Balsam Fir Stands Research Articles

The Origin and Dynamics of Subalpine White Spruce and Balsam Fir Stands in Boreal Eastern North America

Associations among the few tree species in the North American boreal landscape are the result of complex interactions between climate, biota, and historical disturbances during the Holocene. The closed-crown boreal forest of eastern North America is subdivided into two ecological regions having distinct tree species associations; the balsam fir zone and the black spruce zone, south and north of 49°N, respectively. Subalpine old-growth stands dominated by trees species typical of the balsam fir forest flora (either balsam fir or white spruce) are found on high plateaus, some of which are isolated within the black spruce zone. Here we identified the ecological processes responsible for the distinct forest associations in the subalpine belt across the eastern boreal landscape. Extensive radiocarbon dating, species composition, and size structure analyses indicated contrasted origin and dynamics of the subalpine forests between the two ecological regions. In the black spruce zone, the subalpine belt is a mosaic of post-fire white spruce or balsam fir stands coexisting at similar elevation on the high plateaus. With increasing time without wildfire, the subalpine forests become structurally similar to the balsam fir forest of the fir zone. These results concur with the hypothesis that the subalpine forests of this area are protected remnants of an historical northern expansion of the fir zone. Its replacement by the fire-prone black spruce forest flora was caused by recurrent fires. In the subalpine belt of the fir zone, no fire was recorded for several millennia. Harsh climate at high altitude is the primary factor explaining white spruce dominance over balsam fir forming a distinct subalpine white spruce belt above the balsam fir dominated forest.

Short term effects of alternative silvicultural treatments on stand attributes in irregular balsam fir-black spruce stands

The eastern Canadian boreal forest exhibits a specific disturbance regime where forest fires are less frequent than in the western part. This particularity may explain the abundance of irregular stands with distinct ecological features. To ensure sustainable forest management, these characteristics require the implementation of an adapted silviculture regime. In this context, two selection cutting methods were developed and compared with more conventional techniques, initially designed for cutting more regular stands of the boreal forest (cutting leaving small merchantable stems, careful logging preserving advance regeneration). The comparison focused on the capacity of treatments to maintain the primary attributes of irregular boreal forests, including complex vertical structure, abundant tree cover, species composition, and an abundance of dead wood. Mortality and regeneration processes were also compared. The experiment includes three sectors dominated by irregular black spruce ( Picea mariana)-balsam fir ( Abies balsamea) stands. Treatments were replicated in each sector in 0.25 ha plots. Stand characteristics were sampled pre-harvest and monitored for 3 years after cutting. Initial results indicate an important treatment effect on residual structure. Selection cutting maintains an inverse (irregular) J-shaped structure, typical of natural stands. Also, selection cutting does not seem to produce a significant effect on tree species composition (no undesired balsam fir enrichment) and does not modify the abundance of coarse woody debris. From a sustainable forest management perspective, the selection methods tested appear efficient in maintaining the main attributes and processes of the boreal irregular stands over the short term.

Patterns of leaf area index during stand development in even-aged balsam fir – red spruce stands

Leaf area index (LAI) strongly controls forest stand production. Silviculturists can easily manage this biologically important variable by quantifying its relationship to more directly manageable stand elements, such as density. Hypothesized patterns of LAI development over relative stand density (RD) in even-aged stands of balsam fir ( Abies balsamea (L.) Mill.) and red spruce ( Picea rubens Sarg.) were examined using 78 plots from the Cooperative Forestry Research Unit’s Commercial Thinning Research Network located in the Acadian forest zone in Maine. Nonlinear regression indicated that LAI was significantly related to RD, site quality, and stand top height. LAI increased nonlinearly with increasing RD holding stand top height constant. At a given RD, LAI peaked at approximately 13 m in stand top height. Site quality positively and linearly influenced LAI, but this was only apparent after crown closure, which in turn was influenced by initial stand density. Five-year trajectories of LAI–RD remeasurement data showed an increase in LAI and RD for all stands that varied by stand top height and site quality. Taken together, RD, stand top height, and site quality are strong predictors of LAI and can be used by silviculturists to manage for LAI.

