Effects Of Grazing Research Articles

Effects of grazing and fire management on rangeland soil and biocrust microbiomes

Biocrusts play important roles in rangeland ecosystems by protecting soil surfaces and fixing carbon and nitrogen. Their responses to rangeland management practices, however, are poorly understood. Here, we characterised the impacts of cattle grazing and fire management (controlled 2- or 4-yearly burning versus no fire) on the diversity and composition of biocrust and associated soil bacterial communities (0–1 cm depth) in a long-term (30–60 years) field experiment in the Northern Territory, Australia. Both experiments were replicated on two soil types (vertosol, calcarosol). For the grazing experiment, we also characterised samples from 0 to 10 cm depth. Significant effects of grazing on bacterial community composition were only detected in the vertosol, where it was generally associated with enrichments of cyanobacterial taxa in the 0–1 cm samples, and more varied responses in 0–10 cm samples. In contrast, despite some minor reductions in the relative abundances of Bacillus populations in more frequently burned sites (late season 2-yearly burning), we did not observe any significant impacts of fire management on the overall composition of bacterial communities. Our findings indicate that the presence of livestock in rangelands increases the proportional representation of cyanobacteria within biocrust and associated soil microbiomes, and that these communities, at least from a taxonomic perspective, are not strongly impacted by fire management.

The role of livestock grazing in long-term vegetation changes in coastal dunes: a case study from the Netherlands

The vegetation of coastal sand dunes is characterized by high species diversity and comprises some of the rarest vegetation types in North-Western Europe. Among them are dune grassland communities whose species richness relies on grazing. Those communities are assessed as a priority habitat type under the Natura 2000 legislation. In autumn 1990, Galloway cows and Nordic Fjord horses were introduced in the coastal dunes of Meijendel near The Hague (52°7'N, 4°20'E), The Netherlands, to reduce encroachment of tall grasses and shrubs, to develop bare sand patches, and as such facilitating diverse vegetation structures in the dune grasslands. In the 1950s, decades before the introduction of livestock, 41 permanent plots were installed. On average, they were examined every four years. Our study hypothesised that the livestock grazing in the set densities would halt progressive succession and facilitate regressive succession. Up to 1990, we observed an equilibrium between progressive and regressive succession. After 1990, however, our data showed a pronounced progressive succession contradicting the hypothesized effect of the livestock grazing. We relate the main observed patterns with two factors linked to rabbit populations: (i) the myxomatosis outbreak in 1954 and (ii) the rabbit Viral Haemorrhagic Disease (rVHD-1) outbreak in 1989. In addition to livestock grazing, rabbits block progressive succession by feeding on seedlings of shrub and tree species and digging burrows, creating small-scale mosaics of bare sand and initiate blowout development when collapsing. We state that the substantial decrease in rabbit numbers due to the viral diseases likely caused the observed increase of shrubs and trees in the study area's permanent plots. Climate change might have contributed to the observed increase in autonomous blowout development since 2001, as well as a decrease in atmospheric nitrogen deposition since 1990, after a strong increase the decades before.

Nutrient conditions determine the strength of herbivore-mediated stabilizing feedbacks in barrens.

Abiotic environmental conditions can significantly influence the way species interact. In particular, plant-herbivore interactions can be substantially dependent on temperature and nutrients. The overall product of these relationships is critical for the fate and stability of vegetated ecosystems like marine forests. The last few decades have seen a rapid spread of barrens on temperate rocky reefs mainly as a result of overgrazing. The ecological feedbacks that characterize the barren state involve a different set of interactions than those occurring in vegetated habitats. Reversing these trends requires a proper understanding of the novel feedbacks and the conditions under which they operate. Here, we explored the role of a secondary herbivore in reinforcing the stability of barrens formed by sea urchin overgrazing under different nutrient conditions. Combining comparative and experimental studies in two Mediterranean regions characterized by contrasting nutrient conditions, we assessed: (i) if the creation of barren areas enhances limpet abundance, (ii) the size-specific grazing impact by limpets, and (iii) the ability of limpets alone to maintain barrens. Our results show that urchin overgrazing enhanced limpet abundance. The effects of limpet grazing varied with nutrient conditions, being up to five times more intense under oligotrophic conditions. Limpets were able to maintain barrens in the absence of sea urchins only under low-nutrient conditions, enhancing the stability of the depauperate state. Overall, our study suggests a greater vulnerability of subtidal forests in oligotrophic regions of the Mediterranean and demonstrates the importance of environment conditions in regulating feedbacks mediated by plant-herbivore interactions.

