Subarctic Boreal Forest Research Articles

Observation of spatial and temporal patterns of seasonal ground deformation in central Yakutia using time series InSAR data in the freezing season

The seasonal freeze/thaw variations of the active layer cause seasonal ground deformation, such as thaw subsidence in summer and frost heave in winter due to the cyclic phase changes of soil water. The Synthetic Aperture Radar (SAR) remote sensing, especially interferometric SAR (InSAR) techniques, has been proven to be a very useful tool for observing surface displacements of permafrost environments. Most previous studies on seasonal InSAR displacement have been concentrated in several study sites in the Arctic tundra regions. The objective of this study is to extend the InSAR analysis of seasonal ground deformations to boreal forest regions, where monitoring ground deformation is particularly important in terms of better understanding active layer dynamics under various ecological and geological conditions. In this study, we presented a strategy to analyze the time series SAR data in the freezing season to estimate the differential phase for seasonal ground deformation while overcoming the problem of coherence losses due to the rapid growth of vegetation during the short growing season. We applied the SBAS-based InSAR processing method to Sentinel-1 SAR in the central Yakutian lowlands, where boreal forests and thermokarst landforms are widely distributed, and retrieved frost-related displacement signals successfully. In addition to the magnitude of ground deformation in the freezing season, we further examined the temporal deformation pattern related to the progression of the freezing front in the soil during active freezing. Based on the Stefan solution, we proposed a piecewise linear model for the time series deformation. The proposed model divides the time series displacement according to the progression of freezing into three linear segments, and the slope parameter of each linear model can be interpreted as indicating the hydrological characteristics of the upper, middle, and lower parts of the soil. The results for the Yakutian lowlands illustrated the potential of SAR remote sensing to observe and quantify spatial details of the thermal and hydrological properties inside the active layer soil even in highly vegetated subarctic boreal forest areas.

Measurement report: Long-term measurements of aerosol precursor concentrations in the Finnish subarctic boreal forest

Abstract. Aerosol particles form in the atmosphere via the clustering of certain atmospheric vapors. After growing into larger particles by the condensation of low-volatility gases, they can affect the Earth's climate by scattering light and acting as cloud condensation nuclei (CCN). Observations of low-volatility aerosol precursor gases have been reported around the world, but longer-term measurement series and any Arctic data sets showing seasonal variation are close to nonexistent. Here, we present ∼7 months of aerosol precursor gas measurements performed with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. We deployed our measurements ∼150 km north of the Arctic Circle at the SMEAR I (Station for Measuring Ecosystem–Atmosphere Relations) continental Finnish subarctic field station, located in the Värriö strict nature reserve. We report concentration measurements of the most common compounds related to new particle formation (NPF): sulfuric acid (SA), methane sulfonic acid (MSA), iodic acid (IA) and the total concentration of highly oxygenated organic molecules (HOMs). At this remote measurement site, SA originates from both anthropogenic and biological sources and has a clear diurnal cycle but no significant seasonal variation. MSA shows a more distinct seasonal cycle, with concentrations peaking in the summer. Of the measured compounds, IA concentrations are the most stable throughout the measurement period, except in April during which time the concentration of IA is significantly higher than during the rest of the year. Otherwise, IA has almost identical daily maximum concentrations in spring, summer and autumn, and on NPF event or non-event days. HOMs are abundant during the summer months and low in the autumn months. Due to their low autumn concentrations and high correlation with ambient air temperature, we suggest that most HOMs are products of biogenic emissions, most probably monoterpene oxidation products. NPF events at SMEAR I happen under relatively low-temperature (1–8 ∘C) conditions, with a fast temperature rise in the early morning hours as well as lower and decreasing relative humidity (RH, 55 % vs. 80 %) during NPF days compared with non-event days. NPF days have clearly higher global irradiance values (∼450 m−2 vs. ∼200 m−2) and about 10 ppbv higher ozone concentrations than non-event days. During NPF days, we have, on average, higher SA concentrations, peaking at noon; higher MSA concentrations in the afternoon; and slightly higher IA concentration than during non-event days. In summary, these are the first long-term measurements of aerosol-forming vapors from SMEAR I in the subarctic region, and the results of this work will help develop an understanding of atmospheric chemical processes and aerosol formation in the rapidly changing Arctic.

