Long‐term vegetation changes in experimentally grazed and ungrazed back‐barrier marshes in the Wadden Sea

Abstract. Vegetation succession in three back‐barrier salt marshes in the Wadden Sea was studied using a data set comprising 25 years of vegetation development recorded at permanent quadrats. The effect of livestock grazing on succession was assessed by comparing quadrats where grazing was experimentally prevented or imposed. We studied changes at the species level as well as at the level of the plant community. Special attention is given to effects on plant species richness and community characteristics that are relevant for lagomorphs (hares and rabbits) and geese. Inundation frequency and grazing were most important in explaining the variation in species abundance data. The three marshes studied overlap in the occurrence of different plant communities and the observed patterns were consistent between them. Clear differences in frequency and abundance of plant species were observed related to grazing. Most plant species had a greater incidence in grazed treatments. Species richness increased with elevation, and was 1.5 to 2 × higher in the grazed salt marsh. Grazing negatively influenced Atriplex portulacoides and Elymus athericus, whereas Puccinellia maritima and Festuca rubra showed a positive response. The communities dominated by Elymus athericus, Artemisia maritima and Atriplex portulacoides were restricted to the ungrazed marsh. Communities dominated by Puccinellia maritima, Juncus gerardi and Festuca rubra predominantly occurred at grazed sites. As small vertebrate herbivores prefer these plants and communities for foraging, livestock grazing thus facilitates for them.     

Plant species richness responses to grazing protection and degradation history in a low productivity landscape

Questions: Does species richness and abundance accumulate with grazing protection in low productivity ecosystems with a short evolutionary history of grazing, as predicted by emerging theory? How do responses to grazing protection inform degradation history? Location: Mulga (Acacia aneura) dry forest, eastern Australia, generally considered chronically degraded by livestock grazing. Methods: Three paired exclosures (ungrazed, and macropod‐grazed) were compared with open‐grazed areas after 25 years using quadrats located on either side of the fences. Additionally, the regional flora for mulga dry forest was assessed to identify species that may have declined and could be threatened by grazing. Results: Low herbaceous biomass accumulation (<1.3 t ha^?1) with full grazing protection confirmed a low productivity environment. For most plant life forms the highest species richness was in macropod‐grazed exclosures, an intermediate grazing disturbance that best approximates the evolutionary history of the environment. This was the net outcome of species that both declined and increased in response to grazing. Regeneration and subsequent self‐thinning of mulga was promoted with grazing protection, but did not confound interpretation of species richness and abundance responses. At the regional scale only 11 native species out of 407 comprising the mulga dry forest flora were identified as rare and potentially threatened by grazing. Conclusions: Significant increases in richness or abundance of native plants with grazing protection, persistence of perennial grasses, regeneration of mulga and scant evidence of a major decline in the regional flora are not consistent with established assertions that long‐grazed mulga dry forest has crossed functional thresholds that limit recovery. Further, a peak in species richness under intermediate (macropod) grazing is counter to the shape of the response predicted by emerging theory for recovery of species richness in a low productivity environment. The finding prompts a more thorough understanding of the distinction between environments with inherently low productivity and those degraded by grazing.     

Small-scale species richness and its spatial variation in an alpine meadow on the Qinghai-Tibet Plateau

We investigated how the high small-scale species richness of an alpine meadow on the Qinghai-Tibet Plateau, China, is maintained. This area is characterized by strong wind and severe cold during long winters. In winter, most livestock is grazed on dead leaves in small pastures near farmers’ residences, whereas in the short summer, livestock is grazed in mountainous areas far from farmers’ residences. The number of plant species and the aboveground biomass were surveyed for three adjacent pastures differing in grazing management: a late-winter grazing pasture grazed moderately from 1 February to 30 April, an early-winter grazing pasture grazed lightly from 20 September to late October, and a whole-year grazing pasture grazed intensively throughout the entire year. In each pasture, we harvested the aboveground biomass from 80 or 100 quadrats of 0.01 m² along a transect and classified the contents by species. We observed 15.5–19.7 species per 0.01 m², which is high richness per 0.01 m² on a worldwide scale. The species richness in the two winter grazing pastures was higher than that in the whole-year grazing pasture. The spatial variation in species richness and species composition in the two winter grazing pastures in which species richness was high was greater than that in the whole-year grazing pasture in which species richness was lower. Most of the leaves that are preserved on the winter grazing pastures during summer are blown away by strong winds during winter, and the remaining leaves are completely exhausted in winter by livestock grazing. A pasture with a high richess is accompanied by a high spatial variation in species richness and species composition. There is a high possibility that the characteristic of spatial variation is also caused by traditional grazing practices in this area.     

