Boreal Landscape Research Articles

Are shallow-soiled sites sensitive to increased biomass removals? An operational, paired-wise comparison approach

Although commonly cited as being particularly sensitive to biomass/nutrient removals via full-tree harvesting (i.e., entire aboveground portion of the tree is removed and processed at roadside), there have been no long-term experimental trials installed or reported on to date that specifically target shallow-soiled (<20cm) sites common in strongly glaciated boreal landscapes. This study reports on ten year results examining the effects (i.e., regeneration potential, tree growth, soil N availability, and foliar nutrition) of operational full-tree harvesting compared to operational stem only harvesting (i.e., individual stems delimbed and topped at the stump) on replicated, shallow-soiled sites with contrasting soil textures (i.e., sand versus loam) and dominant commercial tree species (i.e., jack pine – Pinus banksiana Lamb. versus black spruce – Picea mariana (Mill.) B.S.P.). The operational harvests at the seven study sites were all conducted during the fall prior to freeze up.In terms of tree regeneration metrics, the harvest treatments only had a significant effect on free-to-grow (>1m) crop tree (jack pine or black spruce) density. Despite the removal of cone-bearing branch material to roadside, the FT harvest treatment blocks had significantly higher densities compared to the SO blocks likely the result of increased mineral soil exposure, improved seedbed receptivity, and warmer soil surface temperatures during the growing season. Initially (5th year), jack pine height growth was better on the FT treatment blocks, but by year 10 this significant effect on total height was gone and the 5-year growth increment was better on the SO treatments. In contrast, black spruce height growth was better on the SO blocks in both year 5 and 10, although the 5-year increment was not significantly different between harvest treatments. Although soil N pools were higher in the SO treatments in year 10, the difference was only reflected in jack pine foliar N, suggesting black spruce may be less sensitive/responsive to declines in soil N pools.The 10-year results would suggest that no additional biomass retention restrictions are necessary for full-tree harvesting operations that are targeting traditional wood products (sawlogs and/or pulp & paper) on these shallow-soiled sites. However, some of the noted shifts in some of the measured parameters between year 5 and 10 would suggest longer-term monitoring of these sites will be necessary to provide more conclusive empirical evidence as to the long-term effects of full-tree harvesting on shallow soils within the boreal forest region.

Multi-year water balance assessment of a newly constructed wetland, Fort McMurray, Alberta

Oil sands mining in Alberta transforms the boreal landscape of forests and wetlands into open pits, tailings ponds and overburden piles. Whereas reclamation efforts have primarily focused on upland forests, rebuilding wetland systems has recently become a motivation for research. Wetland creation and sustainability in this region is complicated by the sub-humid climate and salinity of underlying mining material. In 2012, Syncrude Canada Ltd. completed the construction of the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland system to evaluate wetland reclamation strategies on soft tailings. SFW includes an active pumping system, upland hummocks, a fen wetland and underdrains. To evaluate the influence of management practices on the hydrology of the system, this study reports the water balance from January 2013 to December 2014, the first 2 years after commissioning. A semi-distributed approach was taken to examine the fluxes and stores of water in uplands and lowlands. Natural and artificial inputs and outputs were measured using a series of precipitation gauges and pumps, and evapotranspiration was quantified using three eddy covariance towers. A series of near surface wells recorded water table position. Both 2013 and 2014 were normal rainfall years, with 2013 having more and 2014 less snow than normal. In 2013, inflow/outflow from pumping was the predominant hydrological fluxes, resulting in considerable variability in water table position and storage changes throughout the summer. In 2014, the artificial addition of water was negligible, yet the water table remained near the surface in lowland locations, suggesting that wetland conditions could be maintained under current conditions. Evapotranspiration rates between uplands and lowlands were similar between years and sites, ranging from 2.2 ± 1.8 to 2.5 ± 1.2 mm/day and were largely controlled by climate. These rates were less than nearby older upland systems, suggesting that water balance partitioning will change as vegetation develops. Comparison between years and with natural systems provides insight on how management practices influence hydrologic dynamics and the overall water balance of the SFW. Copyright © 2016 John Wiley & Sons, Ltd.

