Engelmann Spruce Subalpine Fir Research Articles

Forest vegetation change and disturbance interactions over the past 7500 years at Sasquatch Lake, Columbia Mountains, western Canada

Fire is the most important abiotic disturbance in the interior cedar-hemlock (ICH) and Engelmann spruce–subalpine fir (ESSF) forest zone of southeastern British Columbia, Canada. Other disturbances are also important, such as defoliator and boring insect outbreaks, windthrow, diseases, and rapid mass movements. Few studies have examined the interaction between multiple types of disturbances in these forests over long timescales. Here we present high-resolution analyses of biomass burning, erosion, and vegetation assemblage changes at Sasquatch Lake (NEL02), a valley lake in the Columbia Mountains. The 531.5 cm sediment core was radiocarbon dated and provided a 7500-year stratigraphy that was used for pollen, macroscopic charcoal (>150 μm), and sedimentologic analyses. Pollen and charcoal data provided evidence of forest composition changes and fire activity. Magnetic susceptibility, loss-on-ignition, and particle size distribution analyses characterised changes in erosion into the basin. The results show that coniferous forests, with a high abundance of Pinus pollen, had established in the catchment by the beginning of the record and were subject to intermittent burning and high-energy erosive events. Tsuga heterophylla expanded by 4400 cal BP and the modern interior cedar-hemlock forests expanded throughout the lower elevations due to increased regional continentality since 4500 cal BP. High-energy erosional inputs to the lake were less frequent from 3500 to 750 cal BP and rapid mass movements may have increased in frequency during the Little Ice Age. Dendrochronological evidence in these stands suggests a mixed-severity fire regime during past ∼300 years, which has not been fully examined for charcoal-based fire event reconstruction. Here we use identified peaks as an indicator of increased biomass burning and charcoal movement in the catchment in relation to peaks in allochthonous clastic material to understand the potential relationships between biomass burning and erosion events at multiple temporal scales in the catchment. This suggests that post-fire conditions, up to several decades, were subject to increased erosion to the lake and erosion events were more common during the early Holocene. Establishment of dense ESSF and ICH forests decreased siliciclastic input to the lake throughout the mid Holocene until a recent rockslide. The high-resolution sampling of this lake sediment record provides long-term evidence of variability in the relationships between vegetation cover, fire and erosion at a catchment scale.

Twenty years of ecosystem response after clearcutting and slashburning in conifer forests of central British Columbia, Canada.

Forests are being clearcut over extensive areas of western North America, but plant community response to harvesting and slashburning under varying climatic conditions in central British Columbia, Canada is still largely unknown. Evaluation of resilience is hampered by the short history of logging, lack of long-term experiments and methodological limitations. To test the effect of clearcut logging, prescribed burning and reforestation on forest resilience, we recorded vascular plant cover repeatedly after treatment between 1981 and 2008 in 16 permanent research installations in three biogeoclimatic zones: Engelmann Spruce-Subalpine Fir, Interior Cedar-Hemlock and Sub-Boreal Spruce. We created a plant-trait dataset for the 181 recorded species to define plant functional types representing groups of plants that behave in similar ways and/or produce similar ecological outcomes. These plant functional types, along with taxonomic analysis of diagnostic and indicator species, were then used to evaluate plant community response to disturbance. Twenty years post-treatment, species diversity increased in all zones and plant abundance was greatest in the Interior Cedar-Hemlock. Cover of understory plant functional types associated with mature conifer forests increased in all zones, constituting a significant proportion (> 40%) of the vegetation community by year 20. Response patterns varied by zone and with time. Understory species diagnostic of mature forests were present in all zones by year 20, but we identified indicator species sensitive to slashburning or requiring more time for recovery, including white-flowered rhododendron (Rhododendron albiflorum) and devil's club (Oplopanax horridus). Overall, loss of compositional or functional diversity following harvest and site remediation was not detected, suggesting that montane and subalpine forests in British Columbia are resilient to this treatment. However, because these forests can be slow to recover from disturbance, the post-disturbance assessment window of this study may not have been long enough to detect diminishment of ecosystem resilience.

