Grazing Exclusion Research Articles

Difference of soil carbon density under different grazing exclusion duration in Seriphidium transiliense desert with distinct degrees of degradation

Overgrazing and continuous grazing give rise to considerable decreases in aboveground biomass and soil organic carbon. Grazing exclusion (GE) has been determined to be an effective approach to enhance the soil carbon storage of arid and semiarid grasslands in China. However, at present, there is no consensus regarding whether GE affects soil carbon, especially in desert regions with differing degrees of degradation. This paper examines the changes in soil organic carbon density (SOCD), easily oxidizable carbon density (EOCD) and microbial biomass carbon density (MBCD) in slightly degraded desert (SD) and moderately degraded desert (MD) after different periods of GE. The results indicate that GE did not significantly alter SOCD in SD, but GE caused SOCD to decrease by 12.7–25.6% in 0–20-cm soil depth in MD. EOCD and MBCD in all soil surface layers of SD first decreased and subsequently increased with increasing GE duration, whereas in the 0–20-cm soil layer of MD, these values increased linearly with increasing GE duration and aboveground biomass. Therefore, we proposed that carbon density was significantly different among distinctly degraded deserts, and we should consider the degree of degradation and the condition of desert regions before implementing GE.

Effects of grazing exclusion on spring and autumn pastures in arid regions of China: Insights from field surveys and landsat images

Overgrazing has caused serious grassland degradation, and grazing exclusion (GE) has been considered an effective and economic approach for restoring vegetation and soils in degraded grassland. In this study, we evaluated the ecosystem restoration of two types of degraded spring and autumn pasture in arid regions of northwest China, based on field surveys (community structure characteristics, soil C and N) and Landsat images (greenness and wetness). In temperate typical steppe (TS), our findings indicated that GE significantly increased plant height, coverage, biomass, soil C and N, as well as greenness and wetness values from Landsat images, however GE decreased plant density and species diversity. Restoration on greenness and wetness peaked in the fourth and fifth years, respectively, following GE. The restoration of greenness and wetness showed bimodal curves during growing season. In temperate desert (TD), results revealed that community structure characteristics, greenness, and wetness improved after GE, and the restoration of greenness and wetness increased with duration of GE. Soil C and N however, did not recover significantly after six years of GE. The restoration of greenness and wetness remained stable during growing-season months. Our findings suggest that longer GE might be considered in the restoration of TD, whereas short-term (not more than 4–5 years) GE, reduction in the livestock load or mowing regularly may be more appropriate for TS. Decision to adopt measures of GE and the duration of GE should be reasonably determined according to the specific grassland type. This research can provide guidance for the restoration of degraded grassland ecosystems in arid and semi-arid regions all over the world.

Communities of predatory mites (Phytoseiidae and Stigmaeidae) in different environments of the Brazilian Pampa

The Brazilian Pampa presents a high diversity of fauna and flora within a mosaic of environments. The aim of this study was to evaluate the assemblages of predatory mites (Phytoseiidae and Stigmaeidae) in three different Pampa environments: Grassland shrub vegetation, Grazing Exclusions fenced for six years and Riparian Forest with tree vegetation. Phytoseiidae and Stigmaeidae were evaluated with a total of 324 plant sampled from nine sites in three environments. Twenty-two Phytoseiidae species and six Stigmaeidae species were found. Riparian Forest presented the highest abundance of predatory mites (243) and the greatest species diversity. Mites were more abundant in Grazing Exclusions (64) than in Grassland (25) environments, but species diversity was similar. In Riparian Forest, the most abundant species were Amblyseius tamatavensis Blommers, Amblyseius herbicolus (Chant) and Agistemus floridanus González-Rodríguez. Arrenoseius gaucho Ferla, Silva and Moraes and Zetzellia malvinae Matioli, Ueckermann and Oliveira were the most abundant in Grassland environment. Our results demonstrate that the Brazilian Pampa has a high diversity of predatory mites and mite communities seem to be affected by the type of environment, showing the importance of this ecosystem as a reservoir of natural enemies.

