Grazing decisions of Soay sheep,Ovis aries,on St Kilda: a consequence of parasite distribution?

Relationships between the height of grass swards and herbage intake have been established for a number of large herbivores and sward height plays a major role in determining the selection of herbivore diets. However, tall grass swards also represent a more stable damp microclimate for gastrointestinal parasite larvae and tall swards contain generally greater numbers of parasites than short swards. Herbivores may then trade-off the need to maximise nutrient intake through the selection of tall swards with the need to avoid parasite ingestion. Stratified sward sampling techniques were used to determine the distribution of nutrients and parasites in a heterogeneous sward structure on the island of Hirta, St Kilda, which is grazed by a population of feral Soay sheep. The disparity between the short gap vegetation and the tall tussock vegetation was greatest in spring, when gap vegetation was some three-fold shorter than tussock vegetation; this led to tussocks offering greater nutrient and energy intake rate when compared to gap vegetation in spring. Parasites were concentrated in tussocks in spring, thus creating trade-offs. Such trade-offs were not present in summer when parasites were more evenly distributed across the gap/tussock sward structure and the nutritional advantages associated with grazing tussocks were diminished. The diet selection of the resident population of sheep was determined by recording the number of bites taken from gap and tussock vegetation by randomly selected focal animals over repeated 5-min grazing periods. Overall, all animals avoided grazing tussocks, which were most strongly avoided in the spring, and older animals avoided grazing tussocks to a greater extent. Overall, females with lambs and males avoided tussocks to a similar degree and both avoided them less than barren females. Faecal egg counts (FEC) of female sheep were negatively correlated with tussock selectivity and vice versa for male sheep. The interaction between the grazing behaviour of each sex and FEC is discussed in relation to the immunocompetence and nutrient requirements of the different sexes. The maximum disparity between the costs and benefits of the trade-off studied occurred in late winter/early spring which also represents the time of greatest nutrient demand in the Soay sheep, since many are close to starvation and/or are in the advanced stages of pregnancy. Grazing decisions of individuals at this time, determining relative nutrient and parasite intake, may then be related to subsequent fitness and survival.     

Patch dynamics in grazed subtropical native pastures in south‐east Queensland

Abstract Patch formation is common in grazed grasslands but the mechanisms involved in the formation and maintenance of patches are not clear. To increase our knowledge on this subject we examined possible reasons for patch formation and the influence of management on changes between patch states in three experiments in native pasture communities in the Crows Nest district, south‐east Queensland. In these communities, small‐scale patches (tall grassland (dominated by large and medium tussock grasses), short swards (dominated by short tussock grasses and sedges), and lawns (dominated by stoloniferous and/or rhizomatous grasses)) are readily apparent. We hypothesized that the formation of short sward and lawn patches in areas of tall grassland was due to combinations of grazing and soil fertility effects. This was tested in Experiment 1 by applying a factorial combination of defoliation, nutrient application and transplants of short tussock and stoloniferous species to a uniform area of tall grassland. Total species density declined during the experiment, was lower with high nutrient applications, but was not affected by defoliation. There were significant changes in abundance of species that provided support for our hypotheses. With light defoliation and low nutrients, the tall grassland remained dominated by large tussock grasses and contained considerable amounts of forbs. With heavy defoliation, the pastures were dominated by medium tussock grasses and there were significant decreases in forbs and increases in sedges (mainly with low nutrients) and stoloniferous grasses (mainly with high nutrients). Total germinable seed densities and those of most species groups were significantly lower in the heavy defoliation than the light defoliation plots. Total soil seed numbers were not affected by nutrient application but there were fewer seeds of the erect forbs and more sedge seeds in plots with high nutrients. The use of resting from grazing and fire to manage transitions between patches was tested. In Experiment 2 , changes in species density and abundance were measured for 5 years in the three patch types with and without grazing. Experiment 3 examined the effects of fire, grazing and resting on short sward patches over 4 years. In Experiment 2 , total species density was lower in lawn than short sward or tall grassland patches, and there were more species of erect forbs than other plant groups in all patch types. The lawn patches were originally dominated by Cynodon spp. This dominance continued with grazing but in ungrazed patches the abundance of Cynodon spp. declined and that of forbs increased. In the short sward patches, dominance of short tussock grasses continued with grazing but in ungrazed plots their abundance declined while that of large tussock grasses increased. The tall grassland patches remained dominated by large and medium tussock species. In Experiment 3 , fire had no effect on species abundance. On the grazed plots the short tussock grasses remained dominant but where the plots were rested from grazing the small tussock grasses declined and the large tussock grasses increased in abundance. The slow and relatively small changes in these experiments over 4 or 5 years showed how stable the composition of these pastures is, and that rapid changes between patch types are unlikely.     

