Snow Cover Period Research Articles

Annual soil CO 2 effluxes in the High Arctic: The role of snow thickness and vegetation type

Little work has been done to quantify annual soil CO 2 effluxes in the High Arctic region because of the difficulty in taking winter measurements. Since the effects of climate change are expected to be higher in Arctic than in temperate ecosystems, it is important that summer measurements are extended to cover the entire year. This study evaluates the quantity and quality of soil organic C (SOC) and seasonal controls of soil CO 2 effluxes in three soils under three dominating types of vegetation ( Dryas, Cassiope, and Salix) at Svalbard. Measurements included soil CO 2 effluxes in the field and the laboratory, temperature, water content, and snow thickness. About 90% of the variation in soil respiration throughout 1 year was due to near-surface soil temperatures which ranged from −12 to +12 °C. Total annual soil CO 2 effluxes varied from 103 g C m −2 at soils under Cassiope, 152 g C m −2 under Dryas sites, and 176 g C m −2 under Salix, with 20%, 14%, and 30%, respectively, being released during a 6-month winter period. The sensitivity of soil respiration with respect to soil temperature was the same year round and differences in winter CO 2 effluxes at the three vegetation types were mainly related to subsurface soil temperatures controlled by snow depth. The quantity and quality of soil organic matter varied under the different vegetation types. Soils under Salix had the largest and most labile pool of SOC and were characterized by a long period of snow cover. In contrast, soils under Cassiope were more nutrient-poor, more acidic and held the smallest amount of total and labile SOC, whereas soils under Dryas remained snow-free most of the winter and therefore had the coldest winter conditions. Thus, winter soil respiration rates under Dryas and Cassiope were significantly lower than those under Salix; under Dryas this was mainly due to snow depth, under Cassiope this was a combination of snow depth and poor litter quality. It is concluded that winter respiration is highly variable across Arctic landscapes and depends on the spatial distribution of snow, which acts as a direct control on soil temperatures and indirect on vegetation types and thereby, the amount and quality of soil organic matter, which serve as additional important drivers of soil respiration.

Comparative analysis of laboratory freezing methods to establish cold tolerance of detached rhizomes and intact crowns in garden chrysanthemums (Dendranthema×grandiflora Tzvelv.)

Abstract Since 1926, the University of Minnesota herbaceous perennial breeding program has released N = 84 garden chrysanthemum cultivars (Dendranthema × grandiflora) with important traits for northern temperate climates, such as winter hardiness. Recent breeding objectives have identified the need for development of non-destructive phenotypic markers and destructive laboratory freezing tests for co-selection of cold tolerance in Dendranthema, Gaura, and other herbaceous perennial flower crops. Such methods have become critical to flower breeding programs in northern temperate regions during periods of above-average winter temperatures and minimal snow cover due to the ‘el Nino’ effect. Two different, destructive laboratory freezing tests were evaluated for their effectiveness in determining cold tolerance. Acclimated crowns of n = 6 garden chrysanthemum genotypes, ranging from hardy to non-hardy in USDA Z3-4, were used in Omega Block (using detached, emergent rhizomes) and chamber (using entire, intact crowns with emergent, non-emergent rhizomes) freezing test methods. Comparative winter survival in the field was monitored over locations and years. Cold tolerance was assessed at 0 to −12 °C with varying ramp and soak time periods. LT50 temperatures and number of living emergent rhizomes were also determined. Rhizome quality at 1, 3, and 5 cm depths was rated for regrowth on a 0 (dead) to 5 (undamaged) scale. The chamber freezing method was the most powerful to discern accurate LT50 values. Cold tolerant genotypes included ‘Duluth’ and Mn. Selection 98-89-7 (LT50 = −12 °C). Four genotypes were rated as non-hardy (LT50 = ≤−10 °C). Cold-tolerant genotypes also had significantly higher regrowth ratings for rhizomes at 1 and 3 cm depths. Future research will implement the chamber freezing method to assay the inheritance of winter hardiness in intact crowns of segregating populations.

