Grazing management of calcareous grasslands and its implications for the conservation of beetle communities

Calcareous grasslands are an important habitat for floral and faunal communities in the UK and Europe. Declines due to changes in management, scrub invasion and agricultural improvement have left much of the remnants of this habitat in a degraded and fragmented state. Grazing, by cattle or sheep, is one of the main management practices used to maintain and improve the floral and faunal quality of calcareous grassland. The long-term impacts of different grazing regimes, however, are poorly understood, particularly in terms of the invertebrate communities. This study contrasted the impacts of recently introduced and long-term sheep or cattle grazing on beetle communities present on one of the largest areas of calcareous grassland in Europe, the Salisbury Plain military training Area, UK. No effects of grazing management on beetle abundance, species richness or evenness were found, but plant diversity and overall percentage cover of grasses did influence beetle diversity. Proportions of the total number of individuals and overall species richness within beetle guilds (predatory, phytophagous, flower/seed feeders, root feeders and foliage feeders) were strongly influenced by both the duration and type of grazing animal. At the species level, beetle community structure showed significant differences between ungrazed, long-term cattle and long-term sheep grazing treatments. Changes in plant community structure were found to influence beetle community structure. The significance of these results is discussed in terms of the long-term impacts of grazing on beetle community structure, and the benefits of different grazing regimes for the conservation management of calcareous grasslands.     

Habitat use and conservation of bumblebees (Bombus spp.) under different grassland management regimes

Declines in the natural populations of several bumblebee species across Britain and Europe are an increasing cause for concern. In this study the habitat use of bumblebees was investigated on Salisbury Plain Training Area, the largest remaining area of unimproved chalk grassland in north-west Europe. Habitat characteristics influencing the overall abundance, species richness and foraging activity of bumblebees included the diversity and abundance of flowering plant species (particularly of favoured forage plants such as Trifolium pratense), vegetation structure and height. It is suggested that different Bombus species respond to these habitat characteristics depending on their specific foraging and nesting requirements, the case of Bombus humilis being especially relevant. The effects of several grassland management practices were considered in terms of their suitability for the conservation of bumblebee habitats. Cattle grazing was shown to be preferable to both sheep grazing and the absence of any management, although the timing and intensity of such grazing was important. Small-scale disturbances caused by vehicle activity were also of value in producing locally abundant forage resources in less intensively managed grasslands.     

The influence of livestock grazing and weed invasion on habitat use by birds in grassy woodland remnants

Remnants of native vegetation in regions dominated by agriculture are subject to degradation, especially by livestock grazing and weed invasion. Ground-foraging birds are amongst the most threatened bird groups in Australia, and these agents of degradation might be contributing to their decline by causing a reduction in food availability. We studied the foraging behaviour and microhabitat use of seven species of ground-foraging insectivores in south-eastern Australian buloke woodland remnants with native, grazed and weedy ground-layers. If birds must resort to using more energetically expensive prey-attack manoeuvres, or selectively use substrates and microhabitats that are less available in degraded habitats, then such degradation is likely to be negatively impacting on these species. We found evidence of a negative impact of one or both of these types of degradation on five of the seven bird species. Three species that employ a range of foraging manoeuvres to attack prey used potentially more energetically expensive aerial manoeuvres significantly more frequently in weedy remnants than in remnants with a native or grazed ground layer. Red-capped robins Petroica goodenovii and brown treecreepers Climacteris picumnus both selectively foraged near trees in grazed sites, and hooded robins Melanodryas cucullata, red-capped robins and willie wagtails Rhipidura leucophrys avoided foraging in microhabitats with a high percentage cover of exotic grasses in weedy sites. Brown treecreepers were also less likely to be present in weedy sites that had been protected from grazing than in either grazed or native sites. These results suggest that although grazing appears to have a detrimental impact on foraging habitat of ground-foraging birds, the exclusion of livestock grazing from previously disturbed buloke remnants alone is not adequate to restore habitat values for ground-foraging birds. A conservation strategy for this habitat type should consider the exclusion of heavy grazing from sites with an intact cryptogamic crust and the management of weeds in disturbed remnants, potentially through the use of carefully controlled light grazing.     

