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729 results for “Grazing”
Fig. 3 in Value of forest remnants for montane amphibians on the livestock grazed Mount Mbam, Cameroon
Fig. 3. Species accumulation curves of Mount Mbam by land use based on contemporary records.
Botryococcus braunii reduces algal grazing losses to Daphnia and Poterioochromonas through both chemical and physical interference
<p>The data and code provided here is used to analyze and visualize all data associated with the manuscript "<em>Botryococcus braunii</em> reduces algal grazing losses to <em>Daphnia</em><br>and <em>Poterioochromonas </em>through both chemical and physical interference" in the Journal of Applied Phycology under the DOI: 10.1007/s10811-024-03330-x</p> <p>Data should be analyzed in R or R studio. The code in the .Rmd file should execute automatically with no modifications by the user as long as the two csv files are placed in the same working directory that R is set to. The R project (.Rproj) file may also be opened directly to create an R project that is automatically set to the correct directory. Metadata explaining the contents of two data files is provided in the README.csv file.</p> <p>ABSTRACT: Crop protection from algal grazers is a key area of concern, as grazing zooplankton and flagellates can decimate microalgae crops and impede economic viability of cultivation for biofuels and bioproducts. Inhibition of grazing by chemical and physical interference is one promising solution; however, there have been few empirical tests of this approach that use defense traits innate to algal crop species. <em>Botryococcus braunii </em>is of particular interest because a) it excretes high levels of hydrocarbons and exopolysaccharides and b) forms colonies and possesses chemical defenses. Here we conduct a controlled laboratory experiment to test whether <em>B. braunii</em> can mitigate losses to grazing by two distinct grazers, <em>Daphnia magna</em> and <em>Poterioochromonas malhamensis</em>, due to both chemical inhibition and physical interference linked to large/inedible colonies. We show that chemical and physical defenses interactively reduce the total effect of grazing, thus significantly increasing the biomass and growth rates of cultures of <em>B. braunii</em> and <em>Nannochloropsis limnetica</em> when either grazer is present. We also find that <em>B. braunii </em>medium enhances the growth of <em>N. limnetica</em>. Our study demonstrates how community engineering can identify synergies arising from algal co-cultivation (e.g., by using industrially relevant strains for crop protection). While our lab study serves as a proof-of-concept, future research should test this strategy at pilot scale; if successful, such ecological discoveries may help to reduce the costs of large-scale deployment of algal cultivation for sustainable foods, fuels, bioproducts (e.g., bioplastics), and carbon capture.</p>
Sheep Grazing in vineyards - agrovitiforestry (near Mértola, South Portugal)
Open the record for dataset details and reuse information.
Data from: Fire, grazing, and climate shape plant-grasshopper interactions in a tallgrass prairie
1. Species interactions are integral to ecological community function and the structure of species interactions has repercussions for the consequences of species extinctions. Few studies have examined the role of environmental factors in controlling species interaction networks across time. 2. We examined variation in plant-grasshopper network structural properties in response to three major grassland drivers: periodic fire, ungulate grazing and climate. 3. We sequenced a plant barcoding gene from extracted grasshopper gut contents to characterize diets of 26 grasshopper species. Resulting grasshopper species' diets were combined with long-term plant and grasshopper surveys to assemble plant-grasshopper networks across 13-19 years for 6 watersheds subjected to varying fire and grazing treatments. 4. Network modularity, generality, and predicted grasshopper community robustness to plant species loss all increased in grazed watersheds. Temperature decreased predicted grasshopper community robustness to plant species loss. 5. Grasshopper communities were found to be vulnerable to climatic warming due to host plant loss. However, intermediate disturbance from ungulate grazers may maintain grasshopper diversity and buffer community robustness to species loss. Our results suggest that climate and disturbance shape the structure of ecological interaction networks and thus have many indirect effects on species persistence though direct effects on interaction partners.
