Heavy Grazing Site Research Articles

Vegetation diversity and composition in relation to different grazing intensity levels in an arid environment in Jordan

Grazing practices fundamentally shape plant community composition and biodiversity worldwide, more importantly in water-limited environments. This study aimed to investigate plant community composition, species distribution of occurrence and diversity indices in an arid rangeland under different grazing intensities. The quadrat method was used to select 90 × 1 m2 quadrats in heavy-grazing, light-grazing and ungrazed sites. Plant species frequency, relative frequency, abundance, relative abundance and density, as well as species richness, evenness, Shannon diversity index and Simpson’s diversity index were calculated. A total of 46 plant species belonging to 17 families were recorded. The Asteraceæ family was represented with the highest frequency (28%). Overall in the study area, around 95%, 70% and 40% of recorded plant families existed in light-grazing, ungrazed and heavy-grazing sites, respectively. The species richness of identified plants in light-grazing and ungrazed sites was 300% and 200% greater, respectively, than in the heavy-grazing sites. Around 85% of existing plants in heavy-grazing sites were therophyte plants. The species frequency, abundance, density and diversity indices were higher in light-grazing sites compared to those under heavy grazing, which indicates a more diverse, heterogenous and balanced plant community in the light-grazing site. Plant communities in light-grazing and ungrazed sites were similar, except for higher species frequency, density and evenness in light-grazing sites. This suggests that light-grazing intensities in the arid rangelands of Jordan enhance plant diversity more than grazing exclusion, which encourages decision-makers and environmentalists to implement regulations prohibiting intensive grazing in the arid rangelands of Jordan.

Light grazing reduces gaseous nitrogen emissions from temperate grassland soils during freeze‒thaw cycles: An intact core incubation study

Livestock grazing and soil freeze‒thaw cycles (FTCs) can affect the biogeochemical processes of nitrogen (N) and gaseous N (N2O, NO, and N2) emissions from grassland soils. However, the effect of grazing intensity on soil gaseous N emissions during FTCs and the underlying mechanisms are not clearly understood. In this intact core incubation study, soil gaseous N emissions during two FTCs were simultaneously quantified from temperate grasslands that included grazing exclusion (GE), light grazing (LG), and heavy grazing (HG) in Inner Mongolia. Additionally, the abundance of N cycle-related functional genes and the main soil characteristics were determined to better understand the drivers of gaseous N emissions. The results showed that N2 emissions dominate the gaseous N loss from all investigated soils during FTCs, with cumulative N2 exceeding NO and N2O emissions by factors of 47–135 and 71–161, respectively. Increased soil moisture during thawing promoted N2 and N2O emissions from all three sites, except for N2O at the LG site. However, no obvious NO emission peak was observed from all investigated soils during FTCs. Soil C and N availability and aeration changed by grazing regulated soil N2O fluxes, while the abundances of key functional genes generally did not show significant correlations with gaseous N emissions. Moreover, compared to the GE and HG sites, LG substantially decreased the soil N2O and total gaseous N emissions during FTCs, suggesting that light grazing rather than long-term grazing exclusion could be a promising measure to reduce gaseous N losses during spring thaw. Our results highlighted the importance of the simultaneous determination of all kinds of gaseous N emissions during FTCs for closing the ecosystem N balance and developing appropriate strategies for grassland management.

The Role of Plant Functional Diversity in Regulating Soil Organic Carbon Stocks under Different Grazing Intensities in Temperate Grassland, China

Grazing is very common in the grassland ecosystem, and it has a significant impact on the C stocks and cycle. One of the most important drivers of soil C stocks is functional diversity. However, limited studies have attempted to explore the effects of functional diversity on soil C stocks associated with grazing disturbance. This study was carried out in Hulunbeier grassland, Inner Mongolia, and four grazing intensities (no grazing (NG), light grazing (LG), moderate grazing (MG), and heavy grazing (HG)) were identified. The plant functional traits and important soil properties under different grazing intensities were measured. Functional identity and diversity were calculated based on the measured functional traits. The impacts of functional identity and diversity on soil organic carbon stocks (SOCstocks) were analyzed using a multi-model inference (MMI) approach. Our study showed that the functional diversity effect on soil C stocks varies depending on grazing intensity. We identified that functional richness has a significant impact on SOCstocks in NG. The community weighted mean of leaf area became the best predictor of SOCstocks in LG. As grazing intensified, functional divergence best explained SOCstocks in moderate and heavy grazing sites, and their relationship was positive. The major outcomes of this research could shed light on the mechanics of soil carbon storage.