Wood losses and economical threshold of Btk aerial spray operation against spruce budworm

Spruce budworm, Choristoneura fumiferana (Clem.), causes cumulative defoliation and hence annual growth loss of the balsam fir, Abies balsamea (L.) Mill, host tree. Annual growth increments of mixed balsam fir stands were measured by stem analysis over a 9 year period (1994-2002), when Bacillus thuringiensis ssp. kurstaki (Btk) was applied to control spruce budworm defoliation. With this approach, it was possible to quantify the change in stand volume growth after aerial spray applications of Btk. Differences between the periodic volume increment of protected and unprotected plots were statistically significant, while differences between protected and budworm-free plots were not significant. After 9 years, the difference in periodic increment between protected and unprotected plots was 20 m(3) ha(-1), and the difference in periodic mortality was 20.5 m(3) ha(-1). An economic assessment of Btk treatments indicates that biopesticide aerial spraying operations are justified, as they prevented substantial balsam fir mortality and growth losses over the 9 year study.

Can the impact of deer browsing on tree regeneration be mitigated by shelterwood cutting and strip clearcutting?

Silvicultural treatments creating large canopy openings failed to restore regeneration of balsam fir ( Abies balsamea (L.) Mill.) due to browsing pressure from white-tailed deer ( Odocoileus virginianus Zimmermann). Consequently, we tested two alternative silvicultural treatments aimed at improving balsam fir establishment on Anticosti Island (Québec, Canada). In 1998 and 1999, we set up shelterwood seed cutting using three harvest intensities (0, 25 and 40% of basal area) and strip clearcutting with scarification using three different strip widths (15, 30 and 45 m), both with fenced and unfenced regeneration plots, in balsam fir stands. After 8 years, shelterwood seed cutting did not allow the establishment of new balsam fir seedlings, nor the development of unbrowsed balsam fir seedlings. In the strip clearcutting, deer browsing suppressed growth of palatable species in all strip widths. This favoured the development of unpalatable species, especially white spruce ( Picea glauca (Moench) Voss). Our study demonstrates that the use of silvicultural treatments alone is unlikely to restore balsam fir regeneration on Anticosti Island, as long as the deer population remains higher than 20 deer/km 2.

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.

Rapid expansion of lichen woodlands within the closed‐crown boreal forest zone over the last 50 years caused by stand disturbances in eastern Canada

AbstractAim Our two main goals are first to evaluate the resilience of the boreal forest according to latitude across the closed‐crown forest zone using the post‐disturbance distribution and cover of lichen woodlands and closed‐crown forests as a metric, and second to identify the disturbance factors responsible for the regeneration and degradation of the closed‐crown forest according to latitude since the 1950s.Location The study area extends between 70°00′ and 72°00′ W and throughout the closed‐crown forest zone, from its southern limit near 47°30′ N to its northern limit at the contact with the lichen woodland zone at around 52°40′ N.Methods Recent (1972–2002) and old (1954–1956) aerial photos were used to map the distribution of lichen woodlands across the closed‐crown forest zone. Forest disturbances such as fire, spruce budworm (Choristoneura fumiferana (Clemens)) outbreak, and logging were recorded on each set of aerial photos. Each lichen woodland and stand disturbance was validated by air‐borne surveys and digitized using GIS software.Results Over the last 50 years, the area occupied by lichen woodlands has increased according to latitude; that is, 9% of the area that was occupied by closed‐crown forests has shifted to lichen woodlands. Although logging activities have been concentrated in the same areas during the last 50 years, the area covered by logging has increased significantly. Outbreaks by the spruce budworm occurred predominantly in the southern (47°30′ N to 48°30′ N) and central (48°53′ N to 50°42′ N) parts of the study area, where balsam fir stands are extensive. In the northern part of the study area (51°–52°40′ N), extensive fires affected the distribution and cover of closed‐crown forests and lichen woodlands.Main conclusions Over the last 50 years, the area occupied by closed‐crown forests has decreased dramatically, and the ecological conditions that allow closed‐crown forests to establish and develop are currently less prevalent. Fire is by far the main disturbance, reducing the ability of natural closed‐crown forests to self‐regenerate whatever the latitude. Given the current biogeographical shift from dense to open forests, the northern part of the closed‐crown forest zone is in a process of dramatic change towards the dominance of northern woodlands.

