Nonequilibrium dynamics of sedge meadows grazed by cattle in southern Wisconsin

Equilibrium theory predicts that after disturbance, ecosystemseventually regain the structural and functional properties characteristic oftheir predisturbance condition. This study tested this idea by examining theeffects of cattle grazing and exclusion on the long-term structuralcharacteristics of sedge meadows in southern Wisconsin. To compare structuralchanges in mean percentage cover and height, repeated measures analysis wasconducted on two sedge meadows over a twenty year period from 1977 to 1997. Onesedge meadow was recovering from cattle grazing (cattle excluded in 1973) andthe other was a reference area (nearly undisturbed). Both of these study siteschanged structurally from 1977 to 1997, supporting non-equilibrium theory.Additional observations were made in a heavily and lightly grazed sedge meadowthat were surveyed in 1977. As based on the positions of subunits in anordination graph produced using Non-Metric Multidimensional Scaling (NMS), therecovery sedge meadow became less structurally similar to the grazed and moresimilar to the reference site over the 20 year study. However, from theperspective of mean maximum height in another NMS analysis, the recovery sedgemeadow became less similar to the reference site over time likely because by1997, a shrub carr of Cornus sericea had developed in therecovery sedge meadow that had been dominated by graminoids and forbs in 1977(mean maximum height: 1977 vs. 1997; 0 vs. 47 cm). Seedlings ofCornus sericea were invading the grazed sedge meadows andin the recovery sedge meadow (cattle excluded 4 years earlier) in 1977. A shrubcarr did not develop in the reference sedge meadow. Changes in the referencesite were relatively minor over this time interval; certain species eitherincreased or decreased in dominance, e.g., Carex strictaincreased in cover (1977 vs. 1997, 20 and 28 mean percentage (%) cover,respectively). A few short-term species of the recovery sedge meadow followedthe tenets of equilibrium theory. These became less common or disappeared4–9 years after cattle exclusion including Asterlanceolatus, Calamagrostis canadensis,Poa compressa, Solidago altissima andVerbena hastata. Some of these species were eaten andlikely spread by the cattle. This study suggests that the progression of sedgemeadow to shrub carr may not be an inevitable outcome of succession but insteadcan be a consequence of past cattle grazing history. Also, because the recoveryand the reference sedge both changed structurally over time, the tenets ofnon-equilibrium theory were supported by this study.     

Effects of grazing and inundation on pasture quality and seed production in a salt marsh

During a six-year period, changes in the composition of dominant plant species of importance to foraging birds in a salt marsh on the Swedish west coast were followed inside and outside exclosures to document effects of grazing on herbage quality and seed production. Since marshes provide an important habitat for foraging geese and ducks, it was of interest to determine how cattle grazing would affect herbage production inAgrostis stolonifera andPuccinellia maritima and seed and root-tuber production inScirpus maritimus. Measurements of cover and height in permanent plots revealed that a wetter weather type favouredAgrostis, probably through reduced salinity, at the expense ofPuccinellia, which was the most favoured food of both cattle and birds.Agrostis out-competedPuccinellia when grazing pressure was low. Seed production inScirpus maritimus was reduced by cattle grazing, particularly whenPhragmites australis formed part of the vegetation. In the absence of cattle grazing, both herbage- and seed producing plants were gradually reduced, andPhragmites increased. Since high herbage consumption and high seed production are mutually exclusive, grazing rotation in combination with mowing is suggested as a management strategy.     

Plant biodiversity on shortgrass steppe after 55 years of zero,light, moderate,or heavy cattle grazing

Shortgrass steppe rangeland near Nunn, Colorado, USA, has been lightly,moderately, or heavily grazed by cattle, or protected from grazing inexclosures, for 55 years. Plant species biodiversity and evenness were greatestin lightly- and moderately-grazed pastures. Both pastures weredominated by the warm-season shortgrass Boutelouagracilis, but the cool-season midgrasses Pascopyrumsmithii and Stipa comata contributedsignificantly to biomass production on the lightly-grazed pasture, asthey did in the exclosures. Diversity was least in the exclosures, which werestrongly dominated by the cactus Opuntia polyacantha.Buchloë dactyloides, another warm-seasonshortgrass, and Bouteloua gracilis were co-dominantsunder heavy grazing, and diversity was intermediate. Plant community structureand diversity were controlled by selective grazing by cattle and soildisturbance by cattle and rodents. Shortgrass steppe moderately or heavilygrazed by cattle was similar to and probably as sustainable as steppe grazed formillenia by bison and other wild ungulates.     

