Absence Of Grazing Research Articles

Covariation of soil nutrients drives occurrence of exotic and native plant species

Abstract Nutrient enrichment with phosphorus (P) and nitrogen (N) threatens biodiversity globally, particularly because it drives invasion by exotic plant species. However, the effects of nutrients on plants can interact with other ecosystem processes such as competition and grazing, and these interactions can be scale‐dependent. Furthermore, P and N are often correlated, making it difficult to separate the effects of each. After implementing a herbivore‐exclusion experiment for 3 years in grassy woodlands, SE Australia, we assessed the relationship of native and exotic plant species with soil nutrients, grazing and spatial scale. Nitrate (NO3), available P and organic carbon (C) were partitioned into two principle components and further divided into plot‐ and site‐level variation. The correlated components of NO3, P and C (principle component 1) appeared to drive a dominant competitive relationship. Two exotic annual grasses likely out‐competed native and exotic species in areas high in NO3, P and C. In contrast, responses to principle component 2 (gradient from high NO3 to high P) indicated that native and exotic species generally benefitted when NO3 was high relative to P. Plant–nutrient relationships were further modified by grazing and spatial scale. Native and exotic species benefitted from grazing but did so under specific nutrient regimes. Summed occurrence of exotic species and native richness was reduced in the absence of grazing and high values of NO3 relative to P at site scales, but not at plot scales, suggesting competition is more important at a scale of hundreds of square metres while soil properties are most important at the plot scale (25 m2). Synthesis and applications. Dividing soil nutrients into uncorrelated principal components showed that niche space for native and exotic plant species is partitioned by positive and negative covariation of nitrate (NO3), phosphorus (P) and carbon (C), and interactions of these soil properties with grazing and spatial scale. Increasing NO3 relative to P could increase species richness, but requires further experimentation to define beneficial concentrations. Native plant richness can be enhanced with adequate levels of grazing by native herbivores and, in the long term, by reducing P from areas enriched with NO3 and P. These actions will help prevent likely competitive dominance by annual exotic grasses.

Soil carbon and nitrogen stocks, light organic matter, and remaining phosphorus under a crop-livestock integration system

Crop-livestock integration (CLI) is a management system that has been developed for a variety of soil and climatic conditions, which combined with the no-tillage system (NTS), has many variations in Brazil, particularly regarding grazing intensity. The objective of this study was to assess the effects of different grazing intensities and soybean (Glycine max L.) crops on carbon (Cst) and nitrogen (Nst) stocks, light organic matter (LOM), root content of the LOM (RLOM), and remaining phosphorus (Prem) in an Oxisol under CLI. The treatments consisted of three different heights (0.25 m [P25], 0.35 m [P35], and 0.45 m [P45]) of pasture grown in a CLI system. Two control areas, an area without grazing (AWG) and a native vegetation area of the Cerrado biome (NCA), which were adjacent to the experimental area, were compared with the cultivated areas. Soil samples were collected from 0.00-0.05, 0.05-0.10, and 0.10-0.20 m beneath each area in a completely randomized design with six replications. Soil characteristics were evaluated in the post-pasture cycle period (PP) and the post-soybean crop period (PC), which coincided with the wet and dry seasons, respectively. The NCA had more LOM in the 0.00-0.05 m layer during the PC and the 0.05-0.10 m layer during both the PP and the PC, C in the LOM in the 0.00-0.20 m layer during the PP and the PC, N in the LOM in the 0.00-0.05 m layer in the PC and the 0.05-0.10 m layer in the PP and the PC, and Cst in the 0.00-0.20 m layer in the PP and the PC than the cultivated areas, but a lower soil density (SD) and Prem in the 0.00-0.20 m layer during both the PP and the PC. Treatment P35 had more Nst in the PC and RLOM in the PP than the other cultivated treatments and the AWG. The absence of grazing in the AWG decreased the SD from the PP to the PC, while the treatments with different grazing intensities had similar values throughout this period. Our results suggest that production could be intensified under light and moderate grazing intensities in the CLI system.

