Livestock Grazing Intensity Research Articles

Combined effects of grazing and climate warming drive shrub dominance on the Tibetan Plateau

Encroachment of shrubs into the unique pastoral grassland ecosystems of the Tibetan Plateau has significant impact on ecosystem services, especially forage production. We developed a process-based ecohydrological model to identify the relative importance of the main drivers of shrub encroachment for the alpine meadows within the Qinghai province. Specifically, we explored the effects of summer livestock grazing (intensity and type of livestock) together with the effects of climate warming, including interactions between herbaceous and woody vegetation and feedback loops between soil, water and vegetation. Under current climatic conditions and a traditional herd composition, an increasing grazing intensity above a threshold value of 0.32±0.10 large stock units (LSU) ha−1 day−1 changes the vegetation composition from herbaceous towards a woody and bare soil dominated system. Very high grazing intensity (above 0.8 LSU ha−1 day−1) leads to a complete loss of any vegetation. Under warmer conditions, the vegetation showed a higher resilience against livestock farming. This resilience is enhanced when the herd has a higher browser:grazer ratio. A cooler climate has a shrub encroaching effect, whereas warmer conditions increase the cover of the herbaceous vegetation. This effect was primarily due to season length and an accompanied competitive loss of slower growing shrubs, rather than evaporative water loss leading to less soil water in deeper soil layers for deeper rooting shrubs. If climate warming is driving current shrub encroachment, we conclude it is only indirectly so. It would be manifest by an advancing shrubline and could be regarded as a climatic escape of specific shrub species such as Potentilla fruticosa. Under the recent high intensity of grazing, only herding by more browsing animals can potentially prevent both shrub encroachment and the complete loss of herbaceous vegetation.

The Faxinal System: Forest fragmentation and soil degradation on the communal grazing land

The Brazilian faxinal is a traditional agrosilvopastoral system, which combines extensive grazing, subsistence cropping and low impact forest extraction, managed within a communal property system. Today it is at serious risk of disappearing due to increasing grazing pressure and logging activities that are leading to environmental problems such as forest fragmentation and soil degradation. The objectives of the study were to: a) evaluate soil physical degradation levels in different grazing areas within the faxinal system; and b) correlate soil degradation, fodder quantity and livestock dynamics in different pasture areas according to the household's location. Landscape mapping, vegetation surveys, and livestock grazing dynamics were assessed. In addition, soil physical parameters were evaluated for each land use (e.g., resistance, bulk density, porosity, moisture, and water infiltration rates). Results showed that livestock grazing and household locations are the main driving forces that lead to forest fragmentation. The household location creates three interrelated gradients in the communal grazing land: 1) soil physical degradation decreases from the pasture areas to araucaria forests; 2) fodder quantity decreases from pastures to araucaria forests; and 3) the livestock grazing intensity decreases from pastures to araucaria forests. In addition, some management practices to mitigate land degradation, including improvement of pastures, installation of removable troughs for drinking water in the upland areas and restriction of livestock from the riparian zone, have been proposed.

Coupled human-climate signals on the fire history of upper Cachapoal Valley, Mediterranean Andes of Chile, since 1201 CE

Abstract The long-term history of fire regimes in the Mediterranean Andes of Chile is almost unknown. Subalpine woodlands of Austrocedrus chilensis include long-lived trees resilient to low-intensity fires, which can provide valuable tree-ring-based information about fire history. In this work, we performed an annually resolved multicentury reconstruction of past fires from fire-scar records identified in relict Austrocedrus wood found on steep highly-eroded and rocky slopes with coarser fuel structure in the upper Cachapoal Valley, central Andes of Chile. We compared this fire record with historical land-use changes and extensive reconstructions of regional precipitation and temperature, as well as large-scale climatic patterns. The highest fire frequencies were recorded in the Spanish settlement period (1541–1750), when land-clearing activities, cattle ranching, agriculture, and mining practices became widespread after the Spanish conquest. At an interannual time scale, fire occurrence and precipitation were unconnected during the Spanish settlement. By contrast, in the indigenous period (1200–1540), under the influence of the aboriginal Chiquillanes people, fires occurred in wet years with high vegetation productivity. In the livestock grazing period (1751–1950), when large cattle ranches were established, fires occurred in dry years after a wet year. Fires in this period were likely ignited under conditions of high fuel flammability to improve plant production and promote intensive livestock grazing. At a multidecadal time scale, fires were more frequent in cold periods throughout the whole record. These findings suggest that herbaceous fuel accumulation and flammability, modulated by climate variation and human land uses, were the main factors promoting fires spread in this Mediterranean subalpine area. Our research emphasizes the importance of relict Austrocedrus wood for fire history reconstruction and expands knowledge about fire regime shifts over the past eight centuries in southern South America.

