Availability of standing trees for large cavity-nesting birds in the eastern boreal forest of Québec,Canada

Large cavity-nesting birds depend on large-diameter trees for suitable nest sites. The increased spatial extent of commercial timber harvesting is modifying forest structure across the land base and may thus compromise the availability of large trees at the landscape scale. In this study, our objectives were to (1) characterize the availability of large living and dead trees in old-growth stands dominated by different tree species and surficial deposits that encompass the range of natural cover types of eastern Québec's boreal forest; (2) analyze the distribution of trees among decay-classes; and (3) compare the availability of large trees in unharvested, remnant, and harvested stands for the entire range of decay-classes. A total of 116 line transects were distributed across unharvested forests, remnant linear forests, and cutblocks in cutover areas. Unharvested forest stands (black spruce [Picea mariana], balsam fir [Abies balsamea]–black spruce, balsam fir–white spruce [Picea glauca] and balsam fir) reflected a gradient of balsam fir dominance. The remnant forests selected were isolated for 5–15 years. Analyses were performed at two diameter cut-off values. Trees with DBH ≥20 cm were considered for availability of total trees whereas trees with DBH ≥30 cm were considered for availability of large trees. Forest stands comprised high proportions of standing dead trees (33% of all stems, 8% were large dead stems). Availability of total and large standing trees increased with the dominance of balsam fir in stands. Forest stands located on thick surficial deposits showed higher densities of large dead trees for every stand type suggesting a higher productivity on those sites. Availability of stems according to decay-classes showed a dome-shaped distribution with higher densities of snags in intermediate decay stages. However, for large stems, black spruce stands showed a significantly lower availability that was consistent across all decay-classes. In linear remnant forests, pure balsam fir stands were absent. Remnant stands thus showed a much lower availability in large trees when compared with unharvested balsam fir stands. Clearcuts had the lowest densities of dead trees across sampled stands. Current even-aged management practices clearly affect availability and recruitment of large trees, therefore forest-dwelling wildlife relying on these structures for breeding is likely to be affected by large-scale harvesting in coniferous boreal forests.     

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.     

White-tailed deer activity reconstructed from tree-rings in eastern boreal Canada

We evaluated the potential of tree-ring techniques for the reconstruction of recent and past seasonal activity of introduced white-tailed deer in a boreal environment of eastern Canada. Hoof scrape scars on balsam fir stems and trampling scars on roots were used to reconstruct deer activity during the winter and snow-free seasons, respectively. Tree damage showed that there was continuous deer activity in the north-central part of Anticosti Island since the mid-1960s. High scrape scars along tree stems (3–3.5 m from the ground) indicate that 1975, 1976, 1981, 1983 and 1985 were years of intensive food search by deer on high balsam fir foliage. The annual number of hoof scrape scars was low between 1982 and 1985, when severe defoliation by the spruce budworm, combined with deer browsing, led to high fir sapling mortality, food depletion, degradation of the winter shelter forests and a decrease in deer activity. The lowest scrape scars 50 cm above ground correspond to the mean height of the residual snowpack in the shelter forest at springtime, when deer start searching for food in nearby open sites and use logging roads, where dead and bonsai-like fir predominate due to overbrowsing. The trampling scar age frequency distribution from two sites indicated that deer activity during the snow-free season started synchronously in the late 1960s. In response to degradation of winter shelter forests, deer may have moved from the southern part to the north-central part of the island and other sectors to survive. Deer-induced tree damage and tree-ring techniques can thus be used to reconstruct past seasonal activity of white-tailed deer.     

Soil solution,foliar concentrations and tree growth response to 3-year of ammonium-nitrate addition in two boreal forests of Québec,Canada