Threats and challenges related to grazing paddocks: Recovery of extremely overgrazed grassland after grazing exclusion

Overgrazing causes serious problems for rangeland ecosystems and human livelihoods globally. Sheep grazing paddocks with fixed fences have become increasingly widespread in Europe; however, their effects on biodiversity have rarely been discussed. Our aim was to measure the degradation of grassland vegetation in an experimental sheep paddock in Central-Hungary, and evaluate recovery of alkali grasslands after the exclusion of grazing. We compared the vegetation of heavily overgrazed parcels to parcels excluded from overgrazing, treated with three doses of manure (0, 20 and 40t/ha), in the first three years of grassland recovery. The overgrazed parcels were dominated by nutrient-demanding ruderal plant species and the cover of target grassland species was only 19.8% in the third year. After grazing exclusion, the cover of target grassland species increased to 81.0% for Year 3. The dominant grass Festuca pseudovina became more abundant in the excluded parcels (51.1%) than in the overgrazed ones (8.9%). At the end of the experiment, the rate of degradation (0.2 vs. 3.7) and the cover-weighted ecological indicator values for nutrients (3.8 vs. 5.1) were significantly lower in the exclosures than in the overgrazed parcels. Manuring did not have a significant effect on grassland recovery; thus, it is not necessary in the studied ecosystem. We recommend avoiding grazing paddocks with fixed fence especially in areas harboring habitats of high conservation value. Besides resulting in the degradation of grasslands, grazing paddocks also act as landscape scars and propagule sources of problem species that might negatively affect the surrounding landscape.

Grazing strategies for resilience of ryegrass (

Perennial ryegrass (Lolium perenne L.) is a widely sown pasture species in temperate regions. Under heat and moisture-deficit stress, its production is suppressed and tiller mortality increases, particularly when plants are simultaneously exposed to other stresses such as intense defoliation. We investigated the effects of extended grazing exclusion periods in spring and summer on herbage and soils of rotationally grazed, perennial ryegrass-dominant pastures at a summer-wet site and a summer-dry site in sheep and beef hill country in New Zealand. Treatments comprised ‘grazed’ (conventional rotational grazing), ‘early opening’ (grazing exclusion from mid-spring to mid-summer to allow perennial ryegrass to flower), and ‘deferred grazing’ (grazing exclusion from mid-spring to late summer to allow perennial ryegrass to flower and set seed). At both sites, deferred grazing increased perennial ryegrass tiller density and total vegetation cover, and reduced the abundance of broadleaf species and Pseudopithomyces chartarum spores for up to 15 months after exclusion compared with the grazed control. Herbage production was reduced during the deferred period but there was a growth surge thereafter so that herbage production over the study period was similar in the deferred and grazed treatments. Pasture nutritive values were lower in the deferred than the grazed treatment during the exclusion period but were similar in all treatments by the end of the following winter. In the autumn after deferring, seedlings contributed ~50% of the perennial ryegrass tillers present at the summer-dry site but only ~10% at the summer-wet site, where regrowth tillering of existing plants contributed a high proportion of the perennial ryegrass tillers present. Overall, early opening had few effects on the pasture, whereas deferred grazing had numerous positive effects on the pasture but only short-term effects on soil quality.

Floristic Composition Mediates Change in Forage Nutritive Quality of Atlantic Mountain Grasslands after Experimental Grazing Exclusion

Simultaneous reduction of biodiversity and forage nutritive value after grazing abandonment represents a critical agroecological problem observed in temperate mountain grasslands. However, how both processes affect each other after the exclusion of large grazers is not well understood. To address this knowledge gap, we used four Atlantic grassland sites in the Aralar masif (northern Iberian Peninsula) to ask whether floristic composition mediates change in forage nutritive quality after grazing exclusion, and, if so, how much of the effect on forage quality is mediated. To examine the effects of grazing exclusion on forage quality and floristic composition a repeated-measures (2005–10) randomized complete block experiment was used. Then, the direct effects of grazing exclusion on forage quality were disentangled from the indirect effects mediated by concurrent change in floristic composition. Grazing exclusion deteriorated forage mineral content, phosphorus content, neutral detergent fiber and, especially, crude protein and enzymatic digestibility. Concurrent floristic change mediated change in crude protein (80%), enzymatic digestibility (55%) and forage content in calcium (31%). Our study shows that plant diversity and forage quality are intimately linked features of Atlantic mountain grasslands and highlights the importance of preserving leguminous and dicotyledonous species to maintain the nutritive value of these grasslands.