Multi-scale responses of vegetation to removal of horse grazing from Great Basin (USA) mountain ranges

Although free-roaming equids occur on all of the world’s continents except Antarctica, very few studies (and none in the Great Basin, USA) have either investigated their grazing effects on vegetation at more than one spatial scale or compared characteristics of areas from which grazing has been removed to those of currently grazed areas. We compared characteristics of vegetation at 19 sites in nine mountain ranges of the western Great Basin; sites were either grazed by feral horses (Equus caballus) or had had horses removed for the last 10–14 years. We selected horse-occupied and horse-removed sites with similar aspect, slope, fire history, grazing pressure by cattle (minimal to none), and dominant vegetation (Artemisia tridentata). During 1997 and 1998, line-intercept transects randomly located within sites revealed that horse-removed sites exhibited 1.1−1.9 times greater shrub cover, 1.2–1.5 times greater total plant cover, 2–12 species greater plant species richness, and 1.9–2.9 times greater cover and 1.1–2.4 times greater frequency of native grasses than did horse-occupied sites. In contrast, sites with horses tended to have more grazing-resistant forbs and exotic plants. Direction and magnitude of landscape-scale results were corroborated by smaller-scale comparisons within horse-occupied sites of horse-trail transects and (randomly located) transects that characterized overall site conditions. Information-theoretic analyses that incorporated various subsets of abiotic variables suggested that presence of horses was generally a strong determinant of those vegetation-related variables that differed significantly between treatments, especially frequency and cover of grasses, but also species richness and shrub cover and frequency. In contrast, abiotic variables such as precipitation, site elevation, and soil erodibility best predicted characteristics such as forb cover, shrub frequency, and continuity of the shrub canopy. We found species richness of plants monotonically decreased across sites as grazing disturbance increased, suggesting that either the bell-shaped diversity-disturbance curve of the intermediate-disturbance hypothesis does not apply in this system or that most sites are already all on the greater-disturbance slope of the curve. In our study, numerous vegetation properties of less-grazed areas and sites differed notably from horse-grazed sites at local and landscape scales during a wetter and an average-precipitation year. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cattle and Weedy Shrubs as Restoration Tools of Tropical Montane Rainforest

Over the last 150 years, a large proportion of forests in Latin America have been converted to pastures. When these pastures are abandoned, grasses may slow re‐establishment of woody species and limit forest regeneration. In this study, we explored the use of cattle in facilitating the establishment of woody vegetation in Colombian montane pastures, dominated by the African grasses Pennisetum clandestinum (Kikuyo) and Melinis minutiflora (Yaraguá). First, we described woody and herbaceous vegetation in grazed and non‐grazed pastures. Second, we tested the effect of grazing and seed addition on the establishment and growth of woody species. We also determined if the effect of grazing was different in P. clandestinum and M. minutiflora pastures. We found that low stocking density of cattle greatly increased density, number of branches per individual (a measure of “shrubiness”), and basal area of woody species, but also reduced woody plant species richness and diversity. In the grazed area, the shrubs Baccharis latifolia (Chilca) and Salvia sp. (Salvia) were the most abundant. The combined effect of grazing and shading from the shrubs reduced herbaceous vegetation by 52 to 92%. In the grazing/seed addition experiment, grazing increased establishment of woody seedlings, particularly of the shrub Verbesina arborea (camargo), but the largest effect was seed addition. Where grasses are an important barrier to regeneration, grazing can facilitate the establishment of shrubs that create a microhabitat more suitable for the establishment of montane forest tree species.     

Vegetation patch dynamics in rangelands: How feedbacks between large herbivores,vegetation and soil fauna alter patches over space and through time

Aim

Large herbivore grazing is a popular conservation management tool to promote vegetation structural diversity of rangelands. However, vegetation patch dynamics, that is, how patches of grazing-defended tall vegetation and grazer-preferred short lawns shift over space and time, is poorly understood. Here, we describe a new conceptual framework for patch dynamics within rangelands, combining theories of classical cyclical succession, self-organization and multitrophic feedbacks between grazers, vegetation and bioturbating soil fauna.

