institute, Mongolian Academy of Sciences, we seek to refine our understanding. The investigation covers biomass estimation across various Mongolian grassland landscapes, encompassing desert, steppe, and mountain regions. Spanning the grassland growing season from May 2020 to October 2023, the research leveraged diverse ground data types, including surface reflectance measurements, geographic coordinates for satellite data correction, and aboveground dry biomass. These components were instrumental in developing a biomass estimation model reliant on establishing correlations between the satellite-derived Normalized Difference Vegetation Index and biomass. The predicted biomass facilitated the time series map analysis and dynamic analysis. The PlanetScope surface reflectance correlates strongly at 0.97 with field measurements, indicating robust relations. Biomass and the Normalized Difference Vegetation Index show correlations of 0.82 for dry grassland, 0.80 for mountain grassland, and 0.65 for desert grassland, with a combined correlation coefficient of 0.62, revealing distinct characteristics across these grasslands. Time series dynamic analysis reveals rising biomass differences between grazed and ungrazed areas, suggesting potential grassland degradation. Variations in the slope coefficient of biomass differences among grassland types indicate differing degradation patterns, emphasizing the need for effective grazing management practices to sustain and conserve Mongolian grasslands. This highlights the potential of remote sensing in monitoring and managing grassland ecosystems.

Above-ground plant properties are not leading indicators of grazing-induced soil carbon accrual in the Northern Great Plains

A new aim for grassland management is to increase soil organic carbon (SOC) and to offset CO2 emissions by companies. This practice of carbon ranching may be informed by grazing-induced shifts in plant biomass and diversity which may foretell changes in SOC. Unfortunately, little is known about how grazing-induced shifts in plant properties correspond with shifts in SOC stocks. To help fill this gap, we used data from a field experiment to test whether above-ground plant properties (i.e. biomass, species richness) act as leading indicators of grazing-induced SOC accrual in the Northern Great Plains. The 5-yr bovine grazing experiment had a randomized complete block design and pre-treatment data. Moderate summer grazing (control) is widely used in the Northern Great Plains, and treatments that may alter grassland vegetation and SOC included: severe summer grazing, moderate fall grazing, and severe fall grazing. Severe fall and summer grazing increased SOC but had no effect on plant species richness and biomass relative to controls. Fall moderate grazing increased above-ground plant biomass but had no effect on SOC relative to controls. Changes to grazing practices can affect SOC without measurably affecting plant properties and can affect plant properties without measurably affecting SOC. While two drivers of SOC are plant carbon inputs and microbial respiration, our study indicates that grazing-induced change in above-ground vegetation is not predictive of change in SOC.

Grazing reduced greenhouse gas fluxes in Inner Mongolia grasslands: A meta-analysis

Grazing exerts a significant influence on greenhouse gases (GHGs) fluxes within temperate grasslands. While previous studies have explored the impact of varying grazing intensities on GHGs fluxes in meadow steppe, typical steppe, and desert steppe, there remains a knowledge gap regarding how grazing intensities affect GHGs fluxes across different grassland types and seasonal variations. In this study, we conducted a meta-analysis of Inner Mongolia grasslands involving 38 published reports and aggregating 143, 160, and 118 records for the CO2, CH4, and N2O, respectively. Our results demonstrated that grazing reduced annual mean CO2 emission, CH4 uptake, and N2O emission by 15.29%, 10.56%, and 24.73%, respectively (P < 0.05). Specifically, during the freeze-thaw period, grazing induced a decrease of 28.06% and 58.41% in CH4 uptake and N2O emissions, respectively, compared to ungrazed treatments (P < 0.05). Further dissecting the impact, we found that grazing reduced CO2 emissions in desert steppe, typical steppe, and meadow steppe by 20.28%, 15.54%, and 11.79%, respectively. In addition, grazing decreased CH4 uptake in typical steppe by 15.14% and decreased N2O emission in typical steppe, meadow steppe, and sown pasture by 20.25%, 24.18%, 52.91%, respectively. Crucially, the alteration in plant biomass due to grazing-induced changes underlying drivers that govern the responses of GHGs fluxes. These results furnish compelling evidence that grazing, particularly in non-growing season, holds the potential to mitigate grassland GHGs fluxes in temperate grasslands. Our results can deepen the understanding of the grazing effects on GHGs and offer valuable insights for refining grazing management strategies in pastoral regions.

