Southern Interior British Columbia Research Articles

Wind and snow damage nine years following four harvest treatments in a subalpine fir – Engelmann spruce forest at Sicamous Creek in southern interior British Columbia, Canada

We used transect surveys at a large-scale experimental site at Sicamous Creek, B.C. to measure the effects of five treatments on wind and snow damage in an old subalpine fir – Engelmann spruce forest: 10-ha clearcuts, arrays of 1-ha patch cuts, arrays of 0.1-ha patch cuts, individual-tree selection cuts and uncut controls. We also examined edge effects and conditions predisposing trees to damage. Transects were surveyed in 1997, 1999 and 2003 (2.7, 4.7 and 8.7 years postharvest). The increase in wind damage in the four harvested treatments compared to the uncut controls observed after 2.7 years was no longer evident following a snow damage event in the winter of 1998–1999, which was most severe in the uncut controls and leave strips. The damage recorded from this event was predominantly stem snapping rather than uprooting. Subsequent damage was low in all treatments, returning to the level first recorded in the uncut controls. Overall, after 8.7 years, the treatment differences were not statistically significant but the lowest average rates of damage were observed in the 0.1-ha patch cut arrays. The highest damage rates overall were observed within 10 m of the N and E edges of the 10-ha clearcuts. Damage rates in Engelmann spruce continued to be lower than rates for subalpine fir. Stem snapping, caused by some combination of snow loading and wind, is an underreported but widespread disturbance in these stands. Key words: ESSF forest, wind damage, snow damage, snapping, uprooting, subalpine fir (Abies lasiocarpa [Hook] Nutt.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), silvicultural systems, Sicamous Creek

Effects of large woody debris on surface structure and aquatic habitat in forested streams, southern interior British Columbia, Canada

AbstractIt is well known that large woody debris (LWD) plays an important functional role in aquatic organisms' life. However, the influence of LWD on channel morphology and aquatic environments at watershed levels is still unclear. The relationships between wood and surface structure and aquatic habitat in 35 first through fifth order streams of southern interior British Columbia were investigated. Study streams in the channel networks of the study watersheds were classified into four size categories based on stream order and bankfull width: Stream size I: bankfull width was less than 3 m, Stream size II: 3–5 m, Stream size III: 5–7 m, Stream size IV: larger than 7 m. We found the number of functional pieces increased with stream size and wood surface area in stream sizes I, II and III (24, 28 and 25 m2/100 m2, respectively) was significantly higher than that in stream size IV (12 m2/100 m2). The contribution of wood pieces to pool formation was 75% and 85% in stream sizes II and III, respectively, which was significantly higher than those in stream size I (50%) and size IV (25%). Between 21% and 25% of wood pieces were associated with storing sediment, and between 20% and 29% of pieces were involved in channel bank stability in all study streams. Due to long‐term interactions, LWD in the intermediate sized streams (Size II and III) exhibited much effect on channel surface structure and aquatic habitats in the studied watersheds. Copyright © 2008 John Wiley & Sons, Ltd.

Spatial pattern and persistence of historical fire boundaries in southern interior British Columbia

Recent ecosystem and fire management research aims to quantify, model and understand historical fire disturbances focusing on their frequency, size and distribution. Less attention, however, has been paid to fire boundaries and their location on the landscape. Our study presents a spatial method to quantify the location, pattern and persistence of historical fire boundaries using tree ring fire scar data in the lower Stein watershed (British Columbia). Data from Pinus ponderosa and Pseudotsuga menziesii collected in 35 one-hectare plots over a 412-hectare study area were analyzed for the period between 1879 and 1947 using local spatial statistics and boundary detection techniques. Results of the analysis using local spatial statistic Moran’s I showed significant clustering of boundaries near topographic breaks. To determine and test whether fire boundaries between plots were persistent, we used boundary detection methods and developed a spatially restricted randomization test. The results revealed that out of 86 possible boundary links, 8 were significantly persistent (P < 0.025) while another 8 were significantly rare (P < 0.025). These spatial methods can help determine the historical spatial configuration of persistent boundaries and can be used to maintain natural forest dynamics.