The impact of livestock activities and geochemical processes on groundwater quality of fractured volcanic rock aquifer: Lake Çıldır watershed (NE Turkey)

This paper presents the impact of livestock activities and geochemical processes on the water quality of a fractured volcanic rock aquifer in the Lake Çıldır watershed, located at the northeastern part of Turkey. The existence of a high livestock population and animal grazing activities in meadow and pasturelands of the watershed during the short summer period poses serious stress on both surface and groundwater resources being the only drinking water supply for the local communities. Therefore, understanding the effect of grazing and livestock breeding activities occurring in the recharge areas of the fractured volcanic rock aquifer is vital to take precautions in order to protect limited water supplies at the watershed and vulnerable lake ecosystem as well. The mean nitrate content of the groundwater was measured at 6.4 ± 6.6 (std. dev) mg/L in the wet (before grazing) period and 7.1 ± 5.9mg/L in the dry (after grazing) period. Despite low nitrate concentration levels of groundwater, microbial contamination was observed in the spring waters at alarming levels especially after the animal grazing activities. 56%, 26%, and 11% of the groundwater samples showed bacterial contamination in terms of total coliform, fecal coliform, and fecal streptococci contents, respectively, prior to grazing activity, while in pursuit of intense livestock grazing at highland, these microbial indicators have been increased to 92%, 85%, and 77% in the dry period. A significant increase observed in fecal contamination indicates the negative impact of livestock activities on groundwater quality. Al (200-638µg/L) and Fe (66-218µg/L) enrichments locally observed in groundwater were related to advanced argillic alteration (kaolinization) and hematization zones in pyroclastic rocks.

Interactive effects of nutrients and salinity on zooplankton in subtropical plateau lakes with contrasting water depth

Both eutrophication and salinization are growing global environmental problems in freshwater ecosystems, threatening the water quality and various aquatic organisms. However, little is known about their interactive effects on theses stressors and the role of lake depth on these interactions. We used field surveys to compared zooplankton assemblages over four seasons in eight Yunnan Plateau lakes with different trophic states, salinization levels, and water depths. The results showed that: 1) the species number (S), density (DZoop), and biomass (BZoop) of zooplankton exhibited strong seasonal dynamics, being overall higher in the warm seasons. 2) Data collected over four seasons and summer data both revealed highly significant positive relationships of S, DZoop, and BZoop with total nitrogen (TN), total phosphorus (TP), and phytoplankton chlorophyll a (Chl a). 3) S, DZoop, and BZoop displayed a unimodal relationship with salinity, peaking at 400–1000 μS/cm (conductivity, to reflect salinity). 4) The two large-sized taxa (cladocerans and copepods) generally increased at low-moderate levels of TN, TP, Chl a, and Cond and was constant or decreased at high levels. The average body mass (biomass/density) of crustaceans decreased with increasing TN, TP, Chl a, and conductivity. Our findings indicate that zooplankton may be more vulnerable in deep lakes than in shallow lakes when exposed to conductivity stress even under mesotrophic conditions, and the overall decrease in size in zooplankton assemblages under the combined stress of eutrophication and salinization may result in a lowered grazing effect on phytoplankton.

