F. Taube

Grassland responses to grazing: effects of grazing intensity and management system in an Inner Mongolian steppe ecosystem

The major aims of this study were, firstly, to analyse the grazing-induced steppe degradation process and, secondly, to identify an efficient and sustainable grazing management system for the widely degraded Inner Mongolian typical steppe ecosystem. From 2005–2008 a grazing experiment was conducted to compare two grazing management systems, the Mixed System (MS) and the Traditional System (TS), along a gradient of seven grazing intensities, i.e. ungrazed (GI0), very-light (GI1), light (GI2), light-moderate (GI3), moderate (GI4), heavy (GI5), and very-heavy (GI6). Each grazing intensity treatment was considered a production unit comprising two adjacent plots, one for hay-making (single-cut system) and one for grazing. Hay-making and grazing alternated annually in the MS, while in the TS the same plots were used either for hay-making or for grazing. Effects of management system, grazing intensity, and year on end-of-season standing biomass (ESSB), aboveground net primary production (ANPP), relative difference in ANPP between 2005 and 2008 (ANPPDiff), relative growth rate (RGR), and sward characteristics (litter accumulation, soil coverage) were analysed. Litter accumulation of production units was affected by grazing intensity (P < 0.001) and decreased from GI0 to GI6 by 83%. Correspondingly, soil coverage decreased (P < 0.001) from GI0 to GI6 by 43%, indicating an increased vulnerability to soil erosion. We found varying compensatory growth responses to grazing intensity among years, probably because of temporal variability in precipitation. The ability of plants to partially compensate for grazing damage was enhanced in years of greater seasonal precipitation. The ANPP of production units was negatively affected by grazing intensity and decreased from GI0 to GI6 by 37, 30, and 55% in 2006 (P < 0.01), 2007 (P < 0.05), and 2008 (P < 0.001), respectively. The effect of management system × grazing intensity interaction on ANPP (P < 0.05) and ANPPDiff (P < 0.05) suggested greater grazing resilience of the MS as compared to the TS at GI3 to GI6.

Short-term management and stocking rate effects of grazing sheep on herbage quality and productivity of Inner Mongolia steppe

Degradation and decreasing productivity increasingly demand sustainable grazing management practices within Inner Mongolian steppe ecosystems. This study focuses on grazing-induced degradation processes over a wide range of stocking rates and aims to identify short-term sensitive indicators and alternative management practices. Short- term effects of 2 grazing management systems (Mixed System and Traditional System) and 7 stocking rates (SR0, SR1.5, SR3, SR4.5, SR6, SR7.5, and SR9 for 0,1.5, 3, 4.5, 6, 7.5, and 9 sheep/ha, respectively) on yielding performance and herbage quality were measured on experimental plots in which moveable exclosures were used on areas chronically grazed by sheep. The experiment was conducted in a typical steppe ecosystem in Inner Mongolia, P. R. China. Results are presented for 2005 and 2006. Sampling time was the main factor affecting yield and quality. Stocking rate also showed considerable effects on yield. HerbagemassdecreasedlinearlyfromSR0toSR9,by85%and82%in2005and2006,respectively.Herbageaccumulation was also affected by stocking rate, and was highest at SR1.5 and clearly reduced at SR9. Grazing effects on relative growth rate indicated grazing tolerance of plants in the short-term, since up to high stocking rates, relative growth rates remained stable. Precipitation also determined plant responses to increasing levels of grazing. The year of higher rainfall generated higher grazing tolerance of plants and higher herbage growth than the drought year. Despite considerable reduction of herbagemass,consistentshort-termresponsesofherbagequalitytograzingin2005and2006werereflectedonlyintermsof crudeproteinandaciddetergentlignin.HerbagecrudeproteincontentwashighestatSR7.5andSR9,whileligninwaslowest at SR7.5 and SR9. Neither productivity nor herbage quality was affected by the management system, suggesting that both systems may be applicable on typical steppe in the short-term.

