Grazing Exclusion Research Articles

Effect of grazing exclusion and rotational grazing on labile soil organic carbon in north China

AbstractOvergrazing has caused serious grassland soil deterioration and significant soil organic carbon (SOC) losses. Controlled grazing is recommended for restoring grassland and enhancing SOC stocks. Studies have suggested that, in particular, labile organic carbon (C) is a sensitive indicator for soil degradation and SOC recovery, but few studies of the effect of different grassland management practices have been published so far. Here, we investigate the effects of long‐term grazing exclusion and short‐term rotational grazing with different grazing intensities on labile SOC, including hot water extractable organic C (HWEC) and particulate organic C (POC), as well as potential N mineralization (Nmin) rate in soils (0–10 cm) of two grasslands in Xilinhot, Inner Mongolia. Treatments include long‐term (34 years) exclusion, medium‐term (21 years) exclusion and continuous grazing (ambient grazing) at one of the sites, and we investigate no grazing, light grazing, moderate grazing and high‐grazing intensity at the study site for rotational grazing. Our results show that grazing exclusion significantly enhances labile SOC stocks and potential Nmin rate compared to ambient grazing (e.g., POC stock at long‐ and medium‐term exclusion and ambient grazing are 5.71 ± 0.94 Mg C ha−1, 3.25 ± 0.30 Mg C ha−1 and 2.12 ± 0.38 Mg C ha−1, respectively). However, after two decades of exclusion, the potential for further C sequestration is limited. Five years of rotational grazing significantly enhances HWEC, but not POC and potential Nmin rate, when comparing the highest grazing intensity (1.88 sheep ha−1 yr−1) with grazing exclusion during the same period. We conclude that rotational grazing may be a viable alternative to exclusion, offering a more rational use of grassland without causing soil C loss. We also show that HWEC is a particularly sensitive labile SOC indicator and is tightly correlated to POC and potential Nmin rate.Highlights We investigated effects of grazing exclusion and rotational grazing on labile soil organic carbon. Grazing exclusion increased labile SOC and the highest level appeared in medium‐term exclusion. Five years of high‐intensity rotational grazing increased HWEC with no significant effects on POC. Rotational grazing is a viable alternative to grazing exclusion management.

Restoration efficiency of short-term grazing exclusion is the highest at the stage shifting from light to moderate degradation at Zoige, Tibetan Plateau

Grassland degradation has profound negative impacts on ecological functions, local economic development, and social stability. Although there are many studies on the alpine grassland degradation in the Tibetan Plateau, the variation in the response of alpine meadows to degradation and restoration processes, and the underlying mechanisms remain poorly understood. To explore these issues, we selected nine grassland degradation levels along an increasing gradient at Zoige in the Tibetan Plateau, and collected vegetation and soil samples in August 2017 and 2018 to assess the state of the grassland before and after grazing exclusion (GE), respectively. The results showed that above-ground biomass (AGB), below-ground biomass (BGB), Shannon–Wiener index, soil water content (SWC), soil organic carbon (SOC), total nitrogen (STN), and total phosphorus decreased gradually with severe degrees of degradation, whereas soil bulk density and pH increased. SWC in the topsoil presented the sharpest change in slope along the degradation gradient, indicating that SWC was a sensitive indicator of alpine meadow degradation in this area. One-year GE evidently increased SWC, SOC, STN, AGB, and BGB in lightly and moderately degraded grasslands. The restoration efficiency of GE first increased and then decreased along the degradation gradient, with the turning point appearing at the third or fourth degradation level. Based on these results, we can conclude that short-term GE is an effective method for grassland restoration in this humid area, and should be performed at the shift from light to moderate degradation stages when the efficiency of recovery is the highest. These findings could facilitate a better approach for the restoration of degraded alpine meadow ecosystems.

Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China. Grazing exclusion (GE) is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services. Nevertheless, there are still significant controversies concerning GE’s effects on grassland diversity as well as carbon (C) and nitrogen (N) storage. It remains poorly understood in the arid desert regions, whilst being essential for the sustainable use of grassland resources. To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions, we investigated the community structure and plant biomass, as well as C and N storage of plants and soil (0–100 cm depth) in short-term GE (three years) plots and adjacent long-term freely grazing (FG) plots in the areas of sagebrush desert in Northwest China, which are important both for spring-autumn seasonal pasture and for ecological conservation. Our findings indicated that GE was beneficial to the average height, coverage and aboveground biomass (including stems, leaves and inflorescences, and litter) of desert plant community, to the species richness and importance values of subshrubs and perennial herbs, and to the biomass C and N storage of aboveground parts (P<0.05). However, GE was not beneficial to the importance values of annual herbs, root/shoot ratio and total N concentration in the 0–5 and 5–10 cm soil layers (P<0.05). Additionally, the plant density, belowground biomass, and soil organic C concentration and C storage in the 0–100 cm soil layer could not be significantly changed by short-term GE (three years). The results suggest that, although GE was not beneficial for C sequestration in the sagebrush desert ecosystem, it is an effective strategy for improving productivity, diversity, and C and N storage of plants. As a result, GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.

Grazing exclusion did not affect soil properties in alpine meadows in the Tibetan permafrost region

Grazing exclusion (GE) is widely used in the Tibetan Plateau of China to restore degraded grasslands. However, the effects of GE on vegetation and soil properties in alpine meadows are still not well understood. We compared GE with adjacent continuously grazing alpine meadows at five sites to evaluate the impact of GE (10–14 years) on vegetation and soil properties in the permafrost region of the Tibetan Plateau. We collected soil samples at two soil depths (0–20 and 20–40 cm) from GE and adjacent grazing sites. The results showed that GE and Site had significant effects on aboveground biomass and cover, Site but not GE had significant effects on diversity index. GE significantly increased the aboveground biomass and cover in three of the five sites, particularly where vegetation cover was greatest. At each site, GE had inconsistent effects on plant species diversity (a positive effect at one site, no significant effects at three sites, and a negative effect at the other site). No significant differences were found between GE and adjacent grazing grasslands in soil properties (soil organic carbon [SOC], total nitrogen [N], total phosphorus [P], available P, mineral N, microbial biomass carbon [MBC] and nitrogen [MBN] and pH) for both soil depths at each site. A general linear mixed model confirmed that site and sampling depth, rather than GE, significantly affected soil properties (except for MBC). Both total aboveground biomass and cover were positively correlated with soil total P, MBC and MBN, were negatively correlated with available P and pH, and were not significantly correlated with SOC and total N. The results indicate that long-term GE (10–14 years) in alpine meadow did not significantly impact soil properties, and its impact on plant biomass and vegetation cover depends on the vegetation condition of the site. Our results can provide new insights for alpine meadow management in the permafrost region of the Tibetan Plateau.

Cotula alpina (Asteraceae) naturalised in the British Isles

Cotula alpina (Hook f.) Hook f. is an Australian herb that has been naturalised in Britain since the 1970s and is now locally abundant in parts of northern England and northwest Scotland. Its method of arrival is unknown but it is likely to have originated from gardens and perhaps also from wool shoddy. It appears to be spreading rapidly due to high seed production and effective dispersal by sheep, humans and vehicles and is now locally abundant on moorland tracks and in adjacent acid grassland and heather moorland managed for grouse. Due to its evergreen and mat-forming habit it can outcompete community dominants such as Agrostis capillaris and Festuca ovina in areas where levels of grazing are high. It appears to be well suited to the British climate and is therefore likely to spread into similar habitats in other regions where it could pose a threat to localized species associated with short grassland on acidic soils. Its overall abundance and ability to regenerate rapidly from seed means it is unlikely to be easily controlled or eradicated, although exclusion of grazing may help to reduce its abundance in some areas.