Grazing altered soil aggregates, nutrients and enzyme activities in a Stipa kirschnii steppe of Inner Mongolia

Grasslands are a major biome on Earth, and their soils play a dominant role in the overall ecosystem functions and dynamics. Though the majority of global grasslands are used for grazing, the impact of grazing on soil structure and soil quality remains unclear due to large variations among grasslands. In this study, we assessed soil nutrient content, enzyme activities and soil aggregates at 0–30 cm depth under different grazing intensities, including a treatment of grazing exclusion. Heavy grazing reduced content of soil nitrogen, potassium, and soil urease and sucrase activities. While grazing increased the mechanical stability of soil aggregates, it reduced the water stability of soil aggregates. With increasing grazing intensity, water stability of the aggregates was correspondingly weakened, as was the erosion resistance of the soil. The soil urease activity, available soil nutrients, mean weight diameter by wet sieving (w-MWD), and geometric mean diameter by wet sieving (w-GMD) showed significant high sensitivity to grazing intensity in this Stipa kirschnii dominated grassland in Inner Mongolia. Overall, the soil quality at the heavy grazing site appeared poor compared with that at the light grazing site. For developing grazing management strategies, it is clear that heavy grazing should be avoided in this type of grasslands, albeit continued monitoring of soil structure is needed to explore the potential long-term consequences of the grazing.

The Effect of Grazing Intensity on Vegetation Coverage and Nitrogen Mineralization Kinetics of Steppe Rangelands of Iran (Case Study: Nodoushan Rangelands, Yazd, Iran)

Livestock grazing can affect the cycling of nutritional elements in soil by making changes to the vegetation coverage. This study aimed to investigate the effect of rangeland exploitation on vegetation coverage and nitrogen kinetics. To this end, three experimental sites of light, moderate, and heavy grazing in Nodoushan rangelands of Yazd province were selected. The vegetation properties were then measured through systematic random sampling method and three to five bases along the transect were sampled from the current year growth of the dominant plants in the region. The soil samples were collected from 0–15 cm depth in five replications and mixed together to obtain a single composite soil sample on each site. In the first stage, nitrogen (N), carbon (C), C/N, cellulose, hemicellulose, and lignin of the sampled plant as well as nitrogen, carbon, lime, soil texture, saturation moisture percentage, pH, and electrical conductivity (EC) of the soil were measured. As the soil properties did not differ for light and moderate grazing soils, different treatments were conducted on the dominant species of light and heavy grazing sites with 1% organic carbon added to the rangeland soil. Nitrogen mineralization treatments were selected based on vegetation changes that, with increasing livestock grazing intensity, changed the predominance of plant composition from Artemisia sieberi and steppe to percentage Artemisia sieberi and Peganum harmala. The treatments included control, 100% Artemisia sieberi, 75% Artemisia sieberi and 25% Peganum harmala, 50% Artemisia sieberi and 50% Peganum harmala, 25% Artemisia sieberi and 75% Peganum harmala, and 100% Peganum harmala. The soil samples were incubated for pure nitrogen mineralization in three replications of 3 months. The results of nitrogen mineralization revealed that the immobilization of the treated soil with higher Artemisia sieberi and lower Peganum harmala was done at a more rapid rate during the first week. The immobilization was slowly reduced by the third week and then followed a growing rate. Overall, the results show that an increase in grazing intensity was associated with a change in vegetation coverage toward Peganum harmala species, the biochemical characteristics of which elevated the levels of pure nitrogen mineralization in soil.