Grassland dynamics under sheep grazing in an Australian Mediterranean type climate

Grassland dynamics in a degraded disclimax grassland dominated by Danthonia caespitosa Gaudich. are examined using both demographic and multivariate approaches in an experiment designed to determine the effect of grazing intensity and exclosure on pasture dynamics. The experiment ran for 20 years from 1949 to 1968, using permanent quadrats at 3 grazing intensities and within exclosures. Demographic studies of some perennial grass species demonstrated markedly different responses to grazing; Danthonia caespitosa was unaffected by grazing but responsive to seasonal rainfall differences. Enteropogon acicularis survived only on protected sites. Numerical classification of total species set (121 species) for six observation periods demonstrated that community types were sensitive to differences in winter rainfall, and time since the start of experiment. Principal component analysis of permanent quadrat observations for individual years demonstrates quadrat trajectories which confirm this and indicate progressive divergence of the successional trends of the grazed and ungrazed quadrats. Repeated analysis on grazed quadrats only, shows that three components of pasture dynamics can be recognized; these are trend (succession?) and seasonal differences, each of which account for about 20% of the variance, and differences due to soil heterogeneity in the experimental paddock (8% of variance accounted for). No effect of grazing intensity was detected. Multivariate techniques can provide a clear partitioning of types of dynamic behaviour present in grassland communities. It is concluded that partitioning of environmental heterogeneity prior to demographic studies would increase their sensitivity.

     

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.     

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。     

Growth responses of arctic graminoids following grazing by captive lesser snow geese

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0–180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.     

Frequent mowing is better than grazing for the conservation value of lowland tussock grasssland at Pontville,Tasmania

Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction.     

Influence of grazing and soil conditions on secondary savanna vegetation in India

Abstract. Savanna vegetation and pertinent soil features were studied on 43 sites in a dry tropical forest region of India. Grazing intensity ranged from 0.68 to 0.98. Soil moisture was positively related to the proportion of fine soil particles (< 0.1 mm), and the latter decreased while the proportion of coarse particles (2.0-0.5 mm) increased with increasing grazing intensity. Canopy biomass ranged from 28 to 104 g/m² in grazed communities and from 230 to 337 g /m² in ungrazed communities and was positively related to vegetation cover which ranged between 30–72 % in grazed and 68 - 91 % in ungrazed communities. Vegetation cover was negatively related to grazing intensity. Species richness and diversity were highest at low grazing intensity. Using community coefficients and Detrended Correspondence Analysis, the grazed stands were clustered into six and the ungrazed ones into three communities. The grazed communities were recognised as degradation stages and the ungrazed ones as recovery stages. Only five grass species, in various combinations were able to dominate in one of the different stages. Evidently the harsh climatic conditions (high temperatures, high variability in rainfall and a long dry period) in the region permit only a few species already adapted to these conditions to participate in the succession.     

