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• May minimum temperature is the primary driver of budburst in boreal conifers. • P. mariana showed the highest response to warmer springs and P. glauca the lowest. • Precipitation's effect on budburst is limited when compared to temperature. • Changes in bud phenology may disrupt host-insect interactions. • Budburst timing correlates with latitude and ecological provinces. Budburst is a pivotal event in plant life, representing a crucial response to seasonal meteorological shifts. Boreal tree species exhibit species-specific phenologies, and the rate of phenological changes under warming conditions may differ among these species. In this study we aim to investigate the timing of budburst in three coniferous species [Balsam fir (Abies balsamea), black spruce (Picea mariana) and white spruce (Picea glauca) (Pinaceae)]; identify the main drivers of budburst, its rate of advance and the spatiotemporal patterns of budburst in relation to climate across Canada using a time period of 1980–2021. The timing of budburst was observed at 2839 locations stretching from Alberta to Newfoundland. We developed response functions between budburst and climate (air temperature, precipitation and solar radiation) and used the strongest correlations to test their effect on budburst using species, time and the ecoclimatic framework of Canadian ecoprovinces. We applied spatially constrained multivariate clustering and identified natural budburst clustering across Canada. We found a baseline difference of 17 days in the budburst of black spruce relative to that of balsam fir and white spruce. Mean minimum temperature of May was negatively correlated with budburst date. Black spruce advanced budburst at a rate of change per degree of temperature (−3.33 days °C−1), twice that of balsam fir and white spruce (−1.53 and −1.27 days °C−1, respectively). Cluster distribution of budburst timing matched well with the distribution of Canadian ecoprovinces. Budburst within the clusters followed clinal patterns in temperature across Canada. Mean minimum temperature in May is the main factor driving budburst in northern tree species. Under a warmer spring, we project an earlier budburst, with black spruce being the species expected to show the greatest rate of change. The identified clustering patterns did not vary with precipitation, which represents the primary longitudinal gradient across Canada. [ABSTRACT FROM AUTHOR]

• 50+ years of growth and C dynamics at plantation experiment estimated with tree-rings and models. • Productivity greatest at high density, and for red pine relative to black or white spruce. • NEP largest at high density when stands young, similar across all densities as stands matured. • Initial soil C estimate contributed uncertainty to when sites became C sink after planting. Afforestation can result in significant accumulations of carbon (C) in both soils and vegetation, which can make an important contribution to GHG emission mitigation. However, there remains a critical knowledge gap about ecosystem C stocks and fluxes at afforested sites, which is required in order to understand the effect of management choices like species selection and initial planting density. A hybrid biometric modelling approach was used to reconstruct ecosystem C stocks and fluxes at an experimental spacing trial consisting of three species (red pine, white spruce, and black spruce) planted at three densities, 63 years after it was established on former agricultural land in Northwestern Ontario, Canada. Wood volume and increment were larger for closer spacing and for red pine relative to black or white spruce, and translated to analogous differences in estimates of ecosystem C dynamics. At young ages, net ecosystem production was largest at close spacing, but this difference attenuated over time and was similar in recent decades regardless of initial spacing. Estimated carbon stock and flux values were generally congruent with available estimates from independent studies at analogous sites, with the exception of litterfall which showed greater differences. Plots at the site were estimated to be C sinks on an annual basis immediately after establishment under the assumption that the site was previously under long-term agricultural land use, but anywhere from 10 to 20 years following establishment if the site was modelled as if it was a stand in the managed forest historically subject to natural disturbance regimes. [ABSTRACT FROM AUTHOR]

Highlight • Black and white spruce increased in growth following mountain pine beetle outbreak. • White spruce had a higher growth rate than black spruce. • Spruce growth increases as initial tree size and understory light increases. • High spruce/fir competition led to a lower diameter growth but higher height growth. • Both species of spruce have the potential of replacing dead overstory pine trees. Abstract Advanced regeneration of black spruce and white spruce are common in lodgepole pine dominated stands of Alberta. These economically important species have the potential to replace lodgepole pine trees that are killed by mountain pine beetle (MPB). The growth responses of both species of spruce after overstory lodepole pine mortality were examined using data collected from seven sites in the lower foothills of western Alberta, Canada. We sampled understory black and white spruce (>1.3 m in height) and characterize competitive effect of surrounding trees on growth response. Diameter and height growth responses of both species were affected positively by overstory pine mortality with white spruce having a shorter delay in release response than black spruce. While higher mean growth responses were observed for white spruce, both species of spruce increased in growth as initial tree size and understory light increases. Spruce/fir competition around the focal trees resulted in increased height growth and a reduction in diameter growth of both spruces. Overall, our results demonstrate that advance regeneration of both species of spruce can increase in growth and potentially replace pine in the canopy that have been lost to MPB. [ABSTRACT FROM AUTHOR]