Ten year responses of Engelmann spruce and a high-elevation Ericaceous shrub community to manual cutting treatments in southern interior British Columbia

Vegetation management treatments are often applied to high-elevation, Ericaceous shrub-dominated sites in southern interior British Columbia to facilitate reforestation. We studied the effects of manual cutting on an established vegetation community and newly planted to 2-year-old Engelmann spruce ( Picea engelmannii Parry ex Engelm.) over a 10-year period. Spruce survival was significantly higher in the treatment than the control 3 years after brushing ( p = 0.020). Although differences in survival continued to be large after 10 years (79% versus 61%), they were no longer significant due to increased between-site variability. Relative height estimates indicated that brushed spruce were taller relative to the vegetation canopy than control spruce throughout the 10 years assessment period, but growth responses were small even where significant. The cutting treatment significantly increased ground-level diameter after 3 and 5 years, but not after 10 years. The loss of statistical significance is attributed to ongoing mortality of small diameter suppressed stems in the control. After 10 years, shrub cover was still lower in the cutting treatment than the control, but height had recovered within 3 years. Manual cutting increased Shannon diversity in the first year post-treatment ( p = 0.039), after which it returned to control levels. There were no differences in species richness. A competition index based on the first year relationship between spruce and vegetation cover and height (CRH TS1) explained 33% of the variation in spruce diameter 10 years after treatment, and first year total shrub cover (COV TS1) explained 28% of the variation. R 2 values increased slightly over time, suggesting that vegetation competition was still affecting at least some surviving seedlings when they were 10–12 years old. Thresholds for spruce diameter of 139 and 64% were identified for CRH TS1 and COV TS1, respectively.

Geomorphology of a Cordilleran Ice Sheet drainage network through breached divides in the North Cascades Mountains of Washington and British Columbia

The Skagit River valley in northern Washington and southern British Columbia contains long interconnected valleys, barbed tributaries, underfit streams, and low-elevation mid-valley divides. Quantitative measures of connectivity between valleys draining through breached mountain divides, aerial photographs, and a field-verified, process-form model were used to assess the impact of continental glaciation on the drainage pattern and geomorphology of the watershed. Structural control on drainage patterns and intense, repeated continental glaciation rendered the Skagit an extremely interconnected valley, with meltwater routes opening it to the Fraser and Okanagan watersheds. Divide elimination by drainage of large proglacial lakes led to several hundred meters of erosion at 10 breached divides. Other geomorphic effects of recurrent continental glaciation include the bisection of a major mountain valley, divide migration of as much as 50 km, erosion of canyons 15–30 km downstream of breached divides, and deposition of exceptionally large alluvial fans at canyon mouths. Drainage patterns established in the Tertiary were reorganized to accommodate southern drainage of glacial meltwater trapped in mountain valleys at the southern margin of the Cordilleran Ice Sheet. The Skagit basin is now a regional focus for drainage to Puget Sound from the northernmost North Cascades and parts of southern interior British Columbia. The key to establishing this system was the elimination of a regional divide in what is now Skagit Gorge, which resulted in the capture of the upper Skagit valley by the lower Skagit River. Patterns of drainage modification caused by continental glaciation in the Skagit basin are similar to those in other mountain areas. The Skagit's interconnected valleys are similar to the great through-valleys of Scotland, transmountain valleys of British Columbia, and ice portals of Scandinavia.

Evidence for competition and facilitation trade-offs: effects of Sitka alder density on pine regeneration and soil productivity

We suggest that the net outcome of interactions between regenerating conifers and early seral deciduous species depends on trade-offs between competition and facilitation over time. Vegetation management treatments that dramatically reduce competitive effects of deciduous species may constrain the ability of conifers to optimize resource trade-offs (e.g., increased growth response to light at the expense of increased drought mortality), potentially affecting long-term productivity. In a 15-year study in southern interior British Columbia, we investigated whether lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) survival, growth, and resource availability differed among manipulated stand compositions, from pure pine stands to mixtures with native N2-fixing Sitka alder (Alnus viridis subsp. sinuata (Regel) Á. Löve &amp; D. Löve) or herbs. We found that pine growth increases were sustained only in pure stands, where alder and herbs were completely removed, corresponding with short-term increases in light, soil and air temperature, and soil nitrate. However, this came at a significant cost to survival (through loss of protection from browsing, desiccation, and sun scald), as well as dramatic depletions in soil nitrogen mineralization over the longer term. Our results support a competition–facilitation trade-off hypothesis, suggesting that treatment-imposed shifts in resource availability over time could negatively affect forest productivity.

