Effects of Grazing Intensity and Non-local Delay on Vegetation Patterns in Semi-Arid Areas

The research investigating the effects of different grazing intensities on greenhouse gas emissions within typical steppe ecosystems aids in formulating effective management strategies for these ecosystems. Furthermore, it plays a vital role in developing approaches to reduce greenhouse gas emissions. To investigate the effects of different grazing intensities on greenhouse gas emissions in typical steppe ecosystems, four treatments were established： no grazing （CK）, light grazing （LG）, moderate grazing, and heavy grazing （HG）. The greenhouse gas emission fluxes were measured using the static dark chamber infrared spectroscopy method. The results showed that： ① Significant seasonal changes exist in ecosystem respiration and CH4 emission flux. Compared with the CK treatment, the HG treatment significantly reduced the total ecosystem respiration emission by 31.43%, while the total CH4 emission was not significant among all treatments. Compared with the LG treatment, the HG treatment significantly reduced the total N2O emission by 94.03% （P <0.05）. ② A significant linear correlation exists between the values of ecosystem respiration pairs and soil temperature （P <0.001）, and there was a significant linear relationship between ecosystem respiration and soil water content under the CK and HG treatments （P <0.05）, mainly related to soil temperature. Except for the LG treatment, the CH4 emission fluxes of the other treatments showed a quadratic correlation with soil temperature, and the CH4 emission fluxes of all treatments were linearly correlated with soil water content and were mainly correlated with soil water content （P <0.01）. A significant linear correlation exists between N2O emission flux and soil temperature in the LG treatment （P <0.05）. ③ Compared with that in CK, the HG treatment significantly decreased soil water content, soil total carbon, soil total nitrogen, vegetation aboveground biomass, and litter, and significantly increased soil temperature and soil bulk density （P <0.05）. Heavy grazing reduced the total greenhouse gas emissions and total vegetation biomass. Although it reduced the carbon emissions of the grassland ecosystem, it was not conducive to maintaining the ecological balance of grassland. This study can provide reference data and theoretical support for evaluating the effects of grazing on the source-sink functions of grassland ecosystems.

The effect of grazing intensity on pattern dynamics of the vegetation system

Vegetation patterns can reflect the spatial distribution of vegetation in both space and time. In semi-arid regions, the absorption of water by vegetation is a nonlocal process meaning that its roots can absorb water from themselves throughout the region. However, the effects of the nonlocal interaction on the distribution of vegetation pattern are not clear. In this paper, a dynamical model of vegetation pattern with nonlocal delay is investigated. Through the analysis of Turing instability, we obtain the conditions for the generation of stationary patterns. By numerical simulations, various spatial distribution of vegetation in semi-arid areas are qualitatively depicted. It is found that the stripe intervals in pattern decrease with the increase in the intensity of nonlocal delay effect, and then a dot-line mixed pattern appears, which eventually evolves into a high-density dot pattern. This indicates that vegetation has evolved from low-density stripe distribution to high-density point distribution. The results show that the nonlocal delay effect enhances vegetation biomass. Therefore, we can take measures to increase the intensity of nonlocal delay effect to increase vegetation density, which theoretically provides new guidance for vegetation protection and desertification control.

The vegetation pattern generated by aeolian sand movements is a typical type of vegetation patterns in arid and semi-arid areas. This paper presents a vegetation-sand model with nonlocal interaction characterized by an integral term with a kernel function. The instability of the Turing pattern was analyzed and the conditions of stable pattern occurrence were obtained. At the same time, the multiple scales method was applied to obtain the amplitude equations at the critical value of Turing bifurcation. The spatial distributions of vegetation under different delays were obtained by numerical simulation. The results revealed that the vegetation biomass increased as the interaction intensity decreased or as the nonlocal interaction distance increased. We demonstrated that the nonlocal interaction between vegetation and sand is a crucial mechanism for forming vegetation patterns, which provides a theoretical basis for preserving and restoring vegetation.