The role of landscape heterogeneity in regulating plant functional diversity under different precipitation and grazing regimes in semi-arid savannas

1. Savanna systems exhibit a high plant functional diversity. While aridity and livestock grazing intensity have been widely discussed as drivers of savanna vegetation composition, physical soil properties have received less attention. Since savannas can show local differences in soil properties, these might act as environmental filters and affect plant diversity and ecosystem functioning at the patch scale. However, research on the link between savanna vegetation diversity and ecosystem function is widely missing.2. In this study, we aim at understanding the impact of local heterogeneity in soil conditions on plant diversity and on ecosystem functions. For this, we used the ecohydrological savanna model EcoHyD. The model simulates the fate of multiple plant functional types and their interactions with local biotic and abiotic conditions. We applied the model to a set of different landscapes under a wide range of livestock grazing and precipitation scenarios to assess the impact of local heterogeneity in soil conditions on the composition and diversity of plant functional types and on ecosystem functions.3. Comparisons between homogeneous and heterogeneous landscapes revealed that landscape soil heterogeneity allowed for a higher functional diversity of vegetation under conditions of high competition, i.e. scenarios of low grazing stress. However, landscape heterogeneity did not have this effect under low grazing stress in combination with high mean annual precipitation. Further, landscape heterogeneity led to a higher community biomass, especially for lower rainfall conditions, but also dependent on grazing stress. Total transpiration of the plant community decreased in heterogeneous landscapes under arid conditions.4. This study highlights that local soil conditions interact with precipitation and grazing in driving savanna vegetation. It clearly shows that vegetation diversity and resulting ecosystem functioning can be driven by landscape heterogeneity. We therefore suggest that future research on ecosystem functioning of savanna systems should focus on the links between local environmental conditions via plant functional diversity to ecosystem functioning.

How does grazing management influence the functional diversity of oak woodland ecosystems? A plant trait approach

Traditional approaches to conservation often focus on plant species composition. In contrast, trait-based approaches highlight the role plant species play in ecosystem function, with a focus on functional diversity and its importance for ecosystem resilience. Here we utilise a plant-trait approach to explore the association between livestock grazing intensity and plant functional diversity in Atlantic oak woodlands, a conservation priority habitat. In two historically un-grazed woodlands (subject to periods of light sheep grazing in winter) paired with two grazed woodlands (intensively grazed by sheep or feral goats), in north-west Wales, UK, field plant-trait data were recorded in three (30 × 4 m) plots per woodland for trees, saplings and understory plants. For trees and saplings, plant-trait data from the field (specific leaf area (SLA) and leaf dry matter content (LDMC)) were combined with plant tolerance indices from the scientific literature (shade, drought and water-logging tolerance) and used to calculate community weighted means (CWM) and functional diversity for plot-level communities. Three plant traits (LDMC, mean foliage height and growth form) and two Ellenberg indices (light and moisture) were combined to calculate CWM and functional diversity for understory plant communities. Tree and sapling communities from grazed woodlands were characterised by response traits associated with grazing avoidance strategies (high LDMC, low SLA), and higher shade – and drought-tolerance scores but lower water-logging-tolerance scores than in un-grazed woodlands. Tree and sapling communities in the un-grazed woodlands had greater seedling establishment, sapling recruitment and functional diversity than in the grazed woodlands. Plant-trait values and functional diversity did not differ with grazing intensity for understory plants. Land managers are increasingly being asked to manage semi-natural habitats for ‘resilience to future events’ such as droughts or floods. Here we demonstrate how a plant-trait approach, including assessment of community-level tolerance indices, allows us to infer potential associations between grazing management, functional diversity and ecosystem resilience.

