Increasing Snow Depth Research Articles

A long-term assessment of the effect of winter severity on the food habits of white-tailed deer

Nutrition is a critical link between environmental and population variation in northern populations of free-ranging white-tailed deer (Odocoileus virginianus). Yet, few studies have investigated winter food habits of northern free-ranging deer and all of these were short-term studies (1–2 winters). Consequently, little information is available on the effect of inter-annual variation in winter severity on browse availability and diet composition of free-ranging deer. We describe winter browse use by white-tailed deer on 4 study sites in northern Minnesota during 1991–2005. We also tested several a priori predictions about how browse use and availability would change as a function of winter severity. We collected browse data from 1,028 feeding trails and recorded 38 available browse species or species groups. The 4 most common browse species (beaked hazel [Corylus cornuta], mountain maple [Acer spicatum], trembling aspen [Populus tremuloides], and speckled alder [Alnus incana]) accounted for 76% of total available stems, and beaked hazel and mountain maple accounted for 68% of total used stems. As expected, browse use and availability distributions were very similar (i.e., deer used many of the available browse resources). Mean number of browse species used did not increase (decreased selection) with snow depth. However, mean browse rate (functional response) increased with increasing snow depth, and use of speckled alder (starvation food) increased when snow depth exceeded 40 cm. In addition, the number of browse species along feeding trails declined and stem abundance increased, on average, with increasing snow depth. Deep snow and increased use of dense conifer cover in northern Minnesota may restrict deer to greater use of lower quality feeding sites. In landscapes where this may occur, habitat management should attempt to minimize over-browsing on feeding sites in proximity to dense conifer cover by maximizing browse abundance and availability, particularly for beaked hazel and mountain maple. Managers also should consider enhancing alternative early-winter feeding sites. © 2013 The Wildlife Society. © The Wildlife Society, 2013

Rapid responses of permafrost and vegetation to experimentally increased snow cover in sub-arctic Sweden

Increased snow depth already observed, and that predicted for the future are of critical importance to many geophysical and biological processes as well as human activities. The future characteristics of sub-arctic landscapes where permafrost is particularly vulnerable will depend on complex interactions between snow cover, vegetation and permafrost. An experimental manipulation was, therefore, set up on a lowland peat plateau with permafrost, in northernmost Sweden, to simulate projected future increases in winter precipitation and to study their effects on permafrost and vegetation. After seven years of treatment, statistically significant differences between manipulated and control plots were found in mean winter ground temperatures, which were 1.5 ° C higher in manipulated plots. During the winter, a difference in minimum temperatures of up to 9 ° C higher could be found in individual manipulated plots compared with control plots. Active layer thicknesses increased at the manipulated plots by almost 20% compared with the control plots and a mean surface subsidence of 24 cm was recorded in the manipulated plots compared to 5 cm in the control plots. The graminoid Eriophorum vaginatum has expanded in the manipulated plots and the vegetation remained green longer in the season.

Accuracy assessment of MODIS/Terra snow cover product for parts of Indian Himalayas

Snow cover mapping is important for snow and glacier-related research. The spatial and temporal distribution of snow cover area is a fundamental input to the atmospheric models, snowmelt runoff models and climate models, as well as other applications. Daily snow cover maps from Moderate Resolution Imaging Spectroradiometer (MODIS) Terra satellite were retrieved for the period between 2004 and 2007, and pixels in these images were classified as cloud, snow or snow-free. These images have then been compared with ground snow depth (SD) measurements from the four observatories located at different parts of Himalayas. Comparison of snow maps with in situ data showed good agreement with overall accuracies in between 78.15 and 95.60%. When snow cover was less, MODIS data were found to be less accurate in mapping snow cover region. As the SD increases, the accuracy of MODIS snow cover maps also increases.

