Ungrazed Sites Research Articles

Nematode community responses to a moisture gradient and grazing along a restored riparian corridor

Nematode assemblages were assessed to infer soil functions along a stream channel restored with native vegetation in a California on-farm study. Samples were taken at three distances from the water at six sites along the stream channel. Sites represented differences in grazing management and vegetation type. Bacterivorous nematodes, dominated by r-strategists, c–p 1 and 2 (colonizer–persister) categories, were in greater abundance in the ungrazed than the grazed sites. Among the fungivores, c–p 2 were abundant in the ungrazed sites and at positions closest to the water’s edge, while only one genus, c–p 4 Tylencholaimus, was more abundant at the top of the stream bank and in grazed sites. The stream edge had greater abundance of bacterivores than the drier uppermost soil. Nematode faunal analysis suggests that bacterial decomposition channels predominated near the water while fungal channels predominated in drier locations. Higher aboveground herbaceous plant biomass in the ungrazed sites and closer to the water might have contributed to greater abundance of c–p 1 and 2 bacterivores. Overall, nematode communities were not strongly affected by the restoration, possibly due to dampened effects on soil properties after seven years, lack of colonization from other riparian areas, and/or insufficient time for the restored plant communities to shape nematode communities.

Effects of fire, grazing and topographic variation on vegetation structure in tallgrass prairie

AbstractQuestionsHow do fire and grazing by bison affect the composition and structure of tallgrass prairie plant communities and their temporal stability? Are these responses modulated by topographic location?LocationKonzaPrairie Biological Station,Kansas,USA.MethodsPlant community composition was monitored in permanent plots in native grassland sites receiving different long‐term prescribed burning and bison grazing regimes across a topographic gradient (lowlands, slopes, uplands) following 20 yr of variable burning treatments and 13 yr of grazing by bison. A combination of multivariate analyses was used to determine how community structure, life forms and individual species responded to the accumulated effects of long‐term fire and grazing by native bison in upland, slope and lowland soils.ResultsSpecies diversity was maximized in sites that were infrequently burned and grazed by bison with the strongest response on infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites. In general, grass cover was highest in infrequently burned ungrazed sites and lowest on frequently burned grazed sites, while forb richness was highest in infrequently burned and grazed sites. Community response to fire and grazing differed across the topographic gradient. In general, frequent burning favouredC4grasses, which reduced the abundance ofC3forbs, especially in lowland sites. Responses of dominant grasses and forbs to fire and grazing varied depending on topographic position. Community stability was positively correlated with species richness.ConclusionsOverall, we found that fire and grazing are the main determinants of plant community composition and structure in this grassland system, but that topography mediates these effects. A combination of bison grazing and periodic fire is necessary to maximize diversity and community stability across this native grassland landscape.

Labile organic C and N mineralization of soil aggregate size classes in semiarid grasslands as affected by grazing management

Soil labile organic carbon (C) oxidation drives the flux of carbon dioxide (CO2) between soils and the atmosphere. However, the impact of grazing management and the contribution soil aggregate size classes (ASCs) to labile organic C from grassland soils is unclear. We evaluated the effects of grazing intensity and soil ASC on the soil labile organic C, including CO2 production, microbial biomass C, and dissolved organic C and nitrogen (N) mineralization in topsoils (0–10 cm) in Inner Mongolia, Northern China. Soil samples were separated into ASCs of 0–630 μm [fine ASC (fASC)], 630–2000 μm [medium ASC (mASC)] and >2000 μm [coarse ASC (cASC)]. The results showed that heavy grazing (HG) and continuous grazing (CG) increased soil labile organic C significantly compared to an ungrazed site since 1999 (UG99) and an ungrazed site since 1979 (UG79). For winter grazing site (WG), no significant differences were found. CO2 production was highest in cASC, while lowest in fASC. Microbial biomass C and dissolved organic C showed the highest values in mASC and were significantly lower in fASC. Grazing increased N mineralization in bulk soils, while it exhibited complex effects in the three ASCs. The results suggest that the rate of C mineralization was related to the rate of N accumulation. To reduce CO2 emission and nutrient loss, and to improve soil quality and productivity, a grazing system with moderate intensity is suggested.