Effect of grazing exclusion on the temperature sensitivity of soil net nitrogen mineralization in the Inner Mongolian grasslands

Grazing exclusion (GE) is an efficient management practice that prevents grassland degradation. The temperature sensitivity (Q10) of soil net nitrogen (N) mineralization (Nmin) is an important parameter of N cycles, and it directly influences the feedback between the primary productivity of grassland ecosystems and climate warming. However, information remains limited about how GE affects the Q10 of Nmin in N-limited grasslands. In this study, we conducted a laboratory incubation experiment at six temperatures (−10, 0, 5, 15, 25, and 35 °C) and three soil moisture contents (15%, 25%, and 35%) for 35 days by using intact soil cores from three different GE periods grassland (0, 4 and 24 years). The results showed that long-term GE decreased the Q10 of Nmin, which was highest in GE0 (2.62), followed by GE4 (2.36) and GE24 (2.42). In addition, Q10 declined in 15% soil moisture content under all three GE treatments. Furthermore, activation energy (Ea) was negatively correlated with the substrate quality index (Q) in all three GE grasslands. These results support the carbon quality-temperature (CQT) hypothesis, showing that is can be applied to soil N mineralization in grasslands after long-term GE. This study demonstrated that GE potentially reduces the sensitivity of Nmin to increasing temperature under global warming scenarios, which might help prevent N losses in these N-limited grasslands.

Grazing mediates soil microbial activity and litter decomposition in salt marshes

Salt marshes contribute to climate change mitigation because of their great capacity to store organic matter (OM) in soils. Most of the research regarding OM turnover in salt marshes in times of global change focuses on effects of rising temperature and accelerated sea-level rise, while effects of land-use change have gained little attention. The present work investigates the mechanisms by which livestock grazing can affect OM decomposition in salt marsh soils. In a grazing exclusion experiment at the mouth of the Yangtze estuary, China, we assessed soil microbial exo-enzyme activity (EEA) to gain insight into the microbial carbon (C) and nitrogen (N) demand. Additionally, we studied the decomposition of plant litter in soil using the Tea Bag Index (TBI), a widely used standardized litter bag assay to fingerprint soil decomposition dynamics. Based on EEAs, grazing markedly reduced microbial C acquisition, whereas microbial N acquisition was strongly increased. These opposing grazing effects were also evident in the decomposition of standardized plant litter: The decomposition rate constant (k) and the stabilization (S) of litter were not inversely related, as would be expected, but instead both were reduced by livestock grazing. Our data suggest that gazing effects on EEAs and litter decomposition can just partly be explained by grazing-driven soil compaction and resulting lower oxygen availability, which has previously been hypothesized as a main pathway by which grazing can reduce microbial activity in wetland soils. Instead, grazing effects on microbial nutrient demand occurs to be an at least equally important control on soil decomposition processes.

Grazing exclusion altered the effect of plant root diameter on decomposition rates in a semiarid grassland ecosystem, northeastern China

AbstractRoot decomposition often decreases with increasing root diameter, but this relationship is affected by other factors, including the microclimate and land use. The mechanisms that underlie these interactions are unclear. We performed an Artemisia halodendron root decomposition litterbag experiment using fine (&lt;2 mm), medium (2–5 mm) and coarse (&gt;5 mm) roots. We used the same incubation duration (356 days) with five starting dates (May, June, July, October and September) in fenced (grazing exclusion) and grazed plots. Root samples installed in May decomposed faster than those installed in September, and roots decomposed faster in fenced plots than in grazed plots. Root decomposition was the highest for fine roots installed in any month, and medium roots decomposed faster than coarse roots with installation in all the months except May and July. Grazing exclusion and starting incubation time both interacted with root diameter. Root decomposition for a given diameter did not differ significantly between fenced and grazed plots; however, in both land uses, root decomposition decreased significantly with increasing root diameter. Microclimate, especially precipitation, differed among the starting dates, and precipitation patterns (especially in the first growing season) significantly (p &lt; .01) affected coarse root decomposition in the fenced plots. In summary, root decomposition was significantly (p &lt; .01) affected by root diameter. This effect was altered by grazing exclusion and by starting dates. These results highlight the importance of the starting date for root decomposition in a semiarid grassland, suggesting this date should be accounted for in future studies of root decomposition.

