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There is a growing interest in using logging residues as feedstock in the bioeconomy. Quantifying the amount of this resource over large areas has been difficult due to the lack of availability of ...

The litter-bag technique has become common in the estimation of the rates of decomposition, but in many cases the bags are incubated for only a short period, raising the issue of the extent to which short-term incubations represent long-term litter decomposition. We addressed this using 12 years of data from the CIDET study. The CIDET study involved placement of 10 foliar litters on the soil surface and wood blocks on the soil surface and buried across temperate to subarctic Canada. Bags were retrieved 10 times over 12 years at 19 sites and the residual litter mass determined. A literature search revealed that 84% of published litter-bag studies in temperate-boreal-subarctic regions were of 3 years duration or less. The strength of the relationship between the mass loss after 1 year and later years at each CIDET site, expressed as the coefficient of determination (R 2 ) among the 12 litters, decreased with length of incubation, reaching an average of only 0.4 after 12 years. The R 2 value was inversely related to mean annual temperature. The single exponential model of mass remaining (k) declined with length of incubation, and the rate of decline varied among litter types and sites. For 3 litters at 19 sites, the 3- and 12-year k values were strongly related. These results show that caution should be exercised when extrapolating short-term litter-bag studies (e.g. < 3 years), particularly in temperate climates.

We measured changes in mass and in carbon (C), nitrogen (N) and phosphorus (P) concentrations and content of surface-placed and buried wood blocks decomposing over 12 years at 21 sites across Canada to evaluate the influence of the environment on C, N, and P dynamics. Carbon decomposition over time was best described using a sigmoidal fit, which was slightly better than a negative exponential function. Decomposition was slow at cold and wetland sites, with less than 15 % of the original C content lost after 12 years for 4 upland and 3 wetland sites. Decomposition rates were faster for buried than for surface blocks, except in wetlands and in a few upland sites that had high annual precipitation. Nitrogen was gained during the early stages of decomposition, followed by a net N loss once an average C:N mass ratio of 165 was reached for all upland surface-placed blocks, and 200 for upland buried blocks. Critical C:N values were weakly correlated with C:N ratios in the surface organic horizon, suggesting an influence of forest floor properties on decomposition dynamics with N release occurring sooner on more fertile sites. Critical values for N and P mineralization were greater than those reported for foliar litters.

The increasing demand for forest biomass, notably from primary residues of harvested trees for the production of bioenergy, has raised concerns because of potential adverse effects on forest soil productivity. Our aim was to develop and validate spatially explicit planning indicators of site suitability for harvesting residue removal based on mapped forest site properties for four large case study areas located across Canada, each containing field studies on the impact of harvesting residue removal. Sustainability was assessed relative to the baseline scenario of conventional stem-only harvesting, to investigate the incremental effects of the removal of residues associated with whole-tree harvesting in typical operational conditions in Canada. Using information from scientific literature and guidelines from various jurisdictions, eleven planning indicators were developed, from which nine were related to the loss of soil fertility risk and two to erosion risk. Planning indicators were tested for redundancy and validated using response indicators of stand growth and nutrition from field studies. Several relationships between mapped soil properties and the empirical response of stands to harvesting residue removal were found. Planning indicators based on concentrations of organic C, total N and total P in the top 30 cm of the mineral soil best explained stand responses to harvesting residue removal. Despite caveats, the methodology used here demonstrates an approach for developing and empirically testing planning indicators of site suitability for harvesting residue removal. As more information on the impact of this practice becomes available from field studies, it can be used to refine and further validate the indicators.

