Ungrazed Sites Research Articles

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 these fluxes, gaseous N losses (N2O, NO, N2, and NH3) and N losses via export of sheep live mass and wool were of minor relevance. Our N balance calculation indicated mean annual net N losses of 0.9 ± 0.8 g N/m2 (mean ± SD) at the heavily grazed site, whereas the long‐term ungrazed site was an N sink receiving mean annual inputs of 1.8 ± 1.1 g N/m2, mainly due to dust deposition. Heavy grazing reduced pool sizes of topsoil organic N, above‐ and belowground biomass, and N fluxes with regard to plant N uptake, decomposition, gross microbial N turnover, and immobilization. Most N‐related processes were more intensive in seasons of higher water availability, indicating complex interactions between land use intensity and climate variability. The projected increase of atmospheric N depositions and changes in rainfall pattern imposed by land use change will likely affect N sink–source pathways and N flux dynamics, indicating high potential impact on grassland ecosystem functions. Land use practices will be increasingly important for the management of N dynamics in Chinese typical steppe and, therefore, must be considered as key component to maintain, restore or optimize ecosystem services.

Differences in spatial autocorrelation (SAc), plant species richness and diversity, and plant community composition in grazed and ungrazed grasslands along a moisture gradient, North Dakota, USA

AbstractQuestionsHow are plant species richness and diversity related to spatial autocorrelation under grazed and ungrazed conditions in grassland communities? Is spatial autocorrelation dissimilar within different plant communities?LocationThe grasslands of southeast North Dakota, USA.MethodsThe study was conducted during the summer of 2009 in six grasslands under different management (grazed vs ungrazed with fire) along a moisture gradient. Spatial autocorrelation at each site was measured along 50‐m transects among three different landscape positions representing different moisture levels. Dissimogram multivariate analysis was used to measure the nugget, dissimilarity and patch diameter. Additionally, richness and Shannon diversity indices and nonmetric multidimensional scaling analysis were compared to the dissimogram results.ResultsMean patch diameter was significantly higher in grazed mid‐slope sites than in ungrazed sites. Spatial autocorrelation was not different between the landscape positions (higher, dry areas were not different from lower, mesic areas). However, plant species richness, diversity and community composition were found to be different between landscape positions and management, with key differences in the presence of certain invasive species.ConclusionsDisturbance and moisture level were reflected differently in the spatial autocorrelation analysis compared to the richness, diversity and ordination analyses. This indicates that disturbance and management impacted spatial autocorrelation separate from plant community composition and species diversity. This also highlights changes in the plant community caused by different management actions and the spread of invasive species.

Impact of grazing management on silica export dynamics of Wadden Sea saltmarshes

During periods of silica limitation, its supply from tidal marshes is important for the stability of estuarine and coastal food webs. Saltmarshes are highly dynamic, grass dominated ecosystems: their large area, high salinity and location imply that they could efficiently contribute to the buffering of silica depletion events in the coastal zone. As grazing management potentially alters vegetation and sedimentation dynamics in saltmarshes, it could have an indirect impact on silica cycling in these systems. In two saltmarshes of the Wadden Sea coast, concentrations of dissolved and biogenic silica (DSi and BSi) were measured in eight creeks in four seasons under different management conditions. Export rates were calculated using simultaneous discharge measurements. Mean annual DSi concentration in the seepage water was 338 ± 112 μmol l−1. Ungrazed sites had significantly higher seepage water DSi concentrations than sites which were grazed by sheep. BSi concentrations were, in general, lower and more variable. DSi export rates from ungrazed sites (265 ± 155 μmol m−2 day−1) were twice as high as from grazed saltmarshes (126 ± 137 μmol m−2 day−1). DSi concentrations were among the highest values previously reported for saltmarshes and tidal freshwater marshes. Although differences in silica exports from grazed and ungrazed sites might be partly explained by silica uptake of benthic diatoms in the creeks, differences in hydrology appeared to be an overarching factor, controlling silica exports from Wadden Sea saltmarshes.

