Winter Forage Availability Research Articles

Plant and mule deer responses to pinyon‐juniper removal by three mechanical methods

AbstractLand managers in western North America often reverse succession by removing pinyon (Pinus spp.) and juniper (Juniperus spp.) trees to reduce fire risk and increase forage for wildlife and livestock. Because prescribed fire carries inherent risks, mechanical methods such as chaining, roller‐chopping, and mastication are often used. Mechanical methods differ in cost and the size of woody debris produced, and may differentially impact plant and animal responses. We implemented a randomized, complete‐block, split‐plot experiment in December 2011 in the Piceance Basin, northwestern Colorado, USA, to compare mechanical methods and to explore seeding (subplot) interactions. We assessed vegetation 1‐, 2‐, 5‐, and 6‐years post‐treatment, and mule deer (Odocoileus hemionus) response via GPS locations 3–8 years post‐treatment. By 2016, treated plots had 3–5 times higher perennial grass cover and ~10 times higher cheatgrass (Bromus tectorum) cover than untreated control plots. Roller‐chopped plots had both the highest non‐native annual forb cover, and when seeded, the highest density of bitterbrush (Purshia tridentata), a nutritious shrub used by mule deer. Masticated plots had higher bitterbrush use during summer and fall, leaving less forage available for winter. Days of winter mule deer use from GPS point locations in chained and roller‐chopped plots was ~70% higher than in control plots, while winter use in masticated plots was similar to control plots. Mule deer use appears related to a combination of hiding cover, resulting from residual woody debris, and winter forage availability. Roller‐chopped plots provide the best combination of hiding cover and winter forage, but mastication or chaining, applied leaving dispersed security cover, may be better options at large scales or when invasive species concerns exist.

Optimal foraging by a large ungulate in an extreme environment: Wild mountain reindeer select snow-free feeding habitats in winter.

Optimal foraging models predict that individual animals will optimize net energy gain by intensifying forage activity and/or reducing forage energy cost. Then, the free distribution model predicts an animal's distribution in a patchy landscape will match the distribution of the resources. If not modified by other factors, such patterns may be expected to be particularly explicit in variable and extreme, forage‐limited, and patchy environments, notably alpine and Arctic environments during winter. The large ungulate wild mountain reindeer (Rangifer tarandus tarandus) surviving in such environments is used as a model during the forage‐limited winter season. The largest wild reindeer area in Western Europe (Hardangervidda, 8130 km2) is actively managed to sustain 10,000–12,000 wild reindeer. Since 2001, 104 different individuals have been GPS‐tracked at 3‐hr intervals. In winter, mountain reindeer may either choose to seek out and forage in patchy snow‐free habitats, typically on top of wind‐blown ridges, or use energy‐demanding digging through the snow to reach ground forage (cratering). We use late April satellite data from Landsat 5 and 8 (30 × 30 m), airborne laser scanning subsampling (processed to 1 × 1 m grid), and topographic information (1 m resolution) derived from digital aerial photographs (0.25 × 0.25 m resolution) to delineate snow‐free patches, constituting less than 694 km2. By overlaying recorded wild reindeer GPS positions winters 2001–2017 (188,942 positions), we document a strong positive selection for snow‐free patches, which were used about four times more frequently than expected from a “random walk” model. On a daily basis, the preference for snow‐free areas was slightly stronger in the evenings. In the sustainable management of wild mountain reindeer, the area of snow‐free patches is an important predictor of winter forage availability and important winter source areas. It may be derived from remote sensing data.

Recent changes in mountain birch forest structure and understory vegetation depend on the seasonal timing of reindeer grazing