Seasonal interactions between Quagga Mussel grazing and phytoplankton in western Lake Erie: The view from different measuring technologies

Abstract We measured Quagga Mussel grazing-induced changes in seston concentration in 20-L laboratory mesocosms containing lake water, during May-October, as part of a study to investigate the present role of mussel feeding and nutrient excretion in affecting phytoplankton composition. A variety of measuring methodologies including size-fractionated chlorophyll (&amp;lt; 2, 2-20, and &amp;gt;20 µm), phytoplankton groups by FluoroProbe, cyanobacterial genera by 16S rRNA gene sequencing, and particulate C, N, and P gave us different insights into seasonal phytoplankton dynamics and mussel selective feeding and assimilation. High clearance rates and/or high assimilation rates were seen during late May-early July across all size categories, with high rates seen particularly in cryptophytes and diatoms as revealed by FluoroProbe. Starting in late July cyanophytes dominated the phytoplankton and feeding rate on them was generally zero or low. Sequencing analyses suggested that there was a diverse cyanobacterial community present, with Microcystis, contrary to expectation, dominating only in late June. Cyanobium was the dominant genera at most times during summer-fall, and as expected, Microcystis was rejected by mussels relative to other cyanobacteria. Planktothrix, dominant in spring, was readily ingested as well as Anabaena in late June. We show that a combination of methods is helpful to make progress in understanding plankton succession and grazing. These methods were important adjuncts to microscopic analysis (Carrick et al, this issue). Our results support the hypothesis that dreissenid mussels, when abundant, can affect seasonal succession of phytoplankton shifting composition to cyanobacteria and even changes within the cyanobacterial community; however, impacts are likely modest now due low mussel biomass (Carter et al., this issue). Assimilation of C, N, and P was generally high, which is important for mussel population maintenance.

Grazing-induced changes in soil microclimate and aboveground biomass modulate freeze–thaw processes in a Tibetan alpine meadow

Grazing is the most important disturbance to grasslands, especially on the Tibetan Plateau, which sustains the livelihoods of tens of thousands of herders. However, the effects of grazing intensity and associated changes in vegetation on freeze–thaw processes (FTPs) in seasonal permafrost regions remain unclear. Here, two years of continuous in situ observations from a controlled grazing intensity experiment were used to examine FTPs and influencing factors in an alpine meadow on the Eastern Tibetan Plateau. Our results showed that a higher grazing intensity led to a shorter frozen period, extended freezing and thawing periods, and earlier initiation of freezing and thawing periods. Furthermore, grazing increased soil temperature and active (> 0 °C) and effective (> 10 °C) accumulated temperatures. The soil diurnal temperature range increased linearly with grazing intensity, whereas soil moisture did not vary with soil temperature. Our results demonstrated that the freezing and frozen periods were mainly influenced by soil temperature and the diurnal temperature range, whereas soil moisture played a critical role in the variation in the thawing period. The reduction in aboveground biomass elicited changes in FTPs, including shortening of the frozen period and lengthening of the thawing and freezing periods. Collectively, our results highlight that the combination of grazing-induced changes in vegetation and changes in subsurface temperature and moisture leads to changes in freezing and thawing processes.

Effects of grazing intensity on diversity and composition of rhizosphere and non-rhizosphere microbial communities in a desert grassland.