Combined effects of snow depth and nitrogen addition on ephemeral growth at the southern edge of the Gurbantunggut Desert, China

Water and nitrogen (N) inputs are considered as the two main limiting factors affecting plant growth. Changes in these inputs are expected to alter the structure and composition of the plant community, thereby influencing biodiversity and ecosystem function. Snowfall is a form of precipitation in winter, and snow melting can recharge soil water and result in a flourish of ephemerals during springtime in the Gurbantunggut Desert, China. A bi-factor experiment was designed and deployed during the snow-covering season from 2009 to 2010. The experiment aimed to explore the effects of different snow-covering depths and N addition levels on ephemerals. Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast, N addition sharply decreased the density of ephemerals in the same snow treatment. Meanwhile, N addition exhibited a different effect on the growth of ephemeral plants: in the 50% snow treatment, N addition limited the growth of ephemeral plants, showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth (100% and 150% snow treatments), N addition benefited the growth of the dominant individual plants. Species richness was not significantly affected by snow in the same N treatment. However, N addition significantly decreased the species richness in the same snow-covering depth. The primary productivity of ephemerals in the N addition increased with the increase of snow depth. These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply. With plenty of water (100% and 150% snow treatments), N addition contributed to the growth of ephemeral plants; while with less water (50% snow treatment), N addition restricted the growth of ephemeral plants.

Snow cover and extreme winter warming events control flower abundance of some, but not all species in high arctic Svalbard.

The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes.Winter warming events, often occurring together with rain, can substantially remove snow cover and thereby expose plants to cold winter air. Depending on morphology, different parts of the plant can be directly exposed. On this picture, we see Dryas octopetala seed heads from the previous growing season protrude through the remaining ice layer after a warming event in early 2010. The rest of the plant, including meristems and flower primordia, are still somewhat protected by the ice. In the background we can see a patch of Cassiope tetragona protruding through the ice; in this case, the whole plant including flower primordia is exposed, which might be one reason why this species experienced a loss of flowers the following season. Photograph by Philipp Semenchuk.

A Long-Term Assessment of the Variability in Winter Use of Dense Conifer Cover by Female White-Tailed Deer

BackgoundLong-term studies allow capture of a wide breadth of environmental variability and a broader context within which to maximize our understanding of relationships to specific aspects of wildlife behavior. The goal of our study was to improve our understanding of the biological value of dense conifer cover to deer on winter range relative to snow depth and ambient temperature.Methodology/Principal FindingsWe examined variation among deer in their use of dense conifer cover during a 12-year study period as potentially influenced by winter severity and cover availability. Female deer were fitted with a mixture of very high frequency (VHF, n = 267) and Global Positioning System (GPS, n = 24) collars for monitoring use of specific cover types at the population and individual levels, respectively. We developed habitat composites for four study sites. We fit multinomial response models to VHF (daytime) data to describe population-level use patterns as a function of snow depth, ambient temperature, and cover availability. To develop alternative hypotheses regarding expected spatio-temporal patterns in the use of dense conifer cover, we considered two sets of competing sub-hypotheses. The first set addressed whether or not dense conifer cover was limiting on the four study sites. The second set considered four alternative sub-hypotheses regarding the potential influence of snow depth and ambient temperature on space use patterns. Deer use of dense conifer cover increased the most with increasing snow depth and most abruptly on the two sites where it was most available, suggestive of an energy conservation strategy. Deer use of dense cover decreased the most with decreasing temperatures on the sites where it was most available. At all four sites deer made greater daytime use (55 to >80% probability of use) of open vegetation types at the lowest daily minimum temperatures indicating the importance of thermal benefits afforded from increased exposure to solar radiation. Date-time plots of GPS data (24 hr) allowed us to explore individual diurnal and seasonal patterns of habitat use relative to changes in snow depth. There was significant among-animal variability in their propensity to be found in three density classes of conifer cover and other open types, but little difference between diurnal and nocturnal patterns of habitat use.Conclusions/SignificanceConsistent with our findings reported elsewhere that snow depth has a greater impact on deer survival than ambient temperature, herein our population-level results highlight the importance of dense conifer cover as snow shelter rather than thermal cover. Collectively, our findings suggest that maximizing availability of dense conifer cover in an energetically beneficial arrangement with quality feeding sites should be a prominent component of habitat management for deer.

Synoptic conditions of heavy snowfalls in europe

Synoptic conditions of heavy snowfalls at four stations in urope (slo, remen, molensk and udapest) were analyzed using daily data of snow cover depth from 50 winter seasons (1960/1961–2009/2010). Composite maps of the sea level pressure and 500 geopotential height means and anomalies were presented for the days with an increase in snow depth by ≥10 cm, for each station separately. In the same way, maps were presented for the 850-hPa temperature and the precipitable water content. Additionally, 48 h back trajectories of air masses for the chosen days with the highest amount of snowfall were constructed, using the model. Negative anomalies of sea level pressure and 500-hPa heights, which correspond to low‐pressure systems spreading over urope, are prerequisites for the occurrence of heavy snowfalls at each analyzed location. In udapest, heavy snowfalls appear as a result of cyclonic cold fronts from the editerranean ea. Another typical location of snow‐bringing low‐pressure systems is the altic ea region. Negative pressure anomalies over the orth tlantic with a low‐pressure centre over the orwegian ea cause snowfalls in slo. There are two main sources of air masses bringing abundant snowfalls in urope: the tlantic region and editerranean. According to back trajectories, the humid air masses are transported over long distances and on the way they are shifted from the low troposphere in the source regions to the upper layers.