Monaro dieback: simple answers are too simple

ABSTRACTRoss and Brack (2015) reported the first formal survey of dieback of Eucalyptus viminalis occurring across the Monaro Plains of south-eastern New South Wales (NSW). The survey found that the dieback covered about 2000 km2 of public and private land, and that there was no significant correlation between the observed dieback and any of the environmental or management parameters studied. Jurskis (2016) claims that the dieback in the Monaro is ‘not difficult to explain’, as it is simply due to the absence of grazing or regular light fire. We argue that this hypothesis cannot explain the ‘Monaro dieback’, and further research is required to determine the underlying cause/s. Since publication of the original survey, the authors have received a wide range of reports from academic and general observers about dieback of various species in various environments across the country. Recent observations now suggest that the ‘Monaro’ dieback has extended beyond the original boundary and into other Eucalyptus species. We emphasise the need for an agency or organisation to act as a central collection point for geographically referenced and time-stamped photographs or descriptions from the public in order to better monitor tree health across the country.

Effects of grazing on the acquisition of nitrogen by plants and microorganisms in an alpine grassland on the Tibetan plateau

Nitrogen (N) limitation leads to intense competition between plants and soil microorganisms for available N. However, it is unclear how grazing affects the acquisition of N by plants and microorganisms. We conducted short-term 15N tracer experiments during the growing season (June, early growing season; July, mid-growing season; and September, late growing season) in an alpine grassland on the Tibetan Plateau to investigate the effects of grazing on the acquisition of NO3 −-N, NH4 +-N, and glycine-N by plants and soil microorganisms. Three dominant plant species (one graminoid, Kobresia pygmaea, and two forbs, Potentilla bifurca and Potentilla multifida) were selected for the study. As these species represented >90% of the vegetation, the plant recovery of 15N reflected competition at the plant community. Grazing decreased the recovery of 15N by soil microorganisms and plants by 46 and 69%, respectively, indicating that grazing strongly reduced the uptake of 15N by plants and microorganisms and altered the partitioning of 15N between them. Significant interactions were found between grazing, season and the different forms of N. In the absence of grazing, plants acquired relatively more N than soil microorganisms for the three forms of N in July and September, whereas the microorganisms obtained relatively more 15N glycine in July and all three forms of N in September under grazing conditions. Under grazing, the plant root biomass played an important role in controlling plant–microbial N acquisition. Grazing alters the partitioning of inorganic and organic N between plants and soil microorganisms by reducing microbial 15N recovery to a lesser extent than plant 15N recovery. This indicates that heterotrophic microorganisms play an important part in N cycling in N-limited ecosystems.

Combined physical, chemical and biological factors shape Alexandrium ostenfeldii blooms in The Netherlands

Harmful algal blooms (HABs) are globally expanding, compromising water quality worldwide. HAB dynamics are determined by a complex interplay of abiotic and biotic factors, and their emergence has often been linked to eutrophication, and more recently to climate change. The dinoflagellate Alexandrium is one of the most widespread HAB genera and its success is based on key functional traits like allelopathy, mixotrophy, cyst formation and nutrient retrieval migrations. Since 2012, dense Alexandrium ostenfeldii blooms (up to 4500cellsmL−1) have recurred annually in a creek located in the southwest of the Netherlands, an area characterized by intense agriculture and aquaculture. We investigated how physical, chemical and biological factors influenced A. ostenfeldii bloom dynamics over three consecutive years (2013–2015). Overall, we found a decrease in the magnitude of the bloom over the years that could largely be linked to changing weather conditions during summer. More specifically, low salinities due to excessive rainfall and increased wind speed corresponded to a delayed A. ostenfeldii bloom with reduced population densities in 2015. Within each year, highest population densities generally corresponded to high temperatures, low DIN:DIP ratios and low grazer densities. Together, our results demonstrate an important role of nutrient availability, absence of grazing, and particularly of the physical environment on the magnitude and duration of A. ostenfeldii blooms. Our results suggest that predicted changes in the physical environment may enhance bloom development in future coastal waters and embayments.