Dynamic carbon dioxide exchange through snowpack by wind‐driven mass transfer in a conifer‐broadleaf mixed forest in northernmost Japan

CO2 efflux in the period of snow cover can be a large carbon source in the yearly carbon budget of snowy ecosystems. However, the behavior of CO2 in snowpacks and the mechanisms of the snow surface efflux are still unclear. We performed continuous (half‐hourly) midwinter measurements of CO2 concentrations in a conifer‐broadleaf mixed forest snowpack, and found that concentrations in the snowpack fluctuated significantly as wind speeds varied. The snow surface efflux was evaluated as the sum of the CO2 storage change in the snowpack and the CO2 input from the soil to the snowpack, taking into account the mixing due to airflow. The median value over 52 days (49 mmol m−2 d−1) was almost the same as the daily net ecosystem exchange rate in this forest (50 mmol m−2 d−1) estimated by the eddy covariance technique and the storage‐change flux in the air column. These values are clearly larger than the value we estimated using Fick's law of diffusion. These results show that airflow can be a dominant cause of mixing within snowpacks in midwinter. In addition, in the soil pores under the snowpack, the CO2 concentration was primarily related to air temperature, implying that soil respiration responds directly to air temperature, not to soil temperature, even beneath a 1‐m‐thick snowpack. We infer that the air temperature affected the root activity of trees through their trunks and that the variation in root respiration strongly affected the CO2 concentration fluctuation in soil under the snowpack.

Seasonal and diurnal variations in topsoil and subsoil respiration under snowpack in a temperate deciduous forest

We measured soil CO2 concentration at half‐hour intervals with infrared gas analyzers buried in soil at four depths throughout the snow cover season extending from early December to early April in a deciduous temperate forest. We evaluated soil CO2 efflux or total soil respiration, topsoil (the A‐horizon) respiration, and subsoil (the C‐horizon) respiration using a modified flux gradient method. Thereby, we investigated seasonal and diurnal variations in these soil respirations under snowpack. Soil CO2 concentration and soil respiration changed dynamically under the condition of constant soil temperature. Topsoil respiration decreased rapidly in late autumn and relatively constant until mid‐winter, whereas it increased in late winter when snowmelt progressed. On the other hand, subsoil respiration decreased gradually until mid‐winter and increased slightly in late winter. Both topsoil and subsoil respirations showed similar diurnal variations with a peak in early or mid‐afternoon, respectively, independently of soil temperature. These seasonal and diurnal variations in soil respiration were inferred to result from the supply of labile carbon compounds, which were respiratory substrates for microorganisms, into soil from litter with meltwater. The seasonal sum of topsoil, subsoil, and total respirations for the snow cover period of 4 months were 21.4, 48.0, and 69.4 gC m−2, respectively; these accounted for 3.0, 27.3, and 7.7% of the annual sum, respectively. The ratio of topsoil respiration to total soil respiration was 0.31 on average during the snow period, which was considerably lower than that in the summer season.

Water budget of Jyozankei Experimental Watershed during the no snow cover period

Water budget of Jyozankei Experimental Watershed during the no snow cover period

Fluctuation of the seasonal snowpack in a mountainous area of the heavy-snow district in the warm-temperate zone of Japan

AbstractThe seasonal snowpack and meteorological factors associated with the accumulation and ablation of the snowpack were monitored for 11 years in a mountainous area in the warm-temperate zone of Japan. No notable rise was observed in mean wintertime air temperature, but an increase was seen in the difference between the maximum and minimum air temperatures. Precipitation exhibited annual variability but no notable reduction over the measurement period. The length of the continuous snow-cover period increased slightly over the 11 years, but no trend in variability was observed. The maximum snow depth and maximum water equivalent of snow varied greatly from year to year, depending on the amount of snowfall. In a heavy-snow year, about 1600 mm of water, which is almost the mean annual precipitation for the whole of Japan, was found to be temporarily stored in the snowpack.