Livestock grazing reinforces the competitive exclusion of small‐bodied birds by large aggressive birds

Abstract Grazing by domestic livestock is sometimes promoted as a management tool to benefit biodiversity. In many situations, however, it can produce negative outcomes. Here, we examine the impacts of recent and historic livestock grazing on bird communities in the semi‐arid woodlands in eastern Australia, testing the notion that grazing removes the suppressive effect of structurally complex vegetation on miners, thereby reducing the richness and abundance of small birds. We used time‐ and area‐limited searches of 108 sites varying in livestock grazing history and intensity, to explore the direct and indirect effects of grazing, habitat complexity and the abundance of aggressive, large‐bodied birds on smaller‐bodied birds using two‐way analysis of variance and structural equation modelling. Small birds were less abundant and had lower richness in the presence of miners. Our structural equation models indicated that recent grazing had direct suppressive effects on the abundance of miners, and both richness and abundance of all but the largest‐bodied bird groups. However, higher levels of historic livestock grazing reinforced the competitive exclusion of the six small‐bodied bird groups (insectivores, nectarivores, declining woodland birds, small ground‐foraging birds, all small birds and all non‐miners) by aggressive miners via reductions in habitat complexity. Moreover, the strength of any suppressive effects on small birds or positive effects on large birds by miners increased with increasing miner abundance. Synthesis and applications. Our results highlight the importance of vegetation structural complexity, not only for providing habitat for woodland birds, but also as barriers to the invasion and competitive dominance of miners. Our findings suggest that management actions aimed at reducing tree and shrub density to promote open woodlands are likely to have significant negative consequences for the conservation of small woodland birds.

The effects of habitat variables and land use on breeding birds in remnant wetland strips in an arid, rural landscape

The Jordan Valley exemplifies the pressure of multiple human actions including intensive livestock grazing and agriculture on bird diversity. The abundances and occurrence of breeding birds were studied along remnant perennial streams which flow into the River Jordan. A patch – landscape approach was used to study the influences of vegetation cover and disturbances at the local and landscape scales. For 21 species, Principal Component Analysis was used to reveal the importance of each spatial scale and relationships with habitat variables were modeled. The abundances and occurrences of 57% of the species were predicted by local habitat variables only, while most others were apparently influenced by a mixture of habitat and landscape factors. Birds with restricted distribution were associated with less degraded wetland habitat strips with heterogeneous vegetation including reed beds and inundated Tamarix thickets. Some species were negatively influenced by intensive grazing and the spread of invasive mesquite Prosopis juliflora. Most species appeared to be tolerant to low levels of grazing within the habitat and current land use in the surrounding landscape. Based on the results, we emphasize the importance of protecting and managing remnant strips or patches of natural and semi-natural wetland habitats in the Jordan Valley.

Mechanisms regulating the productivity and stability of artificial grasslands in China: Issues, progress, and prospects

China has 400 million hectares of grasslands, occupying 41.7% of the country’s total land area. Due to the overexploitation of grassland’s production functions and the neglect of its ecological functions, intensive livestock grazing in recent decades has resulted in widespread grassland degradation, reduction in ecosystem services, and imbalance between forage production and livestock demands in China. Compared to natural grasslands, artificial grasslands can increase forage yield up to 10–20 times. The development of high-quality artificial grasslands could fundamentally ease the severe shortage of forage supply, break the bottleneck in meat and milk production, curb grassland degradation caused by overgrazing, and thereby restore grassland ecological functions. Therefore, understanding the mechanisms that regulate the productivity and stability of artificial grasslands is a major national strategic need in order to transform the practices of sustainable livestock production based on the scientific and technological advancements, and to promote national ecological security, food security, and the development of ecological civilization. In this study, we examined theoretical basis underlying the regulations of artificial grassland productivity and stability, including theories of ecological stoichiometry, niche differentiation, compensation, mutualism, grazing optimization, and intermediate disturbance. Then, we reviewed current research status and the latest progress that has made in this field. Finally, we proposed fundamental research questions that need to be fully addressed in future studies, regarding the effects of stoichiometry of key nutrient elements, coupled water and nutrient availability, mutualism between forage species and soil microbes, and complementarity of functional traits and multiple forage species on plant carbon assimilation, growth, reproduction, forage quality, biomass allocation, primary productivity, and ecosystem stability. We also highlighted several key biological and ecological mechanisms regulating the productivity and stability of artificial grasslands.