Highlights • We evaluated five different Btk spraying scenarios to protect host trees from spruce budworm. • We hypothesized that less frequent Btk application could protect trees at a lower cost. • Black spruce maintained at least 54% of its residual photosynthetic capacity (RPC), even without protection. • Btk application every 2 years seems to be a relevant alternative to protect balsam fir and white spruce. • This scenario kept RPC above 39% and required 36% fewer applications over 7 years. Abstract Large-scale aerial spray operations against the spruce budworm (Choristoneura fumiferana (Clemens)) (SBW) with the biological insecticide Bacillus thuringiensis ssp. kurstaki (Btk) aim at maintaining trees alive during outbreaks. This objective is thought to be achieved when ≥ 50% of current-year foliage is preserved until the end of the outbreak. This protection target is associated with low balsam fir (Abies balsamea [L.] Mill.) mortality. However, it is unknown whether this approach is always needed or whether less frequent interventions could provide similar results at a lower cost. Between 2010 and 2016, we conducted field experiments in Quebec's Côte-Nord region to determine the efficacy of five different Btk spraying scenarios for protecting balsam fir, white spruce (Picea glauca [Moench] Voss) and black spruce (P. mariana [Mill.] BSP) in mixed stands. We used the residual photosynthetic capacity (RPC) to evaluate the efficacy of the five scenarios. RPC makes it possible to take into account the impact of SBW defoliation on foliage contribution to tree photosynthetic effort over several years, and can be used as a proxy of the risk of tree mortality. We hypothesized that less frequent Btk applications could maintain the required RPC level to keep trees alive. Our results show that areas not protected resulted in great losses of RPC in balsam fir and white spruce. Btk applications every 3 years kept RPC above 50% for 2 years in balsam fir and 4 years in white spruce. RPC losses were above 62% after 4 years in both species. The strategy currently employed in Quebec (spraying every year after a first year of moderate-severe defoliation) and the intensive protection scenario (Btk applications every year) meet the protection goals for these hosts. However, their cost prevents their application at a large scale. Btk applications every 2 years seems a relevant alternative to the current strategy to protect balsam fir and white spruce stands given the adequate level of protection provided (RPC above 39%) and the reduction in the number of Btk applications required (36% fewer applications over 7 years, resulting in 36% lower cost), particularly if the objective is to maintain trees alive. Black spruce maintained at least 54% of its RPC, even without protection. Btk applications every 3 years might be a valid alternative to reduce growth losses in black spruce-dominated stands. The use of different spraying scenarios may allow us to develop cost-efficient treatment strategies to protect Quebec's forests. [ABSTRACT FROM AUTHOR]

Spruce budworm (SBW; Choristoneura fumiferana (Clem.)) defoliation can cause severe growth reduction and mortality to spruce-fir ( Picea-Abies ) species in eastern North America. Consequently, it is important to understand and predict how individual trees respond to defoliation in terms of growth and mortality. To address this, species- and region-specific individual-tree models quantifying the effects of cumulative defoliation on annualized diameter and height increment, crown recession, and mortality were developed using data from an extensive network of 424 and 136 permanent sample plots in Maine, USA and New Brunswick, Canada, respectively, during the last SBW outbreak of 1970–1990s. In general, these models fit well with relatively small bias despite large variation observed in the data. The effects of SBW defoliation on diameter increment, crown recession, and mortality were highly significant but relatively moderate depending on species, possibly because overall mean defoliation was rather moderate. Reduction in diameter increment and increase in mortality were always more significant for balsam fir ( Abies balsamea L.) than for the spruce species. However, diameter increment returned to higher rates irrespective of species in New Brunswick, where the data were collected towards the end of the SBW outbreak. Overall, the results highlight the variability of tree response to SBW defoliation and the array of factors that may influence it. [ABSTRACT FROM AUTHOR]