The Impact of Overgrazing on Dung Beetle Diversity in the Italian Maritime Alps

Dung beetles (Coleoptera: Scarabaeidae) are undoubtedly the most typical and ecologically relevant insects of grazed alpine habitats because they provide valuable ecological services such as biological pest control and soil fertilization. Despite the great ecological contribution of these insects to pasture ecosystem functioning, little is known about their direct or indirect relationships with pastoral activities. The main aim of the study was to assess whether dung beetle diversity was influenced by different intensities of cattle grazing. Dung beetle communities of two adjacent alpine valleys within the Maritime Alps Natural Park (north-western Italian Alps), representing overgrazed and ungrazed pastures, were studied by pitfall trapping. A hierarchical design (three levels: valleys, transects, and replicates) was established for additive partitioning of γ-diversity and Indicator Species Analysis. Evenness and Shannon diversity were significantly higher at the ungrazed than at the overgrazed site because abundances were much more evenly distributed at the former than at the latter site (where one species was dominant over all the others). Dung beetle abundance and species richness of the overgrazed graminaceous pasture vegetation types were in most cases significantly lower than those of the ungrazed nongraminaceous vegetation type. In the additive partitioning of γ -diversity analysis relative to the whole study area, the randomization procedure indicated that the contribution of β to γ-diversity was significantly different from that expected by chance, suggesting that one or more environmental factors has intervened to change the partition of total diversity in the system considered. The analysis of the preferences and fidelity of species (Indicator Species Analysis) showed that only one species chose overgrazed pastures; all the others positively selected the ungrazed site, or the only ungrazed pasture vegetation type (Rumicetum alpini Beger) occurring at the overgrazed site. Results conformed to evidences that overgrazing represents a serious threat to the conservation of alpine dung beetles. To conserve local dung beetle assemblages, especially in protected areas, cattle overgrazing should be avoided. This does not mean, however, that pastoral activities are incompatible with biodiversity conservation. The contemporaneous presence of wild ungulates and low intensity extensive pastoral activities may be useful to preserve both local dung beetle assemblages and alpine pasture ecosystems.

Biological soil crust recovery after long-term grazing exclusion in the Monte Desert (Argentina). Changes in coverage, spatial distribution, and soil nitrogen

Disturbance by domestic grazing is recognized as the most widespread stressor of biological soil crust (BSC) communities. To assess the recovery of the BSC after grazing exclusion, we estimated the composition, cover, and spatial distribution of biological soil crusts, and their influence on soil nitrogen in a protected area after 40 years of grazing exclusion (Reserve MaB of Ñacuñán), and in its surrounding grazed matrix in the central Monte Desert. We considered two spatial scales: at the landscape scale we estimated vegetation and BSC cover in paired grazed and ungrazed sites of Larrea shrublands; at the microsite scale we assessed the influence of the dominant vascular plant, Larrea cuneifolia, on crust cover, and the influence of crust cover on soil nitrogen concentration. Grazing has a negative impact on soil crusts, which only develop under the protection of vascular plants in grazing areas. Grazing exclusion favors crust recovery, allowing black, lichen dominated crusts to develop in exposed areas between shrub canopies. The cover of the moss-dominated crusts was not significantly different at any of the two spatial scales analyzed. Soil nitrogen was higher in areas under L. cuneifolia and without BSC cover, suggesting that litterfall inputs currently exceed those from soil crust N 2 fixation, perhaps because crust function has not yet recovered.