Grazing as a management tool in dune grasslands: Evidence of soil and scale dependence of the effect of large herbivores on plant diversity

In nature management, the introduction of large herbivores into human-influenced grasslands is thought to be effective to maintain or enhance plant diversity. In order to test the validity of this assumption, we studied the effect of grazing by large herbivores on plant species richness and community heterogeneity across a soil acidity gradient at different spatial scales in dry coastal dune grasslands in western Belgium and north-western France. The effect of grazing on plant richness varied with scale and soil acidity. Grazing had a predominantly positive effect on plant species richness in all habitats at the small scale (0.25 × 0.25 m). However, at site scale (8 × 8 m) it had only positive effects in grasslands with higher soil pH (6-7.4). Similarly, grazing resulted in a homogenization of grassland vegetation at lower pH, while heterogeneity increased with grazing on soil with higher pH. In general, grazing increased the number of rare species, independent of soil pH. The results confirm that the impact of grazing on plant diversity depends on the scale considered and that the effects further depend on soil acidity which was correlated to biomass production at the given soil pH range in this study. Although grazing seems an appropriate management tool to maintain and even enhance plant biodiversity under many circumstances, it may negatively affect plant species richness, where soil resources limit plant biomass production.     

Effects of livestock grazing on pollination on a steppe in eastern Mongolia

Widespread degradation of Mongolian grasslands by overgrazing is of global concern. The objective of this study was to reveal the effects of grazing on pollination as an example of interaction biodiversity in Mongolian grasslands. We established three plots according to grazing intensity on the eastern steppe of Mongolia. In each plot, we recorded the numbers of insect-pollinated plants and observed the foraging behavior of pollinators in June and August. The richness of insect-pollinated species was high and these species were most abundant in lightly grazed plots, and formed complex relations with diverse pollinators. But, frequency of flower visitation and pollination index were greater in heavily grazed plots. All pollination properties were poorest in intermediately grazed plots. These results suggest that the forb-biased foraging of sheep and goats reduces the floral diversity of insect-pollinated species, and consequently reduces pollinators in the intermediately grazed plots. In the heavily grazed plots, only limited ruderal species could survive under heavy cattle grazing, and such simple vegetation formed unbalanced but strong bonds with pollinators. Removal simulation showed that the mutual network was more fragile with respect to the extinction of certain species.     

The remarkable resilience of ant assemblages following major vegetation change in an arid ecosystem

In northwestern Mexico, large tracts of native desert scrub and thorn scrub vegetation are being converted to non-native grass pastures at an increasing rate in an effort to increase cattle production. Pasture development has large impacts on vegetation structure and perennial plant diversity, but little is known of the potential ecological consequences of this landscape transformation for other taxa. I compared the abundance, diversity, species composition and structure of ant assemblages in native habitats and non-native grass pastures across a longitudinal rainfall gradient in central Sonora, Mexico. Land conversion resulted in minor reductions of alpha and gamma diversity and had no effect on beta diversity or species turnover. The influence of land conversion on species composition was small in comparison to the influence of other factors. In addition, ant assemblages in native habitats and non-native grass pastures were similar to each other in regards to both species relative abundance distributions and functional group composition. These results suggest that ants are remarkably resilient to the conversion of native desert scrub and thorn scrub habitats to non-native grass pastures, which is consistent with the growing body of research reporting weak and inconsistent responses of ant assemblages to grazing in arid rangelands.     

