Long History Of Grazing Research Articles

Long-term grazing exclusion affects the population genetics and functional traits of Artemisia frigida in Mongolia

Steppes have a long history of grazing, which has affected vegetation and ecosystem functioning to varying degrees depending on local environmental and climatic conditions. While the effects of grazing on plant species' diversity and composition are well documented, effects on plants' functional traits and genetic structures are far less widely studied. Similarly, the effects of climate/land-use interactions on plants’ functional traits or genetic structure have rarely been investigated.We conducted a study on the largest representative example of the Palearctic steppe biome, in Mongolia, using long-term grazing exclusion along a broad climatic gradient. We investigated the influence of grazing on the population genetics and functional traits of the prominent shrub species Artemisia frigida. A total of 187 individuals were sampled from eight locations along the Trans-Mongolian Railway and in the Hustai National Park. Comparisons were made between enclosed (ungrazed) and open (grazed) sites and analyzed using ten microsatellite loci.Grazing had a significant positive effect on genetic diversity but no effect on population genetic differentiation. Climatic and soil variables strongly influenced population genetic structure, with soil nutrient availability being positively associated with genetic diversity. Grazing significantly influenced functional traits (plant height, specific leaf area), however, no relationship was found between genetic diversity and plant functional traits. Overall, given that ungrazed A. frigida populations showed lower genetic diversity, a moderate level of grazing is likely to be beneficial for the species, which may also help stabilize ecosystem functioning in steppes more broadly.

An invasive plant provides refuge to native plant species in an intensely grazed ecosystem

Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.

Grazing exclusion unleashes competitive plant responses in Iberian Atlantic mountain grasslands

AbstractQuestionsDoes the absence of equalizing mechanisms after cessation of grazing unleash strong above‐ground competitors to create large patches in the community? Do these competitive intraspecific aggregations displace and exclude other species, thereby reducing species diversity?LocationAtlantic grasslands, Aralar Natural Park, Basque Country, Northern Iberian Peninsula.MethodsLarge herbivores were experimentally excluded from three sites (50 m × 50 m exclusion fences) during 9 yr in a productive semi‐natural grassland system with a long history of grazing, using adjacent grazed plots as experimental controls. Sampling was carried out by systematically placing 100 quadrats (0.5 m × 0.5 m) in each of the six plots. Floristic composition and abundance, as well as eight hydrological and chemical soil properties, were measured in each quadrat. The spatial structures created by competitive species were analysed usingRDAin conjunction with Moran's eigenvector maps, and soil variables were simultaneously included in the analyses, thus disentangling the structures likely created by niche effects. Competitive exclusion was further determined using linear regressions between species richness and abundance of competitive species.ResultsGrazing exclusion unleashed competitive species such asFestuca microphyllaandAgrostis capillaris, which became dominant in the exclusion plots and created large spatial patches. Furthermore, a negative linear relationship, consistent across exclusion plots, was observed between species richness and abundance of competitive species, indicating that strong above‐ground competitors outcompeted other species when herbivores were excluded. However, the outcome of grazing exclusion across sites depended to some extent on local environmental conditions (niche effects).ConclusionsThis work confirms that the powerful equalizing mechanism of disturbance by herbivores is crucial for species co‐existence in productive grasslands. However, important differences observed in environmental effects across sites suggest that, even in highly productive grasslands, plant traits and local environmental characteristics (niche effects) do matter for species co‐existence.

Moderation is best: effects of grazing intensity on plant--flower visitor networks in Mediterranean communities.

The structure of pollination networks is an important indicator of ecosystem stability and functioning. Livestock grazing is a frequent land use practice that directly affects the abundance and diversity of flowers and pollinators and, therefore, may indirectly affect the structure of pollination networks. We studied how grazing intensity affected the structure of plant-flower visitor networks along a wide range of grazing intensities by sheep and goats, using data from 11 Mediterranean plant-flower visitor communities from Lesvos Island, Greece. We hypothesized that intermediate grazing might result in higher diversity as predicted by the Intermediate Disturbance Hypothesis, which could in turn confer more stability to the networks. Indeed, we found that networks at intermediate grazing intensities were larger, more generalized, more modular, and contained more diverse and even interactions. Despite general responses at the network level, the number of interactions and selectiveness of particular flower visitor and plant taxa in the networks responded differently to grazing intensity, presumably as a consequence of variation in the abundance of different taxa with grazing. Our results highlight the benefit of maintaining moderate levels of livestock grazing by sheep and goats to preserve the complexity and biodiversity of the rich Mediterranean communities, which have a long history of grazing by these domestic animals.