Effects of opening size and microsite on performance of planted tree seedlings in high-elevation Engelmann spruce–subalpine fir forests managed as mountain caribou habitat in British Columbia

Old-growth, high-elevation spruce–fir forests of the Quesnel Highland in south-central British Columbia provide winter habitat for threatened mountain caribou (Rangifer tarandus caribou (Gmelin)) and contain valuable wood resources. A group selection silvicultural system may protect caribou habitat and allow some timber extraction, if combined with timely regeneration and an extended rotation length. Sporadic seed production can limit natural regeneration and planting may be required to ensure successful regeneration after harvest. However, the opening sizes and planting microsites required for adequate tree growth and survival in these high-elevation sites are unknown. We examined, for 15years following planting, how growth and survival of planted subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce (Picea engelmannii Parry ex. Engelm.), and lodgepole pine (Pinus contorta Dougl. Ex Loud.) varied with harvest opening size (0.03, 0.13, 1.0ha), planting microsite (raised, protected, rotten wood, scarified, and a control) and elevation.Survival and growth was less in the higher elevation sites and generally increased with opening size, with the increase greater in the lower elevation sites. Survival varied from 12% for lodgepole pine in small openings at higher elevation to 82% for fir in large openings at lower elevation. Overall, fir had the greatest survival. Fir growth increased the most with opening size at higher elevation; pine growth increased the most with opening size at lower elevation. Survival was generally greater on raised, protected, or rotten wood microsites. Growth varied less across microsites than did survival and also varied less across microsites than across opening sizes or elevations. Increased seedling growth and survival for all species was associated with treatments that had earlier snowmelt and higher soil temperatures. Two cycle budworm (Chroistoneura biennis Freeman) decreased seedling growth in years of heavy infestation. In higher elevation sites, pine had the greatest average height, but relatively low survival and vigor. The poor survival of pine, its lower long-term projected growth rates, and a crown structure which does not facilitate lichen accumulation and its accessibility to caribou, make pine unsuitable for regenerating these forests managed for mountain caribou. Using the group selection silvicultural system on appropriate sites with openings greater than 0.13ha and with optimal planting microsites should allow for some extraction of timber while maintaining the old-growth attributes needed for caribou habitat in these subalpine forests.

Quantification of Dryocoetes confusus-caused mortality in subalpine fir forests of southern British Columbia

The western balsam bark beetle, Dryocoetes confusus Swaine (Coleoptera: Scolytinae), is considered the most destructive mortality agent in high elevation subalpine fir ecosystems, yet the actual impact of this beetle is not well quantified. Past estimates of in-stand losses from D. confusus in subalpine fir-dominated ecosystems have been unreliable due to historically limited and sporadic aerial survey coverage in British Columbia prior to the 1990’s. Tree level aerial assessment of mature subalpine fir in southern British Columbia in 1996–1997, and again in 2014, found mortality from this beetle to be as high as 70%, with mean annual mortality rates ranging from less than one percent to 1.6% in some of the ecosystems surveyed. Over 10% of 101–120year old stands surveyed in 1996–1997 had no visible mortality, and the mean percent mortality of this youngest cohort was 11% compared to over 17% mortality in all older age classes. By the second survey time, all age classes saw mean mortality estimates more than double, and all stands had some level of D. confusus attack. The highest increase in mortality was recorded in stands over 250years of age. Stands surveyed in the driest, coldest Engelmann Spruce-Subalpine Fir ecosystem in southern British Columbia sustained the highest levels of attack between survey times, averaging slightly less than 27% mortality, and by 2014 total subalpine fir mortality averaged more than 46%. The rate of mortality over the past two decades has increased. As extreme weather events become more common, particularly in wetter subalpine fir ecosystems, mortality from western balsam bark beetle will be amplified, causing both ecological and economic repercussions in these ecosystems. Results clearly show that subalpine fir stands over 100years in all ecosystems sustain continuous attack from D. confusus. To minimize future losses to this bark beetle, subalpine fir stands should be managed for a rotation age less than 100years and mixed species stands promoted where climatically feasible.