The growing demand for bioenergy feedstock from forest harvest residues is generating concerns about the potential loss of site productivity through nutrient removal. We used tree-level national biomass equations and a national database of forest plots to develop stand-level biomass equations for the different tree components of 30 major forest tree species found in Canada using basal area as the independent variable. We have also compiled more than 12 800 nutrient concentration values for different components of Canadian tree species from existing databases and the literature. Uncertainties were propagated across biomass equations and through conversion of nutrient concentrations to nutrient contents. Most of the uncertainty in nutrient contents estimates was found to be among the nutrient concentration measurements. The greatest levels of uncertainty were for estimates of phosphorus in woody components and of calcium in foliage. Grouping species into genera gave only a minor loss of precision. The coupling of biomass equations and nutrient concentration data can be used to provide first-order estimates of biomass and nutrients exported by tree component and species when harvesting any commercial stand in Canada. However, the associated uncertainties are important enough to warrant their inclusion in decision making. Resume : La demande croissante pour les residus de coupe ades fins de bioenergie genere des preoccupations de perte de productivite suite al'exportation d'elements nutritifs. Nous avons developpe des equations allometriques de biomasse al'echelle du peuplement pour 30 especes d'arbre dominantes de la foret canadienne utilisant la surface terriere comme variable indepen- dante, apartir d'equations nationales de biomasse al'echelle de l'arbre et de l'information provenant d'un inventaire national de parcelles forestieres. Nous avons aussi compile plus de 12 800 valeurs de concentrations de nutriments pour diverses com- posantes d'arbre et d'especes qui provenaient de bases de donnees existantes et de la litterature. L'incertitude a ete propagee dans les equations allometriques et au travers de la transformation des concentrations de nutriments en contenus. La plupart des incertitudes se retrouvent au niveau des mesures de concentrations de nutriments. Ce sont les estimes du phosphore dans les compartiments ligneux ainsi que ceux du calcium dans le feuillage qui sont les plus incertains. Le regroupement des especes par genre n'a genere qu'une faible perte de precision. Le couplage des equations de biomasse et des mesures de concentrations en nutriments permet d'estimer les quantites de biomasse et de nutriments par composante d'arbre et par espece exportees des peuplements commerciaux lors de leur recolte. Cependant, l'incertitude sur ces estimes est suffisamment importante pour necessiter sa prise en compte pour les prises de decision.

Rapid expansion in biomass production for biofuels and bioenergy in the Americas is increasing demand on the ecosystem resources required to sustain soil and site productivity. We review the current state of knowledge and highlight gaps in research on biogeochemical processes and ecosystem sustainability related to biomass production. Biomass production systems incrementally remove greater quantities of organic matter, which in turn affects soil organic matter and associated carbon and nutrient storage (and hence long-term soil productivity) and off-site impacts. While these consequences have been extensively studied for some crops and sites, the ongoing and impending impacts of biomass removal require management strategies for ensuring that soil properties and functions are sustained for all combinations of crops, soils, sites, climates, and management systems, and that impacts of biomass management (including off-site impacts) are environmentally acceptable. In a changing global environment, knowledge of cumulative impacts will also become increasingly important. Long-term experiments are essential for key crops, soils, and management systems because short-term results do not necessarily reflect long-term impacts, although improved modeling capability may help to predict these impacts. Identification and validation of soil sustainability indicators for both site prescriptions and spatial applications would better inform commercial and policy decisions. In an increasingly inter-related but constrained global context, researchers should engage across inter-disciplinary, inter-agency, and international lines to better ensure the long-term soil productivity across a range of scales, from site to landscape.

Increased interest in biomass harvesting for bioenergetic applications has raised questions regarding the potential ecological consequences on forest biodiversity. Here we evaluate the initial changes in the abundance, species richness and community composition of rove (Staphylinidae) and ground beetles (Carabidae), immediately following 1) stem-only harvesting (SOH), in which logging debris (i.e., tree tops and branches) are retained on site, and 2) whole-tree harvesting (WTH), in which stems, tops and branches are removed in mature balsam fir stands in Quebec, Canada. Beetles were collected throughout the summer of 2011, one year following harvesting, using pitfall traps. Overall catch rates were greater in uncut forest (Control) than either stem-only or whole-tree harvested sites. Catch rates in WTH were greater than SOH sites. Uncut stands were characterized primarily by five species: Atheta capsularis, A. klagesi, A. strigosula, Tachinus fumipennis/frigidus complex (Staphylinidae) and to a lesser extent to Pterostichus punctatissimus (Carabidae). Increased catch rates in WTH sites, where post-harvest biomass was less, were attributable to increased catches of rove beetles Pseudopsis subulata, Quedius labradorensis and to a lesser extent Gabrius brevipennis. We were able to characterize differences in beetle assemblages between harvested and non-harvested plots as well as differences between whole tree (WTH) and stem only (SOH) harvested sites where logging residues had been removed or left following harvest. However, the overall assemblage response was largely a recapitulation of the responses of several abundant species.