Ploughing and grazing alter the spatial patterning of surface soils in a shrub-encroached woodland

Grazing is known to affect the spatial patterning of soil resources through biologically-mediated processes such as the removal of plant biomass and deposition of dung. In dense shrublands, grazing is thought to reinforce the concentration of resources around shrubs (fertile island effect) by enhancing the movement of resources from the interspace to the shrub hummocks. Shrub removal practices such as ploughing, which is commonly used to manage dense shrub patches, has unknown impacts on the distribution of soil properties. In this study we examined the effects of two land management practices, grazing and ploughing, on the spatial distribution of surface soil resources. At the unploughed–ungrazed site, the connectivity (autocorrelation range) of shrub cover was about 3.9m and there was a well-defined pattern in soil labile C that was related to the distribution of the cover of both shrubs and litter. We also observed a strong pattern of biological crust cover and an autocorrelation range of 2.5m, similar to that of mineralisable and mineral N. At the unploughed–grazed site, the autocorrelation range of both shrub and crust cover was reduced to 1.9m and 1.8m, respectively, although the range of litter cover increased to 4.4m. Under a treatment of grazing without ploughing, the autocorrelation range of soil labile C was less related to litter cover. Whilst ploughing slightly increased the autocorrelation range of both shrub and litter cover at sites that were grazed, it obliterated any spatial pattern in biological soil crusts. We attribute changes in the spatial patterns of soil N under grazing to inputs of animal dung rather than soil crust cover. Our results indicate that grazing alone, or in combination with ploughing, leads to reduced connectivity of shrub and crust cover, reduction in crust patterning, and marked effects on shrub–litter–nutrient spatial relationships. The results reinforce the notion that management of shrublands by grazing and ploughing is likely to have marked effects on the distribution of surface soils.

Microstructural development in volcanic ash soils from South Chile

Streaming potential measurements and amplitude sweep tests were performed on a range of Andosols from South Chile to find out about aggregation strength and mechanisms, as well as thixotropy and microstructural stability. Different stages in soil development and types of land use (pasture vs. natural forest) were considered and compared. Younger, alu-andic Andosols along with Al-humus-complexes contained higher levels of volcanic glass, indicated by their low pH values (pHH2O<5), and high ratios of sodium pyrophosphate extractable Al (Alp) to acid ammonium oxalate extractable Al (Alo) (Alp/Alo>0.5). Alu-andic Andosols were also found to have (super)hydrophobicity in addition to typically high contents of amorphous iron (ferrihydrite). On the contrary, in well-developed, sil-andic Andosols (Alp/Alo<0.5), allophane contents increased, accompanied by higher pH values (pHH2O>5 and <7). Based on rheological data, the gel–sol–gel transformation (thixotropy) was better defined in sil-andic Andosols. Integral z, a dimensionless rheological parameter that represents quasi-elasticity was used to quantify stiffness degradation, and to identify single stages of thixotropy in allophanic Andosols. Scanning electron micrographs revealed that mineralogical components were predominated by volcanic glass (e.g. vesicular) and amorphous iron oxides in addition to fungal hyphae in younger acidic Andosols, while these characteristics were absent in well-developed Andosols. Here weathered minerals e.g. biotite, as well as halloysite, (proto)imogolite and allophanes were identified, indicating desilication and a shift from alu-andic to sil-andic Andosols. Zeta potentials derived from conducted particle charge density (PCD) measurements supported the assumptions that (i) Al-humus-complexes promoted aggregation in partially superhydrophobic topsoils of alu-andic Andosols, especially at ungrazed sites (or 1 year under pasture), and that (ii) thixotropic behaviour is related to allophanic, sil-andic Andosols, and better pronounced at sites which had been under pasture for 50 years.

Influence of Winter Grazing on Water and Heat Flow in Seasonally Frozen Soil of Inner Mongolia

Snowmelt infiltration and soil thawing processes are essential for understanding surface and subsurface hydrology under the cold and arid climatic conditions found in grazed Inner Mongolia grassland soils. Over a 6‐yr period (2004–2009), we evaluated the effects of winter grazing and freezing/thawing cycles on (i) soil hydraulic and thermal properties, (ii) the dynamics of field soil moisture and temperature, and (iii) the contributions of snowmelt and soil thawing to the summer water balance. Two adjacent contrasting sites were selected: a site that has been ungrazed since 1999 (UG99), and a site that has been grazed during the winter (WG). The results showed that the freezing/thawing cycles changed soil hydraulic and thermal properties. Associated with those freezing‐induced changes, winter grazing decreased soil moisture by 5–10% throughout the whole year (October 2005 to September 2006), increased soil temperature by 1 to 3°C in summer, and decreased it by 2 to 5°C in winter. The grazed site with lower vegetation/snow cover and larger thermal conductivity had greater freezing rates and larger soil temperature fluctuations on a daily scale than the ungrazed site. Winter precipitation (snow + rainfall) contributed 15% of the total annual water balance for the UG99 site, but only 11% for WG site. We concluded that a detailed analysis of the spring snowmelt infiltration was critical for calculating seasonal water and energy balances in this region to fully understand the hydrological and ecological processes.