Rangeland management and fluvial geomorphology in northern Tanzania

Researchers have independently documented the effects of land use on rivers and threats to river management institutions, but the relationship between changes in institutional context and river condition is not well described. This study assesses the connections between resource management institutions, land use, and rivers by integrating social science, geospatial analysis, and geomorphology. In particular, we measured hydraulic geometry, sediment size distributions, and estimated sediment yield for four rivers in northern Tanzania and conducted semistructured interviews that assessed corresponding resource management institutions. Communities managed rivers through both customary (traditional, nonstate) and government institutions, but the differences in the resource management policies and practices of the study rivers themselves were fairly subtle. Clearer differences were found at broader scales; the four watersheds exhibited substantial differences in land-cover change and sediment yield associated with the location of settlements, roadways, and cultivation. Unexpectedly, these recent land-use changes did not initiate a geomorphic response in rivers. The long history of grazing by domestic and wild ungulates may have influenced water and sediment supplies such that river channel dimensions are more resistant to changes in land use than other systems or have already adjusted to predominant changes in boundary conditions. This would suggest that not all rivers will have the anticipated responses to contemporary land-use changes because of antecedent land-use patterns; over long time scales (centuries to millennia), the presence of grazers may actually increase the ability of rivers to withstand changes in land use. Our findings point to a need for further interdisciplinary study of dryland rivers and their shifts between system states, especially in areas with a long history of grazing, relatively recent changes in land use, and a dynamic social and institutional context.

Effects of long-term protection from grazing on phenotypic expression in geographically separated mountain rough fescue populations

Thompson, D. J. and Willms, W. D. 2014. Effects of long-term protection from grazing on phenotypic expression in geographically separated mountain rough fescue populations. Can. J. Plant Sci. 94: 33–39. Whether or not long-term grazing or protection from grazing alters the genetic makeup of grass populations has been debated. Mountain rough fescue [(Festuca campestris (Rydb.)], which is highly sensitive to summer grazing, and becomes dominant in plant communities with long-term protection, was chosen to address this question. Plants from three geographic sites (Stavely in AB, Milroy in the Kootenay trench, BC and Goose Lake on the BC interior plateau) with divergent grazing histories were vegetatively propagated from tillers. Daughter plants were planted into two field nurseries (at Kamloops, BC, and Stavely, AB) and morphological measurements were taken in two field seasons post-establishment. Plants from all three populations were taller, flowered earlier, and were more productive at the Kamloops nursery site. Of the three geographic sources, plants from the Goose Lake site were most distinct with narrower leaves, later flowering, and greater yield. Plants with a long history of grazing had slightly shorter fertile tillers and leaves than plants with a history of long-term protection.

Are semiarid shrubs resilient to drought and grazing? Differences and similarities among species and habitats in a long-term study

We assessed long-term effects of grazing cessation and drought on the shrub community of a semiarid ecosystem with a long history of grazing, located in the Mediterranean-to-desert transitional zone in Israel. Effects of grazing and drought on the cover of dominant (Sarcopoterium spinosum) and subdominant (Thymelaea hirsuta, Noaea mucronata and Coridothymus capitatus) shrubs were monitored during 12 years in four topographic habitats. With the exception of the toxic shrub T. hirsuta, shrub cover increased by a few (at most five) percentage points soon after the establishment of fenced plots to prevent grazing, but the difference in cover between protected and grazed plots did not increase subsequently. Response of the woody vegetation cover to the drought pulse was more complex because it was affected by both species and habitat; it showed patterns of steady decrease, transient decrease, and transient increase. Recovery after the drought pulse was relatively slow, and total shrub cover did not return to its predrought level within 7 years. Varied responses to drought and grazing preclude consideration of shrubs as a single response group. The findings heighten concern for the stability of the ecosystem in light of the increasing frequency of dry seasons predicted by climate-change models.