Overgrazing-induced grassland degradation has become a serious ecological problem worldwide. The diversity and composition of soil microbial communities are sensitive to grazing disturbances. However, our understanding is limited with respect to the effects of grazing intensity on bacterial and fungal communities, especially in plant rhizosphere. Using a long-term grazing experiment, we evaluated the diversity and composition of microbial communities in both rhizosphere and non-rhizosphere soils under three grazing intensities (light, moderate, and heavy grazing) in a desert grassland and examined the relative roles of grazing-induced changes in some abiotic and biotic factors in affecting the diversity and composition of microbial communities. Our results showed that soil bacteria differed greatly in diversity and composition between rhizosphere and non-rhizosphere zones, and so did soil fungi. Moderate and heavy grazing significantly reduced the rhizosphere bacterial diversity. Grazing intensity substantially altered the bacterial composition and the fungal composition in both zones but with different mechanisms. While root nitrogen and soil nitrogen played an important role in shaping the rhizosphere bacterial composition, soil-available phosphorus greatly affected the non-rhizosphere bacterial composition and the fungal composition in both soils. This study provides direct experimental evidence that the diversity and composition of microbial communities were severely altered by heavy grazing on a desert grassland. Thus, to restore the grazing-induced, degraded grasslands, we should pay more attention to the conservation of soil microbes in addition to vegetation recovery.

Intraspecific trait variation governs grazing-induced shifts in plant community above- and below-ground functional trait composition

In grasslands, grazing can regulate the functional trait composition of plant communities through intraspecific trait variation and species turnover. However, it is not well understood how these variables affect specific plant traits. Here, we partitioned the relative roles of intraspecific trait variation and species turnover to control grazing-induced shifts in community functional composition using a field manipulation experiment with seven levels of grazing intensity in the Inner Mongolia grassland. We concurrently measured six aboveground traits (i.e. plant height, plant aboveground biomass, plant density, leaf area, specific leaf area, SLA; and leaf density) and three root traits (average root diameter, ARD; specific root length, SRL; and root tissue density, RTD) of the first-, second- and third-order roots (1st-, 2nd-, and 3rd-). Our results showed that plant above-ground traits shifted towards grazing avoidance strategies (i.e. plant height and leaf area decreased) as grazing intensity increased, and below-ground traits shifted towards conservation strategies (i.e. 1st-SRL and 2nd-SRL decreased, 1st-RTD and 2nd-ARD increased). Additionally, functional tradeoffs were found between plant individual biomass and plant density, as well as between leaf area and leaf density under grazing. However, community-weighted mean SRL (SRLCWM) and ARD (ARDCWM) exhibited functional coordination under the grazing pressures. Altogether, shifts in community functional trait composition were predominantly governed by intraspecific variation in above- and below-ground traits, while changes in mean trait values among plant species with different resource strategies were mainly triggered by species turnover. Our results demonstrated that both above- and below-ground trait compositions in plant communities shifted towards conservation strategies under high levels of grazing intensity. Ultimately, this study highlights the important role of intraspecific trait variation in governing grazing-induced changes in the community above- and below-ground functional trait composition, which advances fundamental knowledge on the mechanisms of plant community assembly in semiarid grasslands.

Grazing promotes soil phosphorus cycling by enhancing soil microbial functional genes for phosphorus transformation in plant rhizosphere in a semi-arid natural grassland

Soil microorganisms play a key role in soil P transformation and cycling in grassland ecosystems, while the microbial mechanisms of animal grazing mediating soil P processes are not fully understood. We conducted a grazing experiment in a typical steppe grassland in Inner Mongolia, to explore the responses of microbial communities in rhizosphere and bulk soils to grazing intensity for understanding the mechanisms of grazing affecting P cycling. We determined soil physico-chemical properties and alkaline phosphatase activities, and measured soil microbial diversity and the relative abundance of microbial P-transformation genes by metagenomics in the rhizosphere and bulk soils of a Stipa grandis dominated grassland under three grazing intensities (no-, moderate, and heavy grazing). We found that (i) grazing significantly increased soil available P concentration and soil alkaline phosphatase activity; (ii) grazing increased the abundance of bacterial, but not fungal communities, and the enhanced abundance of rhizosphere bacteria promotes the P-cycling potential; (iii) grazing increased the relative abundance of the genes responsible for microbial P-uptake and transport, and inorganic P solubilization and organic P mineralization in rhizosphere soil, but not in bulk soil; (iv) grazing reduced the node degree of the network of the genes involved in P-transformation, but it increased the node degree of the genes encoding alkaline phosphatase and the C–P lyase multi-enzyme complex in the rhizosphere soil. The grazing-induced changes in the abundance of microbial functional genes are beneficial to P-solubilization and mineralization. Our results indicate a divergent effect of grazing on soil microbial communities and their functional genes involved P-transformation in rhizosphere and bulk soils, and represent an important progress towards the understanding of the mechanisms of microbial regulation of P cycling in grassland ecosystems.

