Low Levels Of Grazing Research Articles

A review of the vascular plant flora of the Cairngorms Connect project area, Scotland, and some possible implications of forest expansion to the natural tree line

Cairngorms Connect, a partnership of four adjoining land owners, is committed to a 200-year vision to enhance and restore habitats, species and ecological processes across a 592 km2 area within the Cairngorms National Park. This will be achieved by, inter alia, expanding woodland to its natural altitudinal limit, including high altitude sub-alpine scrub. All or parts of six native Caledonian pinewoods occur here, c.26% of the national total. Ancient, semi-natural woodland within the Cairngorms Connect area is 43% of the National Park total. Modelling of the extent of potential-natural woodland (sensu Peterken, 1981, 1996) indicates that below 600 m all terrestrial habitats are potentially capable of supporting some degree of tree and scrub cover. 899 vascular plant taxa have been recorded here, of which 693 are native to the area. 7.6% of native taxa are endemic to Great Britain (and Ireland) or to Scotland; these are mainly Hieracia (Hawkweeds). Of the native taxa, 23% are of national, and 11% of regional conservation concern. Few native taxa are widespread within the Cairngorms Connect area, most are local or rare. 40% of native taxa have been recorded in five or less monads (1 km squares), with 16% recorded from just a single monad. 12% of native taxa are associated with shaded locations or semi-shade (Ellenberg Light values 3-5). 51% of taxa are found in partial shade to well lit locations (values 6 and 7) and 37% of taxa in well lit to fully lit locations (values 8 and 9). Native taxa with Light values of 6-7 are the most frequent in 92% of monads with more than 10 recorded taxa. 65% of taxa of national conservation concern favour well lit to fully lit locations (Light values 8-9). Shading of plants, at altitudes below the potential tree line, is strongly influenced by the extent of woodland and scrub and its structure, and by herbivore grazing levels determining height and structure of the field layer. To achieve forest expansion to the natural tree line by natural regeneration will require sustained low levels of grazing and browsing, for decades, or longer. This is already leading to a taller field layer and an increased density of tree regeneration. 40% of native taxa may be negatively impacted, if existing and new woodland becomes dense with a high level of shading. Of these 'at risk' taxa, 50% have maximum height less than 50 cm and may be especially at risk from sustained periods of low grazing. Limited disturbance and lack of open sites and bare ground for seedling recruitment is another potential constraint on vascular plants. The issue of vegetation succession and shading, leading to possible loss of plant diversity is likely to be much less of an issue at altitudes around and above the tree line. Here there are likely to be benefits, with possible expansion of tall herb communities.

A spatial simulation model to assess controls upon grassland degradation on the Qinghai-Tibet Plateau, China

Large areas of alpine meadow across the Qinghai-Tibet Plateau (QTP), western China, are undergoing degradation. Drawing upon field and remotely sensed data we develop a spatially explicit grid-based simulation model to explore the long-term dynamics of alpine meadow communities in this area. Our model represents the spatial dynamics of four plant functional types (PFTs) – sedges, grasses, forbs and weeds – together with disturbance from livestock grazing and small mammal activity. The model is most sensitive to parameters related to the reproductive rate and lifespan of the three plant functional types. Comparisons between model outcomes and field observations of vegetation composition suggest that the model produces plausible predictions of community dynamics. Simulation experiments indicate that grazing intensity is a fundamental control of plant community dynamics in these ecosystems. As grazing intensity increases there is a shift from a community dominated by grasses and forbs (very low grazing level) to grasses and sedges (low and moderate grazing levels) to degraded ground (high grazing levels). Severely degraded alpine meadows (locally termed ‘Heitutan’ or ‘black beach’) emerge after 370 simulation years under high levels of grazing pressure, but after only two decades under extreme grazing pressure. Under low to moderate intensity grazing regimes small mammals play an important role in maintaining meadow ecosystems. However, our model suggests that small mammal activity is no longer beneficial to the grassland ecosystem under high grazing pressures, increasing the rate of Heitutan formation. The time frame for a return to a sedge-dominated community is shortest under a moderate intensity grazing regime, but even in this instance it may take several hundred years.

Geographic variation in the sensitivity of an herbivore-induced seaweed defense.