Disturbance maintains native and exotic plant species richness in invaded grassy woodlands

AbstractQuestionCommunity invasion and dominance by exotic species can be abetted by disturbance and elevated nutrient levels. However, impacts of exotics on native species are often manifest through competition, suggesting disturbance or nutrient management could benefit native species. I therefore asked: does nutrient reduction through carbon addition, or disturbance to reduce biomass, contribute to restoration by increasing occurrence and richness of native plant species?LocationSE Australia.MethodsUsing a field experiment spanning 4 yrs, this study assessed the potential for carbon addition, three types of disturbance (burn, crop, slash) and their interaction with native herbivore grazing to reduce exotic, and increase native, plant species in a critically endangered grassy woodland in SE Australia.ResultsAdding carbon reduced occurrence of one native and three exotic species, while increasing one exotic and one native species. The value of adding carbon for restoration was therefore ambiguous. Fencing to exclude the high‐density kangaroo population had temporary beneficial effects, suggesting that grazing reduced the number of native and exotic plant species by up to 56% and 21%, respectively. Species richness declined by year 3 in fenced areas, likely through competitive exclusion. Burn, slash and crop treatments also provided disturbance that maintained species richness and occurrence of many species, both native and exotic. Most grazing interactions reflected the benefit of alternative disturbance in the absence of grazing. However, there was also evidence that two species declined when crop and grazing acted in combination.ConclusionsVery high grazing by native herbivores reduced plant species richness in this study. However, grazing or other forms of disturbance appeared critical for preventing a small number of exotic species from driving down occurrence and richness of many other native and exotic plant species. Although increased exotic species richness is undesirable, disturbance led to a better outcome for conservation than the low‐disturbance alternatives.

Grazing moderates increases in C3 grass abundance over seven decades across a soil texture gradient in shortgrass steppe

AbstractQuestionsHow does long‐term exclusion of cattle grazing influence plant community composition in a semi‐arid grassland? Can spatial variation in the effects of cattle grazing exclusion be explained by variation in soil texture?LocationShortgrass steppe, northeast Colorado, USA, in the North American Great Plains.MethodWe used 16 long‐term (72 yr) cattle exclosures to examine the effects of grazers on plant communities and evaluate whether grazer effects interact with soil texture.ResultsAlthough shortgrass steppe communities are relatively unaffected by grazing in the short‐term (one to two decades), exclusion of cattle grazing for seven decades caused a compositional shift from dominance by a C4 shortgrass (Bouteloua gracilis) to co‐dominance by a C3 midgrass (Pascopyrum smithii) and B. gracilis. The strength of this shift was highly variable across sites. Soil texture was correlated with the abundance of certain plant species, but did not explain variation in the magnitude of grazer effects. Grazed communities contained perennial and annual growth forms with a diversity of strategies to co‐exist with grazers and B. gracilis. Ungrazed communities included increased abundance of annual, ruderal forbs and three woody plant species. Grazing effects occurred against a backdrop of changing plant communities: during the past seven decades, C3 perennial graminoids and sub‐shrubs have increased in relative abundance in both grazed and ungrazed communities.ConclusionsOur long‐term experiment shows that community responses to grazing in this semi‐arid grassland occur very slowly, but are predictable, with C4 shortgrasses eventually giving way to taller C3 grasses and ruderal forbs. Spatial variation in grazing effects across sites (and lack of a relationship with soil texture) may reflect the importance of fine‐scale heterogeneity in C3 grass abundance, and the slow rate at which taller C3 grasses can coalesce into mono‐dominant patches that outcompete C4 shortgrasses. Increased abundance of C3 species over the past seven decades, both in the presence and absence of grazing, may be related to recovery from the severe drought and dust storms of the 1930s as well as enhanced growth of C3 plants under increasing atmospheric [CO2].