Effects on the Function of Arctic Ecosystems in the Short- and Long-term Perspectives

Historically, the function of Arctic ecosystems in terms of cycles of nutrients and carbon has led to low levels of primary production and exchanges of energy, water and greenhouse gases have led to low local and regional cooling. Sequestration of carbon from atmospheric CO2, in extensive, cold organic soils and the high albedo from low, snow-covered vegetation have had impacts on regional climate. However, many aspects of the functioning of Arctic ecosystems are sensitive to changes in climate and its impacts on biodiversity. The current Arctic climate results in slow rates of organic matter decomposition. Arctic ecosystems therefore tend to accumulate organic matter and elements despite low inputs. As a result, soil-available elements like nitrogen and phosphorus are key limitations to increases in carbon fixation and further biomass and organic matter accumulation. Climate warming is expected to increase carbon and element turnover, particularly in soils, which may lead to initial losses of elements but eventual, slow recovery. Individual species and species diversity have clear impacts on element inputs and retention in Arctic ecosystems. Effects of increased CO2 and UV-B on whole ecosystems, on the other hand, are likely to be small although effects on plant tissue chemisty, decomposition and nitrogen fixation may become important in the long-term. Cycling of carbon in trace gas form is mainly as CO2 and CH4. Most carbon loss is in the form of CO2, produced by both plants and soil biota. Carbon emissions as methane from wet and moist tundra ecosystems are about 5% of emissions as CO2 and are responsive to warming in the absence of any other changes. Winter processes and vegetation type also affect CH4 emissions as well as exchanges of energy between biosphere and atmosphere. Arctic ecosystems exhibit the largest seasonal changes in energy exchange of any terrestrial ecosystem because of the large changes in albedo from late winter, when snow reflects most incoming radiation, to summer when the ecosystem absorbs most incoming radiation. Vegetation profoundly influences the water and energy exchange of Arctic ecosystems. Albedo during the period of snow cover declines from tundra to forest tundra to deciduous forest to evergreen forest. Shrubs and trees increase snow depth which in turn increases winter soil temperatures. Future changes in vegetation driven by climate change are therefore, very likely to profoundly alter regional climate.

Comparative Analysis of Laboratory Freezing Methods to Establish Cold Tolerance of Detached Rhizomes and Intact Crowns in Garden Chrysanthemums

Since 1924, the Univ. of Minnesota herbaceous perennial breeding program has released n = 84 garden chrysanthemums (Dendranthema grandiflora). Recent breeding objectives have focused on development of non-destructive phenotypic markers and laboratory freezing tests for continued selection of cold-tolerant Dendranthema, Gaura, and other herbaceous perennial flowers. Such methods have become critical to flower breeding programs during periods of above-average winter temperatures and minimal snow cover. Two different laboratory freezing tests were evaluated for their effectiveness in determining cold tolerance. Acclimated crowns of n=6 hardy and non-hardy garden chrysanthemum genotypes were used in Omega Block (detached, emergent rhizomes) and chamber (intact crowns with emergent/non-emergent rhizomes) freezing test methods. Comparative winter survival in the field was monitored over locations and years. Cold tolerance was assessed at 0 °C to -12 °C with varying ramp and soak time periods. LT50 temperatures and number of living emergent rhizomes were determined. Rhizome quality at 1 cm, 3 cm, and 5 cm depths was rated on a 0 (dead) to 5 (undamaged) scale. The chamber freezing method was the most powerful to discern LT50 values. Cold tolerant genotypes included `Duluth' and 98-89-7 (LT50 = -12 °C). Three genotypes had intermediate cold tolerance (LT50 = -10 °C) and one genotype was not cold tolerant (LT50 = -6 °C). Cold-tolerant genotypes also had significantly higher regrowth ratings for rhizomes at 1cm and 3cm depths. Future research will use the chamber freezing method to assay the inheritance of winter hardiness in intact crowns of segregating populations.