Positive effects of low grazing intensity on East African bee assemblages mediated by increases in floral resources

Effects of grazing intensity on soil thermal properties and heat flux under Leymus chinensis and Stipa grandis vegetation in Inner Mongolia, China

As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities (fenced, mild grazing and severe grazing) across a climatic aridity gradient (semi-arid, arid, very arid and intensively arid zones) in the Inner Mongolia Steppe, northern China during 2012–2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number, seed weight and seed yield were lower in the low precipitation year (2013) than in the high precipitation year (2012). As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.

Although grazing is the primary land use in the savanna lowland of southern Kenya, the effects of grazing on soil carbon dioxide flux (RS) remain unclear. A 12-month study was conducted from January to December 2020 on the effects of six grazing intensities sites (overgrazed (OG), heavily grazed (HG), moderately grazed (MG), moderately to lightly grazed (M-LG), lightly grazed (LG) and no grazing (NG)) on RS on. A camera trap was used to monitor the total number of animals at each site, indicating the grazing intensity. Weekly measurements of RS were taken using static greenhouse gas chambers along with simultaneous measurements of soil temperature (TS) and volumetric soil water content (WS) (depth of 5 cm). Mean RS at HG, MG, M-LG and LG sites was approximately 15–25% higher than at NG and OG sites (p < 0.001). Mean WS increased with decrease in grazing especially in the dry season, while TS increased with increase in grazing. We observed bimodal temporal variation in RS and WS due to two wet seasons in the year. Thus, variation in RS across the study period followed the changes in WS rather than those in TS. Mean values of RS in the wet seasons were significantly higher (>45%) than those in the dry seasons, and WS accounted for 71% of the temporal variability in RS (p < 0.05). In addition, the enhanced vegetation index (EVI, interpreted as a proxy for vegetation cover) explained 60% of the variance of RS, and WS and EVI together explained 75%. EVI showed a negative relationship (p < 0.05) with animal intensity, indicating that more grazing reduced vegetation cover and, consequently, soil organic carbon and biomass. Soil bulk density was lower at less grazed sites. While RS variability was unaffected by total nitrogen content, pH, and texture, correspondence analysis demonstrated that the main factors influencing RS dynamics across the year under different grazing intensities were WS and vegetation cover. Our results contribute to closing the existing knowledge gap regarding the effects of grazing intensity on RS in East Africa savannas. Therefore, this information is of great importance in understanding carbon cycling in savanna grassland, as well as the identification of the potential consequences of increasing land pressure caused by rising livestock numbers, and will assist in the development of climate-smart livestock management in East Africa.

The effect of grazing intensity on plant diversity has been widely studied. In this study, desert steppes with different grazing intensities (no grazing (CK), light grazing (LG), moderate grazing (MG), heavy grazing (HG), and extremely heavy grazing (EG)) in Inner Mongolia were selected to study the changes in species diversity at different spatial scales (α, β, and γ diversity) and the α diversity of different plant groups (dominant species, common species, and rare species).The results showed that the α, β, and γ diversity first decreased and then increased with increasing grazing intensity, and β diversity was observed to be the most sensitive index to the grazing intensity. Grazing had the greatest impact on the α diversity of rare species and the least impact on the α diversity of common species. Therefore, rare species are of great significance for the maintenance and assessment of biodiversity. We concluded that grazing leads to a sensitive response of β diversity, and this sensitive phenomenon is mainly affected by rare species. The results could provide scientific bases for the protection of plant diversity and sustainable grazing in desert steppes.

The effects of different grazing intensities on in situ methane flux and the structure and diversity of the methanotrophic community are measured in the typical grassland of Inner Mongolia. Four grazing intensity sites founded in 1989, control (CK), low-intensity grazing (LG), middle-intensity grazing (MG) and heavy-intensity grazing (HG), were selected. Group-specific PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of 16S rRNA genes for the type I and type II methanotrophs was used to characterize the composition of the methanotrophic community. DGGE patterns were further analyzed using the method of the Shannon-wiener index H and non-metric multi-dimensional scaling (MDS). The results showed that there were no significant differences in methane flux among different sites, yet methanotrophic communities showed significant differences. MDS analysis showed that type I methanotroph community composition at the CK site were significantly different from the three other sites. For type II methanotrophic community composition, it was similar between CK and HG site, and between LG and MG site, while that at the former two sites were significantly different from latter two ones. Additionally Shannon indices of type II methanotrophs were higher at the LG and MG sites than two other sites. Though grazing intensities had an impact on the structure of the methanotrophic community, management-induced changes in the structure of methanotrophic community did not reflect methane consumption capacity across sites. These results suggest that methane consumption is a complex process in soil, and we should be cautious when speculating on the change of methane consumption rates based on a change of methanotrophic community structure.