Simulating carbon dioxide exchange in boreal ecosystems flooded by reservoirs

A process-based reservoir model of Flooded Forest Denitrification Decomposition (FF-DNDC) was developed to simulate carbon dioxide (CO2) exchange from flooded boreal landscapes. The reservoir model is based on Forest-DNDC, a terrestrial biogeochemistry model which supports detailed soil carbon (C) processes including redox chemistry, with modification to represent the disturbed soil and vegetation C dynamics due to the presence of an overlying water column on the ecosystems. Soil decomposition rates and temperature and oxygen profiles were changed, and sedimentation to the soil surface was added. FF-DNDC was evaluated using CO2 exchange measurements from the newly created Eastmain-1 reservoir in northern Quebec, Canada. For the first four years of the reservoir (2006 to 2009), simulated daily CO2 emissions averaged 1.42gCm−2d−1 (ranging from 0.75 to 3.24gCm−2d−1) from the flooded forest and 0.74gCm−2d−1 (ranging from 0.51 to 1.09gCm−2d−1) from the flooded peatland. The simulated emissions were smaller than the thin-filmed boundary layer exchanges based on measured partial pressure of carbon dioxide (pCO2) but were larger than the exchanges measured using an eddy covariance system. However, the temporal patterns of simulated and measured exchanges were similar. We simulated potential CO2 emissions over 100 years, the expected operating lifetime of the reservoir, with assuming no change in climate. Simulated CO2 emissions decreased with time since flooding especially for the first four decades. The 100-year cumulative emissions from the flooded peatland were larger than those from the flooded forest. Sensitivity analysis indicated that vegetation and soil inputs and parameters controlling the quality and/or quantity of decomposable soil C in flooded ecosystems (e.g. woody vegetation biomass, soil organic carbon in organic and mineral layers, and carbon:nitrogen ratio in woody vegetation and soil) were important to the reservoir CO2 emission.

Evidence for nonuniform permafrost degradation after fire in boreal landscapes

AbstractFire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire‐induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. We present a combination of multiscale remote sensing, geophysical, and field observations that reveal details of both near‐surface (&lt;1 m) and deeper (&gt;1 m) impacts of fire on permafrost. Along 11 transects that span burned‐unburned boundaries in different landscape settings within interior Alaska, subsurface electrical resistivity and nuclear magnetic resonance data indicate locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be most vulnerable to future change, and also areas where permafrost has thawed. High‐resolution geophysical data corroborate remote sensing interpretations of near‐surface permafrost and also add new high‐fidelity details of spatial heterogeneity that extend from the shallow subsurface to depths of about 10 m. Results show that postfire impacts on permafrost can be variable and depend on multiple factors such as fire severity, soil texture, soil moisture, and time since fire.

Nitrogen export from a boreal stream network following forest harvesting: seasonal nitrate removal and conservative export of organic forms

Abstract. Clear-cutting is today the primary driver of large-scale forest disturbance in boreal regions of Fennoscandia. Among the major environmental concerns of this practice for surface waters is the increased mobilization of nutrients, such as dissolved inorganic nitrogen (DIN) into streams. But while DIN loading to first-order streams following forest harvest has been previously described, the downstream fate and impact of these inputs is not well understood. We evaluated the downstream fate of DIN and dissolved organic nitrogen (DON) inputs in a boreal landscape that has been altered by forest harvests over a 10-year period. The small first-order streams indicated substantial leaching of DIN, primarily as nitrate (NO3−) in response to harvests with NO3− concentrations increasing by ∼ 15-fold. NO3− concentrations at two sampling stations further downstream in the network were strongly seasonal and increased significantly in response to harvesting at the mid-sized stream, but not at the larger stream. DIN removal efficiency, Er, calculated as the percentage of "forestry derived" DIN that was retained within the stream network based on a mass-balance model was highest during the snowmelt season followed by the growing season, but declined continuously throughout the dormant season. In contrast, export of DON from the landscape indicated little removal and was essentially conservative. Overall, net removal of DIN between 2008 and 2011 accounted for ∼ 65 % of the total DIN mass exported from harvested patches distributed across the landscape. These results highlight the capacity of nitrogen-limited boreal stream networks to buffer DIN mobilization that arises from multiple clear-cuts within this landscape. Further, these findings shed light on the potential impact of anticipated measures to increase forest yields of boreal forests, such as increased fertilization and shorter forest rotations, which may increase the pressure on boreal surface waters in the future.