Soil moisture and soybean physiology affected by drought in an integrated crop-livestock system

Abstract: The objective of this work was to evaluate the impact of grazing intensities after 11 years of an integrated crop-livestock system, under no-tillage, on soil moisture and soybean physiological parameters during a summer season affected by drought. The experiment was established in 2001 on a Rhodic Hapludox. Treatments consisted in the succession of soybean (summer) and a mixed pasture of black oat + Italian ryegrass (winter), under different beef-cattle grazing intensities: intensive grazing, with 0.10-m pasture height; moderate grazing, with 0.20-m pasture height; and no grazing. During the soybean cycle, in the 2011/2012 crop season, rainfall was 40% of the climatological normal. The soil moisture was within the limits of available water both under moderate grazing and no grazing, at 0.00-0.50-m soil depth, but, under intensive grazing, it was below the permanent wilting point, especially up to the grazing height of 0.20 m. Intensive grazing affected negatively the plant physiology parameters, reaching peaks of -2.5 MPa and +6°C for leaf water potential and leaf-air temperature difference, respectively. Moderate grazing or the absence of grazing, during the winter season, results in similar physiological responses, contributing to soybean plant homeostasis.

Light grazing of crop residues by sheep in a Mediterranean-type environment has little impact on following no-tillage crops

Abstract Crop residue is often grazed by sheep after harvest, over the dry summer period from December to March in Mediterranean environments. However, soil cover provided by crop residues is a key component of conservation agriculture for maintaining favourable soil structure and high yields. A series of 31 site × year experiments was conducted to assess the effect of summer stubble grazing on residue levels and following crop yields. Relatively light grazing, with stocking rates below 10 dry sheep equivalent (DSE) and between 90 and 471 DSE days ha −1 , had no significant effect on the amount of residue, soil properties, soil water, weeds or yield in the following crop. The main effect of grazing was to knock down and scatter the standing crop residues. However, longer term grazing at relatively high intensity (956 DSE days ha −1 ) on heavy soil, over both summer and winter, as in a pasture phase, did significantly reduce residue levels, infiltration and yield (by 59%). The effect of summer grazing on soil mineral N was small and inconsistent, with increased mineral N, by about 3–7 kg N ha −1 , following grazing at two of the 13 sites. By contrast, higher mineral N, by 2–15 kg N ha −1 , was measured in the un-grazed plots at three of the 13 sites. This was due to increased growth of legume pastures in the absence of grazing. More research is needed to confirm the yield effects when cropping after an annual pasture/fallow that is grazed over summer and winter, particularly on different soil types.

Effect of Cattle Grazing Routine on Erosion Processes, Harvest Yield and Quality of Fodder in Subalpine Belt of North Ossetia

Background/Objectives: The research is aimed at studying the effect of the pastureland use routine on altering the indicators of the soil fertility and on the erosion process development. Methods/Statistical Analysis: The studies were conducted in the mountains at an altitude of 1570 m above sea level on the mountain meadow subalpine soils with acidic reaction of soil solution (рН=5,9). The chemical analyses of the average runoff sample and that of the washout sample were carried out to determine the contents of the accessible forms of such nourishing elements as nitrogen, phosphorus and potassium. Findings: This study shows that in the middle of the last century a significant amount of agricultural products were produced in the North Caucasus Mountains; this output was significantly reduced due to soil erosion caused by poorly plant-protected surface and livestock congestion. Erosion leads to dispersion of soil horizon structure, megastructure reduction and increase in dust, it also results in increased soil specific weight and solid phase unit weight, in decreased air and capillary porosity with reduction of aggregate water stability and water permeability. In the absence of grazing, the total losses of nitrogen, phosphorus and potassium amounted to 7.84 kg/ha and 296.56 kg/ha with intensive pasturing, which was higher by 37.8 times. With the admissible levels of grazing intensity no reliable data for the productivity alteration was obtained, and in the grazing routine modes of 2/15, 3/10, 3/15 a decrease in the productivity was established. Grazing lowers the grass stand quality, while increasing the proportion of fiber, fat and ash. The yield of nutritional chemicals per 1 hectare increased under optimal grazing conditions and decreased under intensive grazing routines. Applications/Improvements: Recommendations for cattle grazing routines have been developed with regard to degraded and normally functioning pasturelands. It is proposed to avoid excessive grazing routines