Effects of mute swan grazing on a keystone macrophyte

1. This study describes the early summer foraging behaviour of mute swans (Cygnus olor) on the River Frome, a highly productive chalk stream in southern England in which Ranunculus penicillatus pseudofluitans is the dominant macrophyte. 2. A daily maximum of 41 ± 2.5 swans were present along the 1.1 km study reach during the study period (late May to the end of June). The river was the primary feeding habitat. Feeding activity on the river at dawn and dusk was much lower than during daylight, but we cannot rule out the possibility that swans fed during the hours of darkness. 3. The effects of herbivory on R. pseudofluitans biomass and morphology were quantified. Biomass was lower in grazed areas and swans grazed selectively on leaves in preference to stems. A lower proportion of stems from grazed areas possessed intact stem apices and flowering of the plant was reduced in grazed areas. 4. A model, based on the swans’ daily consumption, was used to predict the grazing pressure of swans on R. pseudofluitans. The model accurately predicted the number of bird days supported by the study site, only if grazing was assumed to severely reduce R. pseudofluitans growth. The proportion of the initial R. pseudofluitans biomass consumed by a fixed number of swans was predicted to be greater when the habitat area was smaller, initial R. pseudofluitans biomass was lower and R. pseudofluitans was of lower food value. 5. We concluded that the flux of N and P through the study reach was largely unaffected by swan activity. The quality of R. pseudofluitans mesohabitat (the plant as habitat for invertebrates and fish) was significantly reduced by grazing which also indirectly contributed to reduced roughness (Manning's n) and by inference water depth. Wetted habitat area for fish and invertebrates would also be lowered over the summer period as a consequence of the reduction in water depth. It was estimated that, while grazing, an individual swan may eat the same mass of invertebrates per day as a 300‐g trout. 6. There is a need to manage the conflict between mute swans and the keystone macrophyte, R. pseudofluitans, in chalk streams, and the modelling approach used here offers a potentially useful tool for this purpose.     

Increasing native, but not exotic, biodiversity increases aboveground productivity in ungrazed and intensely grazed grasslands

Species-rich native grasslands are frequently converted to species-poor exotic grasslands or pastures; however, the consequences of these changes for ecosystem functioning remain unclear. Cattle grazing (ungrazed or intensely grazed once), plant species origin (native or exotic), and species richness (4-species mixture or monoculture) treatments were fully crossed and randomly assigned to plots of grassland plants. We tested whether (1) native and exotic plots exhibited different responses to grazing for six ecosystem functions (i.e., aboveground productivity, light interception, fine root biomass, tracer nitrogen uptake, biomass consumption, and aboveground biomass recovery), and (2) biodiversity-ecosystem functioning relationships depended on grazing or species origin. We found that native and exotic species exhibited different responses to grazing for three of the ecosystem functions we considered. Intense grazing decreased fine root biomass by 53% in exotic plots, but had no effect on fine root biomass in native plots. The proportion of standing biomass consumed by cattle was 16% less in exotic than in native grazed plots. Aboveground biomass recovery was 30% less in native than in exotic plots. Intense grazing decreased aboveground productivity by 25%, light interception by 14%, and tracer nitrogen uptake by 54%, and these effects were similar in native and exotic plots. Increasing species richness from one to four species increased aboveground productivity by 42%, and light interception by 44%, in both ungrazed and intensely grazed native plots. In contrast, increasing species richness did not influence biomass production or resource uptake in ungrazed or intensely grazed exotic plots. These results suggest that converting native grasslands to exotic grasslands or pastures changes ecosystem structure and processes, and the relationship between biodiversity and ecosystem functioning.     

Response of vertebrates to fenceline contrasts in grazing intensity in semi‐arid woodlands of eastern Australia