On the decline of ground lichen forests in the Swedish boreal landscape: Implications for reindeer husbandry and sustainable forest management.

Lichens are a bottleneck resource for circumpolar populations of reindeer, and as such, for reindeer husbandry as an indigenous Sami land-use tradition in northern Sweden. This study uses ground lichen data and forest information collected within the Swedish National Forest Inventory since 1953, on the scale of northern Sweden. We found a 71% decline in the area of lichen-abundant forests over the last 60years. A decline was observed in all regions and age classes and especially coincided with a decrease of >60year old, open pine forests, which was the primary explanatory factor in our model. The effects of reindeer numbers were inconclusive in explaining the decrease in lichen-abundant forest. The role that forestry has played in causing this decline can be debated, but forestry can have a significant role in reversing the trend and improving ground lichen conditions.

Nitrogen dynamics in managed boreal forests: Recent advances and future research directions.

Nitrogen (N) availability plays multiple roles in the boreal landscape, as a limiting nutrient to forest growth, determinant of terrestrial biodiversity, and agent of eutrophication in aquatic ecosystems. We review existing research on forest N dynamics in northern landscapes and address the effects of management and environmental change on internal cycling and export. Current research foci include resolving the nutritional importance of different N forms to trees and establishing how tree–mycorrhizal relationships influence N limitation. In addition, understanding how forest responses to external N inputs are mediated by above- and belowground ecosystem compartments remains an important challenge. Finally, forestry generates a mosaic of successional patches in managed forest landscapes, with differing levels of N input, biological demand, and hydrological loss. The balance among these processes influences the temporal patterns of stream water chemistry and the long-term viability of forest growth. Ultimately, managing forests to keep pace with increasing demands for biomass production, while minimizing environmental degradation, will require multi-scale and interdisciplinary perspectives on landscape N dynamics.

Beaver in the drainage basin: an ecosystem engineer restores wetlands in boreal landscape

Beaver in the drainage basin: an ecosystem engineer restores wetlands in boreal landscape

Testing for Bottom—up Effects in an Overbrowsed Boreal Landscape

On Anticosti Island (Quebec, Canada), overbrowsing by white‐tailed deer Odocoileus virginianus has substantially modified plant communities and reduced the recruitment of balsam fir Abies balsamea seedlings over most of the territory. An exception to this phenomenon has been observed in localised patches occurring on a single geological deposit named Chicotte, where the natural recruitment of balsam fir is occurring even in the presence of a large white‐tailed deer population. We hypothesized that edaphic properties within the Chicotte deposit could result in lower forage quality, which in turn could reduce browsing pressure and allow fir regeneration to occur (i.e. bottom—up effects). To test this hypothesis, we measured soil properties and foliage chemistry of four forage species (balsam fir, white spruce Picea glauca, Canada mayflower Maianthemum canadense and Canada bunchberry Cornus canadensis) collected on each of three geological deposits on Anticosti Island: Chicotte, Becscie and Jupiter (the latter two considered as controls). Contrary to expectation, results from principal component analysis suggested that Chicotte was the most fertile, whereas Becsie was the least fertile, of the three deposits. Furthermore, balsam fir foliage chemistry did not respond to geological deposit. Conversely, Mantel et Procrustes tests revealed a significant correlation between soil properties and forage quality for white spruce, consistent with the carbon—nutrient balance hypothesis. Univariate tests confirmed that neutral detergent fiber concentrations in white spruce were higher on the Becscie than on the Chicotte deposit. Likewise, in vitro true digestibility of both white spruce and Canada bunchberry foliage were lower on the Becscie than on the Chicotte deposit. Although we failed to demonstrate why balsam fir recruitment occurs on the Chicotte deposit, our data demonstrate that edaphic properties may affect the quality of some forage types, which potentially affect foraging patterns in overbrowsed boreal landscapes.