Intraspecific variation in primary producer induced defenses may affect how these defenses contribute to population and community regulation. For instance, inducible defenses may play larger roles in primary producer populations that are sensitive to low levels of grazing than populations that only respond to high levels of grazing. Although the incidence of herbivore-induced defenses is well documented, and there are examples of geographic variation in these defenses, we have limited knowledge of the factors that affect sensitivity to grazing (i.e., the minimum grazer density needed to elicit these responses) within and among populations. Filling this gap is necessary to understand the importance of these defenses under different conditions. To address whether the sensitivity of seaweed induced defenses varies geographically, we exposed Northern and Southern California populations of the seaweed Silvetia compressa to five densities of the snail Tegula funebralis, under ambient, regional environmental conditions. Southern seaweeds required high levels of grazing to induce defenses, while all levels of herbivory decreased Northern seaweed palatability. To better understand these different responses to low levels of grazing, we conducted common garden experiments to directly test the roles of experimental environment and herbivore source. Consistent with initial experiments, Northern Silvetia responded to low levels of grazing, regardless of environmental conditions, while Southern Silvetia never responded to low levels of grazing, even after being acclimated to Northern environmental conditions for 24d. Additionally, Southern Silvetia did not respond to grazing by Northern snails, suggesting that herbivore source did not explain this geographic pattern in inducible seaweed defenses. Together, these observations suggest that the seaweed source explains this geographic pattern in sensitivity. Trade-offs with constitutive defenses did not help explain this pattern, as Southern Silvetia had weaker constitutive defenses than Northern seaweeds. This may be due to a combination of low grazing pressure and low predictability of attack in the South. Thus, population variation in sensitivity may be due to long-term differences in environmental histories, resulting in local adaptation or legacy effects from exposure to local conditions. Overall, our results indicate that these herbivore-induced responses may be more important in Northern Silvetia populations than Southern ones.

The Environmental Context and Function of Burnt-Mounds: New Studies of Irish Fulachtaí Fiadh

Burnt mounds, or fulachtaí fiadh as they are known in Ireland, are probably the most common prehistoric site type in Ireland and Britain. Typically Middle–Late Bronze Age in age (although both earlier and later examples are known), they are artefact-poor and rarely associated with settlements. The function of these sites has been much debated with the most commonly cited uses being for cooking, as steam baths or saunas, for brewing, tanning, or textile processing. A number of major infrastructural development schemes in Ireland in the years 2002–2007 revealed remarkable numbers of these mounds often associated with wood-lined troughs, many of which were extremely well-preserved. This afforded an opportunity to investigate them as landscape features using environmental techniques – specifically plant macrofossils and charcoal, pollen, beetles, and multi-element analyses. This paper summarises the results from eight sites from Ireland and compares them with burnt mound sites in Great Britain. The fulachtaí fiadh which are generally in clusters, are all groundwater-fed by springs, along floodplains and at the bases of slopes. The sites are associated with the clearance of wet woodland for fuel; most had evidence of nearby agriculture and all revealed low levels of grazing. Multi-element analysis at two sites revealed elevated heavy metal concentrations suggesting that off-site soil, ash or urine had been used in the trough. Overall the evidence suggests that the most likely function for these sites is textile production involving both cleaning and/or dyeing of wool and/or natural plant fibres and as a functionally related activity to hide cleaning and tanning. Whilst further research is clearly needed to confirm if fulachtaí fiadh are part of the ‘textile revolution’ we should also recognise their important role in the rapid deforestation of the wetter parts of primary woodland and the expansion of agriculture into marginal areas during the Irish and British Bronze Ages.

Ecosystem structure, function, and composition in rangelands are negatively affected by livestock grazing.

Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective.

Do shrubs reduce the adverse effects of grazing on soil properties?

AbstractIncreases in the density of woody plants are a global phenomenon in drylands, and large aggregations of shrubs, in particular, are regarded as being indicative of dysfunctional ecosystems. There is increasing evidence that overgrazing by livestock reduces ecosystem functions in shrublands, but that shrubs may buffer the negative effects of increasing grazing. We examined changes in water infiltration and nutrient concentrations in soils under shrubs and in their interspaces in shrublands in eastern Australia that varied in the intensity of livestock grazing. We used structural equation modelling to test whether shrubs might reduce the negative effects of overgrazing on infiltration and soil carbon and nitrogen (henceforth ‘soil nutrients’). Soils under shrubs and subject to low levels of grazing were more stable and had greater levels of soil nutrients. Shrubs had a direct positive effect on soil nutrients; but, grazing negatively affected nutrients by increasing soil bulk density. Structural equation modelling showed that shrubs had a direct positive effect on water flow under ponded conditions but also enhanced water flow, indirectly, through increased litter cover. Any positive effects of shrubs on water flow under low levels of grazing waned at high levels of grazing. Our results indicate that shrubs may reduce the adverse effects of grazing on soil properties. Specifically, shrubs could restrict access to livestock and therefore protect soils and plants beneath their canopies. Low levels of grazing are likely to ensure the retention of soil water and soil carbon and nitrogen in shrubland soils. Copyright © 2015 John Wiley & Sons, Ltd.