• The performance of various conifer species in boreal lichen woodlands is unknown. • Four conifer species were planted at two sites with contrasting fertility. • Survival rate 5 years after planting was high for all species at both sites. • Soil quality had a large impact on growth but not on aboveground biomass traits. • Jack pine had a better performance and benefited more from increased soil quality. Lichen woodlands (LWs) are persistent unproductive areas of the Canadian boreal forests whose afforestation may potentially remove significant amounts of anthropogenic C from the atmosphere. The choice of species to be planted is nevertheless uncertain given the particular pedoclimatic conditions prevailing in this habitat as well as the rapidly changing climate at northern latitudes. In this study, we assessed the survival and the growth rates of four boreal coniferous species in two LWs with contrasting soil fertility. Five years after afforestation, survival rate was high for all species at both sites, ranging from 60 to 100 %. Tree height and diameter at stump height (DSH) were up to 60 % and 97 % higher at the LW with higher soil fertility, respectively. The height of jack pine (Pinus banksiana Lamb.; JP) trees was on average 15 %, 56 % and 68 % higher than that of tamarack (Larix laricina [DuRoi] K. Koch; TK), black spruce (Picea mariana [Mill.] BSP; BS) and white spruce (Picea glauca [Moench] Voss; WS), respectively. There was a significant species × soil fertility interaction, reflecting a much higher growth difference between the two sites for JP than for the other species. Annual apical growth increased from one year to the other in JP, suggesting its ability to expand its root system and to acquire resources from the mineral soil rapidly after planting. The much larger photosynthetic biomass at the more fertile site was driven by a higher number of needles produced annually rather than by a higher mass of individual needles, which did not vary between sites. The photosynthetic biomass / woody biomass ratio was not significantly impacted by soil fertility. Overall, these results suggest that JP and TK may be good candidates for the afforestation of boreal LWs and that site selection is of crucial importance to optimize plantation productivity in the mid-term. Further studies must be conducted to assess the survival and the C sequestration potential of these species in the long-term. [ABSTRACT FROM AUTHOR]

The late-Holocene shift from Picea glauca (white spruce) to Picea mariana (black spruce) forests marked the establishment of modern boreal forests in Alaska. To understand the patterns and drivers of this vegetational change and the associated late-Holocene environmental dynamics, we analyzed radiocarbon-dated sediments from Grizzly Lake for chironomids, diatoms, pollen, macrofossils, charcoal, element composition, particle size, and magnetic properties for the period 4100–1800 cal BP. Chironomid assemblages reveal two episodes of decreased July temperature, at ca. 3300–3150 (ca −1 °C) and 2900–2550 cal BP (ca −2 °C). These episodes coincided with climate change elsewhere in the Northern Hemisphere, atmospheric reorganization, and low solar activity. Diatom-inferred lake levels dropped by ca. 5 m at 3200 cal BP, suggesting dry conditions during the period 3200–1800 cal BP. P. glauca declined and P. mariana expanded at ca. 3200 cal BP; this vegetational change was linked to diatom-inferred low lake levels and thus decreased moisture availability. Forest cover declined at 3300–3100, 2800–2500 and 2300–2100 cal BP and soil erosion as inferred from increased values of Al, K, Si, Ti, and Ca intensified, when solar irradiance was low. Plant taxa adapted to disturbance and cold climate (e.g. Alnus viridis , shrub Betula , Epilobium ) expanded during these periods of reduced forest cover. This open vegetation type was associated with high fire activity that peaked at 2800 cal BP, when climatic conditions were particularly cold and dry. Forest recovery lagged behind subsequent climate warming (≤+3 °C) by ca. 75–225 years. Our multiproxy data set suggests that P. glauca was dominant under warm-moist climatic conditions, whereas P. mariana prevailed under cold-dry and warm-dry conditions. This pattern implies that climatic warming, as anticipated for this century, may promote P. glauca expansions, if moisture availability will be sufficiently high, while P. mariana may expand under dry conditions, possibly exacerbating climate impacts on the fire regime. [ABSTRACT FROM AUTHOR]