Integrated response of carbon sequestration along co-varying gradients of climate and grazing intensity in a desert steppe ecosystem

The interactive effects of grazing and climate on carbon (C) storage are important for the global C budget and regional C management. In a regional-scale field experiment based on multiple grazing gradients, we examined how changes in grazing intensity and climate affected the C sequestration rate and C storage at five desert steppe sites. The mean total ecosystem C storage at each site ranged from 1502 to 3728 g C m−2 and averaged 2341 g C m−2. The peak value of the C sequestration rate (290 g C m−2 yr−1) occurred in the light grazing intensity. The light grazing and fencing management were more beneficial to C sequestration. The rising temperature would decrease C storage in desert steppe, while rising precipitation would promote C sequestration. Soil nitrogen content plays an important role in the driving mechanism of C sequestration in desert steppe. The soil C pool, which dominated the C dynamics in desert steppe, was influenced by the changes of precipitation and grazing intensity. Grazing affects soil nitrogen content by changing the aboveground C pool. Precipitation changes may change soil C storage by influencing the aboveground C pool to change soil nitrogen content and microbial biomass. Such information improves understanding of the dynamics of C storage and sequestration in desert steppe, and is critical for improving the sustainability of grassland ecosystem services and C management.

Soil organic carbon pool distribution and stability with grazing and topography in a Mongolian grassland

Livestock grazing and topography have long been recognized as essential factors that control soil organic carbon (SOC) dynamics. However, the interplay effects of grazing and topography on SOC pool distribution and stability are not well understood, hindering the precise prediction of the organic carbon (OC) fate over the hillslope grassland. Here, we examine the relationship between grazing and topography on SOC pool distribution and stability in a Mongolian grassland. We determined a suite of OC metrics (e.g., particulate OC (POC), mineral-associated OC (MAOC), dissolved OC (DOC), and microbial biomass carbon (MBC) along a topographic gradient (e.g., upper slope, middle slope, and downslope) with grazing or not, and incubation was conducted to quantify OC stability. The results showed that POC and SOC content was 106–138% and 24–63% greater in the grazed than the ungrazed site at low topographic positions, respectively. Across the landscape, more variations in POC and SOC across the topographic gradient were observed at the grazed sites than at ungrazed sites. The MBC content of the downslope was greater in the grazing than in ungrazed sites. Furthermore, the humic-like substances in the grazing area were lower than those in the enclosed area and showed a significant and positive linear relationship with the aromaticity and humification of DOC. The aggregated boosted tree (ABT) analysis showed that the POC and MBC were the most important OC components to affect OC pool stability (accounting for 40.87%). The structural equation model (SEM) supported that the varies of POC regulated the downstream soil biochemical processes and changed SOC pool stability. Collectively, the results suggest the POC could be primarily responsible for the changes in SOC pools and stability in a hillslope grassland. These findings enhanced our understanding of the ecological mechanisms in SOC sequestration.

Effects of precipitation and grazing on the diversity and productivity of desert steppe

AbstractThe variability of annual precipitation and grazing are primary drivers shaping the structure and function of plant communities in grasslands. Yet it remains unclear on a mechanistic understanding of how annual precipitation and grazing affect the plant community structure, function, and their linkage via direct or indirect pathways. We measured the plant community structure (plant traits, species abundance, and plant diversity), total aboveground biomass, total cover, and species covers in plant communities in responses to annual precipitation variability from 2014 to 2017 and grazing pressure comprising 0, 0.93, 1.82, and 2.71 sheep ha−1 in a desert steppe. Two‐way ANOVAs, ordinary least square regressions, and the structural equation modeling (SEM) were used to test the impacts of annual precipitation variability and grazing pressure on the plant community structure and function. Results showed that higher annual precipitation of 2016 and 2017 increased the relative abundances of forbs; grazing pressure increased the relative abundances of dominant grasses [Stipa breviflora Griseb. and Cleistogenes songorica (Roshev.) Ohwi], but decreased those of subdominant forbs (Convolvulus ammannii Desr. and Artemisia frigida Willd.). Plant traits, such as leaf nitrogen concentration, regulated plant species abundance directly or indirectly via affecting sheep diet selection. Annual precipitation variability and grazing pressure independently regulated plant diversity, aboveground biomass, and total cover, which the former had larger effects. There was slower decrease in grass biomass than that in forb biomass with increasing grazing pressure, indicating that dominant grasses are resilient to grazing but subdominant forbs are sensitive due to their distinct difference in sward palatability. The positive correlation between plant diversity and aboveground biomass was driven by both annual precipitation variability and grazing pressure. These highlight direct and indirect (via traits and abundances of plant species) effects of annual precipitation and grazing in shaping the structure and function of desert steppe ecosystems.