The Effects of Decreasing Winter Diet Quality on Foraging Behavior and Life-History Traits of White-Tailed Deer Fawns

Many high-density populations of wild ungulates have exerted strong negative impacts on their habitat. A decrease in forage quantity and quality may affect individual growth, fecundity, and survival, especially under harsh winter conditions. On Anticosti Island, Québec, Canada, browsing by introduced white-tailed deer (Odocoileus virginianus) negatively affected boreal forest composition. Since the preferred contemporary winter forage of deer, balsam fir (Abies balsamea), has been almost completely extirpated from the island at browse height, deer are forced to increase the proportion of normally avoided forage, such as white spruce (Picea glauca), in their winter diet. We predicted that an increase in the proportion of white spruce in the diet would have detrimental effects on deer body condition and would affect their behavior and life history traits. We experimentally simulated a deterioration of winter forage quality in semi-natural enclosures by increasing the proportion of white spruce in the diet and examined the effects of winter diet quality on 1) forage intake, 2) body condition loss, 3) activity budget, and 4) survival of white-tailed deer fawns. Fawns fed the poor-quality diet maintained a higher forage intake rate throughout the winter than fawns fed the control diet, suggesting a compensatory response to the decrease of forage quality by consuming more forage during winter. Body mass decreased over the winter, but we did not observe any significant effects of diet quality on body mass loss. Diet quality did not influence the activity budget of fawns, but deer decreased activity in cold weather. The main determinant of overwinter survival was individual body mass in early winter. Our study suggests that deer have adapted to the extreme conditions encountered on Anticosti (i.e., harsh and long winters, low-quality browse, and a high-density population). Even though white spruce stands are gradually replacing balsam fir stands, our results suggest that deer on Anticosti could maintain a high-density population by increasing the amount of white spruce in their diet. However, future studies are necessary to address the long-term effects of a diet dominated by white spruce on deer body condition, survival, and reproduction under natural conditions.

Ecological factors explaining the location of the boundary between the mixedwood and coniferous bioclimatic zones in the boreal biome of eastern North America

ABSTRACTAim Climate is often regarded as the primary control determining the location of an ecotone between two vegetation zones. However, other ecological factors may also be important, especially when the northern limit of the dominant species of a vegetation zone extends further than the limit of the zone itself. This study aimed to identify the ecological variables explaining the transition between two zones within the boreal biome in Quebec (eastern Canada): the southern mixedwood forests dominated by balsam fir (Abies balsamea) and white birch (Betula papyrifera), and the northern coniferous forests dominated by black spruce (Picea mariana).Location Quebec (eastern Canada).Methods Data from 5023 sampling plots from the ecological inventory of the Québec Ministry of Natural Resources distributed throughout the two bioclimatic zones were used in logistic regressions to determine the relationships between the presence or absence of balsam fir stands and different abiotic and biotic variables, at both stand and landscape scales.Results The presence of balsam fir stands was negatively related to the thick organic horizons, coarse xeric deposits and low positions on the slope, whereas stands were favoured by high elevations, steep slopes and moderate drainage. These results defined the suitable conditions for the development of balsam fir stands. In the coniferous zone these suitable conditions were less abundant. Furthermore, the saturation level of suitable sites was lower, as well as the incidence of balsam fir stands in unsuitable sites (overflow). Balsam fir stands were mostly located near lakes and rivers. All significant variables at both the stand and landscape scales explained between 34 and 42% of the location of the potential northern distribution limit of the mixedwood zone.Main conclusions Our results suggest the important role of historical factors related to post‐glacial vegetation and past disturbances in determining the relative abundance of balsam fir in both zones of the boreal biome.