Comparison of Modeling Grassland Degradation with and without Considering Localized Spatial Associations in Vegetation Changing Patterns

Grassland ecosystems worldwide are confronted with degradation. It is of great importance to understand long-term trajectory patterns of grassland vegetation by advanced analytical models. This study proposes a new approach called a binary logistic regression model with neighborhood interactions, or BLR-NIs, which is based on binary logistic regression (BLR), but fully considers the spatio-temporally localized spatial associations or characterization of neighborhood interactions (NIs) in the patterns of grassland vegetation. The BLR-NIs model was applied to a modeled vegetation degradation of grasslands in the Xilin river basin, Inner Mongolia, China. Residual trend analysis on the normalized difference vegetation index (RESTREND-NDVI), which excluded the climatic impact on vegetation dynamics, was adopted as a preprocessing step to derive three human-induced trajectory patterns (vegetation degradation, vegetation recovery, and no significant change in vegetation) during two consecutive periods, T1 (2000–2008) and T2 (2007–2015). Human activities, including livestock grazing intensity and transportation accessibility measured by road network density, were included as explanatory variables for vegetation degradation, which was defined for locations if vegetation recovery or no significant change in vegetation in T1 and vegetation degradation in T2 were observed. Our work compared the results of BLR-NIs and the traditional BLR model that did not consider NIs. The study showed that: (1) both grazing intensity and road density had a positive correlation to vegetation degradation based on the traditional BLR model; (2) only road density was found to positively correlate to vegetation degradation by the BLR-NIs model; NIs appeared to be critical factors to predict vegetation degradation; and (3) including NIs in the BLR model improved the model performance substantially. The study provided evidence for the importance of including localized spatial associations between the trajectory patterns for mapping vegetation degradation, which has practical implications for designing management policies to counterpart grassland degradation in arid and semi-arid areas.

Temporary grazing exclusion promotes rapid recovery of species richness and productivity in a long‐term overgrazed Campos grassland

Moderate grazing intensity is considered the basic requirement to enhance ecosystem function in grasslands. Yet, deterioration by overgrazing is common in many biomes, including Campos grasslands in South America. Understanding how grazing management can lead to recovery of ecosystem function is essential to design and implement effective strategies for sustainable use of this resource. In a long‐term field experiment carried out in Southern Brazil, we studied the effects of temporal grazing exclusions (spring or fall) at moderate and severe livestock grazing intensities (maintained by adjusting contrasting forage allowances) on the species richness, botanical composition, forage mass, sward height, and photosynthetic active radiation intercepted. The experiment was arranged in a completely randomized design with three replications of grazing exclusions, applied simultaneously at moderate and severe grazing intensities. Moderate grazing intensity showed a bimodal structure of shorter and taller canopies, and high species richness. Severe grazing created a shorter and homogeneous sward structure characterized by less standing biomass and species loss. In response to grazing exclusions, sward height, standing biomass, and light interception recovered almost to the levels of moderate grazing. Further, within 2 years grass species richness increased and botanical composition changed toward grasses with erect habit prevailing in moderate grazing intensity. Our study confirms that (1) moderate grazing intensities allow the coexistence of high number of species and (2) spring grazing exclusions of long‐term overgrazed grasslands can lead to a quick start to recover the grass species richness, primary productivity, and species composition like that prevailing in well‐managed grasslands.

Restoring the perennial Great Ruaha River using ecohydrology, engineering and governance methods in Tanzania

The Great Ruaha River (GRR) in Tanzania was perennial before 1993. Its source, the Usangu wetlands, was also perennial. Since then, the GRR has started drying out during the dry season, with a trend towards earlier and longer periods of drying. This drying process degrades the surrounding ecosystems along the entire length of the GRR, including the Ruaha National Park (RNP) and impacts human livelihoods throughout its course; it also impairs the economy of Tanzania through reduced hydropower generation at the Mtera and Kidatu power plants. The Usangu wetlands dried up in 2000, 2002 and 2005 during the dry season and its areal extent has been shrinking. Intensive livestock grazing and both dry and wet season irrigated agriculture in the Usangu wetlands, were the main reasons for this water crisis. In 2006, the Government of Tanzania moved to address the crisis by removing livestock from the Usangu wetlands, attempting to regulate water use in the GRR catchment and expanding the RNP to include the Usangu wetlands.The present study uses satellite radar altimetry data dated 1992 to 2015 for the Usangu wetlands, verified using data from water level loggers, to assess the effects of these hydrological changes. The combined data sets show that the perennial Usangu wetlands have become re-established, though somewhat diminished in size, and that as a result of eutrophication from fertilizers leached from irrigated fields, 95% of their surface is now covered by floating vegetation, resulting in reduced loss of water by evaporation. This reduction has extended the water flow to the GRR by one to two months. These figures highlight the important role played by the wetlands vegetation in controlling the water budget.The hydrological model of the Usangu wetlands was further developed and verified, and then used to justify the construction of a low-level V-notch weir at the outlet of the Usangu wetlands; by slowing down the outflow from the wetlands, this construction would reduce the period of zero flow in the GRR during the dry season by one to two months. Additional ecohydrological solutions based on the improvement of water governance upstream of the Usangu wetlands, such as controlling rice and horticultural irrigation activities along the length of the GRR, should be integrated with this engineering solution; this would meet the hydrological needs of the water users all along the GRR.