A 150-year fire history of mulga (Acacia aneura F. Muell. ex Benth.) dominated vegetation in semiarid Queensland, Australia

Changes to fire regimes associated with European colonisation are implicated in declines in biodiversity and productivity in rangelands globally. However, for many areas there is incomplete knowledge of historical fire regimes and purported changes can become accepted wisdom with little empirical evidence. In the Mulga Lands of south-western Queensland, the dominant narrative implicates reduced fire frequency as a cause of woody vegetation thickening. We present a fire history of the Mulga Lands since pastoral exploration in the 1840s based on a review of explorer and early pastoralist journals, newspaper articles, interviews with long-term landholders and collation of satellite imagery. Fires in mulga communities are infrequent and only occur after at least two years of above-average summer rainfall. The assumption of regular pre-pastoral fires is not supported by available evidence. Since pastoral settlement in the 1860s, fire events affecting >1000 km2 have occurred seven times (1891–1892, 1904, 1918, 1950–1951, 1956–1957, 1976–1979 and 2011–2013), with only the 1950s fires affecting a >10% of the total area of mulga-dominated vegetation. We argue that fire is limited by fuel loads, which are in turn limited by rainfall events occurring only a few times a century. Even in the absence of grazing and active fire suppression fire intervals would be extremely long, perhaps 30–50 years in relatively fire-prone communities and much longer throughout most of the region. Combined with quantitative studies of fire and tree and shrub population dynamics, detailed fire histories will allow for more informed and nuanced debates about the role of fire in rangelands subject to abrupt management upheavals.

Pasture production and composition response after killing Eucalypt trees with herbicides in central Queensland

Clearing woodlands is practised worldwide to increase crop and livestock production, but can result in unintended consequences including woody regrowth and land degradation. The pasture response of two eucalypt woodlands in the central Queensland rangelands to killing trees with herbicides, in the presence or absence of grazing and regular spring burning, was recorded over 7 or 8 years to determine the long-term sustainability of these common practices. Herbage mass and species composition plus tree dynamics were monitored in two replicated experiments at each site. For 8 years following herbicide application, killing Eucalyptus populnea F. Muell. (poplar box) trees resulted in a doubling of native pasture herbage mass from that of the pre-existing woodland, with a tree basal area of 8.7 m2 ha–1. Conversely, over 7 years with a similar range of seasons, killing E. melanophloia F. Muell. (silver-leaved ironbark) trees of a similar tree basal area had little impact on herbage mass grown or on pasture composition for the first 4 years before production then increased. Few consistent changes in pasture composition were recorded after killing the trees, although there was an increase in the desirable grasses Dichanthium sericeum (R. Br.) A. Camus (Queensland bluegrass) and Themeda triandra Forssk. (kangaroo grass) when grazed conservatively. Excluding grazing allowed more palatable species of the major grasses to enhance their prominence, but seasonal conditions still had a major influence on their production in particular years. Pasture crown basal area was significantly higher where trees had been killed, especially in the poplar box woodland. Removing tree competition did not have a major effect on pasture composition that was independent of other management impositions or seasons, and it did not result in a rapid increase in herbage mass in both eucalypt communities. The slow pasture response to tree removal at one site indicates that regional models and economic projections relating to tree clearing require community-specific inputs.

Grazing, regional climate and soil biophysical impacts on microbial enzyme activity in grassland soil of western Canada