Harvesting Intensity at Clear‐Felling in the Boreal Forest

The amount of logging residues left on site after clear‐felling has been shown to influence the state of soil nutrient resources, but this effect may depend on soil conditions. In three regions of the boreal zone of Quebec, with contrasting soil characteristics, soil and foliar nutrient status of young (15–20 yr old) stands were compared among sites that were clear‐felled at two harvesting intensities, that is, stem‐only (SOH) and whole‐tree harvesting (WTH). Balsam fir (Abies balsamea) stands were studied in the Forêt Montmorency and Gaspésie regions, while black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) were studied in the Haute‐Mauricie region. Whole‐tree harvesting resulted in lower cation exchange capacity (CEC) compared with SOH, but this effect could be linked to decreased levels of organic C only in the Haute‐Mauricie region, where soils had intrinsically low organic matter content. Lower soil and foliar Ca concentrations after WTH were observed in all three regions. Foliar Ca status was most strongly affected by harvesting intensity in Gaspésie, where soils exhibited the lowest concentration of total Ca in the parent material. In Haute‐Mauricie, where the parent material contained a low level of Mg, foliar nutrition for this element was significantly poorer under WTH compared with SOH. Harvesting intensity did not influence the biogeochemical cycles of K and N. Foliar analysis revealed that jack pine exhibits the strongest nutritional difference between WTH and SOH. Results suggested that the tree species regenerating the harvested sites, as well as the total Ca and Mg contents of the parent material are better indicators of a site's susceptibility to nutritional alteration by WTH than soil available nutrient status.

Influence of pre-commercial thinning of balsam fir on defoliation by the balsam fir sawfly

Pre-commercial thinning, whereby tree densities are reduced to diminish competition and maximize tree growth, is one of the most frequently used silvicultural practices in North America. We carried out field surveys in western Newfoundland and in eastern Nova Scotia, Canada, in pre-commercially thinned and unthinned stands of balsam fir ( Abies balsamea (L.) Mill.) that had been defoliated by the balsam fir sawfly, Neodiprion abietis (Harr.), to determine if pre-commercial thinning increased the susceptibility of stands to insect defoliators. Except for stands sampled at the new and increasing stage of an outbreak, both egg densities of, and defoliation by, N. abietis were higher in thinned than unthinned stands. Higher levels of defoliation in thinned than unthinned stands were usually associated with higher levels of defoliation on intermediate-aged foliage. An estimate of tree vigor, used to predict future tree growth rate, was only weakly related to defoliation levels and it is, therefore, uncertain if higher defoliation in thinned stands would result in lower future growth rates than for trees in unthinned stands.

Growth development of a balsam fir ( Abies balsamea (L.) Mill.) originating from layering

After a disturbance, balsam fir stands ( Abies balsamea (L.) Mill.) regenerate primarily by seedlings, but layering is also known to occur and to contribute to the subsequent population base. We examined in detail the lower part of one balsam fir stem, stump and roots in order to: reconstruct the establishment of one mature balsam fir with evidence of layer-origin. The life history of this tree was then reconstructed by measuring tree-ring widths, dating all the sections, and by identifying the presence or absence of pith to differentiate between stem and root structures. We located a pith structure in this tree 51 cm below ground level. This lowest section with pith was characterized by a diameter of only 3 mm and contained 40 concentric tree-rings, suggesting that it originated from a branch. Radial and height growth measured were small until the beginning of 1930s. This period was abruptly followed by an increase in growth in both height and diameter as well as a massive production of adventitious roots, probably produced by partial harvesting of the parent tree/stand.

Structural changes in coniferous stands along a chronosequence and a productivity gradient in the northeastern boreal forest of Québec

:The influence of stand age and site conditions on the structure of coniferous stands was studied in the boreal forest of Québec’s Côte-Nord, a region with low fire recurrence. Stand diameter diversity was measured in 2202 forest inventory plots in black spruce (Picea mariana), balsam fir (Abies balsamea), and mixed stands using the Shannon-Wiener diversity index. A relative productivity index was developed based on the relationship between height and age of dominant trees. A stepwise regression analysis indicated that this productivity index best explains stand structure variation in all composition types, while stand age seems to influence structure more at the beginning of stand development. The results suggest that productive stands become uneven-sized earlier than unproductive stands and also maintain a greater diameter diversity. These contrasting structural dynamics may be explained by (i) a higher growth rate in richer stands that likely induces earlier senescence and thus an earlier passage to an uneven-sized structure and (ii) a restricted maximum tree diameter in poor stands caused by a scarcity of resources, which in turn reduces the diameter diversity of these stands, even after their break-up time.