Herbivory and drought interact to enhance spatial patterning and diversity in a savanna understory

The combination of abiotic stress and consumer stress can have complex impacts on plant community structure. Effective conservation and management of semi-arid ecosystems requires an understanding of how different stresses interact to structure plant communities. We explored the separate and combined impacts of episodic drought, livestock grazing, and wild ungulate herbivory on species co-occurrence and diversity patterns in a relatively productive, semi-arid Acacia savanna. Specifically, we analyzed 9 years of biannual plant community data from the Kenya long-term exclosure experiment, a broad-scale manipulative experiment that has excluded different combinations of large mammalian herbivores from 18 4-ha plots since 1995. During droughts, we observed low species diversity and random species co-occurrence patterns. However, when rain followed a major drought, areas exposed to moderate cattle grazing displayed high species diversity and evidence of significant species aggregation. These patterns were not apparent in the absence of cattle, even if other large herbivores were present. To explore possible mechanisms, we examined patterns separately for common and rare species. We found that aggregation patterns were likely driven by rare species responding similarly to the availability of open micro-sites. Our results indicate that in a productive, fire-suppressed savanna, the combination of periodic drought and moderate cattle grazing can enhance plant biodiversity and fine-scale spatial heterogeneity by opening up space for species that are otherwise rare or cryptic. Our findings also emphasize that domestic herbivores can have significantly stronger impacts on plant community dynamics than wild herbivores, even in an ecosystem with a long history of grazing.

Contrasting impacts of different-sized herbivores on species richness of Mediterranean annual pastures differing in primary productivity

Vertebrate herbivores can be key determinants of grassland plant species richness, although the magnitude of their effects can largely depend on ecosystem and herbivore characteristics. It has been demonstrated that the combined effect of primary productivity and body size is critical when assessing the impact of herbivores on plant richness of perennial-dominated grasslands; however, the interaction of site productivity and herbivore size as determinants of plant richness in annual-dominated pastures remains unknown. We experimentally partitioned primary productivity and herbivore body size (sheep and wild rabbits) to study the effect of herbivores on the plant species richness of a Mediterranean semiarid annual plant community in central Spain over six years. We also analyzed the effect of grazing and productivity on the evenness and species composition of the plant community, and green cover, litter, and plant height. We found that plant richness was higher where the large herbivore was present at high-productivity sites but barely changed at low productivity. The small herbivore did not affect species richness at either productivity site despite its large effects on species composition. We propose that adaptations to resource scarcity and herbivory prevented plant richness changes at low-productivity sites, whereas litter accumulation in the absence of herbivores decreased plant richness at high productivity. Our results are consistent with predictions arising from a long history of grazing and highlight the importance of both large and small herbivores to the maintenance of plant diversity of Mediterranean annual-dominated pastures.

Biodiversity of soil macrofauna in the New Forest: a benchmark study across a national park landscape

The New Forest National Park is a hotspot for biodiversity in the UK. A long history of grazing by ponies in the New Forest landscape has created a diverse mosaic of habitats that are of international significance. We investigated patterns of species diversity and composition across the New Forest landscape by sampling soil, leaf litter and ground macrofauna from woodland, grassland and heathland plots across the entire landscape. We used a spatially replicated design of hand sorted soil pits, Winkler extraction of leaf litter, and pitfall traps. We concentrated on diversity patterns of the following target groups: Coleoptera, Formicidae, Isopoda, Chilopoda, Diplopoda, Opiliones and Lumbricidae. The most striking difference in species assemblages is between wooded and open areas. Woodlands are the most diverse habitats and have a distinct assemblage, largely due to those leaf litter invertebrate species which are only present under a closed canopy. Open areas are less diverse, with diversity particularly low in the wet grasslands. However, the open areas do have a distinct fauna, especially in the wet and dry heaths which are home to a number of rare species, particularly of Formicidae. We discuss the potential conservation problems facing the New Forest and how these might affect soil macrofauna biodiversity in the future and conclude that climate change; over-grazing; and land use changes represent the largest threats. Although a relatively stable landscape which benefits from protection under UK law, changes in grazing intensity or management practices in the New Forest, particularly for some of the habitats of European importance (e.g. wet heathlands), could negatively affect soil macrofauna biodiversity. Climate change may also exacerbate biodiversity decline as a result of increased grazing intensity or changes in management.