Highlights: [•] Root development and tree growth were compared for ground level and deeply planted spruces. [•] A major part of the root system of black and white spruce trees was adventitious after 17years. [•] Adventitious roots formed early after planting and their size was greater for deeply planted trees. [•] Deep planting increased tree height and basal diameter of white spruce, but only height of black spruce. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the potential of ALOS/PALSAR for estimating the above-ground biomass (AGB) and other biophysical parameters (tree height, diameter at breast height (DBH), and tree stand density) in the boreal forest of Alaska. In July 2007, forest surveys were conducted along a south–north transect (150°W) to profile the ecotone from boreal forest to tundra in Alaska. In situ parameters were measured in 29 forests by a combination of the Bitterlich angle-count sampling method and the sampled-tree measuring method. These in situ values were compared with the backscatter intensity of ALOS/PALSAR. A strong positive logarithmic correlation was found between the backscatter intensity and the forest AGB, with the correlation being stronger in the HV than in the HH polarization mode. No obvious saturation was found in the sensitivity of the HV mode backscatter intensity to the forest AGB up to 120.7 Mg ha−1. Similarly, a robust sensitivity was found in the HV backscatter intensity to both tree height and DBH, but weak sensitivity was observed for tree density. The regression curve of HV backscatter intensity to the forest AGB appeared to be intensified by the uneven forest floor, particularly for forests with small AGB. The geographical distribution of the forest AGB was mapped, demonstrating a generally south-rich and north-poor forest AGB gradient. [Copyright &y& Elsevier]

Abstract: This paper examines the variability in the relationship between climate and radial growth of black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) trees across central Labrador, Eastern Canada. Using climate-sensitive trees, an 11-year running Pearson correlation is applied to local records to examine the relationship between radial tree growth and climate over the last 50 years and the spatial pattern in this relationship with increasing distance inland from the Labrador Sea. Results indicate that there is a high degree of instability in the climate/tree-ring sensitivity despite an overall statistically significant relationship throughout the instrumental time period (1942 to present). Although some periods of reduced climate sensitivity are coincident with insect outbreaks, others cannot be explained by forest disturbance factors. Spatially, the two sites that are most representative of higher elevation areas have more time-stable climate-growth relationships than those inland or along the coast. The results also suggest that the stability of the relationship may be the result of moisture availability, rapid changes in precipitation and temperature, and site-specificity. [Copyright &y& Elsevier]

Abstract: Despite their suitability for dendroclimatological research, the boreal regions of central and western Labrador remain under-researched. In an attempt to evaluate the growth trends and climatic response of this region''s trees, master chronologies have been developed for its four dominant conifer species. Balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) Britton, Sterns, Poggenb.) and eastern larch (Larix laricina (DuRoi) K. Koch) were sampled systematically within a 3×4 grid of twelve sites at the intersection of 62°W, 64°W and 66°W longitude, and latitudes 52°N, 53°N, 54°N and 55°N. The two most dominant species at each site were sampled, yielding a total of twenty-four master chronologies, all of which reflected a highly significant common signal at each site. The chronologies were subjected to a response function analysis to determine the nature of the growth–climate relationships in the region. Summer temperature proved to be the predominant limiting factor with regard to radial growth at most sites. The onset of the optimum temperature regime, however, varies across the network of sites, revealing evidence of a gradient of continentality in the data. Growth–temperature correlations indicated a significant relationship with July temperature at most eastern sites, while western sites tended to correlate with May, June and August temperatures. Central sites tended to correlate with June–July temperatures. We interpret these results as demonstrating the bioclimatic gradient of change between coastally proximal, maritime-influenced sites and inland, continentally influenced locales. This transition occurs approximately 330km inland from the open Labrador Sea. [Copyright &y& Elsevier]