Livestock activity increases exotic plant richness, but wildlife increases native richness, with stronger effects under low productivity

Abstract Grazing by domestic livestock is one of the most widespread land uses world‐wide, particularly in rangelands, where it co‐occurs with grazing by wild herbivores. Grazing effects on plant diversity are likely to depend on intensity of grazing, herbivore type, co‐evolution with plants and prevailing environmental conditions. We collected data on climate, plant productivity, soil properties, grazing intensity and herbivore type, and we measured their effects on plant species richness from 451 sites across 0.4 M km2 of semi‐arid rangelands in eastern Australia. We used structural equation modelling to examine the direct and indirect effects of increasing grazing intensity by different herbivores (cattle, sheep, kangaroos, rabbits) on native and exotic plant species richness across all sites, and in subsets focusing on three woodland communities spanning a gradient in productivity. Direct effects of grazing by all herbivores were strongest under low productivity but waned with increasing productivity. Increases in the intensity of recent and historic livestock grazing corresponded with greater exotic plant richness under low productivity and less native plant richness under both low and moderate productivity. Rabbit effects were greatest under moderate productivity. Overall, the effects of kangaroos were benign. Grazing indirectly affected native and exotic plant richness by increasing soil phosphorus and reducing soil health (i.e. nutrient cycling). Synthesis and applications. Our study shows that livestock grazing increases exotic species richness but reduces native richness, while kangaroo grazing increases native richness in environments with low productivity. The results provide clear messages for land managers and policy makers: (1) the coexistence of livestock grazing and plant diversity is only possible within more productive environments and (2) grazing under low or moderate productivity will impact upon native and exotic plant richness.

Age structure and trends in annual stem increment of Larix sibirica in two neighboring Mongolian forest–steppe regions differing in land use history

Selective logging affects climate sensitivity of Larix sibirica in the Mongolian forest–steppe mediated by changes in age and stand structure. Climate warming increasingly limits the productivity of boreal forests via increased drought stress, especially at the southern fringe of the biome. The southernmost boreal forests are exposed to more intensive human disturbance than most forests at more northern latitudes. We asked the question of how forest use through logging and moderate forest grazing interferes with the climate response of the annual radial stem increment. We conducted a case study in Larix sibirica stands of the Mongolian forest–steppe involving two neighboring forest regions (20 km distance) differing in logging and grazing intensity. One site was subjected to heavy logging until 25 years ago and low intensity of livestock grazing; another site was exposed to moderate selective logging and higher, but still moderate livestock numbers. While the differences in grazing had no detectable effect, former heavy logging led to younger and more even-aged forest stands. Forests at both sites showed recent increases in missing-ring frequency, which probably indicated increased drought vulnerability. Climate-response analysis indicated that heavy logging 25 years ago was associated with high sensitivity of stemwood formation to high summer (especially June) temperatures. These findings suggest that: (1) recent logging under the conditions of climate warming has increased the sensitivity of tree growth to temperature in these southern boreal forests; (2) high replication at the stand level is needed to avoid bias in dendrochronological analyses in regions exposed to spatially heterogeneous logging intensities.

The deep human prehistory of global tropical forests and its relevance for modern conservation.