Characteristics of life-form and growth-form of plant species in an alpine ecosystem of North-West Himalaya

The present study was conducted in the alpine pastures of Tungnath (30° 14′ N and 79° 13′ E) to observe life-form and growth-form patterns of alpine plant species under grazed and ungrazed conditions and to work out the plant life form spectrum. Species were categorized as plant habit, height and length of growth-cycle and life-form classes according to Raunkiaer’s system. The results show that in total of 68 species at grazed site, hemicryptophytes (He) accounted for 50.00% species, followed by cryptophytes (26.47%), chamaephytes (16.18%), phanerophytes (4.41%) and therophytes (2.94%). At the ungrazed site in 65 plant species, hemicryptophytes (He) accounted for 49.23% species, cryptophytes (26.15%), chamaephytes (15.38%), phanerophytes (6.15%) and therophytes (3.08 % species). In general, hemicrptophyte are dominant in both sites i.e. graged and ungrazed. Growth form categories were classified as forbs, shrubs, grasses and sedges and undershrubs, according to plant habit and height. On the basis of length of the growth cycle, species were categorized as plant species of short growth cycle, intermediate growth cycle and long growth cycle. The short forbs of plant habit and height, had the highest emergence, and grasses and sedges had the lowest emergence in representative species. Percentage of species with long growth cycle was highest in both sites.

The Impact of Summer Cattle Grazing on Surface Water Quality in High Elevation Mountain Meadows

Surface waters were tested before and after the arrival of cattle to summer grazing allotments for pathogenic bacteria indicators E. coli, fecal coliform bacteria, and total coliform bacteria in the high elevation mountains of the Stanislaus National Forest, California, USA. Water samples were collected from one control/ungrazed stream site and at four grazed stream sites before cattle grazing began and during the time when livestock were present. All sample sites were higher than 1900 meters in elevation. Samples were transported within 6 hours to a water analysis laboratory, where they were analyzed following standardized lab methods. Results showed that individual and average concentrations of fecal coliform bacteria in surface waters were below regulatory thresholds at the ungrazed site and at the grazed sites before cattle arrived. Mean fecal coliform concentration increased from 9 to 350 CFU/100 mL, and mean E. coli increased from 8 to 240 CFU/100 mL, respectively, after grazing. The increase in mean concentration of fecal coliform at each grazed site was significant (p<0.05). Total coliform bacteria and E. coli concentrations showed the same pattern. Cattle grazing in the sampled high elevation Sierra Nevada meadows resulted in a significant increase in indicator bacteria.

Effects of horse grazing on plant species richness and abundance of Iris setosa in a boreal semi-natural grassland, Japan

We investigated plant community attributes and selected soil characteristics of a Japanese boreal semi-natural grassland among day-grazed (24 h), night-grazed and ungrazed sites in Akkeshi, eastern Hokkaido. We also evaluated the effects of horse grazing on plant species richness and the population of Iris setosa, a hygrophilous target species for conservation. Species richness and iris dominance were the highest and community height was the lowest at the day-grazed site; however, plant coverage and light intensity at ground level did not differ significantly among the sites. Soil aeration and water permeability of the surface soil were the lowest at the day-grazed site. Logistic regression analyses suggested direct and/or indirect positive effects of grazing on the occurrence probability of nine species. Species richness was negatively correlated with community height, soil aeration and water permeability of the surface soil and positively correlated with bulk density and soil hardness. Iris dominance was negatively correlated with aeration and water permeability and positively correlated with surface soil bulk density and volumetric water content. Iris dominance was also positively correlated with species richness. Canonical correspondence analyses demonstrated different species composition among the sites that mainly segregated with grazing intensity, soil bulk density, surface soil aeration and community height. Our results showed that all-day horse grazing in a boreal semi-natural grassland modifies surface soil characteristics and increases plant species richness and dominance of I. setosa.

