Effects of soil temperature on biomass production and allocation in seedlings of four boreal tree species

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.     

Overstory and shrub effects on natural regeneration processes in native Pinus radiata stands

Native Monterey pine (Pinus radiata D. Don) stands on the Monterey peninsula have been significantly modified by natural and anthropogenic disturbances. The exclusion of fire and the introduction of pitch canker (caused by Fusarium circinatum Nirenberg & O’Donnell) created a need for the examination of these changing ecosystems with respect to regeneration, especially as these stands reach mature ages. We established 210 plots on 35 transects distributed throughout five stands in order to describe the current stand structure and quantify the extent and condition of regeneration. The results indicated that Monterey pine seedling establishment varies throughout the peninsula depending on percent canopy cover, duff and litter depth, and percent shrub cover while seedling growth is influenced by percent shrub cover. Canopy cover was also found to inversely influence shrub cover. Our study highlights the importance of understory removal to increase Monterey pine regeneration and seedling growth as canopy cover decreases, especially in areas where coast live oak (Quercus agrifolia Nee) and poison-oak (Toxicodendron diversilobum E. Greene) are abundant.     

Long-term response of planted conifers, natural regeneration, and vegetation to harvesting, scalping, and weeding on a boreal mixedwood site

This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce (Picea glauca [Moench] Voss) and jack pine (Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen (Populus tremuloides Michx.)) and conifer (largely balsam fir (Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation.Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.     

Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39 year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

Corrigendum to: Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39-year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

Lodgepole pine growth as a function of competition and canopy light environment within aspen dominated mixedwoods of central interior British Columbia

Three lodgepole pine and aspen mixedwood sites located in the central interior of British Columbia within the Sub Boreal Spruce (SBS) biogeoclimatic zone were chosen to study the neighbourhood aspen competition and canopy light environment of 14–19-year-old lodgepole pine. All three sites had previously been established as separate research trials designed to explore various silviculture options for controlling aspen competition (aspen brushing, herbicide, thinning and untreated areas). For each site, 33–36 pine trees were selected to represent the observed range of light regimes under the influence of various aspen competition levels. At each sample pine, competition and stand measurements were made and a series of vertical canopy light measurements from the top to the base of the live crown. After an evaluation of a variety of competition indices, the index DRD; sum of the ratio of each of the three nearest neighbour's DBH to the subject pine divided by their distance and, amount of available light at the top of the crown (DIFN_t) were found as the best overall predictors of pine stem volume growth. A site specific exponential relationship of relative pine stem volume growth to DRD was found and minimum growth response competition thresholds were determined, which could provide useful targets where maximizing pine volume is intended. Evaluation of both linear and non-linear models of DIFN_t versus height growth indicated the response to be linear across the observed range of available light. Implications for management are discussed.     

Influence of fire intensity on structure and composition of jack pine stands in the boreal forest of Quebec: Live trees,understory vegetation and dead wood dynamics

North American jack pine (Pinus banksiana Lamb.) stands are generally characterized by an even-aged structure resulting from high intensity fires (HIF). However, non-lethal fires of moderate intensity (MIF), which leave behind surviving trees, have also been reported. The objectives of this study were two-fold: (1) assess the concurrent dynamics of live trees, understory vegetation and different types of coarse woody debris (CWD) during succession after HIF; and (2) document how MIF affects stand structure component dynamics compared to HIF. Stands affected by both HIF and MIF were selected. Tree characteristics and age structure, understory biomass, and CWD volume were assessed. Our results suggest that the structural succession of jack pine stands following HIF comprises three stages: young stands (<48 years), premature and mature stands (58–100 years) and old stands (>118 years). Canopy openness and jack pine density significantly decreased with time since HIF, while black spruce density and CWD volume significantly increased. The highest structural diversity was measured in the premature and mature stands. Compared to HIF, MIF increased mean jack pine basal area, decreased average stand density, delayed the replacement of jack pine by black spruce replacement in the canopy, decreased CWD volume, and significantly increased bryophytes mass. MIF increased the diversity of live trees and generally decreased CWD structural diversity. The study confirms the diversity of natural disturbance magnitude and successional processes thereby initiated. Thereafter, it appeared to be relevant for adjustment of disturbance emulating forest-management systems.     