Impacts of long-term snow climate change on a high-elevation cold desert shrubland, California, USA

Ecological responses to 50-year old manipulations of snow depth and melt timing were assessed using snow fences arrayed across 50 km of a shrub–conifer landscape mosaic in eastern California, USA. We compared how increased, decreased, and ambient snow depth affected patterns of vegetation community composition, fire fuel accumulation, and annual tree ring growth. We also tested the effect of snow depth on soil carbon storage based on total C content under the two co-dominant shrub species (Artemisiatridentata and Purshia tridentata) in comparison with open, intershrub sites. Increased snow depth reduced the cover of the N-fixing shrub P. tridentata but not the water-redistributing shrub A. tridentata. Annual ring growth was greater on +snow plots and lower on −snow plots for the conifer Pinus jeffreyi but not for Pinus contorta. Graminoid cover and aboveground biomass indicated higher fire fuel accumulation where snow depth was increased. Dead shrub stem biomass was greater regardless of whether snow depth was increased or decreased. Results demonstrate community shifts, altered tree growth, feedbacks on carbon storage, and altered fire fuel accumulation as a result of changes in snow depth and melt timing for this high-elevation, snow-dominated ecotone under future climate scenarios that envision increased or decreased snow depth.

Methodological approaches to infer end-of-winter snow distribution on alpine glaciers

AbstractSnow accumulation is an important component of the mass balance of alpine glaciers. To improve our understanding of the processes related to accumulation and their representation in state-of-the-art mass-balance models, extensive field measurements are required. We present measurements of snow accumulation distribution on Findelengletscher, Switzerland, for April 2010 using (1) in situ snow probings, (2) airborne ground-penetrating radar (GPR) and (3) differencing of two airborne light detection and ranging (lidar) digital elevation models (DEMs). Calculating high-resolution snow depth from DEM-differencing requires careful correction for vertical ice-flow velocity and densification in the accumulation area. All three methods reveal a general increase in snow depth with elevation, but also a significant small-scale spatial variability. Lidar-differencing and in situ snow probings show good agreement for the mean specific winter balance (0.72 and 0.78 m w.e., respectively). The lidar-derived distributed snow depth reveals significant zonal correlations with elevation, slope and curvature in a multiple linear regression model. Unlike lidar-differencing, GPR-derived snow depth is not affected by glacier dynamics or firn compaction, but to a smaller degree by snow density and liquid water content. It is thus a valuable independent data source for validation. The simultaneous availability of the three datasets facilitates the comparison of the methods and contributes to a better understanding of processes that govern winter accumulation distribution on alpine glaciers.

Greater Sage-Grouse and Severe Winter Conditions: Identifying Habitat for Conservation

Developing sustainable rangeland management strategies requires solution-driven research that addresses ecological issues within the context of regionally important socioeconomic concerns. A key sustainability issue in many regions of the world is conserving habitat that buffers animal populations from climatic variability, including seasonal deviation from long-term precipitation or temperature averages, and that can establish an ecological bottleneck by which the landscape-level availability of critical resources becomes limited. We integrated methods to collect landscape-level animal occurrence data during severe winter conditions with estimation and validation of a resource selection function, with the larger goal of developing spatially explicit guidance for rangeland habitat conservation. The investigation involved greater sage-grouse (Centrocercus urophasianus) that occupy a landscape that is undergoing human modification for development of energy resources. We refined spatial predictions by exploring how reductions in the availability of sagebrush (as a consequence of increasing snow depth) may affect patterns of predicted occurrence. Occurrence of sage-grouse reflected landscape-level selection for big sagebrush, taller shrubs, and favorable thermal conditions and avoidance of bare ground and anthropogenic features. Refinement of spatial predictions showed that important severe winter habitat was distributed patchily and was constrained in spatial extent (7–18% of the landscape). The mapping tools we developed offer spatially explicit guidance for planning human activity in ways that are compatible with sustaining habitat that functions disproportionately in population persistence relative to its spatial extent or frequency of use. Increasingly, place-based, quantitative investigations that aim to develop solutions to landscape sustainability issues will be needed to keep pace with human-modification of rangeland and uncertainty associated with global climate change and its effects on animal populations.