Abstract Changes in the abundance, species richness and assemblage composition of vertebrates due to grazing by domestic stock were investigated in the semi‐arid woodlands of eastern Australia. Analyses were based on the differences found at 10 fenceline contrast sites. Two species of amphibians, 22 species of reptiles and two species of small mammal were captured in pit traps during the surveys. Kangaroos (red and eastern grey), sheep, goats and 66 species of birds were recorded along line transects. Analyses revealed that abundance of diurnal reptiles and species richness of diurnal reptiles and birds were significantly lower on heavily grazed sites than they were on lightly grazed sites. At a local scale, the gecko, Gehyra variegata, was more abundant where grazing was heavier, while Diplodactylus conspicillatus, Diplodactylus steindachneri and Rhynchoedura ornata responded to variables indirectly related to grazing intensity (kangaroo density, sheep and goat dung mass and sheep density, respectively). Birds more commonly sighted on lightly grazed areas than heavily grazed areas were the apostlebird, brown treecreeper, crested bellbird, grey butcherbird, hooded robin, jacky winter, little woodswallow, Australian magpie‐lark, mulga parrot, splendid wren, white‐browed treecreeper and yellow‐rumped thornbill. Birds more commonly sighted on heavily grazed areas than on lightly grazed areas were the Australian raven and chestnut‐crowned babbler. Most variation in species composition between sites was due to spatial separation and no regional‐level indicator species of grazing were evident. A combination of direct grazing‐related changes (e.g. loss of ground cover) and indirect effects of the pastoral industry (e.g. introduction of artificial sources of water) lead to changes in fauna at different scales of analysis across regions.     

Demography of three dominant sedges under contrasting grazing regimes in the High Arctic

Abstract. Tiller demography of Carex aquatilis ssp. stans, Carex membranacea, and Eriophorum angustifolium ssp. triste was investigated in ungrazed and grazed high arctic vegetation on central Ellesmere Island, Canada. Tiller birth, growth, flowering and death were studied from excavated clonal fragments, and tiller density and biomass were studied from excavated turfs. Five life‐cycle stages were determined: dormant buds, juvenile, mature, flowering and dead tillers. A stage‐based transition matrix model was developed to estimate the long‐term dynamics of the sedge populations and to compare life‐history strategies between ungrazed and grazed populations. Short‐term and retrospective models, based on the growth during the sampling year and during the lifetime of the clonal fragments, respectively, were compared to see how well the short‐term model can describe demography of long‐lived plants. According to the short‐term model, tiller populations were decreasing (λ < 1 except for C. membranacea), whereas the retrospective model indicated that the tiller populations were increasing. Tiller population growth rates did not differ between ungrazed and grazed habitats. Nevertheless, the similar growth rates may be obtained by balanced differences in the vital rates between plants of the two habitats. The plants in the ungrazed habitat tended to remain in their current life‐cycle stage, whereas plants in the grazed habitat moved quickly to the next stage and died earlier. C. aquatilis ssp. stans appears to gain a competitive advantage over the other species under intensive grazing, as indicated by the higher tiller density and greater below‐ground biomass in grazed vegetation. The greater amount of below‐ground biomass apparently buffers C. aquatilis ssp. stans against grazing better than the other species.     

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.     

Life-form composition of alpine plant communities at the Eastern Qinghai-Tibetan plateau

Alpine plants of the eastern Qinghai-Tibetan plateau (Sichuan, China) are developed under long-lasting grazing by wild and domestic yaks. Among morphological features of plants, life forms may reflect their adaptation to grazing. We studied life-form composition of four typical communities within the alpine belt (3930–3960 m a.s.l.) subjected to grazing of various intensity: alpine fen (heavily grazed), alpine shrub meadow (heavily grazed), Spiraea alpina thicket (grazed), and Rhododendron thicket (practically not grazed). The following morphological traits were studied: (1) life form according to Raunkiaer, (2) life form according to Serebryakov, (3) canopy structure, and (4) rate of lateral spreading. We derived life-form spectra based on (1) the number of species per life form and (2) the cumulative abundance of species which have the same life form. One-way ANOVA and nonparametric ANOVA were run to test for significance of differences between spectra. The studied communities differed significantly by the proportion of different life forms. The main life forms are caudex and short rhizome hemicryptophytes, nonclonal species, or species with a low rate of lateral spreading. Therophytes made up 10–11% of the communities except in Rhododendron thickets, where such were absent. These life forms can indicate grazing in the study area.     