Consumption of Caterpillars by Bats During an Outbreak of Western Spruce Budworm

We investigated the diets of insectivorous bats (Chiroptera: Vespertilionidae) in forests with high densities of western spruce budworm (Choristoneura occidentalis, Lepidoptera: Tortricidae), in southern interior British Columbia, Canada. Caterpillars as potential prey were more common and widespread than previously reported. Caterpillar consumption by bats was more frequent where C. occidentalis larvae were more abundant, suggesting that the caterpillars being eaten were C. occidentalis. The frequency of caterpillar consumption was similar for Myotis evotis, which gleans prey from vegetation, and for other bat species that forage primarily by aerial-hawking. We suggest that caterpillars hanging by silk threads were captured by bats that foraged aerially.

Influences of stand composition and age on forest floor processes and chemistry in pure and mixed stands of Douglas-fir and paper birch in interior British Columbia

The influence of stand composition and age on forest floor chemical properties, nitrogen availability, and microbial activity was examined in mixed and pure stands of Douglas-fir ( Pseudotsuga menziesii) and paper birch ( Betula papyrifera). Decomposition of Douglas-fir and birch litter over two years as well as annual litter input was also measured. Mixed and pure stands of each species aged 10–25, 50–65 and >85 years old were selected in the Interior Cedar Hemlock (ICH) zone of southern interior British Columbia. Significantly more total N was mineralized in the forest floor of pure birch compare to that of pure Douglas-fir stands while forest floor of mixed species stands had intermediate N mineralization values. When sampling times were pooled forest floor N mineralization was lowest in the young stands compared to the older stands. Stand composition did not significantly affect litter decomposition were found in litter decomposition, microbial respiration and biomass. Stand age, however, did affect these parameters significantly. More birch litter mass was lost in young stands than in their older counterparts while the opposite trend was observed for fir litter. Generally, lower basal respiration, microbial biomass and C mic/C org was found in young compared to older stands. Concentrations and contents of forest floor total N and exchangeable K and Mg, and pH under pure birch were consistently higher compared to pure Douglas-fir. While forest floor total C, available P contents, exchangeable K and Mg concentrations were lowest in young stands, no differences were observed for total N and exchangeable Ca. All litter nutrient concentrations and contents were highest in pure birch stands. No clear trends could be discerned in litter nutrient concentration data among stand ages, although when converted to nutrient contents, there was a general increase with stand age. Both stand type and age had significant effects on forest floor properties and processes suggesting that stand age is another factor to evaluate when assessing the influence of forest composition on forest floor processes and chemistry. In terms of the effect of mixture, the data indicated that the maintenance of paper birch in mixed stands in these forest may have some effect on nutrient availability and status.

Conifer growth, Armillaria ostoyae root disease, and plant diversity responses to broadleaf competition reduction in mixed forests of southern interior British Columbia

Broadleaf trees are routinely removed from conifer plantations during vegetation management treatments, but whether the removal increases tree productivity or affects root disease and plant diversity is unknown. The effects of manual and chemical reduction of paper birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) on conifer survival, growth, root disease incidence, and plant community diversity were investigated for 5 years in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations in southern interior British Columbia. Broadleaves were reduced by manual, girdling, and cut-stump glyphosate treatments for 5 years but most severely following cut-stump glyphosate and with a delay due to slow death following girdling. Conifer survival was reduced for 3–5 years following manual cutting or girdling of birch because of a 1.5- to 4-fold increase in mortality due to Armillaria ostoyae (Romagn.) Herink, but this did not occur following cut-stump glyphosate treatment of birch or manual cutting of aspen. Conifer diameter increased with treatment intensity and productivity of the vegetation complex. Competition thresholds were identified for diameter but not survival, although Armillaria-caused mortality tended to increase near the minimum growth threshold. Structural diversity increased following manual cutting and cut-stump glyphosate because birch dominants were removed and understory layers increased, but species richness and diversity were unaffected. Forest managers can expect increased conifer growth with birch removal but also small increases in mortality due to Armillaria ostoyae root disease following manual treatments and loss of large birch trees in all treatments.