Effects of different livestock grazing intensities on plant cover, soil properties, and above and below ground C and N pools in arid ecosystems (Jiroft rangeland, Iran)

This study was conducted in Jiroft rangeland, Kerman, Iran to assess the effects of different livestock grazing intensities (low, moderate, heavy) on ecological factors, soil properties, and root and shoot carbon and nitrogen pools. In each plant sampling site, five points were selected and five quadrates (a total of 75 quadrats) were investigated. Soil surface samples were taken in quadrats (75 samples). Data analysis was carried out by analysis of variance (SPSS18.0). Findings indicated that canopy cover (46.23%) had the maximum level in the low grazing site. The diversity index was maximum in the overgrazed site (1.63), while the low grazing site had the minimum species diversity (1.27). In the three sites, the nitrogen and carbon pools were higher in the roots compared to the shoots. In the low grazing site, the plants' nitrogen and carbon pools were notably more than the heavy and moderate grazing sites. Potassium (612.87 mg kg-1), nitrogen (3.30 g kg-1), and organic carbon (39.20 mg kg-1) were considerably higher under heavy grazing conditions. However, the low grazing condition resulted in notable enrichment of phosphorus (11.44 mg kg-1). The soil nitrogen and carbon pool in the overgrazed site were higher. In spite of the fact that the soil nutrients in the heavy grazed site were higher because of livestock manure; we could not interpret it as greater soil fertility. Our results suggest that low grazing can be effective for managing plant community and soil quality in arid ecosystems.

Distribution of soil organic carbon and potential carbon sequestration in an alpine meadow grazed by domesticated yak in Zeku, Qinghai-Tibetan Plateau, China

The effects of grazing on the soil carbon of an alpine meadow on the Qinghai-Tibetan Plateau were studied. The aims were to estimate the effects of grazing on the spatial and vertical distribution of soil organic carbon, estimate the potential carbon sink and provide suggestions for sustainable grassland management. Biomass and soil characteristics of the topmost 1 m soil layer in plots under three different grazing intensities were investigated. Soil organic carbon density (SOCD) and stocks (SOCS) were calculated as weighted averages. Soil organic carbon content (SOCC) decreased with increasing grazing intensity and soil depth, with the highest values observed in the top 30 cm of the soil layer at light grazing (LG) sites. Soil water content, total carbon, and biomass had a positive relationship with SOCC. However, bulk density was negatively correlated with SOCC. The lowest SOCD and SOCS were in the 30–100 cm soil layer at heavy grazing (HG) sites, indicating that HG could have significant negative effects on SOC. It could take at least ∼60 years for C stocks at HG sites to reach a steady state. A regime of low grazing is recommended for combining C sequestration with sustainable development.

Soil hydrology and vegetation as impacted by goat grazing in Vertisols and Regosols in semi-arid shrublands of northern Mexico

Shrubland ecosystems are less studied than grasslands regarding the role of domestic grazing on ecosystem degradation in the world, but particularly in Mexico. Of special concern is the paucity of research on soil hydrological responses to the impact of livestock. Here, we assessed the role that specific soil and surface characteristics play in soil hydrology as a response to goat grazing intensity in two different soil types, Regosol and Vertisol, in the Tamaulipan thornscrub of north-eastern Mexico. At each soil unit, a set of grazing regimes was identified, including heavy grazing (HG), moderate grazing (MG) and a no-grazing (NG) reference area, and selected soil properties and plant cover were evaluated. In Regosol sites, soil organic matter varied among all grazing regimes (4.6% higher on NG and 2.1% higher on MG with respect HG) and no dissimilarities on bulk density were recorded. For Vertisol sites, soil bulk density increased with grazing intensity (16% higher on MG and 37% higher on HG with respect to NG) whereas plant cover linearly decreased from 86% in NG to 29% in MG and 9% in HG sites. Soil organic matter content for Regosol, and plant cover and soil bulk density for Vertisol appeared as the best indicators of water infiltration and moisture retention for the grazing conditions assessed. Differences in those key driving variables may help explain surface hydrology responses to goat grazing in rangeland soils of Tamaulipan thornscrub ecosystems and possibly on similar rangelands around the world. Clear signs of vegetation degradation were also observed, manifested by a loss in species diversity and plant cover, especially under heavy grazing. This reflects unsustainable livestock management practices that should be avoided. This study contributes to improve our understanding of rangeland degradation processes and justifies devising more sustainable grazing management schemes.