Effect of spatial and temporal patterns of stress and disturbance intensities in a sub-Mediterranean grassland

The present study examined a sub-Mediterranean pastoral system in the central Apennines (Italy) with a long history of grazing, where winter cold stress is alternated with summer drought stress. The research goals were to ascertain whether different floristic structures correspond to different stress conditions (xeric and semimesic), and whether peculiar functional plant traits (such as avoidance and tolerance mechanisms) respond to stress/disturbance intensities, and understand how vegetation reacts to changeable livestock pressure (through floristic and plant trait variations). Cluster analysis indicated that separate communities develop under different stress intensities. Other analyses highlighted how avoidance strategies predominate within the pastoral system. Observations of grazed and ungrazed patches conducted in 10-m transects revealed spiny cushion formation in semimesic grassland, where a brief period of overgrazing occurs in late summer, causing variations in plant community structure. All these results confirm the importance of historical grazing and current land use, showing how small disturbances and stress variations cause ecosystem responses. Best practices for management were identified. In xeric conditions, it is advisable that the intensity of disturbance be lessened, while in semimesic grassland overgrazing should be forbidden during the dry period, because it could facilitate the development of spiny patches, and subsequent spread of Brachypodium rupestre.

Looking back in time: can safe pasture utilisation rates be determined using commercial paddock data in the Northern Territory?

A ‘safe’ pasture utilisation rate is defined as the proportion of annual forage growth that can be consumed by domestic livestock without adversely affecting land condition in the long term. Pasture utilisation rates are thus a cornerstone of a sustainable grazing industry because they directly determine livestock carrying capacity. Until now, it has only been possible to determine utilisation rates in the Northern Territory via expensive and time-consuming grazing trials. Reliance on this method has limited the validation of safe utilisation rates for the range of land types used for pastoral production. This study tested an alternative cost-effective method for calculating utilisation rates based on an approach used previously in Queensland. The method retrospectively calculates utilisation rates using cattle records and modelled pasture growth from commercial paddocks in good land condition. The assumption underpinning the method is that paddocks in good land condition, with a long history of grazing, must have been managed in such a way as to achieve a safe level of pasture utilisation. Utilisation rates were calculated for 10 commercial paddocks on three properties in the Barkly Tableland region of the Northern Territory from 1999 to 2009. Animal intake for each paddock was calculated from detailed cattle records held in property databases. Pasture growth was estimated using simulation models and cross-checked with field measurements. An average utilisation rate of up to 25% of annual pasture growth was found to be safe on highly uniform, grey cracking-clays supporting Mitchell grass (Astrebla F. Muell. spp.) pastures. However, this level of utilisation had negative impacts on land condition on less resilient and preferentially grazed pasture communities in paddocks with a mix of land types. The implications of the results for carrying capacity, animal productivity and seasonal risk management are explored in this paper.

Assessment of Grazing Effect on Two Sub-Shrubs (Astragalus schottianus and Thymus sipyleus) Dominated Mountain Bozoğlan Grasslands in the Semi-Arid Central-Southern Anatolian Region of Turkey

In the central-southern Anatolian region of Turkey, vegetation of Mountain Bozoğlan grasslands has severely deteriorated, and two sub-shrubs (Astragalus schottianus and Thymus sipyleus) have become dominant species. We hypothesized that the spatial distribution of these dominant shrubs is closely associated with a long history of grazing, and these species might cause alteration of the grassland plant community. Therefore, our objectives were to determine: (1) the patterns in grassland vegetation; (2) how the dominant species contribute to these patterns; and (3) the differences of patterns between ungrazed and protected grassland areas. Plant cover in ungrazed plots was 6% higher than that of grazed plots. Total sub-shrub cover did not differ significantly, but grazing considerably reduced forbs (5% less) and grass cover (5% less). Though A. schottianus and T. sipyleus did not change between the treatments, Festuca valesiaca had greater cover in ungrazed areas (6%) than in that of grazed plots (3%). Grazing effect, soil properties and bare ground appeared to account for most of the variation on the established gradients. Even after 23 years, grazing and protection had little influence on pattern formation, and grazing have expanded dwarf-shrubs at the expense of forbs and grasses. Grazing neither increased nor decreased spatial heterogeneity, so the patterns in both treatments are similar to one another, and relatively stable assemblages of species were likely derived by high grazing pressure experienced before the exclosure establishment.

Restoration of Degraded Grazing Lands through Grazing Management: Can It Work?

Abstract Grazing lands are the most degraded land use type in the world, particularly in arid and semiarid areas, as a result of improper human activities such as overgrazing coupled with drought. For restoration of degraded grazing lands, large‐scale projects are implemented, which include extensive vegetation improvements (e.g., reseeding, weed control, shrub plantations, reforestations, etc.). Such interventions, apart from being very expensive, often create environmental problems. In situations where the abiotic function of the degraded grazing land has not been irreversibly damaged, application of appropriate grazing management is an ecologically viable solution to their restoration. This is especially necessary for grazed lands with a long history of grazing by large herbivores, including livestock. Excluding domestic animals from such ecosystems may lead to several ecological problems such as loss of biodiversity and devastating wildfires. Appropriate grazing management should include an adjusted stocking rate to the grazing capacity of the restored land, the right kind of animal species, and an appropriate grazing system. In addition, grazing management should be implemented on the basis of a plan that is part of the restoration project. It is concluded that grazing management should become a priority option in restoration of the biotic function of degraded grazing lands, especially in those that have had a long history with the presence of domestic animals.