Post-glacial diatom-inferred aquatic changes in Sicamous Creek Lake, British Columbia, Canada

Diatom analyses of sediments from a high elevation lake situated in an Engelmann Spruce - Subalpine Fir (ESSF) forest of south-central British Columbia, Canada, reveal long-term climate and water chemistry change. During the transition from the late-glacial / Pleistocene to the xerothermic early Holocene, small, benthic Fragilaria diatoms species that grew under low light conditions in Sicamous Creek Lake gave way to planktonic Cyclotella species that require open-water conditions. Warm temperatures in the mesothermic Holocene are indicated by smaller Cyclotella species and large, benthic pennate diatoms. Diatom communities reflected Neoglacial cooling in the late Holocene, with abundant Nitzschia fonticola and Achnanthes minutissima. Small, benthic Fragilaria regained abundance, suggesting cooling and conditions similar to the late-glacial interval. Diatom community composition responded to the deposition of the Mt. Mazama and Mt. St. Helens tephras, though the Mazama eruption caused greater change in relative abundance of various taxa within the assemblage. Correspondence analysis shows distinct communities have occurred since the initiation of sedimentation, likely due to climate controlled landscape and vegetation changes; diatom-inferred pH values using various models and training sets show limited acidification change occurred through the lake’s history.

Decline of planted lodgepole pine in the southern interior of British Columbia

Lodgepole pine is extensively planted across western Canada but little is known about development of these stands beyond the juvenile stage. We quantified stocking status and damage incidence in sixty-six 15- to 30-year-old lodgepole pine plantations that had previously been declared free-growing in the southern interior of British Columbia. The stands were located in six biogeoclimatic zones: Engelmann Spruce-Subalpine Fir (ESSF), Montane Spruce (MS), Interior Cedar-Hemlock (ICH), Interior Douglas-fir (IDF), Sub-Boreal Spruce (SBS), and Sub-Boreal Pine-Spruce (SBPS). Free-growing standards were no longer met on 27% of plantations, with the worst performance (70% no longer free-growing) in the Interior Cedar-Hemlock forests. Natural regeneration was common but it was half the size of lodgepole pine. Biotic damage, especially hard pine stem rusts, was the dominant factor reducing free-growing densities. Stands were at greater risk of reduced stocking where summer precipitation was higher or soil moisture regimes were wetter and where stands had been broadcast-burned prior to planting or received secondary treatments of brushing or pruning. Reforestation policies that encourage widespread planting of lodgepole pine, particularly in areas where lodgepole pine has limited natural occurrence such as in the ICH zone, should be reconsidered given that health problems are extensive and are expected to increase with climate change.Key words: Pinus contorta, lodgepole pine, free-growing, stocking, forest health, damage, disease

Clearcut harvesting effects on soil and creek inorganic nitrogen in high elevation forests of southern interior British Columbia

Responses of both soil and stream inorganic nitrogen (N) after operational clearcut harvesting were explored in two high elevation British Columbia Engelmann spruce-Subalpine fir (ESSF) forests. At one study site, net N mineralization was measured between 1 and 11 yr after harvest. At a second site, for 3 yr after harvesting, available soil ammonium and nitrate were measured using ion exchange resins, and drainage losses of N were estimated using tension lysimeters and soil water balance models. Stream water N concentrations were also measured in one unlogged, and two logged watersheds at the second study area for 12 yr, both pre- and post-clearcut harvesting. Growing season as well as over-winter increases in post-harvest soil nitrate were detected after 3 yr, and the increases were apparent for up to 11 yr. Seasonal losses of N in drainage were greater in clearcut soils than in the forest soils in year 2 for ammonium and in years 2 and 3 for nitrate. A high proportion of the N was lost in drainage during snowmelt. Stream water ammonium in all three streams and nitrate in the unlogged and one harvested creek remained at or below the detection level. In the third creek, the frequency of detection and concentrations of nitrate peaked 2 to 3 yr after 30 to 57% of the watershed was harvested. The annual peak in NO3-N concentrations occurred immediately before the snowmelt-driven stream flow peak. Drainage losses and stream N fluxes were both small, relative to the total soil N content. Key words: Nitrogen, N mineralization, nitrate, harvesting, leaching, stream N, snowmelt