A Meta-Analysis of Soil Organic Carbon Response to Livestock Grazing in Grassland of the Tibetan Plateau

Known as the “roof of the world”, the Tibetan Plateau hosts the largest pastoral alpine ecosystem in the world. Nevertheless, there is currently no consensus on how soil organic carbon (SOC) stock changes after livestock grazing on the grassland of this region. Here, a meta-analysis was performed based on 55 published studies to quantify the livestock grazing-induced changes in SOC stock (0–30 cm) in grassland on the Tibetan Plateau. The results showed that livestock grazing significantly increased bulk density by an average of 11.5%, indicating that significant soil compaction was caused by livestock grazing. In contrast, SOC content and stock significantly decreased by 14.4% and 11.9% after livestock grazing, respectively. The decline rate of SOC stock was higher in alpine meadow (−12.4%) than that in alpine steppe (−8.8%), but there was no significant difference between the two rates. The SOC stocks decreased by 10.1%, 6.2% and 20.1% under light grazing, moderate grazing and heavy grazing, respectively. The decline rate of SOC stock under moderate grazing was significantly lower than that under heavy grazing. For different livestock types, it was observed that yak grazing significantly decreased SOC stock by 15.3%. Although the decline rate induced by yak grazing was higher than those induced by Tibetan sheep grazing and mixed grazing, no significant difference was detected among them. Similarly, the grazing-induced SOC declines also did not differ significantly among subgroups of grazing season. The positive relationships between SOC stock and plant biomass indicated that the decreased plant biomass was a likely reason for the declined SOC stock under grazing condition. The findings suggested that moderate grazing with Tibetan sheep in the warm season may minimize SOC losses from grazing activities in alpine grassland on the Tibetan Plateau.

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.

Effects of different intensities of long-term grazing on plant diversity, biomass and carbon stock in alpine shrubland on the Qinghai-Tibetan Plateau.

Grazing is the main grassland management strategy applied in alpine shrubland ecosystems on the Qinghai-Tibetan Plateau. However, how different intensities of long-term grazing affect plant diversity, biomass accumulation and carbon (C) stock in these ecosystems is poorly understood. In this study, alpine shrubland with different long-term (more than 30 years) grazing intensities (excluded from grazing for 5 years (EX), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) on the Qinghai-Tibetan Plateau were selected to study changes in plant diversity, aboveground biomass and C accumulation, as well as distribution of C stock among biomass components and soil depths. A structural equation model was used to illustrate the impact of grazing on the soil carbon stock (SOC). The results showed that the Shannon–Wiener diversity index and richness index of herbaceous plants, shrubs, and communities first significantly increased and then decreased with increasing grazing intensity, reaching maxima at the LG site. The aboveground and belowground and litter biomass of understory herbaceous plants, shrubs and communities decreased with increasing grazing intensity, reaching maxima at the EX site. The aboveground and belowground biomass C storage decreased with increasing grazing intensity, reaching maxima at the EX site. The SOC stock and total ecosystem C stock decreased with increasing grazing intensity, reaching maxima at the EX and LG sites. A structural equation model showed that grazing-induced changes in the belowground biomass of understory herbaceous plants greatly contributed to the SOC stock decrease. Thus, considering the utilization and renewal of grassland resources, as well as local economic benefits and ecological effects, LG may be a more rational grazing intensity for species diversity conservation and ecosystem C sequestration in alpine shrubland. Our results provide new insights for incorporating grazing intensity into shrub ecosystem C stock and optimizing grazing management and grassland ecosystem C management.

How Biodiversity-Friendly Is Regenerative Grazing?