Responses of vegetation to different land-use histories involving grazing and fire in the North-east Patagonian Monte, Argentina

In arid and semiarid lands around the world, vegetation is distributed in patches within a bare soil matrix. Vegetation in the North-east Patagonian Monte, Argentina is a shrubland steppe, and patches are dominated by shrubs, with grasses, forbs and cryptogams under their canopy. It was hypothesised that grazing increases patchiness; and fires and wind erosion homogenise the distribution of vegetation. It was predicted that there would be: (1) greater cover, specific frequency and richness of shrubs in grazed sites; (2) greater cover, specific frequency and richness of herbs and preferred grasses in ungrazed sites; and (3) a random pattern of distribution in burnt areas. Aerial cover of all perennial species was measured at six sites with different land-use histories: heavily grazed, medium grazed, ungrazed, long exclosure from grazing followed by grazing, burnt and then ungrazed, and burnt and then grazed. Species were grouped into five functional types: shrubs, sub-shrubs, preferred grasses, non-preferred grasses and forbs. The results showed significant differences in the cover of preferred and non-preferred grasses, forbs and total cover with previous grazing but there was no evidence of shrub encroachment. Species frequency and richness decreased especially with increased grazing intensity. The pattern of spatial distribution changed from aggregated in grazed sites to random in ungrazed and burnt sites for all plant functional types. At the population level, the cover of the grass, Poa ligularis, was greatest on ungrazed sites whereas the cover of the shrub, Chuquiraga erinacea, was greatest on burnt sites. It is concluded that, after applying a heterogeneous patchwork of disturbance, such as grazing, or with fire, followed by periods of rest, the plant diversity is increased.

Trait‐based climate change predictions of plant community structure in arid steppes

Summary Global climate change is possibly one of the most important challenges for current and future human populations due to its wide‐ranging effects on ecosystems. Global prediction models suggest that in some areas of the world (e.g. Northern Africa, Central America) an increase in aridity might strongly disturb agricultural production and affect food security. To counterbalance these negative effects, reliable predictive models are needed to anticipate ecosystem changes. We tested the ability of the Community Assembly by Trait‐based Selection (CATS) model that is based on the principle of maximum entropy and trait‐based environmental filtering, to predict actual and future plant community composition in the arid steppes of eastern Morocco. Specifically, we asked whether this model was adequate for predicting actual community composition, based on predicted community‐weighted mean (CWM) traits, and what would be the changes in community composition under various scenarios of climate change for the period 2080—2099. The CATS model could predict &gt; 90% of actual community composition if the actual CWM traits were known but only ˜40% if the CWM values were predicted from estimated aridity and grazing values. The predictions of community composition for 2080—2099 suggested that, regardless of the climate change scenario considered, the dominant group in grazed and ungrazed sites would shift from ruderal species to stress‐tolerant sub‐shrubs, which would constitute up over 80% of total community composition in some cases. Synthesis. Our findings suggest that effects of climate change will strongly modify plant community structure in arid steppes, possibly accentuating the process of desertification, and reducing the pastoral value of the vegetation. Future research efforts should concentrate on the identification of strong trait–environment relationships to improve model predictions.

Does soil seed bank diversity limit post-fire regeneration in small, fragmented, long-unburnt remnants of fire adapted vegetation?