Abstract Subarctic forest‐tundra ecotones dominated by mountain birch (Betula pubescens ssp. czerepanovii) are an important habitat for semi‐domestic reindeer Rangifer tarandus. The seasonal timing of reindeer grazing may direct vegetation trajectories in these systems, because in the summer ranges, mountain birches are subjected to browsing, while in the winter ranges, reindeer feed on understorey vegetation and arboreal lichens but leave the mountain birches intact. Based on earlier research, we predicted that (a) summer browsing dampens ongoing vegetation ‘shrubification’ in semi‐dry and dry mountain birch forests and (b) ‘shrubification’ is accompanied by a decline in lichens. We tested these predictions through re‐analysing forest structure and understorey vegetation after 12 years in areas where winter and summer ranges had been separated since the 1980s. We also tested how changes in lichen abundances align with changes in shrub abundances through correlation analyses. The number of tall mountain birch seedlings had increased twice as fast in winter than summer ranges, while big mountain birches had increased in summer ranges. The dominant evergreen dwarf shrub mountain crowberry (Empetrum nigrum ssp. hermaphroditum) had increased to a greater extent in winter ranges in a semidry habitat, and to a greater extent in summer ranges in a dry habitat. Deciduous dwarf shrub and graminoid biomass had increased similarly in summer and winter ranges. We found no evidence to support that increasing shrub abundances had contributed to a decline in lichens; instead, the lichen cover increased with increasing number of mountain birch seedlings. Synthesis and application. The vegetation trajectories of dry and semi‐dry subarctic mountain birch forests depend greatly on whether the area is used as a winter or a summer range for the reindeer. The recent changes in vegetation are likely to lead to improved summer forage availability for the reindeer, while the opposite may be true for the winter forage availability.

Factors affecting deer pressure on forest regeneration: The roles of forest roads, visibility and forage availability.

Deer pressure on forest regeneration constitutes a serious problem in commercial forests in the northern hemisphere due to the increase in deer populations. However, other drivers, such as climate, landscape structure and the level of human activity, have a strong influence on deer pressure. The direct, density-related impacts of ungulates on forest regeneration have been well studied, but there is limited empirical evidence related to the indirect factors mentioned above. We conducted a field experiment in three forest divisions in Poland to evaluate the role of a common element of human infrastructure, i.e. small, unpaved forestry roads. Additionally, we assessed the modifying effect of visibility driven by vegetation cover and forage availability. The proximity of unpaved roads affected deer habitat use and foraging behaviour, and limited browsing pressure on regenerating forests. Low visibility and higher winter forage availability increased the probability of tree browsing. We observed different responses to roads in two deer species: red deer avoided roads, while roe deer browsed in the vicinity of roads. A typical forest network of unpaved roads creates a landscape of fear for red and roe deer, and limits browsing pressure on regenerating forests due to the changes in deer habitat use, activity patterns and foraging behaviour. Knowledge of the factors influencing browsing pressure can help to spatially optimise the application of protective measures for tree seedlings.

Mediterranean cork oak wooded grasslands: synergies and trade-offs between plant diversity, pasture production and soil carbon

Mediterranean wooded grasslands that emerge from silvopastoral activities are multifunctional systems that result in high biodiversity and offer ecosystem services such as forage production and soil carbon sequestration. During 3 years, ten grazed wooded grassland fields were studied in the Berchidda–Monti long-term observatory, located in NE Sardinia, Italy, with the aim of exploring the synergies and trade-offs between biodiversity and selected ecosystem services. Positions below and outside the canopy of three cork oak trees in each field were randomly selected to compare seasonal pasture production, pasture utilization rate by animals, botanical composition, biodiversity indicators (Shannon index and plant species richness) and soil organic carbon. In autumn, dry matter production of pasture was similar in the two positions; in two winters out of three it was greater below the trees than outside, and in spring it was greater outside than below the trees. While plant species richness and Shannon index were not significantly influenced by the position, the overall wooded grassland plant species richness was 31% higher than that outside of the tree crown. The soil organic carbon content in the 0–40-cm soil layer was also higher below the trees. Our findings highlight that if the main purpose of the wooded grasslands is to provide forage for grazing animals rather than conserving and/or enhancing plant diversity and soil fertility, the presence of trees constrains the overall forage productivity, although the greater forage availability in winter under the trees can contribute to improve the seasonal distribution of forage production.