IMPACT OF WOODY PLANTS SPECIES ON SOIL PHYSIO-CHEMICAL PROPERTIES ALONG GRAZING GRADIENTS IN RANGELANDS OF EASTERN ETHIOPIA

<p class="Default">In the lowlands of arid and semiarid rangelands woody plants<em> </em>plays an important role in soil fertility maintenance, providing food, medicine, cosmetics, fodder, fuel wood and pesticides. A better understanding of the interaction of woody plants on their immediate environment is needed to guide optimum management of native vegetation in the production landscapes. However, the impact of woody plant species on soil properties remains poorly understood. This study evaluates the impact of two dominant woody plant species (<em>A. senegal and B. aegyptica</em>) on soil physico-chemical properties along grazing gradients in rangelands of eastern Ethiopia. Six trees of each species were selected from light, moderate and heavy grazing sites. Soil sample data at two depths (0-15 and 16-30 cm) were collected from under and open areas of <em>A. senegal</em> and <em>B. aegyptica</em> from each grazing sites, and analysed for nutrient contents. The nutrient status of soil under both woody species was significantly higher especially with regard to soil organic matter (4.37%), total nitrogen (0.313%), and available phosphorus (11.62) than the open grassland with soil organic matter (3.82%), total nitrogen (0.246%), and available phosphorus (10.94 mg/Kg soil) for<em> A. Senegal</em>. The soil organic matter (3.93%), total nitrogen (0.285%), available phosphorus (11.66 mg/Kg soil) were significantly higher than open grassland with soil organic matter (3.52%), total nitrogen (0.218%), available phosphorus (10.73 mg/Kg soil) for<em> B. aegyptica</em>. This was more pronounced in the top 15 cm of soil under <em>A. senegal</em> woody plant species and on the light and moderate grazing site. Therefore, this tree has a significant effect on soil fertility improvement in resource poor rangelands and as a result, it is important to retain scattered <em>A. senegal</em> and <em>B. aegyptica</em> plants in the lowlands of eastern Ethiopia.<em></em></p>

Grazing effects on soil characteristics and vegetation of grassland in northern China

Abstract. Large areas of grassland in the agro-pastoral region of northern China were converted into cropland for grain production, and the remaining grasslands are being overgrazed and seriously degraded. The objective of this study was to evaluate how reductions in grazing intensity affect the soil and vegetation characteristics in grasslands of northern China. Soil heterogeneity and vegetation characteristics were evaluated for ungrazed (UG), moderate grazing (MG), and heavy grazing (HG) sites. Grazing increased diversity, but heavy grazing decreased aboveground biomass and increased the non-grass component. The non-grass proportion of total biomass increased with grazing intensity, which was 8, 16 and 48 % for UG, MG and HG sites, respectively. Species richness at the MG and HG sites was significantly higher than at the UG site (P< 0.05) with 3.6, 5.5 and 5.7 for UG, MG and HG sites, respectively. Strong spatial dependence of the examined soil properties at 10 m scale for all grazed sites was revealed by the ratio of nugget to total variation (0–23 %). Overgrazing homogenized soil characteristics at a 10 m scale. The ranges of spatial autocorrelation for soil organic C (SOC) and total N were both > 120 m at the HG site, which was considerably larger than that at the MG and UG sites with corresponding distances of 17.3 and 20.8 m for the MG site and 8.6 and 15.0 m for the UG site, respectively. The sampling density and sampling space for the HG site could be decreased under this scale sampling interval (10 m). Therefore, MG was recommended as the preferred management alternative for grasslands in northern China because of increased plant diversity without negative consequences related to decreased forage quality, forage quantity and soil heterogeneity for the investigated soil properties in northern China's grasslands.

Grazing effects on carbon fluxes in a Northern China grassland

Grazing management is critical and can play a significant role in driving C sink and source activity in grassland ecosystems. In this study, CO2 exchange patterns during the growing season were evaluated in the grasslands of northern China using a closed-chamber technique at three stocking rates sites. The results showed that heavy grazing markedly reduced green biomass, plant standing dead, and litter mass as well as reduced net ecosystem exchange (NEE) (P < 0.05). Principal component analysis (PCA) indicated that spatial and temporal patterns varied in ungrazed, moderate grazing, and heavy grazing sites. High NEE was associated with high biomass, high temperature, and high soil water content (SWC), ecosystem respiration (Re), and soil respiration (Rs). Rs was higher at the moderate and heavy grazing sites than the ungrazed site. In contrast, Re and canopy respiration (Rc) were higher at the ungrazed than the other grazing sites. These results indicated that grazing influenced vegetation and soil characteristics, which altered the spatial and temporal patterns of CO2 fluxes in grasslands of northern China. Therefore, reducing stocking rates on heavily grazed grasslands of northern China to moderate grazing levels would enhance NEE, and benefit biomass and animal production.