Grazing exclusion alters ecological stoichiometry of plant and soil in degraded alpine grassland

Grazing exclusion is one of the most effective practices to recover the degraded alpine grasslands in Tibetan Plateau. In addition, ecological stoichiometry serves as a key regulator of ecosystem function and is also closely related to nutrient process. However, knowledge about the plant-soil interactions of stoichiometry throughout the growing season is still poorly understood. In this study, we examined how grazing exclusion affected the change of C-N-P stoichiometry of plant-soil by carrying out monthly sampling in three sites. The sites were: 9 years grazing exclusion, GE9; 5 years grazing exclusion, GE5; and free grazing, FG in degraded alpine meadow. Plant and soil samples were collected five times during the growing season (May-September) to analyze plant biomass and ecological stoichiometry. Across plots, profound fencing changed plant biomass and ecological stoichiometry. Specifically, increases in green, litter and root biomass were observed under grazing exclusion. Fencing increased plant C content, C:N, C:P, N:P ratios but declined N and P contents. In contrast to the plant, there was an increasing concentrations of soil C, N and P. Our study highlighted, under grazing exclusion, grasslands advanced soil C not only by greater biomass input but also higher plant C content. Greater soil N was mainly fixed by plant production, while enhancement of soil P was mainly due to plant production recovery to stop water erosion. With a continuous improvement of nutrient pools under short-term (< 9 years) grazing exclusion, our results showed that a long-term fencing practice effect ought to be monitored to recovery degraded alpine grassland. These findings also indicated that ecological stoichiometry provides a new insight for better understanding of the mechanisms of grazing exclusion effects on nutrient process.

Effect of grazing exclusion on soil and vegetation characteristics in desert steppe rangelands: a case study from north-western Iran

This case study examined the effect of grazing exclusion on the soil and vegetation characteristics to provide support for the restoration of the degraded desert steppe rangelands of the Arshagh ecoregion. Six sampling sites were selected (three overgrazed and three not grazed sites) from the ecoregion. Vegetation sampling (1 m2 area at 10 intervals) was carried out along 18 pieces of 90 m long transects. Soil samples were collected from the plots at the beginning, middle, and end of each transect from 0–15 cm depths and then combined to get one sample per transect. Differences between vegetation and soil properties of the grazing exclusion and overgrazed sites were analyzed using the t-test statistic. Species richness index (2.32), the diversity index (1.87), and plant cover (69.46%) were maximum at sites after 20-years of grazing exclusion. All species of plant functional types at the exclusion sites were significantly (p < 0.05) different from those at the overgrazed site. Total aboveground net primary production was greater at the exclusion sites (56.50 g/m2) than at the overgrazed sites. Soil pH was significantly (p < 0.05) higher at the exclusion site than at the overgrazed sites. Electrical conductivity was significantly higher at the overgrazed sites than at the exclusion sites. These results imply that livestock exclusion plays an important role in such vegetation parameters as the diversity, cover and soil properties of degraded rangeland ecosystems. Moreover, grazing exclusion in Arshagh rangelands may be a promising management option for the restoration of such rangelands.

A meta-analysis contrasting active versus passive restoration practices in dryland agricultural ecosystems.