Influence of protozoan grazing on magnetotactic bacteria on intracellular and extracellular iron content.

Magnetotactic bacteria (MTB) ubiquitously inhabit the oxic-anoxic interface or anaerobic areas of aquatic environments. MTB biomineralize magnetite or greigite crystals and synthesize an organelle known as magnetosome. This intrinsic ability of MTB allows them to accumulate iron to levels 100-1000 times higher than those in non-magnetotactic bacteria (non-MTB). Therefore, MTB considerably contributes to the global iron cycle as primary iron suppliers in the aquatic environmental food chain. However, to the best of our knowledge, there have been no reports describing the effects of trophic interactions between MTB and their protist grazers on the iron distributions in MTB grazers and the extracellular milieu. Herein, we evaluated the effects of MTB grazing using a model species of protist (Tetrahymena pyriformis) and a model species of MTB (Magnetospirillum magneticum AMB-1). MTB-fed T. pyriformis exhibited a magnetic response and contained magnetite crystals in their vacuoles. Fluorescence imaging using a ferrous ion-specific fluorescent dye revealed that the cellular ferrous ion content was five times higher in MTB-fed T. pyriformis than in non-MTB grazers. Moreover, soluble iron concentrations in the spent media increased with time during MTB predation. This study provides experimental evidence to delineate the importance of trophic interactions of MTB on iron distributions.

Mob grazing: A nature-based solution for British farms producing pasture-fed livestock

Mob grazing is a nature-based solution to boost sustainable livestock productivity by optimising pasture management. It is already used widely in North America, and is now also receiving increased attention in the United Kingdom. In spite of this, its implementation by British farmers has so far remained largely unexplored. To close this gap, we studied how and why mob grazing is being adopted by British pasture-fed beef farmers. Field-level grazing management information was collected on 15 farms and analysed using cluster analysis and ordination analysis, showing the diversity of practices and establishing a gradient of mob grazing implementation. Farmer interviews explored general farming context, and rationale and motivations underpinning each farmer's grazing approach. Four main rotational approaches were identified at the field level: (1) conventional non-mob stocking by farmers still in the initial stages of discovering mob grazing; (2) mob stocking, involving reduced grazing duration at increased stocking densities, with pasture rest periods similar to those used in rotational non-mob stocking; (3) mob grazing, involving similar stocking densities as in mob stocking, but allowing for longer rest periods; and based on one early adopter of mob grazing practices in our sample (4) intensive mob grazing using very high stocking densities and frequent cattle movement, allowing for even longer rest periods. Interviews revealed the shift to mob grazing as a gradual process of farmer adaptation, involving the need to overcome constraints such as fencing and water access. Some early adopters amongst our sample of farmers observed various benefits to sustainability of livestock production, soil and ecosystem health, and animal health. We found much variation across farms, partly due to farmers adopting mob grazing gradually. Also, many farmers in our sample, in varying degree, were influenced by holistic grazing approaches. The ‘systems’ basis underlying such approaches, and variation in mob grazing implementation, mean that interdisciplinary and longer-term investigations may be most appropriate for exploring mob grazing effects. This is also illustrated by a case study involving long-term data from one intensively mob grazed farm.