One-year grazing exclusion remarkably restores degraded alpine meadow at Zoige, eastern Tibetan Plateau

Understanding the influences of grazing exclusion (GE) on soil properties and vegetation characteristics is essential for the assessment of grassland restoration. The objectives of this study are exploring the efficiency of short-term GE in restoring alpine meadow in the Zoige region, eastern Tibetan Plateau, with high rainfall amount. We conducted sampling surveys before and after one-year GE in alpine meadows with seven sequent degraded degrees. The results showed that one-year GE significantly increased soil organic carbon (SOC), soil total nitrogen (STN), soil water content (SWC), and plant biomass, while decreased soil bulk density (SBD) regardless of the degradation degree. These findings suggest that short-term GE may be an effective way to restore degraded alpine meadow. Aboveground and belowground biomass was significantly positively associated with SWC, SOC, STN, soil total phosphorus, and soil available nitrogen, but presented negative relationship with SBD. This shows the complicated interaction between vegetation and soil physiochemical properties that regulates the grassland recovery process. The degraded alpine meadow in this rainfall-rich region could rapidly recover once grazing disturbance was excluded. This study can provide technical support for restoration and sustainable management of alpine meadows on the Tibetan Plateau.

Does Grazing Exclusion Improve Soil Carbon and Nitrogen Stocks in Alpine Grasslands on the Qinghai-Tibetan Plateau? A Meta-Analysis

Grazing exclusion has been widely used to restore the degraded alpine grasslands on the Qinghai-Tibetan Plateau (QTP). However, the dynamics of soil organic carbon (SOC) and soil total nitrogen (STN) pools after grazing exclusion and their controlling factors are currently less understood in this region. Here, a meta-analysis was conducted to quantitatively assess the changes in SOC and STN stocks in topsoil (0–30 cm) following grazing exclusion in three major grassland types (alpine meadow, alpine steppe, and alpine desert steppe) on the QTP and to explore the potential factors controlling the effects of grazing exclusion on SOC and STN stocks. The results showed that overall, grazing exclusion significantly increased SOC stock by 16.5% and STN stock by 11.2%. Significant increases in both SOC and STN stocks were observed after grazing exclusion of alpine meadow. In contrast, grazing exclusion did not improve SOC and STN stocks in the other two grassland types. The difference in mean annual precipitation among grassland types was a likely reason for the different dynamics of SOC and STN stocks after grazing exclusion. The effect sizes of both SOC and STN stocks were positively related to the duration of grazing exclusion, and a positive relationship was detected between the effect size of SOC stock and that of STN stock, demonstrating that the dynamics of SOC and STN were closely coupled during the period of grazing exclusion. However, grazing exclusion had no impact on soil C:N ratio for all grassland types, indicating that soil C:N ratio was generally stable after grazing exclusion. Therefore, it is suggested that the increase in STN can support continuous SOC accumulation following grazing exclusion. In conclusion, the findings suggest that the effects of grazing exclusion on SOC and STN stocks differ among grassland types on the QTP, and grazing exclusion of alpine meadows may provide substantial opportunities for improving SOC and STN stocks in this region.