Grazing effects on microbial community composition, growth and nutrient cycling in salt marsh and sand dune grasslands

The effect of grazing by large herbivores on the microbial community and the ecosystem functions they provide are relatively unknown in grassland systems. In this study, the impact of grazing upon the size, composition and activity of the soil microbial community was measured in field experiments in two coastal ecosystems: one salt marsh and one sand dune grassland. Bacterial, fungal and total microbial biomass were not systematically affected by grazing across ecosystems, although, within an ecosystem, differences could be detected. Fungal-to-bacterial ratio did not differ with grazing for either habitat. Redundancy analysis showed that soil moisture, bulk density and root biomass significantly explained the composition of phospholipid fatty acid (PLFA) markers, dominated by the distinction between the two grassland habitats, but where the grazing effect could also be resolved. PLFA markers for Gram-positive bacteria were more proportionally abundant in un-grazed, and markers for Gram-negative bacteria in grazed grasslands. Bacterial growth rate (leucine incorporation) was highest in un-grazed salt marsh but did not vary with grazing intensity in the sand dune grassland. We conclude that grazing consistently affects the composition of the soil microbial community in semi-natural grasslands but that its influence is small (7 % of the total variation in PLFA composition), compared with differences between grassland types (89 %). The relatively small effect of grazing translated to small effects on measurements of soil microbial functions, including N and C mineralisation. This study is an early step toward assessing consequences of land-use change for global nutrient cycles driven by the microbial community.     

The effects of cattle grazing on tall-herb fen vegetation and molluscs

The effects of light year-round cattle grazing on tall-herb fen vegetation and wetland molluscs were compared to the effects of non-intervention over a period of four years using grazing exclosures. The distribution of cattle within the area of fen was investigated by plotting the position of the herd at 3-4 day intervals throughout the year. Cattle distributed themselves randomly throughout the fen in spring, autumn and winter, but showed a more aggregated distribution in summer. Grazing reduced the biomass of Phragmites australis and increased stem densities of Glyceria maxima, resulting in a shift of dominance from Phragmites to Glyceria. Plant species-richness was also significantly higher in areas open to grazing.Grazing decreased total densities of molluscs and substantially reduced densities of the rare snail Vertigo moulinsiana. V. moulinsiana was particularly associated with areas of fen that had a high water table and high biomass of ungrazed Carex riparia. However, because of the patchy nature of the grazing, V. moulinsiana survived at reasonably high densities in patches of ungrazed vegetation within the grazing unit.     

Habitat selection by the Mediterranean horseshoe bat, Rhinolophus euryale (Chiroptera: Rhinolophidae) in a rural area of southern Italy and implications for conservation

We studied habitat selection by Rhinolophus euryale in a rural area of southern Italy in 1998-2000 by radio-tracking. Two comparisons were carried out, one between habitat occurrence within individual home ranges and within the study area, the other between time spent in each foraging habitat and habitat occurrence within the home range. The first analysis showed that olive groves and conifer plantations were, respectively, the most and the least important habitats. The second analysis highlighted the importance of woodland for R. euryale, while urban sites, open areas and conifer plantations were avoided. We recommend that clearing of continuous, large areas of woodland for tree harvesting should be avoided. Conifers should not be used for reforestation. Urbanisation should be limited in the areas of greatest importance for the species, and linear landscape elements such as tree lines and hedgerows should be maintained.     

Grazing promotes dung beetle diversity in the xeric landscape of a Mexican Biosphere Reserve

We analyze the impact of grazing on dung beetle diversity at the Barranca de Metztitlán Biosphere Reserve, a xeric ecosystem in central Mexico with a long history of use by humans. We compared the community structure, as well as the alpha and beta diversity between two cover conditions (open and closed vegetation) that represent the impact of grazing within a habitat, and between habitat types (submountainous and crassicaule scrublands). From 576 samples we collected 75,605 dung beetles belonging to 20 taxa. While mean species richness and diversity were different between habitat types, cumulative species richness was not. The effects of grazing on vegetation structure influenced the cumulative species richness and diversity of dung beetles in the submountainous scrubland, where grazing has created land mosaics of a grassland matrix with scrubland patches. This was not the case in the crassicaule scrubland where the impact of grazing is not as evident. Beta diversity significantly responds to the effects of grazing on habitat conditions. We discuss the ecological factors that may promote these responses by landscape diversity components. We also identify the species that could act as useful indicators to monitor the effect of land management on biodiversity. Our results indicate cattle farming maintains a diversified land mosaic, and these areas support more diverse dung beetle ensembles than homogeneous areas of closed, shrubby vegetation cover. Thus, controlled grazing activity could certainly favour the conservation of dung beetle biodiversity and improve ecosystem functioning by maintaining dung decomposition rates.     