Economic Effects of Federal Grazing Programs

Livestock grazing supports a considerable amount of economic activity across the United States. Federal grazing permits support numerous ranching operations by providing relatively low-cost grazing on federal lands. While grazing supports employment, labor income, and economic activity within a given state, the extent to which federal grazing permits play a role remains uncertain. In this paper we develop a method for estimating state-level economic contributions of livestock grazing for cattle grazing, as well as sheep and goat grazing, that is applicable to both the US Forest Service and Bureau of Land Management. We report state-level direct response coefficients, defined as the economic effects per 1 000 animal unit months of grazing use. We apply our coefficients to grazing lands for both US Forest Service and the Bureau of Land Management to estimate state-level economic contributions of federal grazing, finding that the economic effects of federal grazing are highest in western states where there are large amounts of public land. The measures of economic impact produced in this study were developed for consistent nationwide analyses. These measures may be used by researchers and land managers for conducting policy impacts and analysis of livestock grazing (e.g., increases or decreases of permitted grazing on public land) but are not intended to replace project- or site-specific economic analyses.

Aridity threshold and grazing effects revealed by ecological interaction networks between leaf, root, and biomass function

Increasing aridity and grazing have multifaceted effects on the ecosystem, of which plant traits interact with each other to coregulate the productivity function including above- and below- ground compartments of plant. The ecological interaction network among plant traits could reflect how ecosystem interact with, influence, and respond to environment change. In this study, the interaction network between leaf, root, and biomass function was revealed to indicate systemic ecosystem response to increasing aridity and grazing by sampling in enclosed plots along the aridity gradient and in neighboring grazing plots of China drylands. Systemic and abrupt changes in the network relationship between leaf, root, and biomass were observed with a threshold value of 1-AI (aridity index) ∼ 0.8. The control effect of roots on other traits and the interaction of leaf and root compartments increased in the opposite direction above the threshold. The change in the relative importance of key traits with increasing aridity caused the different grazing effects. Grazing decreased the leaf area in the area with1-AI ∼ 0.6, whereas it increased the effect of roots in the area with 1-AI ∼ 0.8, thus promoting the interaction of functional traits. This result suggests the essential role of the interaction network between plant traits in ecosystem response to environmental change, which could indicate the ecosystem change in a holistic perspective under global change.

Positive long-term effects of year-round horse grazing in orchid-rich dry calcareous grasslands–Results of a 12-year study

IntroductionDry calcareous grasslands are among the most species-rich habitats worldwide but strongly endangered by abandonment causing a severe decline of characteristic species such as orchids. To counteract further degradation, economically sustainable restoration tools such as megaherbivore grazing, that aim to substitute extinct wild grazers, should be considered. However, the long-term effects on target species of dry grasslands, and in particular for orchid populations, is still unclear.MethodsTo contribute to this knowledge gap, we applied vegetation surveys (5 m × 5 m), as well as large-scale census-based orchid observation and mapping of habitat structures (50 m × 50 m) in a year-round grazing scheme of a Natura 2000 site in Central Germany over 12 years. The horses and their grazing activity were observed via GPS telemetry. We fitted linear mixed models to evaluate whether Ophrys apifera density was affected by horse feeding frequency, habitat structure variables (bare soil patches, woody plant cover), grassland type or years.ResultsA The main results were that the target dry calcareous grassland vegetation significantly increased in species numbers and cover. The total abundance of O. apifera increased from 1,237 (2013) and 1,893 (2018), to 4,652 (2021) individuals. Ophrys apifera density was positively affected by horse feeding frequency as well as grazing-induced enhanced bare soil patches but underlying mechanisms varied between the three classified grassland types.DiscussionOur results indicate that low-intensity year-round horse grazing as a relatively new restoration tool in dry calcareous grasslands has the potential to enhance floristic biodiversity in general, and particularly O. apifera density in the long run. Furthermore, we showed that highvalue xeric grasslands with outstanding orchid abundances can be integrated into the year-round grazing system and that there is no need of fencing off such sections.