Restoration of agricultural drylands globally, here farmlands and grazing lands, is a priority for ecosystem function and biodiversity preservation. Natural areas in drylands are recognized as biodiversity hotspots and face continued human impacts. Global water shortages are driving increased agricultural land retirement providing the opportunity to reclaim some of these lands for natural habitat. We used meta-analysis to contrast different classes of dryland restoration practices. All interventions were categorized as active and passive for the analyses of efficacy in dryland agricultural ecosystems. We evaluated the impact of 19 specific restoration practices from 42 studies on soil, plant, animal, and general habitat targets across 16 countries, for a total of 1,427 independent observations. Passive vegetation restoration and grazing exclusion led to net positive restoration outcomes. Passive restoration practices were more variable and less effective than active restoration practices. Furthermore, passive soil restoration led to net negative restoration outcomes. Active restoration practices consistently led to positive outcomes for soil, plant, and habitat targets. Water supplementation was the most effective restoration practice. These findings suggest that active interventions are necessary and critical in most instances for dryland agricultural ecosystems likely because of severe anthropogenic pressures and concurrent environmental stressors—both past and present.

Wild Herbivore Forage Preferences in Semi-Natural Mountain Hay-Meadows

In the context of increasing grassland abandonment we observed wild herbivore impact on the vegetation in order to understand their influence. To quantify semi-natural grassland usage by wild herbivores, we determined grazing intake in semi-natural hay-meadows surrounded by forest vegetation. Grazing exclusion cages were placed at three locations in the Valea Mare village area situated in Bistriţa-Năsăud County, Romania, from 1 April 2014 – 5 October 2014. Sampling took place at two times during this period, first shortly before the hay meadows were mowed and second at the end of the vegetation growing season. Herbage air dry matter yield was measured using two types of observation plots (cage protected plots and unprotected plots). Plant composition on the studied hay-meadows was analyzed using PC-ORD (in order to explain the preference of herbivores for each location. Although herbage production did not vary significantly between locations, the herbage intake of total dry matter production did vary between locations. Wild animals grazed through the entire growing season and based upon the floristic composition analyses we explained differences in herbage intake based on plant species preference. The management of these meadows maintains an offer of good quality forage throughout summer, and the forest surrounding grasslands provides cover when needed. In order to inhibit woody vegetation and to conserve species-rich open landscape further observation need to be made about the optimal deer species densities.

Effect of grazing exclusion on nitrous oxide emissions during freeze-thaw cycles in a typical steppe of Inner Mongolia

Grazing exclusion of grasslands has traditionally been considered to reduce nitrogen inputs and decrease nitrous oxide (N2O) emissions. However, recent studies have shown that grazing exclusion may increase N2O emissions because of freeze-thaw cycles. In this study, year-round N2O fluxes (including high-frequency measurements during the freeze-thaw cycles) were measured in three sites that included long-term grazing exclusion (ungrazed since 1979, UG79), short-term grazing exclusion (ungrazed since 1999, UG99), and continuously grazed (CG), in Inner Mongolia grassland. The results showed that: 1) across the entire period of observations, mean annual N2O fluxes were the highest at UG99 (12.2 μg m−2 h-1), followed by CG (8.6 μg m−2 h-1) and UG79 (7.5 μg m−2 h-1); 2) during spring freeze-thaw cycles, cumulative N2O emissions were significantly higher at UG99 than UG79 and CG (P < 0.05); 3) freeze-thaw cycles had significant effects on N2O emissions with strong pulse emissions exhibited at the beginning of the spring thaw period; and 4) structural equation model analysis indicated that soil water content was a predominant environmental factor that caused increased N2O emissions, while other factors tended to affect N2O emissions indirectly. The results confirmed that short-term grazing exclusion could increase N2O emissions owing to the high N2O concentration during freeze-thaw cycles, associated with high quantities of snowmelt water. However, the effects of long-term grazing exclusion on N2O emissions showed no differences compared with grazing management. This suggests that grazing exclusion does not always result in an increase in N2O emissions during freeze-thaw cycles as it is more controlled by soil liquid water content. Thus the new finding of the event emissions of N2O should come up with more reliable estimates of soil‐atmosphere trace fluxes.