Soil collected from 38 sites on Kangaroo Island in South Australia, containing small remnants of senescent Eucalyptus cneorifolia-dominated mallee, was subject ex situ to both smoke aerosol and heat treatment to simulate burning. Further soil from a subset of 29 of the sites was left untreated as a control. A total of 113 native plant species and 50 introduced species germinated across all sites. Fifty-three of the native plant species that germinated were absent in the above-ground vegetation, including twelve rare or threatened species, and three species previously unrecorded from Kangaroo Island. Fourteen native species and six introduced species germinated in heat plus smoke treated soil but not in untreated soil from the same sites. Non-metric multidimensional scaling ordination indicated differences in native species composition between sites with a long history of sustained livestock grazing (“grazed” sites) and largely ungrazed sites (“ungrazed” sites). On average, significantly more native species germinated from treated soil sampled from “ungrazed” sites than were found in the standing vegetation, while for “grazed” sites this difference was not significant. This indicates the greater potential for post-fire regeneration of native vegetation from the soil seed bank of ungrazed sites than from that of long grazed sites. Both “ungrazed” and “grazed” sites contained weeds in their soil seed banks, including some species which were stimulated by heat plus smoke. This indicated that competition from weeds is potentially a problem when fire is used as a management tool to regenerate senescent understoreys.

Impact of cattle grazing on the occupancy of a cryptic, threatened rail

Impacts of livestock grazing in arid and semiarid environments are often concentrated in and around wetlands where animals congregate for water, cooler temperatures, and green forage. We assessed the impacts of winter-spring (November-May) cattle grazing on marsh vegetation cover and occupancy of a highly secretive marsh bird that relies on dense vegetation cover, the California Black Rail (Laterallus jamaicensis coturniculus), in the northern Sierra Nevada foothills of California, U.S.A. Using detection-nondetection data collected during repeated call playback surveys at grazed vs. ungrazed marshes and a "random changes in occupancy" parameterization of a multi-season occupancy model, we examined relationships between occupancy and habitat covariates, while accounting for imperfect detection. Marsh vegetation cover was significantly lower at grazed marshes than at ungrazed marshes during the grazing season in 2007 but not in 2008. Winter-spring grazing had little effect on Black Rail occupancy at irrigated marshes. However, at nonirrigated marshes fed by natural springs and streams, grazed sites had lower occupancy than ungrazed sites. Black Rail occupancy was positively associated with marsh area, irrigation as a water source, and summer vegetation cover, and negatively associated with marsh isolation. Residual dry matter (RDM), a commonly used metric of grazing intensity, was significantly associated with summer marsh vegetation cover at grazed sites but not spring cover. Direct monitoring of marsh vegetation cover, particularly at natural spring- or stream-fed marshes, is recommended to prevent negative impacts to rails from overgrazing.

Direct and Indirect Effects of Grazing by Introduced Mammals on a Native, Arboreal Gecko (Naultinus gemmeus)

We examined relationships between livestock grazing and the activity of introduced rodents and population density of Jewelled Geckos, Naultinus gemmeus (Diplodactylidae) on the Otago Peninsula, South Island, New Zealand. We expected livestock grazing to prevent the proliferation of rank grass (which is often associated with high rodent densities) and thereby reduce the frequency of predation by rodents on Jewelled Geckos. Thus, we predicted activity of rodents to be lower, and density of Jewelled Geckos higher, at sites grazed by livestock. We tested this for two habitats: Coprosma spp. shrubland and regenerating kānuka (Kunzea ericoides) forest. We quantified density of Jewelled Geckos using visual searches, photography and mark–recapture (POPAN formulation). We used tracking tunnel surveys to estimate the activity of introduced rodents. The activity of rodents (Rattus spp. and Mus musculus) was significantly higher at ungrazed compared to grazed sites in both habitats. Density of Jewelled Geckos in Coprosma was over four times higher at grazed sites and decreased with increasing rodent activity; however, in kānuka, we found a contrasting result with density being significantly higher at the ungrazed sites. We infer that in ungrazed Coprosma, rank grasses support high rodent densities and, consequently, high predation of Jewelled Geckos. Thus, grazing by introduced livestock may promote the survival of Jewelled Geckos and the persistence of high density populations in Coprosma shrubland. In contrast, grazing in regenerating kānuka may impact on Jewelled Geckos negatively, possibly by removing thermal refugia.