Water balance of several subarctic catchment areas

The scientific article by American hydrologists (Bolton et al. in Water balance dynamics of three small catchments in a Sub-Arctic boreal forest, 2004. https://pdfs.semanticscholar.org/c06b/7bad86cc15c5625fef0d847748bd9468f989.pdf) which is devoted to the water balance of three subarctic catchment areas, evoked great interest and encouraged to continue research in this field. The article deals with water balance elements of three small subarctic catchment areas near Fairbanks, Alaska, USA, published on the Internet (Bolton et al. 2004). The catchment area under study is Cariboo-Pocker Creek (CACPC). It is 48 km to the north of Fairbanks, Alaska. CACPC is situated in the tundra, its territory is 101.5 km2 and the soil below the surface of the ground is always frozen. Three catchment areas within CACPC are: C-2 (5.2 km2), C-3 (5.7 km2) and C-4 (11.4 km2). The catchment areas consist of 3%, 53% and 19% of permafrost, respectively. Taking into consideration the information from the American research, it turned out to be rather interesting to compare some water balance parameters presented in the article with those which are calculated with the help of a new method (Iofin in Proceedings of VI all-Russia hydrology congress, vol 1, pp 62–67, 2004). This new method is based on the linear-correlation theory and linear-correlation equation of water balance. This method has an effect in the catchment areas where hydrological observations are not carried out. Apart from this comparison, it is also of great interest to calculate the value of infiltration capacity in permafrost areas. It is also compelling to learn how accurately evapotranspiration in permafrost areas with lack of observations can be calculated with the help of rather popular Priestley–Taylor equation. The accuracy of calculation of evapotranspiration in a number of regions in the temperate zone made by Russian scientists with the help of different existing empirical formulae was under consideration. It is proved to be unsatisfactory. We had a rare opportunity to use basic data from the permafrost area and to calculate infiltration capacity and evapotranspiration. The comparison of the values of evapotranspiration shows that the calculations made with the help of the linear-correlation model (LCM) and Priestley–Taylor equation differ considerably.

Landscape variability of vegetation change across the forest to tundra transition of central Canada

Widespread increases in the productivity of tundra ecosystems and static trends – or even declines – in boreal ecosystems have been detected since the early 1980s using coarse-scale remote sensing. However, intermediate-scale Landsat studies have shown that these changes are heterogeneous and may be related to landscape and regional variability in climate, land cover, topography and moisture availability. In this study, a Landsat Normalized Difference Vegetation Index (NDVI) time-series (1984–2016) was examined for an area spanning the transition from sub-Arctic boreal forest to Low Arctic tundra in central Canada. This was supplemented by analyses of relationships with a suite of environmental variables and in situ measurements of bulk vegetation volume. Results show that NDVI trends were generally positive (i.e. increasing) across the study area but were smallest in the forest zone and largest in the northern tundra zone. More than one-quarter (27%) of un-masked pixels exhibited a significant (p < 0.05) trend and virtually all (99.3%) of those pixels exhibited an increasing, or “greening”, trend. Greening pixels were most common in the northern tundra zone and the southern ecotone zone. Random Forest modeling of the relationship between NDVI and environmental variables indicated that the magnitude and direction of trends varied across the forest to tundra transition. Areas that experienced larger increases in NDVI include: (i) areas where summer temperatures increased; (ii) areas exhibiting predominantly shrub and forest cover; and (iii) locations closer to major drainage systems, further from major lakes, and at lower elevations. Ground validation in the central portion of the study area reveals a strong relationship (R2 = 0.79) between vegetation volume and NDVI for non-tree functional groups and that alder (Alnus crispa) shrublands and open spruce (Picea mariana and P. glauca) woodland with shrubby understories were most likely to exhibit greening. These findings indicate that the largest positive and more significant NDVI trends were associated with increased productivity in shrub-dominated environments, especially at, and north of the treeline in localities with favorable growing conditions. Smaller and less significant NDVI trends in boreal forest environments south of the treeline were likely associated with long-term successional change following disturbance rather than the variables analyzed here.

