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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 ...

Loss of global forest, and in particular forest that has little human disturbance, is a standard against which we measure progress to conserve Earth’s forests. The value of intact forest landscapes has taken hold in the global psyche. We provide a brief history of the intact forest landscape concept and discuss how this has moved to an operational definition used as a global and regional metric of forest conservation. We distinguish between a conceptual intact forest landscape and an operational definition. For the purposes of this paper we will use the term IFL to mean the operational definition and intact forest landscapes to mean the conceptual idea. We provide an overview of the science that supports the value of intact forest landscapes in a Canadian boreal context and analyse issues with using a standard operationalized IFL definition to both measure and promote conservation of forests at global and regional scales. We found many arguments for protecting large, intact forest landscapes that are relevant to the Canadian boreal forest, including conservation of biodiversity, ecological processes and ecosystem services, existence values, application of the precautionary principle, and the need for scientific benchmarks. But it is clear that the standard operational IFL size threshold of 50 000 ha in the boreal forest is inadequate to meet these broad conservation objectives. However, the concept of intact forest being large enough to allow for all natural processes and biodiversity is likely not logistically feasible in Canada’s managed boreal forest. The scale at which the most extensive processes (e.g., fire and insects) occur and species (e.g., woodland caribou) function is likely too large. Management options incorporating local knowledge of conservation needs and the specifics of ecosystem function and composition are more likely to be effective in conservation than rigid IFL requirements. A standardized approach is useful for global tracking of IFLs but it is not the best approach to meet more regional forest conservation goals. Intact forest landscapes have exceptional value but should be managed in the context of integrated land use planning that includes protected areas, sustainable forest management, species at risk management, and ecosystem restoration.

Research has demonstrated the potential of soil scarification, fertilization, and herbicide application to improve conifer seedling establishment and early growth. However, tree responses to and interactions among silvicultural treatments vary, making it difficult to predict mid- and long-term impacts of silviculture on stand productivity. We thus evaluated the 25-year effects of scarification and herbicide–fertilization combinations on black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) planted on a Kalmia angustifolia-dominated site. Our results show that the effects of scarification and herbicide–fertilization combinations diverged among species. Black spruce was the most responsive species to scarification for height and diameter at breast height. The combination of herbicide and fertilization treatments still had significantly positive effects on the long-term height and diameter growth of all species. Silvicultural treatments resulted in significant reductions in rotation length (based on height) when compared to height in nontreated-plots, depending on the species; reductions in years to attain a given height were greater for black spruce than for the other species. Our results illustrate the need to take species autecology into account when predicting productivity gains associated with early silviculture, and to provide managers with specific guidelines for the reforestation of ericaceous-dominated sites in Canadian boreal ecosystems.

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.

Forests are an increasingly important source of feedstock for bioenergy as global efforts to mitigate atmospheric CO2 concentrations increase. In keeping with the principles of sustainable forest management, it is important that feedstock procurement not have negative impacts on the environment, including biodiversity. Impacts of land use, including forest management, can be evaluated along all stages in the production of these goods and services, using life cycle assessment (LCA), which is a potentially powerful tool for organizing and evaluating the impacts of production. There is growing recognition of the need to integrate land-use impacts into LCA for forest products such as bioenergy, especially on biodiversity. Integrating quantitative indicators of biodiversity into LCAs of biomass production systems is particularly challenging because biodiversity is a multidimensional concept that can never be fully represented by a single number, and yet many proposed approaches rely on this. Reliance on a single metric oversimplifies ‘biodiversity’ and might lead to inappropriate conclusions on local land management practices. LCA is not suited to providing reliable site-specific assessment of forest product systems in regard to the complexities of biodiversity. Nevertheless, the global and comprehensive nature of LCA makes it a useful tool for preventing a shift in environmental problems or burdens across the value chain because of local land management decisions. In this context, complementary site-specific and/or regional studies or analyses may help mitigate against inaccurate conclusions being drawn from LCA. WIREs Energy Environ 2016, 5:670–683. doi: 10.1002/wene.211 For further resources related to this article, please visit the WIREs website.

Impaired soil quality due to compaction and organic matter removal following forest harvesting and mechanical site preparation is of concern, especially on calcareous soils which are believed to be particularly sensitive to disturbance. This study set out to determine the effects of organic matter removal and compaction on soil quality and seedling productivity on calcareous soils of a localized disturbance landscape (2.25 m 2 ). Here we report ten year post-establishment results of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine ( Pinus contorta var . latifolia Engelm.) seedlings across four sites in southern British Columbia, Canada with eight treatment levels incorporating different quantities of organic matter removal and soil compaction. Pine seedlings suffered high rates of mortality when planted in deposits across all sites while Douglas-fir seedling mortality was high when planted in compacted undisturbed treatments at two sites and in deposits on the remaining sites. Douglas-fir volume was greatest on the deposit treatment regardless of site but grew significantly better on the non-calcareous site. Pine seedlings outgrew Douglas-fir seedlings and, after ten years, seedlings were largest on a mildly calcareous site. Seedling growth was generally found to be negatively affected by calcareous soils and compaction; however, the specificity of results, in terms of species and site interaction and changing response as the seedlings aged, reinforced the importance of treatment effects on soil quality and forest productivity across the entire length of a stand rotation.