Shrub influence on soil carbon and nitrogen in a semi-arid grassland is mediated by precipitation and largely insensitive to livestock grazing
<p>Dryland (arid and semi-arid) ecosystems globally provide more than half of livestock production and store roughly one-third of soil organic carbon (SOC). Biogeochemical pools are changing due toshrub encroachment, livestock grazing, and climate change. We assessed how vegetation microsite, grazing, and precipitation interacted to affect SOC and total nitrogen (TN) at a site with long-term grazing manipulations and well-described patterns of shrub encroachment across elevation and mean annual precipitation (MAP) gradients. We analyzed SOC and TN in the context of vegetation cover at ungrazed locations within livestock exclosures, high-inten- sity grazing locations near water sources, and moderate-intensity grazing locations away from water. SOC was enhanced by MAP (p<0.0001), but grazing intensity had little effect regardless of MAP (p = 0.12). Shrubs enhanced SOC (300–1279 g C m2) and TN (27–122 g N m2), except at high MAP where the contribution or stabilization of shrub inputs relative to grassland inputs was likely diminished. Cover of perennial herbaceous plants and litter were significant predictors of SOC (r2 = 0.63 and 0.34, respectively) and TN (r2 = 0.64 and 0.30, respectively). Our results suggest that continued shrub encroachment in drylands can increase SOC storage when grass production remains high, although this response may saturate with higher MAP. In contrast, grazing – at least at the intensities of our sites – has a lesser effect. These effects underscore the need to understand how future climate and grazing may interact to influence dryland biogeochemical cycling.</p>
FIG. 4 in Rodents in grassland habitats: does livestock grazing matter? A comparison of two Alpine sites with different grazing histories
FIG. 4. — Apodemus Spp. caught during the study.
Data for: Grazing effects of wintering geese on grassland yield: A long-term study from NW-Germany
<p>Conflicts between grassland farming and wintering geese stimulated a long-term study on goose-dependent yield losses. In the period 1996-2018 the loss of dry biomass of the first harvest increased from ca. 15 % to 50 % which corresponds with changes in the number and migratory behaviour of the barnacle goose. In contrast we found no decline in grassland yields with increasing number of greater white-fronted geese. The second harvest was not affected by wintering geese. The present study forms the basis for a fair and comprehensible system of compensation payments fo affected farmers.</p>
Changes in plant community assembly from patchy degradation of grasslands and grazing by different-sized herbivores
<p>Grassland degradation caused by increases in livestock grazing threatens a variety of ecosystem services. Understanding changes in plant community assembly during the process of grassland degradation in the presence of grazing is important to help restore degraded grasslands worldwide but has received little attention thus far. The grassland degradation process is typified by heterogeneous degradation, i.e., gradual formation of degraded patches (hereafter "patchy degradation"). Here, we experimentally examined the effects of herbivore grazing and patchy degradation on plant community assembly using nine pairs of non-degraded (intact) and patch-degraded (fragmented) grasslands subject to grazing by different-sized herbivores (i.e., NG, no grazing; SG, sheep grazing; CG, cattle grazing) over four years. Using a null-model approach, we estimated the relative magnitude of deterministic processes of community assembly by comparing the observed and expected β-diversity. We found that in the absence of herbivore grazing, deterministic processes played a greater role in community assembly, regardless of whether patchy degradation had occurred. However, the deterministic processes resulted in plant communities being more spatially similar in non-degraded grasslands while being more dissimilar in patchy degraded grasslands. Compared with non-degraded grasslands, species with strong competitive abilities (i.e., Leymus chinensis) were less dominant in patchy degraded grasslands, indicating relaxed competition and a reduced role of species interactions over plant communities. Instead, patchy degradation added the role of environmental variables over plant communities. Sheep grazing consistently promoted more stochastic plant community assembly in both non-degraded and patch-degraded grasslands, while cattle grazing promoted more stochastic plant community assembly only in the non-degraded state, having no effect in the patch-degraded state. Our study offers important insights into changes in plant community assembly during ongoing patch-degradation of grasslands, indicating the role of increased environmental filtering of soil and reduced species interactions in driving plant community dynamics with increasing grassland patchy degradation. We also uncovered an herbivore species-specific effect on plant community assembly during the process of grassland degradation, which will better inform and improve future grassland restoration planning efforts.</p>