The United Nations Food and Agriculture Organization (FAO) has been reporting country-level area in primary forests in its Global Forest Resource Assessment since 2005. The FAO definition of a primary forest (naturally regenerated forest of native species where there are no clearly visible indications of human activities and the ecological processes are not significantly disturbed) is generally accepted as authoritative and is being used in policy making. However, problems with this definition undermine our capacity to obtain globally coherent estimates. In addition, the current reporting on primary forests fails to consider the complementarily of non-primary forests toward the maintenance of ecosystem services. These issues undermine the appropriate tracking of changes in primary and non-primary forests, and the assessment of impacts of such changes on ecosystem services. We present the case for an operational reconsideration of the primary forest concept and discuss how alternatives or supplements might be developed.

Interest in the use of bioenergy is increasing because of the need to mitigate climate change, the increasing costs and finite supply of fossil fuels, and the declining price of lumber and paper. Sound bioenergy policies must be informed by accurate estimates of potential feedstock production, rights to the production, social values and economics. Two of the main sources of bioenergy feedstock from forests are (i) harvesting residue and (ii) dead wood resulting from natural disturbances (i.e. standing dead timber). We modeled the production of bioenergy feedstock from these two sources from 2005 to 2020 for Canada's managed forest south of 60° N so that this information can be used in provincial and national strategic planning. Published estimates of harvesting residue vary widely, and our objective was to provide more precise estimates based on new forest inventory data and regional modeling. Natural disturbances result in very large quantities of dead wood on the landscape, but estimates of future stocks and annual production have not previously been made. Our estimates included a 50% discount factor to net-down theoretically available quantities to a more realistic estimate of potential ecologically sustainable bioenergy feedstock. The total future annual production averaged 51 ± 17 Tg year−1 from natural disturbances and 20 ± 0.6 Tg year−1 from clearcut harvesting residues. Harvesting residue for the area logged varied spatially from a low of 1.0 ± 0.77 kg m−2 year−1 to a high of 6.7 ± 0.1 kg m−2 year−1. Dead wood production due to insects was forecast to peak in the Montane Cordillera of British Columbia (BC) at 16.7 Tg year−1 due to the current mountain pine beetle outbreak. Total dead wood production due to fire was highest in the western portion of the boreal forest (3.6 Tg year−1 in the Boreal Shield of Saskatchewan), in part due to the high frequency of fires in these ecosystems and the large area of western boreal forest, but the highest density production was in BC: >9 kg m−2 year−1 in the burned area. Our results showed that the dead wood stocks of 331 Tg oven-dry matter potentially available for bioenergy in 2020 are much smaller than the 3100 ± 84 Tg of dead wood stocks estimated based on ecosystem dynamics. While bioenergy use will accelerate the release of greenhouse gases compared to on-site decay, the energy is renewable and can be used as a substitute for fossil fuels. The net benefit to the atmosphere of forest bioenergy use is affected by many factors, and future research should further assess which sustainable wood-based bioenergy strategies yield the greatest net greenhouse gas benefits over the different time scales needed for post-disturbance forest recovery.

Growth rates of young conifers can be poor on disturbed sites dominated by Kalmia angustifolia L. Hence, a conifer revegetation trial was established on a Kalmia -dominated site to evaluate the effects of various silvicultural options and planted species on selected soil organic layer characteristics. Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) BSP seedlings were planted in plots with or without Kalmia control with herbicides. The effect of fertilizer amendment was also assessed. Seventeen years postplanting, organic layer fertility indicators suggest that soil fertility improved after Kalmia control and conifer reestablishment, especially if nitrogen (N) – phosphorus – potassium fertilizer was also applied. When Kalmia was controlled, aerobically mineralizable N and exchangeable sodium concentrations were increased; fertilizer addition to herbicided plots also increased exchangeable potassium and calcium concentrations, and cation exchange capacity compared with untreated control plots. Conifer height, diameter, and canopy closure were Larix > Pinus > Picea. Kalmia cover in control plots was 87%; Kalmia reinvasion in herbicided plots achieved 40%–43% cover but did not differ among the conifer species. Principal component analysis indicated that aerobically mineralizable N and total N were positively correlated with canopy closure. Our results suggest that increases in organic-layer fertility were related to increased conifer size resulting from Kalmia control.