Spatial and temporal variation of soil moisture in dependence of multiple environmental parameters in semi-arid grasslands

Grazing of grasslands changes soil physical and chemical properties as well as vegetation characteristics, such as vegetation cover, species composition and biomass production. In consequence, nutrient allocation and water storage in the top soil are affected. Land use and management changes alter these processes. Knowledge on the impacts of grazing management on nutrient and water fluxes is necessary because of the global importance of grasslands for carbon sequestration. Soil water in semi-arid areas is a limiting factor for matter fluxes and the intrinsic interaction between soil, vegetation and atmosphere. It is therefore desirable to understand the effects of grazing management and stocking rate on the spatial and temporal distribution of soil moisture. In the present study, we address the question how spatio-temporal soil moisture distribution on grazed and ungrazed grassland sites is affected by soil and vegetation properties. The study took place in the Xilin river catchment in Inner Mongolia (PR China). It is a semi-arid steppe environment, which is characterized by still moderate grazing compared to other regions in central Inner Mongolia. However, stocking rates have locally increased and resulted in a degradation of soils and vegetation also in the upper Xilin River basin. We used a multivariate geostatistical approach to reveal spatial dependencies between soil moisture distribution and soil or vegetation parameters. Overall, 7 soil and vegetation parameters (bulk density, sand, silt and clay content, mean weight diameter, mean carbon content of the soil, vegetation cover) and 57 soil moisture data sets were recorded on 100 gridded points on four sites subject to different grazing intensities. Increasing stocking rates accelerated the influence of soil and vegetation parameters on soil moisture. However, the correlation was rather weak, except for a site with high stocking rate where higher correlations were found. Low nugget ratios indicate spatial dependency between soil or plant parameters and soil moisture on a long-term ungrazed site. However, the effect was not found for a second ungrazed site that had been excluded from grazing for a shorter period. Furthermore the most important soil and vegetation parameters for predicting soil moisture distribution varied between different grazing intensities. Therefore, predicting soil moisture by using secondary variables requires a careful selection of the soil or vegetation parameters.

Nitrogen availability in a grazed semi-arid grassland is dominated by seasonal rainfall

In semi-arid grassland ecosystems, soil biogeochemical processes are controlled by seasonal and inter-annual rainfall variation and temperature, which may override the long-term impact of grazers on N availability and N dynamics. In a three-year (2004-2006) case study of an Inner Mongolian grassland, we analysed time-integrated (ion-exchange resins) and instantaneous (soil mineral N extractions) inorganic N availability at three sites of varying grazing intensities and combined these data with information on soil water content (SWC), aboveground net primary productivity (ANPP) and plant N uptake. Additionally, the effects of rainfall and grazing on N-form availability (NO(3)(-)-N, NH(4)(+)-N) were considered. Grazing had less impact on N availability compared to seasonal and annual rainfall distribution. One of the three study years (2004) showed a grazing effect with higher resin-N availability at the ungrazed site compared to the heavily grazed site. Inorganic N availability was low in the driest year (2005) and highest in a year of average rainfall amount and favourable distribution (2004). In general, we found a positive relationship between inorganic N availability and both plant productivity and plant N uptake. Rainfall also controlled the plant available NO(3)(-)-N and NH(4)(+)-N pools; NH(4)(+)-N dominated the available inorganic N-form in times of low SWC, while the available NO(3)(-)-N increased with SWC. We observed N availability and plant productivity in a temporal synchronized pattern. Increased rainfall variability and land-use practices affecting SWC will likely alter N availability dynamics (and the relation of N-forms) and, therefore, important processes of semi-arid natural grassland carbon and N cycling.

Response of soil moisture and temperature to grazing intensity in a Leymus chinensis steppe, Inner Mongolia

Long-term monitoring of soil properties reveals site-specific ecosystem shifts in soil processes due to land use and climate changes. This paper aims to study the effects of physical landscape changes associated with grazing on soil thermal and moisture regime at the plot scale in a semiarid Leymus chinensis steppe of Inner Mongolia, China. The investigated sites were subjected to three grazing intensities: ungrazed since 1979 (UG79), moderately grazed only in winter time (WG), and heavily grazed (HG). At each plot, we recorded the soil moisture and temperature over a 6-year period that spanned between June 2004 and September 2009 and experienced a large range in precipitation (162 to 362 mm). Based on these monitoring data, we divided a year into four hydric periods: (1) growing period (late April to August); (2) transitional period from summer to winter (September–October); (3) winter time (November–first March); and (4) transitional period from winter to summer (March–April). In general, soil moisture in grazed sites was lower than in the ungrazed site, particularly for the 30–50 cm soil layer. Seasonal fluctuation of the soil moisture, due to variable precipitation and atmospheric demands, was most significant in the topsoil (0–10 cm) and was less pronounced in deeper soil. Regardless of hydric seasons, soil moisture was significantly influenced by grazing intensity, whereas soil temperature was slightly influenced. With increasing grazing intensity, soil water storage decreased remarkably. Consequently, grazing reduced plant available water and therefore grassland productivity, which are linked to a great extent with the trampling-induced soil structure change and soil moisture regime.