Differential responses of plant functional trait to grazing between two contrasting dominant C3 and C4 species in a typical steppe of Inner Mongolia, China

Plant functional traits have been widely used to study the linkage between environmental drivers, trade-offs among different functions within a plant, and ecosystem structure and functioning. Here, the whole-plant traits, leaf morphological and physiological traits of two dominant species, Leymus chinensis (C3 perennial rhizome grass) and Cleistogenes squarrosa (C4 perennial bunchgrass), were studied in the Inner Mongolia grassland of China, with a grazing experiment including five stocking rates (0, 3.0, 4.5, 7.5, and 9.0 sheep/ha) in 2008 (wet year) and 2009 (dry year). Our results demonstrated that, for both species, the effects of stocking rate, year, and stocking rate × year on whole-plant traits and leaf morphological and physiological traits were highly significant in most cases. The differential responses of plant trait to variation in precipitation were caused by trait trade-offs between the wet and dry years. L. chinensis adopted the high N content and net photosynthetic rate (Pn) in the wet year but both the low N content and Pn in the dry year under grazed conditions. The trait trade-offs of C. squarrosa were characterized by high specific leaf area (SLA) and Pn in the dry year vs. low SLA and Pn in the wet year. Our findings also indicate that C. squarrosa is more resistant to grazing than L. chinensis in terms of avoidance and tolerance traits, particularly under heavy grazing pressure and in the dry year.

N balance and cycling of Inner Mongolia typical steppe: a comprehensive case study of grazing effects

Increasing grazing pressure and climate change affect nitrogen (N) dynamics of grassland ecosystems in the Eurasian steppe belt with unclear consequences for future delivery of essential services such as forage production, C sequestration, and diversity conservation. The identification of key processes responsive to grazing is crucial to optimize grassland management. In this comprehensive case study of a Chinese typical steppe, we present an in-depth analysis of grazing effects on N dynamics, including the balance of N gains and losses, and N cycling. N pools and fluxes were simultaneously quantified on three grassland sites of different long-term grazing intensities. Dust deposition, wind erosion, and wet deposition were the predominant but most variable processes contributing to N losses and gains. Heavy grazing increased the risk of N losses by wind erosion. Hay-making and sheep excrement export to folds during nighttime keeping were important pathways of N losses from grassland sites. Compared to the...

Vertebrate herbivore‐induced changes in plants and soils: linkages to ecosystem functioning in a semi‐arid steppe

Summary 1. Large grazing herbivores have been reported to determine the structure and function of grassland ecosystems. However, the ecological linkages between structure and functioning components have yet been thoroughly explored. 2. Here, we test the hypothesis of the impact of grazing on soil nematode community (e.g. structure and composition) and linkages to ecosystem functioning (e.g. soil N mineralization and ANPP) via changes in pathways of plant community, soil nutrients and soil environment using a field experiment maintained for 5 years with seven levels of grazing intensity in the Inner Mongolian grassland. 3. A structural equation model (SEM) with nematode abundances as response variables showed that plant-feeding and fungal-feeding nematodes were driven by changes in the plant community, and bacterial-feeding nematodes were affected by soil abiotic nutrients and environment, while omnivorous + carnivorous nematodes were altered by soil environment and bacterial-feeding nematodes. This indicates that the top-down control by grazing leads to bottom-up control in the soil food web. 4. We found that grazing affected the ecosystem functioning via different pathways. Grazing effects soil N mineralization by changing plant community, soil nutrients, soil environment and nematodes community structure, while it affects ANPP by altering soil N mineralization and soil environment. 5. Our findings could provide a better understanding of the responses of plants and soils to grazing and the linkages between structure and functioning of above-ground and belowground in the semi-arid steppe.

