The potential of forest-based bioenergy to reduce greenhouse gas (GHG) emissions when displacing fossil-based energy must be balanced with forest carbon implications related to biomass harvest. We integrate life cycle assessment (LCA) and forest carbon analysis to assess total GHG emissions of forest bioenergy over time. Application of the method to case studies of wood pellet and ethanol production from forest biomass reveals a substantial reduction in forest carbon due to bioenergy production. For all cases, harvest-related forest carbon reductions and associated GHG emissions initially exceed avoided fossil fuel-related emissions, temporarily increasing overall emissions. In the long term, electricity generation from pellets reduces overall emissions relative to coal, although forest carbon losses delay net GHG mitigation by 16-38 years, depending on biomass source (harvest residues/standing trees). Ethanol produced from standing trees increases overall emissions throughout 100 years of continuous production: ethanol from residues achieves reductions after a 74 year delay. Forest carbon more significantly affects bioenergy emissions when biomass is sourced from standing trees compared to residues and when less GHG-intensive fuels are displaced. In all cases, forest carbon dynamics are significant. Although study results are not generalizable to all forests, we suggest the integrated LCA/forest carbon approach be undertaken for bioenergy studies.

Intraspecific assisted migration (ISAM) through seed transfer during artificial forest regeneration has been suggested as an adaptation strategy to enhance forest resilience and productivity under future climate. In this study, we assessed the risks and benefits of ISAM in white spruce based on long-term and multilocation, rangewide provenance test data. Our results indicate that the adaptive capacity and growth potential of white spruce varied considerably among 245 range-wide provenances sampled across North America; however, the results revealed that local populations could be outperformed by nonlocal ones. Provenances originating from south-central Ontario and southwestern Québec, Canada, close to the southern edge of the species' natural distribution, demonstrated superior growth in more northerly environments compared with local populations and performed much better than populations from western Canada and Alaska, United States. During the 19–28 years between planting and measurement, the southern provenances have not been more susceptible to freezing damage compared with local populations, indicating they have the potential to be used now for the reforestation of more northerly planting sites; based on changing temperature, these seed sources potentially could maintain or increase white spruce productivity at or above historical levels at northern sites. A universal response function (URF), which uses climatic variables to predict provenance performance across field trials, indicated a relatively weak relationship between provenance performance and the climate at provenance origin. Consequently, the URF from this study did not provide information useful to ISAM. The ecological and economic importance of conserving white spruce genetic resources in south-central Ontario and southwestern Québec for use in ISAM is discussed.

Boreal forest carbon (C) storage and sequestration is a critical element for global C management and is largely disturbance driven. The disturbance regime can be natural or anthropogenic with varying intensity and frequency that differ temporally and spatially the boreal forest. The objective of this review was to synthesize the literature on C dynamics of North American boreal forests after most common disturbances, stand replacing wildfire and clearcut logging. Forest ecosystem C is stored in four major pools: live biomass, dead biomass, organic soil horizons, and mineral soil. Carbon cycling among these pools is inter-related and largely determined by disturbance type and time since disturbance. Following a stand replacing disturbance, (1) live biomass increases rapidly leading to the maximal biomass stage, then stabilizes or slightly declines at old-growth or gap dynamics stage at which late-successional tree species dominate the stand; (2) dead woody material carbon generally follows a U-shaped pattern during succession; (3) forest floor carbon increases throughout stand development; and (4) mineral soil carbon appears to be more or less stable throughout stand development. Wildfire and harvesting differ in many ways, fire being more of a chemical and harvesting a mechanical disturbance. Fire consumes forest floor and small live vegetation and foliage, whereas logging removes large stems. Overall, the effects of the two disturbances on C dynamics in boreal forest are poorly understood. There is also a scarcity of literature dealing with C dynamics of plant coarse and fine roots, understory vegetation, smallsized and buried dead material, forest floor, and mineral soil.