Geoenvironmental response of the Yenisei Siberia mid-taiga landscapes to global warming during late XX–early XXI centuries

The response of middle boreal landscapes in the Yenisei Siberia to climate warming is considered. Changes in the systems of exodynamics, natural permafrost and nonpermafrost landscapes are analyzed based on a series of studies. Permafrost landscapes are ranked by their susceptibility to climate warming. Changes in the habitats were identified. The aggravating problems of the local population in the sphere of the use of taiga resources, characterizing the current stage of changes in the environment and climate are demonstrated.

Responses of the wetland grass, Beckmannia syzigachne, to salinity and soil wetness: Consequences for wetland reclamation in the oil sands area of Alberta, Canada

Reclamation of the boreal landscape, including both wetlands and uplands integrated into complex watersheds, has presented a challenge over the past decade with few attempts. Relevant today is wetland/peatland reclamation on reclaimed landscapes positioned on saline sand deposits left on ‘in-pits’ from open pit oil sands mining. Part of the reclamation challenge lies in choosing characteristic species that are tolerant of conditions present on the reclaimed landscape. Species need to both survive harsh environmental conditions and facilitate succession from mineral-based wetlands (marshes) to peat-based ones (fens). A two-by-six factorial experiment was implemented in a greenhouse under two moisture levels: saturation to 2.5cm below the soil level (high) and saturation to 7.5cm below the soil level (low) and six salinity treatments: 5mgL−1 Na+, 400mgL−1 Na+, 850mgL−1 Na+, 1250mgL−1 Na+, 1850mgL−1 Na+, and 2700mgL−1 Na+. Water level affected total biomass, with the low water level producing higher biomass. Sodium concentration affected biomass, root:shoot ratio, stomatal conductance, evapotranspiration, and photosynthetic rate; all responses were similar for the lower Na concentrations and declined after the 850mgL−1 treatment. We conclude that B. syzigachne tolerates Na levels of 850mgL−1 and survives with diminished performance at treatment of 850mgL−1 up to 2700mgL−1. With these salinity responses, along with broad tolerance to water levels, B. syzigachne has great potential as an early colonizing annual species for conditions predicted to occur in many of the in-pit reclamation designs.

Beaver-created deadwood dynamics in the boreal forest

Deadwood is a markedly important ecosystem element, and increasingly rare in managed landscapes. Beavers (Castor sp.) are ecosystem engineers of the boreal forest, where they modify riparian forests and wetlands through damming. The subsequent inundation causes extensive die-off of trees in the flood zone. We measured the deadwood volumes and types for six beaver-created flood sites, and compared these to control sites with no beaver influence. Our results show beavers create abundant volumes of deadwood in areas rarely experiencing other disturbance types. Significant amounts of beaver-created deadwood consist of rare types, e.g. snags and deciduous wood. Both coarse and fine woody debris are created. These varying substrates increase deadwood heterogeneity and create differing saproxylic community diversity compared to other disturbances. The roaming lifestyle of beavers cause repeated flooding in boreal landscapes. This upholds deadwood continuity in areas where deadwood levels are very low due to intensive forest management. The reoccurring pulses of deadwood created by beavers may facilitate a wide scope of deadwood-dependent species. The beaver can be used as a deadwood facilitator and engine of restoration in boreal wetlands and riparian forests. This is an economic option compared to costly and time-consuming man-made restoration.