Litterbag experiments provide valuable data for testing the accuracy of predictions of decomposition from soil carbon models. The soil carbon model Yasso describes litter decomposition based on basic climate and litter quality information, and was calibrated using European litterbag data. In this study, we tested the predictive capabilities of Yasso using independent litterbag data for 10 foliage litter types decomposed for 6 years at 18 upland forest sites across Canada (CIDET). The model underestimated mass of leaf litters remaining on CIDET sites, with only a small systematic error in predicting the effects of climate when effective temperature sum was used as the temperature variable in the model. The overall rate of decomposition was predicted correctly when mean annual temperature was used as the temperature variable, but then the model substantially overestimated climatic effects. The model correctly predicted differences in decomposition rates among litter types in the early years of decomposition, but underestimated them in later years. The decomposition rate of the litter type richest in phenolic compounds (larch needles) was systematically overestimated, and that of the litter type richest in O-alkyl compounds (grass leaves) was systematically underestimated. Accounting for these factors would improve the general applicability of the model. However, accounting for the initial nitrogen concentration of litter did not improve the accuracy of the model unless the initial lignin (i.e., acid unhydrolyzable residue) content was also taken into account. We conclude that the model Yasso accounts for most of the effects of climate and initial litter quality on the decomposition of a range of foliage litter types under varying climate conditions. Recalibration of the reference decomposition rates used in the model may improve the accuracy when applying the model outside of Europe.

A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH4+ and NO3− concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH4+ transformations rates ranged between 20 and 120 μg N (g forest floor)−1 day−1 at the ESSF site, and between 15 and 40 μg N (g forest floor)−1 day−1 at the CWH site. Higher temperature increased gross NH4+ transformation rates in forest floor samples at both sites, but the average Q10 value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots (Q10=4.31) than in old-growth plots (Q10=1.98). Gross NO3− transformation rates ranged between 10 and 32 μg N (g forest floor)−1 day−1 at the ESSF site, and between 10 and 24 μg N (g forest floor)−1 day−1 at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO3− transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH4+ flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO3− flush to the proportion of heterotrophic nitrifiers.

We established a field trial on an ericaceous-dominated clearcut in Quebec to determine the effect of Kalmia angustifolia L., Vaccinium angustifolium (Ait.), and V. myrtilloides (Michx.) on the growth and physiology of black spruce (Picea mariana (Mill.) BSP) seedlings and on soil characteristics over the first two growing seasons. Plots undergoing one of three treatments (shrub removal, humus removal, or undisturbed control) were planted with black spruce seedlings that were either unfertilized or spot fertilized at time of planting. In some of the undisturbed control plots, we also used 15NH415NO3 to compare uptake of broadcast N fertilizer by vegetation. The ericaceous shrubs had a significant negative impact on seedling growth. Growth reductions were not related to water stress, soil temperature, or soil moisture. Extractable NH4-N and P concentrations in mineral soil tended to decrease in the presence of ericaceous shrubs, but effects were not significant. Seedling foliar N concentration was also reduced in the presence of ericaceous shrubs. Of the total amount of 15N fertilizer found in vegetation, 64% was immobilized in Vaccinium spp., 31% in Kalmia, and 5% in black spruce, but spruce took up more 15N per unit of root biomass than the ericaceous shrubs. Kalmia had consistently higher predawn xylem water potentials than black spruce.

We compared mineral N concentrations, potential net mineralization rates and gross N mineralization rates in the forest floor of 4-year-old clearcut plots and adjacent mature forest stands, in three distinct coniferous ecosystems in British Columbia (coastal low elevation, coastal montane, interior montane). Our data showed that clearcutting has no effect on forest floor mineral N dynamics in some coniferous ecosystems, and significant effects in others. Among “responsive” sites, we noted contradictory effects of clearcutting on some of the measured N variables. Furthermore, the effects of clearcutting on potential net mineralization were not consistent with changes in gross production rates of mineral N. We discuss these observations in light of our knowledge of the ecology of each site, of the various sources and sinks of mineral N, and of the biotic and abiotic factors controlling mineral N dynamics. Our results suggest that generalizations cannot be made on the effects of clearcutting on mineral N supply to conifer seedlings, as these can lead to incorrect interpretations of ecosystem dynamics, with serious policy-relevant ramifications for the forest industry.