Forage availability and moose winter browsing in forest landscapes

In a large-scale survey, comprising 38 landscapes throughout Sweden, we measured winter forage availability and use by moose within different forest- and land types, and also at three different spatial scales: plot, tract and area.Measured as percent cover of browse species within moose browsing range, young forests contained significantly more browse (16.5 ± 1.20%: mean ± SE) compared with older forests (6.7 ± 0.57%) or non-forest land (5.9 ± 0.67%). Total cover of browse species increased with increasing mean tree height in forests, and peaked at around 22% when the trees were 3–5 m. The relative consumption was highest in young forests (9.2 ± 0.98%) compared with non-forest land (7.8 ± 1.40%) or older forests (5.8 ± 0.78%). The selection order did not vary much among forest- or land types, with aspen, willows, rowan and oak being the most selected species.A multiple regression, including four independent variables (moose index, cover of Scots pine, cover of other species and temperature sum) explained 45% (young forests), 18% (older forests) and 36% (non-forest land) of the variation in relative consumption. In young forests, moose index and cover of Scots pine accounted for 40 and 44%, respectively, of the explained variation. Model selection, using AICc, further emphasized the importance of moose index and cover of Scots pine, as these variables were included in the most parsimonious models for all forest- and land types.At the tract level, we recorded a proportional relationship between total cover of browse species and absolute consumption, suggesting an ideal free distribution. Taking into account the availability of forage, the degree of browsing and the proportion of each land type in the landscape, we calculated that 44.3% of the total forage consumption occurred in young forests, 42.3% in older forests and 13.4% in non-forest land.Our main conclusions are that moose conform to an ideal free distribution based on availability of forage within the landscape, and that all forest- and land types, not just young forests, are important as sources of browse for moose. Thus, it may be possible to release the browsing pressure on damage-sensitive young forests by increasing the food supply in other forest- and land types. Furthermore, managers needs to consider both the size of the moose population and the amounts of browse in the landscape when deciding on prudent management actions.

Environmental correlates of the Late Quaternary regional extinctions of large and small Palaearctic mammals

Most studies of mammal extinctions during the Pleistocene–Holocene transition explore the relative effects of climate change vs human impacts on these extinctions, but the relative importance of the different environmental factors involved remains poorly understood. Moreover, these studies are strongly biased towards megafauna, which may have been more influenced by human hunting than species of small body size. We examined the potential environmental causes of Pleistocene–Holocene mammal extinctions by linking regional environmental characteristics with the regional extinction rates of large and small mammals in 14 Palaearctic regions. We found that regional extinction rates were larger for megafauna, but extinction patterns across regions were similar for both size groups, emphasizing the importance of environmental change as an extinction factor as opposed to hunting. Still, the bias towards megafauna extinctions was larger in southern Europe and smaller in central Eurasia. The loss of suitable habitats, low macroclimatic heterogeneity within regions and an increase in precipitation were identified as the strongest predictors of regional extinction rates. Suitable habitats for many species of the Last Glacial fauna were grassland and desert, but not tundra or forest. The low‐extinction regions identified in central Eurasia are characterized by the continuous presence of grasslands and deserts until the present. In contrast, forest expansion associated with an increase in precipitation and temperature was likely the main factor causing habitat loss in the high‐extinction regions. The shift of grassland into tundra also contributed to the loss of suitable habitats in northern Eurasia. Habitat loss was more strongly related to the extinctions of megafauna than of small mammals. Ungulate species with low tolerance to deep snow were more likely to go regionally extinct. Thus, the increase in precipitation at the Pleistocene–Holocene transition may have also directly contributed to the extinctions by creating deep snow cover which decreases forage availability in winter.

Cratering behaviour and faecal C:N ratio in relation to seasonal snowpack characteristics in a High-Arctic ungulate

ABSTRACTSnow and ice determine winter forage availability for Arctic herbivores. Winter precipitation is anticipated to increase, and icing following warm spells and rain-on-snow (ROS) are likely to become more frequent. While this may reduce herbivore survival, fecundity and population growth, we can also expect behavioural and dietary responses. Here, we tested predictions from optimal foraging theory on how changing snowpack conditions influence choice of feeding craters and diet quality in a large generalist herbivore, the wild Svalbard reindeer. Snow and ice conditions over winter 2012/13 (a ‘normal’ winter with little ROS and icing) were measured in reindeer feeding craters, in paired controls one metre away and in fixed control sites. On average, feeding craters had less snow and integrated ram hardness (IRH, the force needed to reach the ground), but not less ice, than nearby controls. However, on this fine spatial scale, reindeer tended to select for microhabitat with worse snowpack conditions up...