The Vegetation of Sub-Antarctic Campbell Island

The vegetation of Campbell Island and its offshore islets was sampled quantitatively at 140 sites. Data from the 134 sites with more than one vascular plant species were subjected to multivariate analysis. Out of a total of 140 indigenous and widespread adventive species known from the island group, 124 vascular species were recorded; 85 non-vascular cryptogams or species aggregates play a major role in the vegetation. Up to 19 factors of the physical environment were recorded or derived for each site. Agglomerative cluster analysis of the vegetation data was used to identify 21 plant communities. These (together with cryptogam associations) include: maritime crusts, turfs, megaherbfields, tussock grasslands, and shrublands; mid- elevation swamps, flushes, bogs, tussock grasslands, shrublands, dwarf forests, and induced meadows; and upland tundra-like tussock grasslands, tall and short turf-herbfields, bogs, flushes, rock-ledge herbfields, and fellfields. Axis 1 of the DCA ordination is largely a soil gradient related to the eutrophying impact of marine spray, sea mammals and birds, and nutrient flushing. Axis 2 is an altitudinal (or thermal) gradient. Axis 3 is related to soil reaction and to different kinds of animal influence on vegetation stature and species richness, and Axis 4 also appears to have fertility and animal associations. Autecological interpretation of the data demonstrates clear niche segregation of congeneric species and ;species with similar growth forms. The notable megaherbs and giant tussocks may be an adaptation to harvesting nutrients from the aerosol precipitate. Heat harvesting in the cool, cloudy, wet, and windy climate may also be implicated. The history of farming and natural disturbances has resulted in a complex mosaic of vegetation-soil systems of varying maturity. Their putative dynamic interrelationships are depicted in terms of impacts of burning, grazing, marine animals and climate change and subsequent recovery or primary and secondary succession.     

Kobresia tibetica tussocks facilitate plant species inside them and increase diversity and reproduction

Many plant species grow inside tussocks of some graminoids, but the underlying mechanisms remain unclear. We address whether some species occur and flower mainly inside tussocks so that species diversity and sexual reproduction are higher inside than outside tussocks, and whether relieving biological and physical stress is the mechanism associated with the facilitative process. In a heavily grazed grassland on the eastern Tibetan Plateau, where both physical (due to high altitude) and biological conditions (due to heavy grazing) are extremely harsh, we investigated vegetation in paired plots inside and outside 150 Kobresia tibetica tussocks and measured tussock basal area (=plot area). We also measured temperatures at soil surface, 5 and 10 cm depth and the number of animals (yaks, sheep and horses) grazing inside and outside tussocks. Sixty-seven percent of the species occurred and 42% flowered more frequently inside than outside tussocks, but none less frequently. Inside tussocks 78% species flowered, but outside tussocks only 31% did. Consequently, number of species, number of flowering species and number of inflorescences were all markedly larger inside than outside tussocks. Differences in number of species, number of flowering species and number of inflorescences inside and outside tussocks increased with increasing tussock basal area. Soil temperatures were lower inside than outside tussocks, but grazing intensity was much larger outside tussocks. Therefore, tussocks of K. tibetica facilitated the species inside them likely by grazing prevention, but not by increasing warmth. This study provides evidence that plant species colonizing tussocks of graminoids can be facilitated by the tussock species, and facilitation by grazing prevention may be one mechanism causing the coexistence of the species inside tussocks.     

Optimizing Carbon Storage Within a Spatially Heterogeneous Upland Grassland Through Sheep Grazing Management