Effects of Grazing on Carbon Sequestration in Temperate Grassland, Inner Mongolia of North China

Carbon storage in Chinese grasslands comprises a substantial proportion of the carbon pool in worldwide grasslands and in China's terrestrial ecosystem. The objective of this study was to evaluate how carbon sequestration in the steppe ecosystem responds to grazing. Study sites with various grazing conditions were selected. The different grazing conditions included a non-grazing enclosure (NX) that had been fenced for 26 years, a light grazing site (LG) with occasional grazing at 3 sheep/ha in the winter, which represents approximately a 30% utilization of annual forage production for the last 30 years, and a heavy grazing site (HG) with continuous grazing at a constant stock rate of 3 sheep/ha during the entire year, which represents an 80% utilization of annual forage production. Vegetation carbon stocks (from aboveground live plants, standing dead plants, litter and roots) and soil carbon stocks were measured and compared among the three sites. The results demonstrated that different grazing intensities affected the total ecosystem carbon and the various grassland carbon pools. Compared with the nongrazed site, standing dead plant and litter carbon (C) decreased significantly in light grazing conditions, but light grazing did not significantly affect live plant C, total aboveground plant C, total root C (0–60 cm), and soil C (at 0-100-cm depths). Heavy grazing extensively reduced carbon in three pools, total aboveground plant C, subsoil C (at 60–100 cm), and total soil C (at 0–100 cm), but did not affect topsoil C (at 0–60 cm). The lack of an effect on topsoil C can be explained by a slight increase in root C (0–60 cm) and a higher ratio of root to vegetation C in the HG site. We propose that the decrease in subsoil C under heavy grazing is attributable to the organic carbon decomposition due to increased root C as a source of fresh carbon. Total ecosystem C decreased from 150.62 Mg C/ha in the NX site to 143.78 Mg C/ha in the LG site (a 4.5% decrease) and to 122.43 Mg C/ha in the HG site (an 18.7% decrease). Therefore, we conclude that light grazing is a sustainable management option for North China grasslands.

Effects of Grazing Intensity on Soil Water Regime and Flux in Inner Mongolia Grassland, China

AbstractIn the past few decades, the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland, China, due to population growth and shift in the socio-economic system. Two sites with different grazing intensities, continuous grazing site (CG) with 1.2 sheep ha−1 year−1 and heavy grazing site (HG) with 2.0 sheep ha−1 year−1, were investigated at the Inner Mongolia Grassland Ecosystem Research Station (43° 37′ 50″ N, 116° 42′ 18″ E) situated in the northern China to i) characterize the temporal distribution of soil water content along soil profile; and ii) quantify the water fluxes as affected by grazing intensity. Soil water content was monitored by time domain reflectometry (TDR) probes. Soil water retention curves were determined by pressure membrane extractor, furthermore processed by RETC (RETention Curve) software. Soil matric potential, plant available water and water flux were calculated using these data. Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods: 1) wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April; 2) wet summer, rainfall in accordance with plant growth from May to September; 3) drying transition, a decrease of soil water from October to November due to rainfall limit; and 4) dry winter, freezing from December to next February. Heavy grazing largely reduced soil water content by 43%–48% and plant available water by 46%–61% as compared to the CG site. During growing season net water flux was nearly similar between HG (242 mm) and CG (223 mm) sites between 5 and 20 cm depths. However, between 20 and 40 cm depths, the upward flux was more pronounced at HG site than at CG site, indicating that water was depleted by root uptake at HG site but stored at CG site. In semi-arid grassland ecosystem, grazing intensity can affect soil water regime and flux, particularly in the growing season.