Location

We use the cattle-grazed salt marsh of the island Schiermonnikoog, The Netherlands, as a model system. The grazed salt marsh is characterized by distinct tall vegetation patches dominated by the grazing-defended rush Juncus maritimus and grazing-intolerant grass Elytrigia atherica, surrounded by a matrix of grazing lawn (dominated by Festuca rubra).

The Framework

Based on previous observational and experimental studies, we propose a cyclical patch dynamic where plant species composition and structure transitions through four phases: patch initiation (a) occurs when the grazing-defended rush J. maritimus establishes in the grazed lawn. Patch establishment (b) follows when the grazing-intolerant grass E. atherica establishes in the patch due to associational defence by J. maritimus and produces a large amount of litter that attracts the key bioturbating amphipod Orchestia gammarellus. Patch expansion (c) occurs when O. gammarellus activities improve soil properties of the patch, which favours E. atherica growth, leading to E. atherica competitively displacing J. maritimus in the centre of the patch. Patch degeneration (d) follows when cattle enter the enlarged patch to consume E. atherica in the centre, trample the soil, displace O. gammarellus and decrease vegetation cover, opening space for grazing-lawn species to invade. The cycle restarts when remnants of the rush J. maritimus in the degenerated patches (or individuals recently established from seed dispersal) initiate new patches in the grazing lawn.

Synthesis

Our proposed patch-dynamic model provides a means to describe the mechanisms driving vegetation patch dynamics and serves as a foundation for further experimental and observational exploration, not only for this specific system, but more generally for grazed systems worldwide that show patches of typical grazing-defended and grazer-preferred vegetation.     

A numerical study of successions in an abandoned,damp calcareous meadow in S Sweden

Summary Two sites at Örup, SE skåne, Sweden, have been investigated, viz. a grazed, unimproved, tussocky pasture on a calcareous moraine clay; and an originally similar, adjacent area that was abandoned about 1960. On the grazed site the vegetation is extremely rich in species. This vegetation type was formerly widespread, but nowadays it is rare and therefore it is important to try to conserve examples of it. In total, 80 0.1 m² quadrates distributed at random within 4 homogeneous plots were investigated. The species composition and the cover, the height of the vegetation, the position on a tussock or in a depression and the amount of litter were recorded. The cover data were ordinated (PCA). The differentiation between tussocks and depressions and the effects of ceasing grazing were clearly separated. The connections between the vegetation and the position of the quadrat, grazing intensity etc. were investigated. The vegetation of the ungrazed parts had become dominated by Filipendula ulmaria and Carex disticha; on an average there were 5.5 species/0.1 m². The grazed quadrats contained three times as many species and showed much higher spatial variation, important species being Carex panicea, C. flacca, Molinia caerulea, Festuca ovina, Potentilla erecta, Centaurea jacea and Serratula tinctoria.Nomenclature of vascular plants follows Lid (1974), for names of bryophytes see Nyholm (1954–69) and Arnell (1956).This paper is mainly based on a more detailed paper in Swedish (Regnéll 1979).I thank Dr. E. van der Maarel, Prof. Nils Malmer, Fil. lic. Anders Larsson, Fil. Dr. Eva Waldemarsson-Jensén and Fil. kand. Stefan Persson for valuable discussions and encouragement.     

Long- and short-term effects of reindeer grazing on tundra wetland vegetation

We studied long-term (50 years) and short-term (4 years) effects of summer grazing of reindeer on subarctic tundra wetland vegetation. The long-term effects of summer grazing were studied by comparing vegetation on Finnish and Norwegian sides of the fence line separating reindeer grazing regimes. The Finnish side was intensively grazed and trampled throughout the year, whereas the Norwegian side was grazed in winter. Experimental fences were erected to examine short-term effects of grazing exclusion. Both in the long- and short-term, summer grazing decreased the height of Salix lapponum whereas the short-term effects on willow cover were less clear than the long-term effects. In contrast, Carex spp. benefited from grazing. Long-term grazing had little effect on total bryophyte cover. Grazing had negligible effects on the nutrient content of leaves of S. lapponum and Eriophorum angustifolium. We conclude that tundra wetlands can withstand moderately high grazing pressure sustained over several decades.     