Grazing altered the plant diversity-productivity relationship in the Jianghan plain of the Yangtze River basin

PurposeThe Jianghan Plain is located in the middle reaches of the Yangtze River, characterized by high precipitation, flat terrain, and high vegetation cover. Livestock grazing is one of the major agricultural activities. Heavy grazing in some areas causes soil erosion and ecosystem degradation. We aim to quantify the effects of grazing of various grazing intensities on plant diversity and productivity as well as on soil nutrient dynamics in the area. MethodsTo examine the effects of grazing on plant diversity and productivity as well as on soil nutrient dynamics, we measured and compared the above-ground biomass (AGB), species composition (alpha and beta diversity indices), soil total phosphorus (STP), soil total nitrogen (STN), and soil organic carbon (SOC) under three grazing intensity levels: light grazing (LG), moderate grazing (MG) and heavy grazing (HG). ResultsThe results show that grazing intensity levels affected plant diversity, productivity, and soil nutrient dynamics differently. Species turnover refers to the rate of species substitution in different communities. The turnover dissimilarity value of species was 0.233 between LG and HG and 0.313 between LG and HG. AGB, STP, STN, Shannon-Wiener index, and plant productivity were all decreased under HG. In contrast, plant diversity (the Berger-Parker index) increased under HG. The relationships between plant diversity and productivity were also affected by grazing intensity. Under LG and MG, plant diversity was positively correlated with productivity, but became negative under HG. ConclusionsHG reduced plant diversity and altered the relationship between plant diversity and productivity, which caused ecosystem degradation. Thus, grazing management should aim to control the intensity of grazing at light to moderate levels to ensure the long-term sustainability of the ecosystem.

Associational Resistance to Predation by Protists in a Mixed Species Biofilm.

Mixed species biofilms exhibit increased tolerance to numerous stresses compared to single species biofilms. The aim of this study was to examine the effect of grazing by the heterotrophic protist, Tetrahymena pyriformis, on a mixed species biofilm consisting of Pseudomonas aeruginosa, Pseudomonas protegens, and Klebsiella pneumoniae. Protozoan grazing significantly reduced the single species K. pneumoniae biofilm, and the single species P. protegens biofilm was also sensitive to grazing. In contrast, P. aeruginosa biofilms were resistant to predation. This resistance protected the otherwise sensitive members of the mixed species biofilm consortium. Rhamnolipids produced by P. aeruginosa were shown to be the primary toxic factor for T. pyriformis. However, a rhamnolipid-deficient mutant of P. aeruginosa (P. aeruginosa ΔrhlAB) maintained grazing resistance in the biofilm, suggesting the presence of at least one additional protective mechanism. P. aeruginosa with a deleted gene encoding the type III secretion system also resisted grazing. A transposon library was generated in the ΔrhlAB mutant to identify the additional factor involved in community biofilm protection. Results indicated that the Pseudomonas Quinolone Signal (PQS), a quorum sensing signaling molecule, was likely responsible for this effect. We confirmed this observation by showing that double mutants of ΔrhlAB and genes in the PQS biosynthetic operon lost grazing protection. We also showed that PQS was directly toxic to T. pyriformis. This study demonstrates that residing in a mixed species biofilm can be an advantageous strategy for grazing sensitive bacterial species, as P. aeruginosa confers community protection from protozoan grazing through multiple mechanisms. IMPORTANCE Biofilms have been shown to protect bacterial cells from predation by protists. Biofilm studies have traditionally used single species systems, which have provided information on the mechanisms and regulation of biofilm formation and dispersal, and the effects of predation on these biofilms. However, biofilms in nature are comprised of multiple species. To better understand how multispecies biofilms are impacted by predation, a model mixed-species biofilm was here exposed to protozoan predation. We show that the grazing sensitive strains K. pneumonia and P. protogens gained associational resistance from the grazing resistant P. aeruginosa. Resistance was due to the secretion of rhamnolipids and quorum sensing molecule PQS. This work highlights the importance of using mixed species systems.