Transversal tracheid dimension in thinned black spruce and Jack pine stands in the boreal forest

Abstract

Commercial thinning has recently been applied in the boreal forest of Quebec (Canada) to increase the volume growth of the residual trees. We aimed to discover if the growth response influences the transversal tracheid dimension of thinned black spruce (Picea mariana (Mill.) B.S.P.) and Jack pine (Pinus banksiana Lamb.) stands at 0.2 m stem height. All 20 studied stands have shown a significant growth response after the treatment (p<0.0001), especially trees with the lowest radial growth before thinning in comparison with the stand mean. Growing conditions met by suppressed trees before thinning might favour them in the competition for light, water and biomass production after the treatment. Trees with a positive growth response did not significantly modify their measured transversal tracheid dimension except for trees which increased twofold their ring-width after thinning. In this case, lumen area and radial cell diameter extended significantly. However individuals with a growth decrease after thinning registered significantly lower values in their ring width, earlywood and latewood cell numbers (p<0.0001) in both species.     

Effects of opening size and stand characteristics on light transmittance and temperature under young trembling aspen stands

While aspen (Populus tremuloides Michx.) cover provides protection from growing season radiative frosts, reduced light levels can limit growth of understory white spruce (Picea glauca (Moench) Voss). The creation of openings around individual spruce can provide more light, but the chance of radiative frost damage increases as gaps become larger. We examined the relationship between opening size and light and temperature levels in the center of circular gaps created in young aspen stands ranging from 1.8 to 8 m tall. Models for predicting transmittance as a function of sky view factor and transmittance under intact stands are presented. Results indicated a strong relationship between light levels and opening size after considering pre-treatment light levels. The relationship between opening size and temperature was weak with minimum temperatures being more affected by the height and density of the surrounding stand than opening size.     

Long-term influence of fire and harvesting on boreal forest age structure and forest composition in eastern Québec

In boreal forests, historical variations in the area disturbed by natural disturbances or harvesting have rarely been compared. We measured temporal and spatial variations in areas affected by severe fires and clearcutting throughout the 20th century in a 57, 332 km² section of the eastern Canadian boreal forest. We examined the effects of these disturbances on spatio-temporal variations in the abundance of forests >60 years. Natural variability for the abundance of forests >60 years was estimated from simulations of natural disturbance regimes. We also measured compositional and structural differences between three categories of stands originating from relatively recent disturbances (∼50 years; clearcutting, fires, and clearcutting followed by fires), and one category of stands that were undisturbed for at least 200 years. At the regional level, we observed that forests >60 years gradually became scarcer throughout the 20th century due to a gradual expansion of harvested areas, an effect most pronounced in the southern part of the region, where mature and old forest abundance was clearly outside the range of natural variability at the end of the studied period. At the stand level, forest composition and structure differed between stand-origin categories: clearcutting-origin stands contained more balsam fir (Abies balsamea), fire-origin stands more black spruce (Picea mariana), and fire/clearcutting-origin stands more hardwoods (Betula papyrifera and Populus tremuloides). Overall, we estimate that strict forest management targets based on natural disturbance regimes will be difficult to achieve in eastern North-American boreal forests, most notably because contemporary disturbance rates, including both clearcutting and fire, have gradually become higher than the fire rates observed during the preindustrial period.     

Structural changes and potential vertebrate responses following simulated partial harvesting of boreal mixedwood stands