Woody plant invasion of grasslands: establishment of honey mesquite (Prosopis glandulosa var.glandulosa) on sites differing in herbaceous biomass and grazing history

Summary Emergence and survival of honey mesquite (Prosopis glandulosa var.glandulosa Torr.) seedlings was quantified on sites with contrasting grazing histories: long-term continuous grazing (LTG) and long-term protection (LTP) from grazing by cattle. On each site, different levels of heroaceous defoliation were imposed at monthly intervals (no defoliation=ND, moderate=MD and heavy=HD). The two weeks following seed dissemination appeared to be the most critical toProsopis establishment on LTP-ND plots. Openings in the herbaceous layer created by moderate defoliation of grasses on the LTP site increased germination and/or survival 7-to 8-fold during this period. However, increasing the degree of defoliation from moderate to heavy did not stimulate additional emergence on either the LTP or LTG site. Emergence from scarified seed placed in cattle dung (17 to 30%) was lower than that of bare seed placements in various microhabitats (43–60%). However, deposition of scarifiedProsopis seed in dung in conjunction with graminoid defoliation may be the most likely combination of events when livestock are present. Emergence from seeds transported into grasslands by other fauna likely would be low, unless seeds were deposited in areas where grasses had been defoliated.Prosopis survival was comparably high in dung and bare seed placements after one growing season. survival of seedlings present two weeks after seed dissemination ranged from 74 to 97% at the end of the second growing season. Seedling survival and shoot development (biomass, leaf area and height) were similar on LTP and LTG sites, regardless of the level of herbaceous defoliation or seed placement. In addition, the magnitude and patterns of net photosynthesis, stomatal conductance and xylem water potential were comparable among one-year-old seedtings on ND, MD and HD plots, even though differences in herbaceous species composition and above- and below-ground biomass between these treatments were substantial. Such data suggest competition for soil resources between grasses andProsopis may be minimal early in the life cycle ofProsopis. High rates ofProsopis emergence and establishment on LTP-MD plots are counter to the widespread assumption that long-term and/or heavy grazing is requisite forProsopis encroachment into grasslands. Results are discussed with regard to factors contributing to the recent, widespread invasion of this woody legume into grasslands of southwestern North America.Abbreviations LTG long-term grazed - LTP long-term protected from grazing - ND non-defoliated - MD moderate defoliation - HD heavy defoliation     

Responses of Shrub Midstory and Herbaceous Layers to Managed Grazing and Fire in a North American Savanna (Oak Woodland) and Prairie Landscape

Worldwide, savanna remnants are losing acreage due to species replacement with shade-tolerant midstory forest species as a response to decades of fire suppression. Because canopy closes grasses and other easily ignitable fuels decline, therefore, fire, when reintroduced after years of absence, is not always effective at restoring the open structure original to these communities. Our study sought to determine if managed grazing is an alternative tool for reducing shrub densities and restoring savanna structure without the impacts on soils and native vegetation observed with unmanaged grazing. We compared effects of fire and managed grazing on shrub and herb composition within degraded oak savanna and tallgrass prairie of the U.S. Upper Midwest using a randomized complete block design. The vegetation response to treatments differed by species and by vegetation type. Total shrub stem densities declined 44% in grazed and 68% in burned paddocks within savanna and by 33% for both treatments within prairie. Within savanna, cattle reduced stem densities of Rubus spp. 97%, whereas fire reduced Ribes missouriense stems 96%. Both fire and grazing were effective at reducing stem numbers for several other shrub species but not to the same degree. Native forbs were suppressed in grazed savanna paddocks, as were native grasses in grazed prairie paddocks along with a minor increase of exotic forbs. We did not observe changes in soil bulk density. We conclude that managed grazing can serve as a valuable supplement but not as a replacement to fire for controlling shrubs in these systems.     

