Long-term grazing improved soil chemical properties and benefited community traits under climatic influence in an alpine typical steppe.

Grazing and climate change both contribute to diversity loss and productivity fluctuations. Sensitive climate conditions and long-term grazing activities have a profound influence on community change, particularly in high-altitude mountain grassland ecosystems. However, knowledge about the role of long-term continuous grazing management on diversity, productivity and the regulation mechanisms in fragile grassland ecosystems is still rudimentary. We conducted a long-term grazing experiment on an alpine typical steppe in the Qilian Mountains to assess effects of grazing intensity on soil, diversity, productivity and the regulation mechanisms. Plants and soil were sampled along grazing gradients at different distances from the pasture entrance (0, 0.3, 0.6, 0.9, 1.2 and 1.5 km) under the non-growing (WP) and the growing season grazing pasture (SAP). The results revealed that community diversity and biomass did not change significantly on a time scale, while the concentration of soil organic carbon and total phosphorus increased significantly. Heavy grazing (0-0.3 km) decreased community diversity and biomass. Grazing increased soil chemical properties in heavy grazed areas of WP, while the opposite was recorded in SAP. Soil chemical properties explained the largest variances in community diversity and community biomass. The prediction model indicates that grazing in WP mainly affects community diversity through soil chemical properties, and promotes a positive correlation between community diversity and community biomass; in SAP, the direct effect of grazing gradients on community diversity and biomass is the main pathway, but not eliminating the single positive relationship between diversity and biomass, which means that diversity can still be used as a potential resource to promote productivity improvement. Therefore, we should focus on the regulation of soil chemical properties in WP, such as the health and quality of soil, strengthening its ability to store water, sequester carbon and increase nutrients; focus on the management of livestock in SAP, including providing fertilizer and sowing to increase diversity and production in heavily grazed regions and reducing grazing pressure through regional rotational grazing. Ultimately, we call for strengthening the stability and sustainability of ecosystems through targeted and active human intervention in ecologically sensitive areas to cope with future grazing pressures and climate disturbances.

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

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

The effects of herbivore aggregations at water sources on savanna plants differ across soil and climate gradients.

Water sources in arid and semiarid ecosystems support humans, wildlife, and domestic animals, forming nodes of activity that sculpt surrounding plant communities and impact critical grazing and soil systems. However, global aridification and changing surface water supply threaten to disrupt these water resources, with strong implications for conservation and management of these ecosystems. To understand how effects of herbivore aggregation at water impact plant communities across contexts, we measured herbivore activity, plant height, cover (trees, grasses, forbs, and bare ground), diversity, and composition at 17 paired water sources and matrix sites across a range of abiotic factors in a semiarid savanna in Kenya. The effects of proximity to surface water and herbivore aggregation on plant communities varied substantially depending on soil and rainfall. In arid areas with nutrient-poor sandy soils, forb and tree cover were 50% lower at water sources compared to neighboring matrix sites, bare ground was 20% higher, species richness was 15% lower, and a single globally important grazing grass (Cynodon dactylon) dominated 60% of transects. However, in mesic areas with nutrient-rich finely textured soils, species richness was 25% higher, despite a 40% increase in bare ground, concurrent with the decline of a dominant tall grass (Themeda triandra) and increase in C. dactylon and other grass species near water sources. Recent rainfall was important for grasses; cover was higher relative to matrix sites only during wet periods, a potential indication of compensatory grazing. These findings suggest that effects of herbivore aggregation on vegetation diversity and composition will vary in magnitude, and in some cases direction, depending on other factors at the site. Where moisture and nutrient resources are high and promote the dominance of few plant species, herbivore aggregations may maintain diversity by promoting grazing lawns and increasing nondominant species cover. However, in arid conditions and sites with low nutrient availability, diversity can be substantially reduced by these aggregations. Our results highlight the importance of considering abiotic conditions when managing for effects of herbivore aggregations near water. This will be particularly important for future managers in light of growing global aridification and surface water changes.

The impact of grazing on biodiversity and forest succession in the Brazilian dry forest region is constrained by non-equilibrium dynamics.

The impacts of grazing on rangelands have historically been studied within the framework of the equilibrium model, which predicts significant impacts of grazing on ecosystems. However, in recent decades, studies have observed a non-equilibrium pattern, suggesting that abiotic factors play a primary role compared to grazing. These studies are primarily focused on rangelands, despite animal husbandry occurring in other biomes, such as seasonally dry tropical forests. Our study examines the influence of goat grazing on biodiversity and forest succession in the Brazilian dry forest (Caatinga). Considering its high interannual precipitation variability, we hypothesize a response that aligns with the non-equilibrium paradigm. We established a gradient of grazing intensity and history in areas at different stages of vegetation succession. A survey of tree - shrub and herbaceous species was conducted at each site and the biomass of both strata was quantified. Linear mixed models and Permanova were employed to assess differences in richness, composition, structure, and biomass among the areas. Our results suggest that grazing (history and intensity) and forest fallow age did not affect species richness, but only species composition. Low and high grazing intensity drive ecosystems toward similar compositions, which align with the non-equilibrium model predictions. Biomass in the herbaceous layer remained unaffected by grazing history, intensity, or forest fallow age, whereas woody biomass was influenced by grazing intensity in older forest fallows. Although trees in low-intensity grazing sites were significantly taller compared to those in other levels, overall, grazing did not disrupt the natural succession process. Older forest fallows exhibited greater diversity and higher basal area compared to new forest fallows, irrespective of grazing intensity. Our findings suggest that: a) grazing has minimal effects on biodiversity and biomass due to non-equilibrium dynamics, and b) with appropriate management, grazing can coexist with the conservation of the Caatinga.

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Grazing disturbance is one of the ways to influence plant traits, and plant leaf traits actually reflect the adaptability of plants to the environment. In this study, taking Stipa krylovii steppe under different grazing intensities in Hulunbuir as research area, the relationships of leaf traits and the variation of plant traits among plant life-form functional groups was investigated. Results showed that plant traits with different life-forms had no significant difference in S. krylovii steppe. However, the relationships between plant traits were strongly correlated. The leaf phosphorus content (LPC) and the ratio of nitrogen and phosphorus (N/P) in the heavy grazing treatment had significant difference from those in the moderate grazing and the light grazing treatments. For different life-form functional groups, grazing disturbance had significant effect on LPC and N/P in the perennial forbs, indicating the perennial forbs were sensitive to grazing, and the plant nutrient utilization strategy was changed by heavy grazing. It was suggested that reasonable grazing could improve the nutrient traits of plants and restrain the degradation in S. krylovii steppe.