Enhancement of nutrient resorption efficiency increases plant production and helps maintain soil nutrients under summer grazing in a semi-arid steppe

Grazing regime is the most important factor that alters nutrient cycling in grassland ecosystems. Grazing exclusion has been used for restoration of degraded natural grasslands in Northern China during past two decades, while we propose that 'summer grazing' could be a better management than grazing exclusion for this purpose. Summer grazing allows plants to resorb more nutrients in autumn, thus preventing grazing-induced grassland degradation while keeping grassland in production. However, our understanding of grazing effects on nutrient resorption remains limited. In the present study, we examined plant nitrogen (N) and phosphorous (P) resorption at plant species and community levels in a natural steppe grassland that had experienced contrasting 'summer grazing' versus no-grazing treatments over a 6-year period in central Inner Mongolia. Plant community nutrient resorption efficiency (RE) and resorption fluxes were estimated, along with nutrient return fluxes via animal excreta and litter deposition. We found that (1) Summer grazing at moderate intensity increased plant production, but did not alter soil quality indicators such as soil organic carbon, total nitrogen, and total and plant available phosphorous. (2) Summer grazing increased plant community nutrient RE as the post-grazing plant re-growth with elevated nutrient concentration compensated for the nutrient removal by defoliation. Summer grazing increased nitrogen RE in Leymus chinensis and Cleistogenes squarrosa, but not in Stipa krylovii; and increased phosphorous RE in L. chinensis, but decreased that in S. krylovii and C. squarrosa. (3) Summer grazing accelerated nutrient cycling via animal excreta and litter deposition, but did not reduce plant nutrient resorption fluxes in autumn, which is a major mechanism for plant production enhancement and soil nutrient maintenance under the grazing regime. Our findings provide the key evidence to support moderate-intensity summer grazing as a sustainable grassland management regime to improve plant production while maintaining soil nutrients.

Long-term ecological research in southern Brazil grasslands: Effects of grazing exclusion and deferred grazing on plant and arthropod communities.

Grazing exclusion may lead to biodiversity loss and homogenization of naturally heterogeneous and species-rich grassland ecosystems, and these effects may cascade to higher trophic levels and ecosystem properties. Although grazing exclusion has been studied elsewhere, the consequences of alleviating the disturbance regime in grassland ecosystems remain unclear. In this paper, we present results of the first five years of an experiment in native grasslands of southern Brazil. Using a randomized block experimental design, we examined the effects of three grazing treatments on plant and arthropod communities: (i) deferred grazing (i.e., intermittent grazing), (ii) grazing exclusion and (iii) a control under traditional continuous grazing, which were applied to 70 x 70 m experimental plots, in six regionally distributed blocks. We evaluated plant community responses regarding taxonomic and functional diversity (life-forms) in separate spatial components: alpha (1 x 1 m subplots), beta, and gamma (70 x 70 m plots), as well as the cascading effects on arthropod high-taxa. By estimating effect sizes (treatments vs. control) by bootstrap resampling, both deferred grazing and grazing exclusion mostly increased vegetation height, plant biomass and standing dead biomass. The effect of grazing exclusion on plant taxonomic diversity was negative. Conversely, deferred grazing increased plant taxonomic diversity, but both treatments reduced plant functional diversity. Reduced grazing pressure in both treatments promoted the break of dominance by prostrate species, followed by fast homogenization of vegetation structure towards dominance of ligneous and erect species. These changes in the plant community led to increases in high-taxa richness and abundance of vegetation-dwelling arthropod groups under both treatments, but had no detectable effects on epigeic arthropods. Our results indicate that decision-making regarding the conservation of southern Brazil grasslands should include both intensive and alleviated levels of grazing management, but not complete grazing exclusion, to maximize conservation results when considering plant and arthropod communities.