Ammonium nitrate (NH₄NO₃) was applied monthly (from June to October) for 3 years in a balsam fir (Abies balsamea (Linné) Miller) and a black spruce (Picea mariana (Mill.) BSP) boreal forest in Québec (Canada). The design was composed of nine experimental units of 10 m × 10 m for each site. Application rates were 3 and 10 times the atmospheric N deposition measured at each site which was 6 and 3 kg ha⁻¹ year⁻¹ for the fir and the spruce sites, respectively. Soil solution composition (30 and 60 cm), tree growth, and foliar concentrations were analysed. The inorganic N in the soil solution of the control plots of both sites was low, particularly at the spruce site indicating that these forests are actively accumulating the atmospheric deposited N. Nitrogen additions regularly caused sudden and large inorganic N increases in the soil solution at both sites, both treatments and both sampling depths. However, these increases were transitory in nature and no persistent changes in inorganic N were observed. It was estimated that more than 95% of the added N was retained above the rooting zone at both sites. Nitrogen addition increased N, Ca, Mg and Mn foliar concentrations at the black spruce site but had no effects at the balsam fir site. After 3 years of N application, tree growth was similar in the control and the treated plots at both sites. Our results show that slow growing black spruce boreal forests with low ambient N deposition are responsive (in term of foliar N, Ca, Mg and Mn concentrations) to even small increases in N inputs, compared to higher growth balsam fir boreal forests with higher N deposition.     

Study of landscape change under forest harvesting and climate warming-induced fire disturbance

We examined tree species responses under forest harvesting and an increased fire disturbance scenario due to climate warming in northern Wisconsin where northern hardwood and boreal forests are currently predominant. Individual species response at the ecosystem scale was simulated with a gap model, which integrates soil, climate and species data, stratified by ecoregions. Such responses were quantified as species establishment coefficients. These coefficients were used to parameterize a spatially explicit landscape model, LANDIS. Species response to climate warming at the landscape scale was simulated with LANDIS, which integrates ecosystem dynamics with spatial processes including seed dispersal, fire disturbance, and forest harvesting. Under a 5 °C annual temperature increase predicted by global climate models (GCM), our simulation results suggest that significant change in species composition and abundance could occur in the two ecoregions in the study area. In the glacial lake plain (lakeshore) ecoregion under warming conditions, boreal and northern hardwood species such as red oak, sugar maple, white pine, balsam fir, paper birch, yellow birch, and aspen decline gradually during and after climate warming. Southern species such as white ash, hickory, bur oak, black oak, and white oak, which are present in minor amounts before the warming, increase in abundance on the landscape. The transition of the northern hardwood and boreal forest to one dominated by southern species occurs around year 200. In the sand barrens ecoregion under warming conditions, red pine initially benefits from the decline of other northern hardwood species, and its abundance quickly increases. However, red pine and jack pine as well as new southern species are unable to reproduce, and the ecoregion could transform into a region with only grass and shrub species around 250 years under warming climate. Increased fire frequency can accelerate the decline of shade-tolerant species such as balsam fir and sugar maple and accelerate the northward migration of southern species. Forest harvesting accelerated the decline of northern hardwood and boreal tree species. This is especially obvious on the barrens ecoregion, where the intensive cutting regime contributed to the decline of red pine and jack pine already under stressed environments. Forest managers may instead consider a conservative cutting plan or protective management scenarios with limited forest harvesting. This could prolong the transformation of the barrens into prairie from one-half to one tree life cycle.     

Effects of management, environment and landscape conditions on establishment of hardwood seedlings and saplings in central Japanese coniferous plantations

There is an increasing need to restore natural hardwood forests in landscapes dominated by monocultural conifer plantations. A convenient restoration approach is to exploit natural regeneration processes. Natural regeneration, however, is affected by diverse interacting factors, for which better understanding is required, in order to optimize restoration programs. To identify optimal management practices for improving natural regeneration of hardwood trees in coniferous plantations, we examined the effects of multiple factors on the abundance of seedlings, small saplings and large saplings (height <0.3, 0.3-1.3 and ?1.3 m, respectively) of hardwood tree and shrub species in both line thinned (LT) and unthinned (UT) plantations of sugi (Cryptomeria japonica) and hardwood forests (HF) in central Japan. The effects of management practices (number of the times of weeding and cleaning, thinning method, years after thinning and forest age), environment (slope position, slope angle and canopy openness), and landscape conditions (distance from nearest hardwood forest, altitude and landuse before planting) on the number of hardwood individuals were examined by using the data obtained from the LT plantations. We also compared hardwood density between LT and UT plantations to examine the effect of line thinning. Finally, we examined species composition of LT plantations and HF to identify hardwood forest components in the thinned plantations. The effects on hardwood regeneration of environmental conditions, landscape factors and management practices applied in the plantations varied, depending on the size class and life form of the regenerating species. The abundance of large saplings of tall tree species was affected by several management factors, especially number of the times of weeding. Landscape conditions (distance from the nearest hardwood forest and altitude) affected the abundance of small saplings and seedlings of tall tree species, but not the other classes. Seedlings and small saplings of many tall tree species that contribute to hardwood forest canopies were less abundant in the LT plantations. The results show that numerous factors affect the establishment and abundance of naturally regenerating hardwood tree species, and suggest that successful establishment during early plantation stages can have long-lasting effects on natural regeneration of tall tree species.     