Grazing effects of Black Swans Cygnus atratus (Latham) on a seasonally flooded coastal wetland of eastern Australia

Little is known about the effects of grazing by birds on seasonally flooded Australian wetlands. Grazing by Black Swans Cygnus atratus (Latham) has an obvious visual impact in Little Broadwater, an ecologically important wetland on the Clarence River floodplain on the east coast of Australia. We measured the impact of grazing by swans in this wetland from March to September 2007 by comparing the structure and biomass of marsh vegetation (emergent and submerged macrophytes) in sites from which swans had been excluded and sites to which they had access. In grazed sites, after 135 days, the mean above-sediment biomass of the dominant sedge Eleocharis equisetina C. Presl was 52% less than in ungrazed sites. This difference was mostly because of the loss of leaf biomass above the waterline in grazed sites where biomass had been reduced by 99% compared with ungrazed sites. This created more habitat for other birds such as wading birds (e.g., Royal Spoonbills Platalea regia Gould) and dabbling ducks (e.g., Grey Teal Anas gracilis Buller). Where water levels can be artificially manipulated, local wetland managers could attempt to restore the flood pulse to wetlands that are large enough to sustain Black Swan populations to retain a variety of other waterbirds that require open water.

Twice-Over Rotational Grazing and Its Impacts on Grassland Songbird Abundance and Habitat Structure

The majority of native prairie has been lost throughout North America. Much of the remaining prairie is used for livestock grazing, so conservation of prairie species depends on sustainable grazing practices. Our objective was to evaluate the benefits of twice-over rotational grazing, in comparison with continuous season-long grazing and ungrazed “idle” fields, in conserving prairie songbirds. Northern mixed-grass prairie in southwest Manitoba, Canada is near the northern range limits for many endangered grassland birds, and thus is an important area for evaluating the contribution of twice-over grazing in the conservation of songbirds, including species at risk. In 2008 and 2009, we compared the relative abundances and diversity of grassland birds on 22 twice-over rotation, 15 season-long, and 8 ungrazed sites, using multiple 100-m fixed-radius point-count plots per site. Analyses were conducted using generalized linear mixed models. Although one obligate grassland bird, Savannah sparrows (Passerculus sandwichensis), had significantly higher relative abundances on twice-over than season-long sites in 2009, season-long pastures had higher species richness and diversity of obligate grassland birds in both years. Season-long grazing may actually benefit grassland bird communities by creating spatially heterogeneous but temporally stable areas of high and low livestock use within the pasture, thus increasing diversity of microhabitats. We found little evidence that twice-over grazing contributed to the conservation of grassland songbirds in subhumid northern mixed-grass prairies.

Assessing light to moderate grazing effects on grassland production using satellite imagery

Understanding the influences of grazing intensity on grassland production is essential for grassland conservation and management improvement. Grazing at light to moderate intensity theoretically enhances grassland production, thus benefiting grassland ecosystems. However, inconsistent results of the beneficial effects of light to moderate grazing on grassland production were reported due to the lack of accurate and repeatable techniques for discriminating grazing effects from other abiotic factors. Advanced remote-sensing techniques provide a promising tool for filling this gap in grazing effects research due to their high spatial and temporal resolution. In this article, the influences of light to moderate grazing on grassland production in mixed grasslands were investigated for the period 1986–2005, using spectral data derived from satellite images. The effects of precipitation on the detection of grazing-induced production change were also analysed. The results revealed that the normalized canopy index (NCI) showed superior performance in quantifying grassland production in mixed grasslands. Significant differences in grassland production between grazed and ungrazed treatments occurred in the three years with above-average and average growing-season precipitations (April–August), but not in the dry years. Most of the variation in production (75%) was explained by growing-season precipitation for both grazed and ungrazed sites. Our results demonstrate the feasibility of using remote-sensing data to monitor long-term light to moderate grazing effects and the important role of precipitation, especially growing-season precipitation, in modulating production in mixed-grassland ecosystems.

Aggregate stability and physical protection of soil organic carbon in semi‐arid steppe soils