Effects of grazing management system on plant community structure and functioning in a semiarid steppe: scaling from species to community

Under the aim of searching for a more sustainable grazing management system, a mixed management system (grazing and haymaking alternate annually) was proposed and tested against traditional management system (used consistently either for grazing or haymaking) in the semiarid grassland of Inner Mongolia with a field manipulation experiment. The responses of aboveground biomass to the two grazing management systems were examined across different levels of organization (i.e., species, plant functional group, and community) and in five consecutive years from 2005 to 2009. The effects of the two systems on seed production potential of four dominant species (Leymus chinensis, Stipa grandis, Agropyron cristatum, Cleistogenes squarrosa) were also investigated. Our results demonstrate that, in the traditional system, aboveground biomass production across all the levels of organization was reduced by grazing. In mixed system, however, no significantly negative relationship between the biomass response and stocking rate was detected at all organization levels. Precipitation fluctuation had strong influence on biomass responses, and compared to the traditional system the slope of the biomass-precipitation relationship tends to be higher in the mixed system. This effect might be attributed to the more positive response of L. chinensis and A. cristatum to increase in precipitation. In the traditional system, both the ratio and the density of reproductive tillers of the grazing subplots were significantly reduced compared to the haymaking or ungrazed control plots. In the mixed system, there was no significant difference between the haymaking subplots and the ungrazed control plots, regardless of the grazing pressures imposed on the haymaking subplots in the previous growing season. Our findings suggest that the mixed system mitigates the sheep grazing-induced species shift and it tends to be more responsive to increasing precipitation as compared to the traditional system. Therefore, replacement of the traditional grazing strategy with the mixed system could provide an important contribution to sustainable land-use of the Inner Mongolia grasslands.

Effects of Grazing Intensity and Environmental Factors on Species Composition and Diversity in Typical Steppe of Inner Mongolia, China

In the present study, we aim to analyze the effect of grazing, precipitation and temperature on plant species dynamics in the typical steppe of Inner Mongolia, P.R. China. By uncoupling biotic and abiotic factors, we provide essential information on the main drivers determining species composition and species diversity. Effects of grazing by sheep were studied in a controlled experiment along a gradient of seven grazing intensities (from ungrazed to very heavily grazed) during six consecutive years (2005–2010). The results show that plant species composition and diversity varied among years but were little affected by grazing intensity, since the experimental years were much dryer than the long term average, the abiotic constraints may have overridden any grazing effect. Among-year differences were predominantly determined by the abiotic factors of precipitation and temperature. Most of the variation in species dynamics and coexistence between C3 and C4 species was explained by seasonal weather conditions, i.e. precipitation and temperature regime during the early-season (March-June) were most important in determining vegetation dynamics. The dominant C3 species Stipa grandis was highly competitive in March-June, when the temperature levels were low and rainfall level was high. In contrast, the most common C4 species Cleistogenes squarrosa benefited from high early-season temperature levels and low early-season rainfall. However, biomass of Stipa grandis was positively correlated with temperature in March, when effective mean temperature ranges from 0 to 5°C and thus promotes vernalization and vegetative sprouting. Our results suggest that, over a six-year term, it is temporal variability in precipitation and temperature rather than grazing that determines vegetation dynamics and species co-existence of grazed steppe ecosystems. Furthermore, our data support that the variability in the biomass of dominant species, rather than diversity, determine ecosystem functioning. The present study provides fundamental knowledge on the complex interaction of grazing – vegetation – climate.