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.

Department of Civil Engineering, University of Toronto, 35St. George Street, Toronto, Ontario M5S 1A4, CanadaAbstractForest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions asso-ciated with energy production. We assessed changes in GHG emissions resulting from displacement of coal withwood pellets for the Atikokan Generating Station located in Northwestern Ontario, Canada. Two contrastingbiomass sources were considered for continuous wood pellet production: harvest residue from current harvestoperations (residue scenario) and fibre from expanded harvest of standing live trees (stemwood scenario). Forthe stemwood scenario, two metrics were used to assess the effects of displacing coal with forest biomass onGHG emissions: (i) time to carbon sequestration parity, defined as the time from the beginning of harvest towhen the combined GHG benefit of displacing coal with biomass and the amount of carbon in regenerating for-est equalled the amount of forest carbon without harvest for energy production; and (ii) time to carbon debtrepayment, defined as the time from the beginning of harvest to when the combined GHG benefit of displacingcoal with biomass and the amount of carbon in the regenerating forest equalled forest carbon at the time of har-vest. Only time to carbon sequestration parity was used for the residue scenario. In the residue scenario, carbonsequestration parity was achieved within 1 year. In the stemwood scenario, times to carbon sequestration parityand carbon debt repayment were 91 and 112 years, respectively. Sensitivity analysis showed that estimates wererobust when parameter values were varied. Modelling experiments showed that increasing growth rates forregenerating stands in the stemwood scenario could substantially reduce time to carbon sequestration parity.We discuss the use of the two metrics (time to carbon sequestration parity and time to carbon debt repayment)for assessing the effects of forest bioenergy projects on GHG emissions and make recommendations on terminol-ogy and methodologies for forest bioenergy studies.

Displacement of fossil fuels by forest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions. However, GHG savings are not realised until the avoided fossil emissions offset the loss of atmospheric carbon (C) that would have been sequestered if the biomass was not used for bioenergy (i.e. time to C sequestration parity). We estimated the potential for mitigating GHG emissions and the timing of these atmospheric benefits when substituting conventional natural gas (NG) with renewable natural gas (RNG) produced from different forestry feedstocks within three Canadian provinces, and assessed the uncertainty among these estimates. We calculated the GHG balance of RNG using the alternative fate of biomass and the use of NG as base-case scenarios. Immediate to long-term time to C sequestration parity was typically in the order of residues burned

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.

Forest bioenergy feedstock production and harvesting systems range from small-scale fuelwood gathering to large-scale industrial plantations and the potential removal of all available aboveground and belowground biomass from intensively managed forests. Across this wide range of options for production and extraction, there is an equally wide range of potential impacts. It is critical that forest biomass procurement systems do not adversely impact forests or the environment; therefore, effective standards and planning tools, based on the best available scientific knowledge, must be in place to prevent these impacts from being realized, and hence ensure a sustainable industry. Sustainable forest management (SFM) certification schemes are one mechanism for applying measurable environmental standards (in the form of criteria and indicators, or C&I) to forest management systems. How existing SFM certification schemes and frameworks, such as C&I and Adaptive Forest Management, can be used to help guide sustaina...

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.

Sustainable forest management (SFM) is a cornerstone of forest management, whether the resulting forest products are destined for the manufacturing sector or for the emerging bioenergy feedstock market. In British Columbia, research on the environmental effects of forest management has generated scientific knowledge that has informed two linked areas of government responsibility: a comprehensive set of science-based regulations and policies to ensure soil and water conservation, anda monitoring program to ensure the effectiveness of these regulations and policies.An increasing amount of biomass is being harvested from British Columbia’s forests as a feedstock for bioenergy, and these removals have the potential to incrementally increase machine traffic and organic matter removals from forest sites, compared to harvesting operations focused solely on roundwood for timber or pulp. To the extent that existing standards support SFM, they may be sufficient for ensuring that biomass harvesting is also s...