Influence of livestock grazing on meadow pipit foraging behaviour in upland grassland

Changes in grazing management are believed to be responsible for declines in populations of birds breeding in grassland over the last decades. The relationships between grazing management regimes, vegetation structure and composition and the availability of invertebrate food resources to passerine birds remain poorly understood. In this study, we investigated the foraging site selection of meadow pipits (Anthus pratensis L.) breeding in high intensity sheep-grazed plots or low intensity mixed (i.e. sheep and cattle)-grazed plots. We sampled above-ground invertebrates, measured vegetation height and density and conducted a vegetation survey in areas where meadow pipits were observed to forage and areas that were randomly selected. Birds foraged in areas with a lower vegetation height and density and in areas containing a lower proportion of the dominant, tussock-forming grass species Molinia caerulea. They did not forage in areas with a total higher invertebrate biomass but at areas with preferred vegetation characteristics invertebrate biomass tended to be higher in foraging sites than random sites. The foraging distance of meadow pipits was higher in the intensively grazed plots. Our findings support the hypothesis that resource-independent factors such as food accessibility and forager mobility may determine patch selection and are of more importance as selection criteria than food abundance per se. Food accessibility seems to become an even more important selection criterion under high grazing intensity, where prey abundance and size decrease. In our upland grazing system, a low intensity, mixed grazing regime seems to provide a more suitable combination of sward height, plant diversity, structural heterogeneity and food supply for meadow pipit foraging activity compared to a more intensive grazing regime dominated by sheep.     

The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen,Denmark

The aggregated effect of cattle and sheep grazing on Puccinellion maritimae and other salt-marsh vegetation has been studied together with changes in species composition, the percentage cover of each species, total cover and the percentage of bare ground, six years after grazing had been prevented by construction of experimental exclosures. The results of these experiments are discussed in relation to the natural development of the vegetation that occurred in a permanent plot in the ungrazed part of the salt marsh. Six years without grazing caused a marked increase in total cover and a dramatic reduction in the amount of bare ground. The species composition of the Puccinellia maritima community did not change during these six years, but all species increased in cover. Whereas Artemisia maritima migrated into the Festuca rubra community and only two species Festuca and Halimione portulacoides, increased in cover, all other species showed reduced cover and Salicornia europaea disappeared from the plot after six years without grazing. During the same period of time, three species, Salicornia europaea, Suaeda maritima, and Glaux maritima, disappeared from the plot in the ungrazed marsh as a result of natural development. During thirty-five years the vegetation originally dominated by Puccinellia maritima and Salicornia europaea has changed into a community dominated by Halimione portulacoides, whereas the grazed salt marsh is still dominated by Puccinellia maritima and Salicornia europaea. These results are discussed in relation to the literature on the effect of cattle and sheep grazing on salt-marsh vegetation.     

Long-term changes of salt marsh communities by cattle grazing

Over a period of 9 years a grazing experiment was carried out in the mainland salt marsh of the Leybucht (Niedersachsen) with three stocking rates, namely, 0.5 ha^-1, 1 ha^-1, and 2 cattle ha^-1. These were also compared with an abandoned area. The results are based on sampling of the invertebrates in 1980, 1981, 1982, and 1988, and of the vegetation in 1980 and 1988. The rate of sedimentation is highest in the Puccinellia maritima-zone and decreases with the increase of stocking rates. The Elymus pycnanthus vegetation type becomes dominant in the higher salt marsh in the abandoned site. The canopy height decreases with increasing stocking rate, whereas a gradient in the structure of the vegetation develops with the lowest stocking rate. The population densities, the species-richness and the community diversity of invertebrates increases after the cessation of grazing. The high rate of sedimentation in the abandoned site promotes the immigration of species from higher salt marsh levels and adjacent grasslands, and eventually halotopophilous species and communities may disappear. On the other hand grazing reduces numerous species living both in or on upper parts of the vegetation or being sensitive to trampling by cattle. The community structure shows that the salt marsh ecosystem changed from a food web dominated by plant feeding animals to a food web dominated by animals foraging on detritus. The salt marsh management has to be differentiated into both ungrazed and lightly grazed areas (each 50%) or an overall grazing in large areas with less than 0.5 cattle ha^-1.     