Ground-dwelling spider diversity in rare European oak and yew woodlands and the impact of grazing

In Ireland only 2 % of the total land area is native woodland, which tends to be small and fragmented. Killarney National Park in south-west Ireland contains the most extensive semi-natural woodland in the country, and includes oak (Quercus petraea) and yew (Taxus baccata) woodlands which are internationally protected. Here, over-grazing by large populations of red deer (Cervus elaphus) and Asian sika deer (Cervus nippon) have lead to changes in overstory and understory vegetation species composition and structure. This study presents the first description of ground-dwelling spider fauna in the rare woodlands of Killarney National Park and asked (1) do these rare woodlands support rare or specialist species, (2) does deer grazing have an effect on spider abundance, richness and species composition in the park, (3) what management recommendations can be made for deer in the park? Active ground-dwelling spiders were sampled in the oak and yew woodlands of the park by pitfall trapping within deer-proof exclosures and adjacent grazed controls. Four spider species classified as vulnerable were collected from these woodlands: Agyneta subtilis occurred in the oak and yew woodlands but Saaristoa firma, Tapinocyba insecta and Walckenaeria dysderoides were collected only in the oak woodland. Killarney National Park may be important for five species, not typically found in plantation forests, which rely on nationally scarce habitats. Deer grazing was linked with decreased ground-dwelling spider abundance and species richness in the oak woodland by reducing structural diversity of the habitat. Fewer effects of grazing were detected in the yew woodland, possibly due to increased culling in the area. Results provide evidence that controlling deer grazing is important for woodland biodiversity in Killarney National Park. Incorporating deer into woodland management in the park is recommended to maintain low grazing levels which will prevent woodland closure and maintain ground vegetation diversity.

Demographic patterns of a widespread long-lived tree are associated with rainfall and disturbances along rainfall gradients in SE Australia.

Predicting species distributions with changing climate has often relied on climatic variables, but increasingly there is recognition that disturbance regimes should also be included in distribution models. We examined how changes in rainfall and disturbances along climatic gradients determined demographic patterns in a widespread and long-lived tree species, Callitris glaucophylla in SE Australia. We examined recruitment since 1950 in relation to annual (200–600 mm) and seasonal (summer, uniform, winter) rainfall gradients, edaphic factors (topography), and disturbance regimes (vertebrate grazing [tenure and species], fire). A switch from recruitment success to failure occurred at 405 mm mean annual rainfall, coincident with a change in grazing regime. Recruitment was lowest on farms with rabbits below 405 mm rainfall (mean = 0–0.89 cohorts) and highest on less-disturbed tenures with no rabbits above 405 mm rainfall (mean = 3.25 cohorts). Moderate levels of recruitment occurred where farms had no rabbits or less disturbed tenures had rabbits above and below 405 mm rainfall (mean = 1.71–1.77 cohorts). These results show that low annual rainfall and high levels of introduced grazing has led to aging, contracting populations, while higher annual rainfall with low levels of grazing has led to younger, expanding populations. This study demonstrates how demographic patterns vary with rainfall and spatial variations in disturbances, which are linked in complex ways to climatic gradients. Predicting changes in tree distribution with climate change requires knowledge of how rainfall and key disturbances (tenure, vertebrate grazing) will shift along climatic gradients.