Significant human impacts on tropical forests have been considered the preserve of recent societies, linked to large-scale deforestation, extensive and intensive agriculture, resource mining, livestock grazing and urban settlement. Cumulative archaeological evidence now demonstrates, however, that Homo sapiens has actively manipulated tropical forest ecologies for at least 45,000 years. It is clear that these millennia of impacts need to be taken into account when studying and conserving tropical forest ecosystems today. Nevertheless, archaeology has so far provided only limited practical insight into contemporary human-tropical forest interactions. Here, we review significant archaeological evidence for the impacts of past hunter-gatherers, agriculturalists and urban settlements on global tropical forests. We compare the challenges faced, as well as the solutions adopted, by these groups with those confronting present-day societies, which also rely on tropical forests for a variety of ecosystem services. We emphasize archaeology's importance not only in promoting natural and cultural heritage in tropical forests, but also in taking an active role to inform modern conservation and policy-making.

Understory Responses to Tree Thinning and Seeding Indicate Stability of Degraded Pinyon-Juniper Woodlands

Depauperate understory plant communities resulting from intensive livestock grazing in pinyon-juniper woodlands of the western United States may represent degraded stable states, resistant to ecological restoration treatments. In this study, we analyzed 10-yr understory plant community responses to restoration treatments that included tree thinning to approximate historical densities of pinyon pine (Pinus edulis) and juniper (Juniperus osteosperma), scattering of thinning slash to improve soil conditions, and seeding at two woodland sites (Craig Ranch and Goose Pond) in northwestern Arizona. Results showed that thinning resulted in significant reductions in tree density at both sites, as well as reductions in tree basal area at the Goose Pond site. Boles, branches, and tops of the thinned trees scattered across the study sites resulted in few changes to woody surface fuel loading. Thinning and addition of woody material, along with seeding, resulted in only minor changes in understory cover and species richness at both sites. However, plant cover and species richness were both negatively correlated with tree density. Degraded conditions at the sites appeared to be stable, and we suggest that treatments implemented in our studies may have not been intensive enough to produce significant understory responses and meet restoration objectives. Managers aiming to restore understory diversity at similar sites may be required to use heavier thinning prescriptions and repeated seeding. More work is needed to test new restoration approaches that are designed to drive degraded pinyon-juniper woodlands over resilience thresholds toward more diverse understory communities.

Behavioural flexibility does not prevent numerical declines of harvester ants under intense livestock grazing

1. Human‐induced rapid environmental change may decrease food resources and create unfavourable conditions for native species. Organisms showing a flexible foraging behaviour can exploit novel or alternative foods and are more likely to persist, whereas less flexible organisms might suffer starvation and numerical reductions.2. This study assessed whether declines in the quality and availability of seeds prompted by grazing provoke behavioural and numerical responses in Pogonomyrmex mendozanus ants, and aimed to test whether behavioural flexibility buffers habitat degradation and prevents numerical declines.3. Heavy grazing caused seed reductions, especially of the highly consumed and preferred grass seeds, and triggered two kinds of ant responses. Ants expanded their diet by incorporating a greater proportion of non‐seed items, and they reduced foraging activity. As a consequence, the rate of food intake per colony lessened, particularly that of carbohydrate‐rich seeds like grass seeds. Colony density under heavy grazing also fell.4. Habitat degradation triggered a cascade of mechanisms that starts with a decrease in the seed resources and continues with changes in ant behaviour. However, behavioural responses were insufficient to prevent ant numerical declines. The results of this study suggest that the reduction in the colony density under habitat degradation was provoked by ant nutritional deficit and starvation, and predict a deterioration in body condition, colony performance and reproduction of ants, which deserve further assessment.

Livestock grazing in intermountain depressional wetlands: effects on breeding waterfowl

Livestock grazing is a prevalent land use in western North American intermountain wetlands, and physical and biotic changes related to grazing-related disturbance can potentially limit wetland habitat value for waterfowl. We evaluated breeding waterfowl use in 34 wetlands in relation to water retention, amount of wetlands on the landscape, and livestock grazing intensity. The study was conducted over 2 years in the southern intermountain region of British Columbia, Canada. For a subset of 17 wetlands, we measured aquatic invertebrate abundance over 1 year. Waterfowl breeding pairs and broods were classified into three functional groups: dabbling ducks, and two types of diving ducks, overwater and cavity nesters. We evaluated candidate models with variables considered singly and in combination using the Akaike Information Criterion. When selected, bare ground (an indicator of grazing intensity) and wetland density were negatively associated with breeding use while wetland fullness and invertebrate density were positively associated. Each factor was a significant predictor in at least one of the models, but unexpectedly, grazing intensity was the most consistent predictor of waterfowl wetland use (e.g., it was present in more ‘best models’ than wetland fullness). Grazing was associated with declines in the number of waterfowl pairs and broods, likely mediated through effects on wetland vegetation and aquatic macroinvertebrates. Models with site- and landscape-scale variables generally performed better than simpler models. Waterfowl breeding use of wetlands can be improved by reduced livestock grazing intensity adjacent to wetlands and by grazing later in the season. Wetland water retention is also an important constraint on waterfowl use of wetlands and may become more limiting with a shifting climate.