What factors determine cyclic amplitude in the snowshoe hare (Lepusamericanus) cycle?

Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9–10 year cycles throughout much of their North American range. These cycles show large variations in cyclic amplitude and we ask what factors could cause amplitude variation. We gathered data from 1976 to 2012 on hare numbers in the boreal forest of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe the amplitude of hare fluctuations and to evaluate four possible causes. First, weather could cause variation in amplitude via hare reproduction or survival, but this mechanism does not fit our data. Second, bottom-up processes involving forest succession could explain amplitude variation through changes in winter forage availability, but succession is too slow a variable in our study areas. Third, plant defenses entrained by hare over-browsing in one cycle can produce variation in plant quality and quantity in subsequent cycles. A mathematical model suggests this is a possible explanation. Fourth, predator recovery following the cyclic low is inversely related to hare cyclic amplitude, and the existing data are consistent with this mechanism. A standardized regional monitoring program is needed to improve our understanding of cyclic amplitude variation in hares and the possible role of predators and winter foods in affecting amplitude.

Predicting non-inventoried forest elements using forest inventory data: The case of winter forage for woodland caribou

Growing development pressures and expectations that forest managers provide future wildlife habitat require better understanding of species' habitat needs, particularly food, cover, and space requirements, and an ability to spatially depict these needs. In forest management in Canada, the primary data used to identify and quantify wildlife habitat reside in remotely sensed forest resource inventories (FRI) that were originally developed to assess timber values for merchantable tree species. Although FRI- and field-based sampling do not always show strong agreement, research has shown that FRI can be informative for wildlife habitat assessments. However, much uncertainty remains when investigating forest characteristics that are not visible to the interpreters, such as sub-canopy features. Here, we used 152 plots in northwestern Ontario to compare the ability of field-based and remotely sensed forest inventories to predict Cladonia lichen cover, a primary winter food source for woodland caribou. The best model for field-based data, which included percentage of jack pine and black spruce in the tree canopy, tree height, stand age, soil moisture, and stem density, correctly predicted 92% of cases where Cladonia spp. were absent (n = 107 plots) and 62% of cases where they were present (i.e., cover >1%; n = 45 plots). FRI performed poorly by contrast, with corresponding percentages of 96 and 19%. FRI provide weak data support for differentiating winter forage availability for woodland caribou, an important habitat factor at the stand level. These findings have important implications for predictions of herd productivity, and suggest that improved remote-sensing capabilities are required in order to assess woodland caribou winter habitat.

Reproductive success and failure: the role of winter body mass in reproductive allocation in Norwegian moose

A life history strategy that favours somatic growth over reproduction is well known for long-lived iteroparous species, especially in unpredictable environments. Risk-sensitive female reproductive allocation can be achieved by a reduced reproductive effort at conception, or the subsequent adjustment of investment during gestation or lactation in response to unexpected environmental conditions or resource availability. We investigated the relative importance of reduced investment at conception compared with later in the reproductive cycle (i.e. prenatal, perinatal or neonatal mortality) in explaining reproductive failure in two high-density moose (Alces alces) populations in southern Norway. We followed 65 multiparous, global positioning system (GPS)-collared females throughout the reproductive cycle and focused on the role of maternal nutrition during gestation in determining reproductive success using a quasi-experimental approach to manipulate winter forage availability. Pregnancy rates in early winter were normal (≥0.8) in all years while spring calving rates ranged from 0.4 to 0.83, with prenatal mortality accounting for most of the difference. Further losses over summer reduced autumn recruitment rates to 0.23-0.69, despite negligible predation. Over-winter mass loss explained variation in both spring calving and autumn recruitment success better than absolute body mass in early or late winter. Although pregnancy was related to body mass in early winter, overall reproductive success was unrelated to pre-winter body condition. We therefore concluded that reproductive success was limited by winter nutritional conditions. However, we could not determine whether the observed reproductive allocation adjustment was a bet-hedging strategy to maximise reproduction without compromising survival or whether females were simply unable to invest more resources in their offspring.