Simulated Siberian snow cover response to observed Arctic sea ice loss, 1979–2008

The loss of Arctic sea ice has wide‐ranging impacts, some of which are readily apparent and some of which remain obscure. For example, recent observational studies suggest that terrestrial snow cover may be affected by decreasing sea ice. Here, we examine a possible causal link between Arctic sea ice and Siberian snow cover during the past 3 decades using a suite of experiments with the National Center for Atmospheric Research Community Atmospheric Model version 3. The experiments were designed to isolate the influence of surface conditions within the Arctic Ocean from other forcing agents such as low‐latitude sea surface temperatures and direct radiative effects of increasing greenhouse gases. Only those experiments that include the observed evolution of Arctic sea ice and sea surface temperatures result in increased snow depth over Siberia, while those that maintain climatological values for Arctic Ocean conditions result in no snow signal over Siberia. In the former, Siberian precipitation and air temperature both increase, but because surface air temperatures remain below freezing during most months, the snowpack thickens over this region. These results suggest that Arctic Ocean surface forcing is necessary and sufficient to induce a Siberian snow signal, and that other forcings in combination can modulate the strength and geographic extent of the response.

The role of declining Arctic sea ice in recent decreasing terrestrial Arctic snow depths

The dramatic decline in Arctic sea ice cover is anticipated to influence atmospheric temperatures and circulation patterns. These changes will affect the terrestrial climate beyond the boundary of the Arctic, consequently modulating terrestrial snow cover. Therefore, an improved understanding of the relationship between Arctic sea ice and snow depth over the terrestrial Arctic is warranted. We examined responses of snow depth to the declining Arctic sea ice extent in September, during the period of 1979–2006. The major reason for a focus on snow depth, rather than snow cover, is because its variability has a climatic memory that impacts hydrothermal processes during the following summer season. Analyses of combined data sets of satellite measurements of sea ice extent and snow depth, simulated by a land surface model (CHANGE), suggested that an anomalously larger snow depth over northeastern Siberia during autumn and winter was significantly correlated to the declining September Arctic sea ice extent, which has resulted in cooling temperatures, along with an increase in precipitation. Meanwhile, the reduction of Arctic sea ice has amplified warming temperatures in North America, which has readily offset the input of precipitation to snow cover, consequently further decreasing snow depth. However, a part of the Canadian Arctic recorded an increase in snow depth driven locally by the diminishing September Arctic sea ice extent. Decreasing snow depth at the hemispheric scale, outside the northernmost regions (i.e., northeastern Siberia and Canadian Arctic), indicated that Arctic amplification related to the diminishing Arctic sea ice has already impacted the terrestrial Arctic snow depth. The strong reduction in Arctic sea ice anticipated in the future also suggests a potential long-range impact on Arctic snow cover. Moreover, the snow depth during the early snow season tends to contribute to the warming of soil temperatures in the following summer, at least in the northernmost regions.

Degrading Mountain Permafrost in Southern Norway: Spatial and Temporal Variability of Mean Ground Temperatures, 1999–2009

ABSTRACTA ten‐year record (1999–2009) of annual mean ground surface temperatures (MGSTs) and mean ground temperatures (MGTs) was analysed for 16 monitoring sites in Jotunheimen and on Dovrefjell, southern Norway. Warming has occurred at sites with cold permafrost, marginal permafrost and deep seasonal frost. Ongoing permafrost degradation is suggested both by direct temperature monitoring and indirect geophysical surveys. An increase in MGT at 6.6–9.0‐m depth was observed for most sites, ranging from ~0.015 to ~ 0.095°C a‐1. The greatest rate of temperature increase was for sites having MGTs slightly above 0°C. The lowest rate of increase was for marginal permafrost sites that are affected by latent heat exchange close to 0°C. Increased snow depths and an increase in winter air temperatures appear to be the most important factors controlling warming observed over the ten‐year period. Geophysical surveys performed in 1999 to delineate the altitudinal limit of mountain permafrost were repeated in 2009 and 2010 and indicated the degradation of some permafrost over the intervening decade. Copyright © 2011 John Wiley & Sons, Ltd.

