Vegetation changes following sheep grazing in abandoned mountain meadows

Abstract. Sheep grazing was investigated as an alternative to traditional management of meadows in the Krkono?e Mts. Until the second World War these meadows were mown in mid‐summer and grazed by cattle for the rest of the season. Subsequent abandonment of the meadows has resulted in decreasing species richness. Degradation phases of the former communities have been replacing the original species‐rich vegetation. Significant changes were apparent six years after the introduction of sheep grazing. In grazed plots the proportion of dominant herbs (Polygonum bistorta and Hypericum maculatum) decreased and grasses (Deschampsia cespitosa, Festuca rubra, Agrostis capillaris, Anthoxanthum alpinum) increased. The increase in grasses was positively correlated with an increase in several herbs. The proportion of some herbs increased despite being selectively grazed (Adenostyles alliariae, Melandrium rubrum, Veratrum lobelianum). Any losses caused by grazing of mature plants were probably compensated by successful seedling establishment. Cessation of grazing resulted in significant changes in vegetation within three years. The cover of nitrophilous tall herbs and grasses (e.g. Rumex alpestris, Holcus mollis, Deschampsia cespitosa, Geranium sylvaticum) increased in the abandoned plots. In the plots grazed for nine years cover of species‐rich mountain meadow species increased (e.g. fine‐leaved grasses, Campanula bohemica, Potentilla aurea, Viola lutea, Silene vulgaris). The main conservation risk is the expansion of a competitive species with low palatability, Deschampsia cespitosa. This species can be suppressed by a combination of grazing and mowing. In order for grazing to be effective, the number of sheep should be proportional to meadow production. This may be difficult to maintain as production is variable and is impossible to predict at the beginning of a growing season. A large part of the biomass may thus remain intact in some years. Negative effects of grazing may be, at least partly, eliminated by a combination of cutting and grazing.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

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.     

Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in Lapland

Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground‐dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H’) of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H’/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites.     

Woodland regeneration on grazed former arable land: A question of tolerance,defence or protection?

Ecological restoration of native woodlands and wooded pastures on former agricultural land is an important topic in modern conservation practice. The introduction of large herbivores is increasingly used to achieve these aims. We investigated how grazing, resistance traits of plants (concerning herbivory) and associational resistance interact and affect the establishment pattern of woody species on abandoned arable land (N-Belgium, W-Europe). In these early successional tree assemblages, we tested whether grazing increased or decreased spatial heterogeneity, which is supposed to be a crucial factor for biodiversity.With repeated measurements, 2-3 and 5-7 years after the cessation of agricultural use, we sampled 87 grazed and 56 ungrazed plots (314 m²) in 14 sampling areas (former arable land) on nutrient rich, (sandy) loam soils. We recorded established tree frequencies, related to grazing, time, resistance traits and unpalatable/spiny vegetation cover in the herb and low shrub layer. We investigated horizontal and vertical heterogeneity using variances in establishment frequencies and variances in frequencies of trees that were able to grow beyond the browse line, respectively.We found massive colonisation of grazing tolerant and resistant woody species in early successional stages. Grazing decreased frequencies and height of the most abundant tolerant species (mainly Salix caprea L.). After 5-7 years, frequencies of defensive and tolerant species were equal, but the former (mainly Betula pendula Roth) were able to grow beyond the browse line. When the cover of unpalatable/spiny vegetation was high enough (>60% of plot size), it also provided suitable nurse sites for tolerant species to grow out. In early assemblages, grazing increased horizontal and vertical heterogeneity, resulting in intermediate successional stages. In the long-term, the mechanism of associational resistance will also allow non-resistant and tolerant species to grow beyond the browse line and promote forest succession and the order of species establishment and replacement.     