Stump extraction for forest health has been carried out operationally in British Columbia (BC) for many years. Emerging bioenergy opportunities plus the anticipated need for more fibre because of reductions in timber supply may increase interest in stump harvesting, but there are numerous environmental, economic and policy barriers that must be overcome first before industrial-scale stump harvesting can be seriously considered in BC. The potential for a future change in practice provides an opportunity to learn from the existing literature and identify knowledge gaps. In this article we review the available literature on stump harvesting from the European Union within the context of BC's forests, economy, biodiversity, environment and policies. We provide recommendations on how the government of BC could move forward if they decide to enable stump harvesting for fibre and bioenergy, including assessment of net economic and carbon benefits and environmental effects, improvements in inventory and t...

Forest biomass is increasingly being considered as a source of sustainable energy. It is crucial, however, that this biomass be grown and harvested in a sustainable manner. International processes and certification systems have been developed to ensure sustainable forest management (SFM) in general, but it is important to consider if they adequately address specific impacts of intensified production and harvesting methods related to forest fuels. To explore how existing SFM frameworks address sustainable forest fuel production, criteria and indicators (C&I) from 10 different international processes and organizations and 157 international, national and sub-national forest management certification standards under the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC) were reviewed. International processes include indicators that require identification or reporting of availability, harvested amounts, value, or share in energy consumption of forest fuels. Forest certification standards address several specific woodfuel issues, but not always in a consistent manner. It seems that developed countries more frequently address environmental consequences of harvesting residues or whole trees on soil fertility and biodiversity, while developing countries more frequently address social issues, such as local people’s access to firewood and working conditions in charcoal production. Based on findings, options to improve SFM standards for sustainable forest fuel production are discussed. These options include clarification of terminology, systematic inclusion of important management impacts unique to forest fuel production, coordination of efforts with other related governance processes, including tools promoting sustainability at more integrated levels, such as landscape, supply chain and global levels.

Ontario's forest sector is undergoing a significant shift owing to declining markets for traditional products; this shift is further exacerbated by a cyclical industry downturn. These factors are leading to extensive job losses in Ontario's north as well as rural community upheaval. Governments are striving to reverse these effects by stimulating new industries focused on using forest biofibre for products such as fuel for energy, specialty chemicals, and polymers. In light of these new demands, provincial and federal policy and science experts are examining the range of potential forest biomass utilization opportunities in terms of their long-term implications for sustainability, role in an emerging bioeconomy, and the possible influences of, for example, a changing climate and technological advances. Current research and broad-scale monitoring projects are helping to answer several important questions in the ecological, economic, policy, resource supply, and technological realms, while new questions must be continually addressed. In this paper, we describe the legislative, policy, and administrative context in which the sustainable biofibre industry may exist. We argue that social, economic, and environmental goals for a sustainable forest biofibre industry in Ontario can best be achieved by adhering to the principles of adaptive management. Market forces and third-party certification, which can influence the biofibre sector, are also discussed.

We examined how tannin structure influences reactivity in tannin assays and carbon and nitrogen mineralization. Condensed tannins from the foliage of ten tree and shrub species and from pecan shells (Carya illinoensis) had different proportions of: (a) epicatechin (cis) and catechin (trans) isomers, (b) procyanidin (PC) and prodelphinidin (PD) monomers, and (c) different chain lengths. The response of each tannin to several widely used tannin assays was determined. Although there was some variation in response to proanthocyanidin (butanol/HCl) and Folin Ciocalteu assays, we did not deduce any predictable relationship between tannin structure and response to either assay. There was little variation in protein precipitation among the different tannins. To assess biological activity, six of the tannins were incubated with forest humus for 22 days. We determined that, while PC-based tannins remained at least partly extractable for the duration of the incubation, tannins with a high proportion of PD subunits rapidly became unextractable from soil. There was a positive correlation between net nitrogen mineralization and cis chemical structure. Carbon mineralization was enhanced initially by the addition of tannins to humus, but after 22 days, a negative correlation between the proportion of cis subunits and respiration was determined. Overall, we were not able to demonstrate consistent effects of structure on either microbial mineralization or reactivity to chemical assays; such relationships remain elusive.

There is a growing interest in using forest biomass as an energy source. The main objectives of this paper are to give somefigures and perspectives on Canadian forest biomass supply with respect to Canada’s energy demand and to examine thepotential of using this feedstock for reducing our greenhouse gas (GHG) emissions. Published estimates of forest biomasssupply as harvest residues are reported and discussed. The range of estimates listed here indicates that this source ofenergy is important but that it is still a fraction of our energy demands. The potential of using this biomass to reduce ourGHG emissions is strongly dependent, among other factors, on the technological pathways that are used, with direct heatproduction and combined heat and power (CHP) ranking amongst the best options available. The relative scarcity of theresource behooves us to use it efficiently. Key words: forest biomass, residue, greenhouse gas, mitigation, energy, sustainable forestry

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.