Drought neutralizes positive effects of long-term grazing on grassland productivity through altering plant-soil interactions
<p>Livestock grazing is among the most intensive land-use activities in grasslands and can affect plant communities directly or indirectly via grazing-induced soil legacies. Under climate change, grasslands are threatened globally by recurrent drought. However, the extent to which drought influences grazing-induced soil legacy effects on plant biomass production and community composition remains largely unexplored.</p> <p>We grew five naturally co-occurring plant species (three dominants and two subordinates) in mixed communities in a glasshouse experiment in live and sterilized soil that had or had not been subjected to 19 years of grazing; these plant communities were then exposed to a subsequent drought. We tested the treatment effects on plant community biomass, proportional aboveground biomass of individual species, arbuscular mycorrhizal (AM) fungal root colonization, and soil nutrient availability.</p> <p>Under drought-free conditions, soils from grazed plots produced significantly higher plant aboveground and total community biomass compared to soils from ungrazed plots. In contrast, plant aboveground and total community biomass were similar between grazed and ungrazed soils under drought conditions. Similarly, soils from grazed plots increased the proportional biomass of dominant species but decreased the proportion of subordinate species; however, the proportional biomass of dominant and subordinate species was similar between grazed and ungrazed soils under drought conditions. Soil NO3--N in grazed soil was significantly higher compared to ungrazed soil. Drought dramatically increased soil NO3--N in sterilized soil and had a more pronounced increase in grazed soil than in ungrazed soil. Arbuscular mycorrhizal fungal root colonization from grazed soil was lower compared to ungrazed soil. Drought significantly increased the soil available phosphorus concentration, as well as plant community AM fungal root colonization.</p> <p>Synthesis. Our study suggests that drought can neutralize positive grazing effects on plant community biomass production via altered plant-soil interactions. Also, we found that drought can alleviate the negative effects of grazing legacies on subordinate species by reducing the competitiveness of dominant species. Our study provides new insights for understanding the underlying mechanisms of grazing effects on grassland productivity under climate change.</p>
Data from: Long-term grazing intensity by reindeer alters the response of the soil micro-food web to simulated climate change in subarctic tundra
<p><span>Top-down control by nematodes over soil microorganisms – considered stronger over bacteria than fungi - may dampen microbial responses to global changes in tundra. To test whether large grazers alter the responses of belowground trophic networks to global changes, we employed factorial warming and nitrogen fertilization treatments in adjacent sites with different reindeer grazing intensities for the past 50 years. Lightly grazed tundra is dominated by dwarf shrubs and a more fungal-based microbial community, while in heavily grazed tundra, high reindeer densities during autumn migration have induced shift into graminoids and more bacterial-based microbial community. We analysed the soil micro-food web, <em>i.e.</em>, the nematode density, trophic structure, and species composition as well as fungal, bacterial and total phospholipid fatty acids (PLFAs) after four growing seasons of warming and fertilization both before and during reindeer migration. We predicted that bacterivore densities are higher and fungivore densities lower under heavy than light grazing (<em>i.e.</em>, nematode populations before migration reflect grazing effects via the base of food web), whereas reindeer migration induces negative impact on nematode densities under heavy grazing (<em>i.e</em>., disturbance by trampling is the driving factor). We further predicted that nematodes negate treatment effects on microbial biomass to a stronger extent in the bacterial-based heavily grazed than the fungal-based lightly grazed tundra. Fungivore densities were higher under light than heavy grazing, but nematodes did not respond to trampling. Warming increased fungivores and the fungal PLFAs irrespective of grazing and timing, but under heavy grazing, increased bacterivores while the bacterial PLFAs remained steady. Fertilization increased carnivores and influenced nematode species composition, diversity and maturity interactively with warming. Our data suggest that large grazers affect tundra soil nematodes via bottom-up effects through microbial community composition and biomass, which in turn may alter the strength of their top-down control soil bacteria under climate warming. </span></p>