Grazing plays a critical role in the sustainable development of grassland. It has been convinced that grazing affects grassland productivity, however, researches on the relationship between grazing intensity and grassland soil quality remain inadequate in the alpine environment. This study compared ten soil quality indexes (SQIs) to quantitative assess the effect of different grazing intensities [no grazing (NG); light grazing (LG); moderate grazing (MG); heavy grazing (HG)] on the soil quality of alpine meadow in the 0–10 cm and 10–20 cm soil layers. Principal component analysis (PCA) and minimum data set (MDS) were applied to indicator selection and weight assignment. The fitting relationship and correlation between SQI-TDS and SQI-MDSs and the sensitivity index (SI) of ten SQIs were used to select the optimal SQI method. Our results showed that compared with NG and LG, HG and MG significantly decreased soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and cation exchange capacity (CEC) (p < 0.05), whereas increased bulk density (BD) and pH. Besides, TN, TP, TK, SOM, Sand content, soil phosphatase activity (PHO), soil sucrase activity (SUC), and soil catalase activity (CAT) could well replace the TDS method to evaluate soil quality. The SQI calculated by the MDS4 with the non-linear scoring method (SQI-NL-MDS4) had the best performance in soil quality evaluation among ten SQIs. Compared with NG and LG, HG had a stronger negative effect on alpine meadow soil quality, especially in the 0–10 cm soil layer, which potentially aggravated leading to aggravating grassland degradation. We propose that reasonable grazing intensity management should be advocated to maintain the sustainable development of alpine meadow productivity.

Background Herbivory and extreme soils are drivers of plant evolution. Adaptation to extreme soils often implies substrate-specific traits, and resistance to herbivory involves tolerance or avoidance mechanisms. However, little research has been done on the effect of grazing on plant communities rich in edaphic endemics growing on extreme soils. A widespread study case is gypsum drylands, where livestock grazing often prevails. Despite their limiting conditions, gypsum soils host a unique and highly specialised flora, identified as a conservation priority. Methods We evaluated the effect of different grazing intensities on the assembly of perennial plant communities growing on gypsum soils. We considered the contribution of species gypsum affinity and key functional traits of species such as traits related to gypsum specialisation (leaf S accumulation) or traits related to plant tolerance to herbivory such as leaf C and N concentrations. The effect of grazing intensity on plant community indices (i.e., richness, diversity, community weighted-means (CWM) and functional diversity (FD) indices for each trait) were modelled using Generalised Linear Mixed Models (GLMM). We analysed the relative contribution of interspecific trait variation and intraspecific trait variation (ITV) in shifts of community index values. Results Livestock grazing may benefit gypsum plant specialists during community assembly, as species with high gypsum affinity, and high leaf S contents, were more likely to assemble in the most grazed plots. Grazing also promoted species with traits related to herbivory tolerance, as species with a rapid-growth strategy (high leaf N, low leaf C) were promoted under high grazing conditions. Species that ultimately formed gypsum plant communities had sufficient functional variability among individuals to cope with different grazing intensities, as intraspecific variability was the main component of species assembly for CWM values. Conclusions The positive effects of grazing on plant communities in gypsum soils indicate that livestock may be a key tool for the conservation of these edaphic endemics.