Grazing dampens the positive effects of shrub encroachment on ecosystem functions in a semi‐arid woodland

Summary The encroachment of woody plants into grasslands, open woodlands and savannah has been widely reported over the past few decades. Overgrazing is a probable cause of shrub encroachment and could be a stronger driver of declining ecosystem structure and functioning in shrublands than encroachment per se. We examined the relative effects of changes in shrub cover and grazing rate on ecosystem functions at sandy and loamy sites in eastern Australia varying in shrub cover and grazing. Our aim was to test the notion that the negative effects on ecosystem functioning commonly attributed to encroachment are more likely due to grazing than to increase in shrub cover per se. Structural equation modelling indicated a generally strong positive effect of increasing shrub cover, and a generally negative, or slight effect of grazing on multiple measures of ecosystem function related to plant productivity, water infiltration, nutrient cycling and surface stability. On loamy soils, grazing generally dampened the positive effects of increasing shrub cover on most response variables. On sandy soils, however, although there were generally stronger effects of grazing, most attributes did not change in response to increasing shrub cover. Synthesis and applications. Our results indicate that, contrary to the prevailing opinion, increasing shrub cover was generally associated with increases (or no change) in functional and structural measures indicative of healthy systems. The dampening of the positive effects of shrub cover caused by grazing was site (soil texture) specific, reinforcing the notion that the effects of increasing shrub cover and their interaction with grazing are context dependent. Our study provides the basis for improved understanding and management of shrublands for a number of competing goals and suggests that managing grazing rates is a better strategy than focusing on shrub removal. Using low levels of grazing is likely to maximize the benefits from shrublands, such as the maintenance of biodiversity, water infiltration and C sequestration, while maintaining a productive herbaceous community.

Drove roads as local biodiversity reservoirs: effects on landscape pattern and plant communities in a Mediterranean region

AbstractQuestionWhat are the effects of traditional drove roads on landscape pattern and plant communities?LocationMadrid Autonomous Region, Central Spain.MethodsWe selected four study localities in different landscape units. Within each locality, we selected eight sites and within each site, we established three 1‐ha plots, each corresponding to one of three situations: drove road, adjacent matrix or distant matrix. The landscape pattern of each plot was characterized by the cover of the different patch types, the patch type richness ha−1 and the patch type evenness ha−1. At one site per locality, we also recorded vegetation by randomly distributing twenty 20 cm × 20 cm quadrats per plot. We characterized each quadrat by its species richness, plant species composition and plant functional composition. We also analysed species richness by constructing rarefaction curves for each plot.ResultsIn the localities situated in croplands, sub‐mediterranean forests and coniferous forests, drove roads were found to be an important source of spatial heterogeneity and a reservoir for a large number of plant species. In contrast, drove roads did not differ from the matrix habitats in rangelands, suggesting that the processes shaping drove road vegetation are similar to the general processes that shape grazed systems. Drove roads did not imply a significant increase in functional diversity. Our results were heavily scale‐dependent: while drove roads provided heterogeneity at the local scale, they showed a remarkable similarity at the large scale.ConclusionsDrove roads act as authentic local biodiversity reservoirs, especially in environments with low grazing levels. At the same time, drove roads imply structural and functional continuity on a large scale, increasing potential connectivity at the regional level. We recommend the preservation of drove roads in a functional state, because of their benefits to plant biodiversity conservation, and claim that these benefits should be considered when designing livestock policies with different intensification scenarios.

Cattle Grazing and Conservation of a Meadow-Dependent Amphibian Species in the Sierra Nevada

World-wide population declines have sharpened concern for amphibian conservation on working landscapes. Across the Sierra Nevada's national forest lands, where almost half of native amphibian species are considered at risk, permitted livestock grazing is a notably controversial agricultural activity. Cattle (Bos taurus) grazing is thought to degrade the quality, and thus reduce occupancy, of meadow breeding habitat for amphibian species of concern such as the endemic Yosemite toad (Anaxyrus [ = Bufo] canorus). However, there is currently little quantitative information correlating cattle grazing intensity, meadow breeding habitat quality, and toad use of meadow habitat. We surveyed biotic and abiotic factors influencing cattle utilization and toad occupancy across 24 Sierra Nevada meadows to establish these correlations and inform conservation planning efforts. We utilized both traditional regression models and Bayesian structural equation modeling to investigate potential drivers of meadow habitat use by cattle and Yosemite toads. Cattle use was negatively related to meadow wetness, while toad occupancy was positively related. In mid and late season (mid July–mid September) grazing periods, cattle selected for higher forage quality diets associated with vegetation in relatively drier meadows, whereas toads were more prevalent in wetter meadows. Because cattle and toads largely occupied divergent zones along the moisture gradient, the potential for indirect or direct negative effects is likely minimized via a partitioning of the meadow habitat. During the early season, when habitat use overlap was highest, overall low grazing levels resulted in no detectable impacts on toad occupancy. Bayesian structural equation analyses supported the hypothesis that meadow hydrology influenced toad meadow occupancy, while cattle grazing intensity did not. These findings suggest cattle production and amphibian conservation can be compatible goals within this working landscape.