Distribution of carabid beetles among 40-year-old regenerating plantations and 100-year-old naturally regenerated forests in Southwestern China

Effects of reforestation by native tree species on species assemblages of carabid beetles were studied between 40-year-old regenerating plantations and 100-year naturally regenerated forests in Southwestern China. Two old naturally regenerated forest types (ca.100 years old) were chosen: hemlock-spruce forests (Tsuga chinensis and Picea brachytyla) and birch forests (Betula albo-sinensis). Three young regenerating forest types (ca. 40 years old), including spruce plantations (P. brachytyla), larch plantations (Larix kaempferi and Larix mastersian), and natural broad-leaved forests, were established after the logging of the old naturally regenerated forests. Using pitfall traps, we compared the distribution of carabid beetles in the five forest types. Three replicated plots for each forest type were chosen, and each plot was investigated with four trap sites twice each month during the growing season (May to October) in 2004. Our results showed that species richness and abundance were significantly higher in the young regenerating forests than in the old naturally regenerated forests. Analysis of complementarity in carabid species lists across the forest ages and types showed that the old naturally regenerated birch forests had the lowest similarity with the young regenerating larch plantations, and the highest similarity was shown between the two young regenerating plantations. Although PCoA ordination grouped the carabid assemblages according to forest type and forest age, the overall similarity among all forest types was high. Moreover, quantitative character species analysis did not detect significant species associated with forest types and ages. Based on the specificity and fidelity, most carabid species were abundant in all habitats, and only a few species were restricted in one or two forest types. Multiple linear regression between the species richness, abundance and Shannon diversity of carabids and of five environmental variables showed that the cover of canopy and herbaceous layer, and the depth of leaf litter had significant effects in determining richness, abundance and diversity of carabid beetles. Thus, the young regenerating forests at the mature stage could provide an appropriate habitat for most forest species of carabids survived in adjacent old naturally regenerated forests and might replace the role in part of the old-growth forests in sustaining the diversity of carabid assemblages. But some species are still restricted in old naturally regenerated forests, so in order to protect the diversity of carabid assemblages, it is necessary to sustain the intact old naturally regenerated forests when reforesting with some native tree species following natural succession.     

Are endoparasites of common shrews (<Emphasis Type="Italic">Sorex araneus</Emphasis>) sensitive to tree species conversion in sub-Arctic birch forests?

Shrews (Soricomorpha) are among the most numerous small forest dwelling mammals in boreal forests ecosystems. In Norway large areas of sub-Arctic birch (Betula pubescens) forests have gradually been replaced by non-native spruce (Picea abies) plantations during the last century. This conversion has led to changes in forest floor vegetation and soil conditions which negatively influence invertebrates serving as prey for shrews and intermediate hosts for shrew endoparasites (helminths). In this trapping study we assessed if abundance and individual condition of common shrews (Sorex araneus) and prevalence and species richness of associated helminths, responded to spruce plantations in a manner that could indicate community level changes. Shrews colonized plantations in autumn, but never attained abundances comparable to the birch forest types. Shrews in plantations had lower body mass compared to those trapped in the birch forests. We identified 15 helminth species, and detected large differences in prevalence. Only one common helminth had significantly higher prevalence in the birch forest. By analysing prevalence of all species jointly, the highest prevalence was in moist birch forests and lowest in spruce plantations. Species richness estimates were lower in plantations, however not statistically significant. Although prevalence and species richness of helminths in common shrews were affected by tree species conversion, we judge the responses to be too weak and uncertain and the sampling and analysis too laborious to make shrew endoparasites suitable for monitoring purposes. However, monitoring abundance of common shrews is likely an efficient way of detecting changes in the forest floor fauna resulting from modern forestry practices.     