Characteristics of foraging sites and protein status in wintering muskoxen: insights from isotopes of nitrogen

Identifying links between nutritional condition of individuals and population trajectories greatly enhances our understanding of the ecology, conservation, and management of wildlife. For northern ungulates, the potential impacts of a changing climate to populations are predicted to be nutritionally mediated through an increase in the severity and variance in winter conditions. Foraging conditions and the availability of body protein as a store for reproduction in late winter may constrain productivity in northern ungulates, yet the link between characteristics of wintering habitats and protein status has not been established for a wild ungulate. We used a non‐invasive proxy of protein status derived from isotopes of N in excreta to evaluate the influence of winter habitats on the protein status of muskoxen in three populations in Alaska (2005–2008). Multiple regression and an information‐theoretic approach were used to compare models that evaluated the influence of population, year, and characteristics of foraging sites (components of diet and physiography) on protein status for groups of muskoxen. The observed variance in protein status among groups of muskoxen across populations and years was partially explained (45%) by local foraging conditions that affected forage availability. Protein status improved for groups of muskoxen as the amount of graminoids in the diet increased (−0.430 ± 0.31, β± 95% CI) and elevation of foraging sites decreased (0.824 ± 0.67). Resources available for reproduction in muskoxen are highly dependent upon demographic, environmental, and physiographic constraints that affect forage availability in winter. Due to their very sedentary nature in winter, muskoxen are highly susceptible to localized foraging conditions; therefore, the spatial variance in resource availability may exert a strong effect on productivity. Consequently, there is a clear need to account for climate–topography effects in winter at multiple scales when predicting the potential impacts of climatic shifts on population trajectories of muskoxen.

Relationships Among Habitat Quality, Home Range Size, Reproductive Performance and Population Density: Comparison of Three Populations of the Japanese Serow (Capricornis crispus)

Abstract. To elucidate the relationships between the Japanese serow (Capricornis crispus) and their habitat, we conducted a survey of the population density, home range size, reproductive performance, and forage quality and availability mainly in winter. We compared these traits among three populations living in different habitats, Shimokita, Asahi and Kamikochi, based on field observation and published data. Reproductive rate, based on the number of kids that mothers reared to one year old, was highest for Shimokita (37.0%), followed in order by Asahi (29.6%) and Kamikochi (12.0%). Correlations were found among winter forage availability, home range size, reproductive rate and population density, when evergreen coniferous species were considered to have low food value for serows. We concluded that all of these factors could be useful indicators of habitat quality for the Japanese serow. The present results suggest that a small range size and high reproductive success, supported by appropriate food condit...

Late Summer Management Can Improve Forage Yield Distribution and Nutritive Value in Temperate Grassland

Chemical defoliation (glyphosate spraying) at the end of summer and fertilization are practices proposed to improve winter forage availability in native grasslands of the Flooding Pampa of Argentina. However, there is no preceding work comparing the effect of either practice on the yield and botanical composition of these grasslands. In 2002 and 2003, three defoliation treatments were applied in mid‐February: control (C) without summer defoliation; severe summer defoliation (D) to 2‐ to 3‐cm stubble height and glyphosate, isopropylamine salt of N‐[phosphonomethyl] glycine, G, applied at 2.2 kg a.i. ha−1. Additionally, the effect of three rates of N, 0, 35, and 70 kg N ha−1and P, 0, 11, and 22 kg P ha−1 applied in combination with the three late summer defoliation treatments were researched. Early changes during fall in the biomass components ryegrass (Lolium multiflorum Lam.), warm‐season grasses (WSG), dead matter, and litter were evaluated after defoliation treatments. The effect of defoliation treatments along with N and P fertilization was followed on seasonal and annual forage yield, botanical composition, in vitro dry matter digestibility (IVDMD), and crude protein (CP). Glyphosate application increased annual ryegrass contribution while reducing WSG and legumes, mostly narrow leaf trefoil (Lotus tenuis Waldst & Kit.) and annually yielded 29% less forage dry matter (DM) than the intense mechanical defoliation. Forage IVDMD and CP were increased by D and G in fall the first year. In the second year CP was low in G in winter and spring. Changes in botanical composition can explain the differences observed in quality DM traits. Fertilizer increased forage yield 2 to 10 kg DM per kg N and 8 to 24 kg DM per kg P applied. Severe defoliation applied in late summer increased fall and winter forage availability and quality without the negative effect on legumes observed with glyphosate that had a negative impact on DM accumulation and quality in spring.