Contribution of unburned boreal forests to the population of black-backed woodpecker in eastern Canada

ABSTRACTBlack-backed woodpecker is known to be a disturbance-associated species, being more abundant in disturbed forest stands than in undisturbed habitats, but its demography and population dynamic still need to be clarified. The present study was conducted in central Quebec within coniferous forests shaped largely by timber harvest and wildfire. The objectives were to compare the age composition of breeding black-backed woodpeckers, nest survival rate and productivity in both disturbed and undisturbed habitats (respectively recently burned and unburned habitats). In addition, we evaluated the general productivity of both habitat types in a simulated boreal landscape. There was a positive relationship between nest age and daily survival rates. Older woodpeckers were the most abundant breeders in unburned habitats and younger birds in one-year-old burns. Although nests in recently burned forests produced more nestlings per successful nest, our simulation of a boreal forest landscape showed that unburned habitat produced about two-thirds more fledglings per year than burned habitat. Globally, unburned habitat may provide woodpeckers more temporally stable resources. Population dynamics of the black-backed woodpecker, at least in our study area, may be explained by resource pulse interactions where populations benefit opportunistically from short-term high-quality habitat, and rely on unburned habitats for long-term persistence.

Water use by Swedish boreal forests in a changing climate

Summary The rising levels of atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to substantially affect the terrestrial water and energy balance by altering the stomatal conductance and transpiration of trees. Many models assume decreases in stomatal conductance and plant water use under rising [CO2], which has been used as a plausible explanation for the positive global trend in river run‐off over the past century. Plant water use is, however, also affected by changes in temperature, precipitation and land use, and there is yet no consensus about the contribution of different drivers to temporal trends of evapotranspiration (ET) and river run‐off. In this study, we assessed water‐use responses to climate change by using both long‐term monitoring and experimental data in Swedish boreal forests. Historical trends and patterns in ET of large‐scale boreal landscapes were determined using climate and run‐off data from the past 50 years, while explicit tree water‐use responses to elevated [CO2] and/or air temperature were examined in a whole‐tree chamber experiment using mature Norway spruce (Picea abies (L.) Karst.) trees. The results demonstrated that ET estimated from water budgets at the catchment scale increased by 18% over the past 50 years while run‐off did not significantly change. The increase in ET was related to increasing precipitation and a steady increase in forest standing biomass over time. The whole‐tree chamber experiment showed that Norway spruce trees did not save water under elevated [CO2] and that experimentally elevated air temperature did not increase transpiration as decreased stomatal conductance cancelled the effect of higher vapour pressure deficit in warmed air. Our findings have important implications for projections of future water use of European boreal coniferous forests, indicating that changes in precipitation and standing biomass are more important than the effects of elevated [CO2] or temperature on transpiration rates.

Combining near infrared spectra of feces and geostatistics to generate forage nutritional quality maps across landscapes.

An important asset for the management of wild ungulates is recognizing the spatial distribution of forage quality across heterogeneous landscapes. To do so typically requires knowledge of which plant species are eaten, in what abundance they are eaten, and what their nutritional quality might be. Acquiring such data, however, may be difficult and time consuming. Here, we are proposing a rapid and cost-effective forage quality monitoring tool that combines near infrared (NIR) spectra of fecal samples and easily obtained data on plant community composition. Our approach rests on the premise that NIR spectra of fecal samples collected within low population density exclosures reflect the optimal forage quality of a given landscape. Forage quality can thus be based on the Mahalanobis distance of fecal spectral scans across the landscape relative to fecal spectral scans inside exclosures (referred to as DISTEX). The Gi* spatial autocorrelation statistic can then be applied among neighboring DISTEX values to detect and map "hot spots" and "cold spots" of nutritional quality over the landscape. We tested our approach in a heterogeneous boreal landscape on Anticosti Island (Québec, Canada), where white-tailed deer (Odocoileus virginianus) populations over the landscape have ranged from 20 to 50 individuals/km2 for at least 80 years, resulting in a loss of most palatable and nutritious plant species. Our results suggest that hot spots of forage quality occur when old-growth balsam fir stands comprise >39.8% of 300 ha neighborhoods, whereas cold spots occur in laggs (i.e., transition zones from forest to peatland). In terms of ground-level indicator plant species, the presence of Canada bunchberry (Cornus canadensis) was highly correlated with hot spots, whereas tamarack (Larix laricina) was highly correlated with cold spots. Mean DISTEX values were positively and significantly correlated with the neutral detergent fiber and acid detergent lignin contents of feces. While our approach would need more independent field trials before it is fully validated, its low cost and ease of execution should make it a valuable tool for advancing both the basic and applied ecology of large herbivores.