Annual dynamics and resilience in post-fire boreal understory vascular plant communities

Boreal forests in western North America are considered to be resilient to wildfire disturbance, demonstrated by paleoecological evidence and adaptive regenerative traits possessed by many species. However, little is known about drivers of fine-scale temporal changes in understory communities in boreal forests immediately following fire. Knowledge of these changes, and their relationships with burn severity and pre-fire forest stand conditions, could help us determine recovery of forests as wildlife habitat. Such information is urgently needed in the face of climate warming-induced changes in fire frequency and severity. We used a high-quality, long-term dataset of annual measurements of understory vascular plant communities in sub-arctic boreal forest stands dominated by jack pine (Pinus banksiana), black spruce (Picea mariana), or a mix of the two in the Northwest Territories, Canada. Here, we describe the initial 10years of annual post-fire understory plant community dynamics and assess the important drivers shaping understory composition during this critical period of post-disturbance community assembly. First, we determined the relative importance of burn severity, pre-fire forest type, bare ground, woody debris, and number of years post-fire on understory species richness and composition dynamics following fire. Second, we explored annual dynamics in these communities and determined if compositional change was directional and predictable over time. We found that pre-fire forest type, burn severity, bare ground, woody debris, and number of years post-fire were important predictors of post-fire species richness and composition. Pre-fire forest type explained the greatest variation in understory plant composition, followed by burn severity. Across forest types, most species established within 1–3years following fire and initial species composition determined directional changes in composition. Our results suggest that targeting monitoring efforts in the years immediately post-fire may be sufficient to understand forest successional direction with respect to composition and the important drivers of those changes over the first decade post-fire. However, the recent and ongoing impacts of climate change in boreal regions of western North America leads to uncertainty surrounding the continued ability of these forests to demonstrate resilience under an altered fire regime so these interactions should continue to be considered across a range of forest types and burn severities.

Adaptive root foraging strategies along a boreal-temperate forest gradient.

The tree root-mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C):N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root-mycorrhiza-bacteria continuum along climate and soil C:N gradients.

Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada

Forest fires are one of the most important natural disturbances in boreal forests, and their occurrence and severity are expected to increase as a result of climate warming. A combination of factors induced by fire leads to a thawing of the near-surface permafrost layer in subarctic boreal forest. Earlier studies reported that an increase in the active layer thickness results in higher carbon dioxide (CO2) and methane (CH4) emissions. We studied changes in CO2, CH4 and nitrous oxide (N2O) fluxes in this study, and the significance of several environmental factors that influence the greenhouse gas (GHG) fluxes at three forest sites that last had fires in 2012, 1990 and 1969, and we compared these to a control area that had no fire for at least 100years. The soils in our study acted as sources of CO2 and N2O and sinks for CH4. The elapsed time since the last forest fire was the only factor that significantly influenced all studied GHG fluxes. Soil temperature affected the uptake of CH4, and the N2O fluxes were significantly influenced by nitrogen and carbon content of the soil, and by the active layer depth. Results of our study confirm that the impacts of a forest fire on GHGs last for a rather long period of time in boreal forests, and are influenced by the fire induced changes in the ecosystem.

Are the climatic factors combined with reindeer grazing affecting the soil CO2 emissions in subarctic boreal pine forest?

In this work, we investigated how the reindeer grazing in subarctic boreal Scots pine forests and climate (air temperature and the amount of precipitation) affects soil temperature, soil water content, and ultimately the CO2 efflux from forest soils. The study was carried out in years 2013 and 2014, where 2013 was an extremely dry year (especially the summer), while 2014 was a “normal” year. Our work showed that in subarctic mature pine forests, soil temperatures were higher, and soil water content was fluctuating more on grazed areas compared to non-grazed areas in both years. On both years, the soil water content on the grazed area was higher in June and the situation changed in the second half of July when the moisture content in the non-grazed area remained higher. There was a negative correlation between soil water content and soil temperature. The soil CO2 effluxes were mostly affected by the year of measurement, time of measurement (different months through growing season), soil temperature and also by the management (grazed or non-grazed) resulting in higher CO2 emissions on the grazed areas. Soil moisture content was not affecting the soil CO2 efflux. The average soil CO2 efflux values were significantly higher in the year 2014 compared to the year 2013 mainly due to differences in soil temperature at the beginning of season.

Detecting Late Holocene cultural landscape modifications using LiDAR imagery in the Boreal Forest, Susitna Valley, Southcentral Alaska

The subarctic boreal forest, or taiga, is the largest biome in the world but has received minimal archaeological research because of its remoteness and difficult working conditions. In Southcentral Alaska the most common archaeological sites are surface manifestations of proto-historic semi-subterranean caches once used for food storage and living structures. However, in dense summer vegetation, these small-scale features are difficult to locate without high intensity pedestrian survey. To test the usefulness of LiDAR data for archaeological prospection in the taiga, we compare LiDAR imagery to the known distribution of small-scale semi-subterranean cultural features. The use of LiDAR, when complemented with Sky-View Factor, has proven valuable in identifying relatively small semi-subterranean features though it does not replace on-the-ground investigation. Nevertheless, the application of LiDAR to locate low density and small-scale cultural features is widely applicable across the subarctic in densely vegetated contexts and may assist in significantly expanding our current knowledge of land-use patterns and site distributions in logistically challenging places.