Grazing effects on seasonal dynamics and interannual variabilities of spectral reflectance in semi-arid grassland in Inner Mongolia

Detecting the influences of land management on seasonal dynamics and interannual variabilities of grassland surface reflectance is of scientific and practical importance as it can help to monitor grazing effects on the grassland ecosystem. We conducted spectral reflectance measurements at five differently grazed sites in Inner Mongolia, China, during the growing seasons of 2005 and 2006 using a portable, highly resolving spectrometer. Through analyses of the measured surface reflectance spectra and the derived visible albedo and NDVI, we found that grazing influences the reflectance spectrum shape and affects the visible albedo and NDVI seasonal pattern; visible albedo and NDVI of grazed sites are more sensitive to precipitation than that of ungrazed sites. In addition, we observed a well-defined linear relationship between total shortwave and visible (PAR) albedo, with R = 0.83 and R = 0.94 for 2005 and 2006, respectively, and between NDVI and total shortwave albedo with R = −0.92. Thus, NDVI spectrometer measurements and total shortwave albedo pyranometer measurements are interchangeable when addressing different grazing intensities.

Modeling grazing effects on coupled water and heat fluxes in Inner Mongolia grassland

Overgrazing is a major cause of grassland degradation in semi-arid regions. To evaluate how soil water and heat fluxes respond to grazing, investigations on soil, plant and meteorological parameters were conducted at four sites with different grazing intensities through three growing periods (2004–2006) in a steppe ecosystem of Inner Mongolia. The grazing intensities were (1) ungrazed since 1979, (2) ungrazed since 1999, (3) moderately grazed, and (4) heavily grazed. In comparison to other treatments, heavy grazing had decreased total pore and macropores volumes. The impacts of these grazing-induced changes of soil pore structure on water and heat fluxes were simulated by the processed-based hydraulic model HYDRUS-1D. To account for the site-specific boundary condition, we partitioned evapotranspiration as a function of dynamic cover area index of green and dead plant materials, used the root growth model related with root length density, and estimated interception using the SHAW model. Furthermore, the uncertainty of soil hydraulic parameters on model results was evaluated using three simulation approaches: (i) laboratory-derived hydraulic properties (LDP), (ii) neural network (NN) analysis, and (iii) inverse optimization (Inverse). On the basis of previous calibrations, HYDRUS-1D was validated with a good agreement between modeled and measured soil moisture and temperature, which provided a basis to evaluate the grazing effects on water and energy balance. Of the three approaches used, the Inverse expressed the best simulation, and the LDP was better than the NN due to more precise reflection of soil structural functions. Model result showed that, due to the changed soil structure and soil surface coverage, grazing increased soil heat fluxes. There was no significant difference on water budget components between the two ungrazed sites and moderate grazing, while heavy grazing significantly decreased interception from 17 to 7 mm and transpiration from 121 to 74 mm, and increased evaporation from 88 to 128 mm. We conclude that intensive grazing in Inner Mongolia grassland deteriorated soil functions and reduced plant available water, and consequently reduced grassland productivity and enhanced the risks for wind and water erosion.