Temporary grazing exclusion as a passive restoration strategy in a dryland woodland: Effects over time on tree regeneration and on the shrub community

Passive restoration is acknowledged as a cost-effective approach to restore forest ecosystems. In this approach, restoration implies simply ceasing the disturbance causing degradation. But an efficient allocation of restoration efforts requires an understanding of the recovery trajectories of different ecosystem components.In Mediterranean oak open woodlands (called montado in Portugal), livestock grazing drives important plant community composition changes, and may hamper tree regeneration, threatening the long-term sustainability of this ecosystem. A temporary grazing exclusion may, thus, be an efficient restoration measure. However, how beneficial changes occur with time after exclusion on tree regeneration and on the structure and diversity of the ecosystem, are less clear.In this work, we studied the effects of grazing exclusion as a passive restoration strategy on a cork oak woodland, focusing on cork oak tree (Quercus suber) regeneration and on the structure and diversity of the understory shrub community. We assessed oak seedlings and saplings abundance and height, shrub structure, compositional and functional diversity at sites with 0, 5, 9 and 13 years of grazing exclusion.Cork oak individuals were similarly abundant throughout the chronosequence, but time had a positive effect on the height of saplings, until 9 years of exclusion. Shrub cover increased within 5 years after exclusion, and remained stable thereafter. Shrub taxonomic diversity increased continuously along the chronosequence, while functional diversity did not change consistently.Our results suggest that grazing exclusion may be an effective passive restoration measure, although different components of the ecosystem have different timings of recovery. In the case of the studied cork oak woodlands, tree regeneration may be promoted by a 5–10 years period of exclusion, after which it decreases, while conservation of taxonomic shrub diversity may require at least 13 years of exclusion. Our results highlight the importance of optimizing restoration plans depending on the restoration objective.

Does mixed vs separate sheep and cattle grazing reduce soil compaction?

AbstractDegradation of soil in the United Kingdom (UK) is compromising the ecosystem services that flow from this natural capital asset, including water flow regulation. Soil compacted by grazing livestock, for example, results in an increase in overland flow following rainfall and is thought to be one of the key factors contributing to increased severity of UK winter flooding in recent years. Practical farm‐scale changes in livestock management that lead to improvements in water flow regulation therefore need to be identified. This pilot study aimed to assess the impact of (i) changing stocking composition, and (ii) temporary grazing exclusions, on soil natural capital quality on a sheep and beef cattle farm in Northumberland, England. I found evidence of improved soil bulk density under mixed sheep and cattle grazing compared to cattle‐only grazing over a 3‐month summer grazing season; bulk density in 'cattle‐only' pastures increased from 0.836 to 0.875 g cm−3 from June to September 2017, compared with a small decrease of 0.875–0.871 g cm−3 in 'cattle to mixed sheep and cattle' pastures (difference significant at p &lt; .05 level). Changing from sheep‐only grazing to mixed grazing, and exclusion of grazing, did not significantly influence bulk density change (p &gt; .05). This study indicates that rapid improvements in soil physical properties can be achieved through realistic changes to livestock management. If this finding can be confirmed over multiple grazing seasons, this potentially offers a straightforward means to enhance soil health on grazed land in the UK, improving delivery of water flow regulation and other ecosystem services.

The effect of grazing on winter survival of midday gerbil (Meriones meridianus) of different genders.

The objective of this study was to investigate the effects of grazing on midday gerbil (Meriones meridianus) population characteristics and survival of animals of different genders. The experiment used a randomized complete block design and was conducted in Alxa Left Banner, Inner Mongolia, China, in 2002 (The agricultural reclamation plots set up in 1994). From April 2006 to October 2010, midday gerbils were live‐trapped in 3 light grazing plots, 3 overgrazed plots, and 3 grazing exclusion plots. The quantity of vegetation was investigated in the two different grazing intensity areas and grazing exclusion area to determine the relationship between gerbils and plant food availability. The results suggested that there was higher gerbil density, individual body mass, and daily body mass growth rate in the grazing exclusion sites than the other sites across the whole year. Females had higher survival in grazing exclusion areas than in other treatments, but the males’ survival showed the opposite pattern. Our results indicated that grazing negatively influenced the midday gerbil population by reducing food availability. Grazing influenced the survival rates of male midday gerbils positively, but had negative effects on females. The reason for gendered differences in survival rates of midday gerbils requires further investigation.