Simulation of Water and Energy Fluxes in an Old-Growth Seasonal Temperate Rain Forest Using the Simultaneous Heat and Water (SHAW) Model

In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasizes the need for a mechanistic understanding of the interactions between forest canopies and hydrologic processes. Detailed measurements during the 1999 and 2000 hydrologic years were used to modify the Simultaneous Heat and Water (SHAW) model for application in forested systems. Major changes to the model include improved representation of rainfall interception and stomatal conductance dynamics. The model was developed for the 1999 hydrologic year and tested for the 2000 hydrologic year without modification of the site parameters. The model effectively simulated throughfall, soil water content profiles, and shallow soil temperatures for both years. The largest discrepancies between soil moisture and temperature were observed during periods of discontinuous snow cover due to spatial variability that was not explicitly simulated by the model. Soil warming at bare locations was delayed until most of the snow cover ablated because of the large heat sink associated with the residual snow patches. During the summer, simulated transpiration decreased from a maximum monthly mean of 2.2 mm day21 in July to 1.3 mm day21 in September as a result of decreasing soil moisture and declining net radiation. The results indicate that a relatively simple representation of the vegetation canopy can accurately simulate seasonal hydrologic fluxes in this environment, except during periods of discontinuous snow cover.

An Andosol–Cambisol toposequence on granite in the Austrian Bohemian Massif

In Europe, non-allophanic Andosols are linked with Hercynian basic and metabasic rocks in smoothed highlands with a cool and humid climate. We describe an Andosol–Cambisol toposequence derived from Variscan coarse-grained granite in Northern Austria (Bohemian Massif), where Andosols have formed on plateaus and Cambisols on steep slopes. The climate is continental, cool and humid (mean annual temperature and rainfall: 5.4 °C and 914 mm), with a 100-day mean annual period of snow cover. The forest is dominated by beech and spruce trees. Both soils are rich in organic matter and strongly acidic, but the Andosol is more strongly weathered than the Cambisol. Below the 15-cm-thick litter in the Andosol, the 38-cm-thick AB-Bw solum is dark reddish brown to strong brown, has a large C content (9.0–4.4%), and meets all the requirements of an andic horizon. In these horizons, oxalate extractable iron content (1.6–2.8% Fe o) represents 76–84% of free iron, and is much larger than Al o (0.8–1.5%). Both biotite and plagioclase are sources of Fe and Al. The formation of non-allophanic Andosol from granite was likely due to the combination of the following factors: cool and humid climate, large accumulation of organic matter, high infiltration rate, intense water percolation during spring thawing and significant content of weatherable minerals. As such conditions are not rare in European highlands, andic soils are probably more widespread in Europe than is currently thought.

Carbon dynamics of wetland in the Sanjiang plain

Methane (CH4) and carbon dioxide (CO2) emission was measured from mires in the Sanjiang Plain, Northeast China, by using a static chamber technique during free snow-covered periods. The seasonal mean emission of CH4 was 12.4mg/(m2·h) and the emission range of CO2 was 8.7–16.6g/(m2·d) (gross CO2 flux) during plant growth period. CO2 emission rate in the day was stronger than that at night, and the daily peak appears at 19:00. The mire plants in the Sanjiang Plain begin to sprout at the end of April. The aboveground biomass of the mire plants increased from zero to the peak from July to September and showed single peak form. The aboveground biomass of Carex lasiocarpa (464.8g/m2) was lower than that of Deyeuxia platyphylla (530.8g/m2), but the underground biomass was higher than that of Deyeuxia platyphylla. Gross CO2 flux showed the significance positive correlation relationship with plant biomass. Gross CO2 flux and CH4 emission were also correlated with soil temperature (0–5cm) and water temperature. However, the highest CH4 emission rate lagged behind the highest soil temperature in the root area during plant growth period. The data also indicated that wet and warm conditions during the early spring led to greater value of CH4 emission flux. Inundation is the necessary condition for the existence of methane bacteria, but there is no significant positive correlation between the inundation depth and CH4 emission rate in this region. Within the same growing season and under the same inundation condition, the variations of CH4 emission rate could be markedly different.