The effect of grazing and reclamation on rodent community stability in the Alxa desert

Ecosystem stability has been of increasing interest in the past several decades as it helps predict the consequences of anthropogenic disturbances on ecosystems. A wild rodent community under reclamation and different grazing disturbances in the Alxa Desert was investigated using live trapping from 2006 to 2011. We studied the rodent community composition, community diversity, and variability of different life history strategies. These results showed that reclamation reduced rodent community stability by increasing temporal variability of community, reducing rodent community resistance as shown by decreasing dominance of KSS strategists, and increased the resistance variability of the rodent community by increasing the variability of abundance and richness for KSS strategists. Grazing reduced rodent community resilience by reducing the dominance of rRF strategists, and increased the resilience variability of the rodent community by increasing the variability of abundance and richness for rRF strategists. Those results may answer the three ecological questions about how ecosystems respond to disturbances from a diversity perspective. The ecosystems with intermediate disturbance are more stable, in other words, with higher resistance and resilience. The increase of KSS strategists means the increase of resistance of the community. The increase of rRF strategists means the increase of community resilience.

Grazing effects of wintering geese on grassland yield: A long‐term study from Northwest Germany

Abstract Escalating conflicts between grassland farming and wintering geese in northern Germany stimulated a long‐term study in order to promote a fair and workable system of compensation of harvest loss. Between 1996 and 2018 standardized experiments were carried out to quantify changes in yield loss and herbage quality. Simultaneously, we weekly monitored the number of geese to relate yield losses to goose numbers and to identify the impact of the different species. Exclosure experiments were established on conventionally managed grasslands. The number of investigated fields differed over the study period (1990s: n = 6, 2000s: n = 14, 2010s: n = 2–18). On each field, we established 12 marked plots (4.5 m2), six with exclosures from early November until the first cut of grass in May and six with access for the geese. In all plots dry biomass and the quality of herbage (contents of energy, crude protein, crude fibre and ash) were determined at first and second harvest. The total goose‐dependent yield losses at first harvest increased from 15% in the year 1996/97 to 50% at the end of the 2010s. The increase corresponds with changes in the maximum numbers and the migratory behaviour of the barnacle goose Branta leucopsis. Yield reductions correlated positively with densities of barnacle geese present in April. In contrast, we found no decline in grassland yields with increasing numbers of greater white‐fronted geese Anser albifrons. In all periods second harvest was not affected. The combined maximum number of both geese which were counted over approximately 23,000 ha of grasslands increased until 2002/03 but levelled off with numbers around 100,000 birds thereafter. While the maximum wintering population of greater white‐fronted geese dropped since 2007/08, the maximum number of barnacle geese increased until mid of 2010s. An increasing proportion of barnacle geese delayed their departure until May. Within each year grazed plots possessed higher energy and crude protein contents than ungrazed controls, suggesting that the geese maximize their potential nutrient intake rate by grazing. Synthesis and applications. The present study reveals a significant increase in goose‐related loss of grassland yields which form the basis for a fair and comprehensible system of compensation payments to affected farmers.

Plant Phenology of High-Elevation Meadows: Assessing Spectral Responses of Grazed Meadows

Groundwater-dependent ecosystems are biologically diverse and productive ecosystems but constitute a small fraction of total land area in semiarid regions. Efforts to link remotely sensed data from satellite-based platforms to measurements of vegetation structure and function at smaller spatial scales have increasingly received attention, due to the need to manage diverse landscapes at scales relevant to management. In the semiarid western United States, grazing is a dominant land use and meadows can receive a high degree of grazing pressure. In this study we examined satellite-based and near-surface imagery to determine if they were useful in assessing grazed systems with different grazing management. We compared meadows that were chronically grazed by feral horses in conjunction with periodic cattle grazing to a meadow managed and grazed by cattle only. We examined the agreement between near-surface digital cameras (PhenoCams) and satellite-based indices of greenness and production for meadows in the Central Great Basin, United States. We also verified them with field-collected data on percent foliar cover by dominant functional groups. There was strong agreement between the Landsat normalized difference vegetation index and PhenoCam Green Chromatic Coordinate (GCC) (Pearson's r ≥ 0.61). Gross primary production modeled using Landsat satellite imagery and integrated over the growing season had a strong linear relationship with GCC integrated over the growing season (R2 = 0.89). Furthermore, despite differences in spatial and temporal resolution, integrated metrics from both platforms were able to discern differences in grazing pressure. Meadows with chronic feral horse grazing plus 3 mo of livestock grazing had reduced integrated gross primary production and GCC in comparison with a meadow that had short-term grazing (for 2 mo) by livestock only. The ability to detect differences in grazed systems from PhenoCams and satellite platforms provides important tools for quantifying the effects of grazing in groundwater-dependent ecosystems.