Evaluating the effect of precommercial thinning on the resistance of balsam fir to windthrow through experimentation, modelling, and development of simple indices

A tree-pulling experiment was carried out in stands of balsam fir (Abies balsamea (L.) Mill.) to evaluate the effects of early thinning on windthrow resistance. Forty trees from four stands were pulled over. Two stands had received a precommercial thinning 9 and 14 years previously, respectively, and the two others were unthinned controls. There were no significant inter-stand differences in the relationship between the critical turning moments required to overturn or snap the trees and their stem mass. The results were input into a model calculating critical wind speeds using the approach developed for the ForestGALES model. Simulations were run for four different stand densities. The mensurational characteristics for each run were taken from the results of a spacing trial established in balsam fir stands at Green River, New Brunswick. For stem breakage, the model predicted a gradual increase in critical wind speeds with wider spacing. The increase was smaller for tree overturning. The pattern of differences remained very similar after a simulated commercial thinning removing 30% of the basal area. Reductions in critical wind speeds were on the order of 4 m·s–1 in all cases. Simple indices were developed that could estimate the relative results given by the model.

Comparaison des caractéristiques des gros chicots entre une sapinière primitive et une sapinière aménagée sur la péninsule gaspésienne, Québec

Snags (i.e., dead standing trees), and more particularly those of larger dimensions, are recognized as playing a major role in the maintenance of forest biodiversity. This study aimed to describe the characteristics of large snags in a primeval balsam fir forest in the Gaspé Peninsula (Quebec) and to compare them with those of an adjacent area composed of mature second-growth balsam fir stands. For snags ≥20 cm in diameter at breast height (DBH), mean density reached 51 snags/ha in the primeval forest and 24 snags/ha in the managed forest. The distribution of snags among DBH classes was similar in both areas. However, well-decayed snags made up a larger proportion of the snags in the primeval forest than in the managed forest. The proportion of snags with evidence of woodpecker feeding was higher in the managed forest than in the primeval forest. To ensure temporal and spatial continuity of snags in different decay stages, some stands could be left untouched for several rotations, and single snags could be kept or created in logged areas.

The eastern boreal old-growth balsam fir forest: a distinct ecosystem

The objective of this project was to assess the importance of pristine forests in maintaining the botanical biodiversity of the humid boreal balsam fir forest of eastern Canada. The study was based on a comparative analysis of silviculturally mature second-growth stands and pristine forest stands at two stages of development (senescent and old growth) in the Gaspé Peninsula. The structure and composition of the stands was described, and the abundance of structural attributes evaluated. The communities of nonvascular plant species (mosses, liverworts), lichens, and saprophytic fungi were compared. The study demonstrated that the pristine forest landscape studied was composed largely of old-growth and senescent stands. Old-growth forests are differentiated by their irregular structure. The results regarding nonvascular plant species, lichens, and saprophytic fungi show higher species diversity in old-growth forests, corresponding to higher habitat diversity. Species assemblages were comparable between the pristine forests, but different from those of second-growth stands. Rare species are found more frequently in the old-growth forests. The results indicate that the old-growth balsam fir stands of the Gaspé Peninsula constitute critical habitats for maintaining a large number of species threatened by the gradual disappearance of primeval stands.Key words: forest management, biodiversity, old-growth forest, humid boreal fir forest, nonvascular plants.

Changes in root morphology after precommercial thinning in balsam fir stands

Precommercial thinning is often used to control stand density in naturally regenerated balsam fir (Abies balsamea (L.) Mill.) stands. Early stand density control could have beneficial effects on longer term stand stability through a modification of stem shape and root development. To assess the effect of precommercial thinning, two thinned and two unthinned stands were selected. Root sections were collected at 25 cm from the centre of the stem for all major roots (diameter greater than 2 cm). A disk was also cut at breast height level. From these disks, response in radial growth was determined. Detailed root measurements were taken on the sample disks to assess treatment effect on the following variables: asymmetry in root cross-sectional area (CSA) distribution, individual root shape, as well as changes in root shape over time. A quick and pronounced response in root growth occurred. This response was greater than that observed in the trunk. No asymmetry in root CSA distribution was observed at the stand level. Trees allocated more to radial growth above the biological centre of the root both in treated and control stands, but this trend was increased by thinning. Roots also tended to develop T-beam shapes over time, both in control and thinned stands. Most roots initially did not possess an I-beam shape and did not develop one during the course of the study. According to our results, trees respond quickly to the new growing conditions created by thinning by increasing biomass allocation to parts of the roots where mechanical stresses are greater.