Assessing the contribution of combustion-derived contaminants to a remote subarctic environment from traffic on the Tibbitt to Contwoyto winter road (Northwest Territories, Canada)

Remote mining operations in Canada's Northwest Territories and Nunavut are supported by a 600km winter road, which spans the transition from subarctic boreal forest in Yellowknife to low Arctic tundra. Each year, thousands of truckloads of fuel, large equipment, and other heavy loads are hauled up the winter road. We investigated whether diesel emissions from commercial truck traffic is a major source of metals and polycyclic aromatic compounds (PACs) to aquatic ecosystems along the winter road. In March 2014, at the end of the hauling season, we collected integrated snow samples, water, and sediment from nine lakes located along the winter road, as well as from six lakes located within the city of Yellowknife. Examination of PAC composition and diagnostic ratios in snow samples showed that wildfires are an important source of PACs to lakes along the winter road, while anthropogenic sources are more prevalent in snow from Yellowknife lakes. Concentrations of PACs, including those associated with diesel emissions, were variable in snow, water, and sediment across all sites. The highest concentrations of PACs in snow were reported in winter road lakes located in the subarctic boreal forest, where forest fires are common. No compositional differences were observed for PACs in sediment and water samples between Yellowknife and winter road lakes. We did not observe any evidence of metal contamination in snow collected along the winter road, and metal concentrations in snow from winter road sites were consistently lower than Yellowknife sites. Our results show that a high contribution of PACs from natural sources can obscure potential contributions from diesel traffic emissions along the winter road.

Factors influencing permafrost temperatures across tree line in the uplands east of the Mackenzie Delta, 2004–20101This article is one of a series of papers published in this CJES Special Issue on the theme of Fundamental and applied research on permafrost in Canada.2Polar Continental Shelf Contribution 03611.

Air and near-surface ground temperatures, late-winter snow conditions, and characteristics of the vegetation cover and soil were measured across the forest–tundra transition in the uplands east of the Mackenzie Delta, Northwest Territories, in 2004–2010. Mean late-winter snow depth decreased northward from 73 cm in the subarctic boreal forest near Inuvik to 22 cm in low-shrub tundra. Annual near-surface ground temperatures decreased northward by 0.1–0.3 °C/km near the northern limit of trees, in association with an abrupt change in snow depth. The rate decreased to 0.01–0.06 °C/km in the tundra. The freezing season is twice as long as the thawing season in the region, so measured differences in the regional ground thermal regime were dominated by the contrast in winter surface conditions between forest and tundra.

Wet deposition mercury fluxes in the Canadian sub-Arctic and southern Alberta, measured using an automated precipitation collector adapted to cold regions

This paper reports mercury (Hg) concentrations and fluxes in precipitation that was collected from 2006 to 2008 at three sites in Canada: sub-Arctic boreal forest, sub-Arctic coast, and southern Alberta, using cold-adapted precipitation collectors which operated reliably at temperatures below −30 °C during the study. The southern Alberta site (Crossfield) may be influenced by Calgary urban air, whereas the sub-Arctic coastal (Churchill, Manitoba) and boreal forest (Fort Vermilion, Alberta) sites are in more remote northern areas. Annual mean Hg concentrations in precipitation (5.0–9.2 ng L −1) at the study sites were in the lower half of the range reported for southern Canada and the USA by the Mercury Deposition Network (MDN). But owing to typically low precipitation rates, gross wet Hg fluxes (0.54–2.0 μg m −2 yr −1) were among the lowest reported by MDN, with Crossfield having about twice the flux in 2007 of the other two sites. Flux was significantly correlated with precipitation, and thus was highest in summer (June–August) and lowest during winter, a pattern typical of other temperate continental locations. There was no evidence of higher wet Hg fluxes or concentrations in springtime at Churchill where atmospheric mercury depletion events (AMDEs) occur. Measured gross deposition fluxes at the study locations were ∼2–8 times lower than estimated by GEOS-Chem and GRAHM atmospheric models. The largest discrepancy occurred for Churchill, which raises the question of how well Hg deposition from AMDEs is described by current models. Better agreement between measurements and models was obtained from MDN stations in Alberta and Alaska, where wet Hg fluxes were 2–10 times higher than the study sites either because of power plant emissions (Alberta), or because of high precipitation rates (Alaska).