Partial harvesting, where different numbers and arrangements of live trees are retained in forest stands, has been proposed for maintaining late-successional structure and associated vertebrate species within managed boreal forests. Using the stand dynamics model SORTIE-ND, we examined 80-year patterns of structural change in response to different intensities (30-70% basal area removal) and spatial patterns (22-273 m² mean patch size) of harvesting. We also applied habitat models for seven late-successional vertebrates to the structural conditions present after harvesting to assess potential species responses.Partial harvesting increased understory and downed woody debris (DWD) cover and decreased overstory structure for the first 25 years after harvest, in comparison to unharvested stands, with this effect subsequently reversing as harvest-induced regeneration reached the canopy. Although harvesting enhanced long-term structural development in this regard, large trees, large snags, and large DWD all remained below unharvested levels throughout the simulation period. Harvesting also produced transient increases in early-decay DWD and ground exposure. Most changes in structural attributes increased in proportion to harvest intensity, but structural differences among harvest patterns were generally small. Dispersed harvesting induced somewhat less pronounced decreases in vertical structure, and produced more post-harvest slash, than aggregated harvesting.All seven vertebrate species decreased in abundance as harvest intensity increased from 30 to 70%. In comparison to their pre-harvest abundances in old stands, vertebrates associated with DWD (redback salamander, marten, red-backed vole) showed neutral or positive responses at one or more harvest intensities, whereas those associated with large trees and snags (brown creeper, flying squirrel) consistently exhibited substantial adverse impacts.     

Planning timber harvest of residual forest stands without compromising bird and small mammal communities in boreal landscapes

Numerous efforts have been invested in designing and configuring residual forest stands in Canadian boreal forest to preserve their overall biodiversity. Now that several landscapes have been partially logged, the next issue in forest management involves the planning of residual forest stand harvesting without compromising wildlife populations. Residual stands can be cut when adjacent regeneration reaches 3 m in height according to current regulations in several Canadian provinces (e.g., Québec, Ontario, Alberta, and British-Columbia). However, little is known on whether such regenerating habitat (RE-3m) can maintain wildlife communities similar to those found in unharvested mature forest (CO). We estimated the relative abundance of small mammals and forest birds in RE-3m and CO habitats and characterized landscape and stand structures. These variables were then compared between the two contrasting successional stages and were used to build habitat use models (HUMs) for 21 species. CO and RE-3m differed with regard to several landscape characteristics and stand structure variables as a result of logging. Snowshoe Hare, Northern Flicker, Alder Flycatcher, Ruby-crowned Kinglet, White-throated Sparrow and Magnolia Warbler were more abundant in RE-3m than CO, while Red-backed Vole, Brown Creeper and Golden-crowned Kinglet exhibited lower abundances in RE-3m. No significant differences in abundance were observed for the 12 other species. Species HUMs were highly significant and explained between 64.3 and 99.1% of the total variability in abundance. Following variance partitioning, stand structure variables accounted for most of the explained variability (54.2%) while landscape characteristics accounted for only 28.7%. No difference in species richness was observed but community evenness was greater in CO than RE-3m. Our results suggest that current regulations may threaten the maintenance of 3 out of 21 censused species for which abundances were significantly lower in regenerating 3 m tall stands. As stand structure explained a large amount of variability in abundance, it should be considered during timber harvest planning in both mature and regenerating stands. Until we know more on whether the current regulations are suitable for maintaining overall biodiversity, our results suggest that some mature forest stands should be maintained within managed landscapes for a complete logging rotation period.     

The effects of herbaceous and woody competition on planted white pine in a clearcut site

We investigated the effects of herbaceous and woody vegetation control on the survival and growth of planted eastern white pine (Pinus strobus L.) seedlings through six growing seasons. Herbaceous vegetation control involved the suppression of grasses, forbs, ferns, and low-shrubs, and was maintained for 0, 2, or 4 years after white pine seedlings were planted. Woody control involved the removal of all tall-shrub and deciduous trees, and was conducted at the time of planting, at the end of the second or fifth growing seasons, or not at all. Seedling height and basal diameter responded positively and proportionally to duration of herbaceous vegetation control. Gains associated with woody control were generally not significant unless some degree of herbaceous vegetation control was also conducted. Only herbaceous control increased pine crown closure and rate of crown closure. Herbaceous control and the presence of 5000–15,000 stems per ha of young overtopping aspen were associated with reduced weevil (Pissodes strobi Peck.) injury and increased pine height growth. The study suggests that white pine restoration strategies on clearcut sites should focus on the proactive, early management of understory vegetation and the gradual reduction of overtopping cover from woody vegetation to create a seedling light environment that supports acceptable growth with minimal weevil damage.     