Abstract: Stem form is often used as a sawlog assortment criterion and has an important effect on lumber recovery and mechanical properties. Based on 7018 stems collected from the natural stands in 3 regions in eastern Canada, this study quantified the variations in stem form (taper, sweep and eccentricity) for five major commercial softwood species, viz., jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana), white spruce (Picea glauca), red spruce (Picea rubens) and balsam fir (Abies balsamea). The majority of the stems had a diameter at breast height (DBH) ranging from 10 to 32cm and total tree height from 10 to 20m. Stem taper and butt taper increased steadily from 0.38 to 1.75cm/m and from 0.74 to 4.23cm/m, respectively, with DBH increasing from 8 to 48cm. Stem sweep and basal sweep ranged from 0.12 to 7.28cm/m and from 0.12 to 9.85cm/m, respectively, with mean values of 0.87 and 0.95cm/m. There were no significant differences in stem sweep and basal sweep between DBH classes and both sweeps distributed over a wide range within DBH classes, species and regions. About 0.77% of the stems and 1.2% of the butt logs had seriously curved shapes (sweep >3.0cm/m). Eccentricity (ratio of smaller diameter to larger diameter) at the breast height (0.96) was very close to 1. Balsam fir and jack pine had the best and worst stem forms, respectively, while stem forms in black spruce were in-between. Butt logs were most seriously curved in red spruce and most tapered in white spruce. Region C (mainly eastern Quebec and the Atlantic Provinces) produced stems with smaller butt taper, basal sweep and stem sweep and larger eccentricity compared with other regions in eastern Canada. Overall stems in eastern Canada have a good stem form in terms of taper, sweep and eccentricity. The evaluation of stem form provides valuable timber quality information for the wood industry to optimize wood processing as well as for forest managers to define appropriate silvicultural regimes to improve stem form and economic value. [Copyright &y& Elsevier]

Abstract: We conducted this investigation in response to criticisms that the current Alaska Interagency Fire Management Plans are allowing too much of the landscape in interior Alaska to burn annually. To address this issue, we analyzed fire history patterns within the Yukon Flats National Wildlife Refuge, interior Alaska. We dated 40 fires on 27 landscape points within the refuge boundaries using standard dendrochorological methods. Fire return intervals based on tree ring data ranged from 37 to 166 years (mean=90±32 years; N =38) over the 250 year time frame covered by this study. We found no significant differences in the frequency of fire occurence over time. There was no evidence to suggest that changes in fire management policy have significantly altered the fire regime in the Yukon Flats area. However, the lack of significant differences over time may be due in part to the relatively short time period that fires were actively suppressed in Alaska. The full suppression era (1939–1984) may have been too short to significantly alter the fire regime in all areas of interior Alaska. [Copyright &y& Elsevier]

Abstract: Long-term interactive effects of site preparation, brush control and fertilization treatments on productivity, composition and structure were examined on jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana [Mill.] B.S.P.), white pine (Pinus strobus L.) and white spruce (Picea glauca [Moench] Voss) plantations, 15 years after planting in Ontario, Canada. For all crop species, growth performance increased significantly with site preparation intensity on sites without brush control, but did not change on sites with brush control. The effect of brush control and site preparation on stand volume of crop trees varied among plantations while fertilization had no effect. For the jack pine plantation, stand volume of crop trees increased with brush control and site preparation intensity, while volume of non-crop trees did not differ among treatments. For the black spruce plantation, brush control increased and site preparation marginally affected stand volume of crop trees. However, brush control decreased non-crop tree hardwood volumes, resulting in a significant increase in total stand volume. In the white pine and white spruce plantations, stand volume of crop trees increased while that of non-crop trees declined, resulting in no difference in total stand volume. However, there was a significant shift of stand composition from hardwood dominated, mixed, to crop trees dominated with silvicultural intensity. Height structure changed with increasing silvicultural intensity for all plantations, showing a shift from a hardwood dominated multi-layer canopy (a canopy of two or more layers mixed of crop trees and non-crop trees) to a crop tree dominated canopy with an understory of naturally established shade-tolerant seedlings. We conclude that intensive silviculture is a useful tool for managing stand composition and structure of boreal and northern temperate plantations, but increases in total stand volume may not occur as expected. [Copyright &y& Elsevier]