Scleractinian coral recruitment patterns at Salt River submarine canyon,St. Croix,U.S. Virgin Islands

Scleractinian coral recruitment patterns were studied at depths of 9, 18, 27 and 37 m on the east and west walls of Salt River submarine canyon, St. Croix, U.S. Virgin Islands, by censusing coral juveniles which settled on experimental settling plates placed on the reef for 3–26 months as well as coral juveniles within quadrats on the reef. The most common species in the juvenile population within quadrats were Agaricia agaricites, Porites astreoides, Madracis decactis, Stephanocoenia michelinii, and A. lamarcki. The only species settling on settling plates were Agaricia spp., Madracis decactis, Porites spp., Stephanocoenia michelinii and Favia fragum. A total of 271 corals settled on 342 plates, with 51% of the juveniles on the east wall and 49% on the west wall. Of these 34% settled on horizontal surfaces and 66% on vertical surfaces. Based on results from quadrats, Agaricia agaricites and Porites astreoides had high recruitment rates relative to their abundance on the reef. In contrast, Agaricia lamarcki, Montastraea annularis, M. cavernosa and Siderastrea siderea had high amounts of cover compared to their abundance as juveniles within quadrats. The mean number of juveniles per m² within quadrats ranged from 3 to 42. In general, there was a decrease in the mean number of juveniles and the number of species with depth. Total number of juveniles on settling plates was highest at 18 m on both walls. The largest number within quadrats was at 18 m on the east wall, followed by 9 m and 18 m on the west wall. High rates of coral recruitment tended to be associated with low algal biomass and relatively high grazing pressure by urchins and fishes.     

Use of vegetation classification and plant indicators to assess grazing abandonment in Estonian coastal wetlands

Question: What are the effects of grazing abandonment on the vegetation composition of Estonian coastal wetlands? Location: Vormsi Island and Silma Nature Reserve in western Estonia, Europe. Methods: Local knowledge and field reconnaissance were used to identify current and historical management levels of wetland sites within the west Estonian study area. Nine study sites, with varying management histories, were selected comprising an area of 287 ha. A total of 198 quadrats were taken from 43 distinct vegetation patches in five of the sites. TWINSPAN analysis was used to identify community type, and a phytosociological key was constructed for character taxa. This vegetation classification was then applied within a GIS‐based context to classify all the study sites, using a ground survey technique and 1:2000 scale air photos. Results: We identified 11 different brackish coastal wetland community types. Indicator species were defined with community characteristics for the seven main vegetation types readily recognisable in the field. Coastal wet grasslands were most extensive in grazed sites, or sites that had been more intensively grazed, while abandoned sites were largely composed of Phragmites australis stands, tall grassland, and scrub. Site variations based on vegetation composition were significantly correlated with past grazing intensity. Plant community types showed significant edaphic differences, with particularly low soil moisture and high conductivity and pH for open pioneer patches compared to other vegetation types. Conclusion: Abandonment of traditionally grazed coastal grasslands threatens their characteristic biodiversity. This study found that grazing abandonment reduced the extent of coastal wetland grasslands of particular conservation value. Nevertheless, plant species of conservation interest were found across the sequence of community types described. The study shows that grazing is an important factor influencing coastal wetland plant communities but suggests that vegetation distribution is affected by environmental variables, such as topography.     

How season of grazing and herbivore selectivity influence monsoon tall-grass communities of northern Australia

Abstract. The hypothesis that season of defoliation and herbivore selectivity may be as important as level of use in determining plant community response to grazing was tested in a monsoon grassland in northern Australia. Plots, dominated by the tussock grasses Themeda triandra and Chrysopogon fallax, were grazed by cattle at low, medium and high rates of utilization in either the early wet, late wet or dry seasons. Effects of grazing on species composition were greatest in the early wet season when high rates of utilization significantly reduced the proportion and occurrence of Themeda and increased the proportion of forbs. Grazing in the dry season had no significant effect on composition. At medium and high levels of utilization in the early wet season, the pasture responded negatively to defoliation, only partially compensating for plant tissue lost to herbivory. The negative response to defoliation carried over to the next wet season when these same medium and high-grazing treatments produced only 80 % and 60 % growth, respectively, of that in treatments grazed at low levels of utilization or those grazed during the dry season. The frequency of Themeda was still lower, and that of annual grasses and non-leguminous forbs higher, in plots that had been grazed at a high rate of utilization for just eight weeks in the early wet season two years previously. Species richness and diversity were also significantly affected by this grazing disturbance. If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.     