Impact of cattle grazing and inorganic fertiliser additions to managed grasslands on the microbial community composition of soils

A study was undertaken to determine if cattle grazing on managed grasslands had an impact on the microbial community composition of soils. Microbial community molecular profiles of bacteria, actinomycetes, pseudomonads and fungi were generated by polymerase chain reaction (PCR) amplification of rDNA sequences from community DNA isolated from soils. PCR products were profiled using denaturing gradient gel electrophoresis (DGGE) and analysed by principal co-ordinate analysis. PCR–DGGE profiles indicated that cattle grazing had an impact on the pseudomonad community structure only, and that the addition of inorganic nitrogen (N) fertiliser impacted on bacterial, actinomycete and pseudomonad community structure. There was no difference in the community profiles of fungi from grazed and N fertilised grassland plots. Analysis of phospholipid fatty acid (PLFA) profiles revealed that both cattle grazing and N fertiliser impacted on microbial community structure. The abundance of individual PLFAs differed between treatments, with bacterial (15:0), actinomycete (10Me18:0) and fungal (18:2ω6) PLFAs not affected directly by grazing cattle and N fertiliser, however, there were significant grazing–fertiliser interactions. Bacterial plate counts were highest in the N fertilised plots and fungal plate counts were highest in the cattle grazed plots. Analysis of molecular microbial community profiles with PLFA and background soil data revealed several significant correlations. Notably, soil pH was positively correlated with PCO1 of the pseudomonad community profiles and negatively correlated with the fungal PLFA 18:2ω6. Fungal DGGE profiles were negatively correlated with the fungal PLFA 18:2ω6, and bacterial and fungal plate counts positively correlated with each other. Correlation analysis using PC1 from PLFA profile data showed no significant relationship with soil organic matter, pH, total C and total N. The results indicate that cattle grazing and N fertiliser addition to grasslands impact on the community composition of specific groups of micro-organisms. The consequences of such changes in population structure may have implications regarding the dynamics of nutrient turnover in soils.     

Effects of grazing by horses and/or cattle on the diversity of coastal grasslands in western France

In the coastal grasslands of western France, extensive mixed grazing by cattle and horses has been practised for many centuries. The vegetation of these old embanked grasslands varies along a topographical gradient with a hygrophilous plant community in low-lying depressions seasonally flooded, a mesophilous community on high level flats that are never flooded, and a meso-hygrophilous community on slopes where the soil remains saline. Recently, fewer horses have been grazed on these pastures and so a 6-year study was designed to investigate the effects of monospecific and mixed grazing by horses and cattle on plant community structure, composition and diversity. Mixed grazing produced the most species-rich and structurally diverse swards. Mixed grazing enhanced the development of rosette, sub-halophyte and halophyte species where the soil is saline, due to additive effects between the two herbivore species. Mixed grazing also limited the strongly competitive Elymus repens and Agrostis stolonifera on horse latrine areas, cattle grazing, thus showing a compensatory effect. The combination of additive and compensatory effects with mixed grazing could be used to manage plant diversity, heterogeneity in vegetation structure and communities of conservation value at the scale of the grassland ecosystem.     

