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Abstract: Aspen and balsam poplar regeneration from root suckers were assessed in boreal mixedwood forests nine years after logging in a variable retention experiment (EMEND Project—Ecosystem Management Emulating Natural Disturbance) located north of Peace River, Alberta, Canada. Five levels of retention of mature trees (2%, 10%, 20%, 50% or 75% of the original basal area) were applied in stands dominated by aspen, white spruce or mixtures of the two species. Basal area of aspen (or that of aspen plus balsam poplar combined) prior to logging strongly influenced sucker density of aspen (or aspen+balsam poplar combined) and in some cases their growth. Nine years after harvest there was a decline in sucker density and volumeha−1 with increasing retention levels of aspen (or both poplars combined); sucker density declined by 50% when only 20% of the original basal area was left in the stand. Retaining mature spruce trees in the stand had little influence on the number of suckers but did affect their total volumeha−1. Thus, we suggest that by knowing stand aspen and balsam poplar density prior to logging and varying levels of retention of aspen and balsam poplar or conifers at harvest, the density of Populus regeneration can be predicted by managers, thereby allowing them to create a range of mixedwood conditions. [Copyright &y& Elsevier]

Abstract: Land-use and land cover strongly influence carbon (C) storage and distribution within ecosystems. We studied the effects of land-use on: (i) above- and belowground biomass C, (ii) soil organic C (SOC) in bulk soil, coarse- (250–2000μm), medium- (53–250μm) and fine-size fractions (<53μm), and (iii) 13C and 15N abundance in plant litter, bulk soil, coarse-, and medium- and fine-size fractions in the 0–50cm soil layer in Linaria AB, Canada between May and October of 2006. Five adjacent land-uses were sampled: (i) agriculture since 1930s, (ii) 2-year-old hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantation, (iii) 9-year-old Walker hybrid poplar plantation, (iv) grassland since 1997, and (v) an 80-year-old native aspen (Populus tremuloides Michx.) stand. Total ecosystem C stock in the native aspen stand (223MgCha−1) was similar to that of the 9-year-old hybrid poplar plantation (174MgCha−1) but was significantly greater than in the agriculture (132MgCha−1), 2-year-old hybrid poplar plantation (110MgCha−1), and grassland (121MgCha−1). Differences in ecosystem C stocks between the land-uses were primarily the result of different plant biomass as SOC in the 0–50cm soil layer was unaffected by land-use change. The general trend for C stocks in soil particle-size fractions decreased in the order of: fine>medium>coarse for all land-uses, except in the native aspen stand where C was uniformly distributed among soil particle-size fractions. The C stock in the coarse-size fraction was most affected by land-use change whilst the fine fractions the least. Enrichment of the natural abundances of 13C and 15N across the land-uses since time of disturbance, i.e., from agriculture to 2- and then 9-year-old hybrid poplar plantations or to grassland, suggests shifts from more labile forms of C to more humified forms of C following those land-use changes. [Copyright &y& Elsevier]

Abstract: Survival and growth of planted white spruce was assessed under partial harvest treatments and different site preparation techniques in mixedwood forests of two compositions prior to logging: deciduous dominated (d-dom) – primarily comprised of mature trembling aspen (Populus tremuloides Michx.) and coniferous dominated (c-dom) – primarily comprised of mature white spruce (Picea glauca (Moench) Voss). Levels of overstory retention were 0% (clearcut), 50% and 75% of original basal area, and site preparation techniques were inverted mounding, high speed mixing, scalping and control (no treatment). The survival and growth of white spruce were assessed seven years after planting. The experiment was established as a part of the Ecosystem Management Emulating Natural Disturbance (EMEND) experiment located in northern Alberta, Canada. In the c-dom, the 50% and 75% retention of overstory resulted in reduced growth and survival of white spruce seedlings compared to clearcuts. In contrast, in the d-dom, the seedlings performed best in sites that had 50% of the overstory retained. For the c-dom, the mounding and mixing treatments yielded the best growth of spruce seedlings, while scalping yielded the worst. In the d-dom, spruce growth was highest in sites with the mixing treatment. In the d-dom, growth and survival of the planted spruce was greater than in the c-dom. The natural regeneration of deciduous trees was suppressed by the retention of canopy regardless of original composition. [Copyright &y& Elsevier]