Impact of large herbivores on mountain forest stands in the Beskydy Mountains

The impacts of three herbivorous mammals (brown hare Lepus europaeus, roe deer Capreolus capreolus and red deer Cervus elaphus) on woody species were investigated in the Kněhyně supra-regional biocentre (Beskydy Mountains, Czech Republic, 950–1257 m a.s.l.) in relation to forest management. The study focused on the question of whether large herbivores may prevent shrub layer development, and thereby disturb natural forest regeneration. Rowan ( Sorbus aucuparia) was used as a model woody species for the study. The browsing intensity on rowan annual shoots showed that large herbivores delayed the growth of saplings, though stand development was essentially not disturbed. Moderate winter browsing (approximately 30%) was determined by the fact that roe deer and red deer stay in the region only from spring to autumn and tend to move to lower altitudes during the period of continuous snow cover. The density of hares, which remain in the region throughout the course of the year is permanently low. Summer browsing is low (approximately 10%) as a result of a plentiful availability of good quality food in the vegetation period. Leaves of Rubus idaeus form approximately 80% by volume of the diet of roe deer and red deer, while brown hares feed on grasses. For the Kněhyně biocentre management, it appears unnecessary to take any regulation measures to reduce the impact of large herbivores on vegetation. Similar conclusions would probably apply to other mountain areas under the same conditions. However, this conclusion might not apply to other mountains where there are different environmental conditions (different density of large herbivores and different food supply in the herb and shrub layers).

Characteristics of the displacement of a landslide with shallow sliding surface in a heavy snow district of Japan

The displacement of a landslide with shallow sliding surface in a heavy snow district was automatically monitored for over 4 years by a newly developed displacement gauge. Meteorological properties, meltwater and/or rainfall (MR), water equivalent of snow and other factors were simultaneously observed. Pore-water pressure was monitored but only for a limited period of time since the displacement of the landslide was too large. Statistical analyses showed that maximum daily displacements of each year were observed not in snow melting periods but immediately before or at the beginning of a snow cover period. There are three types of annual variation pattern with peaks in mid-November to mid-December, mid-April and mid-July. The variation pattern of displacement from the beginning of March to the beginning of June showed the least total displacement of those three types. Therefore, snow cover is likely to affect the displacement of a landslide. Detailed investigation of the landslide displacement during snow cover periods showed that the rate of displacement slowed as the snow cover deepened, meaning a decrease in MR and increase in water equivalent of snow. The displacement ratio for the unit antecedent MR effect during snow cover periods dropped when the snow started to accumulate on the ground in all 4 years. The reduction was likely attributable to snow load since it was found to have a negative logarithmic relation with the water equivalent of snow. Changes in pore-water pressure and the relationship between pore-water pressure and displacement during the snow cover periods differed from those in the other periods. Therefore, the displacement of a landslide that has a shallow sliding surface in a snowy region was considered to be affected by snow accumulation conditions, especially water equivalent of snow.

Inter-annual carbon dioxide uptake of a wet sedge tundra ecosystem in the Arctic

The CO2 flux of a wet sedge tundra ecosystem in the Arctic, at Barrow, Alaska, has been measured by the eddy correlation method since spring 1999, and the CO2 uptake by the vegetation during the spring and growing periods was examined between 1999 and 2000. CO2 flux changed to a sink immediately after the spring thaw in 1999 and the photosynthetic activity was high in the first half of the growing period. At this time the air temperature was low and solar radiation was high. In the 2000 season, the temperature was approximately 5°C lower during the snow-covered period, and increased up to 5 oC higher right after the spring thaw but the solar radiation decreased to two thirds of that in 1999. Thus, we found different CO2 accumulation during the snowmelt and the following two weeks between both years. The difference in the climate at beginning shoulder period of the growing season resulted in the difference of CO2 accumulation through the growing period. The maximum level of photosynthetic potential (Pmax) in late July was analyzed as being almost the same at 20 gCO2 m−2 d−1 for both years. However, the weekly average peak CO2 uptake was 16.4 and 11.9 gCO2 m−2 d−1 in 1999 and 2000, respectively, with the lower number in 2000 caused by the low radiation with high air temperatures. The CO2 accumulation during the spring and through the growing periods was a net sink of 593 gCO2 m−2 in 1999 and a sink of 384 gCO2 m−2 in 2000. High CO2 accumulation in 1999 was caused by earlier development of the vegetation, and the lower CO2 uptake in mid summer in 2000 was caused by unseasonable weather.