Multi-Decadal Changes in Tundra Environments and Ecosystems: Synthesis of the International Polar Year-Back to the Future Project (IPY-BTF)

Understanding the responses of tundra systems to global change has global implications. Most tundra regions lack sustained environmental monitoring and one of the only ways to document multi-decadal change is to resample historic research sites. The International Polar Year (IPY) provided a unique opportunity for such research through the Back to the Future (BTF) project (IPY project #512). This article synthesizes the results from 13 papers within this Ambio Special Issue. Abiotic changes include glacial recession in the Altai Mountains, Russia; increased snow depth and hardness, permafrost warming, and increased growing season length in sub-arctic Sweden; drying of ponds in Greenland; increased nutrient availability in Alaskan tundra ponds, and warming at most locations studied. Biotic changes ranged from relatively minor plant community change at two sites in Greenland to moderate change in the Yukon, and to dramatic increases in shrub and tree density on Herschel Island, and in subarctic Sweden. The population of geese tripled at one site in northeast Greenland where biomass in non-grazed plots doubled. A model parameterized using results from a BTF study forecasts substantial declines in all snowbeds and increases in shrub tundra on Niwot Ridge, Colorado over the next century. In general, results support and provide improved capacities for validating experimental manipulation, remote sensing, and modeling studies.

Growth and Reproductive Responses of Cassiope tetragona, a Circumpolar Evergreen Shrub, to Experimentally Delayed Snowmelt

While there has been a general trend of climate warming in the Arctic causing early snowmelt and prolonged growing season, climate change models for some areas in the High Arctic suggest increased snow accumulation, delayed spring melt, and consequently shorter growing season. We tested the vegetative and reproductive responses of Cassiope tetragona, an arctic shrub, to increased snow depth and delayed snowmelt using a snow fence experiment in Adventdalen, Norway (78°54′N, 18°01′E). We recorded seasonal shoot length, number of leaves, and capsules per shoot for three summers (2005–2007): two prior and one after the treatment began. Phenological events were recorded in 2007. The number of seeds per capsule was counted and seed germination was tested. Phenological development was significantly delayed behind fences, with lower shoot length, number of leaves, capsules, and seeds per shoot segment (16, 20, 54 and 11%, respectively) compared to controls, but there was no difference in these parameters between plots prior to fence establishment. Seed viability was unaffected by treatment. A delay in start of growing season due to delayed snowmelt decreased vegetative and reproductive performance of C. tetragona; earlier melt may therefore improve performance. This may lead to floral composition change in some high arctic locations.

A weeding-duration model for Larix kaempferi plantations in Hokkaido, northern Japan

In this study, a weeding-duration model for Larix kaempferi plantations was developed that employs a generalized linear model. The number of years that weeding is necessary is the response variable, and elevation, slope, maximum snow depth, annual precipitation, geological type, soil type, site index, slope aspect, and vegetation type are explanatory variables. Among the explanatory variables, geological type, soil type, slope aspect, and vegetation type are categorical data. We assumed a Poisson distribution for the response variable. The link function was log. Among the models that could be developed from these variables, we chose the model with the smallest Akaike's information criterion (AIC). The weeding-duration model can be written as follows: years that weeding is necessary = Exp (−0.0172833 × site index + 0.0014053 × maximum snow depth (cm) + 1.7417731). The results of this study imply that weeding of Larix kaempferi plantations is needed for more years as the maximum snow depth increases and fewer years as the site index increases. This model is useful for cost–benefit analyses of afforestation or reforestation with Larix kaempferi.

Evidence of Nonlinearity in the Response of Net Ecosystem CO2 Exchange to Increasing Levels of Winter Snow Depth in the High Arctic of Northwest Greenland

Winter snowfall is increasing in many Arctic regions and climate models predict this trend will persist in the coming century. We examined the effects of two levels of increased winter snow accumulation on soil microclimate, plant and soil nutrient status, plant phenology and ecosystem CO2 exchange after five years of treatment in a widespread High Arctic ecosystem. Increased snow cover resulted in greater winter CO2 efflux, altered growing season soil nutrient availability and greater leaf nitrogen concentrations during the snow-free season. Modest increases in snow cover (+0.25 m above ambient) increased gross ecosystem photosynthesis (GEP) without increasing ecosystem respiration (ER), while the deepest snow cover (+0.75 m above ambient) increased both GEP and ER. The area of intermediate snow addition was a smaller source of CO2 to the atmosphere during the growing season when compared to the ambient and deep snow areas. The intermediate and deep snow areas apparently had similar effects on the functioning of the vegetation community (increased GEP), but divergent effects on the soil microbial respiration, as evidenced by the changes in ER. This nonlinear response to increasing snow depth demonstrates the potential for complex High Arctic ecosystem responses to changes in winter precipitation.