Spatial inaccessibility of soil organic carbon (SOC) for microbial decay within soil aggregates is an important stabilization mechanism. However, little is known about the stability of aggregates in semiarid grasslands and their sensitivity to intensive grazing. In this study, a combined approach using soil chemical and physical analytical methods was applied to investigate the effect of grazing and grazing exclusion on the amount and stability of soil aggregates and the associated physical protection of SOC. Topsoils from continuously grazed (CG) and ungrazed sites where grazing was excluded from 1979 onwards (UG79) were sampled for two steppe types in Inner Mongolia, northern China. All samples were analysed for basic soil properties and separated into free and aggregate‐occluded light fractions (fLF, oLF) and mineral‐associated fractions. Tensile strength of soil aggregates was measured by crushing tests. Undisturbed as well as artificially compacted samples, where aggregates were destroyed mechanically by compression, were incubated and the mineralization of SOC was measured. For undisturbed samples, the cumulative release of CO2‐C was greater for CG compared with UG79 for both steppe types. A considerably greater amount of oLF was found in UG79 than in CG soils, but the stabilities of 10–20‐mm aggregates were less for ungrazed sites. Compacted samples showed only a slightly larger carbon release with CG but a considerably enhanced mineralization with UG79. We assume that the continuous trampling of grazing animals together with a smaller input of organic matter leads to the formation of mechanically compacted stable ‘clods’, which do not provide an effective physical protection for SOC in the grazed plots. In UG79 sites, a greater input of organic matter acting as binding agents in combination with an exclusion of animal trampling enhances the formation of soil aggregates. Thus, grazing exclusion promotes the physical protection of SOC by increasing soil aggregation and is hence a management option to enhance the C sequestration potential of degraded steppe soils.

Modeling regional variation in net primary production of pinyon–juniper ecosystems

Spatial dynamics of carbon fluxes in dryland montane ecosystems are complicated and may be influenced by topographic conditions and land tenure. Here we employ a modified version of the Carnegie Ames Stanford Approach (CASA) ecosystem model to estimate annual net primary production (NPP) at a fine spatial resolution (30m) in pinyon–juniper (P–J) woodlands of the Colorado Plateau. NPP estimated by CASA was generally comparable to validation data from a statistical NPP model and field observations. We then compared modeled NPP results with spatial layers of topography and managed grazing to assess the influences of these factors on NPP. At the regional scale, there was a positive correlation between elevation and NPP (r2=0.20, p<0.0001), mainly due to an orographic effect, but slope and slope facing-derived dryness indices failed to explain modeled variation in NPP. Topographic analyses based on six terrain aspect classes showed that cooler and wetter north-facing slopes yielded higher NPP than did south-facing slopes. A multiple regression consisting of three numerical topographical attributes (elevation, slope and a dryness index) yielded the highest predictability for CASA NPP (adjusted r2=0.24, p<0.0001). Modeled NPP of a grazed site was significantly higher than that of an ungrazed site. Combining the results from this study and previous research efforts suggests that grazing may be correlated with higher woody vegetation cover, which elevates NPP in P–J woodlands of the Colorado Plateau. The findings reveal that the spatial pattern of NPP is complex, and can be strongly affected by topographic and/or anthropogenic factors even in relatively remote areas of this dryland region.

Long-term experimental restoration in a calcareous grassland: Identifying the most effective restoration strategies

Calcareous grasslands are among the most diverse habitats, supporting species-rich vegetation. Propagule limitation and availability of microsites for germination represent major constraints to the successful restoration of these grasslands. To date, little information is available on the effectiveness of seed addition and soil disturbance on the restoration success of encroached semi-natural calcareous grasslands. Here, we conducted a 1year before –9year after control-impact (BACI) study aimed at testing the effect of the addition of seeds of native species and livestock grazing on calcareous grasslands. Each restoration measure and their combination differed in their impact on these communities and varied over time. Grazing had a significant, beneficial, impact on these communities, although the impact was species-specific. On average, grazed plots were characterized by a higher number of species and a lower vegetation cover. Nine years after treatment application, grazed site were dominated by Trifolium incarnatum subsp. molinerii, Xeranthemum cylindraceum, Orlaya grandiflora, Teucrium chamaedrys and Bromus erectus while ungrazed sites were dominated by B. erectus, X. cylindraceum, O. grandiflora and Prunus spinosa. Only 8 out of 34 species responded significantly to disturbance or/and disturbance and seed addition while 22 species were significantly affected by the sampling year and 18 by a blocking factor. The low recruitment from added seeds and the fact that seed addition is a time-and labor-consuming activity suggests that an adequate level of disturbance and natural regeneration represent the most cost-effective approach to the restoration of these calcareous grasslands.