A multi-agent system model of pastoralist behaviour in Kazakhstan

We present a model of household decision-making in Kazakhstan. Traditionally, long-distance livestock migration of livestock occurred in Kazakhstan's rangelands, exploiting seasonal differences in forage availability. After independence, the rural economy collapsed and migrations stopped. We use multi-agent system modelling to examine trade-offs in allocation of wealth between capital and flocks. Winter forage availability is the key determinant of overall livestock numbers, while availability and price of winter fodder is an important determinant of livestock sector productivity. Seasonal migrations are only likely to reestablish if distant pastures have very poor winter forage. Otherwise, as total flock size increases, larger herds are predicted to settle away from villages. These predictions match field observations.

Demography of Grazed Tussock Grass Populations in Patagonia

Abstract The cover of Festuca gracillima (coiron fueguino), a native tussock grass that dominates grass steppes of Southern Patagonia and Tierra del Fuego, has diminished under continuous sheep grazing. This loss is a concern, because it also reduces forage availability in winter, biodiversity, and soil stability. In the present study, the hypothesis that tussock grass birth and mortality rates are balanced only under moderate-grazing or exclusion regimes was tested with two 5-year records of demographic data obtained from 3 sheep grazing regimes: exclosure (no grazing), low (0.0348 AU·ha −1 ·y −1 , where AU represents animal units equivalent to the consumption of a 450-kg cow), and high (0.1043 AU·ha −1 ·y −1 ). Tussocks were outlined in photographs and marked in the field at two 5-year intervals. The initial total number of plants for the 3 grazing regimes ( n = 358) increased to 384 plants at the end of the 10-year period. No recruitment from seed was observed; plant number changed as a balance of yearly rates of tussock mortality (1.48%), amalgamation (0.75%), and subdivision (2.04%). Intensely grazed populations showed greater (2.13%) mortality rates than ungrazed (1.20%) or moderately grazed (0.78%) populations. Tussocks in intensely grazed populations were smaller (167 cm 2 ·plant −1 ) than those in moderately grazed (197 cm 2 ·plant −1 ) or ungrazed (300 cm 2 ·plant −1 ) populations. Transition matrices showed eigenvalues of 0.701 (high grazing), 0.794 (exclosure), and 0.876 (low grazing). All growth rates of demographic models were negative; the largest rate of population decrease was found under high-intensity grazing, for which projections show that half the tussocks would be lost in 37 years. Under low-intensity grazing and exclosure, a similar tussock loss would take place in 87 and 74 years, respectively. Results show 1) the importance of vegetative processes for tussock demography, 2) the extremely slow dynamics of population changes, and 3) that tussocks may suffer increased mortality as a consequence of subdivision or fragmentation, a process that can be viewed as a small-scale example of the generalized effect of patch subdivision under grazing.

Demography of Grazed Tussock Grass Populations in Patagonia

The cover of Festuca gracillima (coirón fueguino), a native tussock grass that dominates grass steppes of Southern Patagonia and Tierra del Fuego, has diminished under continuous sheep grazing. This loss is a concern, because it also reduces forage availability in winter, biodiversity, and soil stability. In the present study, the hypothesis that tussock grass birth and mortality rates are balanced only under moderate-grazing or exclusion regimes was tested with two 5-year records of demographic data obtained from 3 sheep grazing regimes: exclosure (no grazing), low (0.0348 AU ha-1 y-1, where AU represents animal units equivalent to the consumption of a 450-kg cow), and high (0.1043 AU ha-1 y-1). Tussocks were outlined in photographs and marked in the field at two 5-year intervals. The initial total number of plants for the 3 grazing regimes (n = 358) increased to 384 plants at the end of the 10-year period. No recruitment from seed was observed; plant number changed as a balance of yearly rates of tussock mortality (1.48%), amalgamation (0.75%), and subdivision (2.04%). Intensely grazed populations showed greater (2.13%) mortality rates than ungrazed (1.20%) or moderately grazed (0.78%) populations. Tussocks in intensely grazed populations were smaller (167 cm2 plant-1) than those in moderately grazed (197 cm2 plant-1) or ungrazed (300 cm2 plant-1) populations. Transition matrices showed eigenvalues of 0.701 (high grazing), 0.794 (exclosure), and 0.876 (low grazing). All growth rates of demographic models were negative; the largest rate of population decrease was found under high-intensity grazing, for which projections show that half the tussocks would be lost in 37 years. Under low-intensity grazing and exclosure, a similar tussock loss would take place in 87 and 74 years, respectively. Results show 1) the importance of vegetative processes for tussock demography, 2) the extremely slow dynamics of population changes, and 3) that tussocks may suffer increased mortality as a consequence of subdivision or fragmentation, a process that can be viewed as a small-scale example of the generalized effect of patch subdivision under grazing.