Evaluation of restoration approaches on the Inner Mongolian Steppe based on criteria of the Society for Ecological Restoration

AbstractEcological restoration is becoming an increasingly common management tool worldwide. However, a challenge still exists on how to effectively monitor restoration outcomes and evaluate restoration success for ecological restoration managers. In this review, the goal is to evaluate whether the research in a degraded area has been sufficient for fostering efficient restoration measures and follow‐up of restoration success based on the Society for Ecological Restoration (SER) criteria. We selected the Inner Mongolian Steppe (IMS) in China as a model system. This area has been the subject of substantial research over the most recent years to understand degradation processes and restoration outcomes. We put together the variables used to assess degradation and restoration needs in the IMS and analyzed restoration results based on SER's nine criteria for evaluating restoration success. We found that the accomplished research in the IMS only partially supplied the data needed for evaluation of restoration success. The available results were sufficient for a proper evaluation of species composition and tentatively supported assessments of another seven criteria but not self‐sustainability. Grazing exclusion led to the fastest and most successful recovery of degraded steppe, but landscape‐scale processes during restoration in the IMS are still incompletely known. Our review supports large‐scale restoration of the IMS and emphasizes the need for long‐time monitoring for a more complete evaluation of the outcome of the IMS restoration following all SER's criteria.

Grazing exclusion erodes the forbs functional group without altering offspring recruitment composition in a typical steppe

AbstractThe underlying mechanism of grazing exclusion on grassland community structure and dynamics may be determined by offspring recruitment. However, little is known about the role of plant functional groups in community recruitment. A chronosequence of grazing‐excluded grasslands was selected to analyze the aboveground community composition and offspring recruitment based on plant functional groups. Grazing exclusion significantly increased grasses biomass (111.7–480.7%), height (95.6–241.8%), and coverage (84.8–148.5%) and decreased grasses density (10.2–59.7%). Grazing exclusion eroded total species richness (13.2–25.0%) and forbs richness (16.6–39.4%). Grazing exclusion shifted the dominance from forbs to grasses. Grasses functional group (GFG) determined community structure, but forbs functional group (FFG) regulated species diversity in typical steppe. Clonal recruitment played a decisive role in the community regeneration, especially tiller recruit mode by GFG. Grazing exclusion had different effects on offspring recruitment of grasses and FFG. Total asexual, grasses asexual, and tiller offspring density both first significantly increased and then significantly decreased with grazing exclusion time. Forbs asexual offspring density did not significantly decrease in 10‐ and 20‐year grazing exclusion grasslands but significantly reduced after 30 years. Change in community dominance caused by grazing or grazing exclusion did not alter the tiller recruitment dominance in this area. Our results indicate that grazing exclusion presents a negative effect on community regeneration and biodiversity conservation in the studied typical steppe.

Differences in the photosynthetic and physiological responses of Leymus chinensis to different levels of grazing intensity

BackgroundGrazing is an important land use in northern China. In general, different grazing intensities had a different impact on the morphological and physiological traits of plants, and especially their photosynthetic capacity. We investigated the responses of Leymus chinensis to light, medium, and heavy grazing intensities in comparison with a grazing exclusion control.ResultsWith light grazing, L. chinensis showed decreased photosynthetic capacity. The low chlorophyll and carotenoid contents constrained light energy transformation and dissipation, and Rubisco activity was also low, restricting the carboxylation efficiency. In addition, the damaged photosynthetic apparatus accumulated reactive oxygen species (ROS). With medium grazing, more energy was used for thermal dissipation, with high carotene content and high non-photochemical quenching, whereas photosynthetic electron transport was lowest. Significantly decreased photosynthesis decreased leaf C contents. Plants decreased the risk caused by ROS through increased energy dissipation. With high grazing intensity, plants changed their strategy to improve survival through photosynthetic compensation. More energy was allocated to photosynthetic electron transport. Though heavy grazing damaged the chloroplast ultrastructure, adjustment of internal mechanisms increased compensatory photosynthesis, and an increased tiller number facilitated regrowth after grazing.ConclusionsOverall, the plants adopted different strategies by adjusting their metabolism and growth in response to their changing environment.