Factors influencing winter home ranges and activity patterns of raccoon dogs Nyctereutes procyonoides in a high-altitude area of Japan

Between October 2006 and June 2007, we radio-tracked six adult raccoon dogs Nyctereutes procyonoides (Gray, 1834) in a high-altitude area of Japan to determine which factors influenced home ranges, daily movements, and activity patterns of Japanese raccoon dogs, with an emphasis on the winter season. The home-range sizes for the six individuals were smaller in winter than in autumn. In winter, the daily movement distances significantly decreased in response to decreasing temperature and increasing snow depth, suggesting these environmental factors contributed to a decrease in the home-range sizes during this period. Moreover, during daytime, raccoon dogs were more active in winter than in the snow-free periods (autumn and spring), and the proportion of the daytime movement distances to the total daily movement distances significantly increased as the mean daily air temperatures decreased. Therefore, it appears that the raccoon dogs in our study area passed the winter by minimizing their energy expenditure by restricting their movements when temperatures were at their lowest and snow depth was highest, and by moving more during the daytime when temperatures were higher.

Late snowmelt delays plant development and results in lower reproductive success in the High Arctic

In tundra areas where the growing season is short, any delay in the start of summer may have a considerable effect on plant development, growth and reproductive success. Climate models suggest long-term changes in winter precipitation in the Arctic, which may lead to deeper snow cover and a resultant delay in date of snow melt. In this paper, we investigated the role of snow depth and melt out date on the phenological development and reproductive success of vascular plants in Adventdalen, Svalbard (78°10′N, 16°06′E). Effects of natural variations in snow accumulation were demonstrated using two vegetation types (snow depth: meadow 21 cm, heath 32 cm), and fences were used to experimentally increase snow depth by over 1 m. Phenological delay was greatest directly after snowmelt in the earlier phenological phases, and had the largest effect on the early development of those species which normally green-up early (i.e. Dryas, Papaver, Salix, Saxifraga). Compressed growing seasons and length of the reproductive period led to a reduced reproductive success in some of the study species. There were fewer flowers, fewer plots with dispersing seeds, and lower germination rates. This can have consequences for plant establishment and community composition in the long-term.

Interacting effect of wolves and climate on recruitment in a northern mountain caribou population

There is limited research on the influence of Pacific-based climate in large herbivore populations. Additionally, much of our understanding on the effect of large-scale climate on ungulate population dynamics has occurred on forage-limited rather than predator-limited populations. We compared the influence of the Pacific Decadal Oscillation (PDO), North Pacific Index, and local weather on recruitment in a predator-limited mountain-dwelling caribou Rangifer tarandus caribou population in the Yukon Territory, Canada, across a range of wolf Canis lupus densities. A large-scale wolf removal program allowed us to examine the role of Pacific climate and weather when wolves were reduced to ∼15% of their pre-removal levels. Recruitment was best explained by the interaction of wolf density and April-PDO, with wolf density explaining the most deviance. Predicted recruitment during good springs was 0.45 (SE = 0.04) during wolf removal and 0.29 (SE = 0.03) with no wolf removal. During poor springs (low PDO, increased snow depth) predicted recruitment was 0.55 (SE = 0.10) during wolf removal and 0.12 (SE = 0.03) with no wolf removal. With non-altered wolf densities, there was a positive relationship between April-PDO and recruitment due to reduced snow depth at calving, allowing parturient females to disperse up in elevation away from predators. When wolf densities were substantially reduced there was a slight negative relationship between April-PDO and recruitment, possibly due to a more rapid vegetation green-up reducing the temporal availability of highly nutritious forage necessary for lactation and subsequent calf growth. Attempts to find general relationships between climate and ungulate population dynamics have proven difficult due to different ecological mechanisms by which climate affects individuals across populations. Temporally varying factors, such as predator density, may also play an important role in uncovering the mechanistic relationship between climate and population dynamics.