Grazing responses in herbs in relation to herbivore selectivity and plant traits in an alpine ecosystem

Herbivores shape plant communities through selective foraging. However, both herbivore selectivity and the plant's ability to tolerate or resist herbivory may depend on the density of herbivores. In an alpine ecosystem with a long history of grazing, plants are expected to respond to both enhanced and reduced grazing pressures, and the interaction between plant traits and changes in species abundance are expected to differ between the two types of alteration of grazing regime. To understand the mechanisms behind species response, we investigated the relationship between sheep selectivity (measured in situ), plant traits and experimentally derived measures of change in species abundance as a response to the enhancement (from low to high density) or cessation (from low to zero density) of sheep grazing pressure over a six-year time period for 22 abundant herb species in an alpine habitat in south Norway. Sheep selected large, late-flowering herbs with a low leaf C/N ratio. Species that increased in abundance in response to enhanced grazing pressure were generally small and had high root/shoot ratios, thus exhibiting traits that reflect both resistance (through avoidance) and tolerance (through regrowth capacity) strategies. The abundance of selected species remained stable during the study period, and also under the enhanced grazing pressure treatment. There was, however, a tendency for selected species to respond positively to cessation of grazing, although overall responses to cessation of grazing were much less pronounced than responses to enhanced grazing. Avoidance through short stature (probably associated with increased light availability through the removal of tall competitors) as well as a certain amount of regrowth capacity appear to be the main mechanisms behind a positive response to enhanced grazing pressure in this study. The plant trait perspective clearly improves our insight into the mechanisms behind observed changes in species abundance when the disturbance regime is altered.

Seventy-Eight Years of Vegetation Dynamics in a Sandhills Grassland

Abstract The Nebraska Sandhills are a unique and valuable grassland resource within the Great Plains with a long history of grazing. In 1926, a vegetation study was established at the Nebraska National Forest Bessey Ranger District to investigate plant community changes in response to heavy grazing. At the time, heavy grazing was being used to shift the grassland plant community dominance from Schizachyrium scoparium (Michx.) Nash (little bluestem) to Bouteloua hirsuta Lag. (hairy grama) in order to create a natural firebreak to protect the adjacent forest from wildfires. Species frequencies were collected from 48, 1-m2 permanent plots in 1926, 1927, 1929, 1931, 1938, 1948, and 1979 to 2004. We evaluated long-term vegetation dynamics by investigating the influence of summer grazing and precipitation on the plant community using Detrended Correspondence Analysis (DCA) and correlations. We determined that grazing had more influence on the plant community than precipitation, with the DCA axis 1 representing ...

HAWAIIAN HONEYCREEPER HOME RANGE SIZE VARIES WITH HABITAT: IMPLICATIONS FOR NATIVE ACACIA KOA FORESTRY

Reforesting degraded landscapes with native, high‐value timber trees may contribute to biodiversity protection while also increasing the economic value of the land. Ideally, reforested areas should have the habitat characteristics to support viable populations of native fauna. We investigated habitat use by Akiapolaau (Hemignathus munroi), an endangered Hawaiian honeycreeper, in three habitat types: a relatively intact old‐growth forest, an old‐growth forest with a long history of grazing, and a native Acacia koa plantation. We quantified habitat characteristics, calculated foraging preferences, mapped home ranges, measured territoriality, and determined reproductive success at all sites. We found that Akiapolaau were highly selective foragers, foraging primarily on A. koa despite its relative scarcity in the environment, and then secondarily on several subcanopy species. Home range size was significantly smaller at the intact old‐growth site and the A. koa plantation, the two sites with the greater cover of A. koa and of the subcanopy species preferred by Akiapolaau. Birds at these sites were also less territorial, supporting behavioral theory that predicts a nonlinear relationship between food availability and territoriality. Overall, our results show that the A. koa plantation, the site with the highest percentage of A. koa, the smallest Akiapolaau home ranges, and the least territoriality, supported the highest density of birds with no apparent reproductive cost. Because A. koa is an extremely high‐value hardwood and thus can be selectively harvested, there is tremendous potential for conservation advocates to work with landowners to grow A. koa for economic benefit while also enhancing biodiversity.