Reducing paper birch density increases Douglas-fir growth rate and Armillaria root disease incidence in southern interior British Columbia

Paper birch ( Betula papyrifera Marsh.) is routinely chemically or mechanically weeded from Douglas-fir ( Pseudotsuga menziesii var. glauca (Beissn.) Franco) plantations to increase conifer productivity, but these practices are controversial because of unknown effects on forest health and diversity. This study examined effects of paper birch density reduction treatments on productivity and disease incidence of Douglas-fir saplings in the southern interior of British Columbia. Five paper birch density treatments (0, 400, 1111, 4444 stems ha −1 and an un-thinned control of >7000 stems ha −1), where paper birch was manually cut at the root collar in 1999, were replicated on four sites in a randomized block design. After 2 years, Douglas-fir survival did not differ significantly among treatments, but where Armillaria ostoyae (Romagn.) Herink was present in untreated stands, mortality due to root disease increased significantly with increasing paper birch thinning intensity. Mean diameter increment and height:diameter ratio of Douglas-fir improved where paper birch was completely removed or partially thinned compared with the control. Mean light transmittance and soil moisture content increased with decreasing paper birch density, but Douglas-fir foliar N status was unaffected. Our results suggest that Douglas-fir growth can be improved and root disease incidence minimized by thinning paper birch to 4444 stems ha −1 in young mixed stands, but that subsequent release treatments may be necessary to maintain Douglas-fir growth rates.

Influence of wildfire and harvest on biomass, carbon pool, and decomposition of large woody debris in forested streams of southern interior British Columbia

Large woody debris (LWD) is an important component in the biogeochemistry cycle of carbon and nutrients in forested stream ecosystems. In-stream LWD volume, biomass and carbon pool were investigated in 19 forested streams in the south central interior of British Columbia. The stream channels were classified into four disturbance categories based upon condition of the adjacent riparian forest. The categories are: (1) riparian forest harvested approximately10 years ago (HT10), (2) riparian forest harvested approximately 30 years ago (HT30), (3) riparian forest burned by a wildfire approximately 40 years ago (WF), and (4) undisturbed old-growth riparian forest (OF). Streams with riparian forests that were affected by wildfire or were recently harvested were observed to have significantly higher LWD volumes, biomass, and carbon pool as compared to streams flowing through old-growth riparian forests. LWD stocks averaged 376 m −3 ha −1 (volume), 112 Mg ha −1 (biomass), 52 Mg C ha −1 (carbon) in WF, 258 m −3 ha −1, 78 Mg ha −1 and 36 Mg C ha −1 in HT10, 180 m −3 ha −1, 52 Mg ha −1 and 23 Mg C ha −1 in HT30, and 114 m −3 ha −1, 37 Mg ha −1 and 17 Mg C ha −1 in OF. Volume, biomass, and carbon stock were 2.3, 2.0, 2.1, and 1.3, 1.1 and 1.1 times higher in WF and HT10 than in OF, respectively, but LWD loading did not differ significantly between HT30 and OF. Major differences were also observed in the state of decay of LWD between the four disturbance categories based upon three decomposition classes. Our study supports the conclusion that harvesting creates a short-term increase in LWD stocks. However, harvesting may greatly reduce LWD loadings over the long-term due to relatively rapid decomposition of LWD due to increased rate of decay, transport, and reduced recruitment from the adjacent riparian forest. In the study streams, the wood density of LWD ranged from 0.273 to 0.427 g cm −3 depending upon the species and decomposition level. An average decay rate constant of 0.0095 year −1 was calculated for the LWD based upon wood density. Based upon this decay rate, the time required to loss 50% ( t 0.5) and 95% ( t 0.95) of wood is 74 and 316 years, respectively.

Chemical, grazing, and manual cutting treatments in mixed herb–shrub communities have no effect on interior spruce survival or growth in southern interior British Columbia

Interior spruce ( Picea engelmannii Parry × glauca [Moench] Voss) plantations are commonly weeded of herbs, ferns, and shrubs using foliar glyphosate, livestock grazing, or manual brushing treatments, but it is unknown whether they result in improved conifer survival or growth. We found that despite reducing vegetation for 1–5 years, these treatments applied to mixed herb–shrub communities in southern interior British Columbia had no effect on 5-year survival or growth of interior spruce. Biogeoclimatic zone was the factor that most influenced spruce performance, with greater survival and height growth in the Interior Cedar Hemlock (ICH) zone than in the colder, higher elevation Engelmann Spruce–Subalpine Fir (ESSF) zone. Glyphosate caused larger reductions in vegetation cover and height than did grazing or manual cutting. Glyphosate also reduced plant species richness after 5 years, but none of the treatment methods affected species or structural diversity of the plant community. Structural richness was slightly greater in the ICH than ESSF zone. Our results indicate that the vegetation management treatments operationally applied to herb–shrub communities in southern interior British Columbia have been ineffective at releasing interior spruce.