Grazing animals have contrasting effects on foliar pathogens by changing plant community characteristics
<p><span>Large herbivore grazing has substantial effects on plant community structure and ecosystem functioning, however, the impacts of grazing on plant diseases remain poorly understood. Here, we used a grazing experimentand a removal experiment manipulating plant density and litter biomass in northeast China to evaluate how large vertebrate herbivores (cattle and sheep) affect different foliar fungal diseases (biotrophs and necrotrophs). We found that cattle grazing significantly reduced pathogen load, of both biotrophs and necrotrophs, while sheep grazing increased biotrophic pathogen load, but did not affect necrotrophic pathogen load. </span><span> Mechanistically</span><span>, grazing effects were indirect and mediated by changing </span><span>plant community characteristics</span><span>. Moreover, litter biomass play an important role in affecting necrotrophs and by reducing litter build up the cattle reduced necrotrophic pathogen infection</span><span>. Our results demonstrate that </span><span>cattle and sheep grazing have</span><span> contrasting impacts on </span><span>pathogen load. This finding has important implications for improving disease management through grazing regimes in grassland systems.</span></p>
Grazing in a megagrazer-dominated savanna does not reduce soil carbon stocks, even at high intensities
<p>Recent studies suggest that wild animals can promote ecosystem carbon sinks through their impacts on vegetation and soils. However, livestock studies show that intense levels of grazing reduce soil organic carbon (SOC), leading to concerns that rewilding with large grazers may compromise ecosystem carbon storage. Furthermore, wild grazers can both limit and promote woody plant recruitment and survival on savanna grasslands, with both positive and negative impacts on SOC, depending on the rainfall and soil texture contexts. We used grazing lawns in one of the few African protected savannas that are still dominated by megagrazers (>1000 kg), namely white rhinoceros (<em>Ceratotherium simum</em>), as a model to study the impact of prolonged and intense wild grazing on SOC stocks. We contrasted SOC stocks between patches of varying grazing intensity and woody plant encroachment in sites across different rhino habitat types. We found no differences in SOC stocks between the most- and least-grazed plots in any of the habitats. Intermediately grazed plots, however, had higher SOC stocks in the top 5 cm compared to most and least grazed plots, but only in the closed-canopy woodland habitat and not in the open habitats. Importantly, we found no evidence to support the hypothesis that wild grazing reduces SOC, even at high grazing intensities by the world's largest megagrazer. Compared to the non-encroached reference plots, woody encroached plots had higher SOC stocks in soils with low clay content and lower SOC stocks in soils with high clay content, although only in the top 5 cm. Accordingly, our study highlights that wild grazers may influence SOC indirectly through their impact on tree-grass ratios in grassy ecosystems. Our study thus provides important insights for future nature-based climate solutions that focus on wild grazer conservation and restoration.</p>
Data from: Community-level canopy reflectance in grazed grasslands is linked to the habitat preferences of individual plant species
<p class="MsoNormal">Spectral remote sensing provides tools for biological monitoring and can be used to characterize habitat quality in grasslands. These data have been used to study the relationships between plant community composition and remotely sensed canopy reflectance in grazed grasslands. The study area is located on the island of Öland, Sweden, and the data were collected in grazed grasslands that represent a succession from previously arable fields to old semi-natural pastures. All included grassland sites have been assigned to three different classes of grassland age, defined by the grazing continuity in years: <span>young (5–14 years), intermediate-aged (15–49 years), and old (>50 years).</span></p> <p class="MsoNormal">The plant community data consist of presences/absences for 100 vascular plant species in 104 (4 m × 4 m) sample plots positioned in open grassland vegetation. Information on species' habitat preferences is included and has been used to explain the associations between plant species' occurrences and the variation in community-level canopy reflectance.</p> <p class="MsoNormal">The remote sensing data consist of 317 hyperspectral bands in the wavelength regions 414–1322 nm, 1496–1797 nm, and 2050–2351 nm, and show the mean reflectance in each spectral band for the 104 sample plots. The main gradient in the hyperspectral data is characterized by contrasting reflectance values between bands located in the NIR spectra and bands located in the red, blue, and SWIR spectra.</p> <p class="MsoNormal">Grassland canopy reflectance was able to explain variation in the occurrences of individual plant species, particularly those with distinct habitat preferences. Species' habitat preferences indicated that vegetation reflectance in the red, blue, SWIR, and NIR spectra was linked to the plant-availability of mineral nitrogen. In contrast, species' phosphorus preferences showed stronger associations with reflectance in the green and red-edge spectra.</p>