Potentials of Natural Tree Regeneration after Clearcutting in Subalpine Forests

Abstract Regeneration of interior mountain forests still is not adequately understood, although these forests are subject to intensified use over the last decades. We examined factors influencing the success of natural tree regeneration after harvesting in the Engelmann spruce–subalpine fir zone of the Monashee Mountains, British Columbia, Canada. Distance from the forest edge was an important factor for regeneration; at distances exceeding 70 m from the forest edge only 50% of plots showed sufficient natural regeneration to meet stocking targets compared with 90% of plots closer to forest edges. Seedling density and growth were superior in the more protected southern portions of clearcuts. Seedling growth was less in plots containing high cover of downed woody debris. There was no relationship between understory plant diversity or composition and tree seedling regeneration. However, cover of fireweed (Epilobium angustifolium) had a significant negative relationship with density but not growth of tree seedlings, particularly for lodgepole pine (Pinus contorta var. latifolia). Cover of fireweed decline substantially within the first 10 years after clearcutting. We conclude that natural regeneration of trees has potential to help achieve stocking targets and also to maintain natural diversity of tree species if spatial constraints, especially thresholds in clearcut size, are considered.

Holocene Climatic Change and Landscape Response at Cathedral Provincial Park, British Columbia, Canada

Environmental sensitivity to temperature change was established by comparing pollen, plant macrofossils, macroscopic charcoal, and sediment yield data from Lake of the Woods, Cathedral Provincial Park in the Cascade Mountains of southern British Columbia, Canada, to an independent record of midge-inferred paleotemperature. Steppe vegetation with some spruce and fir occurred initially, developing into pine forests in the warm early Holocene. These forests burned often, preventing spruce and fir succession. Once established, the forests retained an Engelmann Spruce-Subalpine Fir character. After 8000 cal BP, in warm but wetter conditions, the forest contained less pine and fires burned less frequently. About 4000 cal BP, cooler temperatures resulted in closure of the Engelmann Spruce-Subalpine Fir forests and a further reduction in fire frequency. Sediment yield results suggest a stable environment throughout the Holocene, likely due to sediment trapping in two upstream lakes. Midge-inferred temperatures correspond closely with a consensus reconstruction of temperatures from southern British Columbia, however Cathedral Provincial Park terrestrial ecosystems were not as sensitive to past climate change when compared to other nearby Engelmann Spruce-Subalpine Fir sites.

The influence of wildfire, logging and residual tree density on bird communities in the northern Rocky Mountains

By emulating natural disturbances like wildfire, managers hope to maintain biodiversity in managed forests. Leaving residual live trees in harvested areas is an important component of this strategy. However, the influence of this approach on songbird communities is largely unknown. We surveyed songbirds in 166 stands in the Rocky Mountains in BC, Canada, that had been logged or burned by wildfire. Stands were located in mid or high elevation biogeoclimatic zones, and varied from 7 to 45 years since disturbance and in density of residual trees from 0 to 320 conifer overstory, 0 to 832 conifer understory, and 0 to 68 broadleaf trees/ha. Although differences in bird communities between burned and logged stands of similar ages were detected, these differences were not consistent between biogeoclimatic zones, nor did they explain a large amount of the variation in bird communities. Logged stands had a higher density of birds, but expected species richness did not differ between logged and burned stands. All but a few rare species were detected in both disturbance types. Of 26 species analysed in detail, densities of 14 were greater in logged stands, 6 were greater in burned stands, and 6 were not significantly different between disturbance types. The bird community, bird abundance and densities of individual species were influenced by residual tree density and type. As time since disturbance increased, bird communities in burned and logged stands in the Engelmann Spruce-Subalpine Fir zone became more similar, but those in the Montane Spruce zone became less so, likely due to differences in residual tree density. Results suggest differences in bird communities in logged and burned stands ≥7 years post-disturbance are mainly in abundance rather than community composition, but abundances of individual species can be significantly influenced by residual tree density and type. Managers can influence the abundance of some species in harvested areas by manipulating the type and density of residual trees.

Spatial and temporal variation in historic fire regimes in subalpine forests across the Colorado Front Range in Rocky Mountain National Park, Colorado, USA