Livestock grazing is known to influence carbon (C) storage in vegetation and soil. Yet, for grazing management to be used to optimize C storage, large scale investigations that take into account the typically heterogeneous distribution of grazers and C across the landscape are required. In a landscape-scale grazing experiment in the Scottish uplands, we quantified C stored in swards dominated by the widespread tussock-forming grass species Molinia caerulea. The impact of three sheep stocking treatments (‘commercial’ 2.7 ewes ha^?1 y^?1, ‘low’ 0.9 ewes ha^?1 y^?1 and no livestock) on plant C stocks was determined at three spatial scales; tussock, sward and landscape, and these data were used to predict long-term changes in soil organic carbon (SOC). We found that tussocks were particularly dense C stores (that is, high C mass per unit area) and that grazing reduced their abundance and thus influenced C stocks held in M. caerulea swards across the landscape; C stocks were 3.83, 5.01 and 6.85 Mg C ha^?1 under commercial sheep grazing, low sheep grazing and no grazing, respectively. Measured vegetation C in the three grazing treatments provided annual C inputs to RothC, an organic matter turnover model, to predict changes in SOC over 100 years. RothC predicted SOC to decline under commercial sheep stocking and increase under low sheep grazing and no grazing. Our findings suggest that no sheep and low-intensity sheep grazing are better upland management practices for enhancing plant and soil C sequestration than commercial sheep grazing. This is evaluated in the context of other upland management objectives.     

Shrub succession and invasibility in a New Zealand montane grassland

Abstract Two successive shrub invasions of a short tussock grassland induced by grazing and burning were examined in montane South Island, New Zealand. The first invasion was by a native shrub, matagouri (Discaria toumatou Raoul). The second invasion was by an exotic shrub, Scotch broom (Cytisus scoparius (L.) Link), which invaded the matagouri shrubland that had developed over the grassland. The invasions were investigated using analysis of spatial patterns of both shrubs and tussocks, and age, growth rates and size structure of the shrubs. Competition between the two shrub species was examined using spatial patterns and comparing allometric relationships. After initial invasion by matagouri of the grasslands, stand density increased by consolidation about its initial colonization points. Current matagouri distribution is often negatively associated with tussocks. Scotch broom occurs most frequently in a dense sward of introduced grasses and occasionally in tussocks in interstices among matagouri shrubs. Despite the palatability of Scotch broom to sheep that graze the site, there was no evidence that the spiny matagouri facilitates invasion by protecting Scotch broom seedlings; rather there was negative association between the shrub species. The two species probably compete for above-ground space. However, diameter and height growth rates of Scotch broom far exceed those of matagouri so Scotch broom is likely to increase in biomass rapidly at the site. The autogenic organization and disturbance history of the resident plant communities have rendered each vulnerable to successive invasions.     

Influence of pastoral management on plant biodiversity in a depleted short tussock grassland, Mackenzie Basin

This study investigated the effects of different management inputs (fertiliser and seed) and grazing patterns on plant biodiversity in a short tussock grassland with a strong Hieracium pilosella component. Cover abundance of vascular and non-vascular plants and environmental variables were measured in 32 10×10-m plots located in five blocks with different management treatments. Ordination of the floristic data separated the block with the highest management inputs from other blocks. Several adventive species were significantly more abundant in this block, while several native species were either absent or uncommon, but were significantly more abundant in other study blocks. H. pilosella was significantly more abundant in blocks with lower management inputs. Diversity was significantly higher in the block with the highest management inputs. The native tussock Poa colensoi had significantly greater cover abundance while Festuca novae-zelandiae tussocks were significantly taller in this block. Our results suggest that high management inputs reduce the abundance of H. pilosella and diversity of native species, but increase the abundance of other adventive species and the cover and vigour of native tussocks. Our results highlight an interesting management conundrum for short tussock grasslands. No-input management is likely to result in a decline in native biodiversity, as well as production values, as H. pilosella mats deplete soil nutrients and restrict regeneration of native species. However, input of fertiliser and adventive seeds to enhance production values, although resulting in an increase in the vigour and abundance of some native species (mainly tussocks) and a reduction in H. pilosella abundance, will also result in a decline in overall native species richness.     

Vegetative structure,microclimate, and leaf growth of a páramo tussock grass species,in undisturbed,burned and grazed conditions