Changes in soil nutrients, vegetation structure and herbaceous biomass in response to grazing in a semi-arid savanna of Ethiopia

The effect of grazing was studied on vegetation structure, herbaceous biomass, basal and bare ground covers, together with soil nutrient concentrations in two locations in an Ethiopian semi-arid savanna. The lightly grazed sites had significantly higher herbaceous diversity, total abundance, basal cover and aboveground biomass, and a lower percentage of bare ground compared with the heavy grazed sites. Grazing pressure had no effect on the density and number of woody species as well as on the proportion of encroaching woody species. The light grazing sites had higher organic carbon, phosphorus and exchangeable bases, and therefore a higher pH and higher electrical conductance, indicating an improved soil nutrient status compared with heavy grazing sites, mainly attributed to the higher basal cover and standing biomass at light grazed sites, and the export of nutrients through grazing and dung collection from the heavily grazed sites. There were significantly higher soil nutrients, species diversity, aboveground biomass and basal cover in the light grazing sites compared with heavy grazing sites. We concluded that changes in herbaceous vegetation, standing biomass and soil compositions are caused by interactions between grazing, soil and vegetation, and these interactions determine the transitions of semi-arid savannas.

Above and belowground net primary productivity of grassland influenced by supplemental water and nitrogen in Inner Mongolia

While water availability determines grass- land productivity in semiarid regions, nutrient avail- ability is the main limiting factor under wet conditions. An experiment was conducted in 2008 at two sites in Inner Mongolia with histories of heavy grazing (HG) and moderate grazing (MG) to study the interactive effects of water and nitrogen on above- and belowground net primary productivity (ANPP and BNPP), biomass partitioning, and plant species composition. The study comprises two water treat- ments (no irrigation and irrigated when soil water content was below 70% of the field capacity), and two nitrogen (N) levels (0 and 100 kg N ha �1 ). Mean values of ANPP at the peak biomass time reached 1,028±95 SD g m �2 at the HG site and 568±32 SD gm �2 at the MG site in irrigated and fertilized treatment. Nitrogen use efficiency (NUE) was signif- icantly higher at irrigated plots compared to rain-fed plots at both HG and MG sites. Water use efficiency (WUEt) based on total water input and ANPP decreased with irrigation at the HG site. Meanwhile, N application significantly increased WUEt, WUEp (based on precipitation), and WUEi (based on irrigation water) at both sites. BNPP was significantly higher at irrigated plots compared to rain-fed plots at both HG and MG sites, and it tended to decrease with N addition. However, the fraction of belowground to total biomass (fBNPP = BNPP/(ANPP+BNPP) de- creased with the addition of supplemental resources and exhibited a negative correlation with ANPP. Species diversity remained lower at the HG site compared to the MG site; it decreased with the addition of supplemental resources at the latter site. The annual Salsola collina contributed the most to the total biomass under irrigation. Based on global climate models, more frequent extreme climates are predicted in the future, which can result in changes in resource availabilities. Therefore, our research results have important implications for predicting the pro- duction and other properties of grassland ecosystems.

Ambiguous effects of grazing intensity on surface soil moisture: A geostatistical case study from a steppe environment in Inner Mongolia, PR China

Does grazing intensity lead to changes in the mechanisms of water distribution and water storage in the topsoil? We attempt to answer this question by comparing temporal and spatial soil moisture variation on sites with different grazing intensities ranging from ungrazed to heavily grazed. The research was carried out in a semi-arid steppe environment in northern China. During the growing season, evapotranspiration rates usually exceed the amount of rainfall in these areas, so the ability to store water in the plant–soil system is crucial for biomass growth. In June 2005, the spatial variation of soil moisture in five grazing treatments (two ungrazed sites, one winter grazing, one continuous grazing and one heavy grazing site) was monitored on seven consecutive days after a precipitation event. We used capacitance sensors to measure volumetric soil moisture down to a depth of 0.06 m. The measurements were analysed with respect to the spatial correlation of data points (variogram analysis and kriging interpolation). The five sites did reveal some spatial patterns, but these were not very distinct. The capability of retaining water in the topsoil declined along the grazing gradient from ungrazed (wettest site) to heavily grazed (driest site). However, this pattern is disturbed, as the two ungrazed sites (ungrazed since 1979 and ungrazed since 1999) reacted differently to wetting and drying and showed significant differences on all sampling days.