Effects of livestock breed and grazing pressure on ground‐dwelling arthropods in Cantabrian heathlands

Abstract 1. The effects of different goat breeds and grazing pressures on epigeal arachnids (Lycosidae and Opiliones) and ground beetles (Carabidae) were assessed in a heath–gorse shrubland located in the north of the Iberian Peninsula. Three treatments (low grazing pressure with Cashmere breed, high grazing pressure with Cashmere breed, and high grazing pressure with local Celtiberic breed) with three replicates of each treatment were allocated randomly to nine plots. 2. Arthropod fauna abundance, diversity, and species richness were estimated using pitfall trapping over 3 years (2003, 2004, and 2005). Vegetation cover, composition, and height were assessed along transects and above‐ground plant biomass was sampled in quadrats. 3. Lower grazing pressure led to lower herbaceous cover and higher heather cover than high grazing pressure. Overall, it did not enhance arthropod diversity or abundance, but the abundance and species richness of carabids, and abundance of lycosids like Pardosa pullata, were higher under high stocking rates, whereas Opiliones were favoured by the low stocking rates. Although it has been assumed that traditional breeds enhance biodiversity, the present study found no significant differences for both arthropod fauna and vegetation between the goat breeds. 4. Arthropod–vegetation relationships were examined by constrained ordination. Fauna assemblages followed a gradient from closed canopy shrubland areas, in the lowest grazing pressure, to grassier open canopy areas resulting from higher grazing pressure, revealing the importance of grazing management as a driver of arthropod community structure of the heathland.     

After grazing exclusion,is there any modification of strategy for two guerrilla species: <Emphasis Type="Italic">Elymus repens</Emphasis> (L.) Gould and <Emphasis Type="Italic">Agrostis stolonifera</Emphasis> (L.)?

Elymus repens (L.) Gould and Agrostis stolonifera (L.), are competitive grasses with guerrilla strategy that invade grasslands with a low stocking rate. In this work, we tested the hypotheses that grazing exclusion facilitates vegetative development of rhizomes and stolons of these clonal grasses and that such change is a key mechanism for their abundance in set-aside grasslands. The competitive capacities of these two guerrilla species were characterised by samples in plant community (species richness and biomass) and on the level of individual species (morphometric measurements on stolons and rhizomes) during a growing season. Compared to grasslands where grazing was excluded for three years, species richness was higher in grazed site and the plant community structure differed. Indeed, with grazing exclusion, a shift from annual species with a diversified growth-form to perennial species with a tall tussock and graminoid growth-form was monitored. In ungrazed situation, Elymus repens and Agrostis stolonifera were the dominant grasses, and the standing biomass for the lowland community showed a significant increase compared to the grazed site. Vegetative development increased competitive capacities of these two guerrilla species and led by phenomenon of competitive exclusion to the disappearance of annuals species. With grazing cessation, Elymus repens was found to increase the size of aerial traits (shoot length and the number of leaves per shoot) and this may both be propitious for achieving dominance within plant communities and also maintaining its competitive local advantage. By contrast, Agrostis stolonifera showed an increase in a root trait, i.e. rhizome length, in the fenced site, which provide good ability for spatial propagation and then to explore adjacent patches. We concluded that Elymus repens presented a morphological capacity to change its colonising strategy from a guerrilla strategy to a phalanx strategy, by morphological variability of aerial organs, when it was submitted to competitive stress and environment modifications. Agrostis stolonifera showed a capacity to escape aerial competition resulting from grazing cessation, than to increase underground propagation capacity. The present study highlighted the capacities of Elymus repens to respond in an adaptative way to competitive pressure.