AbstractAim The historical variability of fire regimes must be understood in the context of drivers of the occurrence of fire operating at a range of spatial scales from local site conditions to broad‐scale climatic variation. In the present study we examine fire history and variations in the fire regime at multiple spatial and temporal scales for subalpine forests of Engelmann spruce–subalpine fir (Picea engelmannii, Abies lasiocarpa) and lodgepole pine (Pinus contorta) of the southern Rocky Mountains.Location The study area is the subalpine zone of spruce–fir and lodgepole pine forests in the southern sector of Rocky Mountain National Park (ROMO), Colorado, USA, which straddles the continental divide of the northern Colorado Front Range (40°20′ N and 105°40′ W).Methods We used a combination of dendroecological and Geographic Information System methods to reconstruct fire history, including fire year, severity and extent at the forest patch level, for c. 30,000 ha of subalpine forest. We aggregated fire history information at appropriate spatial scales to test for drivers of the fire regime at local, meso, and regional scales.Results The fire histories covered c. 30,000 ha of forest and were based on a total of 676 partial cross‐sections of fire‐scarred trees and 6152 tree‐core age samples. The subalpine forest fire regime of ROMO is dominated by infrequent, extensive, stand‐replacing fire events, whereas surface fires affected only 1–3% of the forested area.Main conclusions Local‐scale influences on fire regimes are reflected by differences in the relative proportions of stands of different ages between the lodgepole pine and spruce–fir forest types. Lodgepole pine stands all originated following fires in the last 400 years; in contrast, large areas of spruce–fir forests consisted of stands not affected by fire in the past 400 years. Meso‐scale influences on fire regimes are reflected by fewer but larger fires on the west vs. east side of the continental divide. These differences appear to be explained by less frequent and severe drought on the west side, and by the spread of fires from lower‐elevation mixed‐conifer montane forests on the east side. Regional‐scale climatic variation is the primary driver of infrequent, large fire events, but its effects are modulated by local‐ and meso‐scale abiotic and biotic factors. The low incidence of fire during the period of fire‐suppression policy in the twentieth century is not unique in comparison with the previous 300 years of fire history. There is no evidence that fire suppression has resulted in either the fire regime or current forest conditions being outside their historic ranges of variability during the past 400 years. Furthermore, in the context of fuel treatments to reduce fire hazard, regardless of restoration goals, the association of extremely large and severe fires with infrequent and exceptional drought calls into question the future effectiveness of tree thinning to mitigate fire hazard in the subalpine zone.

Advanced regeneration and seedling establishment in small cutblocks in high-elevation spruce–fir forest at Sicamous Creek, southern British Columbia

We examined the potential of natural regeneration for stocking 1-ha patch cuts in high-elevation Engelmann spruce (Picea engelmannii Parry) – subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests. Using the Sicamous Creek Silvicultural Systems site, which was harvested during winter 1994–1995, we established 1-m2 plots in patch cuts, forest edge, and untreated control forest. We marked and recorded microsite characteristics for all advanced regeneration and new recruits for up to 5 years; over 12 000 individuals were included. Advanced regeneration was abundant and was about one-quarter spruce. Spruce and fir germinants occurred in all years, but numbers varied greatly, with a very large cohort in 1998. Both advanced regeneration and new recruits were concentrated on decaying logs. Mortality of advanced regeneration was high in the patch cuts following harvest, but subsequent survival was good, approaching rates in the untreated forest within 4 years. Survival rates were higher for spruce than fir, but differed little among surface types and microtopographic positions. Survival of new recruits was high, approximately 50% the first year and 70% during the second, and was similar between spruce and fir. If the 1998 cohort has similar survival, the patch cuts could be adequately stocked. Use of natural regeneration, in combination with infill planting, is a viable option for stocking small openings in wet high-elevation forests in southern British Columbia.

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.

Resistance of forest songbirds to habitat perforation in a high-elevation conifer forest

We examined responses of songbirds breeding in high-elevation Engelmann spruce – subalpine fir (Picea englemannii Parry ex Engelm. – Abies lasiocarpa (Hook.) Nutt.) forests to four perforation harvest patterns near Sicamous, British Columbia. Each treatment removed approximately 30% of the timber volume but varied the size of openings from 10-ha clearcuts to small gaps (<0.01 ha), where individual trees were removed. Abundance and diversity of breeding songbirds were monitored over a 4-year period, including 2 years each of pre- and post-harvest conditions. Two-thirds of the original songbird assemblage consisted of mature forest species that showed only modest changes in relative abundance following harvest. Two species showed significant responses to harvesting: golden-crowned kinglet (Regulus satrapa Lichtensteins) declined significantly postharvest, with the largest declines occurring in single-tree and 10-ha treatments; and dark-eyed junco (Junco hyemalis L.) responded positively to harvest. At high elevations, 30% volume removal allowed much of the songbird community to be accommodated immediately after harvest. Future research should address whether the apparent short-term accommodation of high-elevation birds persists across time and as more of the continuous forest cover is removed.