Benthic Macroinvertebrate Responses to Increasing Levels of Cattle Grazing in Blue Ridge Mountain Streams, Virginia, USA

The relationship between benthic macroinvertebrate assemblages and cattle density was assessed from fall 2002 through spring 2004 in five small streams that represented a gradient of cattle grazing intensity. All study stream reaches were in pasture with no woody riparian vegetation, but varied in the intensity of cattle grazing (0 cattle ha(-1) at site 1 to 2.85 cattle ha(-1) at site 5). Regression analysis indicated highly significant and strong macroinvertebrate metric responses to cattle density during most sampling periods. The majority of metrics responded negatively to increased grazing, while a few (total taxa richness, number of sensitive taxa, and % collector filterers) increased along the gradient before declining at the most heavily grazed sites. Total number of sensitive taxa and % Coleoptera had the strongest relationship with cattle density throughout the study period. During some sampling periods, nearly 80% of the variation in these metrics was explained by cattle density. The elmid beetle, Oulimnius, had a particularly strong negative response to the grazing gradient. Study site groupings based on taxa composition, using detrended correspondence analysis (DCA), indicated that benthic samples collected from the reference site and light rotational grazing site were more similar in macroinvertebrate taxa composition than samples collected from the intermediate grazing and heavy grazing sites. Our findings demonstrate that biological integrity, as measured by benthic macroinvertebrate metrics and assemblage composition, is highly related to cattle density in small streams in the Blue Ridge mountains, Virginia, USA. This suggests that the degree of agricultural intensity should be given consideration in stream assessments, as well as land use planning and regulatory decisions.

A Study of the Characteristics of CO2 Flux and Concentration of Different Ecosystems

AbstractBy utilizing the micrometeorology data of net radiation, soil heat flux, and the CO2 concentration, temperature, relative humidity, and wind speed at two heights measured by the Japanese and Chinese cooperation team at Naiman District in Inner Mongolia, this paper has made a close study of the characteristics of CO2 flux and concentration from different ecosystems (namely dune, grassland, light grazing site, medium grazing site, heavy grazing site, maize field and soybean field). First, CO2 flux of these ecosystems is calculated according to the micrometeorology data using the aerodynamics method. Figures of diurnal variation of CO2 flux are compared. Furthermore, in order to analyze the photosynthesis strength and environmental and man‐made factors of different ecosystems, the relationship between CO2 concentration and net radiation, temperature and wind speed is investigated. Finally, several conclusions are drawn and the results show that: because of different plant coverage and above ground biomass, CO2 flux from different ecosystems varies greatly; grazing seriously destroyed vegetation conditions of grassland, resulting in the exposure of sand. Therefore, the strength of photosynthesis of this kind of grassland is weak and the range of daily CO2 flux is comparatively narrow; the diurnal variation of CO2 concentration is closely related to the diurnal variation of net radiation, temperature and wind speed. The former diminishes as the latter increases, but a little slower; the rate of photosynthesis and CO2 transportation can also be influenced by weather conditions. For example, clouds reduce photosynthesis rate, while wind enhances the transportation of CO2 from the plants to the atmosphere.

Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha −1, while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha −1, was approximately twice that of the LG site. Soil respiration measurements showed that CO 2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q 10 value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO 2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO 2 m −2 y −1 to the atmosphere, which was about one third more than the 1530 g CO 2 m −2 y −1 released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO 2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem.

Changes in abundance and diversity of microarthropods associated with Fescue Prairie grazing regimes

Summary Livestock grazing influences plant community structure, soil quality and health, and is likely to also affect the populations and diversity of soil biota. In our study, we determined the abundance and family level diversity of soil mites under very heavy and light grazing regimes, and a very heavy grazing exclosure, and asked whether there were differences in abundance of mite taxa that reflected the severity of disturbance. The field experiment we sampled was established in 1949 on a Rough Fescue Prairie with Orthic Black Chernozemic (Udic Haploboroll) soils near Stavely Alberta Canada. Soil cores were taken from the light (L)(1.2 AUM (animal unit month) ha –1 ) and very heavy (VH) (4.8 AUM ha –1 ) grazing regimes and the grazing recovery exclosure (Ex) in the very heavy grazing site in June and October 1999. The results showed that the soil temperature, moisture and bulk density varied between the grazing regimes, soil depth and the sampling times. Collembola were not abundant at any of the sites compared with Acari. Among Acari, prostigmatid mites were significantly more abundant in VH site and all the grazing treatments at both depths and sampling times. Oribatida, and to a lesser extent Mesostigmata, were more closely associated with reduced and undisturbed habitats than the Prostigmata, and there was a positive relationship between increased grassland productivity and the abundance and diversity of soil microarthropods. Our results suggest that Acari are sensitive to soil disturbance.