Cascading effects of livestock grazing on insect functional groups associated to flowers in arid lands

Abstract Disturbances affect plant diversity with consequences on other trophic levels, like the associated insect communities. Domestic livestock is a major disturbance affecting flowering plant abundance at the bottom of insect food webs with unpredicted consequences on ecosystem functioning. This work evaluated livestock effect on flower‐associated insect functional groups (i.e., predators, herbivores and pollinators) hypothesizing that plant damage produced by grazing exerts bottom up effects on insect populations, affecting their interactions. On contrary, livestock might supply food resources for several dipteran pests (e.g., scavengers, parasites or bloodsucking) or benefit predator species by increasing habitat transparency with grazing. Seven independent rangelands within the same arid environment and increasing livestock density, were used to test these hypotheses using a regression approach. Insect, herbivore and pollinator diversity decreased with increasing livestock density, and increased with increasing vegetation. Bare soil affected solitary bees (but not all the pollinators) and habitat transparency benefited predators, as expected. Dipteran pests quadratically decreased with increasing livestock density, rejecting the hypothesis of food supply. Apparently, predators reduced the abundance of almost all insect groups. Grazing reduce vegetation positively affecting predators, which negatively affect other insect groups (top‐down), potentially altering species complex interactions and ecosystem functioning. Resumen Las perturbaciones afectan a la diversidad vegetal con consecuencias en otros niveles tróficos, como las comunidades de insectos asociadas. El ganado doméstico es una perturbación importante que afecta la abundancia de plantas con flores, siendo la base de las redes tróficas de insectos, con consecuencias impredecibles en el funcionamiento del ecosistema. Este trabajo evaluó el efecto del ganado sobre grupos funcionales de insectos asociados a las flores (es decir, depredadores, herbívoros y polinizadores) con la hipótesis de que el daño producido por el pastoreo a las plantas ejerce efectos de abajo hacia arriba sobre las poblaciones de insectos, afectando sus interacciones. Por el contrario, el ganado podría estar suministrando recursos alimenticios para varias plagas de dípteros (por ejemplo, carroñeros, parásitos o hematófagos) o estar beneficiando a especies depredadoras al aumentar la transparencia del hábitat con el pastoreo. Se utilizaron siete campos independientes con creciente densidad de ganado dentro del mismo ambiente árido para probar las hipótesis, utilizando un enfoque de regresión. La diversidad de insectos, herbívoros y polinizadores disminuyó con el aumento de la densidad ganadera, y aumentó con el aumento de la vegetación. El suelo desnudo afectó a las abejas solitarias (pero no a todos los polinizadores) y la transparencia del hábitat benefició a los depredadores, como se esperaba. Los dípteros disminuyeron cuadráticamente con el aumento de la densidad ganadera, rechazando la hipótesis del suministro de alimentos. Aparentemente, los depredadores redujeron la abundancia de casi todos los grupos de insectos. El pastoreo reduce la vegetación afectando positivamente a los depredadores, que afectan negativamente a otros grupos de insectos (efecto de arriba hacia abajo), alterando potencialmente las interacciones complejas de las especies y el funcionamiento del ecosistema.

Changes in plant community assembly from patchy degradation of grasslands and grazing by different-sized herbivores.

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, that is, 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 4 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. SG consistently promoted more stochastic plant community assembly in both non-degraded and patch-degraded grasslands, while CG 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.