Successful regeneration following harvesting or natural disturbance is a fundamental prerequisite for sustainable forest management. However, some regenerating stands have poor juvenile growth rates, which compromise sustainable management objectives. In particular, the presence of some ericaceous species that proliferate after forest disturbance, such as Kalmia angustifolia, can slow succession of boreal stands to the point that ecosystem retrogression is induced. We used data from a silvicultural field trial established in central Newfoundland to evaluate how various combinations of silvicultural treatments (trench scarification, herbicide application, fertilization at planting) influenced growth of three conifer species planted on a Kalmia-dominated cutover. Ground-level diameter (GLD), height, diameter at breast height (DBH), and percent Kalmia cover were assessed at the end of 15 growing seasons after planting. We detected several interactions between silvicultural treatments and planted conifer species. Globally, height and estimates of foliar biomass of all conifer species responded positively to scarification. Fifteen-year height in both scarified and unscarified treatments was in the order Picea mariana < Pinus banksiana < Larix laricina. Black spruce and jack pine height increased when Kalmia was controlled with herbicide, but height of tamarack was not. The use of herbicide significantly increased 15-year GLD and volume index of all three conifer species, but only black spruce responded positively to fertilization at planting. Our results confirm that species-specific responses to silvicultural treatments are to be expected when managing Kalmia-dominated sites. Although chemical vegetation management has great silvicultural potential, our results suggest that mechanical site preparation can also be effective in promoting early conifer seedling growth that leads to rapid canopy closure. It is anticipated that canopy closure will lead to exclusion of Kalmia later in the rotation through natural successional pathways. Key words: Kalmia angustifolia, vegetation management, scarification, herbicide, fertilizer, black spruce, jack pine, tamarack

A renewed interest in the intensive harvesting of forest biomass as a source of bioenergy in North America raises concerns about the impacts that this practice may have on the maintenance of forest soil productivity. In Canada, such concerns were first voiced in the 1970s, and studies were launched to investigate and predict the impact of intensive forest biomass removal on site productivity. Most of these studies focused on static nutrient budgets. In Canada and around the world, more detailed process models were also developed to study carbon, nitrogen and base cation cycles under different forest harvesting intensities. However, the validity of modelling results is still constrained by our lack of knowledge on the capacity of ecosystems to supply nutrients. A few sets of field trials have been established in Canada to gather empirical data on the impact of biomass removal on soil nutrient reserves as well as on tree nutrition and growth. Although still fairly recent, these field trials, along with the older ones established in other countries with similar site conditions and climates, provide opportunities to refine our understanding of the resilience of ecosystem processes and of the impacts of intensive biomass removal on ecosystem functions. Although numerous knowledge gaps and questions remain, some jurisdictions around the world have nevertheless issued policy directives and developed guidelines for biomass harvesting. As described by the concept of adaptive forest management, ecological monitoring of harvesting operations, scientific field testing and modelling can all interact to produce better knowledge that could then help improve policy directives. Key words: bioenergy, biomass, intensive harvesting, environmental sustainability

Bioenergy from sustainably managed forest ecosystems could provide a renewable, carbon-neutral source of energy in many nations and communities throughout the world. In order for forest bioenergy to be an ecologically sustainable fuel source, woodfuel procurement systems must not adversely impact forest ecosystems or the environment. Sustainable forest management (SFM) certification schemes are one mechanism for applying standards and monitoring regimes to forest management systems to ensure ecological sustainability. This paper provides a global review of the main environmental risks to forest ecosystems that can arise from household- to industrial-scale woodfuel production systems, including forest soil quality and site productivity, water resources, biodiversity and carbon budgets. A set of regionally adaptable principles, criteria, indicators and verifiers of sustainable forest management were developed, based on criteria and indicators from existing internationally recognized certification frameworks and scientific literature and tailored to address issues relevant to producing and harvesting forest bioenergy feedstocks. A variable monitoring approach and a three-tiered certification approach are proposed as two methods for enabling the adoption of certification and associated monitoring requirements across a wide range of forest operations in regions with widely differing levels of development. The importance of the Adaptive Forest Management framework inherent in certification systems to ensuring the efficacy and continual improvement in woodfuel sustainability is stressed. The proposed principles, criteria, indicators and verifiers can be adapted to local conditions and incorporated into existing sustainable forest management and green energy certification schemes, as well as other criteria and indicator frameworks, to ensure the environmental sustainability of woodfuel production systems.

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.

Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was used to compare changes in organic chemistry of 10 species of foliar litter undergoing in situ decomposition for 1 to 12 years at four forested sites representing a range of climates in Canada. Three types of foliar litter (conifer, black spruce; deciduous, trembling aspen; and a grass, fescue) were studied on all four sites plus seven additional types (Douglas, fir; western red cedar; white birch; jack pine; beech; bracken fern; and tamarack) studied at the warmest site (Morgan Arboretum [MAR]). For all litter samples, DRIFT spectra were collected, and carbon and N were contents determined. A subset of samples (10 types x 5 years for MAR, three types x 5 years for the other sites) was analyzed by classical chemical methods for proximate fractions. Spectra for subsets of chemically analyzed samples from MAR were used to prepare partial least squares calibration equations for each chemical variable. These calibrations were then used to predict chemical concentrations for samples in a reserved subset, in intervening years, and from the three other sites, and then validated against measured values. Results indicated a trend of decline in proportion of nonpolar and water-soluble extractables with an increase in proportion of acid unhydrolyzable residue. The DRIFT was demonstrated as a fast and simple analysis method for analyzing large numbers of samples to give good estimates of litter chemistry. A single nondestructive sampling using as little as 0.1 g of sample gave reasonable values of carbon, N, and proximate fractions.

The MASS (Montane Alternative Silvicultural Systems) trial was established in the coastal mountains of British Columbia to compare clearcut, patch cut, green tree and shelterwood systems. A number of studies were carried out at the MASS trial to determine the extent to which these variable levels of stand retention retained old-growth attributes of N cycling and associated ecological processes. Harvesting led to increases in N mineralization in the forest floor (2×) and mineral soil (10×), and fluxes of N through the upper 25 cm of mineral soil (2× to 3×). However, fluxes of N were not large (< 0.35 kg ha-1 per growing season). Nitrogen mineralized was predominantly ammonium and not nitrate in the forest floor (> 95% in all but clearcut, > 75% in clearcut) and upper mineral soil horizon (42–86%). The nitrate component came from heterotrophic decomposition of organic matter, not conversion of ammonium to nitrate by autotrophs, and nitrate increases resulted from decreased gross nitrate consumption with harvesting, rather than increased nitrate production. The increases in soil N availability resulting from harvesting were reflected in only slight increases in seedling foliar N concentrations for two to four years after logging (peak of ~ 2% for western hemlock and ~ 1.6% for amabilis fir) before decreasing to below deficiency thresholds for both species. Overall, estimated losses of N from the rooting zone after harvesting (1 kg ha-1 yr-1) were minimal in comparison to estimated N inputs (4 kg ha-1 yr-1), N exports in logs at harvesting (250 kg ha-1) and soil reserves (11 400 kg ha-1). Although unlikely to affect future site productivity, losses of N could be reduced somewhat through the use of shelterwood harvesting. This is an electronic version of an article published as: Titus, B.D., Prescott, C.E., Maynard, D.G., Mitchell, A.K., Bradley, R.L., Feller, M.C., … Koppenaa, R. (2006). "Post-harvest nitrogen cycling in clearcut and alternative silvicultural systems in a montane forest in coastal British Columbia." The Forestry Chronicle, 82(6), 844-859. The Forestry Chronicle is available online at: http://pubs.cif-ifc.org/journal/tfc and this article is available at: http://pubs.cif-ifc.org/doi/abs/10.5558/tfc82844-6 https://viuspace.viu.ca/bitstream/handle/10613/2703/BeesePost-Harvest.pdf?sequence=3

Salal (Gaultheria shallon Pursh), which is widely used for floral greenery, is an important non-timber forest product (NTFP) from the coastal forests of the Pacific Northwest of North America. However, there are no known studies on the impacts of commercial salal harvesting on subsequent growth. A study was therefore initiated to quantify the growth of salal 1 year after commercial harvesting, and to compare this with growth of unharvested salal. The amount of biomass removed from shrubs through commercial harvesting (131 g m−2) was the same as the amount of annual growth in adjacent undisturbed plots (135 g m−2). One year later, the amount of regrowth in previously harvested plots (144 g m−2) was greater than the amount of new growth in adjacent undisturbed plots (111 g m−2). As there was little difference in the weight per current stem, the increased biomass after commercial harvesting was attributed to the observed increase in stem number (60 stems m−2) as compared to undisturbed salal (50 stems m−2). Our study does not incorporate either repeated annual harvesting or variable harvesting intensities, both of which have been anecdotally reported to affect levels of re-growth and therefore sustainability.

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.

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH4-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of ...

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.