Data from: Dominant species determine grazing effects on the stability of herbaceous community production at multiple scales in drylands
<p><span>Sustainable provision of critical ecosystem services in drylands is reliant on their stability under anthropogenic disturbances. Livestock grazing and shrub encroachment are the primary drivers of disturbance that impact their biodiversity and production dynamics. However, the effects of grazing on the stability at multiple scales, particularly following the transition from grass-dominated to shrub-encroached drylands, is still largely unexplored</span><span>.</span></p> <p><span>Here, we conducted comparable sheep-grazing experiments in two types of drylands (grass-dominated vs. shrub-encroached grasslands) on the Mongolia Plateau to explore the effects of grazing and shrub encroachment on biodiversity and stability at multiple scales. We examined how grazing affected the temporal stability of aboveground biomass in herbaceous communities in both grass-dominated and shrub-encroached grasslands, through two potential mechanisms: insurance effects and changes in the population-level stability of individual species.</span></p> <p><span>We found that an increase in sheep grazing intensity had significant and negative effects on insurance effects by decreasing both species asynchrony and spatial asynchrony but it had no effects on population stability, consequently leading to reductions in herbaceous community stability of the grasslands. However, grazing-increased insurance effects canceled out grazing-decreased population stability, contributing to no changes in the community stability of shrub-encroached grasslands. Likely, because grazing-induced reductions in the relative abundance of the dominant species were more noticeable in shrub-encroached grasslands than that of in grasslands. Moreover, the grazing-decreased abundance of dominant species was directly correlated to increases in insurance effects in shrub-encroached grasslands but not in grasslands, despite the positive relationships between population stability and the relative abundance of the dominant species in both grass-dominated and shrub-encroached drylands. </span></p> <p><em><span>Synthesis and applications.</span></em><span> Our results indicate that grazing can decrease the stability of herbaceous production in drylands, but this negative effect is attenuated with the transition from grasslands to shrub-encroached grasslands, suggesting that grazing effects on herbaceous community stability can be altered by shrub encroachment in drylands. Furthermore, the stability of dominant grasses plays a crucial role in stabilizing herbaceous communities, and should be considered in promoting sustainable ecosystem functioning and services in drylands.</span></p>
Rotational grazing with cattle-free zones supports the coexistence of cattle and wild herbivores in African rangelands
<p>African wildlife populations are declining at an alarming rate. To stop further population declines and restore ecosystems, more areas for wildlife are needed. Community-based conservation with wildlife-livestock coexistence in the vast rangelands of Africa presents a major opportunity. However, the efficacy of wildlife conservation in mixed land-use areas remains an outstanding question. To assess the ecological outcomes of land-sharing between regulated livestock herds and wildlife populations in African savannas, we test how rotational cattle grazing affects spatiotemporal dynamics of 15 large herbivore species in the Maasai Mara, Kenya.</p> <p>First, we tested how wild herbivore distributions across the Greater Mara Ecosystem (the Mara, ~2,600 km2) are related to cattle density and environmental variables using 584,561 observations of wild herbivores (ecosystem scale). In a second analysis, we tested how rotational cattle grazing affects wild herbivore distributions in a 300 km2 subsection of the Mara using 30,583 observations (landscape scale). Finally, we tested how functional traits of wild herbivores affect species-level spatiotemporal responses to cattle grazing. </p> <p>At the ecosystem scale, the presence of five wild herbivore species was positively correlated with cattle density, while cattle effects on wild herbivore abundances were species-dependent with both increases and decreases. At the landscape scale, rotational cattle grazing strongly impacted the spatiotemporal habitat selection of wild herbivores, resulting in distinct lag periods with which different species are attracted to areas previously grazed by cattle. These lag periods were linked to functional traits, with body mass and herd size explaining 35% of the interspecific differences. Small to medium-sized herbivores with large herds select areas recently grazed by cattle, whereas large species with large herd sizes and small species with small herd sizes avoid recently grazed areas.