Evaluation of mature conifer plantations as secondary habitat for epigeic forest arthropods (Coleoptera: Carabidae; Araneae)

Spiders (Araneae) and ground beetles (Coleoptera, Carabidae) were studied in a woodland of the Northwest German lowland. An ancient oak–beech stand (170 years old) growing on mineral soil as well as a 110-year-old Scots pine (Pinus sylvestris) and a 55-year-old spruce (Picea spp.) forest growing on peat were investigated by pitfall trapping. A total of 155 species (39 carabids, 116 spiders) and 16,887 individuals (5269 carabids, 11,618 spiders) was recorded. Beetle diversity was high in the oak–beech stand and the spruce forest, but significantly lower in the pine forest. In both conifer plantations the activity density of carabids was considerably lower. Spider diversity was significantly higher in the spruce forest when compared to the beech and pine stand, respectively. Analyses of assemblage similarity distinguished clearly the fauna of all three stands. For each forest type, indicator species were detected. Although both conifer plantations were planted on former bogs, spider species typical of bogs were present only in the pine stand, not in the spruce stand. In both animal taxa, species typical of deciduous forests were more numerous and abundant in the oak–beech stand when compared to the conifer plantations. Although they were in direct contact, the conifer stands on peat only to a very low extent serve as secondary habitats for the epigeic fauna of the autochthonous deciduous woodland. During the 1990s, various agricultural programmes in Central Europe promoted such conifer plantations – in contrast, such afforestation measures on extensively used or fallow land of former bogs are not supported by the results of this study.     

Partial cutting in mixedwood stands: Effects of treatment configuration and intensity on stand structure,regeneration, and tree mortality

In temperate and boreal mixedwood forests of eastern North America, partial disturbances such as insect outbreaks and gap dynamics result in the development of irregular forest structures. From a forest ecosystem management perspective, management of these forests should therefore include silvicultural regimes that incorporate medium- to high-retention harvesting. We present 12-year results of a field experiment undertaken to evaluate the effects of variable retention harvesting on stand structure, recruitment, and mortality. Treatments were gap harvesting (GAP), diameter-limit harvesting (DL), careful logging (CL), and careful logging followed by scarification (CL + SCAR), and an unharvested control. Although post-harvest basal area in the GAP treatment was significantly lower than that of controls, it maintained a diameter distribution profile and densities of balsam fir regeneration similar to those of pre-harvest conditions. Lower retention treatments (DL, CL, and CL + SCAR) tended to favor regeneration of pioneer, shade-intolerant species. Except for black spruce (for which mortality was highest in DL), stem mortality was similar among harvesting treatments. From an ecosystem management perspective, this study suggests that gap harvesting can maintain, in the short term, forest stand composition and structure similar to unharvested forests, and could be used where management objectives include the maintenance of late successional forest conditions.     

Regeneration of Populus nine years after variable retention harvest in boreal mixedwood forests

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 volume ha⁻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 volume ha⁻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.     

Broadleaf competition interferes with balsam fir regeneration following experimental removal of moose

Changes to ecosystems caused by introduced herbivores can be predictable, stepwise transitions or unpredictable and even irreversible state changes. This study's objectives were to explore effects on forest succession and soil development 5 years after moose (Alces alces L.) were fenced out of areas within and adjacent to a national park in Newfoundland, Canada. Study plots spanned a range of understorey broadleaf plant associations with regenerating balsam fir (Abies balsamea (L.) Mill.), an important winter forage plant for moose and a dominant canopy tree throughout Newfoundland. After 5 years, height–diameter ratios were significantly larger for larger basal diameters of understorey balsam fir in unfenced, but not in fenced subplots, suggesting that growth of the conifer is compromised within the exclosure. In contrast, for most broadleaf trees and shrubs, moose removal by fencing results in greater heights and basal diameters than in control subplots. The competitive advantage of broadleaf trees and shrubs over balsam fir in the short-term may be a result of past sustained heavy moose browsing benefiting plants that are better at investing resources into below-ground growth or benefiting plants that have broader leaf canopies. It is not clear how long the broadleaf transition state we document will continue. Restorative actions intended to mimic usual patterns of forest regeneration in this region of Newfoundland might best consider moose removal with site preparation and/or planting to historic densities.     