Mechanisms responsible for conifer growth “check” on cutovers invaded by Kalmia angustifolia L. in central Newfoundland were studied by examining effects of added Kalmia and balsam fir ( Abies balsamea (L.) Mill) condensed tannins on black spruce humus N dynamics and microbial community development over 10 weeks using microcosms. Because of the silvicultural implications, interactions of tannins with fertiliser N, applied as (NH 4 ) 2 SO 4 , were also studied. Both tannin types significantly reduced NH + 4 –N leaching, whereas only Kalmia tannins reduced NO − 3 –N leaching, and then only from non-fertilised humus. Tannins did not significantly affect mineral N leaching from fertilised humus. Fertiliser N increased gross N mineralisation rates such that the increase in actively cycling N was many times greater than the increase in N leaching due to fertiliser N addition. Gross N mineralisation rates were higher in fertilised humus amended with tannins, suggesting possible toxicity of tannins on microbes at high N concentrations. Recovery of added tannins in leachate and in post-treatment humus samples was low. Net anaerobic N mineralisation decreased with tannin additions but increased with fertiliser N additions. There were few significant treatment effects on microbial properties derived from humus respirometry. Microbial biomass and basal respiration rates of all treatments declined by 30 and 37% respectively, indicating a general loss of available C during the experiment. The ratio of C mic -to-N mineralised as well as the nutrient deficiency index was lowest in humus amended with Kalmia tannins, suggesting higher microbial N deficiency in this treatment. Utilisation rates of various C sources by microbial communities showed distinctive patterns between pre-treatment and post-treatment humus samples, but did not reveal distinctive patterns among different treatments. Overall, results suggested that (1) condensed tannins decreased mineral N cycling abiotically by binding to and sequestering organic N sources, (2) fertiliser N counteracted negative effects of condensed tannins on humus N cycling, (3) microbial communities were N limited, which prevented abundant leaching of fertiliser N while maintaining fertiliser N in an active pool, and (4) the physiology and functional diversity of soil heterotrophic communities were controlled by C availability but were unaffected by tannin or fertiliser N additions. Further work is needed to determine the ecological importance of Kalmia tannins, relative to tannins produced by other plants, in reducing humus N availability on spruce cutovers.

In northern temperate and boreal zones, long-term sampling of the soil solution using lysimeter systems requires (i) a lysimeter that can be installed with a minimum of soil disturbance, (ii) a lysimeter that is small enough to install in stony soil but large enough to representatively sample the soil solution, (iii) a system with a constant tension that integrates soil solution sample collection over time, and (iv) a system that will not break under freezing conditions. A lysimeter system that meets these requirements was designed, and consists of a lysimeter (a fritted glass plate mounted on a glass casing) connected in series to a sample bottle and a tension-generating unit. The glass casing of the lysimeter has two ports: a drainage port for continuous flow of soil solution to the sample bottle, and an access port that can be used (i) for air entry to facilitate complete sample retrieval, (ii) for cleaning, (iii) for re-wetting the fritted glass plate, or (iv) for winterizing the lysimeter with alcohol. A 1-m hanging water column was used to supply a constant tension of approximately 10 kPa. A potential 93% efficiency rate of sample collection can be achieved, and the systems are capable of sampling soil solution beneath organic horizons, as well as in the rooting zone of mineral horizons. The system is presently being used to evaluate the effects of different harvesting and silvicultural treatments on nutrient cycling processes in the soil. Almost 700 of these lysimeter systems are in use in the Atlantic provinces of Canada. The lysimeters have been functioning satisfactorily for over 10 yr and are suitable for long-term monitoring of the soil solution. Key words: Lysimeter design, soil monitoring methodology, nutrient cycling

Post-clearcut silvicultural treatments, to improve tree growth and reduce salal (Gaultheria shallon) competition, were established in five different forest blocks on northern Vancouver Island, in 1984. Plots were either left untreated, brushed of competing salal vegetation, fertilized [(250 kg N + 100 kg P) ha-1], or brushed + fertilized. Three of these blocks were revisited 13 years later, in the summer of 1997, and various chemical, biochemical and microbial parameters were measured in forest floor humus samples to determine long-term effects of treatments on nutritional site quality. Brushing resulted in lower humus pH and extractable base cations, whereas fertilization increased Bray-extractable P. Over a 20-week aerobic incubation, significantly more N was mineralised in humus from fertilized plots than from brushed plots. Over a 14-d anaerobic incubation, significantly more N was mineralised in humus from the fertilized treatment than other treatments. Similarly, gross transformation rates of NH4 +and NO3 -, measured by 15N-dilution, were higher in humus from the fertilized treatment than other treatments. Ecophysiological indices of microbial communities (basal respiration, specific death rate, metabolic quotient, and energy deficiency index), derived by humus respirometry, suggested that there was higher available C in fertilized and brushed + fertilized treatments than in the brushed and control treatments. Total microbial biomass was equal to C-limited microbial biomass, which further confirmed that available C was the growth-limiting factor for microbial communities in all treatments. The prokaryotic fractions of microbial biomass in all treatments were approximately equal (≈ 65%). PCA ordination of microbial communities, based on C source utilisation patterns, showed a distinct clustering of humus samples taken from one of the sites. Within the cluster of samples taken from the other two sites, samples from fertilized plots scored separately from those from control plots. In salal foliage, concentrations of condensed tannins were higher in brushed and control plots than in fertilized and brushed + fertilized plots. In spite of other studies that have reported increased tree height following fertilization and/or removal of salal, results of the present study suggest improvement in nutritional site quality occurs only with fertilization, whereas brushing may in fact be detrimental. The long-term growth of hemlock observed in fertilized plots may be the result of changes to key ecosystem structures and processes brought about by increased speed of succession and accelerated canopy closure.