Rehabilitation of indigenous browse plant species following exclosure established on communal grazing lands in South Tigray, Ethiopia, and implication for conservation

BackgroundDespite the wide use of indigenous browse plant species, there is almost no information on the rehabilitation of indigenous browse species following area exclosure (AE) established on communal grazing lands (CGL) in Southern Tigray. The objectives of this study were to assess the rehabilitation of browse plant species following AE establishment on CGL. A total of 61 and 59 plots of 10 × 10 m2 size were laid down at 50-m intervals along parallel line transects at AE and GCL, respectively. Data collected on vegetation attributes were subjected to analysis of t test (unequal variances) using R-software.ResultsThe Shannon diversity index of the browse plant species was 1.25 and 0.81 in AE and CGL, respectively (P < 0.001). The overall population structure of browse plant species in the AE shows a reverse J-shaped population curve and “good” regeneration status, which reveals that the future communities may be sustained. Leaf biomass and basal area of browse plant species were significantly higher in the AE than in CGL (P < 0.001). After exclusion of grazing, AE was found to have positive effects on diversity and aboveground biomass of browse plant species.ConclusionsThe study gives an understanding of the diversity, the pattern of population and regeneration of the browse plant species, which may help in the management and conservation of the species. Our results indicate that grazing exclusion is an effective management strategy to restore browse plant species. We concluded that the establishment of AE had a positive effect on the rehabilitation of browse plant species diversity and improved population structure and regeneration potentials of degraded grazing lands. Long-term monitoring and evaluation systems will be required to gain an informed understanding of the roles played by area exclosures in the rehabilitation and conservation of browse palnt species diversity.

Using mechanical clearing and goat grazing for restoring understorey plant diversity of embankments in the Rhône valley (Southern France)

Consumption by animals remains one of the key points to assess the effectiveness of grazing impacts in woodland for increasing understorey plant diversity. To limit the spread of the brambles and restore understorey plant diversity on an artificial embankment an original system of clearings connected by paths was created by mechanically crushing brambles and allowing them to be grazed by rustic goats. The analysis of the indices of consumption of bramble under GIS has been used to provide an estimation of the volume ingested and an estimation of the effectiveness of the goats. The impacts of three different managements (goat grazing, brush clearing and grazing, clearing and exclusion of grazing) and control without management were then tested during a three-year period. The monitoring of the vegetation on permanent plots provided evidence that goat grazing significantly increased in the short term the species-richness and heterogeneity of herbaceous plants communities, in complement with prior clearing. Thus, the objectives of the managers to open up the area and reduce the bramble cover were achieved, but the prior introduction of goats and the installation of mobile enclosures would be advisable in order to ensure the sustainability of these measures on plant diversity in the long term.

Effects of grazing exclusion on the abundance of functional genes involved in soil nitrogen cycling and nitrogen storage in semiarid grassland

We investigated the effects of grazing exclusion on the abundance of functional genes (nifH, amoA-AOA, amoA-AOB, narG, nirK, nirS, and nosZ) involved in soil nitrogen cycling in soil profiles (0-10, 10-20, 20-40 and 40-60 cm) from a chronosequence of grazing exclusion (0, 7, 18, 27 and 35 years) in the semiarid grasslands of the Loess Plateau. The relationship between abundance of functional genes and soil nitrogen storage was evaluated. The results showed that 35 years exclusion increased the abundance of nifH and amoA-AOB genes by 67.8% and 17.6% compared with the grazed grassland, respectively, and decreased that of nirK genes. The abundance of nifH, narG, and nirS genes in surface soil (0-10 cm) were significantly higher than that in deep soil (20-40 and 40-60 cm), indicating that those genes had surface accumulation effects. Grazing exclusion increased soil nitrogen storage. Soil nitrogen storage in 0-60 cm layer was the highest at 27 years (20.96 mg·hm-2), indicating that 27 years might be the optimum for grazing exclusion. The abundance of nifH, amoA-AOA and amoA-AOB had a significant linear relationship with nitrogen storage, suggesting that microbes harboring these genes played an important role in soil nitrogen accumulation. Total nitrogen, bulk density, and available phosphorus content were the dominant factors affecting the abundance of functional genes involved in soil nitrogen cycling. Our results provided a scientific reference for understanding soil nitrogen cycling and restoration of degraded grassland.