Experimental reduction of native vertebrate grazing and addition of logs benefit beetle diversity at multiple scales

Summary 1. High densities of vertebrate herbivores can be a significant barrier to ecological restoration in many parts of the world because of their impact on vegetation biomass. A common method for managing vertebrate herbivores is the use of exclosure fences, but very few studies have examined how small-scale structural refugia (e.g. logs) can mitigate grazing impacts. We examined how beetles responded to experimentally manipulated kangaroo Macropus giganteus grazing levels using both exclosure fences and addition of logs over a 16-month period. 2. We analysed beetle responses across (a) one-hectare sites, by focusing on the interaction between grazing level and log volume, and (b) microhabitats, by focusing on the interaction between grazing level and microhabitat structure (in open ground or at experimental logs). 3. At the site scale, we detected significant negative effects of grazing and positive effects of logs on beetle abundance and species richness. Beetle trophic groups responded in the same direction across grazing levels with herbivores, detritivores and predators all having higher abundance and species richness at low grazing levels. Logs applied at 20 t ha−1 in clumped arrangements had the largest positive effect on beetles at low grazing levels. At the microhabitat scale, beetles sampled adjacent to experimental logs showed an increase in abundance and species richness compared with beetles sampled from open ground, indicating logs are acting as microhabitat buffers from grazing. 4. Synthesis and applications. A reduction in grazing level had benefits for the abundance and species richness of beetles at the site scale. Further benefits were achieved at both site and microhabitat scales when logs are used in combination with exclosure fencing. For ecological restoration, exclosure fences and logs can be used to manage the impacts of vertebrate herbivores at different spatial scales. The rapid response of beetles suggests there may be potential for cascading effects on other biota as a consequence of reduced grazing, including increased food availability for insectivorous vertebrates.

At the interface of historical and present-day ecology: ground beetles in woodlands and open habitats in Upper Galilee (Israel)

Mediterranean landscapes have been used by humans for thousands of years, particularly some areas of the East Mediterranean, e.g. in Israel. This land use has had profound effects on the dynamics of the woodlands in time and space, with the result that woodland regeneration has only been possible during periods of low human population density and hence low levels of grazing. The aim of this paper is therefore to find out how woodland species have been able to cope with the rapidly changing habitats. For this purpose, ground beetles were sampled over a period of one year using 10 pitfall traps per study site at two sites located in the Upper Galilee (northern Israel). The sites comprise two old-growth woodlands, two recent woodlands and two open habitats. The wing development of all sampled species was checked. Carabid beetles belonging to 21 genera and 34 species were found. Most individuals were found in old-growth woodlands On the basis of a detrended correspondence analysis (DCA), the habitat preferences of three ground beetle groups could be distinguished: old-growth woodland species, species of recent woodlands and species of open habitats. We found that two-thirds of the group of open habitat species are brachypterous and three out of the four woodland species are macropterous. Since woodlands with a long ecological continuity are also important for other groups of organisms such as saproxylic beetles, we recommend the conservation of all woodland development stages in the study area.

Effects of Grazing Intensity, Precipitation, and Temperature on Forage Production

Abstract Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass ( Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ± animal unit months [AUM] · ha -1 ), moderate grazing (2.7 ± AUM · ha -1 ), heavy grazing (4.4 ± AUM · ha -1 ), and extreme grazing (6.9 ± AUM · ha -1 ; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha -1 ), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha -1 less on the ungrazed treatment and 909 kg · ha -1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha -1 ), moderate (4 360 kg · ha -1 ), and heavy treatments (4 362 kg · ha -1 ; P s 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.