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.

Kalmia angustifolia L. is an ericaceous shrub that frequently invades black spruce (Picea mariana Mill.) clear-cuts in central Newfoundland. Field observations suggest that on many sites where K. angustifolia grows, black spruce seedlings become chlorotic and stunted. Previous laboratory research has suggested that allelochemicals of K. angustifolia affect the growth and development of black spruce as well as the growth of certain ectomycorrhizal (ECM) fungi associated with black spruce. Black spruce seedlings close to ( 1 m) K. angustifolia were sampled from a clear-cut in central Newfoundland. The ECM community structure, degree of mycorrhizal infection, height, mass, root:shoot ratio, and the foliar concentrations of N, P, K, Ca, and Mg of spruce seedlings growing close to and far from K. angustifolia were examined. Seedlings close to K. angustifolia had significantly lower foliar concentrations of N and P, had a lower rate of mycorrhizal infection, and were more frequently associated with Phialocephala dimorphospora Kendrick, a potential root pathogen of black spruce, than seedlings growing far from K. angustifolia. There were positive linear relationships between black spruce foliar N concentration and total seedling height and biomass for seedlings growing away from K. angustifolia, but not for seedlings in close proximity to K. angustifolia. Hypotheses suggesting possible roles for nutrient competition, allelopathy, and K. angustifolia's ability to increase the occurrence of the pseudomycorrhizal P. dimorphospora on black spruce are proposed.

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 effects of conventional stem-only and whole-tree harvesting on nutrient losses in biomass removal and in leachate fluxes over a 3-yr period after cutting three white birch stands in central Newfoundland were determined. Losses of nutrients in biomass were proportionately greater with more intensive harvesting as tree components with higher nutrient concentrations (branches, foliage) were removed. Stem-only harvesting removed 126, 9, 51, 126 and 23 kg ha–1 of N, P, K, Ca and Mg in biomass, respectively. Whole-tree harvesting led to a 19% increase in biomass removal as compared to stem-only harvesting, but nutrient removals with whole-tree harvesting increased by 127% for N, 138% for P, 151% for K, 72% for Ca and 90% for Mg. Nutrient losses in deep percolation of soil solution during the first 3 yr after harvesting were generally greater following stem-only than whole-tree harvesting. This may be the result of increased leaching from slash, increased mineralization beneath slash, and retardation by slash of the successional vegetation that could act as a nutrient sink. In the first 3 yr following harvesting, leaching losses after whole-tree harvesting were 4, 0.2, 8, 23 and 7 kg ha–1 of N, P, K, Ca and Mg, respectively, as compared with 9, 0.1, 7, 28 and 9 kg ha–1 of N, P, K, Ca and Mg after stem-only harvesting. Nutrient losses in leachate were generally small compared to losses in biomass removal. Key words: Intensive harvesting; slash; nutrient budget; sustainable site productivity; Betula papyrifera (Marsh.)

Glucose-C was repeatedly added to organic Kalmia humus from two sites of contrasting spruce productivity (i.e. rich and poor) and basal respiration, microbial biomass and metabolic quotient ( q CO 2 ) were measured over a 438 day incubation and compared to post-incubation soil mineral-N pools, anaerobic N mineralization rates, the nutritional deficiency index (NDI) of soil microbial communities and final soil weights. Repeated measures analysis of variance revealed a strong overall soil effect on basal respiration and microbial biomass and a strong overall glucose effect on microbial biomass and q CO 2 , whereas the analysis of within-subjects effects revealed strong interactions of the time factor with both soil and glucose on all three measurements. In the poor soil, glucose supported high microbial biomass and therefore low q CO 2 , until the end of the incubation, whereas in the rich soil, glucose also supported high microbial biomass and low q CO 2 , but these converged towards control (i.e. no glucose) values before the end of the incubation. Mineral-N pools were high in the rich control treatment only, whereas the NDI was high only in the rich + glucose treatment. Anaerobic N mineralization rates did not differ statistically among treatments. Glucose significantly decreased mass loss in the rich soil but not in the poor soil. The data support the conclusion that glucose addition to the rich soil inhibits microbial utilization of nutrient-containing soil OM for maintenance energy thus exacerbating nutritional defiencies, whereas glucose addition to the poor soil does not affect soil N cycling. Based on results of analytical pyrolysis performed on soil subsamples prior to the incubation, we hypothesize that higher amounts of tannins measured in the poor humus may have chemically immobilized and ultimately controlled availability of N.