Land use and drought interactively affect interspecific competition and species diversity at the local scale in a semiarid steppe ecosystem

Few studies have considered interactive effects of grazing and drought on species composition and the relative contribution of species to total biomass, although it is important to understand the short-term dynamics and community succession in grazed ecosystems. We monitored species diversity and relative biomass contribution at one site protected from grazing since 1979 (UG79), and at winter grazing (WG) and heavily grazed (HG) sites. Continuous heavy grazing resulted in lower plant height and more but small individuals (tillers or stolons). Drought significantly reduced total plant density on all sites. Grazing affected species diversity more than drought. Species richness at site UG79 was significantly higher than at sites WG and HG, while drought only tended to reduce species diversity. Drought stress and grazing disturbance interactively controlled species competition and functional groups. Both perennial grasses and forbs had greater contribution to total biomass at site UG79, and perennial grasses contributed more than 97% of total biomass at site WG. The contribution to total biomass of annual forbs and semi-shrubs significantly increased at site HG after two dry years. The significant decrease in Potentilla acaulis and a substantial increase in annual species at this site indicate that the perennial vegetation of this ecosystem is in great danger of extinction under conditions of prolonged drought.

Spatial distribution of livestock concentration areas and soil nutrients in pastures

Livestock concentration areas can be significant point sources of nutrient pollution. Our objective was to determine the spatial distribution of livestock concentration areas in pastures at the farm scale, along with the distribution of soil nutrients at the individual livestock concentration area scale. We georeferenced and measured the size of all livestock concentration areas in cool-season grass-legume pastures on five farms (four grazing dairies and a beef cattle farm) in Maryland, Pennsylvania, and New York during two years. Soil of selected concentration areas on each of the farms was sampled to 0 to 5 and 0 to 15 cm (0 to 2 and 0 to 6 in) depths to compare nutrient levels with paired unaffected areas of the pasture. On one farm, we sampled two concentration areas more densely (20 to 25 samples, 0 to 5 cm depth along each of five 100 m [328 ft] transects) to measure spatial distribution of soil nutrients. The transects were arranged radially to encompass variation both up and downslope. We installed runoff plots at three locations on and near the two concentration areas to measure nutrients in surface water runoff from simulated rainfall. On the five farms, concentration areas occurred most frequently at paddock gates (38% of sites). Although fewer in number, concentration areas at feeding sites were often larger than those at gates or other locations and accounted for most (48%) of the area affected by livestock congregation. Most concentration areas were small (median area 100 m2 [1,076 ft2]), isolated (median distance, 61 m [200 ft] from a water body), and surrounded by vegetation. Intensive sampling on one farm showed that soil within 20 to 40 m (66 to 132 ft) of concentration areas was enriched in phosphorus, which contributed to higher phosphorus concentration in the runoff from simulated rainfall compared with the rest of the pasture. Pastures used as holding and feeding areas with highly elevated soil nutrients and no surrounding vegetation to filter runoff represented a direct threat to surface water quality. Many concentration areas, however, were surrounded by vegetation, which would mitigate this risk.

Nitrogen, phosphorus and potassium nutritional status of semiarid steppe grassland in Inner Mongolia

In grazed semiarid steppe ecosystems, much attention has been paid to aspects of growth limitation by water. So far, potential limitation of primary production by plant nutrients was rarely considered. This knowledge is essential for identification of sustainable land-use practices in these large and important ecosystems on the background of over-exploitation and climate change. In the present study plant nutrient concentrations and ratios were investigated with factorial additions of water and N fertilizer at two sites with contrasting soil nutrient availability. Combined analysis of nutrient concentrations, contents, biomass production, and plant N:P ratios consistently confirmed primary growth limitation by water and a strong N limitation when sufficient amounts of water were supplied. P limitation only occurred at the site with low P availability when in addition to the natural supply, water and N fertilizer were given. According to reported thresholds of N:K and K:P ratios, K was not limiting in any plot. The observed nutritional patterns in the plant community were related to the dynamics of species composition and their specific nutrient status. Stipa grandis had the highest N:P ratio whereas Artemisia frigida showed lowest N:P. These nutrient characteristics were related to growth strategies of dominant species. Accordingly, the relative biomass contribution of S. grandis and A. frigida strongly affected the nutrient status of the plant community. Plant N:P ratios indicate the relative limitation by N or P in the semiarid grasslands under sufficient water supply, but other methods of nutritional diagnosis should be used when plant N:P ratios remain below critical values.