Spontaneous steppe restoration on abandoned cropland in Kazakhstan: grazing affects successional pathways

After the collapse of the Soviet Union in 1991, 12 million ha of cropland were abandoned in the steppe zone of Kazakhstan. At the same time livestock numbers crashed, leaving large areas of steppe without any grazing. We aimed to investigate, to which degree spontaneous succession on former cropland leads to the restoration of native steppe vegetation, and how this process is influenced by changing grazing patterns. We recorded biomass and vegetation characteristics as well as local soil and landscape variables in 151 quadrats of 100 m², covering 89 plots on former cropland abandoned in the early 1990s and 62 reference plots of near-natural steppe grassland that was never ploughed. About half of the plots of each category were located in a remote region where grazing has been absent for ca. 20 years, whereas the other half was located in a region with moderate livestock grazing. While there were no differences in the diversity, structure and plant life form composition of currently grazed and un-grazed near-natural steppe grasslands, corresponding successional plots on abandoned arable land exhibited significant differences. Grazed plots on former fields showed higher species richness and a higher cover of dwarf shrubs (mostly Artemisia spec.), ruderals and perennial herbs. At the same time, immigration of typical steppe species was much more successful. Contrary, in the absence of any grazing we found species-poor swards dominated by Stipa lessingiana and Leymus ramosus exhibiting an increasing frequency of wildfires due to litter accumulation. After 15–20 years, secondary steppe grasslands still differed substantially from their near-natural references. Our results suggest that grazing is mandatory to fully restore the original near-natural steppe vegetation and the underlying processes of pyric herbivory.     

Vegetation change in a man‐made salt marsh affected by a reduction in both grazing and drainage

Abstract. In order to restore natural salt marsh in a 460‐ha nature reserve established in man‐made salt marsh in the Dollard estuary, The Netherlands, the artificial drainage system was neglected and cattle grazing reduced. Vegetation changes were traced through two vegetation surveys and monitoring of permanent plots over 15 yr after the management had been changed. Exclosure experiments were started to distinguish grazing effects from effects of increased soil waterlogging caused by the neglect of the drainage system. Both vegetation surveys and permanent plots demonstrated a dichotomy in vegetation succession. The incidence of secondary pioneer vegetation dominated by Salicornia spp. and Suaeda maritima increased from 0 to 20%, whereas the late‐successional (Phragmites australis) vegetation from 10 to 15%. Grazing intensity decreased towards the sea. The grazed area contracted landward, which allowed vegetation dominated by tall species to increase seaward. Grazing and increased waterlogging interacted in several ways. The impact of trampling increased, and in the intensively grazed parts soil salinity increased. This can probably be explained by low vegetation cover in spring. Framework Ordination, an indirect‐gradient‐analysis technique, was used to infer the importance of environmental factors in influencing changes in species composition. Many changes were positively or negatively correlated with soil aeration and soil salinity, whereas elevation was of minor importance. Grazing accounted for only a few changes in species frequency. Changes in permanent plots were greater during the first than during the second half of the study period. In exclosures that were installed halfway through the study period, there was a relatively rapid recovery of previously dominant species that had decreased during the first half of the study period. Species richness per unit area in the reserve increased. At the seaward side of the marsh, the altered management allowed succession to proceed leading to establishment of stands of Phragmites australis, whereas on the landward side, the combination of moderate grazing with neglect of the drainage system appeared an effective measure in maintaining habitats for a wider range of halophytic species.     

Vegetation changes in restored semi-natural meadows in the Turku Archipelago of SW Finland

In the Turku Archipelago of SW Finland the traditional animal husbandry dramatically decreased in 1950s after which the unused semi-natural pastures and meadows began to develop into less species rich shrub and tree communities. Restoration of some semi-natural meadows and pastures started in the late 1970s. Removing trees and shrubs, grazing, mowing, and pollarding deciduous trees were used as restoration of practises. Vegetation changes were followed from forty-one permanent sample plots established on restored areas. In this paper the data before restoration and 7–8 years after the first monitoring was analysed with parametric tests. The sample plots were divided into three restoration groups where the main restoration practises were: group 1. grazing, group 2. thinning (clearing plots from shrubs and removing some trees), group 3. thinning, mowing, and grazing (old wooded meadows). The results showed that: (1) The vegetation changed during analysed time. The number of species increased in all restored areas even though the changes were more pronounced in grazed areas and wooded meadows than in thinned areas. During restoration many common herb and grass species immigrated into the sample plots, but very few new indicator species of meadows were recorded. Most of the new species were found in few numbers in a sample plot which led to the significant increase in the number of sparse species (percentage cover < 1) in all restoration groups. The grasses benefited more from the restoration than herbs increasing their percentage cover significantly in grazed areas and in wooded meadows. In thinned areas the total percentage cover of the ten most dominant herb and grass species increased significantly. (2) The different restoration groups changed vegetation quite similarly. In grazed areas and in wooded meadows significant changes were slightly more numerous than in thinned areas. (3) The differences between the islands in vegetation changes were not pronounced. The added variance components among islands increased during restoration which probably indicated that the restoration practises as well as the species pool of the islands influenced the success of restoration.     