Variation in post-wildfire regeneration of boreal mixedwood forests: underlying factors and implications for natural disturbance-based management

To test the direct regeneration hypothesis and support natural disturbance-based forest management we characterized the structure and composition of boreal mixedwood forests regenerating after large wildfires and examined the influence of pre-fire stand composition and post-fire competing vegetation. In stands which had been deciduous (Populus sp.)-dominated, conifer (white spruce)-dominated, or mixed pre-fire we measured regeneration stocking (presence in 10 m² plots), density and height 10–20 years post-burn in five wildfires in Alberta, Canada. Most plots regenerated to the deciduous or mixed stocking types; plots in the older fire and in stands that were pure conifer pre-fire had higher amounts of conifer regeneration. Surprisingly, regeneration in pre-fire ‘pure’ white spruce stands was most often to pine, although these had not been recorded in the pre-fire inventory. Pre-fire deciduous stands were the most resilient in that poplar species dominated their post-fire regeneration in terms of stocking, density and height. These stands also had the highest diversity of regenerating tree species and the most unstocked plots. High grass cover negatively affected regeneration density of both deciduous and conifer trees. Our results demonstrate the natural occurrence of regeneration gaps, pre- to post-fire changes in forest composition, and high variation in post-fire regeneration composition. These should be taken into consideration when developing goals for post-harvest regeneration mimicking natural disturbance.     

Snag dynamics in post-harvest landscapes of western Newfoundland balsam fir-dominated boreal forests

We examined changes in standing dead tree (snag) density and biomass with time following harvest across a chronosequence of balsam fir (Abies balsamea) dominated boreal forests in western Newfoundland, Canada. Current snag management practices in Newfoundland recommend a minimum of 10 snags/ha on the post-harvest landscape. Snags declined significantly in the first two decades of the chronosequence. The rapid rate of decline in snag density which occurred immediately post harvest was likely attributable to windfall and domestic harvest for firewood. A second rapid rate of snag density decline occurred 10–15 years post harvest which potentially reflected the average lifespan of snags in western Newfoundland. Average snag densities approximated the minimum management goal during the period from 15 to 60 years since harvest (YSH). However, 53–60% of sites sampled in the 15–60 YSH period contained <10 snags/ha. Snag densities then increased with forest age, again reaching high levels 81–100 YSH which were comparable to the density at the beginning of the chronosequence. Achieving the goal of 10 snags/ha on all post-harvest sites in western Newfoundland, especially between 15 and 60 YSH, will require changes to current forest management practices.     

Ecophysiology and growth of advance red spruce and balsam fir regeneration after partial cutting in yellow birch-conifer stands

We investigated ecophysiological and growth responses of short (0.4 to 1.3 m in height) advance regeneration of red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea L.) six years after removal of 0, 40, 50, 60 and 100% of the overstory basal area (BA) in two yellow birch-conifer stands. Partial cuts significantly increased stomatal conductance of red spruce only. Light-saturated photosynthesis (leaf-area basis) of both species increased with BA removal, but unlike red spruce, specific leaf area (SLA) of balsam fir decreased with increased cutting intensity. Partial cuts appreciably increased the concentration of N and Ca in red spruce and balsam fir foliage, respectively, and resulted in decreased foliar concentrations of K in red spruce and Mg in balsam fir. The height and lateral growth of both species increased with BA removal, although partial cuts were more beneficial to balsam fir. The data suggest that short advance regeneration of red spruce and balsam fir can coexist under partial overstory conditions, but balsam fir has physiological characteristics and a capacity for morphological adjustment (SLA) that places it at an advantage when in competition with red spruce.     

Species differences in total and vertical distribution of branch- and tree-level leaf area for the five primary conifer species in Maine, USA

Vertical distribution of leaf area largely governs both tree structure and function. Models of this important tree attribute have been constructed for several commercially important conifers. However, a limited number of studies have compared alternative modeling techniques and inherent species differences. This study used several existing datasets for the five primary conifer species in Maine, namely balsam fir [Abies balsamea (L.) Mill.], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)] to examine species variation in total and vertical distribution of projected leaf area at the individual branch- and tree-levels. In addition, multiple methods for modeling the vertical distribution of leaf area were examined across the species. For a given branch diameter and location within the crown, eastern hemlock branches held the greatest amount of leaf area, followed by balsam fir, northern white-cedar, white pine, and red spruce. At the tree-level, eastern white pine held the greatest amount of leaf area followed by eastern hemlock, balsam fir, red spruce, and northern white-cedar for a given tree size. Across species, the two-parameter, right-truncated Weibull distribution performed the best for predicting vertical distribution of leaf area when compared to the four-parameter beta and Johnson's S_B distributions (reduction of root mean square error of 1.7–21.1%). Northern white-cedar had a relative distribution of leaf area distinctly different than other species in this study with a mode shifted towards the upper crown. In contrast to red spruce and white pine, the mode of the relative distribution of leaf area for balsam fir and eastern hemlock occurred lower in the crown. Results of this study suggest that differences in total and vertical distribution of leaf area exist between species, but significant amounts of their variation are largely accounted for by bole and crown size.     