Disentangling effects of habitat diversity and area on orthopteran species with contrasting mobility

Loss of semi-natural grasslands and reduction of habitat diversity are considered major potential threats to arthropod diversity in agricultural landscapes. The main aim of this study was to investigate how area and habitat diversity, mediated by shrub encroachment after grassland abandonment, affect species richness of orthopterans in island-like grasslands, and how contrasting mobility might alter species richness response to both factors. We selected 35 isolated patches in landscapes dominated by arable land (durum wheat) in order to obtain two statistically uncorrelated gradients: (i) one in habitat area ranging from 0.2 to 55 ha and (ii) one in habitat diversity ranging from patches dominated by one habitat (either open grasslands or shrublands) to patches with a mosaic of different habitats. Habitat loss due to land-use conversion into arable fields was associated with a substantial loss of species with a positive species-area relationship (SAR), with sedentary species having a steeper and stronger SAR than mobile species. Halting habitat loss is, therefore, needed to avoid further species extinctions. Shrub encroachment, triggered by abandonment, presented a hump-shaped relationship with habitat diversity. An increase in habitat diversity enhanced species richness irrespective of patch area and mobility. Maintaining or enhancing habitat diversity, by cutting or burning small sectors and by reintroducing extensive sheep grazing into abandoned grassland, are suggested as complementary strategies to mitigate further decline of orthopteran diversity in the remnant patches. This would be equally important in both small and large patches.     

Adaptive range selection by golden eagles in a changing landscape: A multiple modelling approach

Land abandonment is causing considerable woodland expansion in many mountainous areas of Europe, with potential repercussions on conservation-sensitive species typical of open habitats. We examined the potential impact of such changes on an alpine golden eagle population, by estimating the ranges potentially used by the eagles for foraging through different techniques (concentric circles of different radii and a tessellation-method based on telemetry data). Compared to randomly located territories, eagles selected ranges farther away from conspecifics, characterised by a rugged topography and rich in main prey species and in open habitats favoured by their main prey species, such as grassland, shrubs, xerophytic vegetation and rocky outcrops. Similarly, nest spacing and breeding success were related to the availability of optimal foraging habitats, also favoured by the main prey species of the eagles. Even though woodland-variables did not enter any of the stepwise models, eagles were dependent on grassland habitats, currently lost to woodland at a rate of about 0.5-1% per year, and on shrub vegetation rapidly evolving into woodland, which accounted on average for almost 10% of the eagle ranges. Long-term loss of such habitat may imply up to a 66% woodland increase for some eagle ranges. Given the complexity of the uncovered relationships and difficulty to make firm predictions, subsidies to halt the abandonment of traditional agro-pastoral practices seem urgently needed.     

Building large-scale spatially explicit models to predict the distribution of suitable habitat patches for the Greater rhea (Rhea americana), a near-threatened species

We developed large-scale spatially explicit models to predict the distribution of suitable habitat patches for the Greater rhea (Rhea americana), a near-threatened species, in two areas of central Argentina with different land use: a grassland area (ca. 4943 km²) mainly devoted to cattle grazing and an agro-ecosystem area (ca. 4006 km²) mostly used for crop production. The models were developed using logistic regression and were based on current records of Greater rhea occurrence coupled with remote sensing data, including land cover and human presence variables. The habitat suitability maps generated were used to predict the suitable habitat patch structure for wild rhea populations in each area. Fifty-one percent of the total grassland area was suitable for the species, being represented by a single large patch that included 62% of the individual locations. In the agro-ecosystem, only 28% of the total area was suitable, which was distributed among four patches. Seventy percent of rhea observations were in suitable habitat, with all rheas grouped in the largest patch. Conservation efforts for preserving wild rhea populations should be focused on maintaining habitats similar to grasslands, which are less profitable for landowners at present. Consequently, the protection of the pampas grasslands, a key habitat for this species as well as for others with similar habitat requirements, will demand strong conservation actions through the reconciliation of interests between producers and conservationists, since the proportion of croplands is increasing.     

Altitudinal pattern of grazing exclusion effects on vegetation characteristics and soil properties in alpine grasslands on the central Tibetan Plateau

Journal of Soils and Sediments - Grazing exclusion by fencing has been widely used for restoring degraded alpine grasslands, but rarely studies have considered the altitudinal difference of grazing...     