Assessment of interspecific competition using relative height and distance indices in an age sequence of seral interior cedar–hemlock forests in British Columbia

Treatments that reduce neighbour density are widely applied in the belief they will improve conifer growth in mixed forests. However, our understanding of stand composition and age effects on competition is poor. We used neighbourhood analysis for 748 target conifer trees to examine interspecific competition within 11-, 25-, and 50-year-old mixed, even-aged stands of paper birch (Betula papyrifera Marsh.), Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), western redcedar (Thuja plicata Donn ex D. Don), and western larch (Larix occidentalis Nutt.) in southern interior British Columbia. Critical neighbourhood height and distance were identified where competition accounted for the greatest variation in target conifer diameter. Competition processes were emperically examined using relative height indices. We found that critical neighbourhood distance increased with stand age and was greater for larch than for cedar. Critical neighbourhood height was higher for cedar than for Douglas-fir or larch in the 11-year-old stands but lower in the older stands. The most important competitors in the 11-year-old stands were tall neighbours, whereas those in the older stands were short neighbours. We found asymmetrical relationships between target conifers and neighbours for all species and age-classes, indicating a resource preemption mode of competition. To be useful in developing prescriptions for competition management in mixed species stands, competition indices should consider neighbour identity and critical height for each target species. Assessment radius must also be sufficiently large to adequately characterize competition.

Impact of cattle grazing on prostigmatid mite densities in grassland soils of southern interior British Columbia

Soil mesofauna are an important part of soil ecosystems, but little is known about them in grassland ecosystems of southern interior British Columbia. In this s tudy, 12 300 organisms were examined and prostigmatid mites were most abundant, representing 95% of the total collection. Cattle grazing, sample depth and season of sampling influenced prostigmatid mite densities. However, grazing was the most significant factor, explaining 29% of the variation in prostigmatid mite density. Key words: Soil fauna, mesofauna, Prostigmata, Acari, range management

Fluorescent pseudomonad population sizes baited from soils under pure birch, pure Douglas-fir, and mixed forest stands and their antagonism towardArmillaria ostoyaein vitro

The relationship between forest stand composition in southern interior British Columbia and fluorescent pseudomonad bacteria populations was investigated using seedling bioassays. The objectives of this study were to (i) compare the relative population sizes of fluorescent pseudomonads baited from soils in pure paper birch (Betula papyrifera Marsh.), pure Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and mixed stands of the two species and (ii) determine if fluorescent pseudomonads from these soils have inhibitory effects against the root pathogen Armillaria ostoyae (Romagn.) Herink in vitro. Soil from birch stands supported four times more pseudomonads on seedling baits than soil from Douglas-fir stands, with the mixed stands intermediate. Soil from young stands yielded twice as many rhizosphere pseudomonads as soil from mature stands. Pseudomonad population size was positively correlated with percent cover and density of birch, and negatively correlated with basal area of Douglas-fir, percent cover of Douglas-fir, and carbon/nitrogen ratio of the soil. Greater than 50% of the fluorescent isolates reduced radial growth of A. ostoyae by more than 20% and greater than 90% reduced biomass of the fungus in dual culture tests. Cell-free bacterial culture filtrates added to the growth medium also reduced growth of A. ostoyae. This study provides evidence that paper birch provides a more favorable environment for fluorescent pseudomonads than Douglas-fir and suggests a mechanism by which paper birch can positively influence the susceptibility of managed forest stands to Armillaria root disease.

Dynamics of an old-growth, fire-initiated, subalpine forest in southern interior British Columbia: tree-ring reconstruction of 2 year cycle spruce budworm outbreaks

Tree-ring width chronologies of three species from a 330-year-old subalpine forest were used to reconstruct outbreaks of 2 year cycle spruce budworm (Choristoneura biennis Freeman). The growth of host species, Engelmann spruce (Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.), was compared with that of the nonhost, lodgepole pine (Pinus contorta Dougl. ex Loud.) with and without the removal of the effects of climate on growth. Seven periods, 1989–1991, 1943–1957, 1911–1927, 1869–1875, 1839–1861, 1823–1829, 1785–1801, were identified in which the growth of both host species was reduced relative to the non-host; this includes the single known outbreak from 1944 to 1956. Spectral analysis indicated a periodicity for growth reduction of the host relative to non-host species of ca. 45 years for both spruce and fir. For three periods, the known outbreak in the 1940–1950s, and two inferred outbreaks in the 1910–1920s and 1840–1850s, we calculated the four measures of radial growth first proposed by Brubaker and Greene (L.B. Brubaker and S.K. Greene. 1979. Can. J. For. Res. 9: 95–105): the maximum rate of growth loss, 1-year and 5-year losses, and the rate and time to recovery. Growth losses were greater for fir than for spruce during all three periods. During the 1940–1950s, growth losses were severe, but losses were less in the 1910–1920s. The impact of C. biennis has varied among outbreak periods but, overall, has made a pronounced contribution to present stand conditions. Our work suggests that budworms have been a frequent agent of disturbance with major effects on forest dynamics in southern British Columbia, especially in spruce–fir forests when long periods occur between fires.