火烧迹地柽柳灌丛资源岛特征及植被的自然恢复

干旱半干旱地区灌丛资源岛特征及形成机制多有报道,但资源岛土壤对群落稳定性与火烧迹地植被的自然恢复作用尚不明确。以酒泉盐碱地柽柳灌丛地火烧3年后,自然恢复的柽柳(Tamarix ramosissima)及其冠下草本群落为研究对象,构建柽柳枯立株体量指数(SSI,Shrub Size Index)和恢复力综合指数,探讨了资源岛特征与植被恢复、冠下草本群落多样性的关系,量化不同大小柽柳灌丛的恢复力稳定性。结果表明:(1)在不同SSI的柽柳枯立株下土壤有机质和含水率明均显高于灌丛间地,形成了明显的资源岛特征。土壤有机质最大值出现在0—10 cm土层,中灌丛的肥力积聚效果最明显。(2)土壤主要以中性盐为主,在0—40 cm土层,灌丛区域土壤可溶性盐低于冠外,呈明显的盐谷特征,中灌丛的盐谷分布最为明显。(3)随着枯立株SSI的增大,柽柳新生枝条的数量及其高度均有所增大,冠下植物的高度、盖度、密度和地上植物量也明显高于灌丛间地,且灌丛越大恢复效果越明显。(4)灌下植物Simpson指数、Shannon⁃Wiener指数、Margalef指数和Pielou指数随着枯立株SSI的增大均先降后升,多样性指数低,群落结构简单。(5)恢复力综合指数随着枯立株SSI的增大呈先升后降的趋势,当SSI=52.17时灌丛群落的稳定性最强。柽柳较小时主要是冠下草本植物的恢复维持群落稳定性,随着灌丛的增大逐渐以柽柳灌木的恢复来维持群落稳定性。柽柳灌丛形成的高养低盐的土壤环境对植物群落稳定性的维持和植被的恢复有促进作用,对荒漠生态系统火烧迹地植被恢复和生态保护具有重要意义。     

Herbivory of clonal populations: cattle browsing affects reproduction and population structure of Yucca elata

The hypothesis that cattle browsing on inflorescences of the soaptree Yucca elata reduces reproductive success was investigated by comparing recruitment and population structure in six populations protected from grazing, six grazed during the flowering season and five grazed outside the flowering season. Cattle consumed 98% of inflorescences, which were found to be highly nutritious. Reduced recruitment in flower-grazed populations could not be attributed to reduced flower survival, as recruitment in non-flower grazed populations was also reduced. Changes in population structure were due to cattle browsing small caudices, including both genets and ramets. An alternate hypothesis of limited germination in soils compacted by cattle was not supported. Cattle browsing of inflorescences reduced reproductive effort, which may be due to the inability of the plants to resorb nutrients after flowering. Browsing also increased branching, probably through lack of apical dominance, whereas physical trampling increased procumbency. Cattle browsing implies a lack of genetic recruitment, possible local extinction of the yucca moth Tegeticula yuccasella, the exclusive pollinator of Y. elata, and local reduction in insect and bird biodiversity.     

放牧对鄂尔多斯高原油蒿草场生物量及植被-土壤碳密度的影响

以围封保护和自由放牧油蒿草场为研究对象,通过野外调查与室内分析,研究了围封和放牧条件下沙地草场生物量和植被-土壤碳密度。结果表明:(1)自由放牧使油蒿群落中植物种类增加,但降低了植物群落盖度。自由放牧不仅导致油蒿草场地上、地下总生物量降低,也使得油蒿地上、地下生物量占群落地上、地下总生物量的比例减小。生长季自由放牧样地凋落物生物量显著大于围封保护样地(P0.05);(2)围封保护样地植被碳密度大于自由放牧样地,土壤碳密度却小于自由放牧样地,但两个样地间差异不显著(P0.05);(3)油蒿草场90%以上的碳储存于土壤中,围封保护样地和自由放牧样地油蒿草场土壤碳密度占植被-土壤系统碳密度的91%、93%;(4)围封保护油蒿草场碳密度为2.29 kg/m2,自由放牧油蒿草场碳密度为2.68 kg/m2,两个样地间差异不显著,自由放牧对油蒿草场碳密度影响不大。     

The impact of grazing intensity on soil characteristics of Stipa grandis and Stipa bungeana steppe in northern China (autonomous region of Ningxia)