Impacts of cattle grazing on small-rodent communities: an experimental case study

We used experimental cattle ungrazed and grazed sites to evaluate what impact different intensities of cattle grazing have on deer mice ( Peromyscus maniculatus (Wagner, 1845)) and meadow voles ( Microtus pennsylvanicus (Ord, 1815)). Live-trapping of these small rodents was conducted on paired treatment plots (grazed and ungrazed) at Sheep River Provincial Park in southwestern Alberta, Canada. Before grazing started, both rodent species were equally abundant in either grazed or ungrazed sites. Introduction of grazing resulted in strong but differing responses by both rodent species. Deer mice had higher population density (measured as individual animals trapped) in the grazed than in ungrazed plots, but their body mass was negatively correlated with increasing grazing pressure. Meadow voles were more heavily affected by grazing, as a strong avoidance of cattle-grazed plots was observed already at low grazing intensity. In addition, cattle grazing had noticeable effects, impacting the survival, sex and age ratios, and the ectoparasite prevalence of these two rodent populations. We conclude that there are diverse and different levels of impact of cattle grazing on those two rodents, leading to much more complex species interactions than previously thought. We suggest that the presence or absence, density, and body condition of small mammals could be used as a tool for ecosystem health assessment.

Local Adaptation and the Effects of Grazing on the Performance of Nassella pulchra: Implications for Seed Sourcing in Restoration

The use of local seed sources for revegetation is accepted practice to reduce the potential that propagules will be poorly adapted to site conditions. However, data are often lacking to determine the distance within which seed sources represent local genotypes. Short‐term reciprocal transplant studies represent a class of tools to detect local adaptation of target species. We conducted a reciprocal transplant of Nassella pulchra between two central California locations to test for adaptation to local environmental conditions over a 3‐year period. Experimental plots at one location were split between grazed and ungrazed sites to evaluate the potential influence of livestock grazing on the detection or magnitude of local adaptation. During each year of the study, evidence of a home‐site advantage depended on the location, traits studied, and population. At the end of the 3‐year study period, however, we detected consistent evidence of a home‐site advantage for seedling biomass among grazed sites at one location and ungrazed plots at the other location. In effect, local adaptation was only apparent in the final year of the study. Short‐term reciprocal transplant studies are an effective tool to guide the selection of seed sources most likely to germinate and to become established at a restoration site, but such studies cannot rule out local adaptation, which may not be immediately detectable.

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

The increase of grazing intensity may alter the fluxes of mass and energy in grassland ecosystem due to fast population growth and distinct land-use change. To understand effects of different grazing intensities on soil thermal properties and heat flux, 5 sites under two representative vegetation types: Leymus chinensis (LC) and Stipa grandis (SG) in Inner Mongolia, China were investigated: two un-grazed sites since 1979 (LCUG79 and SGUG79), two moderately grazed sites which are winter grazed in LC (LCWG, 0.5 sheep units ha −1 year −1) and continuously grazed in SG (SGCG, 1.2 sheep units ha −1 year −1), and one heavily grazed site (LCHG, 2.0 sheep units ha −1 year −1). Soil water content and temperature were registered in the growing seasons: 2008 and 2009. The results in the more sensitive top 20 cm layer showed that heavy grazing induced the lowest soil water content, followed by winter grazing in the LC region. Continuous grazing caused higher soil moisture compared with un-grazed in SG region, which can be explained by the on site adjusted grazing intensity. For all sites, soil volumetric heat capacity and thermal conductivity increased with depths, which was in accordance with soil moisture. In LC region, the thermal conductivity was greater at the LCHG site than at the LCUG79 and LCWG sites, but the volumetric heat capacity was not significantly different between them. In SG region, these properties were greater at SGCG site than at SGUG79 site. Net soil heat flux generally moved downwards during the growing season. The greatest value was at LCHG site but lowest at LCUG79 site in LC region. On the contrary, a lower value was observed at SGCG site because of higher soil water content compared with SGUG79. For two un-grazed sites, heat flux was greater under SG vegetation than under LC vegetation. The long-term rainfall induced upward heat flux, but short-term rainfall caused a sharply downward increase. Without raining, the daily maximum and minimum of heat flux concurred with those of air temperature at LCHG site, but delayed at other sites. In conclusion, we can state that grazing intensity affects the soil thermal properties and heat flux, but vegetation type was only verified to impact heat flux. An appropriate grazing intensity improves soil water and thermal regimes compared with the long-term un-grazed sites.