Effects of overstory retention and site preparation on growth of planted white spruce seedlings in deciduous and coniferous dominated boreal plains mixedwoods

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.     

The natural regeneration pattern and process of Korean pine population under natural Poplar-birch forest in Xiaoxing’an Mountains

According to a great deal of field investigation and detailed indoor analysis, the natural regeneration pattern and process of Korean pine population under natural Poplar-birch forest has been uncovered. The results show that the regeneration quantity and quality of Korean pine population under mountainous Poplar-birch forest and mountainous white birch forest are better than those under valley moss-grass White Birch forest and virgin broad-leaved Korean pine forest. Korean pine population shows aggregated distribution, the mass-occurrence period of Korean pine population is behind the mass-occurrence period of Poplar-birch population. Various aged Korean pines growth is affected by different stand structure factors. Man-made lighting tending can accelerate the regeneration process and increase the regeneration quality of Korean pine population. It is feasible to set up regeneration recombination of upper layer White Birch and lower layer Korean pines.     

Spatial distribution,architecture, and development of the root system of Pinus banksiana Lamb. in natural and planted stands

In the province of Québec, Canada, the majority of planted jack pine (Pinus banksiana Lamb.) seedlings are produced in rigid wall containers. More than 95% of them exhibit deformations of the root system which may induce stem instability. Studies of the root architecture of planted jack pine have been limited to a 30 cm radius from the stem, as barely any studies have been devoted to naturally regenerated stands. Moreover, only a few researches have focused on temporal evolution of root systems. The aim of the present study was to characterize the architectural, spatial, and temporal development of jack pine roots in natural and planted stands. Study sites were located in the continuous boreal forest of Quebec. The plantation was done in 1987, so that the trees were 15 years old at the time of sampling. Trees from natural stand had regenerated after a fire in 1983 and were 13–16 years old. The root systems of 14 jack pine trees per site were manually excavated up to a <5 mm diameter, without regard to their distance from the stem. The number, length, diameter, and the spatial and temporal development of roots were analyzed according to three scales of root architecture: the root system, axes, and segments. Overall, the numbers and lengths of roots were higher with planted pines. However, naturally regenerated trees displayed a better distribution of their roots around the stem and at depth, combined with more rapid length growth during the first years. In natural stands, all the trees had a taproot and 30% of the main roots originated at a depth of more than 20 cm, and they are regularly distributed around the stems. Planted trees did not present a taproot and 97% of the main roots originated in the first 20 cm beneath the soil surface. Moreover, 50% of root length was located in one-third of the area surrounding the stems, an area that corresponded to the furrow. Finally, the annual development of lateral roots in planted stand displayed a 5-year delay when compared with natural stand, which also affected maximum growth length and development of the branching pattern. Root distribution and temporal development are known to play a major role in the stability of aerial parts. Seedling production methods, container type, site preparation and planting techniques need to be examined in greater detail in order to assess their effect throughout the development of the root system. It is necessary to compare different sylvicultural practices and with natural/planted stands to gain a clearer understanding of this problem.     

Influence of woody and herbaceous competition on microclimate and growth of eastern white pine (Pinus strobus L.) seedlings planted in a central Ontario clearcut

The influence of woody and herbaceous plant competition, either alone or in combination, on microclimate and growth of planted eastern white pine (Pinus strobus L.) seedlings was examined over four consecutive growing seasons in a central Ontario clearcut. Treatments that manipulated the comparative abundance of these two plant functional groups significantly affected light availability, soil moisture, and air and soil temperature regimes. These microclimate alterations, coupled with the relative competitiveness of herbaceous and woody vegetation, corresponded to temporal changes in vegetation cover and dominance. The more rapid colonization and growth of the herbaceous plant community, dominated by bracken fern (Pteridium aquilinum) and ericaceous shrubs (Kalmia sp., Vaccinium sp.), resulted in this form of vegetation being a comparatively important early competitor for soil moisture. As the woody plant community, dominated by naturally regenerated trembling aspen (Populus tremuloides Michx.), grew in height and leaf area, it became a comparatively strong competitor for both light and soil moisture. For all vegetation treatments combined, white pine seedling growth responses were strongly correlated with total cover of competing vegetation and its relative influence on above- and belowground microclimatic variables. Higher total cover of competing vegetation was generally associated with lower light and soil moisture availability and cooler soil temperatures. Multiple regression analyses indicated that pine seedling relative height growth increased with soil moisture content and growing season soil heat sum, while seedling relative diameter and relative volume growth increased with light availability.     