Regenerative grazing management (ReGM) seeks to mimic natural grazing dynamics to restore degraded soils and the ecological processes underpinning sustainable livestock production while enhancing biodiversity. Regenerative grazing, including holistic planned grazing and related methods, is an adaptive, rotational stocking approach in which dense livestock herds are rotated rapidly through multiple paddocks in short bouts of grazing to defoliate plants evenly and infrequently, interspersed with long recovery periods to boost regrowth. The concentrated “hoof action” of herds in ReGM is regarded vital for regenerating soils and ecosystem services. Evidence (from 58 studies) that ReGM benefits biodiversity is reviewed. Soils enriched by ReGM have increased microbial bioactivity, higher fungal:bacteria biomass, greater functional diversity, and richer microarthropods and macrofauna communities. Vegetation responds inconsistently, with increased, neutral, or decreased total plant diversity, richness of forage grasses and invasive species under ReGM: grasses tend to be favored but shrubs and forbs can be depleted by the mechanical action of hooves. Trampling also reduces numerous arthropods by altering vegetation structure, but creates favorable habitat and food for a few taxa, such as dung beetles. Similarly, grazing-induced structural changes benefit some birds (for foraging, nest sites) while heavy stocking during winter and droughts reduces food for seedeaters and songbirds. With herding and no fences, wildlife (herbivores and predators) thrives on nutritious regrowth while having access to large undisturbed areas. It is concluded that ReGM does not universally promote biodiversity but can be adapted to provide greater landscape habitat heterogeneity suitable to a wider range of biota.

UAV−Enabled Quantification of Grazing-Induced Changes in Uniformity of Green Cover on Semiarid and Mesic Grasslands

Coverage of living (green) vegetation influences rangeland processes and biodiversity but remains a challenge to quantify at small spatial grain. We describe a technique for rapid airborne (unmanned aerial vehicle) measurements of continuous spatial coverage of living vegetation at a resolution (spatial grain) of 8 cm ground sampling distance. We then applied this technique at the pasture (paddock) scale (tens of hectares) in two contrasting grassland ecosystems (semiarid shortgrass steppe in northeastern Colorado, United States and mesic grassland in central Texas, United States) to determine effects of locally relevant grazing treatments on spatial variability and dependence (pattern) in fractional coverage of green vegetation (fractional vegetation cover; FVC). Site-specific regression models developed using reflectance in visible and near-infrared wavebands explained 90% and 89% of variance in FVC for semiarid and mesic grassland, respectively. Mean FVC was similar among shortgrass steppe pastures differing in grazing treatment (light or heavy grazing by cattle, moderate cattle grazing with prairie dogs present). In contrast, FVC was lower with rotational compared with continuous, year-long grazing in the mesic grassland. Heavy grazing in shortgrass steppe and rotational grazing in mesic grassland increased the spatial uniformity in FVC by reducing spatial variability and increasing spatial dependence in FVC, the latter by increasing the similarity in FVC values among spatially separated patches. Unmanned aerial vehicle−enabled remote sensing provides for FVC at sufficiently small spatial grain to characterize spatial variation in FVC at the pasture scale. Results can be used to evaluate the effectiveness of management actions intended to alter spatial variation in FVC to achieve conservation or diversity objectives. Enhanced capacity to monitor FVC at small spatial grain promotes adaptive management of grasslands.

Long-term impact of domestic ungulates versus the local controls of the litter decomposition process in arid steppes

Soil processes in arid ecosystems are strongly controlled by resource scarcity. Grazing intensification can induce changes in ecosystem processes through multiple pathways, adding new constraints to those of local conditions. We focus on grazing-induced changes in litter traits and soil environment that may affect litter decomposition and N dynamics in temperate grass-shrub steppes. We performed three litterbag decomposition experiments to evaluate: i) the effect of litter traits in a common garden (ex situ), ii) the effect of soil environment using a foreign common litter substrate (in situ), and iii) the interactive effects of litter traits and soil environment (grazed vs. exclosure communities, reciprocal transplants in situ). Field experiments were replicated in three blocks with paired plots under a long-term exclosure (> 25 years) and under year-round sheep grazing. Local litter included mixtures of species of grasses and shrubs, separately. Grazing exclusion did not alter litter decomposition rates, either through changes in litter traits or in soil environment. Nevertheless, N released during grass litter decomposition was 286% higher in exclosures than in grazing communities. The difference was associated to changes in litter C:N ratio. The effects were maintained when results were integrated to the entire litter community. Our study suggests that litter decomposition rates in arid steppes are strongly controlled by local drivers. Ungulate grazing does not have an important influence on litter mass loss, but it can exert a strong control on N flux during decomposition, by changing grass litter traits.