Temperature sensitivity of mineral N transformation rates, and heterotrophic nitrification: possible factors controlling the post-disturbance mineral N flush in forest floors

A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH 4 + and NO 3 − concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH 4 + transformations rates ranged between 20 and 120 μg N (g forest floor) −1 day −1 at the ESSF site, and between 15 and 40 μg N (g forest floor) −1 day −1 at the CWH site. Higher temperature increased gross NH 4 + transformation rates in forest floor samples at both sites, but the average Q 10 value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots ( Q 10=4.31) than in old-growth plots ( Q 10=1.98). Gross NO 3 − transformation rates ranged between 10 and 32 μg N (g forest floor) −1 day −1 at the ESSF site, and between 10 and 24 μg N (g forest floor) −1 day −1 at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO 3 − transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH 4 + flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO 3 − flush to the proportion of heterotrophic nitrifiers.

Analytical methods for defining stand–clearcut edge effects demonstrated for N mineralization

Edge effects are becoming an important forest management consideration, but information regarding the influence of edges on N cycling variables has not been well documented. In addition, the quantification of edge effects can benefit from the application of complementary spatial analysis methods. Forest floor N mineralization and environmental variables were intensively measured 5 years after harvest along transects crossing the north and south edges of a 1-ha clearcut, in a high-elevation Engelmann spruce – subalpine fir forest. Wavelet analysis and depth-of-edge influence (DEI) methods were used to locate and measure the spatial extent of edge effects on N mineralization. Then variance partitioning (partial redundancy analysis) was used to examine the influence of edges on N mineralization relative to the influence of other environmental factors. Initial NO3-N content and net nitrification markedly increased in the opening within 2–6 m of each edge. Net ammonification did not exhibit obvious edge-related spatial patterns. Spatial patterns of nitrification appeared to be more closely related to spatial changes in substrate quality than to soil temperature and moisture. Results of the wavelet and DEI analyses provided quantification of locations and functional extents of edge effects.

Small mammal response to group selection silvicultural systems in Engelmann spruce-subalpine fir forests

We measured small mammal response to several different group selection silvicultural systems that varied by opening size (0.03, 0.13, and 1.0 ha) but maintained a consistent 30% area removal. The southern redbacked vole (Clethrionomys gapperi), followed by the common shrew (Sorex cinereus) and dusky shrew (S. monticolus), were the most abundant species pre- and post-harvest. There was no evidence that the minimum number alive estimates for red-backed voles differed significantly (α = 0.05) among treatments pre-harvest (ρ = 0.67) or post-harvest (1993, ρ = 0.98; 1994, ρ = 0.84). However, red-backed voles used harvested openings less than the surrounding forest within each treatment. Common shrews showed some preference for the unlogged controls and the treatment units containing 1.0-ha openings. Dusky shrews showed no treatment preference. Overall, we conclude that the group selection silvicultural systems did not substantially change the relatively rich, abundant small mammal community present before harvesting.

Litterfall, growth, and turnover of arboreal lichens after partial cutting in an Engelmann spruce – subalpine fir forest in north-central British Columbia

Dynamics of canopy lichens were investigated for 2 years after group and single-tree selection harvesting in a Picea engelmannii Parry ex Engelm. – Abies lasiocarpa (Hook.) Nutt. forest in north-central British Columbia. Litter fall was collected in 1-m2 traps set on the forest floor and estimates of Alectoria sarmentosa (Ach.) Ach. and Bryoria spp. litterfall adjusted for decomposition in the snowpack. Growth rates of A. sarmentosa and Bryoria fuscescens (Gyeln.) Brodo & D. Hawksworth were measured by repeatedly weighing samples maintained in mesh enclosures in the canopy. Standing crop of canopy lichens was measured in concurrent studies. There appeared to be a small postharvest pulse of litterfall in the single-tree selection area, but it was largely masked by natural variation. Ninety percent of the lichen litterfall was deposited within 10 m of the nearest tree. Annual relative growth rates of A. sarmentosa and B. fuscescens ranged from 2.7% to 10.4% and from 2.4% to 9.1%, respectively. Growth rates of both species were as high in the single-tree selection area as in the unlogged control area but were reduced along the edges of group selection openings. Growth and turnover (annual litterfall as a percentage of standing crop) of Alectoria were approximately in balance, but growth of Bryoria exceeded turnover. In situ decomposition of Bryoria may account for the difference.