In neotropical alpine grasslands (páramo), the natural tussock grass vegetation is extensively grazed and occasionally burned. The low productivity of the tussock grass seems to be the reason for the disappearance of this growth form in the most frequently intervened areas. The structure, microclimate and leaf elongation rates of new emerging leaves were studied for the dominant tussock grass species Calamagrostis effusa, at an undisturbed, a moderately grazed (7 year after fire) and a heavily grazed (3.5 years after fire) site. In absence of grazing and burning, the tussocks had a high standing crop (1.07±0.09 kg DW · m^-2) and leaf area per projected tussock cover (LAI: 9.6±1.4). Two thirds of the total mass was dead and more than half of the leaves were in horizontal position. The tussock growth form protects the meristems from severe climatic conditions. At midday, the temperature was higher at meristem level than in the rest of the tussock. At this level, photosynthetic irradiance (PI) was almost extinct at 2.9±0.74% of PI above the vegetation. The red/far red ratio (R/FR) was strongly decreased. Initial leaf elongation of new born leaves was 2.3 mm · day^-1, and constant during the year; estimated net annual production was 198±73.8 g m^-2. At the moderately grazed and the heavily grazed study sites, the tussocks were smaller, greener and more erect than those at the undisturbed site. More PI reached the meristems and R/FR was higher at the base of grazed tussocks. Leaf elongation rates were lower. Most of the litter disappeared during the fires. The lower elongation rate of leaves in the grazed areas might be a response to defoliation, resulting in increased tillering and a lack growth associated with poor temperature insulation and more UV-B damage.     

Does decomposition of standard materials differ among grassland patches maintained by livestock?

Grazing can modify vegetation structure and species composition through selective consumption, modifying plant litter quality and hence decomposability. In most grasslands, moderate stocking rates maintain a mosaic of high‐quality patches, preferentially used by herbivores (‘grazing lawns’), and low‐quality tall patches, which are avoided. In grazing lawns decomposition rates can be accelerated because of the higher litter quality of its component species and, besides, through the indirect effect of increased nutrient availability in soil. We aimed at testing this indirect effect using standard materials, comparing their decomposition in grazing lawns, open and closed tall tussock grasslands. We selected 10 patches of each type and sampled floristic composition, soil variables and cattle dung deposition. Standard materials were filter paper and Poa stuckertii litter. We prepared litterbags of 0.3 mm (thin mesh) and 1 mm mesh size (coarse mesh). Samples were incubated for 65 days in two ways: above‐ground (thin and coarse mesh) and below‐ground (only thin mesh), aiming at analysing the conditions for decomposition for surface litter and buried litter or dead roots, respectively. Physical and chemical soil variables did not differ among patch types, despite the differences in species composition. Closed tussock grasslands showed the lowest dung deposition, confirming the less intense use of these patches. Soil nitrogen availability (N‐NO₃^‐ and N‐NH₄⁺) was not significantly different among patch types. Each standard material followed a different decomposition pattern across patch types. For above‐ground incubated samples, Poa litter decomposed significantly faster in lawns, and slower in open tussock grasslands. Filter paper decomposed significantly faster in closed tussock grasslands than in the other two patch types. Decomposition of below‐ground incubated samples did not significantly differ among patch types, in line with results for soil variables. Above‐ground differences in decomposition may be associated with differences in microclimatic conditions resulting from differences in vegetation structure.     

Rapid recovery of kohekohe (

Soil conditions, vegetation features and soil fauna were recorded in montane tall tussock grassland dominated by narrow- leaved snow tussock Chionochloa rigida ssp. rigida up to 30 months after a spring fire. Burning reduced the stature of tussocks and the size and density of tillers in the first growing season. After two growing seasons, tussock canopy development and tiller size remained below those found in the unburnt grassland nearby. New tillers and tussocks established following the prolific fire-induced flowering one year after burning. After the fire and sheep grazing, intertussock cover became progressively dominated by introduced grasses and herbs. While soil pH, moisture content, bulk density, surface litter and total nematodes showed significant treatment (burning) effects, these properties also showed significant year-to-year variation. The greatest increase in any nematode group was in Paratylenchus, a distinctive genus widespread in tussock grasslands and apparently responsive to environmental fluctuation and root development; its population was 100x and 29x greater in the burned area than in the control area 16 and 30 months after burning. Subject to detailed testing, populations of mites and collembola may provide relatively simple indicators of recovery of ecosystem function of such grasslands after burning.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary The annual replacement of tillers of Agropyron desertorum (Fisch. ex Link) Schult., a grazing-tolerant, Eurasian tussock grass, was examined in the field following cattle grazing. Heavy grazing before internode (culm) elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation, which elevates apical meristems, increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Unexpectedly, tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in late spring. These responses of twice-grazed tussocks, however, were still less than those of ungrazed tussocks or tussocks grazed moderately in early spring. The presence of ungrazed tillers on partially grazed tussoks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. These observations at the tiller (ramet) level of organization in individual tussocks (genet) may explain the often noted reduction in stand (population) longevity with consistent heavy grazing.     