Long-term grazing exclusion greatly improve carbon and nitrogen store in an alpine meadow on the northern Qinghai-Tibet Plateau

Grazing management is known to be one of the most important strategies for regulating plant community structure and soil carbon and nitrogen content for alpine meadows, but very few studies about the effect of long-term grazing management on soil and plant characteristics. In this study, biomass and soil samples were collected during the grazing and grazing-exclusion periods to determine the biomass and soil properties, two-way ANOVA was used to examine the effects of grazing management on plant and soil properties. Our results show that the aboveground biomass was reduced during the grazing period but increased during the grazing exclusion period. Furthermore, the response of plant functional groups to grazing management was different. Whereas the belowground biomass increased during the grazing period but decreased during the grazing-exclusion period. Interestingly, the 0–10 cm and 30–40 cm soil organic carbon (SOC) increased significantly during grazing and grazing exclusion period, respectively. The 0–30 cm total nitrogen (TN) and 0–40 cm available nitrogen (AN) increased significantly during the grazing-exclusion period but showed no significant change during the grazing period. The 0–40 cm SOC and TN were both significantly affected by the year, with grazing management exerting only a marginal effect on SOC. 0–40 cm AN was significantly affected by grazing management and the interaction between year and grazing management. Our results suggest that long-term grazing exclusions could greatly improve both above vegetation biomass and soil condition such as soil carbon and nitrogen content.

Are N, P, and N:P stoichiometry limiting grazing exclusion effects on vegetation biomass and biodiversity in alpine grassland?

Nitrogen (N), phosphorus (P), and N:P stoichiometry have been proposed as an index to assess plant nutrient limitation in grassland. The alpine grasslands in Tibet were investigated to evaluate the relationships between N, P, N:P ratio and vegetation biomass and species biodiversity by comparing free grazing (FG) and grazing exclusion (GE) grasslands. Grazing exclusion had no significant effect on N, P concentrations and N:P ratio of both plant shoot and root, but significantly reduced soil N, P concentrations by 15.5% and 12.6%, respectively. In general, both biomass and biodiversity indicators positively correlated with shoot P, negatively correlated with shoot N:P ratio. Nevertheless, they had different correlation patterns with soil stoichiometry, the biomass indicators positively correlated with soil N and N:P ratios, but the biodiversity indicators negatively correlated with them. Furthermore, the effect sizes of above-ground biomass were significantly correlated with the ratio of soil N:P between GE and FG plots and the effect sizes of biodiversity indicators were significantly correlated with the ratio of soil P between GE and FG plots. Therefore, how extent of grazing exclusion effects on biomass allocation depends on how difference of soil N:P ratio between inside and outside of fencing, while how extent of grazing exclusion effects on biodiversity depends on how difference of soil P ratio between them.

Short-term grazing exclusion impacts using brush packs on soil and grass layers in degraded communal rangelands of semi-arid South Africa and implications for restoration and pasture utilization

Brush packs from very thorny tree branches were used to simulate grazing exclosures to measure differences in herbaceous vegetation and soil characteristics over 2 years on small ungrazed plots and large continuously grazed communal rangelands on 3 semi-arid soil types [shallow, red stony ground (SRSG); shallow, dark sandy loam (SDSL); and deep, dark clay-loam (DCL)]. Pasture presentation yields within exclosures exceeded those on continuously grazed areas for all soil types by: 98% (SRSG), 128% (SDSL) and 152% (DCL). Herbage samples harvested from the exclosures contained higher acid detergent fiber (P≤0.001) and acid detergent lignin (P&lt;0.05) concentrations than those from the grazed areas. In SRSG and SDSL soils, herbage samples harvested from the exclosures were deficient in phosphorus (P) for all livestock species. Depending on soil type(s), soil magnesium, organic carbon, nitrogen, P and manganese concentrations were significantly higher within exclosures than in continuously grazed areas (P≤0.05). Any response from nutrients supplied by leaf drop from the brush packs could not be separated from response due to absence of grazing, and this deserves further investigation. Our results indicate that grazing exclusion for short periods (2 years) on these semi-arid rangelands allowed pastures to produce significant growth, demonstrating that pastures were still productive. Our experiences highlighted the difficulties in erecting and retaining conventional fences to exclude livestock from given areas because of theft. Grazing immediately after vegetation recovery may necessitate judicious nutritional intervention with protein, energy and mineral supplementation to get effective utilization of the available forage.