Northernmost Precontact Maize in North America

Corn (Zea mays ssp. mays) was a key economic plant in the Americas, yet little information exists on the northern limit of maize consumption before European contact. Based on the analysis of carbonized food residue on pottery for plant microfossils (phytoliths and starch granules) from 58 precontact archaeological sites, we report the first evidence of maize consumption in the subarctic boreal forest. Recovery of maize microfossils from several widely distributed Laurel phase (Middle Woodland/Initial Shield Woodland) vessels indicates that the diffusion of corn into this region was surprisingly early (ca. A.D. 500) and may have initially spread through long-distance exchange networks linking temperate and boreal North America during the Woodland period. After A.D. 1000 maize was a widespread component of diet and was consumed by every major Late Woodland culture in the region. These results have profound implications both for the history of this cultigen and for small-scale human societies in northern North America.

The environment and permafrost of the Mackenzie Delta area

AbstractThe Mackenzie Delta, prograding northwestwards into the Beaufort Sea, is North America's largest arctic delta. This Holocene feature is bounded by rolling uplands to the east and the Richardson Mountains to the west. Treeline traverses the region, separating the subarctic boreal forest in southern parts from low‐shrub tundra and sedge wetlands at the coast. The region is experiencing rapid climate change, and mean annual air temperature has increased by more than 2.5°C since 1970. The area was at the margin of the Wisconsinan ice sheet, so that in the uplands the mean annual ground temperature and glacial history control permafrost thickness, which varies from &gt;700 m to &lt;100 m. Ground temperatures in the delta are distinct from the uplands due to the thermal influence of numerous lakes and shifting channels. In the uplands, ground temperatures decrease northwards across treeline in association with a decrease in the thickness of snow cover. Ground temperatures have increased since 1970 in the uplands by approximately 1.5°C in association with rising annual mean air temperature. The increase has been less in the delta south of treeline due to the extensive thermal influence of water bodies on ground temperature. However, in the outer delta, the ground is currently more than 2.5°C warmer than in 1970. The impact of climate change on permafrost is also evident in the thickness of the active layer, which increased on average by 8 cm at 12 tundra sites on northern Richards Island from 1983–2008. Copyright © 2009 John Wiley &amp; Sons, Ltd. and Her Majesty the Queen in right of Canada.

The size- and time-resolved composition of aerosols from a sub-Arctic boreal forest prescribed burn

Aerosols from wildfires are the primary aerosols in the Arctic atmosphere during the summer months. These aerosols occur in large, increasing quantities and impact the sensitive radiative balance in the Arctic. FROSTFIRE, a controlled burn in a Long-Term Ecological Research Area 50 km north of Fairbanks, Alaska, was designed to quantify the impacts of wildfire on sub-Arctic boreal forest ecosystems in permafrost regions. However, it provided a unique opportunity to examine smoke aerosols collected in the middle of a sub-Arctic boreal forest fire. A battery-powered eight-stage aerosol impactor (i.e. a Davis Rotating-drum Unit for Monitoring), mounted at the top of a 10 m meteorological tower in the burn zone, collected size- and time-resolved aerosol samples with 19.45 min resolution for 24 h during the burn. The samples underwent Proton Induced X-ray Emission (PIXE) and Proton Elastic Scattering Analysis (PESA) to determine the sizes and elemental compositions of the collected aerosols. Throughout the fire, the smoke reaching the sampler was strongly monodisperse with most of the aerosol mass in the optically active 0.56–1.15 μm in aerodynamic diameter size range. Fine organics comprised almost all of the mass in this optically active size range and the concentrations of the organics were high throughout the sampling period. However, unlike the fine organics, the potassium concentrations in the smoke decreased exponentially during the sampling period as the fire progressed from an active flaming to a smoldering behavior. The major findings from this field experiment are the dramatic differences in aerosol composition as a function of fire type (i.e. smoldering or active flaming) and that the largest emission of organics occurs during the smoldering phase, unaccompanied by the potassium emissions often used as a smoke tracer. These results agree with recent laboratory experiments.

Energy Balance Of A Sparse Coniferous High-Latitude Forest Under Winter Conditions

Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12–24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow surface. Therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. The sensible heat flux above the forest was fairly large, reaching more than 100 W m-2. The measurements of sensible heat flux within and above the forest revealed that the sensible heat flux from the snow surface is negligible and the sensible heat flux above the forest stems from warming of the trees. A simple model for the surface energy balance of a sparse forest is presented. The model treats the diffuse and direct shortwave (solar) radiation separately. It introduces a factor that accounts for the shading of the ground at low solar elevation angles, and a parameter that deals with the partial transparency of the forest.

