G. Peter Kershaw

Snow ecology : an interdisciplinary examination of snow-covered ecosystems

Acknowledgements 1. Snow cover and the climate system Pavel Ya. Groisman and T. D. Davies 2. Physical properties of snow John Pomeroy and E. Brun 3. The chemistry of snow Martyn Tranter and H. G. Jones 4. Microbial ecology of snow and fresh-water ice with emphasis on snow algae Ron Hoham and Brian Duval 5. The effect of snow cover on small animals C. W. Aitchison 6. Snow vegetation interactions in tundra environments D. A. Walker, W. D. Billings and J. G. de Molenaar 7. Tree-ring dating of past snow regimes Yves Begin and Simon Boivin Index.

Microtopographic patterns in an arctic baydjarakh field: do fine-grain patterns enforce landscape stability?

Recent observations suggest that while some arctic landscapes are undergoing rapid change, others are apparently more resilient. In this study, we related surface cover and energy balance to microtopography in a degraded polygonal peat plateau (baydjarakh field) near Churchill, Manitoba in mid-summer 2010. The landscape consists of remnant high-centered polygons divided by troughs of varying widths. Historical aerial photos indicate these topographical features have been stable for over 80 years. Our goal was to explore patterns that might explain the apparent stability of this landscape over this time period and to evaluate remote sensing methods for characterizing microtopographic patterns that might resist change in the face of climate warming. Summertime surface albedo measurements were combined with several years of winter snow depth, snow heat flux, summer thaw depth and annual surface temperature, all of which had striking contrasts between wet troughs and high polygon centers. Measurements of albedo and the snowpack heat transfer coefficient were lowest for wet troughs (areas of standing water) dominated by graminoids, and were significantly higher for high polygon centers, dominated by dwarf shrubs and lichens. Snow depth, surface temperature and thaw depth were all significantly higher for wet troughs than high polygon centers. Together these patterns of cover and energy balance associated with microtopographic variation can contribute to the stability of this landscape through differential heat transfer and storage. We hypothesize that local thermal feedback effects, involving greater heat trapping in the troughs than on the baydjarakh tops, and effective insulation on the baydjarakh edges, have ensured landscape stability over most of the past century. These results suggest that high-resolution remote sensing, combined with detailed field monitoring, could provide insights into the dynamics or stability of arctic landscapes, where cover often varies over short distances due to microtopographic effects.

THE SELECTION OF SNOWPATCH ES AS RELIEF HABITAT BY WOODLAND CARIBOU (RANGJFEIR TARANDUS CARIBOU), MACMILLAN PASS, SELWYN/MACKENZIE MOUNTAINS, N.W.T., CANADA

Woodland caribou (Rangifer tarandus caribou Gmelin) occupy the Mackenzie and Selwyn Mountains of the Yukon and N.W.T, Canada. During the warm weather months they move into alpine areas and are frequently observed to utilize late-lying snowpatches. Microclimatic observations confirm that at 0.5 m height the snowpatch is consistently 3?C cooler than adjacent areas. Insect trap data indicated that significant differences in numbers and species occur between snowpatches and adjacent snow-free areas at the same and lower elevations. Indices of harassment correlated with biting insect numbers and with higher air temperatures (11.3 to 20.4?C, shielded temperatures) and below-average wind speeds (<2.5 m s-1). Group size on snowpatches was significantly greater than on adjacent snow-free areas. While on snowpatches animals ingested snow and otherwise spent most of their time standing or lying. These activities we interpreted as behavioral thermoregulation. However, based on our data it was not possible to separate definitively microclimatic conditions from insect harassment as cause for snowpatch selection as relief habitat.

Midwinter Snowpack Variation across the Arctic Treeline, Churchill, Manitoba, Canada

ABSTRACT The study area spans the 15-km-wide ecotone between coastal tundra and open subarctic forest near Churchill, Manitoba, Canada. Study sites include Black Spruce Wetland, White Spruce Forest, Burned Forest, Forest-tundra Tree Island, and Tundra. These ecosystems are representative of ones that dominate the circumpolar north. Mid-winter snowpack characteristics were measured during 2002, 2003, and 2004, including depth, density, and snow water equivalent. These studies reveal differences induced by changing vegetation characteristics and associated microclimates. Despite the dramatic differences in canopy, the post-fire forest snowpack differed little from that of the unburned forests. Interannual variations were much less than intersite variations in most snowpack characteristics. These studies are intended to be repeated annually in order to establish a longitudinal study of snowpack variation across the Arctic treeline during a period of predicted dramatic change in climate.

Multi-scale Analysis of Environmental Conditions and Conifer Seedling Distribution Across the Treeline Ecotone of Northern Manitoba, Canada

Treeline represents not only an important physiognomic boundary but also an important transition between disjunct mesoclimates and environmental limitations on establishment of tree species. The circumboreal treeline is controlled by some still to be understood physiological mechanism dependent on air temperatures, though younger life stages are increasingly influenced by numerous other biotic and abiotic factors at finer spatial and temporal scales. The goal of this study was to evaluate environmental and reproductive characteristics across treeline around Churchill, Manitoba, and to determine which factors are most important for successful seedling establishment by tamarack, white spruce and black spruce. We examined mid-winter snowpack, soil characteristics, seed viability, seedling establishment, and dominant vegetation at sites within forest and at treeline. Growing season was longer at treeline due to less snow accumulation, though soil temperatures were more variable throughout the year when compared with forest. Conifer seed germination was greater than 88% for most of the region and total seedling density was relatively consistent between sites. Seedlings were negatively associated with other plants within the forest, but low stature vegetation seemed to facilitate establishment at treeline. The associations between seedling establishment and habitat availability observed at several sites suggest that treeline advance in the Churchill area could be contingent on the facilitative effects of plants at and beyond treeline. The results of this study support the premise that fine-scale biotic and abiotic patterns and processes such as snowpack and facilitation by neighboring vegetation certainly cannot be overlooked in analyses of patterns at treeline in a changing Subarctic.