The relative and combined effects of herbivore assemblage and soil nitrogen on plant diversity.

Plant diversity can be affected by both herbivore grazing and soil resources. However, it is unclear if the joint effects of herbivores and soil resources might vary with components of plant diversity. Here, we evaluated the relative and combined effects of herbivore assemblage and soil nitrogen (N) quantity and heterogeneity on the α and β components of plant diversity in a grassland that was subjected to four years of grazing under differing herbivore assemblages (no grazing, cattle grazing, sheep grazing, and mixed grazing). We found that herbivore assemblage combined with soil N quantity explained 41% of the variation in plant α-diversity, while herbivore assemblage combined with soil N heterogeneity explained 15% of the variation in plant β-diversity. The independent effects of herbivore assemblage explained more than those of soil N for both α- and β-diversity (α-diversity: 12% vs. 4%; β-diversity: 18% vs. 16%). We concluded that the effects of herbivores are stronger than those of soil N, and that grazing-induced changes in soil resources are important drivers of plant diversity change, especially α-diversity. Therefore, we suggest that managing herbivore species by accounting for the effects that their grazing can have on soil resources may be significant for plant diversity maintenance.

Moderate grazing increases the structural complexity of soil micro-food webs by promoting root quantity and quality in a Tibetan alpine meadow

Livestock grazing can affect both above- and below-ground communities, however, the effects of grazing intensity on vertical distribution of root traits and their associations with belowground food webs are still unclear. Based on a 5-year grazing intensity experiment (i.e., no grazing, moderate grazing and heavy grazing) in a Tibetan plateau meadow, we investigated how grazing-induced changes in root traits affected soil biota (microbes and nematodes) from the surface (0–10 cm) and subsurface soils (10–20 cm). Our results showed that moderate grazing increased nematode abundance and structure complexity of the soil micro-food webs compared to no and heavy grazing, and predominantly increased herbivores and fungivores regardless of soil layers. Shifts in herbivores and fungivores were mainly driven by root quantity and quality, emphasizing the stronger bottom-up effects on the lower trophic levels of nematodes. Grazing decreased the number of omnivores-predators in the surface soil compared to no grazing, which therefore weakened predation pressure on soil nematodes lower in the trophic structure, including root herbivores, while that effect was far less pronounced in the subsurface soil. Our study demonstrated that changes in root quantity and quality were highly associated with the complexity of the soil micro-food webs under grazing scenarios. These findings warranted the ideas that combined aboveground herbivore-root-soil micro-food webs as an ecological holo is essential for sustainable management of grassland.

Grazing impacts on ecosystem functions exceed those from mowing

Land use change due to the increasing anthropogenic activities is the most important driver leading to alteration of multiple ecosystem functions. Overgrazing is thought to be one of most pervasive and significant degrading processes in grasslands, but direct comparisons with other comparable drivers of land use intensification are lacking. Our results aimed to test how single land use practices (grazing, mowing), and combined land use practices (both grazing and mowing), influence biodiversity, soils and plant function, and the coupling of aboveground and belowground functions and properties in a Eurasian steppe grassland. We examined changes in individual functions associated with aboveground and belowground plant and soil compartments, and multiple combined functions (hereafter ‘multifunctionality’) at 317 sites along an extensive climatic gradient in Northern China. Further, we investigated the correlations (coupling) between aboveground and belowground processes under the three land use scenarios. We found a mixture of effects of grazing, mowing and mowing plus grazing. However, values of many aboveground and belowground attributes were lower when sites were grazed. Although grazed sites had lower values of soil carbon and nutrients, there were no grazing-induced changes in root carbon, nitrogen and phosphorus. More importantly, the most intense land use scenario (grazing combined with mowing) decoupled the correlations between belowground and aboveground functions compared with that of single land uses. Our study demonstrates that mowing is a better long-term management method than grazing for semi-natural grasslands in the Eurasian steppe are heavily grazed. Our results demonstrate that additional land use pressures imposed when mowing and grazing are applied together can decouple the positive associations between plant richness and functions. This knowledge is critical if we are to adopt strategies to maintain diverse grassland ecosystems and the important services and functions that they provide.