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.

Representing randomly oriented fields in a magnetic tape: 38254 Reiderman, A.F.; Shur, M.L.; Dyakin, V.V. Soviet Journal of Nondestructive Testing, Vol. 23, No. 4, pp. 246–251 (Dec. 1987)

Aerosols from wildfires are the primary aerosols in the Arctic atmosphere during the summer months. These aerosols occur in large, increasing quantities and impact the sensitive radiative balance in the Arctic. FROSTFIRE, a controlled burn in a Long-Term Ecological Research Area 50 km north of Fairbanks, Alaska, was designed to quantify the impacts of wildfire on sub-Arctic boreal forest ecosystems in permafrost regions. However, it provided a unique opportunity to examine smoke aerosols collected in the middle of a sub-Arctic boreal forest fire. A battery-powered eight-stage aerosol impactor (i.e. a Davis Rotating-drum Unit for Monitoring), mounted at the top of a 10 m meteorological tower in the burn zone, collected size- and time-resolved aerosol samples with 19.45 min resolution for 24 h during the burn. The samples underwent Proton Induced X-ray Emission (PIXE) and Proton Elastic Scattering Analysis (PESA) to determine the sizes and elemental compositions of the collected aerosols. Throughout the fire, the smoke reaching the sampler was strongly monodisperse with most of the aerosol mass in the optically active 0.56–1.15 μm in aerodynamic diameter size range. Fine organics comprised almost all of the mass in this optically active size range and the concentrations of the organics were high throughout the sampling period. However, unlike the fine organics, the potassium concentrations in the smoke decreased exponentially during the sampling period as the fire progressed from an active flaming to a smoldering behavior. The major findings from this field experiment are the dramatic differences in aerosol composition as a function of fire type (i.e. smoldering or active flaming) and that the largest emission of organics occurs during the smoldering phase, unaccompanied by the potassium emissions often used as a smoke tracer. These results agree with recent laboratory experiments.

Effects of experimental crude oil spills on subarctic boreal forest vegetation near Norman Wells, N.W.T., Canada

Data are presented on the effects of experimental crude oil spills made on two subarctic boreal forest plant communities near Norman Wells, N.W.T. Spray spills of fresh unweathered crude oil at an intensity of 9.1 ℓ/m2 had a general herbicidal effect and caused the death of any green tissue coming in direct contact with the oil. Death of lichens and mosses was rapid and complete. For some higher plants, a considerable lag period occurred between the time of the spill and the time of death (up to 4 years for some individuals of Picea mariana). For others, death occurred during the first winter, with marked effects on cover values in the spring. These effects resulted in large decreases in total plant cover and frequency at spill sites. However, within a few weeks, and in subsequent years, some species developed regrowth shoots. Other species survived as underground rhizomes for a number of years prior to their reappearance above ground (i.e., Equisetum scirpoides). Limited seedling establishment by vascular plants was first observed in the fourth postspill growing season, when some sporeling establishment was also noted for several bryophyte species. No Picea mariana regeneration has occurred in the spill plots in the six postspill growing seasons monitored thus far.Crude oil spills made in winter were found to be less damaging than equivalent summer spills in their short-term biological effects and on rates of recovery and species affected. Initial observations indicate that a summer diesel oil spill shows roughly equivalent toxicity to a summer crude oil spill of the same intensity. Comparisons between an intensive spill (8500 ℓ) made at one point and dispersed spray spills indicate that the former are far less damaging per unit of oil applied to the plant community, with severe detrimental effects being largely limited to areas of direct surface contamination. In the point spill examined, most of the oil percolated downwards and then laterally. Surface vegetation growing above areas with subsurface horizons contaminated by oil was not greatly affected in the first 2 years. An increased area of damage appeared in postspill years 5 and 6, including death of Picea mariana. Oil also appeared to move laterally in 1976 when severe rains occurred, and the oiled area increased somewhat.Limited short-term effects of the spill treatments on depth of active layer thaw have been noted in this study, but these initial effects were not maintained after the first postspill growing season. The low rates of oil application make the conclusions about the effects of large spills on active layer stability conjectural. Potential effects on vegetation are much more firmly based. Oil in the boreal forest soil appeared to retain toxic properties throughout the 5-year study period.