Silvopastoralism in the Alps: Native plant species selection under different grazing pressure

To evaluate the suitability of wood pastures as a managing tool in subalpine regions it is essential to know more about the influence of grazing on the ground vegetation. This study assessed native plant species selection by cattle at different stocking rates, feeding habits and site preferences of cattle. Based on the results, conclusions concerning the value of silvopastoral systems in the Alps were drawn. A field study on six different wood pasture areas, grazed by cattle at different stocking rates, was accompanied by an experiment on three adjoining areas of 0.51 ha each, stocked with either three, six, or nine heifers. Plant species were recorded in plots of 20 cm × 20 cm before and after grazing, and the intensity of grazing on each species was assessed. At low stocking rates, grasses and tall species were most intensely grazed, while at higher stocking rates the intake of forbs and small species increased. Since no relationship was found between nutritional value and species preference, other factors such as accessibility of a plant seem to be important for the feeding preferences of cattle. The preference for grasses at low and medium stocking rates suggests that an increased growth of forbs might lead to an increase in plant species diversity.     

Restorative mowing on an abandoned semi‐natural meadow: short‐term and predicted long‐term effects

Abstract. When management, in the form of cattle grazing and mowing, ceases the abundance of competitively superior plant species tends to increase in abandoned semi‐natural meadows. Litter accumulation elevates the soil nutrient levels and hinders seedling recruitment. We surveyed changes in plant cover and species composition of a formerly grazed meadow in permanent plots for six years. Some plots were unmown, while others were mown and raked annually in August. The cover of grasses decreased and herb cover remained unchanged regardless of the treatment. Mowing and raking significantly reduced litter accumulation and increased the number of ground layer species. The expected long‐term effects of abandonment and restorative mowing were studied by calculating the transition probabilities for unmown and mown plots and simulating the course of succession as projected by the transition matrices. During a simulation period of 30 yr, abandonment led to (1) a decrease in the cover of small herbs, (2) a slight increase in the cover of tall herbs and (3) a slight decrease in the cover of grasses. In contrast, the cover of small herbs on the mown plots remained unchanged or slightly increased during the course of simulation. These results suggest that mowing late in the season is primarily a management tool for the maintenance of the existing species diversity and composition. However, it may not be an effective restorative tool to induce overall changes in the resident vegetation of abandoned grass‐dominated meadows. Grazing or mowing early in the season may be more effective in this respect. Consequently, mowing early or, alternatively, late in the season may provide management strategies for the maintenance and restoration of species diversity, respectively.     

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

Riparian savanna habitats grazed by hippopotamus or livestock experience seasonal ecological stresses through the depletion of herbaceous vegetation, and are often points of contacts and conflicts between herbivores, humans and their livestock. We investigated how hippopotamus and livestock grazing influence vegetation structure and cover and facilitate other wild herbivores in the Mara region of Kenya. We used 5 km-long transects, each with 13 plots measuring 10 × 10 m², and which radiate from rivers in the Masai Mara National Reserve and adjoining community pastoral ranches. For each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, herbivore abundance and species richness. Our results showed that grass height was shortest closest to rivers in both landscapes, increased with increasing distance from rivers in the reserve, but was uniformly short in the pastoral ranches. Shifting mosaics of short grass lawns interspersed with patches of medium to tall grasses occurred within 2.5 km of the rivers in the reserve in areas grazed habitually by hippos. Hence, hippo grazing enhanced the structural heterogeneity of vegetation but livestock grazing had a homogenizing effect in the pastoral ranches. The distribution of biomass and the species richness of other ungulates with distance from rivers followed a quadratic pattern in the reserve, suggesting that hippopotamus grazing attracted more herbivores to the vegetation patches at intermediate distances from rivers in the reserve. However, the distribution of biomass and the species richness of other ungulates followed a linear pattern in the pastoral ranches, implying that herbivores avoided areas grazed heavily by livestock in the pastoral ranches, especially near rivers.     