Effects of grassland abandonment, restoration and management on butterflies and vascular plants

When semi-natural pastures are abandoned, specialized grassland species are lost as a consequence of succession. As a counter-measure, previously abandoned grasslands may be restored by clearing shrubs and trees and re-introducing grazing livestock. In order to examine the effects of this type of habitat restoration, we compared species richness of plants and of specialized plants thought to be dependent on continuous management and species richness and abundance of butterflies and red-listed butterflies in 12 sets of matched continuously managed, abandoned and restored grassland in southern Sweden. We found no differences in species richness or abundance between the three grassland types. There were, however, some negative effects of abandonment. The number of management-dependent plants decreased with increasing cover of trees and shrubs, and in restored sites species richness of all groups decreased with increasing cover of trees and shrubs before restoration. Also the present management significantly affected both butterflies and plants. Species richness of both groups increased with increasing vegetation height and differed between sites depending on the species of grazers, with negative effects of sheep compared to cattle or horses. Our study indicates that for grassland management to be efficient, the restoration actions should mainly be directed towards sites where the post-abandonment succession has not proceeded too far.     

Application of central-place foraging theory shows the importance of Mediterranean dehesas for the conservation of the cinereous vulture, Aegypius monachus

The dehesa (oak woodland) is an extensive agro-pastoral ecosystem characteristic of the Western Mediterranean countries which is suffering a great transformation process since 1950. Although its distribution largely overlaps with several endangered species, there is scarce information on how they use this human-transformed habitat. We studied the foraging habitat selection of one of them, the cinereous vulture Aegypius monachus. We radio-tracked 14 cinereous vultures in one of the largest European colonies from 1998 to 2000. Used and available habitats were compared at two scales using compositional analysis. Moreover, we developed a distance-based GLMM for assessing habitat selection in this central-place forager species, by taking into account the spatial distribution of habitat patches in relation to the location of the colony. Home ranges overlapped over a total surface of 592,527 ha around the colony, and both individual home ranges and travel foraging distances (mean 27.86 km, maximum 86 km) were larger during the breeding season. All cinereous vultures avoided agricultural lands within their home ranges throughout the year. Habitat use in relation to the distance to the colony pointed out that dehesas were positively selected in spite of being on average far away from the colony than other habitats, a result that was consistent among individuals and seasons. The cinereous vulture thus depends for its conservation not only on the protection of breeding areas, as has been so far considered, but also on the maintenance of well-conserved dehesas close to the colonies. Preserving the cinereous vultures could contribute to the economic sustainability of dehesas by attracting PAC funds for their traditional low-intensity exploitation. Although other species may also benefit from this study since cinereous vulture could be a “flagship” for the large-scale conservation of Mediterranean oak woodlands and associated biodiversity, more fine local management guidelines should be performed on the basis of studies on more sensitive species.     

Hedgerows in an agri-natural landscape: Potential habitat value for native bees

Recent declines in North American honeybee populations have highlighted the importance of native bee conservation, and the need for research on the ecological requirements of native bees in farmland. In this study, we investigated the value of hedgerows as foraging habitat for native bees in mosaics of small-scale agriculture and natural vegetation in two riparian landscapes in southeast Arizona, USA. In the summers of 2002 and 2003, we surveyed bees and flowers in four habitats: hedgerows, agricultural fields, woodlots, and native woodland. We asked: (1) How do hedgerows compare to other available habitats in bee abundance and species richness? (2) How does bee species composition in hedgerows compare to species composition in agricultural fields and woodland? (3) How do flower resources in hedgerows compare to those in fields and woodland?We found that hedgerows were attractive foraging habitat for native bees, especially in early summer, when hedgerows tended to have higher species richness than other agricultural or natural habitats. Cumulative species richness was highest in agricultural fields, although cumulative species richness did not significantly differ among fields, hedgerows, and woodland. While bee faunas overlapped among habitats, bee assemblages in hedgerows were more similar to those in woodland than to those in fields. The hedgerow herbaceous flora was roughly intermediate to that of fields and woodland; hedgerows also supported high densities of woodland-characteristic shrubs. These flowering shrubs were important in attracting bees that were otherwise uncommon in the landscape, including some species that are potentially valuable pollinators of agricultural crops.