Grasslands cover more than 25% of the terrestrial surface of the Earth and hold 30% of the world’s terrestrial carbon (C) pool. While nearly all native grassland ecosystems are used for livestock production, sustainably managed grasslands also provide many ecosystem goods and services such as C storage. Despite the importance of grasslands to the global C cycle, little is known about how long-term management practices, including the presence or absence of grazing, directly and indirectly affect the soil microbial processes that regulate C and nutrient cycling. We measured the effect of long-term cattle grazing on microbial extra cellular enzyme activity (EEA) at 12 locations stratified among three distinct grassland types (foothills fescue, aspen parkland, and mixed grass prairie) across Alberta, Canada. Each location included paired grazed and non-grazed plant communities managed this way for at least 30 years. Specifically, we quantified EEA of enzymes responsible for C (β-1,4-glucosidase, β-d-cellobiosidase, β-xylosidase), C and nitrogen (N-actyl-glucosaminidase), and phosphorous (phosphatase) cycling in soil from 0 to 15 and 15–30cm depths. Although grazing effects on EEA remained weak (0.05≤p≤0.10) they were relatively consistent among enzymes (n=3/5), with β-d-cellobiosidase, N-actyl-glucosaminidase, and phosphatase EEAs all greater in non-grazed plant communities than in grazed communities. All EEAs were greater in the foothills fescue and mixed grass regions than in the parkland with the exception of β-1,4-glucosidase, which was relatively high at all locations. Multivariate analyses suggested the soil properties that best describe EEA are soil pH, organic matter and moisture content, together with total nitrogen (N). Additionally, EEAs were correlated with the cover of several dominant plant species. Four of five EEAs were positively correlated with the grassFestuca campestris, while N and C degrading enzymes were negatively correlated with the grasses Bouteloua gracilisandKoeleria macrantha, respectively. Net C cycling appears to be strongly controlled by β-1,4-glucosidase. In conclusion, grazing and associated changes in plant communities appear to decrease the EEAs of some enzymes, suggesting that microbes in non-grazed communities are actively decomposing a relatively greater amount of organic matter. However, when working across broad spatial ranges, our marginally significant results and post-hoc power analysis suggest the need for larger sample sizes (>23 replicates) to further elucidate relationships between EEAs and low intensity disturbances such as cattle grazing.

Herbivory and Competition of Tibetan Steppe Vegetation in Winter Pasture: Effects of Livestock Exclosure and Plateau Pika Reduction.

Rangeland degradation has been identified as a serious concern in alpine regions of western China on the Qinghai-Tibetan plateau (QTP). Numerous government-sponsored programs have been initiated, including many that feature long-term grazing prohibitions and some that call for eliminating pastoralism altogether. As well, government programs have long favored eliminating plateau pikas (Ochotona curzoniae), assumed to contribute to degraded conditions. However, vegetation on the QTP evolved in the presence of herbivory, suggesting that deleterious effects from grazing are, to some extent, compensated for by reduced plant-plant competition. We examined the dynamics of common steppe ecosystem species as well as physical indicators of rangeland stress by excluding livestock and reducing pika abundance on experimental plots, and following responses for 4 years. We established 12 fenced livestock exclosures within pastures grazed during winter by local pastoralists, and removed pikas on half of these. We established paired, permanent vegetation plots within and outside exclosures and measured indices of erosion and biomass of common plant species. We observed modest restoration of physical site conditions (reduced bare soil, erosion, greater vegetation cover) with both livestock exclusion and pika reduction. As expected in areas protected from grazing, we observed a reduction in annual productivity of plant species avoided by livestock and assumed to compete poorly when protected from grazing. Contrary to expectation, we observed similar reductions in annual productivity among palatable, perennial graminoids under livestock exclusion. The dominant grass, Stipa purpurea, displayed evidence of density-dependent growth, suggesting that intra-specific competition exerted a regulatory effect on annual production in the absence of grazing. Complete grazing bans on winter pastures in steppe habitats on the QTP may assist in the recovery of highly eroded pastures, but may not increase annual vegetative production.

Grassland Arthropods Are Controlled by Direct and Indirect Interactions with Cattle but Are Largely Unaffected by Plant Provenance.