The effects of grazing intensity on selected soil characteristics in the feather-grass steppes of the autonomous region of Ningxia (northern China) were investigated by a comparison of non-grazed areas (grazing intensity 0), slightly grazed areas (grazing intensity I), moderately grazed areas (II), intensively grazed areas (III) and over-grazed areas (IV). Even in areas used only minimally for grazing activities (I), a serious increase (doubling) in soil hardness was apparent in the upper soil layer. A continual decrease in organic matter in the surface soil can be correlated directly to soil compaction. The content of organic matter in soil of degree IV amounts to only a third of the organic matter found in non-grazed areas. This decrease can be attributed partly to the poor living conditions for soil organisms in compacted soils, but also to a significant reduction in litter. This is because intensive grazing causes reduced vegetation cover leading to litter being blown away by wind or washed away by heavy rainfall. Thus in level III hardly any plant litter remained to be incorporated into the soil as humus. Likewise root density also suffered its largest decrease in areas with a grazing intensity level III. With regard to the content of nitrogen and phosphorous (total and available) hardly any difference between soils of grazing intensity 0 and I was observed, whereas a noticeable decrease was apparent between levels I and II. Available Potassium was similar for all grazing levels. The pH-value of the soil solution is not significantly affected by grazing. We did not observe differences in the soils of the two main types of steppe vegetation (Stipa grandis and Stipa bungeana steppe) in response to grazing. Only the amount of litter in the S. grandis-steppe in non-grazed or slightly grazed areas is noticeably higher than in the S. bungeana steppe.     

Management of calcareous grasslands for Nickerl’s fritillary (<Emphasis Type="Italic">Melitaea aurelia</Emphasis>) has to consider habitat requirements of the immature stages,isolation, and patch area

We analysed the habitat preferences of adult stages and oviposition electivity of Melitaea aurelia in calcareous grasslands in the Diemel Valley (central Germany) to assess the key factors for successful management. Egg-laying and adult habitats of M. aurelia were more or less congruent. Oviposition electivity at the host plant (Plantago media) was best explained by a combination of host plant quantity and vegetation structure. Habitat quality, isolation and patch area explained 86% of the current patch occupancy of M. aurelia. With M. aurelia preferentially inhabiting transitional vegetation types, management requires a balance between abandonment and disturbance. Disturbances provide open soil that facilitates germination of the host plant Plantago media. On the other hand, immature and adult stages of M. aurelia perform best on calcareous grasslands with a high amount of host plants and low disturbance intensity. Traditional rough grazing regimes seem to be the most favourable tool for developing the necessary spatial and temporal heterogeneity in patches. The best results may be achieved by rotational grazing where only a subset of inhabited patches is grazed intensively each year. Our analysis of patch occupancy indicates that it would be desirable to restore patches in close proximity to occupied sites.     

Neighbourhood effects on the risk of an unpalatable plant being grazed

Most studies on the importance of the neighbourhood on a plant's risk ofherbivory have focused on palatable plants and how they are protected byunpalatable neighbours. This study examined the grazing intensity of arelatively unpalatable shrub, Buxus sempervirens, indifferent neighbours. Exactly 2683 plants of Buxussempervirens (including 172 controls) were sampled in 12 enclosedpastures belonging to 4 sheep farms. The enclosures were grazed at 3 differentseasons (spring, summer and autumn). Plants were divided in 4 age/hight classes(first year, < 4 cm, 4–10 cm, 10–40cm) and into 8 neighbourhoods. The first of these wascharacterisedby the absence of any plants within a radius of 5 cm around theBuxus individual and the 7 others by the identity of thedominant species in contact with the Buxus plant. Theintensity of grazing on the neighbouring plants were also recorded. At the endof one year's monitoring, 26.2% of Buxus sempervirensplants had been grazed. The proportion of plants grazed was significantlyhigherin spring than in the other two seasons. It decreased with increasing plantage.It was higher in neighbourhoods that were intensively grazed than in those withlight grazing. The proportion grazed in the absence of a neighbour plant wasintermediate between the previous two. The probability of a plant of aninvadingspecies being grazed is influenced by factors other than its life-historytraits. Some neighbourhoods consisting of unpalatable plants facilitate theestablishment of Buxus sempervirens by protecting theyoungplants from grazing, whereas other highly palatable neighbourhoods are readilygrazed by sheep, thus indirectly increasing the proportion of Buxussempervirens that are grazed. The young and short (< 4cm in height) Buxus plants, which are lessrecognisable by sheep, are most sensitive to the impact of grazing.