Indirect effects of exotic grazers: livestock decreases the nutrient content of refuse dumps of leaf‐cutting ants through vegetation impoverishment

1 We present evidence of how exotic grazers can indirectly change the nutrient availability on the soil surface by affecting the quality of refuse dumps of leaf-cutting ants through changes in vegetation. Understanding the mechanisms involved in this process is vital to propose proper control and restoration practices. 2 In the Monte Desert of Argentina, we sampled seven paddocks with similar environmental conditions but different stocking rates (individuals ha−1). In each paddock we measured grazing intensity, plant species number and cover, leaf-cutting ant nest density, leaf-cutting ant diet and the nutrient content of the external ant refuse dumps and of the adjacent non-nest soils. We found higher content of N, C and P in refuse dumps than in non-nest soils, but the strength of this effect decreased with an increase in stocking rates. As stocking rate increased, plant richness and cover, the number of plant species harvested by ants and the nutrient content of their refuse dumps all decreased. Nest density was not affected by stocking rates. 3 These results suggests that livestock reduce plant richness and cover through grazing, affecting ant diet with the subsequent alteration of the nutrient content of their external refuse dumps. A decrease in the nutrient quality of the refuse dumps may affect plants that establish and grow on this substrate and the rate of nutrient cycling. 4 Synthesis and applications. We have shown that negative effects of exotic grazers on plants may spread throughout native insect herbivores to affect soil nutrient availability. These results can provide useful information to prevent soil impoverishment and restore the nutrient content of soils in this managed system. A slight reduction in stocking rates can restore the contribution of ants to soil fertility. Additionally, refuse dumps from paddocks with low grazing levels should be employed as fertilizer to restore soil quality in paddocks with high grazing intensities.

Impacts of Livestock Grazing and Tree Clearing on Birds of Woodland and Riparian Habitats

We investigated the impact of pastoral management on birds in subtropical grassy eucalypt woodland in southeastern Queensland, Australia, where the patterns of land management have made it possible to disentangle the effects of livestock grazing from those of tree clearing. We recorded changes in bird species composition, density, and relative abundance across two woodland habitat types (riparian and nonriparian) and two levels of clearing (wooded and nonwooded) and three levels of livestock grazing (low, moderate, and high) replicated over space (1000 km(2)) and time (2001-2002). We predicted that species that depend on understory vegetation would be most negatively affected by livestock grazing. A Bayesian generalized linear model showed that the level of grazing had the greatest effect when trees were present. When trees were absent, the impact of grazing was overshadowed by the effects of a lack of trees. Over 65% of species responded to different levels of grazing, and the abundance of 42% of species varied markedly with habitat and grazing. The most common response to grazing was high species relative abundance under low levels of grazing (28% of species), species absence at high levels of grazing (20%), and an increase in abundance with increasing grazing (18%). Despite having similar bird assemblages, the effect of grazing was stronger in riparian habitat than in adjacent woodland habitat. Our results suggest that any level of commercial livestock grazing is detrimental to some woodland birds, particularly the understory-dependant species, as predicted. Nevertheless, provided trees are not cleared, a rich and abundant bird fauna can coexist with moderate levels of grazing. Habitats with high levels of grazing, on the other hand, resulted in a species-poor bird assemblage dominated by birds that are increasing in abundance nationally.

Does vegetation cover affect the rate of capture of ground-active lizards in pitfall traps?

Pitfall traps are commonly used to capture terrestrial vertebrates, but it is not known whether differences in vegetation structure affect the efficiency of these traps. Studies that investigate the effects of fire, grazing or vegetation rehabilitation on faunal populations usually compare sites that differ in vegetation structure and the validity of using pitfall traps to sample populations under these circumstances is open to question. This study tests whether vegetation structure affects the rate at which lizards are captured in pitfall traps by cutting ground vegetation in a controlled experiment conducted in field enclosures. The study was undertaken in an area of mulga (Acacia aneura) shrubland in central Australia. Ground cover, consisting of grasses and forbs, was reduced from ~27% to 10% in treatment enclosures. These levels of cover correspond broadly to the range of ground covers encountered in this habitat, including areas with high and low levels of grazing. No difference was detected in the rate at which lizards were captured in enclosures where grass was cut compared with the control enclosures or rates of capture before grass was cut. These results indicate that pitfall trapping is a valid technique for comparing lizard populations in arid mulga shrublands within the range of vegetation covers used in this study, including areas that are subject to different levels of grazing.