Cattle grazing and invasion by non-native plant species are globally-ubiquitous changes occurring to plant communities that are likely to reverberate through whole food webs. We used a manipulative field experiment to quantify how arthropod community structure differed in native and non-native California grassland communities in the presence and absence of grazing. The arthropod community was strongly affected by cattle grazing: the biovolume of herbivorous arthropods was 79% higher in grazed than ungrazed plots, whereas the biovolume of predatory arthropods was 13% higher in ungrazed plots. In plots where non-native grasses were grazed, arthropod biovolume increased, possibly in response to increased plant productivity or increased nutritional quality of rapidly-growing annual plants. Grazing may thus affect plant biomass both through the direct removal of biomass, and through arthropod-mediated impacts. We also expected the arthropod community to differ between native and non-native plant communities; surprisingly, arthropod richness and diversity did not vary consistently between these grass community types, although arthropod abundance was slightly higher in plots with native and ungrazed grasses. These results suggest that whereas cattle grazing affects the arthropod community via direct and indirect pathways, arthropod community changes commonly associated with non-native plant invasions may not be due to the identity or dominance of the invasive species in those systems, but to accompanying changes in plant traits or functional group composition, not seen in this experiment because of the similarity of the plant communities.

The impact of grazing management on Orthoptera abundance varies over the season in Mediterranean steppe-like grassland

As semi-natural grassland has a high level of biological diversity, understanding the effects of grazing and its variation over time is important in order to identify sustainable grazing practices. We measured temporal variation in Orthoptera abundance and spatial vegetation structure during seasonal grazing in an extensive sheep-farming system. We studied five grazed pasture areas (pre-grazing and post-grazing) and two adjacent ungrazed grasslands. We recorded the total abundance of Orthoptera and described the vegetation structure of 175 replicate plots (25 per pasture/grassland) during six field sampling sessions. We demonstrated that the impact of grazing on Orthoptera abundance is species-specific and greatly varies over the grazing season. The decrease of phytovolume is significant after 4–7 weeks of sheep grazing. Total Orthoptera abundance was higher in pre-grazed plots than in ungrazed plots, and higher in ungrazed plots than in post-grazed plots. These differences were particularly high during the peak of adult abundance. No difference in species richness was observed between grazing intensities. Total Orthoptera abundance positively correlated to phytovolume only when grazing pressure was high. However, the relationship between abundance and phytovolume differed between species. Extensive grazing by sheep tends to homogenize spatial vegetation structure and to temporarily reduce total Orthoptera abundance at pasture scale. However, rotational grazing allows spatial and temporal heterogeneity in vegetation structure to be maintained at farm scale, heterogeneity that is beneficial for Orthoptera. In contrast, absence of grazing has a negative impact on Orthoptera abundance as it favours the accumulation of litter, which is detrimental for a high proportion of xerothermophilic Orthoptera associated with bare ground and short vegetation.

Effects of nutrient enrichment on coevolution of a stoichiometric producer-grazer system

A simple producer-grazer model based on adaptive evolution and ecological stoichiometry is proposed and well explored to examine the patterns and consequences of adaptive changes for the evolutionary trait (i.e., body size), and also to investigate the effect of nutrient enrichment on the coevolutin of the producer and the grazer. The analytical and numerical results indicate that this simple model predicts a wide range of evolutionary dynamics and that the total nutrient concentration in the ecosystem plays a pivotal role in determining the outcome of producer-grazer coevolution. Nutrient enrichment may yield evolutionary branching, trait cycles or sensitive dependence on the initial values, depending on how much nutrient is present in the ecosystem. In the absence of grazing, the lower nutrient density facilitates the continuously stable strategy while the higher nutrient density induces evolutionary branching. When the grazer is present, with the increasing of nutrient level, the evolutionary dynamics is very complicated. The evolutionary dynamics sequentially undergo continuously stable strategy, evolutionary branching, evolutionary cycle, and sensitive dependence on the initial values. Nutrient enrichment asserts not only stabilizing but also destabilizing impact on the evolutionary dynamics. The evolutionary dynamics potentially show the paradox of nutrient enrichment. This study well documents the interplay and co-effect of the ecological and evolutionary processes.