Community dynamics of desert grasslands: influences of climate,landforms, and soils

Abstract. Permanently marked vegetation transects in Big Bend National Park, Texas, USA were monitored to follow temporal dynamics of desert grassland communities on a variety of landforms and soil types over a 26-yr period after the removal of domestic livestock. Historic records indicate that the park area was severely overgrazed prior to its establishment, and our results show that the species present increased in both cover and density after the removal of livestock. However, the timing of recovery corresponded to multiyear periods of above-average precipitation. Little change was observed in between 1955 and 1960, a period dominated by several consecutive years of drought. The cover of two large shrubs common to the Chihuahuan Desert, Larrea tridentata and Flourensia cernua, increased from 1960 to 1967, a period dominated by summer drought and frequent wet winters. The cover and density of forbs, perennial grasses, and most shrubs increased on nearly all landforms between 1967 and 1981, when summers were wetter than average. In contrast, the cover of Larrea tridentata decreased during this period. Comparisons among the plant communities on each landform showed that they diverged through time after domestic livestock were removed. Presumably, differences in topographic position and soil texture influence water availability which was reflected in the species composition on each soil series. Unfortunately, we cannot isolate the effects of recovery from grazing from the effects of climate because the study design did not include control plots located within grazed pastures. Certainly, the directional trajectory of change and the regrowth of grasses into inter-shrub spaces, must, at least in part, be the result of recovery from grazing. However, our data also indicate that the desert grassland communities are sensitive to multi-year periods of above- or below-average precipitation. Clearly, the dynamics between shrubs and grasses cannot be explained by a simple successional paradigm that views increased shrub dominance as retrogression from a climax grassland. Many alternate hypotheses have been forwarded to explain the dynamics that control the vegetation composition in the desert and desert grassland region of North America. Experimental tests of these hypotheses are needed to indentify the interactions between biotic and abiotic factors that control dominance by shrubs or grasses.     

Effects of grazing on patch structure in a semi‐arid two‐phase vegetation mosaic

Abstract. Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two‐phase vegetation mosaic? Location: Patagonian steppe, Argentina. Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions. Results: The vegetation was spatially organized in a two‐phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions. Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.     

Effects of grazing and cultivation on forest plant communities in Mount Elgon National Park, Uganda

Plant communities in the montane forest of Mount Elgon National Park were studied in order to assess the impact of grazing and cultivation on species composition. Present and former land uses, tree, shrub and herb species, soil properties and the percentage cover and height of trees, shrubs and herbs were determined in 40 plots. An indirect ordination of these plots showed that species composition was primarily determined by successional stage and agricultural disturbance. In forest plots (ordinated separately) where the widest range of former and current grazing intensities had occurred, evidence of grazing history, soil phosphorus and vegetation height correlated negatively with the strongest ordination axis. Least grazed forest plots had fewer tree seedlings and saplings than more intensively grazed plots. This may be due to the increase in Mimulopsis alpina (Acanthaceae) in less grazed forest where tree regeneration might otherwise be more advanced. Tree seedlings and saplings were uncommon in the forest, rarely exceeding 30cm in height and there was no tree understorey. Although grazing is important for preserving species diversity in Mount Elgon National Park through the maintenance of species-rich grasslands, long-term effects on montane forest communities must be considered in future park management.     