Secondary Succession 24 Years after Disturbance of a New Zealand High-alpine Cushionfield

Abstract Severe road-making disturbance of a New Zealand high-alpine cushionfield initiated a secondary succession which has been assessed against the adjacent undisturbed community with permanent transects over 24 yrs. The succession has recently (yrs 11–24) accelerated as areas of bare soil-stone pavement continue to be colonized. Total plant cover has increased on the disturbed sites over this period (from 36 to 48%) and is now within the range of that in the intact cushionfield (48–59%), while the early dominant graminoids, particularly Poa colensoi, are now declining as other species establish. Floristic richness in the recovering system (33 species) now exceeds that of the intact cushionfield (21–27 species) with establishment of nine apparently seral species plus several mainly cushion species characteristic of the undisturbed cushionfield. Transition probabilities among seven recognized cover states for the most recent period (1986–1999) further clarify the succession by showing the “other species” category increasing in importance at the expense of the other six states. This contrasts with the relative stability of the intact cushionfield where autotransitions predominate over the same period. The severe high-alpine environment rather than physical differences between the disturbed and undisturbed sites appears to be limiting the rate of succession toward the undisturbed state. Despite establishment of several characteristic cushionfield species, the still minor role of its dominant, Dracophyllum muscoides (1% vs. 26–32% cover), indicates that the succession remains far from complete. Among the various succession models, autosuccession is untenable given the establishment of nine apparently seral species; only the inhibition and intermediate disturbance hypotheses could be entertained with the results to date.

Late winter snow-landscape relationships in the subarctic near Hoarfrost River, Great Slave Lake, Northwest Territories, Canada

Late winter sampling of snowpack depth and density was conducted in five subarctic forest and forest-tundra landscape types north of the east arm of Great Slave Lake, Northwest Territories between March 28 and April 9, 1990. Tree and sampling density were nonnormal in distribution in study sites with stems <1500 ha−1, and normally distributed in dense forest. For the Hoarfrost River area, average snow depth, density, and water equivalent were 40.7 ± 7.9 cm, 0.17 ± 0.05 g cm3, and 6.58 ± 1.99 cm, respectively. Variation in snowpack depth and density was low within each site, indicative of relatively homogeneous snow conditions. Snow density was negatively correlated with tree stem density. For the Hoarfrost River area, both snow depth and variability in snow density increased with tree stem density. Variability in snow depth increased with variability in snow density. Snow depth was more variable in forest-tundra than in forest sites.

The influence of a simulated transport corridor on snowpack characteristics, Fort Norman, N.W.T., Canada

Between November 1985 and February 1989, six snowpack sampling sessions were completed (at least annually) at the Studies of the Environmental Effects of Disturbances in the Subarctic (SEEDS) site ...

Snowpack Characteristics Following Wildfire on a Simulated Transport Corridor and Adjacent Subarctic Forest, Tulita, N.W.T., Canada

A simulated transport corridor research site established in a permafrost-affected upland black spruce forest in 1984 was burned by a wildfire in 1995. A data set consisting of four mid-winter snow surveys conducted prior to the fire was supplemented by two postfire surveys (including a new, unburned forest control). Mean daily winter winds increased significantly on the cleared rights-of-way/ simulated pipeline trench (ROW/trench). Increased winds were attributed to postfire reductions in stem density and surface roughness, which offered less resistance to the wind. Maximum winter winds were not significantly greater at 1.5 m on the postfire ROW/trench where the postfire modification of the forest reduced funnelling and acceleration of winds along the cleared ROW/trench. ROW/ trench snowpack depth increased and water equivalence declined after the fire, except in leading-edge forest sites where the reverse occurred. Depth and water equivalence changes resulted from the altered wind regime, where reduction in effective wind erosion on ROW/trench locations left more snow in these areas and reduced the amount available for deposition in leading-edge forest sites. The postfire snowpack was generally less dense on the anthropogenic disturbances, and with greater insulation potential, less heat loss should occur through the snowpack. The postfire forest snowpack was unchanged in comparison to prefire characteristics which suggests that thaw season conditions have the greatest effect on active layer thickening and surface subsidence following wildfire.

Modeling the spatial distribution of subarctic forest in northern Manitoba using GIS-based terrain and climate data

Northern forested ecosystems are predicted to change dramatically in response to climate change during the next century. The purpose of this paper was to use logistic regression analysis to model the effects of climate and topography on the spatial distribution of the northern forest around Churchill, Manitoba, Canada. Climate maps were modeled using kriging interpolation of actual climate data collected from 34 long-term monitoring sites distributed throughout the study area, and topographic information was derived from commercially available digital elevation models. Five of the 18 independent variables contributed appreciably (p < 0.15) to the final logistic regression model: distance from the Hudson Bay coast, summer soil temperature, snow density, slope, and snow water equivalent. Current forest distribution was predicted with 66% accuracy using the final model, and Kappa statistics indicated significant agreement between modeled and actual forest extents. Significant explanatory variables demonstrate important synergistic effects of Hudson Bay, wind, and snow in determining forest distribution. Modeled forest extents were further south than actual forest limits, which suggest that the treeline is not likely in equilibrium with the present climate.