KOPPENAAL, R. S., TSCHAPLINSKI, T. J., and COLOMBO, S. J. 1991. Carbohydrate accumulation and turgor maintenance in seedling shoots and roots of two boreal conifers subjected to water stress. Can. J. Bot. 69: 2522-2528. Water potential components and organic solutes werc examined in shoots and roots of potted jack pine (Pittiis batlksiat~n Lamb.) and white spruce (Picea glouca (Moench) Voss) seedlings after exposure to 7 days of water stress. The osmotic potential at the turgor loss point ( $ , . , , , ) decreased in shoots and roots of water-stressed seedlings of both species, resulting in the maintenance of positive turgor at lower xylem water potentials ($, ) compared with nonstressed seedlings. Following water stress, ~JJ, . , , of shoots and roots declined by 0.28 MPa and 0.14 MPa, respectively, in jack pine, and 0.19 MPa and 0.28 MPa, respectively, in white spruce. The osmotic potential at saturation ($,,,,,J was significantly lower after water stress only in jack pine roots. Active osmotic adjustment during water stress was confirmed by higher concentrations of organic solutes in white spruce shoots (1.4 x increase relative to nonstressed plants) and roots (1.7 x ) and in the roots (2.2 x ) but not the shoots of jack pine. Carbohydrates, particularly fructose and glucose, were the primary organic solutes accumulating in both species. Tissue elasticity was greater in the roots than the shoots of both jack pine and white spruce regardless of treatment. Consequently, the relative water content at the turgor loss point was 22% and 18% lower in the roots than in the shoots of jack pine and white spruce, respectively. Osmotic adjustment in the roots and shoots of these two boreal conifers suggests that preconditioning planting stock by exposure to water stress may increase carbohydrate concentrations and enhance seedling drought tolerance. Key ,vords: carbohydrate accumulation, drought tolerance, organic solutes, osmotic adjustment, Picea glrrrrco, Pittr1.s barksiorra, water potential components. KOPPENAAL, R. S., TSCHAPLINSKI. T. J., et COLOMBO, S. J. 1991. Carbohydrate accumulation and turgor maintenance in seedling shoots and roots of two boreal conifers subjected to water stress. Can. J . Bot. 69 : 2522-2528. Les composantes du potentiel hydrique et les solutes organiques ont kt6 examines dans des tiges et des racines de pins gris (Pinrrs barlksinrlu Lamb.) et d'epinette blanche (Picerr glcrrrco (Moench) Voss) cultivCs en pot, apres 7 jours d'expositionii un stress hydrique. Le potentiel osrnotique au point de perte de turgescence ($,.,L.l) dirninue dans les tiges et les racines des plantules sournises au stress hydrique chez les deux especes, ce qui conduit au rnaintient.d'une turgescence positive au potentiel hydrique du xylkme le plus faible ($, ) comparativement aux plantules non-stressees. A la suite d'un stress hydrique, la valeur (t),,.,.,,) des tiges et des racines diminue ii environ 0,28 MPa et 0,14 MPa, respectivement, chez le pin gris, et 0,19 MPa et 0,28 MPa, respectivement chez I'epin...

In the spring of 2012, conifers in a large area in northwestern Ontario exhibited severe needle browning prior to budbreak, affecting more than 250 000 ha of forests north and west of Thunder Bay. Examination of weather data suggests that damage was caused by a combination of warm temperatures in March resulting in dehardening followed by freezing temperatures in April that were below a critical value. Damage was similar in nature to that observed in 2007 in northeastern Ontario, but in this case occurred earlier in the year and affected a larger area. Areas of northern Ontario where trees were affected were easily separated from those where no damage was observed using daily minimum temperature and cumulative growing degree day data. We suggest that a new term, winter freezing damage, be used to describe conifer needle and bud damage prior to budbreak when a period of warm temperatures in late winter/early spring followed by a period of sufficiently cold freezing temperatures causes damage to forest stands.Keywords: conifer winter damage, mature needle and bud mortality, late March warming, early dehardening, freezing résumé Au printemps 2012, les conifères d'une grande partie du nord-ouest de l'Ontario montraient un brunissement important de leurs aiguilles avant le débourrement printanier, et ce sur plus de 250 000 ha de forêts situées au nord et à l' ouest de Thunder Bay. L' étude des données météorologiques indique que les dommages ont été provoqués par une combinaison de températures chaudes au cours du mois de mars qui ont interrompu la dormance, suivies de températures très froides en avril, inférieures au seuil critique. Les dommages étaient de même nature que ceux observés en 2007 dans le nord-est de l'Ontario, mais qui étaient survenus plus tôt dans la saison, affectant une plus grande étendue. Les secteurs du nord de l'Ontario où les arbres ont subi des dommages se distinguaient clairement de ceux sans dommage apparent sur la base des données de température minimale moyenne et des degrés-jours de croissance accumulés. Nous suggérons d'utiliser le néologisme « dommage de gel hivernal » pour décrire les dommages aux aiguilles et aux bourgeons de conifères survenant avant le débourrement lorsqu'un redoux suivi d'une période de températures sous le point de congélation survient à la fin de l'hiver ou au début du printemps, provoquant des dommages aux peuplements forestiers. Description of conifer browningIn the spring of 2012, severe needle browning (i.e., needle death) developed in jack pine (Pinus banksiana Lamb.) (Fig. 1, Fig. 2, and Fig. 3), white spruce (Picea glauca [Moench] Voss) (Fig. 4), (Fig. 5), and black spruce (Picea mariana [Mill.] BSP) stands in a large area of northwestern Ontario. Affected trees were mostly young conifers between 5 and 25 years old, but in some areas mature overstory trees were also damaged. Among species, white spruce and balsam fir sustained the most damage and black spruce the least. Damage was first noticed prior to budbreak during late April and early May 2...