</p> <p><strong><em>Synthesis and applications</em></strong> Our results revealed that the effect of cattle on wild herbivores varies considerably among species, suggesting that cattle-wildlife interactions range from facilitation to competition. To maintain species that strongly avoid cattle, designated livestock-free zones remain essential, also in rotational grazing systems. Rotational grazing systems with regulated livestock densities present an important opportunity to better manage wildlife-livestock coexistence and thus improve wildlife conservation in African rangelands.</p>
Top-down vs. bottom-up: Grazing and upwelling regime alter patterns of primary productivity in a warm-temperate system
<p>Community structure is driven by biological interactions and physical processes that can vary across environmental gradients and spatial scales. Early ecological models focused on the role of resource availability (i.e. bottom-up effects), predicting that the strength of top-down control varied along gradients of primary productivity and that local species interactions determined community structure. However, the role of regional scale oceanographic processes in determining species interactions and community structure is now widely recognized, with bottom-up effects such as coastal upwelling driving regional scale patterns of resource availability. Such nutrient subsidies can significantly alter primary production and drive changes in algae-herbivore interactions in rocky intertidal habitats. However, despite the potential for upwelling to alter these interactions, studies investigating the effects of upwelling and grazing pressure are scarce, particularly for warm-temperate systems, and generally cover narrow geographical ranges. Using in-situ herbivore exclusion experiments replicated across multiple upwelling regimes, we investigated the effects of both grazing pressure and upwelling, as well as their interactions, on the sessile invertebrate community and primary production of macroalgal communities in a warm-temperate system. Invertebrate cover remained consistently low at upwelling sites and was reduced at non-upwelling sites when grazers were excluded. Macroalgal cover was greater at upwelling sites when grazers were excluded and there was a strong effect of succession throughout the experimental period. Grazing pressure was greater at upwelling sites, particularly during winter months. There was a non-significant trend towards greater grazing pressure on early than later successional stages. Our results show that the positive impacts of bottom-up effects of nutrient supply on algal production do not overwhelm top-down control in this warm-temperate system. We speculate that global increases in air and sea-surface temperatures in warm-temperate systems will promote top-down effects in upwelling regions by increasing herbivore metabolic and growth rates.</p>
Data for: Cessation of grazing causes biodiversity loss and homogenization of soil food webs
<p><span>There is widespread concern that cessation of grazing in historically grazed ecosystems is causing biotic homogenization and biodiversity loss. We used 12 montane grassland sites along an 800-km north-south gradient across the United Kingdom, to test whether cessation of grazing affects local ɑ- and β-diversity of belowground food webs. We show cessation of grazing leads to strongly decreased ɑ-diversity of most groups of soil microbes and fauna, particularly of relatively rare taxa. In contrast, the β-diversity varied between groups of soil organisms. While most soil microbial communities exhibited increased homogenization after cessation of grazing, we observed </span><span>decreased homogenization for soil fauna after cessation of grazing. Overall, our results indicate that exclusion of domesticated herbivores from historically grazed montane grasslands has far-ranging negative consequences for diversity of belowground food webs. This underscores the importance of grazers for maintaining the diversity of belowground communities, which play a central role in ecosystem functioning. </span></p>
Heatwave grazing kelp microbes sequences