Changes in vegetation states in grazed and ungrazed Mackenzie Basin grasslands, New Zealand, 1990-2000

Changes in vegetation from 1990 to 2000 were examined at 10 high country localities, representing four grassland types: fescue tussock (Festuca novae-zelandiae), snow tussock (Chionochloa rigida), red tussock (C. rubra), and silver tussock (Poa cita). At each locality, three treatments were established: ambient sheep+rabbit grazing, rabbit grazing only, and no grazing. The mutivariate methods of classification and ordination were used on individual-quadrat cover data to define vegetation states and to examine transitions between them over time. Vegetation states in quadrats already dominated by Hieracium pilosella(> 50% cover) in 1990 showed little change in species composition regardless of grassland type and grazing treatment. In fescue tussock grassland, H. pilosellaincreased regardless of grazing treatment in states with low initial H. pilosellacover (< 5%), while the cover of Carex colensoi, Aira caryophyllea and Rumex acetosella decreased. In the single silver tussock locality, Poa citadecreased markedly in the ungrazed treatment as adventive species such as Dactylis glomerataand Echium vulgare increased. However, Poa citaalso decreased, probably due to drought, in the grazed treatment. Snow tussock and red tussock grassland states were more stable than those in short tussock grasslands, but there was also a general trend towards increasing H. pilosellacover in intertussock vegetation regardless of treatment. However, at one snow tussock locality, transitions from H. piloselladominated to C. rigida-dominated states occurred in ungrazed quadrats, while the reverse occurred in grazed vegetation. Implications for the management of tussock grasslands for conservation are discussed.     

Edaphic patchiness influences grassland regeneration from the soil seed‐bank in mountain grasslands of central Argentina

The soil seed‐banks in the main natural vegetation patches that make up mountain grasslands on granite substrates in central Argentina were studied. The main natural vegetation types are moist swards, tall‐tussock grasslands and stony grasslands. Ten compound soil samples from each community at two soil depths (0–5 and 5–10 cm) were taken. The density of soil seed‐banks was highest in moist swards, intermediate in stony grasslands and lowest in tall‐tussock grasslands. Low levels of similarity were found between the established vegetation and total soil seed‐bank in tall‐tussock grasslands and stony grasslands, but the similarity was higher in swards. In all three communities the seed‐bank was most frequently transient in nature. Short‐term persistent and long‐term persistent seed‐banks were less frequent. Regeneration from the seed‐banks after disturbance is expected to differ among communities on different edaphic patches. On the basis of the density and longevity of the soil seed‐banks and the similarity to the established vegetation, potential for in situ regeneration should be lower in tall‐tussock grasslands, intermediate in stony grasslands and higher in moist swards.     

Grazing in heterogeneous environments: infra- and supra-parasite distributions determine herbivore grazing decisions

We tested the hypothesis that the infra-gastrointestinal parasite population of herbivores affects their grazing behaviour in relation to the supra-parasite population of parasites in the environment. Our first objective was to create a naturally heterogeneous sward structure of gaps and tussocks using a continuous grazing scheme. We then demonstrate that a nutrition vs. parasitism grazing trade-off occurs within that sward structure and that infra-gastrointestinal parasite populations affect the grazing decisions of herbivores faced with the trade-off. A pool of 50 naturally parasitised female Soay sheep and their lambs were used to create a heterogeneous tall, faeces-contaminated tussock/short, non-contaminated gap sward structure in a 1-ha experimental plot. Tussocks offered approximately 1.5 times greater forage intake but contained 5.5 times the number of strongyle parasites compared to the gaps. Following a 10-week period in which the heterogeneous sward structure was created, two 5-day periods of observations of sward structure selection (i.e. gap vs. tussock) were carried out. Twenty female Soay lambs were divided into two groups of ten (balanced for live-weight) immediately prior to the start of the observation period. One of the groups of lambs was treated with an anthelmintic drench before the start of the second observation period creating two levels of parasitism (high and low). On each observation day 5-min focal observations were carried out on each animal at least twice a day, during which time the number of bites taken from gaps and tussocks were recorded along with the number of steps. During the first period of observations, all animals rejected the relatively tall, faeces-contaminated tussocks for grazing to a similar extent and had similar bite and step rates. During the second period of observations all animals showed reduced rejection of the tussocks relative to the first week, however, animals with a reduced parasite population showed a greater reduction in rejection as compare to the highly parasitised animals. We conclude that the infra- and supra-distributions of parasites within herbivore hosts and the environment greatly impact on herbivore grazing behaviour and foraging decisions and thus the structure and heterogeneity of grazed ecosystems.     