Evaluating Relationships between Spatial Heterogeneity and the Biotic and Abiotic Environments

While most studies of heterogeneity have focused on describing patterns of species or communities, few have focused on the relationships between biotic and abiotic environmental landscape-level gradients. Our study was designed to determine relationships between grazing (heavy, moderate, ungrazed), topographic position (upland vs. riparian), vegetation structure and the thermal environment (i.e., soil-surface temperatures) and determine the influence on landscape patterns of heterogeneity. Biotic and abiotic patterns of heterogeneity were evaluated by establishing 200-m transects that were centered on and perpendicular to a riparian zone so that spatial patterns of variability could be determined along each transect which transcends the maximum level of landscape heterogeneity. Vegetation cover and structure and soil-surface temperatures were recorded at 1-m intervals along the transect. Bare ground increased and leaf litter, grass cover, vegetation heights and angle of obstruction decreased with grazing intensity. However, mean soil-surface temperatures did not differ between grazing treatments. Tree canopy cover associated with riparian areas generally reduced soil-surface temperatures 20 C below that of upland temperatures. In fact, 96% of observations of riparian soil-surface temperature were ≤ 39 C, while 94% of upland soil-surface temperatures were ≥ 40 C regardless of grazing intensity. Vegetation characteristics and soil-surface temperatures were correlated (P < 0.05), but correlation coefficients were small because soil-surface temperature was highly variable. Grazing influenced patterns of landscape heterogeneity, but effects were inconsistent among biotic and abiotic variables. Although grazing had little influence on moderating mean soil-surface temperatures, results suggest that grazing intensity influences thermal heterogeneity at a variety of spatial scales. For instance, thermal heterogeneity (in moderately grazed treatments) is highest at smaller (lag distances ≤ 20 m) and larger (lag distances ≥ 48 m) spatial scales but was lowest at moderate scales (lag distances 22–45 m). For all variables, other than soil-surface temperature and forb cover, semi-variances of moderately grazed sites generally lie intermediate between heavy and ungrazed sites. Nearly all ungrazed vegetation characteristics, except leaf litter, fit a spherical model that reached a sill at a lag distance ≤ 20 m and became spatially independent thereafter, while heavily and moderately grazed sites typically fit an exponential model, indicating a high degree of continuity. Patterns of thermal variability (on uplands) are not related directly to any one vegetation variable, hence, landscape patterns based on vegetation parameters alone are of limited value since patterns of thermal variability are effected by the integration of vegetation and environmental variables within the ecosystem.

Effects of large herbivore exclusion on southern Mongolian desert steppes

Large areas of Mongolia have been subject to semi-nomadic pastoralism for centuries, but recently increasing livestock numbers have raised concerns about possible degradation effects. We assessed the impact of grazing in southern Mongolian desert steppes (mean precipitation <150 mm) over eight years in order to capture the high interannual variation, as well as possible medium-term trends in the management regime. We assessed whether the impact of varying precipitation levels (coefficient of variation >30%) exceeds the effects of grazing on vegetation composition, species richness, plant flowering activity, biomass production, and soil nutrient content. The data presented here originate from a set of nine fenced exclosures established in 1999. Plant community composition and species richness showed interannual changes over years of varying precipitation levels: mean species numbers on ungrazed plots ranged between 8 and 19 per 100 m 2. Grazing effects were apparent but light, as grazed plots had, on average, 1–2 species fewer than ungrazed plots. There was also no evidence of directed succession under grazing exclusion. Mean numbers of flowering species on ungrazed plots ranged between 2 and 14 over the years while numbers on grazed plots were slightly lower (range 1–12). In one moist year, mean biomass production in previously ungrazed plots was higher than in previously grazed plots (ca. 800 kg/ha vs. 250 kg/ha), but differences in a subsequent drier year were negligible. This was paralleled by soil phosphorus content, which tended to be higher inside the exclosures. The overriding effects of precipitation variability are in line with the non-equilibrium theory of rangeland science and imply that the risk of direct degradation is low in southern Mongolian drylands. However, small but statistically significant differences between grazed and ungrazed sites suggest that herbivore impact is apparent and can alter plant reproduction and, ultimately, soil conditions and productivity.