<p class="MsoNormal"><span>The range-expansion of tropical herbivores due to ocean warming can profoundly alter temperate reef communities by overgrazing the seaweed forests that underpin them. Such ecological interactions may be mediated by changes to seaweed-associated microbiota in response to warming, but empirical evidence demonstrating this is rare. We experimentally simulated ocean warming and marine heatwaves (MHWs) to quantify effects on two dominant temperate seaweed species and their microbiota, as well as grazing by a tropical herbivore. The kelp <em>Ecklonia radiata</em>'s microbiotain sustained warming and MHW treatments were enriched with microorganisms associated with seaweed disease and tissue degradation. In contrast, the fucoid <em>Sargassum linearifolium</em>'s microbiota was unaffected by temperature<em>.</em> Consumption by the tropical sea-urchin <em>Tripneustes gratilla </em>was greater on <em>Ecklonia</em> where the microbiota had been altered by higher temperatures, while <em>Sargassum</em>'s consumption was unaffected. Elemental traits (carbon, nitrogen), chemical defences (phenolics) and tissue bleaching of both seaweeds were generally unaffected by temperature. Effects of warming and MHWs on seaweed holobionts (host plus its microbiota) are likely species-specific. The effect of increased temperature on <em>Ecklonia</em>'s microbiota and subsequent increased consumption suggest that changes to kelp microbiota may underpin kelp-herbivore interactions, providing novel insights into potential mechanisms driving change in species' interactions in warming oceans.</span></p>
Relationships between plant species richness and grazing intensity in a semiarid ecosystem
<p>Plant species richness is an important property of ecosystems that is altered by grazing. In a semiarid environment, we tested the hypotheses that (1) small-scale herbaceous plant species richness declines linearly with increasing grazing intensity by large ungulates, (2) precipitation and percent sand interact with grazing intensity, and (3) response of herbaceous plant species richness to increasing intensity of ungulate grazing varies with patch productivity. During January to March 2012, we randomly allocated 50, 1.5-m x 1.5-m grazing exclosures within each of six 2,500 ha study sites across South Texas, USA. We counted the number of herbaceous plant species and harvested vegetation in 0.25-m<sup>2</sup> plots within exclosures (ungrazed control plots) and in the grazed area outside the exclosures (grazed treatment plots) during October and November 2012–2019. We estimated percent use (grazing intensity) based on the difference in herbaceous plant standing crop between control plots and treatment plots. We selected the negative binomial regression model that best explained the relationship between grazing intensity and herbaceous plant species richness using the Schwarz Bayesian Information Criterion. After accounting for the positive effect of precipitation and percent sand on herbaceous plant species richness, species richness/0.25 m<sup>2</sup> increased slightly from 0 to ~ 30% grazing intensity and then declined with increasing grazing intensity. Linear and quadratic responses of herbaceous plant species richness to increasing grazing intensity were greater for the least productive patches (<15.7 g/0.25 m<sup>2</sup>) than for productive patches (≥15.7 g/0.25 m<sup>2</sup>). Our results followed the pattern predicted by the intermediate disturbance hypothesis model for the effect of grazing intensity on small-scale herbaceous plant species richness.</p>
Stability of C3 and C4 grass patches after fire and simulated grazing
<p class="MsoNormal"><span>As the woody legume, </span><em>Prosopis glandulosa</em><span> (honey mesquite) has encroached into grasslands and rangelands in the southern Great Plains, USA, two grass species, C<sub>4</sub> shortgrass, </span><em>Buchloe dactyloides</em><span> (buffalograss), and C<sub>3</sub> mid-grass, </span><em>Nassella leucotricha</em><span> (Texas wintergrass), have increased in dominance. Occurrence of more productive C<sub>4</sub> mid-grasses and herbaceous diversity have declined. We measured effects of various combinations of spring clipping (to simulate cattle grazing) and summer and/or winter fire treatments on the stability of monoculture patches of these two grass species over an eight-year period, with the goal of reducing </span><em>Nassella</em><span> and increasing C<sub>4</sub> mid-grass cover. All fire treatments top-killed most </span><em>Prosopi</em><span><em><span>s</span></em> trees that subsequently resprouted. </span><em>Buchloe</em><span> cover declined in the No Clip + No Fire treatment but remained intact</span> with clipping and/or fire. Frequent clip<span>ping reduced </span><em>Nassella</em><span> cover across all fire treatments. </span><em>Buchloe </em><span>encroachment into </span><em>Nassella</em><span> patches was greatest in the Clip + Alternate Season fire treatment. C<sub>4</sub> mid-grass cover increased to 15–25% in </span><em>Nassella</em><span> patches in several fire-only or Clip + Fire treatments; greatest gains were observed in treatments that included summer fire. In contrast, C<sub>4</sub> mid-grass gains were lower in </span><em>Buchloe </em><span>patches. These results suggest that C<sub>4</sub> mid-grass restoration was linked with treatments that reduced</span><em> Nassella </em><span>cover.</span></p>
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