Plant communities affect the species–area relationship on Carex sempervirens tussocks

The species–area relationship (SAR) has been extensively studied in a wide range of plant communities, but very few studies have directly addressed how plant communities affect the SAR and what are the underlying mechanisms. Many graminoids form distinct tussocks where many other plant species grow, but no study has investigated whether the SAR holds true for the vegetation on tussocks. In four plant communities on an abandoned subalpine pasture in the Swiss National Park, we made releves on 600 tussocks of Carex sempervirens and measured tussock basal area and other tussock traits. In all four communities, species richness on C. sempervirens tussocks was strongly positively related to tussock basal area (R²0.74), while other tussock traits explained very little (R²<0.04). Slope and intercept of the SAR on C. sempervirens tussocks differed significantly among the four communities. This was because plant communities affected richness in smaller tussocks (basal diameter <10 cm) but not that in large tussocks (basal diameter10 cm). We conclude that the SAR holds true for vegetation on C. sempervirens tussocks and changes with plant communities. Changes in the SAR on C. sempervirens tussocks are very likely because smaller tussocks are less independent of the plant communities than the larger ones, regarding disturbance or nutrients.     

Impact of grazing regime on a Mongolian forest steppe

Question: What is the impact of grazing regime on plant species abundance, plant growth form, plant productivity and plant nutrient concentrations in a forest steppe? Location: Hustai National Park in the forest steppe region of Mongolia. Methods: On the Stipa steppe we applied three different grazing regimes by using; (1) one type of exclosure which excluded grazing by large mammalian herbivores, mainly takh (Przewalski horse), (2) another type of exclosure that excluded both large and small (Siberian marmots) mammalian herbivores, and (3) control plots which were freely grazed. We measured species frequencies, tiller densities, plant biomass and nitrogen concentrations of the vegetation. Results: Exclusion from grazing by takh and marmots significantly increased plant standing crop, but marmot grazing and full grazing did not show significant differences. Protection from grazing decreased forage quality, shown by a lower N-concentration of the standing crop. However, this was solely the result of the lower live-dead ratio of the vegetation. The frequency of the rhizomatous Leymus chinensis decreased under reduced grazing, as did the frequency of the total of rhizomatous species. The frequency of Stipa krylovii increased under reduced grazing, as did its basal areas, tiller density and tussock height. Conclusion: Reduced grazing leads to a lower abundance of rhizomatous species and an increase in tussock species.     

Kaimanawa Feral Horses and Their Environmental Impacts

Feral horses (Equus caballus L.) occupy 64 000 ha of montane- subalpine tussock grassland in the south-western Kaimanawa Mountains, an area zoned for military training. Since 1979, the population has increased at 16.7% per annum, reaching 1102 in 1990. The most extensive habitat, red tussock (Chionochloa rubra) grassland, was variably affected by horses; tussocks in restricted mesic sites were heavily grazed and mostly eliminated, but those in extensive xeric grasslands showed little impact. The mixed hard tussock (Festuca novaezelandiae)/red tussock grasslands on basin floors and plateaux, which had already been degraded by early European farming, were suffering further depletion from horse grazing. The restricted, high altitude Chionochloa pallens tussock communities were being eliminated rapidly through preferential grazing. Oligotrophic bogs, on the summits and basin floors were largely intact, whereas high nutrient flushes were severely affected by trampling and grazing. Horses appeared to have had little impact upon Nothofagus forest understoreys. Ten plant species, several of which are vulnerable nationally, occur in the North Island only within the wild horse range. The habitats of five of them were damaged by horses. Throughout the wide basins and plateaux of the north, horses compromised floristic, rare plant habitat, and landscape nature conservation values. Their numbers may therefore have to be controlled.     

Is vegetation inside Carex sempervirens tussocks highly specific or an image of the surrounding vegetation?