Annual CO2 balance of a subarctic fen in northern Europe: Importance of the wintertime efflux

The annual balance of CO2 was measured on a subarctic flark fen located in northern Finland (69°08′N, 27°17′E). Measurements were conducted using the micrometeorological eddy covariance method during the period from April 1998 to April 1999. Special emphasis was put on the importance of the wintertime CO2 balance as a component of the annual budget. The CO2 fluxes observed during the winter were relatively small (0.0055 mg CO2 m−2 s−1), but due to the long duration of the snow cover period, they play an important role in the annual balance of CO2. The efflux during the coldest periods, when soil surface temperatures fell below −10 °C, was enabled by markedly higher peat temperatures (close to 0 °C) in deeper layers. The typical nighttime respiration observed in summer was 0.10 mg CO2 m−2 s−1. The net photosynthesis had a typical daytime peak value of about −0.20 mg CO2 m−2 s−1 in July. Corresponding with the instantaneous CO2 fluxes, the highest daily sink balances of about −9 g CO2 m−2 d−1 were observed in July, while the highest daily respiration balances of about 2.5 g CO2 m−2 d−1 were observed before and after the sink period. The CO2 balance for the winter period (105 g CO2 m−2) was greater than the absolute value of the total annual balance (−68 g CO2 m−2), which shows the importance of the wintertime efflux. After taking into account estimates for CH4 efflux and carbon leaching, an annual carbon balance of −7 ± 5 g C m−2 was obtained for the fen.

Development of a Method for Forest Cafeteria Tests for Evaluating Chemical Deterrents against Bark Stripping by Sika Deer (Cervus nippon yesoensis)

Damage caused by sika deer (Cervus nippon yesoensis) is a serious problem in commercial and environmental (non-harvested) forests in Hokkaido, northern Japan. Cafeteria tests in forests may be useful for evaluating the efficacy of chemical deterrents against bark stripping by deer. To develop a method for forest cafeteria tests in the continuous snow cover period, two experiments were carried out. In the experiments, logs were produced from tree trunks, and used as carriers of chemical deterrents. Carriers were installed in forests and fed to deer. The first experiment was to find suitable sites and installation methods for carriers. Criteria for the local suitability and the installation methods were as follows: a) Sites where deer are active should be selected; b) Carriers should be installed along actively used deer trails; c) Installation sites of carriers should be changed in response to deer movement; d) Carriers should be produced from tree species that deer naturally prefer; and e) Each carrier should be partially buried in the snow. The second experiment evaluated the feasibility of a cafeteria test method based on the results of the first experiment. The method was used for 13 sets of the cafeteria test, in which the deterrent effectiveness of 5 chemicals (wood tar, rosin, wood vinegar, and 2 pyroligneous liquors) was examined. We obtained results from all the sets. The chemicals tested did not deter bark stripping by deer. Nevertheless, the method used in the present study was practical for the cafeteria tests.

Circumpolar Ecosystems 2000

During February 2000, the Churchill Northern Studies Centre hosted the Fourth Circumpolar Ecosystems Conference and Workshop. ..., the objective of the Circumpolar Ecosystems meeting was to bring together Northerners and scientists to exchange information and discuss relevant options for sharing indigenous knowledge and scientific research. This has been done in the traditional winter environment that dominates northern processes and lifestyles. A number of themes were developed at the meeting. One theme was adaptation to the changing climate. Although in general the ongoing warming has brought a decline in the period of annual snow and ice cover, the timing of seasons has become unpredictable. Changes in large-scale atmospheric circulation have been associated with a greater input of contaminants from southern latitudes, which is a major cause of concern. Another theme was that the approach to the coastal marine environments must be consolidated. For example, aspects of the Hudson Bay ecosystem involve the jurisdictions of three provinces and one territory, as well as aboriginal, federal, and international jurisdictions. It was suggested that a cooperative framework is needed in approaching systems like that of Hudson Bay. The final theme was that we need strong north-south communication and the establishment of a comprehensive northern ecological monitoring and assessment network in support of the issues relating to the other themes. The discussions relating specifically to Hudson Bay have been published by the Churchill Northern Studies Centre (2000) as a report entitled Addressing Climate Change in Hudson Bay: An Integrated Approach. ...

Patterns of winter desiccation in krummholz forms of abies lasiocarpa at treeline sites in glacier national park, montana, usa

Winter desiccation‐induced foliage loss at high‐elevation locations is an important determinant of positive carbon balance for trees and thus influences the location of the alpine treeline ecotone. In this study, data are presented that describe the amount of winter desiccation incurred by krummholz growth forms of subalpine fir (Abies lasiocarpa (Hook) Nutt.) at treeline locations in Glacier National Park, Montana, USA, for the winter of 1998/1999. An average 8.68% of the krummholz canopy was lost due to desiccation.Winter desiccation is not predictable based on any single environmental variable. When outliers are removed, winter desiccation shows a strong correlation with elevation (r= 0.97). Patch level winter desiccation amounts are, however, highly predictable from elevation, slope, aspect and topographic context when considered together. In general, injury increases with elevation and on more southwesterly facing hillslopes. High slopes and sheltered locations decrease winter desiccation.Within patches, most winter desiccation is located at the windward edge of the patch. This trend may be modified by the presence of leaders above the mean canopy surface of the krummholz patch, or by local microtopographic features such as dead branches or the proximity of large rocks.The winter of 1998/1999 was a high winter desiccation year compared to the two previous winters. The winter of 1998/1999 had high snowfall, and meltout did not occur until later than the previous two winters. The extended period of snow cover is hypothesized to be one of the causes of the increased winter desiccation for the 1998/1999 winter.

The surface energy balance of a snow cover: comparing measurements to two differentsimulation models

We compared two one-dimensional simulation models for heat and water fluxes in the soil-snow-atmosphere system with respect to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable field in central Sweden (Marsta), covering two years (1997–1999) of soil temperature, snow depth and eddy-correlation measurements were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10 cm and bare soil resulted in similar discrepancies. The simulated net radiation and sensible heat flux were in good agreement with that measured during snow-covered periods, except for situations with snowmelt when the downward sensible heat flux was overestimated by 10–20 Wm−2. The results showed that the uncertainties in parameter values were more important than the model formulation and that both models were useful in evaluating the limitations and uncertainties of the measurements.

Biogeophysical impacts of land use on present-day climate: near-surface temperature change and radiative forcing

Changes in land cover affect climate through the surface energy and moisture budgets, but these biogeophysical impacts of land use have not yet been included in General Circulation Model (GCM) simulations of 20th century climate change. Here, the importance of these effects was assessed by comparing climate simulations performed with current and potential natural vegetation. The northern mid-latitude agricultural regions were simulated to be approximately 1–2K cooler in winter and spring in comparison with their previously forested state, due to deforestation increasing the surface albedo by approximately 0.1 during periods of snow cover. Some other regions such as the Sahel and India experienced a small warming due to land use. Although the annual mean global temperature is only 0.02K lower in the simulation with present-day land use, the more local temperature changes in some regions are of a similar magnitude to those observed since 1860. The global mean radiative forcing by anthropogenic surface albedo change relative to the natural state is simulated to be −0.2Wm2, which is comparable with the estimated forcings relative to pre-industrial times by changes in stratospheric and tropospheric ozone, N2O, halocarbons, and the direct effect of anthropogenic aerosols. Since over half of global deforestation has occurred since 1860, simulations of climate since that date should include the biogeophysical effects of land use.