BackgroundForage nutritive value analysis is an essential indicator of rangeland status regarding degradation and livestock nutrient demand. Thus, it is used to maintain healthy and sustainable rangelands that can provide the livestock with sufficient quantity and quality of forage. This study is conducted with the aim of investigating the effects of grazing intensity combined with seasonal variation on the nutritive values of dominant grass species in the Teltele rangeland.MethodsThe studied area is classified into no-grazed, moderately grazed, and overgrazed plots based on the estimated potential carrying capacity. Sampling data is collected during both rainy and dry seasons. The collected forage samples are analyzed for concentrations of crude protein (CP), acid detergent organic fiber (ADF), neutral detergent fiber (NDF), acid detergent lignin (ADL), ash, dry matter digestibility (DMD), potential dry matter intake (DMI), and relative feed/forage value (RFV).ResultsThe results show significant (P < 0.05) effects of both grazing intensity and season to grazing intensity interactions on all forage nutrient content concentrations across all grass species both within and between treatments. The recorded CP concentrations of all grass species are high in the overgrazed site and low at the no-grazed site, while the fiber concentration is high in NG and low in OG. RFV data also varies greatly, with high value recorded in OG in the rainy season and low value found in NG mainly during the dry season. As a result, it is recommended that moderate grazing should be practiced on the study site to maintain the quality and quantity of forage and to manage it in a sustainable manner.

Grazing, as one of the most important methods of utilizing natural grasslands, can significantly impact the accumulation and stabilization of soil organic carbon within grassland ecosystems. Soil microbial necromass carbon (MNC), including fungal necromass carbon (FNC) and bacterial necromass carbon (BNC), is an important source of soil organic carbon (SOC) and plays a critical role in the formation and stabilization of SOC. However, the effects of grazing intensity on soil MNC and its underlying drivers remain unclear. We investigated differences in soil MNC, FNC, BNC, plant and soil factors following a grazing experiment with four grazing intensities (control, 0 sheep units ha-1a-1; light grazing, 0.91 sheep units ha-1a-1; moderate grazing, 1.82 sheep units ha-1a-1; heavy grazing, 2.71 sheep units ha-1a-1) in the Stipa breviflora desert steppe of Inner Mongolia, China. The main objective was to explore the effects of different grazing intensities and soil depths on soil MNC and its contribution to soil organic carbon. Compared with the control, light grazing significantly increased MNC, FNC, and BNC by 10.55%, 10.59%, and 10.48%, respectively, in the 0-30cm soil layer, whereas heavy grazing significantly decreased MNC and FNC by 9.26% and 10.94%, respectively. Compared with the 0-10cm soil layer, MNC and BNC in the 20-30cm soil layer significantly decreased by 6.45% and 16.24%, respectively. FNC had consistently greater contributions to SOC than did BNC in desert steppe soils. Soil nitrogen associated nutrients (soil total nitrogen, ammonium nitrogen, and microbial biomass nitrogen) and phosphorus associated nutrients (soil total phosphorus and available phosphorus) were direct drivers of MNC and FNC accumulation, while phosphorus associated nutrients (soil total phosphorus and available phosphorus) were the main drivers of BNC accumulation. This study highlights that light grazing can increase soil MNC accumulation, potentially contributing to organic carbon sequestration in desert steppe ecosystems. The grazing-induced decrease in soil phosphorus is a key factor regulating soil MNC, FNC and BNC in the desert steppe, while the decrease in soil nitrogen is the main driver of MNC and FNC. These findings provide a theoretical basis for optimizing grazing management to enhance soil organic carbon storage in arid grassland ecosystems.

Three experiments (2a, 2b and 2c) were carried out to examine the effects of different grazing intensities imposed during spring on subsequent herbage composition and milk production measured in summer.Increased intensity of grazing imposed during spring (including the period of reproductive development in ryegrasses) produced swards in early summer with lower pre‐grazing herbage masses, which contained higher concentrations of green leaf, clover and digestible nutrients, but lower concentrations of grass stem and senescent material.In the first and second experiment cows were given a common daily allowance of total herbage dry matter (DM). The cows grazing on low‐mass swards in early summer produced larger daily yields of milk, fat and protein than those grazing on the high‐mass swards.In the third experiment, cows were given a common daily allowance of green leaf DM from three swards which differed in pre‐grazing herbage mass and in herbage composition. The allowances of total DM required differed widely between the treatments. There were no significant differences in milk yields between the swards despite the large differences in herbage composition.The practical implications of these results are discussed.