Comparison of potential non-timber forest products in intensively managed young stands and mature/old-growth forests in south-central British Columbia

Development of understory vegetation has been influenced by the many densely stocked second-growth forest stands in North America, which have an extended stem exclusion successional stage. Understory composition and structure is important for ecosystem functioning, while also having social and economic value through the harvest of certain herb and shrub species. The potential for co-management of young and mature, managed and unmanaged stands for timber and non-timber forest products (NTFPs) was assessed in two separate replicated experiments. Experiment A examined pole-sized lodgepole pine (Pinus contorta) stands that had been pre-commercially thinned (PCT) to target densities of 250, 500, 1000, and 2000 stems/ha. Half of each of these four thinning units was repeatedly fertilized, resulting in eight experimental units. Experiment B examined six different stand types: young plantations, pole-sized lodgepole pine stands either PCT, PCT plus repeated fertilization, or unthinned, mature, and old growth. Fifty-four herb and shrub species were identified as potential NTFPs, with the responses of individual species, as well as mean total herb, shrub, berry-producing and overall total NTFPs being assessed. In Experiment A, mean total abundance (crown volume index) of NTFPs, as well as mean total herb NTFPs were significantly greater in fertilized than in unfertilized stands. Thinning treatments did not significantly affect NTFP volume, however, fertilization treatments produced five significant responses by individual species (Achillea millefolium, Epilobium angustifolium, Taraxacum officinale, Arctostaphylos uva-ursi, Rubus idaeus). In Experiment B, four of the six species responses that were significant had greater abundance in young, managed stands (young plantation, thinned, or thinned-fertilized) than in the unmanaged stands. Mean total NTFP volume and mean total herb NTFP volume also followed this pattern. A. uva-ursi, E. angustifolium, Lonicera involucrata, Sorbus sitchensis and Thalictrum occidentale all had significantly higher abundance in young, managed stands than in all other treatments. Results suggest that co-management for timber and NTFPs is possible in this ecosystem, with further research needed to evaluate livelihood values of these crops.     

Establishment and growth of white spruce on a boreal forest floodplain: Interactions between microclimate and mammalian herbivory

White spruce (Picea glauca (Moench) Voss) is a dominant species in late-successional ecosystems along the Tanana River, interior Alaska, and the most important commercial timber species in these boreal floodplain forests. Whereas white spruce commonly seed in on young terraces in early primary succession, the species does not become a conspicuous component of the vegetation until after 60–80 years. To address what abiotic and/or biotic factors may explain the paucity of spruce in earlier stages of succession, we examined germination and growth of planted white spruce seedlings across an environmental gradient that included variation in soil physico-chemical properties in the presence and absence of mammal browsing. The effect of browsing pressure over the first four years after planting was most noticeable on the older terraces. Likewise, direct effects of hare browsing on spruce seedling mortality were only manifested at the oldest sites. Spruce germination and survival was inversely proportional to soil cation concentrations, which was largely controlled by temperature-driven evapotranspiration. High light intensities and high air temperatures significantly reduced seedling growth, whereas variation in soil moisture only explained a significant amount of variation in seedling survival. Temperatures within the needle clusters on terminal shoots reached values that adversely affect photosynthesis (>32 °C) on multiple occasions over the growing season. We conclude that the direct (temperature) and indirect (soil chemistry) effects of high insolation are major factors constraining spruce performance on early successional terraces, and that these effects can be significantly exacerbated by mammal browsing on associated deciduous vegetation.     

Snag degradation pathways of four North American boreal tree species

Many studies have highlighted the importance of deadwood, whether standing (snags) or fallen, in boreal ecosystems dynamics. However, a dearth of literature exists regarding the persistence and degradation pathways of these structures in northeastern American boreal species.