Un laboratorio di campo permanente nel Parco Nazionale del Pollino: dinamismo vegetazionale in formazioni prative d'alta quota

By virtue of its ecological and floristic diversity, the Pollino National Park plays a key role for biodiversity conservation in the Mediterranean context. The historical interest of botanists for this areas has provided a lot of descriptive information on its flora and vegetation. Nonetheless, data concerning the effects of current environmental transformations (i.e. land-use changes, climate warming) on local plant richness are still poor. For this reason, the Ente Parco Nazionale del Pollino has promoted a long-term monitoring plan to investigate biodiversity variations in orophylous herbaceous vegetation under two experimental scenarios: absence of grazing, and climate warming. To date, two years of observation revealed significant but contrasting responses in plant communities well differentiated by ecological and floristic features. To better understand the biodiversity variations caused by the experimental regime, the monitoring trials need to be continued over a longer timeframe.

Determining the Effects of Cattle Grazing Treatments on Yosemite Toads (Anaxyrus [=Bufo] canorus) in Montane Meadows

Amphibians are experiencing a precipitous global decline, and population stability on public lands with multiple uses is a key concern for managers. In the Sierra Nevada Mountains (California, USA), managers have specifically identified livestock grazing as an activity that may negatively affect Yosemite toads due to the potential overlap of grazing with toad habitat. Grazing exclusion from Yosemite toad breeding and rearing areas and/or entire meadows have been proposed as possible management actions to alleviate the possible impact of cattle on this species. The primary objective of this study was to determine if different fencing treatments affect Yosemite toad populations. We specifically examined the effect of three fencing treatments on Yosemite toad breeding pool occupancy, tadpoles, and young of the year (YOY). Our hypothesis was that over the course of treatment implementation (2006 through 2010), Yosemite toad breeding pool occupancy and early life stage densities would increase within two fencing treatments relative to actively grazed meadows due to beneficial changes to habitat quality in the absence of grazing. Our results did not support our hypothesis, and showed no benefit to Yosemite toad presence or early life stages in fenced or partially fenced meadows compared to standard USDA Forest Service grazing levels. We found substantial Yosemite toad variation by both meadow and year. This variation was influenced by meadow wetness, with water table depth significant in both the tadpole and YOY models.

Herbaceous vegetation response to grazing exclusion in patches and inter-patches in semi-arid pasture and woody encroachment

Semi-arid rangelands have strong feedbacks between vegetation and abiotic factors (rainfall and soil), which manifest at the small patch/inter-patch scale. The effects of excluding grazing at the small patch scale have not been studied in these systems, despite fine-grained patch/inter-patch mosaics determining landscape-scale ecosystem function and productivity. We established small (1m×1m) grazing exclosures and monitored change in herbaceous vegetation cover quarterly over 2 years, in grazed and ungrazed patches (high herbaceous vegetation cover) and inter-patches (low herbaceous vegetation cover), in woody encroachment and pasture sites in semi-arid eastern Australia. Prior to excluding grazing, herbaceous groundcover in pasture patches (63–67%) was significantly greater than in woody encroachment patches (15–16%) or inter-patches in both vegetation states (0–1%). The effect of grazing exclusion on herbaceous cover varied between patch type and vegetation state. In the absence of grazing, herbaceous cover was significantly greater in pasture patches than in woody encroachment patches at every monitoring time. Initial differences in herbaceous cover between woody encroachment patches and pasture patches was significantly less pronounced with continued grazing pressure, indicating that grazing pressure can negatively influence the positive effect of a lack of woody plants on herbaceous growth in pastures. Grazed pasture patches had significantly less herbaceous cover than ungrazed pasture patches at every monitoring time, whereas in woody encroachment, grazed patches had less herbaceous cover than ungrazed patches on only two occasions in the second year. Inter-patches in both vegetation states failed to respond to grazing exclusion in the 2-year study period. Herbaceous cover change in semi-arid rangelands is a function of grazing, rainfall and woody plant incidence. If grazing pressure in pasture patches is not carefully managed to maintain herbaceous cover, the positive effects of high rainfall and low woody plant abundance on herbaceous cover can rapidly diminish. Improving herbaceous groundcover overall will require an interventionist approach to overcome barriers to plant establishment in inter-patch areas such as the lack of resource retention.