The role of pasture management for sustainable livestock production in semi-arid subtropical mountain regions

Grazing livestock is an important asset to the livelihoods of people in most semi-arid environments, where natural resources cannot be used directly for human consumption. However, overgrazing commonly reduces pasture productivity and therefore threaten people's long-term food security. Ligneous and herbaceous vegetation on grazed and ungrazed sites in the Hajar Mountains, Oman, was studied to evaluate the possibilities of improving pasture management to maintain fodder production. Foliar biomass was 3–6 t dry matter ha −1 on the grazed and ungrazed plateau areas and 41 t dry matter ha −1 in the shallow valleys. Herbaceous yields changed over seasons and contributed ≤13% to accessible biomass, stressing the importance of ligneous foliage for livestock nutrition in particular during dry periods. While botanical composition and biomass of the vegetation differed between grazed and ungrazed sites, canopy cover and biomass yields were similar in a 15-year old enclosure and on a naturally ungrazed mountain plateau. Despite the climatic conditions, pastures encompass characteristics of equilibrium systems, where vegetation is strongly influenced by grazing livestock but recovers in its absence. The sustainable use of the natural fodder resources through improved pasture management is therefore a valuable alternative to intense supplement feeding or the introduction of zero-grazing management.

The Effects of Winter Burning and Grazing on Resources and Survival of Texas Horned Lizards in a Thornscrub Ecosystem

ABSTRACT The ecological effects of land‐use practices on reptiles, especially endangered or threatened species, are of conservation and scientific interest. We describe the effects of rotational livestock grazing and prescribed winter burning on resources and survival of the Texas horned lizard (Phrynosoma cornutum) during the summers of 1998 to 2001 in southern Texas, USA. We evaluated survival rates of Texas horned lizards (n = 111) on 6 study sites encompassing 5 different burning and grazing treatments. We also measured indices of cover (i.e., vegetation) and food abundance (i.e., harvester ants [Pogonomyrmex rugosus]). We telemetered and relocated adult lizards daily. We divided the study into 2 seasons, spring (15 Apr–30 Jun) and summer (1 Jul–15 Aug), corresponding to the relative activity of horned lizards. Winter burning provided an increase in food resources and led to increased survival of Texas horned lizards in the second growing season after fire, but grazing‐induced changes in vegetation cover reduced survival, likely by increasing lizard vulnerability. Fire and grazing reduced litter and increased bare ground and forb cover but did not affect woody vegetation. Ant activity was greater in burned sites and varied with grazing level, season, and year. Summer survival functions of horned lizards varied by burning treatment, with higher survival observed on burned sites in the second year after burning. Survival rates were ordered from highest in ungrazed sites to lowest in heavily grazed sites. We recognize the limitations of our work resulting from a lack of spatial replication of treatments. However, our mensurative study provides fertile ground for future hypothesis testing regarding the effects of land management on shrubland and grassland reptiles. We propose that future studies focus on the population consequences of variation in burn frequency, burn timing, and grazing intensity.

Pathways of Grazing Effects on Soil Organic Carbon and Nitrogen

Grazing modifies the structure and function of ecosystems, affecting soil organic carbon (SOC) storage. Although grazing effects on some ecosystem attributes have been thoroughly reviewed, current literature on grazing effects on SOC needs to be synthesized. Our objective was to synthesize the effects of grazing on SOC stocks in grasslands, establishing the major mechanistic pathways involved. Additionally, and because of its importance for carbon (C) biogeochemistry, we discuss the controls of soil organic nitrogen (N) stocks. We reviewed articles analyzing grazing effects on soil organic matter (SOM) stocks by comparing grazed vs. ungrazed sites, including 67 paired comparisons. SOC increased, decreased, or remained unchanged under contrasting grazing conditions across temperature and precipitation gradients, which suggests that grazing influences the factors that control SOC accumulation in a complex way. However, our review also revealed some general patterns such as 1) root contents (a primary control of SOC formation) were higher in grazed than in their ungrazed counterparts at the driest and wettest sites, but were lower at sites with intermediate precipitation (,400 mm to 850 mm); 2) SOM C:N ratios frequently increased under grazing conditions, which suggests potential N limitations for SOM formation under grazing; and 3) bulk density either increased or did not change in grazed sites. Nearly all sites located in the intermediate precipitation range showed decreases or no changes in SOC. We grouped previously proposed mechanisms of grazing control over SOC into three major pathways that can operate simultaneously: 1) changes in net primary production (NPP pathway), 2) changes in nitrogen stocks (nitrogen pathway), and 3) changes in organic matter decomposition (decomposition pathway). The relative importance of the three pathways may generate variable responses of SOC to grazing. Our conceptual model suggests that rangeland productivity and soil carbon sequestration can be simultaneously increased by management practices aimed at increasing N retention at the landscape level.