As part of efforts to address the root causes of climate change and non-renewable resource depletion, many regions in the world are considering sustainable biomass feedstocks for renewable energy production. Prior to making such large-scale shifts in primary energy feedstocks, location-specific research is still needed to understand the environmental impacts and benefits of biomass associated with its many potential applications. The objective of this study was to evaluate environmental and energy impacts associated with generating 1 MJ of thermal energy from direct combustion of short rotation willow (SRW) pellets for 2 purposes: to determine where improvements could be made in the life cycle of SRW bioenergy to reduce impacts, and to compare SRW bioenergy to fossil fuel (light fuel oil and natural gas) for thermal energy. Life cycle assessment (LCA) was conducted using primary data on SRW biomass production collected from field trials at the Guelph Agroforestry site in Guelph, Ontario, Canada, as well as carbon sequestration rates modeled based on local conditions. Results showed that direct combustion of SRW pellets reduced global warming potential (GWP) by almost 85% relative to the fossil fuels. However, relative to fossil fuels, SRW energy had higher impacts in certain categories (e.g. eutrophication and respiratory effects), due to biomass combustion and N inputs (inorganic fertilizer and SRW leaf inputs) for biomass production. Soil nitrous oxide emissions, from the N inputs, dominated the GWP, but a sensitivity analysis showed that soil carbon sequestered by SRW biomass during growth could reduce the GWP by 23%. Pelletizing the SRW biomass prior to combustion affected the energy ratio and accounted for almost 85% of non-renewable energy use in the life cycle of bioenergy. Location-specific factors that affected environmental performance of the bioenergy system included agro-climatic conditions, management practices, and conversion technologies. Nevertheless, most of the impacts associated with SRW thermal energy generation can be minimized through better fertilizer management, by using alternate sources of fertilizer, by improving yields, and by the use of cleaner wood combustion technologies with emissions controls. [ABSTRACT FROM AUTHOR]

We developed allometric equations for small-diameter woody species growing on mixed forest marginal lands, which are potential sources of biomass for bioenergy. Eleven species of trees and shrubs were sampled from a site located in eastern Canada. Equations derived in this study generally performed better than equations from the literature. Also, fixed-area plots (FAP) and line-intersect sampling (LIS) methods using both random or systematic selection of sampling units were compared to determine which method required the lowest number of measurements to estimate stand biomass for the same precision. The fixed-area plots method was successfully used to estimate relatively accurately oven-dry biomass per hectare. Results indicated that potentially harvestable woody biomass (oven dry basis) varied between 33-41 and 12–13 t ha −1 for the most and least productive marginal sites respectively. On the most productive site, LIS estimates (between 20 and 42 t ha −1 ) were usually lower than those obtained using different FAP sampling methods (i.e. systematic or random, small (50 m 2 ) or large (100 m 2 ) plots), but similar on the more open sites (between 10 and 14 t ha −1 ). Small FAP resulted in a plot without measurements in one case. Moreover, estimates based on small FAP were generally higher, even if not significantly different from larger plot estimates. We therefore suggest using FAP with 100 m 2 plots to estimate small-diameter woody biomass on marginal lands with dense vegetation, while LIS, even if promising for open stands, needs further evaluation before recommendation. [ABSTRACT FROM AUTHOR]

Short-rotation intensive culture (SRIC) for bioenergy production is at its pre-commercial stage in Canada. To be economically viable, these types of plantations need an accurate examination of actual yields, which requires precise and efficient estimation methods (i.e., specific allometric equations and sampling methods). At six SRIC plantations from three Canadian provinces (Quebec, Ontario and Alberta), 6 willow and 10 poplar clones were sampled and clone allometric equations were developed to estimate plant biomass. A stem selection approach was successfully used to develop plant allometric equations, reducing the number of stems to be measured by up to 81% in coppiced plantations relative to traditional stem equations. Clone-specific equations were more accurate than equations for groups of clones, but the difference in terms of RMSE% was generally small (less than 5%). Using extensive measurements of all the plants inside a plantation and a simulation approach, we also compared five sampling methods (simple random sampling, stratified sampling, systematic sampling, random and systematic cluster sampling) to estimate total biomass inside the plantation. Simple random sampling and stratified random sampling were the most efficient methods (i.e., increased precision for equal sample size) for the estimation of average plant biomass, survival and total plantation biomass. Stratified random sampling (based on the position inside the plantation) made it possible to reduce the sample size as compared to simple random sampling, but only at higher levels of precision (e.g., 25 less plants at 5% precision). Applications of sampling using remote sensing techniques and GIS are briefly discussed. [ABSTRACT FROM AUTHOR]