Long-term vegetation change in the Western Tien-Shan Mountain pastures, Central Asia, driven by a combination of changing precipitation patterns and grazing pressure

In mountain pastures worldwide, studies investigating vegetation changes due to long-term grazing and environmental changes are sparse, especially regarding the effects of changes in snowmelt patterns. The outstanding availability of historical vegetation data from Kyrgyz mountain pastures creates unique opportunities to study past and forecast future changes, making them ideal model ecosystems. Using a resurvey approach, we explored the response of mountain vegetation to management and environmental changes in the Western Tien-Shan to investigate whether plant communities of six vegetation types (ecozones) had changed over 42 years, whether changes were related to management or ecological causes and whether species' mean elevational ranges had changed. We assembled historic vegetation data (1973–1987) in six ecozones that were resurveyed annually from 2008 to 2015 and connected them with species' management-related traits and ecological indicator values. Overall, a homogenization of vegetation within and among ecozones was observed. Mountain steppe, meadow-steppe, and subalpine meadows showed the strongest convergence towards a dominance of mesic shrubs, related to increasing precipitation changing soil moisture and soil-salt regimes. In the high mountain steppe and the alpine ecozone, cushion dwarf shrubs increased, driven by increased soil moisture following faster snowmelt. Changes in the semidesert were related to highly variable spring soil moisture. Compositional changes accelerated over time. Mostly palatable species declined in abundance. More competitive unpalatable species replaced abundant (1973) unpalatable species. Mean elevation shifted significantly for 35 species (out of 136), with 60% shifting >100 m, more often upward (low and high elevations) than downward (mid-elevations). These mountain ecosystems seem more sensitive to changing precipitation than temperature- or grazing-induced changes, making climatic change a more important driver than management. Further adaptive management should consider the response of the vegetation to environmental changes and promote alternative land-use options to maintain ecosystem functioning. In mountain ecosystems worldwide, the observed acceleration of changes might go unnoticed, calling for long-term studies and global climate-vegetation-management interaction models.

Grazing intensity induced alternations of soil microbial community composition in aggregates drive soil organic carbon turnover in a desert steppe

Grazing is the primary land-use strategy for livestock production in grasslands, which regulate the health of grassland ecosystems. However, our understanding of grazing-induced changes in soil microbial community structure and their links to organic carbon (C) in soil aggregates is limited. By using a long-term enclosed grazing desert steppe, we examined impacts of different grazing intensity on the diversity and composition of soil microbial community in different aggregates and their contribution to soil organic C (SOC) turnover. The results showed that 15-year grazing induced a notable increase in the SOC content of the large macroaggregate (> 2 mm) and silt and clay (SC: < 0.053 mm) fractions, but did not change bulk soil organic C content. Soil prokaryotic communities were significantly impacted by grazing intensity and aggregates fractions (p < 0.01). Microaggregate (0.053−0.25 mm) and the SC fraction hosted relative more sequences of Acidobacteria, Gemmatimonadetes, and Rokubacteria than macroaggregates (0.25−2 mm), but relatively less sequences of Actinobacteria and Bacteroidetes. Co-occurrence network analysis revealed that microaggregates hosted a much more complex network and harbored more keystone taxa than macroaggregates and the SC fraction. Gemmatimonadetes was the dominant phylum (relative abundance ∼9%) and keystone taxa largely belong to this phylum, and its abundance was positively correlated with the level of SOC. Overall, grazing practice altered the soil prokaryotic community, which led to increase in the organic C level in the large macroaggregate and SC fractions, the early indicators of change in SOC dynamics. Together, our findings suggest that removing livestock from these lands would reduce SOC with probable impact on the productivity of the desert steppe and that proper grazing is an import factor of long-term sustainability of the desert steppe.