Grazing exclusion promotes grasses functional group dominance via increasing of bud banks in steppe community

To understand the bud banks response to grazing exclusion, we conducted a demographic experiment in long-term grazing exclusion (20 year and 30 year) typical steppe. Results showed that grass functional group constituted the vast majority of the aboveground vegetation and belowground bud bank in all treatments. Long-term grazing exclusion significantly increased total aboveground biomass (2.5 and 2.6 times in 20y and 30y grazing exclusion grasslands, respectively), and decreased total stem density (31% and 37% in 20y and 30y grazing exclusion grasslands, respectively). Grazing exclusion for 20 and 30 years increased grass aboveground biomass respectively by 6.0 and 8.0 times, and decreased grass stem density by 38% and 33%. Grazing exclusion had different effects on belowground bud density of grass and forb functional group. Long-term grazing exclusion significantly increased plant buds and bud bank size (25% and 37% in 20y and 30y grazing exclusion grasslands, respectively), especially for grass functional group (49% and 95% in 20y and 30y grazing exclusion grasslands, respectively), but had no significant effects on forb bud density. Changes of aboveground community were significantly related to changes of belowground bud bank under both grazing and grazing exclusion grasslands. The bud bank density of grass functional group was significantly positive with total (R2 = 0.33, P < 0.05) and grass aboveground biomass (R2 = 0.36, P < 0.01), while negative related with total (R2 = −0.27, P < 0.05) and grass stem density (R2 = −0.22, P < 0.05). Grazed grasslands, 20y and 30y grazing exclusion grasslands all were not meristem limited and had large reserve bud banks, which would completely replace the aboveground stem population during the growing season. These findings indicate that grazing exclusion could not only improve a large bud bank for grassland restoration but also improve the dominance of grass functional group by increasing grass belowground bud banks in typical steppe community. We propose that the belowground bud bank might be a good approach to indicating potential succession direction of aboveground community.

Short-term grazing exclusion improved topsoil conditions and plant characteristics in degraded alpine grasslands

Abstract Grazing exclusion by fencing is one of the most effective practices to recover the degraded alpine grasslands in Tibetan Plateau. In the present study, the effects of 8-year (GE8) and 4-year (GE4) grazing exclusion were studied in comparison with free grazing (FG) in the plant-soil ecosystems of alpine grasslands. Within fencing, improved plant characteristics such as aboveground biomass (AGB), belowground biomass (BGB) and plant total cover developed without grazing and trampling were observed. Also, there were significant improvements of soil organic carbon (SOC), ammonia nitrogen (NH4+-N) and dissolved organic carbon (DOC) concentrations usually in the topsoil (0–30 cm) but a stable C:N ratio with the number of years of grazing exclusion. Fencing enhanced soil main enzyme (invertase, phosphatase, urease and β-glucosidase) activities by providing sufficient substrates for microbial activities. Unexpectedly, GE4 had higher soil invertase, phosphatase, urease and β-glucosidase activities than GE8, which had less plant diversity, richness and higher total cover causing a lowering of soil temperature. Additionally, the results supported the allometric allocation hypothesis for the ABG versus BGB in the grasslands of Tibetan Plateau. Our results indicated that SOC and BGB can be used as indicators of the restoration process of degraded alpine grassland. Cautions should be taken for a long-term fencing in degraded alpine grasslands because of the loss of plant richness, diversity and soil enzyme activities. The present results also suggested that a suitable grazing regime combined with fencing should be focused in the future study of the alpine grasslands. Research results obtained in the present study should, therefore, be helpful to offer a better guidance towards the management practices of the degraded alpine grasslands.