Morphological characteristics of poplar and willow clones were determined in order to identify main characteristics leading to superior growth under increased plant competition with low or high nitrogen (N) availability. Seven hybrid poplar ( Populus spp. including one hybrid aspen) and five willow ( Salix spp.) clones were grown under greenhouse conditions for 13 weeks at three spacings (20 × 20, 35 × 35, and 60 × 60 cm) and two N levels (20 and 200 mg kg −1 ). The decrease in spacing from 60 to 20 cm reduced leaf area by 50% but clones had similar aboveground biomass per tree under all spacings, with increasing their height per unit leaf area. More productive clones had greater leaf area (+102%), leaf area per unit plant biomass (+12%) and lower root-to-shoot ratios (−27%) compared to less productive clones. There were positive relationships between leaf area and above-ground biomass per tree for both more and less productive clones. Compared to low N level and 60 cm spacing, trees growing in high N level and 20 cm spacing reached similar root collar diameter, crown width, and leaf area values and even greater height, suggesting that an addition of N could help mitigate negative effects of tree competition. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid poplar (HP) is an important fast-growing crop with the potential to provide a reliable supply of biomass for the pulp and bioenergy industries while also sequestering carbon (C) in the soil. We used the eddy-covariance technique to measure CO2, water vapor and sensible heat fluxes above a three-year-old HP plantation on high productivity land near St Albert, Alberta. Measurements showed that the annual C balance of the plantation shifted from a C source of about 1.54 Mg C ha−1 y−1 in the 2nd year (2010) to a C sink of 0.80 Mg C ha−1 y−1 in the 3rd year (2011). Water use or evapotranspiration (E) for 1 June – 31 October increased from 272 mm in 2010 to 321 mm in 2011, and exceeded the respective values of total precipitation of 251 mm and 298 mm for the same period. Annual E in 2010 of 364 mm was less than annual precipitation of 398 mm. In 2011, annual E (442 mm) exceeded annual P (411 mm) by 31 mm; it also exceeded the annual plantation water use E wb, estimated using a water balance method assuming no drainage from the root zone, by 40 mm. However, both courses of cumulative E and E wb closely followed cumulative P. Monthly E increased with increasing net radiation and gross primary productivity. Growing season mean albedo increased from 0.16 in 2010 to 0.21 in 2011 and was consistent with the increase in broadband NDVI. Values of albedo during winter months (November–April) exceeded 0.80. The results suggested that as the plantation grows, growing season albedo, annual C sequestration, and annual water use will increase with the possibility that the latter may exceed annual precipitation. This emphasizes the need to study the long-term sustainability of HP plantations in relation to annual P and its temporal distribution, especially when HP plantations will likely be established on large contiguous areas to supply biomass feedstock for the expanding pulp and bioenergy industries in Western Canada. [Copyright &y& Elsevier]

Abstract: Quantifying the carbon (C) balance of short-rotation woody crops is necessary for validating the C sequestration potential of these systems. We studied the changes in net ecosystem productivity (NEP) and ecosystem C storage 2–4 and 9–11 years after converting an agricultural land (planted to canola, Brassica napus L.) to hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantations in the Parkland region in central Alberta, Canada. The NEP across land uses ranged between 0 and 13MgCha−1 year−1, while changes in C storage over two years (2006–2008) ranged between 1 and 7MgCha−1 year−1 as biomass C and between −1 and 6MgCha−1 year−1 as soil organic C. When agricultural land was converted to hybrid poplar plantations, soils under hybrid poplar plantations were initially large sources of C losing a total of 8MgCha−1. As cultivation ceased and net primary productivity (and thus litter input) increased, the soil started to become a net C sink by year 2, reaching its pre-plantation level by year 7. At the ecosystem level, hybrid poplar plantations were a source of C in the first 2 years, due to the small contribution of plant biomass and litter relative to soil C loss. Thereafter, the ecosystem acted as a net C sink and reached its pre-plantation level by year 4. We conclude that growing hybrid poplars on rotations longer than 4 years in the study area would create a net C sink and converting agricultural land to fast-growing short-rotation woody crops has the potential for mitigating future climate change. [Copyright &y& Elsevier]