Structural retention requirements for a key ecosystem engineer in conifer-dominated stands of a boreal managed landscape in eastern Canada

The concept of retention forestry brings a new point of view for forest management as more emphasis is put on what is retained as opposed to what is removed during harvesting. Details of retention harvesting prescriptions vary among forest ecosystems reflecting differences in their disturbance dynamics, stand composition and condition, and landscape context. Although recent studies underlie the important role of trembling aspen (Populus tremuloides) in cavity networks of Canadian western temperate forests, limited information exists for conifer-dominated forests such as the black spruce (Picea mariana) forests of central Québec where the proportion of deciduous trees is generally <10%. We used the habitat requirements of an ecosystem engineer of eastern boreal forests, the Black-backed Woodpecker (Picoides arcticus), to determine harvesting prescriptions likely to preserve most of the biodiversity of this ecosystem. We describe the mean physical characteristics of trees selected for nesting, quantify nesting habitat selection at two scales (nest tree and nesting stand), and identify quantitative targets for forest managers to select types and amounts of retention structures that will offer optimal resources to cavity nesting birds and dead wood associated species in managed boreal landscapes. During the three years of this project, we found 18 Black-backed Woodpecker nests: 9 were in old coniferous, 6 in young cuts, and 1 nest in each of the other habitats (barren land, young coniferous and old cut). Selection of nest trees by Black-backed Woodpeckers was influenced primarily by tree species (jack pine; Pinus banksiana) and also by the dbh of trees, while their selection of nesting stand habitat was influenced positively by the mean density of recent-solid snags and negatively by the mean basal area of live trees. Our results show that forest stands with ⩾200 recently decayed snags/ha (⩾9cmdbh) exhibit higher predicted probability of selection for nesting by Black-backed Woodpeckers, and most of the cutblocks with a nest tree originate from harvesting with advance regeneration protection with at least that many snags. Moreover, cutblocks should contain suitable candidate nest trees, with retention of ⩽10 live and dead trees/ha with a dbh⩾27cm, and retention of jack pine snags in proportion of their availability before harvesting in black spruce-dominated forest stands. We recommend that, where forest stands present suitable structures, every stand harvested with retention harvesting should retain ⩾200 recent-solid snags/ha (⩾9cmdbh), which represents about 1 recent-solid snag each 7m (50m2). The medium and long-term persistence of dead wood associated species may not rely only on retention forestry, thus we recommend the protection of patches (100ha) of old forest stands (⩾120y) inside these agglomeration of cutblocks to ensure the dynamic of dead wood creation within the managed landscape.

The relative influence of land cover, hydrology, and in‐stream processing on the composition of dissolved organic matter in boreal streams