GRAZING EFFECTS ON RANGELAND DIVERSITY: A SYNTHESIS OF CONTEMPORARY MODELS

Two independent models concerning the effects of grazing on vegetation have gained wide acceptance in the last decade: Westoby et al.'s state‐and‐transition (S– T) model, and Milchunas et al.'s generalized model of the effects of grazing on plant community structure and diversity (MSL model). These two prevailing models, as they stand, are conceptually divergent. The MSL model implicitly assumes that, at a given site, for each grazing intensity there is a single equilibrium situation with a single diversity value. The S–T model suggests that rangeland dynamics include irreversible transitions and alternative equilibria. Here we propose a modification of the original MSL model, to encompass a wider range of real situations and to place it within the context of the S–T model. The four extreme cases proposed in the original MSL model are revisited, taking into account that (1) the “moisture” gradient can be generalized as a “productivity” gradient; (2) the selective pressure of herbivores on systems with long history of grazing has fluctuated over time, allowing the development of different pools of species adapted to low or high grazing intensities; and (3) systems with long evolutionary history of grazing have developed resilience mechanisms that allow reversible shifts in floristic composition with changes in grazing intensities. The grazing intensity vs. diversity curves thus postulated for systems with a long evolutionary history of grazing are similar to those proposed by the original MSL model because resilience mechanisms allow for reversible changes associated with grazing intensity. In contrast, the curves postulated for systems with short evolutionary history of grazing include different alternative branches, indicating irreversible transitions, because resilience mechanisms to grazing were not fully developed. By incorporating these modifications, the divergence between the original MSL and S–T models can be resolved. A set of published examples from real systems is presented and compared with the predictions of the modified model. The modified MSL model is applicable to a wider range of real situations than the MSL model in its original formulation.

Refuge effects of a cactus in grazed short‐grass steppe

Abstract. Question: Which factors influence the effectiveness of biotic refuges for harbouring grazing‐sensitive species in pastures with a long history of grazing by large herbivores? Previous research showed that spiny clumps of the cactus Opuntia polyacantha provided refuges from cattle grazing for plants and for inflorescence production on short‐grass steppe. In this paper, seven factors that may have a potential positive influence on the refuge effects of cactus at a landscape scale were assessed.Location: Short‐grass steppe of the Great Plains of North America.Methods: The study was conducted in eight long‐term grazed pastures and their respective ungrazed controls that were established 60 years ago.Results: Heavy grazing intensities were necessary for some positive effects of cactus to manifest, and some refuge effects changed to negative effects under lower grazing pressure. Refuge effects increased with plant community productivity due to greater abundances of grazing‐sensitive species, and greater grazing intensities in the more productive areas. Cover of cactus cladodes (spine‐covered pads) inside clumps appeared to be the main limiting factor for refuge effects, probably by limiting available space for grazing‐sensitive species in the clumps. Other factors such as size and density of cactus clumps, and the presence of large refuges in the proximity of clumps had minor influence on the effectiveness of cactus refuges.Conclusions: The effects of biotic refuges largely varied with ecological conditions and structural characteristics of the refuge. Refuge effects were mainly influenced by grazing intensity, plant community productivity, and structural characteristics of the biotic refuges. A conceptual model of factors influencing refuge effects at a local landscape scale in plant communities grazed by large herbivores is presented.

Refuge effects of a cactus in grazed short-grass steppe

Abstract Question: Which factors influence the effectiveness of biotic refuges for harbouring grazing-sensitive species in pastures with a long history of grazing by large herbivores? Previous research showed that spiny clumps of the cactus Opuntia polyacantha provided refuges from cattle grazing for plants and for inflorescence production on short-grass steppe. In this paper, seven factors that may have a potential positive influence on the refuge effects of cactus at a landscape scale were assessed. Location: Short-grass steppe of the Great Plains of North America. Methods: The study was conducted in eight long-term grazed pastures and their respective ungrazed controls that were established 60 years ago. Results: Heavy grazing intensities were necessary for some positive effects of cactus to manifest, and some refuge effects changed to negative effects under lower grazing pressure. Refuge effects increased with plant community productivity due to greater abundances of grazing-sensitive species, and gre...