Short-term impacts of aboveground herbivory (grasshopper) on the abundance and 14C activity of soil nematodes in conventional tillage and no-till agroecosytems

This study was designed to monitor the responses of soil nematodes to different levels of aboveground herbivory and to test the hypothesis that the low level of aboveground herbivory facilitates soil nematode activities and high herbivory suppresses soil nematode activities. Three herbivory levels were established by introducing four pairs, two pairs and no grasshoppers to graze on corn plants ( Zea mays) for 2 h. The experiment was conducted in conventional tillage (CT) and no-till (NT) agroecosystems at Georgia piedmont. In NT, bacterivorous and fungivorous nematode numbers were more abundant 24 h after herbivory treatment at high grazing level compared to controls, but this was not observed at low grazing level. In NT, the 14C activity of soil nematodes was significantly higher at both low and high grazing levels than the controls. In CT, however, we did not observe any effects caused by aboveground herbivory on the abundance and 14C activity of soil nematodes. The abundance of other trophic groups of soil nematodes (phytophages, predators and omnivores) was not affected by aboveground herbivory treatments under either NT or CT regimes. The curvilinear relationship between the nematode activity and the grazing intensity was not found in this study, we suggested that a grazing gradient of leaf area loss ranging from 0 to 100% might be more desirable for future research. We hypothesized that root associated materials might be more important to soil organisms in NT than in CT since the effect of aboveground herbivory on soil nematodes was only observed in NT.

Livestock grazing in subtropical pastures: steps in the analysis of attribute response and plant functional types

SummaryIn order to investigate the use of plant functional types as an alternative to floristic descriptions of response to grazing, we analysed plant communities from a cattle grazing experiment conducted in grassy eucalypt woodland in subtropical Queensland, Australia. The two variables analysed (landscape position and stocking rate) accounted for similar proportions of variation in the vegetation ground layer, although forbs were more sensitive to slope position and perennial grasses were more sensitive to stocking rate.As grazing pressure increased, perennial grasses declined, while the relative proportion of forbs and annual grasses increased. Detailed functional group analyses were conducted for the perennial grass and forb life‐forms. Annual grasses were represented by only two species, preventing identification of functional types within this life‐form.We conducted a five‐step analysis for both perennial grasses and forbs as follows: (i) defining grazing‐related species response groups; (ii) defining species groups based on natural attribute correlations; (iii) identifying attributes that changed significantly with grazing; (iv) identifying syndromes by relating (ii) and (iii); (v) describing functional types from (iii) and (iv), and assessing them against actual species response.Eight grass and eight forb functional types were identified. Of the taxa that had an observed response to grazing, 54% of the grass taxa and 57% of the forb taxa corresponded to one of these functional types in terms of meeting both grazing response and trait criteria. The five‐stage analysis provided a comprehensive but complex approach to functional type identification.The functional types identified can be summarized as follows. Low levels of grazing were associated with more medium‐sized, moderately leafy perennial grasses with wind‐dispersed or adhesive seeds, and more erect or twining forbs with large to medium sized seeds. High levels of grazing were associated with: more annual grasses; low‐growing leafy perennial grasses with small seeds having no dispersal appendages; mat‐forming large‐seeded forbs; and low‐growing, scrambling, small‐seeded forbs.

Grazing‐activated production of dimethyl sulfide (DMS) by two clones of Emiliania huxleyi

Emiliania huxleyi clones CCMP 370 and CCMP 373 produced similar amounts of dimethylsulfoniopropionate (DMSP) during axenic exponential growth, averaging 109 mM internal DMSP. Both clones had detectable DMSP lyase activity, as measured by production of dimethyl sulfide (DMS) during in vitro assays of crude cell preparations, but activities and conditions differed considerably between clones. Clone 373 had high activity; clone 370 had low activity and required chloride. For both strains, enzyme activity per cell was constant during exponential growth, but little DMS was produced by healthy cells. Rather, DMS production was activated when cells were subjected to physical or chemical stresses that caused cell lysis. We propose that DMSP lyase and DMSP are segregated within these cells and reaction only under conditions that result in cell stress or damage. Such activation occurs during microzooplankton grazing. When these clones were grazed by the dinoflagellate Oxyrrhis marina, DMS was produced; ungrazed cells, as well as those exposed to grazer exudates and associated bacteria, generated no DMS. Grazing of clone 373 produced much more DMS than grazing of clone 370, consistent with their relative in vitro DMSP lyase activities. DMS was only generated when cells were actually being grazed, indicating that ingested cells were responsible for the DMS formation. We suggest that even low levels of grazing can greatly accelerate DMS production.