One-year-old seedlings of black spruce (Picea Mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss.), jack pine (Pinus banksiana Lamb.) and aspen (Populus tremuloides Michx.) were exposed to 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures for 4 months. The rate of net photosynthesis (A), stomatal conductance, mid-day xylem water potential, the internal to ambient CO2 concentration ratio (Ci/Ca), and specific leaf area (SLA) were evaluated 3 months after the initiation of the treatments. The responses of the above variables generally showed a bell-shaped curve except the Ci/Ca ratio. The relationships between soil temperature and the ecophysiological variables (except Ci/Ca) were modeled using third-order polynomials. The models suggest that jack pine generally had the highest optimal soil temperature among the four species, followed sequentially by black spruce, trembling aspen and white spruce. Aspen was generally more sensitive to low soil temperatures than the conifers while black spruce was more sensitive to high soil temperatures than other species. Jack pine and trembling aspen generally showed different response patterns than black and white spruce. The photosynthesis in aspen and jack pine was progressively less limited by stomatal conductance (relative to mesophyll limitation) as soil temperature increased from 5 to 35 °C whereas in the spruces, stomatal conductance was the least limiting to photosynthesis at moderate soil temperatures (10–15 °C for white spruce, 15–20 °C for black spruce). The xylem water potential of jack pine and aspen was more sensitive to low soil temperatures while that of the spruces was more sensitive to high soil temperatures. The specific leaf area of jack pine and aspen showed large variations with changes in soil temperature while that of the spruces was relatively constant throughout the range of soil temperatures. Most of the conifer seedlings in the 35 °C soil temperature treatment died at the end of the experiment while all aspen seedlings survived. [Copyright &y& Elsevier]

One-year old seedlings of trembling aspen (Populus tremuloides Michx.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.) were subject to seven soil temperatures (5, 10, 15, 20, 25, 30 and 35 °C) for 4 months. All aspen seedlings, about 40% of jack pine, 20% of white spruce and black spruce survived the 35 °C treatment. The seedlings were harvested at the end of the fourth month to determine biomass and biomass allocation. It was found that soil temperature, species and interactions between soil temperature and species significantly affected root biomass, foliage biomass, stem biomass and total mass of the seedling. The relationship between biomass and soil temperature was modeled using third-order polynomials. The model showed that the optimum soil temperature for total biomass was 22.4, 19.4, 16.0 and 13.7 °C, respectively, for jack pine, aspen, black spruce and white spruce. The optimum soil temperature was higher for leaf than for root in jack pine, aspen and black spruce, but the trend was the opposite for white spruce. Among the species, aspen was the most sensitive to soil temperature: the maximum total biomass for aspen was about 7 times of the minimum value while the corresponding values were only 2.2, 2.4 and 2.3 times, respectively, for black spruce, jack pine and white spruce. Soil temperature did not significantly affect the shoot/root (S/R) ratio, root mass ratio (RMR), leaf mass ratio (LMR), or stem mass ratio (SMR) (P>0.05) with the exception of black spruce which had much higher S/R ratios at low (5 °C) and high (30 °C) soil temperatures. There were significant differences between species in all the above ratios (P<0.05). Aspen and white spruce had the smallest S/R ratio but highest RMR while black spruce had the highest S/R but lowest RMR. Jack pine had the highest LMR but lowest SMR while aspen had the smallest LMR but highest SMR. Both LMR and SMR were significantly higher for black spruce than for white spruce. [Copyright &y& Elsevier]

The objective of this review was to summarize the expected yield gains of black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), white spruce (Picea glauca (Moench) Voss) and red pine (Pinus resinosa Ait.), to correct provenance-progeny selection, first generational selection strategies and second generational selection strategies, based on a systematic assessment of the scientific literature. The procedure consisted of four sequential steps: (1) searching electronic databases for relevant forest tree improvement studies employing a meta-analytical protocol; (2) attaining and assessing the identified publications for their specific applicability; (3) collating the results of the resultant study subset in terms of relative height growth gains; and (4) estimating rotational consequences in terms of merchantable productivity via prediction models. The results of the systematic search indicated that documented long-term yield responses to tree improvement were paucity in nature. Specifically, the majority of the published studies consisted of short-term results pertaining to provenance-progeny experiments. Furthermore, studies reporting yield responses to first and second generational selection strategies were practically non-existent. Consequently, expert opinion and unpublished preliminary results derived from ongoing tree improvement experiments were used to augment the limited published information available for these selection strategies. Overall, the results indicated that correct provenance-progeny selection could yield juvenile height growth gains of approximately 15% at 15 years for black spruce, 7% at 21 years for jack pine, 12% at 20 years for white spruce and 8% at 15 years for red pine. Corresponding merchantable productivity (mean annual merchantable volume increment) gains at rotation (50 years) for plantations established at nominal initial densities on medium-to-good quality sites were approximately 17, 15, 26 and 7%, respectively. Preliminary estimates derived from individual case-studies indicated that (1) first generational selection strategies could increase merchantable productivity by approximately 13% at 50 years for black spruce, 28% at 40 years for jack pine, and 20% at 45 years for white spruce, and (2) second generational selection strategies could increase merchantable productivity by approximately 31% at 50 years for black spruce. [Copyright &y& Elsevier]