Influence of livestock grazing on vegetation in a saline area in Northeast Thailand

The influence of grazing by water buffalo (Bubalas bufalis) and cattle (Bos taurus) was estimated for vegetation inside and outside cages in a saline area at Khon Kaen, Northeast Thailand. The home range of water buffalo and cattle shifted in response to the period of rice cultivation: during the rice-growing season these animals grazed on roadsides and abandoned places such as the study area; after rice harvest they grazed mainly rice stubble on the paddy. The vegetation in the study area was divided into three types: 1) dominated by the annual grassesChloris barbata andIschaemum rugosum; vegetational cover and plant height in the cage increase due to the increase of these grasses; 2) thorny shrub patch ofMaytenus mekongensis; other species in this patch almost died a year after experimental elimination of this shrub; this salt-tolerant shrub not only protected the co-existing species from grazing, but also suppressed salt accumulation; 3) almost pure stand ofPanicum repens; livestock preferred this perennial grass over others. Electrical conductivity (EC) of surface soil did not increase under the vegetation protected from grazing. Litter and other organic matter in the soil suppressed the upward movement of brine. Grazing led to an increase of bare ground where NaCl accumulated, and modified the heterogeneity of vegetation, which was reflected in the degree of salt accumulation.     

Recovery of plant species composition and ecosystem function after cessation of grazing in a Mediterranean grassland

Short- and long-term changes in species composition, plant biomass production, and litter decomposition after cessation of grazing were examined in a Mediterranean grassland with high dominance of annual species and strong seasonality in biomass production. Short-term changes were assessed during three consecutive years in plots previously exposed to different grazing pressures and compared to plots in long-term (30–40 years) exclosures. Short-term cessation of grazing led in the short-term to an increase in relative biomass of annual crucifers and tall annual and perennial grasses, while biomass of annual legumes, annual thistles and short annual grasses decreased. Consequently, similarity increased between vegetation recently excluded from grazing and vegetation in long-term protected plots. Our research showed that in systems with high dominance of grasses and annual species, the rapid changes in plant species composition that occur after grazing cessation were associated with a fast recovery of the potential for biomass production to levels found in long-term protected plots, while litter decomposition rate did not change even after long-term cessation of grazing. Moreover, previous history of grazing did not affect plant litter decomposition, despite higher litter quality in grazed treatments. This study provides new insights about the processes involved in the diverse responses of ecosystem functions resulting from shifts in species composition associated with grazing cessation and land use change in Mediterranean grasslands.     

Relationships between the effects of insect herbivory and sheep grazing on seasonal changes in an early successional plant community

Summary The effects of spring grazing by sheep and of natural levels of insect herbivory were studied in 1985 on a limestone field abandoned from arable land for four years. A split-plot design was adopted in which paddocks, arranged in Latin squares, were either left ungrazed or heavily grazed by sheep for ten days in April. Within each paddock plots were either sprayed regularly with Malathion-60 or untreated.Natural levels of insect herbivory, compared to the reduced levels in insecticide-treated plots, had effects of similar magnitude to those from the short burst of spring grazing. Many attributes of the grazed/insecticide-treated sward were either increased or decreased by a factor of two within a season. Both types of herbivore caused changes in the direction of plant succession as well as in its rate. Effects on early successional species were large and similar when caused by either type of herbivore. Effects on later successional species were often smaller, but also showed differences in the action of the two herbivore types, as did effects on sward height, species richness and total cover. The effects of sheep and insect herbivory were not always additive or in the same direction.The results suggest that manipulations of both mammal and insect herbivores may be powerful tools for directing changes in plant community composition.     

The role of landuse and natural determinants for grassland vegetation composition in the Swiss Alps