Factors influencing deer browsing damage to red spruce ( Picea rubens) seedlings in coastal red spruce–balsam fir stands of southwestern Nova Scotia

The impact of deer browsing on the distribution and growth of naturally regenerating red spruce seedlings established within recently harvested and mature, coastal red spruce–balsam fir stands was evaluated. More specifically, we examined browsing frequency and severity in relation to distance from forest cover, stand age, and seedling height. Relative height increment and condition of browsed (20% removal of total biomass) and non-browsed seedlings after one growing season were also compared. A significant distance×stand age interaction was observed for browsing frequency, largely the result of differences among recently harvested stands. Browsing damage within mature stands was negligible, but when occurring, was restricted to taller seedlings within 20 m of the forest edge. Eleven percent of all seedlings within harvested stands were browsed, with seedlings between 50 and 100 cm tall being preferred. Most of the seedlings (92%) sustained less than 30% biomass removal. Fifty-two percent of these seedlings experienced less than 10% biomass loss. Relative height increase of browsed seedlings was significantly reduced. Most seedlings were able to recover from clipping damage, regaining much of the initial height and biomass originally lost by the end of summer. Seedling condition was not detrimentally affected by the clipping rate, although overall biomass gain of affected seedlings was lower. If no further browsing damage is sustained, biomass increment may be delayed by approximately one growing season, relative to undamaged seedlings of equal size and established under similar micro-environmental conditions. Current population densities of deer appear to have minimal impacts on re-establishment of coastal red spruce–balsam fir stands in southwestern Nova Scotia. Low impacts may be due to high seedling densities, as more than adequate numbers of seedlings remained untouched throughout the harvested stands.

Windthrow After Shelterwood Cutting in Balsam Fir Stands

Abstract The use of partial cutting in balsam fir stands has been greatly restricted by the fear of windthrow. This applies to shelterwood cutting, for which very little quantitative information on windthrow is available. This study was conducted in 50-yr-old balsam fir stands. The aim of the study was to quantify windthrow losses associated with three patterns of seed cuts. The study consists of five replicates of four treatments: uncut control, uniform shelterwood, group shelterwood, and strip shelterwood. Complete windthrow monitoring was performed at 2, 4, and 6 yr after cutting. The effect of treatment, wind exposure, and stand characteristics was assessed after 6 yr. A simulation with the ForestGales model was conducted to better understand the seed cut pattern effect in identical stands. Results showed that a shelterwood method involving a low intensity seed cut can be applied in relatively sheltered balsam fir stands. Topographic exposure and stand characteristics did not contribute to the amount of windthrow observed. The major factor explaining the amount of windthrow seems to be the presence of adjacent cuts that funneled wind into the plots. North J. Appl For.20(1):5–13.

Predicting the effect of thinning on growth of dense balsam fir stands using a process-based tree growth model

A tree-level process-based model of forest growth is used to investigate the effects of thinning on the growth of balsam fir (Abies balsamea (L.) Mill.) in stands that have almost reached commercial maturity but that have never been thinned. The model is applied to predict the 20-year growth of a stand following a recently established thinning experiment in which four thinning treatments were tested. The combination of stand properties and treatment type is quite particular and the resulting long-term effect on growth cannot be evaluated based on past experiments. The objectives of the study are to provide estimates of treatment outcome and of their errors over the appropriate time frame for decision making. This is achieved by representing growth processes through functions empirically adjusted to field observations while limiting the inputs of the model to what are usually available through regular forest inventory. Simulations suggest that 20-year growth of individual trees from the smaller diameter classes is improved by the treatments, but the growth of larger trees (>0.1 m3) is left unchanged. When the model error is not taken into account, the results after 20 years suggest, with a confidence level greater than 95%, that the merchantable volume of the treated plots does not recover to the level found in the untreated control plots, a result contrary to the initially expected effect of such thinning. By including modelling uncertainty, however, the confidence level associated with such a result is reduced to 70%. Such an inclusion prevents the misuse of the model predictions too far into the future.