• Both nutrient supply and root interaction between seedlings influenced responses to CO 2 elevation. • CO 2 stimulation to photosynthesis was much greater under low than high nutrient supply. • CO 2 elevation substantially reduced low nutrient limitation to photosynthesis. • The degrees of responses were very different between black spruce and white spruce. The carbon dioxide concentration ([CO 2) in the atmosphere has been increasing since the start of the industrialization. The impact of increasing [CO 2 on the physiology and growth of plants and on the composition, dynamics and productivity of plant communities have been studied extensively in the past few decades. However, the responses to CO 2 elevation can be altered by other environmental and biological factors. Such interactions, particularly those involving multiple factors, are complex and not well understood. In this study, we investigated the interactive effects of CO 2 elevation, nutrient availability and root interaction between plants on the total seedling photosynthesis, growth, and biomass allocation of two boreal conifer tree species, black spruce and white spruce. Seedlings were exposed to two [CO 2 (380 vs. 720 µmol mol−1) and two nutrient levels (low vs. high) with or without root interaction. We found that each of the three treatments influenced the effects of others and the two species also responded differently to those interactions. Root interactions reduced seedling growth only when nutrient supply was high. White spruce was more sensitive root interaction than black spruce while black spruce was more sensitive to the negative impact of low nutrient supply than white spruce. Surprisingly, CO 2 elevation and its interactions did not significantly affect seedling growth. The CO 2 elevation significantly increased total seedling photosynthesis while root interaction reduced it and the reduction was greater under the elevated CO 2. The photosynthetic response to CO 2 elevation was more sensitive to nutrient availability in white spruce than in black spruce. Seedling biomass was more sensitive to the negative impact of root interaction and low nutrient supply in black spruce than white spruce. Root interaction reduced biomass allocation to leaf and the impact was reduced by low nutrient. Biomass allocation to leaf was more sensitive to low nutrient supply in black spruce than white spruce. CO 2 elevation reduced but root interaction increased root/leaf mass ratio, partially offsetting each other when both treatments were applied. The root/leaf ratio of white spruce was more sensitive to CO 2 elevation while that of black spruce was more sensitive to root interaction and nutrient supply. Low nutrient supply and root interaction both had positive effect on root/leaf ratio and their effects were confounded when both were applied simultaneously. Therefore, their effects were observed only when one of them was absent. [ABSTRACT FROM AUTHOR]

In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) occurred in New Brunswick, Canada. Datawere collected from ten plots established in an area infested from 1992-1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of totaldefoliation (all age classes of foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill.) B.S.P.). Stand responsewas assessed and related to cumulative defoliation. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fir trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p<0.05) related to tree size, in both lightly and severely defoliated plots; trees with DBH <11cm sustained 22-48% higher mortality than larger trees. Mortality of balsam fir, in terms of both percent stems/ha and m3/ha merchantable volume, increased exponentially in relation to three estimates of cumulative (summed) plot mean defoliation. The strongest relationships (r2=0.75-0.79) were between mortality and the ocular defoliation assessment for 1990-1993 foliage. Tree mortality caused by the looper outbreak ranged from 4-14% stems/ha in lightly defoliated and from 32-100% in severely defoliated plots; merchantable volume killed was 3-14m3/ha and 51-119m3/ha, respectively. Relationships between mortality and defoliation were similar when defoliation was assessed for 1987-1993 and 1990-1993 foliage age classes. [ABSTRACT FROM AUTHOR]