The Alps provide a high habitat diversity for plant species, structured by broad- and fine-scale abiotic site conditions. In man-made grasslands, vegetation composition is additionally affected by the type of landuse. We recorded vegetation composition in 216 parcels of grassland in 12 municipalities representing an area of 170×70 km in the south-eastern part of the Swiss Alps. Each parcel was characterized by a combination of altitudinal level (valley, intermediate, alp), traditional landuse (mown, grazed), current management (mown, grazed, abandoned), and fertilization (unfertilized, fertilized). For each parcel we also assessed the abiotic factors aspect, slope, pH value, and geographic coordinates, and for each municipality annual precipitation and its cultural tradition. We analysed vegetation composition using (i) variation partitioning in RDA, (ii) cover of graminoids, non-legume forbs, and legumes, and (iii) dominance and frequency of species. Species composition was determined by, in decreasing order of variation explained, landuse, broad-scale abiotic factors, fine-scale abiotic factors, and cultural tradition. Current socio-economically motivated landuse changes, such as grazing of unfertilized former meadows or their abandonment, strongly affect vegetation composition. In our study, the frequency of characteristic meadow species was significantly smaller in grazed and even smaller in abandoned parcels than in still mown ones, suggesting less severe consequences of grazing for vegetation composition than of abandonment. Therefore, low-intensity grazing and mowing every few years should be considered valuable conservation alternatives to abandonment. Furthermore, because each landuse type was characterized by different species, a high variety of landuse types should be promoted to preserve plant species diversity in Alpine grasslands.     

Livestock exclusion increases the spatial heterogeneity of vegetation in Colorado shortgrass steppe

Abstract. Spatial heterogeneity, an important characteristic in semi‐arid grassland vegetation, may be altered through grazing by large herbivores. We used Moran's I, a measure of autocorrelation, to test the effect of livestock grazing on the fine scale spatial heterogeneity of dominant plant species in the shortgrass steppe of northeastern Colorado. Autocorrelation in ungrazed plots was significantly higher than in grazed plots for the cover of the dominant species Bouteloua gracilis, litter cover and density of other bunchgrasses. No species had higher autocorrelation in grazed compared to ungrazed sites. B. gracilis cover was significantly auto‐correlated in seven of eight 60‐yr ungrazed exclosures, four of six 8‐yr exclosures, and only three of eight grazed sites. Autocorrelograms showed that B. gracilis cover in ungrazed sites was frequently and positively spatially correlated at lag distances less than 5 m. B. gracilis cover was rarely autocorrelated at any sampled lag distance in grazed sites. The greater spatial heterogeneity in ungrazed sites appeared linked to patches characterized by uniformly low cover of B. gracilis and high cover of C₃ grasses. This interpretation was supported by simple simulations that modified data from grazed sites by reducing the cover of B. gracilis in patches of ca. 8 m diameter and produced patterns quite similar to those observed in ungrazed sites. In the one exclosure where we intensively sampled soil texture, autocorrelation coefficients for sand content and B. gracilis cover were similar at lag distances up to 12 m. We suggest that the negative effect of sand content on B. gracilis generates spatial heterogeneity, but only in the absence of grazing. An additional source of heterogeneity in ungrazed sites may be the negative interaction between livestock exclusion and B. gracilis recovery following patchy disturbance.     

Directional and non‐directional vegetation changes in a temperate salt marsh in relation to biotic and abiotic factors

Abstract. The effects of reduction and cessation of sheep grazing on salt‐marsh vegetation were studied on a formerly intensively grazed salt marsh in northern Germany. Plant species cover was recorded in 45 permanent plots from 1992 to 2000. In 1995, physical and chemical soil parameters were analysed. Results of Redundancy Analysis (RDA) indicated that salinity and the depth of anoxic conditions below the surface were the most important soil factors related to the spatial vegetation pattern. Furthermore, plant species distribution was influenced by present and past grazing intensity, by soil grain size and nitrogen content. Vegetation changes over 9 yr were analysed by non‐linear regression. The cover of Aster tripolium, Atriplex portulacoides, and, to a lesser extent, Artemisia maritima and Elymus athericus increased due to reduced grazing pressure, whereas the cover of Salicornia europaea decreased. After a strong increase in the first years Aster decreased 2 to 6 yr after abandonment. In the mid salt‐marsh zone Puccinellia maritima was replaced by Festuca rubra. The cover of Puccinellia, Festuca, Suaeda maritima, Glaux maritima and Salicornia fluctuated strongly, probably due to differences in weather conditions and inundation frequency. Species richness per 4 m² generally increased while vegetation evenness decreased during the study period. Only in the high salt marsh abandoned for 9 yr did the number of species decrease slightly. Thus far, cessation of grazing did not lead to large‐scale dominance of single plant species.