AbstractLow‐order boreal streams are particularly sensitive interfaces where dissolved organic matter (DOM) is transported from soils to inland waters. Disentangling the relative influence of key environmental factors suspected to influence stream water DOM composition is highly relevant to predicting the reactivity and fate of terrestrial DOM entering inland waters. Here we examined changes to DOM composition using absorbance and fluorescence, from 17 boreal streams ranging from first to fourth orders, over 14 months, including the rarely studied winter season, and two snowmelt periods (n = 836). We also analyzed soil pore water samples from three forest soil lysimeters to a depth of 70 cm (n = 60). Of five identified fluorescing parallel factor analysis components, two (C4 and C5) expressed a clear mire wetland or forest signature, providing distinct molecular markers of dominant land cover. In fact, land cover alone explained 49% of the variability in DOM composition. In contrast, seasonal fluctuations in hydrology only contributed to minor shifts (8%) in the composition of stream water DOM, while in‐stream transformations to DOM composition were undetectable. These findings suggest that low‐order boreal streams act as a passive pipe, since in‐stream processing of DOM is restricted by short water residence times (6 h to 2 days). In addition, we demonstrated the sensitivity of optical approaches to distinguish between key terrestrial sources of DOM in the boreal landscape. By distinguishing the proportional leverage of key environmental controls on headwater stream DOM composition, we are better equipped to predict where and when key DOM transformations occur in the aquatic conduit.

Climatic Variation of the Arctic Front during the Warm Period and their Infl uence on the Northern Landscapes

The duration of growing seasons and the reaction of the plant component of landscape depending on the average position of the Arctic Front (AF) in different climatic episodes according to observations in the sub-arctic (tundra and forest-tundra) and boreal (northern taiga and middle taiga) landscapes in European Russia and in Western Siberia, north of 60° N, is analyzed. The dynamics of climatic characteristics such as gradients of temperature and precipitation, sum of air temperatures above +10° C (sum of active temperatures), Satellite Climatic Extremes Index (SCEI), vegetation index gradients (NDVI AVHRR (1982–2000) and NDVI MODIS (2000–2012)) was used for the estimation. The regularities of the active temperatures sum increase and slight moisture variation were found. It was caused by the quasistationary and increasing intensity of frontal processes at the Arctic front in summer. All these reasons will cause the advance of the boreal forests to the north.

Using beaver works to estimate colony activity in boreal landscapes

ABSTRACTBeaver ponds and beaver‐impounded vegetation are indicators of past or present beaver activity that can be detected from aerial photography. A method to quantitatively relate these beaver works with the density of active beaver colonies could benefit beaver management, particularly in areas lacking beaver population data. We compared historical maps (1961–2006) of beaver works at Voyageurs National Park, Minnesota, USA with concurrent aerial surveys of beaver colonies. We tested 2 landscape‐scale models of beaver colony density previously developed for a period of beaver population expansion (1940–1986), but they failed to predict colony density after 1986, a period of declining beaver population. We developed a new landscape‐scale regression, calculating that 2.15% of the landscape would be flooded by every 100 additional beaver colonies (R2 = 0.53, P = 0.027). Classification tree analysis of individual pond sites showed that open water pond and impounded marsh area were the primary predictors of beaver colony presence or absence, but that the classification trees were far better at identifying inactive sites (&gt;93% correct) than active sites (35–38% correct). The area of open water in beaver ponds is a good but not perfect indicator of beaver activity that can be used by wildlife managers as a landscape‐scale indicator of beaver colony density. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Metagenomic insights into strategies of aerobic and anaerobic carbon and nitrogen transformation in boreal lakes.

Thousands of net-heterotrophic and strongly stratifying lakes dominate the boreal landscape. Besides their central role as emitters of greenhouse gases, we have only recently begun to understand the microbial systems driving the metabolic processes and elemental cycles in these lakes. Using shotgun metagenomics, we show that the functional potential differs among lake types, with humic lakes being particularly enriched in carbon degradation genes. Most of the metabolic pathways exhibit oxygen- and temperature-dependent stratification over depth, coinciding with shifts in bacterial community composition, implying that stratification is a major factor controlling lake metabolism. In the bottom waters, rare and poorly characterized taxa, such as ε-Proteobacteria, but also autotrophs, such as photolithotrophic Chlorobia were abundant. These oxygen-depleted layers exhibited high genetic potential for mineralization, but also for fixation of carbon and nitrogen, and genetic markers for both methane production and oxidation were present. Our study provides a first glimpse of the genetic versatility of freshwater anoxic zones, and demonstrates the potential for complete turnover of carbon compounds within the water column.