To determine the nature of the negative influence of Kalmia angustifolia L. on black spruce (Picea mariana (Mill.) BSP) seedling growth and foliar nutrient concentrations, the effect of proximity to Kalmia on spruce seedlings was studied on two Kalmia-dominated sites of contrasting soil characteristics in central Newfoundland. Spruce seedlings and the soil at the base of their stems were sampled, and spruce leader length and foliar N and P concentration, as well as various physicochemical soil characteristics, were determined. Path analysis was used to determine the strength of direct and indirect relationships among variables hypothesized to be causally linked. Path diagrams were generated based on current knowledge of nutrient cycling in boreal ecosystems and mechanisms previously hypothesized to account for the influence of Kalmia on black spruce. On the wetter and richer site, proximity to Kalmia was associated with reduced spruce growth and humus extractable NH4-N, suggesting nutrient competition. On the drier and poorer site, results were consistent with a direct negative effect of Kalmia on the N nutrition of spruce. On both sites, we also found evidence for a direct effect of Kalmia on spruce growth that is consistent with allelopathic effects on spruce function.

The effects of litter quality and climate on decomposition rates of plant tissues were examined using percent mass remaining (MR) data of 10 foliar litter types and 1 wood type during 6 years exposure at 18 upland forest sites across Canada. Litter-quality variables used included initial nutrient contents (N, P, S, K, Ca, Mg) and carbon fractions (determined by proximate analysis and 13C nuclear magnetic resonance spectroscopy). Climate variables used included mean annual temperature; total, summer, and winter precipitation; and potential evaptranspiration. A single-exponential decay model with intercept was fit using the natural logarithm of 0- to 6-year percent MR data (LNMR) for all 198 type by site combinations. Model fit was good for most sites and types (r2 = 0.64–0.98), although poorest for cold sites with low-quality materials. Multiple regression of model slope (Kf) and intercept (A) terms demonstrated the importance of temperature, summer precipitation, and the acid-unhydrolyzable residue to N ratio (AUR/N) (r2 = 0.65) for Kf, and winter precipitation and several litter-quality variables including AUR/N for A (r2 = 0.60). Comparison of observed versus predicted LNMR for the best overall combined models were good (r2 = 0.75–0.80), although showed some bias, likely because of other site- and type-specific factors as predictions using 198 equations accounted for more variance (r2 = 0.95) and showed no bias.

The effect of litter quality and climate on the rate of decomposition of plant tissues was examined by the measurement of mass remaining after 3 years’ exposure of 11 litter types placed at 18 forest sites across Canada. Amongst sites, mass remaining was strongly related to mean annual temperature and precipitation and amongst litter types the ratio of Klason lignin to nitrogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean annual precipitation and Klason lignin:nitrogen ratio explained 73% of the variance in mass remaining for all sites and tissues. Using three doubled CO2 GCM climate change scenarios for four Canadian regions, these relationships were used to predict increases in decomposition rate of 4–7% of contemporary rates (based on mass remaining after 3 years), because of increased temperature and precipitation. This increase may be partially offset by evidence that plants growing under elevated atmospheric CO2 concentrations produce litter with high lignin:nitrogen ratios which slows the rate of decomposition, but this change will be small compared to the increased rate of decomposition derived from climatic changes.

Betula papyrifera (White birch) is a common tree throughout the boreal forest of Canada; makes up 12 % of the total tree volume in insular Newfoundland. It forms pure stands after harvesting and wildfire disturbance and it is a common component in most softwood stands. Little is known regarding the environmental impact of whole-tree or conven- tional harvesting of this species and variation in impact related to variation in soil and site conditions.

The influence of NPK-fertilizer on decomposition of litter layers and deposited logging residues (brash) on a clearfelled Sitka spruce stand was followed during two years by zero-tension lysimetry and litterbags. Root development of second rotation planted trees on this peaty gley soil are restricted to the litter layers (LFH) and without fertilizer are dependent on its decomposition for release of nutrients. A comparison of fertilized and control plots showed few site differences and similar hydrological properties.