Habitat selection by forest-dwelling caribou in managed boreal forest of eastern Canada: Evidence of a landscape configuration effect

Habitat alteration caused by forest harvesting seems to contribute to the decline of forest-dwelling caribou, an ecotype of woodland caribou (Rangifer tarandus caribou) inhabiting the boreal ecosystem. To serve as basework to the establishment of conservation measures for the species, we have studied the hierarchical habitat selection of forest-dwelling caribou in a boreal landscape of Québec strongly impacted by logging. Fifteen females were surveyed by GPS telemetry between April 2004 and March 2006. Home ranges showed a high proportion of 90–120 year-old forests, a low proportion of regenerating forests (20–40 years old) and a tendency to include a greater proportion of 6–20 year-old clearcuts in relation to their availability in the study area. At the home range scale, selection patterns differed between periods, possibly reflecting specific requirements linked to caribou life cycle. Caribou selected open lichen woodlands throughout the year while mature closed forests (≥50 years) were selected uniquely during summer. The 6–20 year-old clearcuts were avoided during calving, in summer and during the rutting period but were selected during spring. Our results indicate that mature forest and open lichen woodlands are highly selected forest cover types by caribou at both spatial scales. Although clearcuts were generally avoided at the home range scale, such avoidance was not observed at the larger scale, the search for 90–120 year-old forests being hampered by a uniform distribution of clearcuts. An a posteriori landscape analysis highlighted the spatial association between 6–20 year-old clearcuts and 90–120 year-old forests, an association that can be explained by the current regulations used in Québec. Our results underline the importance of pursuing research concerning the impact of such an exploitation regime on the long-term maintenance of the forest caribou in the boreal landscape.     

Impacts of hemlock looper defoliation on growth and survival of balsam fir, black spruce and white birch in Newfoundland, Canada

Hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir (Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce (Picea mariana (Mill.) B.S.P.) and white birch (Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71-100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70-80% for black spruce and white birch. Lower defoliation severity (1-2 years of moderate (31-70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10-15% with 1 year of moderate-severe defoliation, 35-40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years.     

Synergistic effects of past historical logging and drought on the decline of Pyrenean silver fir forests

The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir (Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km². We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.     

UK conifer forests may be growing faster in response to increased N deposition, atmospheric CO2 and temperature

Site studies have shown that conifer plantations in northernBritain have increased in General Yield Class (GYC) by 1 m³ha^–1 a^–1 per decade or more (20–40 per cent)since the 1930s. Large increases in forest productivity havealso occurred in many other regions of Europe. Are these increasesdue to improved silvicultural practices or to increases in Ndeposition, CO₂ and temperature? Two process-based mathematicalmodels of forest growth were used to simulate the responsesof conifer forests growing in the Scottish southern uplandsto increases in atmospheric N deposition, CO₂ concentrationand temperature, during this century and next century. The modelsdiffered substantially in the ways in which underlying processeswere represented: one simulated a managed plantation, the othera natural forest. Nevertheless, both showed that: (1) increasesin N deposition, CO₂ and temperature together might accountfor up to half of the observed increase in GYC this century;(2) increased N deposition and CO₂, considered separately, probablyincreased forest productivity by a modest amount (7–14per cent), but their combined effect has been approximatelyadditive; (3) increased temperature, even when combined withincreasing CO₂ concentrations, promoted growth less than expectedfrom site studies relating GYC to temperature; and (4) substantialfurther increases in productivity, GYC, leaf area index andstanding biomass are forecast during the next century as a resultof increasing CO₂ concentrations and continued N deposition,with or without climatic warming. The predicted increases inGYC could be large enough to have profound effects on the forestindustry.