Questions : How do species diversity, frequency and composition in tussocks differ from those in similar sized plots outside tussocks? Does the extent of the differences depend on community types or environmental conditions? Location : A sub‐alpine grassland in the Swiss National Park. Methods : In each of the two communities (short grass and tall graminoid) differing in species composition, grazing intensity and soil nutrient availability, relevés were made in 40 pairs of small circular plots, with one plot located inside a randomly selected Carex sempervirens tussock and the other outside. Results : We found 92 vascular species, of which 46 had a frequency higher than 5%. Species richness (S), pooled cover, Shannon's diversity (H) and cumulative species number (CS) were higher outside than inside the C. sempervirens tussocks, but evenness (J) was lower. S, H and CS differed more in the tall graminoid community than in the short grass community. However, dissimilarity between the paired relevés inside and outside tussocks did not differ between the two communities. Of the 46 most frequent species, 12 were statistically more and only one less frequent outside than inside the tussocks. Vegetation inside and outside tussocks could be clearly distinguished in the ordination space. Conclusion : Vegetation inside C. sempervirens tussocks is different from that in the surrounding area and represents an impoverished but homogenized version of the surrounding vegetation. Although tussocks of C. sempervirens were systematically avoided by grazers, there is little evidence that tussocks facilitate the species growing inside them.     

Does intensive goose grazing affect breeding waders?

Increasing goose population sizes gives rise to conflicts with human socioeconomic interests and in some circumstances conservation interests. Grazing by high abundances of geese in grasslands is postulated to lead to a very short and homogeneous sward height negatively affecting cover for breeding meadow birds and impacting survival of nests and chicks. We studied the effects of spring grazing barnacle geese Branta leucopsis and brent geese Branta bernicla on occupancy of extensively farmed freshwater grasslands by nesting and brood‐rearing waders on the island Mandø in the Danish Wadden Sea. We hypothesized that goose grazing would lead to a shorter grass sward, negatively affecting the field occupancy by territorial/nesting and chick‐rearing waders, particularly species preferring taller vegetation. Goose grazing led to a short grass sward (<5 cm height) over most of the island. To achieve a variation in sward height, we kept geese off certain fields using laser light. We analyzed effects of field size, sward height, mosaic structure of the vegetation, proximity to shrub as cover for potential predators, and elevation above ground water level as a measure of wetness on field occupancy by nesting and chick‐rearing waders. The analysis indicated that the most important factor explaining field occupancy by nesting redshank Tringa totanus, black‐tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus and lapwing Vanellus vanellus as well as by chick‐rearing black‐tailed godwit and lapwing was short vegetation height. Distance to shrub cover and elevation were less important. Hence, despite very intensive goose grazing, we could not detect any negative effect on the field occupancy by nesting nor chick‐rearing waders, including redshank and black‐tailed godwit, which are known to favor longer vegetation to conceal their nests and hide their chicks. Possible negative effects may be buffered by mosaic structures in fields and proximity to taller vegetation along fences and ditches.     

Dung‐associated arthropods influence foraging ecology and habitat selection in Black‐necked Cranes (Grus nigricollis) on the Qinghai–Tibet Plateau

Variation in grassland vegetation structure influences the habitat selection of insectivorous birds. This variation presents a trade‐off for insectivorous predators: Arthropod abundance increases with vegetation height and heterogeneity, but access to arthropod prey items decreases. In contrast, grazing by large herbivores reduces and homogenizes vegetation, decreasing total arthropod abundance and diversity. However, the presence of livestock dung may help counteract the overall reduction in invertebrates by increasing arthropods associated with dung. It is unclear, however, how the presence of arthropod prey in dung contributes to overall habitat selection for insectivorous birds or how dung‐associated arthropods affect trade‐offs between vegetation structure, arthropod abundance, and access to prey. To explore these relationships, we studied habitat selection of the Black‐necked Crane (Grus nigricollis), a large omnivorous bird that breeds on the Qinghai–Tibet Plateau. We assessed the relationships between habitat selection of cranes and vegetation structure, arthropod abundance, and the presence of yak dung. We found that Black‐necked Cranes disproportionately foraged in grassland patches with short sward height, low sward height heterogeneity, and high numbers of dry yak dung, despite these habitats having lower total arthropod abundance. Although total arthropod abundance is lower, these habitats are supplemented with dry yak dung, which are associated with coleopteran larvae, making dung pats an indicator of food resources for breeding Black‐necked Cranes. Coleopteran adults and larvae in yak dung appear to be an important factor influencing the habitat selection of Black‐necked Cranes and should be considered when assessing grassland foraging trade‐offs of insectivorous birds. This research provides new insights into the role of livestock dung in defining foraging habitats and resources for insectivorous predators.