Plant community composition and structure under short-term grazing exclusion in steppic arid rangelands

Grazing exclusion has been proved to be an effective approach for naturally restoring degraded rangelands. Still, the effect of this management practice on plant community composition and structure is ambiguous, especially under prolonged and repeated drought events. Here, we investigated the responses of community composition (i.e. incidence-based) and structure (i.e. abundance-based) to short-term sheep grazing exclusion under severe drought episode in the arid steppes of Alfa-grass (Stipa tenacissima L.) with a long evolutionary history of grazing. Individual species responses were tested based on species occurrence and abundance in either grazed or grazing-excluded steppes. Besides, indicator species analysis was used to identify species indicative of grazing-excluded steppes. Likewise, incidence-based and abundance-based α-diversity, β-diversity and functional groups’ diversities were quantified using Hill Numbers and compared between the two steppe managements types. Under severe drought conditions, sheep grazing exclusion allowed the apparition of a large number of increasers, colonizers, and native indicator plant species. It also improved the size of regional species pool and increased overall incidence-based and abundance-based α-diversity. Moreover, grazing exclusion decreased the abundance-based β-diversity at local scale but increased it at landscape scale. The incidence-based β-diversity significantly decreased at the landscape scale. Grazing exclusion enabled a significant spatial structuration of abundance-based β-diversity components by maintaining high balanced variation in species abundance at large spatial scale and greater abundance-gradient at fine-scale. Our results suggest that the implementation of short-term grazing exclusion in arid steppes would be the appropriate management practice for vegetation and habitat during prolonged droughts since it permits the recovery of native plant species and affects positively the size of the regional species pool, the overall incidence- and abundance-based α-diversity as well as the abundance-based β-diversity (chiefly at landscape scale).

Significant soil acidification caused by grazing exclusion across China’s grassland areas

AbstractSoil pH is strongly associated with soil biogeochemical cycles and biodiversity in terrestrial ecosystems. Grazing exclusion (GE) has been widely adopted as an effective practice to restore degraded grasslands. However, the effect of GE on soil pH is still poorly understood and remains inconclusive. We synthesized data for 63 sites from the peer‐reviewed literature and 43 additional field sites and investigated the differences in soil pH following grazing exclusion across China’s grasslands. The mean pH across all samples decreased by 0.13 units with grazing exclusion (mean pH 8.15 and 8.02 for the grazed and grazing exclusion groups, respectively, p &lt; 0.001). The pH of the surface soil (0–20 cm) showed the greatest rates of decrease in grazing exclusion grasslands, whereas the pH of the deep soil layers (20–100 cm) showed a limited response to grazing exclusion. In general, the largest rate of decrease in soil pH occurred after medium‐term periods (5–15 years) of grazing exclusion, whereas a smaller rate of change was found over short‐ (≤5 years) and long‐term periods (≥15 years) of grazing exclusion. Of the environmental factors examined, the climatic conditions, accumulation of biomass and the soil carbon and nitrogen dynamics were important factors influencing soil pH following grazing exclusion. Our results indicate that grazing exclusion causes significant soil acidification, especially in surface soils and humid areas. Our results provide an important reference for the future management of China’s grasslands.

Vegetation and soil covariation, not grazing exclusion, control soil organic carbon and nitrogen in density fractions of alpine meadows in a Tibetan permafrost region

The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau.