Subarctic Forest Research Articles

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

ABSTRACTThe 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.

Controlling factors on the interannual CO2budget at a subarctic black spruce forest in interior Alaska

Controlling factors on the interannual CO₂budget at a subarctic black spruce forest in interior Alaska

Controlling factors on the interannual CO2 budget at a subarctic black spruce forest in interior Alaska

The eddy covariance method was applied to measure net ecosystem CO2 exchange (NEE) at a subarctic black spruce forest in interior Alaska during 2003 and 2004. To clarify the budget of CO2, we divided photosynthesis and respiration by applying the Carbon Budget Analysis Tool, in which the potential photosynthetic rate, the light use efficiency, and the suppression factors on photosynthesis were evaluated.The potential photosynthetic rate and the light use efficiency were related with the understory leaf area index. The determined optimal temperature of photosynthesis was higher than 15 ◦C, which was higher than that of other boreal forests. Drought in midsummer of 2004 suppressed both photosynthesis and respiration, but the suppression was more effective in photosynthesis, resulting in a slightly decreased NEE. Cumulative respiration and photosynthesis were 2.29 and -2.50 kg CO2 m-2 in 2003, and 2.37 and -2.44 kg CO2 m-2 in 2004, resulting in calculated annual CO2 sink budgets of -210 and -70 g CO2 m-2 in 2003 and 2004, respectively.

Plant Community Structure After Wildfire in the Subarctic Forests of Western Labrador

Abstract We compared western Labrador (Canada) plant communities on 12 10-ha plots representing five forest ages (2, 18, 40, 80, and 140 years) on subhygric sites and two 140-year-old sites on an atypical, moist, well-drained soil. Species richness was less variable and lower on the 80-year-old sites, and conifers did not dominate a site until 40 to 80 years after a disturbance. Herbs were dominant on 2- and 18-year-old sites, whereas woody shrubs were common across all successional stages. Cladina spp. were most abundant on our 40-year-old sites but were replaced by pleurocarpous mosses on our ≥80-year-old sites. Our results are consistent with others who found a delay in conifer establishment that may have resulted from poor seed beds due to the accumulation of unburned duff and inhibitory chemicals from Cladina spp. If these factors are inhibiting conifer establishment, this may conflict with the objectives of forest managers considering emulating natural disturbance in forest operations.North. J. Appl. For. 22(4):229–235.

Response of ericoid mycorrhizal colonization and functioning to global change factors

Summary • Here, we investigated effects of increased atmospheric CO 2 concentration, increased temperatures, and both factors in combination on ericoid mycorrhizal colonization, mycorrhizal functioning and below-ground carbon allocation in a subarctic forest understorey, to evaluate the hypothesis that photosynthesis is a primary driver for mycorrhizal colonization. •T reatment effects on ecosystem processes were investigated using 14 C-pulse labelling and photosynthesis measurements in combination with analysis of ergosterol content in roots. The effects on δ 15 N in leaves were also studied. •E rgosterol content in hair roots was positively correlated with ecosystem photo- synthesis and was higher in heat- and CO 2 -treated plots. Leaves from CO 2 plots tended to be more depleted in 15 N compared with controls both for Vaccinium myrtillus and V. vitis-idaea . • Our results suggest that changes in ecosystem photosynthesis, plant carbon (C) allocation may give rise to changing mycorrhizal colonization under elevated CO 2 and temperature. The role of mycorrhizas in ecosystem N-cycling may change on a long-term basis as inorganic N availability declines with increasing levels of atmospheric CO 2 .

Heavy metals in soils near the nickel smelter: chemistry, spatial variation, and impacts on plant diversity.

Air pollution induced changes were observed both in plant communities and in soil chemistry in forest ecosystems near the nickel-copper smelter in the Kola Peninsula, Russia. All measured forest plant community parameters describing their floristic composition and structure were affected by pollution. Heavy metals were significantly concentrated in organic horizons of forest soils. The concentrations of ammonium acetate-extractable nickel and copper in organic horizons near the smelter were approximately two orders of magnitude higher than the background levels in the region. Based on pH values, air pollution has not resulted in a detectable topsoil acidification near the smelter. However, concentrations of extractable magnesium, potassium and nitrogen in organic horizons tended to be lower towards the smelter. The spatial variability of data obtained results in necessity of the two complementary, macroscopic and microscopic, approaches to ecosystem investigation. The macroscopic approach better revealed the influence of pollution. The ordination of the major species diversity indexes was highly related to soil properties, suggesting that the content of heavy metals and nutrients is the best soil related predictor of species diversity in polluted areas. Besides direct input of pollutants from the atmosphere, soil contamination and nutritional disturbance contribute significantly to the observed vegetation damage in subarctic forest ecosystems.

The Annual Carbon Budget for Fen and Forest in a Wetland at Arctic Treeline

Three separate research efforts conducted in the same wetland-peatland system in the northern Hudson Bay Lowland near the town of Churchill, Manitoba, allow a comparison of two carbon budget estimates, one derived from long-term growth rates of organic soil and the other based on shorter-term flux measurements. For a tundra fen and an open subarctic forest, calculations of organic soil accumulation or loss over the last half-century indicate that while the fen on average has lost small amounts of carbon from the ecosystem, the adjacent forest has gained larger amounts of atmospheric carbon dioxide. These longer-term data are supported by shorter-term flux measurements and estimates, which also show carbon loss by the fen and carbon uptake by the forest. The shorter-term data indicate that the fen's carbon loss is largely attributable to exceptionally dry years, especially if they are warm. The forest may gain carbon at an increased rate as it matures and during warm growing seasons. Also, the changes in relief of the dynamic hummock-hollow landscape in the fen may inhibit photosynthesis.

Use of ground observations to simulate the seasonal changes in the backscattering coefficient of the subarctic forest

RADARSAT synthetic aperture radar (SAR) data acquired at C Band, HH polarization, and for the 20/spl deg/-27/spl deg/ and 45/spl deg/-49/spl deg/ incidence angle ranges were available over northern Quebec, Canada, (54/spl deg/N, 72/spl deg/12'W), in the fall of 1996, the winter of 1997, and the spring of 1997. The main land occupation of this area is sparse black spruce (Picea mariana) forests. Vegetation characteristics are jointly used with snow and soil observations coinciding with the satellite overpasses to simulate the seasonal changes in the backscattering coefficient of the subarctic forest. The aim of this study is twofold. First to evaluate the effects of the seasonal changes in vegetation on the RADARSAT SAR data, and second to use backscattering models as a tool for a better interpretation and understanding of the RADARSAT SAR data over snow-covered forested areas. Simulations show the importance of the surface-vegetation interaction term and the wet snow surface roughness on the discrimination between open forest and denser forest, and on the contrast between wet snow and dry snow covers. When comparing the simulations to the RADARSAT SAR data, the poorest results are obtained in the spring for a rough wet snow. It is shown that they are mainly due to a crude evaluation of the vegetation dielectric constant rather than to uncertainties introduced by the spatial variability in the wet snow surface roughness.

The Roots of North America's First Comprehensive Public Health Insurance System

askatchewan, sandwiched between Alberta and Manitoba, is one of three prairie provinces in Canada. The province consists mainly of dry prairie in the south (where it borders the states of Montana and North Dakota) and subArctic forest, giving away to tundra along its border with the North West Territories. It was opened for European settlement after the building of the Canadian Pacific Railway at the end of the nineteenth-century and grew slowly, stabilizing at a population of between 900,000 and one million after the 1940s. Until the 1950s, this sparsely settled province was sustained by a one-crop wheat economy. Saskatchewan's population distribution reflected this, as most people lived in rural areas. There were only two medium-sized cities (Regina and Saskatoon) and six smaller ones ‘which anchored a network of villages and towns that covered an expanse of agricultural land larger than France’. Although less than eight per cent of Canadians lived in Saskatchewan in the 1940s, this province has played a large role in the development of national social policy. Western Canada, particularly Saskatchewan and Manitoba, was the crucible of the nation's Social Democratic movement which was based largely on the strong tradition of co-operative prairie wheat farming and marketing. Canada's first Social Democratic party, the Cooperative Commonwealth Federation (CCF), the forerunner of the New Democratic Party, was born during the Great Depression in Manitoba and Saskatchewan. The party came to power in the Saskatchewan pro-

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.

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.

Breeding songbird abundance related to secondary succession in the subarctic forests of western Labrador

To describe the effects of natural disturbance on birds in western Labrador, we mapped songbird territories in fourteen 10-ha plots originating by natural fire. Plots were 2, 18, 40, < 70 (young conifer) and < 135 years old (mature conifer and mature white birch, Betula papyrifera, forests). Three species, dark-eyed junco, white-throated sparrow and ruby-crowned kinglet, accounted for 50% of all bird records. Bird density and species richness peaked in 2-year-old burns and mature forest stages. High bird densities in 2-year-old burns were likely due to high snag densities. Most species were not unique to a particular age since disturbance, but there were different species in early, < 40-years-old burns, and later stages. Some birds such as yellow-bellied flycatcher and Swainson’s thrush were exclusive to white birch forests, a rare forest type in western Labrador.

The Subarctic Forest–Tundra: The Structure of a Biome in a Changing Climate

The Subarctic Forest–Tundra: The Structure of a Biome in a Changing Climate

CONTROLS ON ENERGY AND CARBON FLUXES FROM SELECT HIGH-LATITUDE TERRESTRIAL SURFACES

While the physical processes driving energy fluxes in the high latitudes are universal, some of the controlling factors such as permafrost, temperature, and vegetation play a special role. Annual net radiation at Arctic treeline is larger over subarctic forest than over tundra as a result of smaller albedo during the snow-cover period. The absorbed solar radiation is notably larger in late winter. During the snow-free period, in well-watered areas, there is a hierarchy in potential evaporation from very high rates for shallow tundra lakes and ponds to low rates for well-drained upland heath terrain. With abundant moisture and warm conditions, open coniferous forests, dwarf deciduous forests, and sedge fens have similar energy and water balances. During the growing season when moisture is limiting, a sedge fen, more so than a coniferous forest, curtails its evaporation rate. Under cold conditions, however, coniferous forest has the smaller evaporation. Soil heat fluxes in summer comprise from 10% to 15% of the net radiation and are fairly uniform both temporally and spatially. The carbon budget of peatlands, which are major global repositories of carbon, responds strongly to air and soil temperatures and to the water balance. Warm and wet conditions support strong photosynthesis and a substantial methane flux. Warm and dry conditions favor strong respiration carbon losses from plants and soil. In a 2 × CO2 world, substantial changes in temperature, precipitation, and energy and water balances are anticipated and these will drive substantial changes in the high-latitude carbon budget. [Key words: energy and carbon fluxes, high latitudes.]

Advances in Canadian forest hydrology, 1995-1998

Approximately 42% of Canada is covered by forests, which in turn can be subdivided into nine distinct forest ecozones. Many forested ecozones are located in northern Canada, where cold winters and cool summers provide forest environments that are less well-understood that those in more temperate locations. A number of major developments in recent years have stressed the need for enhanced understanding of hydrological processes in these forest landscapes. These include an increased emphasis on sustainable forest management in Canada as well as major scientific initiatives (e.g. BOREAS) examining water, carbon and energy fluxes in forest ecosystems, with a particular focus on boreal and subarctic forests. Recent progress in our understanding of forest hydrology across Canada is reviewed. Studies of hydrological processes across the spectrum of forest ecozones are highlighted, as well as work on hydrological responses to forest disturbance and recovery. Links between studies of hydrological processes in Canada's forests and other fields of research are examined, with particular attention paid to ongoing efforts to model hydrological impacts and interactions with the climate, biogeochemistry, geomorphology and ecology of forested landscapes.

Influence of snowfall and melt timing on tree growth in subarctic Eurasia

The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temperature for recent decades1,2, compared to earlier this century, are unknown. This sensitivity change is problematic, in that relationships between tree-ring properties and temperature are widely used for reconstructing past climate. Here we report an analysis of tree-ring and climate data from the forest–tundra zone, in combination with a mechanistic model of tree-ring growth, to argue that an increasing trend of winter precipitation over the past century in many subarctic regions3,4,5 led to delayed snow melt in these permafrost environments. As a result, the initiation of cambial activity (necessary for the formation of wood cells) has been delayed relative to the pre-1960 period in the Siberian subarctic. Since the early 1960s, less of the growth season has been during what had previously been the period of maximal growth sensitivity to temperature. This shift results not only in slower growth, but also in a reduced correlation between growth and temperature. Our results suggest that changes in winter precipitation should be considered in seeking explanations for observed changes in the timing of the ‘spring greening’ of high-latitude forests6, and should be taken into account in the study of the role of the Siberian subarctic forest in the global carbon cycle.

Analysis of Multi-Temporal ERS-1 SAR Data of Subarctic Tundra and Forest in the Northern Hudson Bay Lowland and Implications for Climate Studies

RÉSUMÉDes données satellite radar ERS-1 out été utilisées pour analyser les variations annuelles de la rétrodiffusion dans la tundra sub-arctique et la forêt dans la partie nord des basses terres de la Baie d'Hudson (HBL) près de Churchill, Manitoba. On utilise des données de terrain relatives aux conditions physiques, écologiques et météorologiques acquises dans le cadre de cette étude afin d'interpréter les variations de la rétrodiffusion à partir de cinq sites représentant des types de terrain caractéristiques des terres basses de la Baie d'Hudson (fen, plage soulevée, arbustes de saule/bouleau, forêt ouverte et lac). Les plus grandes variations de rétrodiffusion observées à l'intérieur d'un même type de terrain au cours d'un cycle annuel entier (août 1992 à août 1993) sont associées à des périodes de gel et dégel et à l'humidité de surface (humidité du sol et quantité d'eau dormante). Les différences des valeurs de rétrodiffusion entre les sites dépendent de la nature de la surface qui détermine l'ampleur du processus de rétrodiffusion (volume ou surface). L'impact de l'utilisation des données satellite multidate sur les recherches en cours dans le domaine des études climatiques dans la région des basses terres est mis en relief.

Small-scale dynamics of plant communities in an experimentally polluted and fungicide-treated subarctic birch-pine forest

Pollution from the Cu-Ni smelter at Monchegorsk, Kola peninsula, has resulted in major changes in the plant communities surrounding the smelter. However, very little pollution reaches northern Finland, which makes it possible to use this area for field experiments to study the mechanism of community change under pollution load. A field experiment was established to study the possible effect of pollution on the subarctic forest community, with Cu-Ni pollution and acid rain (AR) used as treatments. A fungicide (F)-treatment was also added to estimate the significance of plant-fungus interactions in community response. Floristic similarity decreased during the experiment, both within and between treatments. Cu-Ni- and AR-treatments did not have any effect on species richness. The Cu-Ni treatment reduced significantly the number of new species arrivals in plots, whereas the number of local extinctions remained constant. The heavy metal treatment resulted in a decrease in the bryophyte cover. The cover of Linnea borealis increased slightly due to the Cu-Ni-treatment, but decreased due to the AR-treatment. The F-treatment also resulted in a lower richness than in the untreated variant. Again, this effect was due to the reduced number of arrivals, whereas the number of local extinctions remained unchanged. The F-treatment also resulted in a higher cover of bryophytes and dwarf shrubs. Changes in species richness of subarctic understorey plant communities were mainly caused by the differential arrival of species under different environmental conditions. As the number of arrivals was negatively correlated to the F-treatment, the presence of (presumably positive) interactions between vascular plants and fungi may have an influence on the response of a community to pollution.

Impact of increased UV-B on plant ecosystems

Elevated levels of UV-B are known to inhibit plant growth, development and physiological processes, although sensitivity to UV-B varies within plant species. Conifers and many evergreens are long-lived with long generation times, and damage by UV-B is likely to accumulate over the years. Three pilot experiments in closed chambers and greenhouses have revealed variable responses in subarctic forest plants and trees to enhanced UV-B radiation. These responses have been identified as changes in morphology and growth. Our current project seeks to identify and quantify the effects of UV-B radiation on the growth and development of Scots pine needles under field conditions.

Productivity and Population Increase of Subarctic Breeding Canvasbacks

Effective waterfowl management is dependent upon adequate population and productivity information from all portions of a species' breeding range, but productivity of canvasbacks (Aythya valisineria) breeding in the boreal forest has not been assessed adequately. We measured indices of productivity for canvasbacks breeding in the subarctic boreal forest near Yellowknife, Northwest Territories, during 1985-95. Mean clutch size was 7.05 ± 0.16 eggs. Size of broods was 4.25 ± 0.30 for Class I and 4.00 ± 0.37 for Class II. Brood size values generally were lower than those measured in parkland habitats. Apparent nest success averaged 69% and was consistently high. Production of broods per pair (0.3) and young per pair (1.4) was low but similar to values reported for some parkland breeding populations. Comparison of survey data between the periods 1962-65 and 1985-95 indicated a 10-fold increase in the number of canvasback pairs and broods on our study area. Productivity was inadequate to account for this increase, which suggests that high survival rates or immigration were contributing factors.