Dynamics of an old-growth, fire-initiated, subalpine forest in southern interior British Columbia: tree size, age, and spatial structure

We used dendrochronological analysis of over 2000 trees in four 50 × 50 m plots to reconstruct the history and dynamics of a 330-year-old, fire-initiated spruce-fir forest. All lodgepole pine (Pinus contorta Dougl. ex Loud.), half of the canopy Engelmann spruce (Picea engelmannii Parry ex Engelm.), but less than 10% of the canopy subalpine fir (Abies lasiocarpa (Hook.) Nutt.) dated from the first 50 years of stand development. Tree-ring patterns of individual surviving trees showed no evidence of disturbance during the first 200 years after stand initiation; subsequently, episodes of disturbance are indicated by periods of release in understory fir. Although many fir owe their canopy position to release after disturbance, few canopy fir in the current stand established in response to either the stand-initiating event or subsequent partial disturbances. A seedling bank of long-lived fir appears critical to the dynamics of this forest. In contrast, establishment of almost all canopy spruce can be related to disturbance. This stand, although fire initiated, was structured primarily by a combination of partial disturbances and autogenic processes. We suspect that most old, fire-initiated stands in many forest regions are similarly structured and emphasize that the contribution of partial disturbances and autogenic processes should be fully assessed when examining their dynamics or managing such forests.

Windthrow following four harvest treatments in an Engelmann spruce - subalpine fir forest in southern interior British Columbia, Canada

We used transect surveys at a large-scale experimental site at Sicamous Creek, B.C., to measure the effects of five treatments on windthrow: 10-ha clearcuts, arrays of 1-ha patch cuts, arrays of 0.1-ha patch cuts, individual-tree selection cuts, and uncut controls. We also examined edge effects and conditions predisposing trees to windthrow. Windthrow of subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in the 2.7 years following harvesting increased from 0.6% of basal area per year in uncut forest to 0.8-1.8% per year in harvested treatments, with highest rates in individual tree selection units and lowest rates in 0.1-ha patch-cut arrays. Engelmann spruce (Picea engelmannii Parry ex Engelm.) showed similar patterns of windthrow but lower rates (0.2-0.7% of basal area per year in harvested treatments). Windthrow was concentrated near north and east edges of 1-ha and 10-ha openings but was dispersed throughout the more uniform treatments. Windthrown trees did not differ from random trees in diameter but had lower height/diameter ratios, probably reflecting the greater windthrow observed in subxeric sites on complex, elevated topography. The rates and distribution of windthrow in different harvest treatments have implications for ecological processes, salvage, long-term windthrow potential, and mitigation possibilities.

Stand development in an old-growth subalpine forest in southern interior British Columbia

The dynamics of an old-growth Engelmann spruce (Picea engelmannii Parry) - subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forest were investigated using stand-history reconstruction. Age and size structures, tree location, and radial increment patterns were used to link establishment and growth to disturbances. The spatial distribution of trees was used to infer patterns of establishment and mortality. The forest originated in the 1650s, probably after fire. Initial establishment took almost 80 years, after which fir continued to recruit effectively, but spruce did not. The tree-ring record showed no evidence of widespread disturbance during the first 200 years, but from about 1855 to 1900 a major period of canopy mortality caused by bark beetles released suppressed trees and provided opportunities for establishment and rapid growth of seedlings of both species. Most current canopy trees established or released during this period of disturbance; thus, many canopy trees are fairly young in this old-growth forest and canopy turnover is high. A short period of disturbance (1927-1932) caused by the balsam bark beetle (Dryocoetes confusus Swaine) resulted in release of suppressed trees but did not promote seedling establishment. At the time of study (1994), the stand was undergoing another minor disturbance caused by this insect. Bark beetles appear to be of fundamental importance in controlling the dynamics of spruce-fir forests during the long intervals that often occur between fires in cool, wet climates.

Stand development in an old-growth subalpine forest in southern interior British Columbia

Stand development in an old-growth subalpine forest in southern interior British Columbia