Seasonality constraints to livestock grazing intensity.

Increasing food production is essential to meet the future food demand of a growing world population. In light of pressing sustainability challenges such as climate change and the importance of the global livestock system for food security as well as GHG emissions, finding ways to increasing food production sustainably and without increasing competition for food crops is essential. Yet, many unknowns relate to livestock grazing, in particular grazing intensity, an essential variable to assess the sustainability of livestock systems. Here, we explore ecological limits to grazing intensity (GI; i.e. the fraction of net primary production consumed by grazing animals) by analysing the role of seasonality in natural grasslands. We estimate seasonal limitations to GI by combining monthly net primary production data and a map of global livestock distribution with assumptions on the length of nonfavourable periods that can be bridged by livestock (e.g. by browsing dead standing biomass, storage systems or biomass conservation). This allows us to derive a seasonality-limited potential GI, which we compare with the GI prevailing in 2000. We find that GI in 2000 lies below its potential on 39% of the total global natural grasslands, which has a potential for increasing biomass extraction of up to 181 MtC/yr. In contrast, on 61% of the area GI exceeds the potential, made possible by management. Mobilizing this potential could increase milk production by 5%, meat production by 4% or contribute to free up to 2.8 Mio km² of grassland area at the global scale if the numerous socio-ecological constraints can be overcome. We discuss socio-ecological trade-offs, which may reduce the estimated potential considerably and require the establishment of sound monitoring systems and an improved understanding of livestock system's role in the Earth system.

Spatio-temporal patterns of birch regrowth in a Western Norwegian treeline ecotone

The study investigates spatio-temporal patterns of birch regrowth in a mountain valley in which intensive livestock grazing was formerly practised. Vegetation changes were identified through analysis of three sets of aerial photographs. The results of GIS analyses, one-way ANOVA and PCA showed that regrowth patterns are complex. In the early phase of succession, grazing history has a strong impact on where new forest establishes, both at a distance from the seasonal farmsteads where grazing intensity prior to abandonment was highest, and close to previously existing forest. Sprouting is most likely to be the dominating regeneration strategy in this early phase. In a later phase of succession, the impact of grazing history on forest distribution patterns decreases, as exemplified by the increasing distance from existing forest. The largest amounts of birch forest then establish in warm locations with moderate moisture. Protection against wind appears to be important for birch establishment.

The Influences of Climate Change and Human Activities on Vegetation Dynamics in the Qinghai-Tibet Plateau

Grasslands occupy nearly three quarters of the land surface of the Qinghai-Tibet plateau (QTP) and play a critical role in regulating the ecological functions of the QTP. Ongoing climate change and human interference have greatly affected grasslands on the QTP. Differentiating human-induced and climate-driven vegetation changes is vital for both ecological understanding and the management of husbandry. In this study, we employed statistical analysis of annual records, various sources of remote sensing data, and an ecosystem process model to calculate the relative contribution of climate and human activities to vegetation vigor on the QTP. The temperature, precipitation and the intensity and spatial pattern of livestock grazing differed between the periods prior to and after the year 2000, which led to different vegetation dynamics. Overall, increased temperature and enhanced precipitation favored vegetation growth. However, their combined effects exhibited strong spatial heterogeneity. Specifically, increased temperature restrained vegetation growth in dry steppe regions during a period of slightly increasing precipitation from 1986 to 2000 and in meadow regions during a period of precipitation decline during 2000–2011, thereby making precipitation a dominant factor. An increase in precipitation tended to enhance vegetation growth in wet meadow regions during warm periods, and temperature was the limiting factor in Tibet during dry periods. The dominant role played by climate and human activities differed with location and targeted time period. Areas dominated by human activities are much smaller than those dominated by climate. The effects of grazing on grassland pasture were more obvious under unfavorable climate conditions than under suitable ones.