RESUMELa regeneration de l'epinette noire (Picea mariana (Mill.) B.S.P.) au centre de Terre-Neuve faisant suite a une perturbation causee par le feu ou des operations forestieres peut etre affectee par la presence de l'arbuste ericaceen Kalmia angustifolia L. La presente etude a ete realisee afin de tester les donnees de teledetection acquises en 1994 par le capteur multispectral CASI (Compact Airborne Spectrographic Imager) pour la detection de differentes densites de couvert de Kalmia sur des sites perturbes dans le centre de Terre-Neuve. Une approche basee sur la classification discriminante a ete developpee pour differencier les peuplements de Kalmia, plus de trois classes de couvert de Kalmia (couvert faible, moyen et dense) et les autres grands types de couvert tels que l'epinette noire, l'aulne, les secteurs de coupe sans Kalmia et les zones humides. Des images de quatre secteurs differents ont ete utilisees, couvrant trois periodes de l'annee. Les resultats de la classification ont ete testes par ...

Two species of boreal tree seedlings, paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.), and the ericaceous shrub Kalmia angustifolia L. were grown in pots with humus from a birch-dominated site and two spruce-Kalmia sites. Root systems interacted with humus form in controlling soil-N cycling as well as energy and nutritional deficiencies of soil microorganisms. In general, Kalmia seedlings affected microbial dynamics and N cycling differently than birch and spruce seedlings did. Birch and spruce seedlings reduced gross N mineralization and immobilization rates, soil mineral-N pools and the amounts of NH\(_4^ + \)–N accreted on buried cation exchange resins in all three soils. Compared to birch and spruce seedlings, the growth of Kalmia resulted in significantly higher gross N mineralization rates, soil mineral-N pools and resin-NH\(_4^ + \) accretion in soil from the fertile birch site. Gross N immobilization rates in all soils were generally higher with Kalmia than with spruce or birch seedlings. All three species of seedlings acquired N from the birch site soil, whereas only Kalmia seedlings acquired N from the two spruce-Kalmia site soils. Relative to control treatments, the amount of N mineralized anaerobically increased in the birch-site soil and decreased in the poor spruce-Kalmia site soil with all three species of seedlings. All seedlings increased the microbial biomass in the birch-site soil. Kalmia humus and Kalmia root systems increased microbial energy-deficiency and decreased microbial nutritional deficiency compared to the other humus and seedlings used. Results are discussed in terms of each species' nutrient acquisition mechanism and its competitive ability during secondary succession.

Three white birch stands of differing site quality (good, intermediate, rich) in central Newfoundland were monitored using porous cup lysimeters to study changes in nutrient concentrations (NH4N, NO3N, PO4P, K, Ca, Mg, pH) in the soil solution following stem only and whole tree harvesting. Ammonium concentrations on the good and intermediate sites were not greatly affected by cutting, but stem only (STO) harvesting on the rich site led to increased concentrations that persisted for 3 y. Nitrate concentrations increased more on the intermediate than on the good site, but increases were smallest on the richest site. This was attributed to a combination of uptake by more vigorous advance regeneration (mainly alders) on the rich site, as well as wetter soil conditions that limited nitrification. Phosphorous concentrations were not greatly affected by harvesting. Potassium concentrations increased immediately after harvesting as K leached from slash on the STO treatments, plant remains and the forest floor, and decreased as these sources were depleted. Vegetation uptake and leaching associated with movement of NO3N were also controlling mechanisms on some sites. Calcium and Mg concentrations were correlated, and initially increased with harvesting, but on the richest two sites decreased below control stand levels after whole tree harvesting (WTH) at the end of 3 y. Movement of Ca and Mg was associated with NO3N on sites where there was a significant increase in NO3N concentrations following harvesting. Acidity decreased on the good site, increased after STO, but decreased after WTH on the intermediate site, and increased after both intensities of harvesting on the rich site. Nutrient concentrations in the soil solution were generally higher when slash was retained in STO treatments rather than removed in WTH treatments. This was attributed to a combination of increased mineralisation beneath the slash, increased leaching from the slash, and decreased plant uptake. In general, the soil solution data suggest that harvesting effects last for no more than 3 y for most nutrients on these birch sites in Newfoundland, and that whole tree harvesting generally had less impact on nutrient concentrations than stem only harvesting. However, this does not necessarily mean that net losses from sites were less with WTH, as this does not take into account nutrient fluxes or nutrient removals in slash.