Grazing‐induced alterations of soil hydraulic properties and functions in Inner Mongolia, PR China

AbstractIncreasing grazing intensities of sheep and goats can lead to an increasing degradation of grasslands. We investigated four plots of different grazing intensities (heavily grazed, winter‐grazed, ungrazed since 1999, and ungrazed since 1979) in Inner Mongolia, PR China, in order to study the effects of trampling‐induced mechanical stresses on soil hydraulic properties. Soil water transport and effective evapotranspiration under “heavily grazed” and “ungrazed since 1979” were modeled using the HYDRUS‐1D model. Model calibration was conducted using data collected from field studies. The field data indicate that grazing decreases soil C content and hydrophobicity. Pore volume is reduced, and water‐retention characteristics are modified, the saturated hydraulic conductivity decreases, and its anisotropy (vertical vs. horizontal conductivity) is influenced. Modeling results revealed higher evapotranspiration on the ungrazed site (ungrazed since 1979) compared to the grazed site (heavily grazed) due to wetter soil conditions, more dense vegetation, litter cover, and decreased runoff and drainage, respectively. Grazing modified the partitioning of evapotranspiration with lower transpiration and higher evaporation at the grazed site owing to reduced root water uptake due to reduced evaporation and a patchy soil cover.

Influence of Livestock Grazing and Climate on Pinyon Pine (Pinus edulis) Dynamics

Abstract Over the last century there has been marked expansion and infilling of pinyon ( Pinus spp.)–juniper ( Juniperus spp.) woodlands into grassland and shrubland ecosystems across the western United States. Although range expansions in pinyon-juniper populations have been documented with changing climate throughout the Holocene, over the last century, local scale impacts such as livestock grazing, changes in fire regimes, and increasing atmospheric CO 2 concentrations are thought to be more recent drivers of pinyon-juniper woodland distribution. Our objective was to examine the role of historical livestock grazing relative to past climate in regulating pinyon ( Pinus edulis Engelm.) recruitment and growth over the last century in a persistent pinyon-juniper woodland. We compared pinyon dynamics on a remote mesa site, minimally grazed by domestic livestock, to a nearby historically grazed site in southeastern Utah. The presence of a significant number of old trees (> 200 yr) at both sites suggests that these populations were well established prior to the 20th century. No differences in pinyon density or basal area were observed between grazed and ungrazed sites. Stand age structure data showed that pinyon recruitment across these sites was highly synchronous, with a large recruitment event occurring during the early 1900s; 17% of the pinyons on both sites dated to the 1920s. Climatic conditions during this decade were consistently cool and wet—conditions known to support enhanced recruitment and growth in pinyon pines. Pinyon growth was also strongly synchronous across sites ( r = 0.96). Pinyon growth was significantly correlated with winter/spring precipitation and negatively correlated with June temperature. Taken together, our results suggest that past climate may be more important in structuring pinyon populations than historical land use in these persistent pinyon-juniper woodlands. Given future climate projections of increasing temperature and more extended drought periods, regeneration of pinyon populations following the recent regional-scale dieback may be slow. Moreover, prolonged drought combined with potentially slow regeneration times for pinyon under future climate scenarios could result in substantial declines in pinyon populations across the region, a result that land managers should consider when planning for future restoration treatments in persistent pinyon-juniper woodlands.