A landscape‐scale model for optimal management of sheep grazingin the Magellanic steppe

Abstract. Effective management of rangelands requires the development of landscape‐scale models for predicting spatial and temporal variability of forage. In the Magellanic tussock steppes, as in other cold‐temperate regions, grazing capacity is dependent on the winter season. To develop a management tool for the region, we analysed links between winter forage availability, weather, stocking rate and vegetation structure. We studied four paddocks over five years with a range of stocking rates from 0 to 1.53 sheep.ha‐1. We sampled forb and non‐tussock graminoid biomass, vegetation structure and faecal pellet abundance at the end of each summer. Daily temperature and rainfall data were also recorded. A regression model explained the amount of winter forage as a positive function of graminoid cover, spring minimum temperature, annual precipitation and a negative function of dwarf shrub canopy, bare soil and stocking rate (R2= 0.59). Interactions of structural variables with precipitation and stocking rate were detected, indicating strong fluctuations of forage availability in lawn communities dominated by short graminoids. The most probable causes of this response would be higher utilisation and lack of canopy structure. Our results illustrate how maps of vegetation structure, obtainable from satellite images, with weather and stocking rate data could be used for predicting optimal stocking rates in large, heterogeneous sheep paddocks.ed.

A landscape-scale model for optimal management of sheep grazing in the Magellanic steppe

Abstract Effective management of rangelands requires the development of landscape-scale models for predicting spatial and temporal variability of forage. In the Magellanic tussock steppes, as in other cold-temperate regions, grazing capacity is dependent on the winter season. To develop a management tool for the region, we analysed links between winter forage availability, weather, stocking rate and vegetation structure. We studied four paddocks over five years with a range of stocking rates from 0 to 1.53 sheep.ha–1. We sampled forb and non-tussock graminoid biomass, vegetation structure and faecal pellet abundance at the end of each summer. Daily temperature and rainfall data were also recorded. A regression model explained the amount of winter forage as a positive function of graminoid cover, spring minimum temperature, annual precipitation and a negative function of dwarf shrub canopy, bare soil and stocking rate (R2 = 0.59). Interactions of structural variables with precipitation and stocking rate we...

Limiting effects of snow on seasonal habitat use and diets of caribou (Rangifer tarandus groenlandicus) on Coats Island, Northwest Territories, Canada

The insular population of barren-ground caribou (Rangifer tarandus groenlandicus) on Coats Island, Northwest Territories, is ultimately limited by winter food resources. This study was undertaken to assess forage biomass available during summer and to determine the effects of snow on forage availability in winter. Vegetation was low in density and diversity, but provided ample forage of high quality in summer for the 2000–2500 caribou existing on the island. Aboveground green biomass averaged only 50–60 g∙m−2 in mesic and wet meadows, the most productive habitats. Caribou fed almost exclusively in meadows throughout the snow-free period; willows (Salix spp.) constituted 80–90% of rumen contents in caribou collected during the summer. Lichens were scarce and were a major food only at the beginning and end of winter. During mid and late winter, hard-packed snow averaged 4000–9000 g∙cm−2 in hardness and 50–80 cm in depth on all low-lying vegetation. Under these conditions, caribou cratered only where snow was less than 10–20 cm deep; consequently feeding was limited to the slopes of wind-blown ridges and the tops of high-centre polygons. Forage available under these winter conditions was drastically reduced in quantity and quality compared with forage available in summer. During winter 1983 – 1984, snow accumulated rapidly and prolonged deep snow cover was associated with high calf mortality.