Coarse woody debris in the old-growth forests of British Columbia

This paper synthesizes data extracted from the literature and data collected in various studies by the author on the quantity, characteristics, and functional importance of coarse woody debris (CWD) in the old-growth forests of British Columbia (B.C.). There is little agreement in the literature about the minimum diameter of CWD or the number of decay classes recognized. In western North America, five decay classes are commonly used, but recent studies suggest fewer decay classes are preferable. Comparisons among decay classes and biogeoclimatic zones and subzones in B.C. reveal that quantities and volumes are greatest (up to approximately 60 kg/m2 and approximately 1800 m3/ha, respectively), and CWD persists the longest (sometimes in excess of 1000 years) in the Coastal Western Hemlock (CWH) biogeoclimatic zone. The quantity and ground cover of CWD increase with forest productivity. Persistence of CWD has varied from less than 100 to over 800 years in two coastal (CWH and Mountain Hemlock (MH)) and three interior (Interior Douglas-fir (IDF), Interior Cedar–Hemlock (ICH), and Engelmann Spruce – Subalpine Fir (ESSF)) biogeoclimatic zones. Trends in CWD quantity with forest age in managed coastal B.C. forests suggest a U-shaped curve, with greater quantities occurring in recent cutovers than in old-growth forests, and lowest quantities occurring in middle-aged forests. This may be the normal trend in CWD with forest age, with departures from this trend resulting from disturbance- or environment-specific factors. Relatively large amounts of data exist on the characteristics of CWD in the CWH, IDF, ICH, ESSF, and Boreal White and Black Spruce (BWBS) biogeoclimatic zones, but such data for the Coastal Douglas-fir, Sub-Boreal Pine–Spruce, Sub-Boreal Spruce (SBS), and Spruce–Willow–Birch biogeoclimatic zones appear relatively sparse. There have been few studies of the functional role of CWD in B.C. forests, but those studies that have been completed indicate that CWD is an important habitat component for some plant and animal species. A total of 169 plant species, including >95% of all lichens and liverworts, were found to grow on CWD in old-growth forests in the CWH, MH, IDF, ICH, and ESSF biogeoclimatic zones. One third of these species were restricted to CWD. Studies in several biogeoclimatic zones have found that CWD provided preferred habitat for and was associated with higher populations of some small animal species, such as shrews, some voles, and some salamanders, in old-growth forests, but the effects varied with species and biogeoclimatic zone. The nutrient cycling role of CWD is not yet well known, but it currently appears to be relatively insignificant in B.C. old-growth forests. Although it has been considered that CWD could increase mineral soil acidification and eluviation, no evidence for this was found in a study of the CWH, MH, IDF, ICH, ESSF, BWBS, and SBS biogeoclimatic zones. Future studies of the functional role of CWD should consider both scale (square metre vs. hectare) and temporal (changes in CWD with forest age) issues, as studies including these are sparse and both may be important. Key words: biogeoclimatic zones, British Columbia, coarse woody debris, old-growth forests.

Effects of harvesting on fine root biomass and decomposition in an Engelmann spruce – subalpine fir forest

The effect of timber harvesting on the biomass, nutrient standing crop, and decomposition of fine roots (<2 mm) was studied in a high elevation, Engelmann spruce (Picea engelmannii Parry ex Engelm.) – subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forest. Root dynamics were compared in openings of different sizes. The sequential core method was used to collect fine root samples over 4 years. Differences in fine root biomass between opening sizes were most significant for the active fine root portion and were most pronounced in the fall compared with the spring. Active fine root biomass was significantly lower in the 10-ha clearcuts (164 kg/ha) compared with control plots (275 kg/ha). Furthermore, active fine root biomass was often lower in the 1.0-ha opening than in the 0.1-ha and control plots. A similar trend was established for inactive fine root biomass, although this was not consistent over sampling years. Nutrient concentrations of K, but no other elements, were higher in control plots. Nutrient standing crops, however, followed trends observed in fine root biomass. In the 10-ha clearcuts, the largest changes in fine root biomass occurred at the edge of the opening. The findings suggest that small (<10 ha) cutblocks may maintain greater fine root longevity.