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  • 1
    Publication Date: 2007-06-01
    Description: We compared prefire and postfire organic-layer depths in boreal forest types (14 fires) across Canada, and examined tree recruitment as a function of depth. There was extensive within-stand variation in depth, much of it due to clustering of thinner organic layers around boles. There were no significant differences in postfire organic-layer depth among sites with different prefire forest species composition, but sites in the eastern boreal region had thicker postfire organic layers than those in the western boreal region. Mean organic-layer depth was much greater in intact stands than after fires; overall, fire reduced organic-layer depth by 60%, largely because of increases in the area of thin (
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 2
    Publication Date: 2004-02-01
    Description: Composition, structure, and diversity of vascular and nonvascular plant communities was compared 3 years after wildfire and clear-cutting in mesic trembling aspen (Populus tremuloides Michx.) forests of the southern Canadian boreal forest. We examined mean response to disturbance and variability around the mean across four to five spatial scales. Four 1997 wildfires were located near Timmins, Ontario, and ten 19961997 clearcuts were located adjacent to the wildfires. We randomly located plots within mesic, aspen-dominated stands selected to minimize predisturbance environmental differences. Correspondence analysis separated wildfire and clearcut samples based on community composition: wildfires had more aspen suckers, Diervilla lonicera Mill., and pioneering mosses; clearcuts had more under story tall shrubs, forbs, bryophytes, and lichens. Live tree basal area averaged 1.7 m2/ha in wildfires and 1.8 m2/ha in clearcuts (p = 0.59), and understory community structure (the horizontal and vertical distribution of live and dead plant biomass) was not markedly different. Clearcuts had higher species richness with greater variance than wildfires across all spatial scales tested, but differences in beta and structural diversity varied with spatial scale. Generally, clearcutwildfire differences were more evident and wildfire variability greater at larger analytical scales, suggesting that plant biodiversity monitoring should emphasize cumulative effects across landscapes and regions.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 3
    Publication Date: 2005-08-01
    Description: Organic matter removal and reduced soil aeration porosity during logging are important factors influencing the sustained productivity of managed forest ecosystems. We studied the 4-year effect of these factors on diversity and composition of a trembling aspen (Populus tremuloides Michx.) plant community in northeastern British Columbia, Canada, in a completely randomized experiment with three levels of organic matter removal (tree stems; stems and slash; stems, slash, and forest floor) and three levels of soil compaction (none; intermediate (2-cm impression); heavy (5-cm impression)). Tree stem removal caused the greatest change in species diversity (30% of variance; ANOVA p ≤ 0.01), increasing the dominance of aspen and Calamagrostis canadensis (Michx.) Beauv. over other species. Slash removal had little effect. Forest floor removal caused the greatest compositional change (37% of variance; MANOVA p = 0.001), favoring ruderal over bud-banking species. Presence or absence of forest floor better explained these changes than any soil physical or chemical parameter. Although dominance of aspen over Calamagrostis was positively correlated with soil aeration porosity (R2 = 0.50, n = 27, p 
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 4
    Publication Date: 2017-12-01
    Description: Lodgepole pine (Pinus contorta var. latifolia Engelm.) ecosystems of central British Columbia face cumulative stresses, and management practices are increasingly scrutinized. We addressed trade-offs between “light-on-the-land” versus more aggressive silvicultural approaches by examining plant communities and indicator species (non-natives, berry producers, epiphytes, mycotrophs, pine rust alternate hosts) across a gradient of five or six site preparation treatments at the Bednesti trial (established 1987). We tested whether more severe site preparation (i) caused plant community composition to diverge from a 35- to 46-year-old reference forest, (ii) accelerated succession by hastening crown closure, or (iii) delayed succession by promoting seral species. Nonmetric multidimensional scaling (NMDS) ordination showed all treatments converging toward the reference forest composition. At 10 years, succession was incrementally delayed by more severe treatments; at 25 years, only burned windrows were still delayed. Mixed-effects models based on site preparation severity were better than crown closure models for 11 of 13 variables tested, suggesting that mostly belowground processes drive succession in these infertile ecosystems. Invasive hawkweeds persisted on all treatments at 25 years. Limited, contradictory data did not support using mechanical or fire treatments to reduce alternate hosts of pine stem rusts. Long-term trials such as Bednesti highlight the need for ecosystem-specific strategies and diverse approaches to accommodate conflicting benefits and risks of disturbance in forests.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 5
    Publication Date: 2005-08-01
    Description: Retaining organic matter and preventing soil compaction are important factors affecting the sustainability of managed forests. To assess how these factors affect short-term ecosystem dynamics, pre-treatment and 1 year and 5 year post-treatment soil properties and post-treatment tree growth responses were examined in a boreal trembling aspen (Populus tremuloides Michx.) dominated ecosystem in northeastern British Columbia, Canada. The experiment used a completely randomized design with three levels of organic matter removal (tree stems only; stems and slash; stems, slash, and forest floor) and three levels of soil compaction (none, intermediate (2-cm impression), heavy (5-cm impression)). Removal of the forest floor initially stimulated aspen regeneration and significantly reduced height growth of aspen and white spruce (Picea glauca (Moench) Voss). The compaction treatments had no effect on aspen regeneration density. At year 5, heights of both aspen and white spruce were negatively correlated (r2 〉 0.31, p 〈 0.0001) with upper mineral soil bulk density and were lowest on forest floor removal treatments, where minimal recovery from compaction was observed. There was some evidence for recovery of soil properties to preharvest conditions where expansion of herbaceous vegetation increased soil organic matter.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 6
    Publication Date: 1995-10-01
    Description: Effects of forest disturbance and soil moisture levels on establishment of red alder (Alnusrubra Bong.) seedlings were studied at four sites representing a climatic moisture gradient within the central Coast Range of Oregon. On average, there was no difference in seedling emergence between recent clearcuts and second-growth forests, but emergence was much higher on mineral soil than on organic seedbeds. Emergence, on both types of seedbed, was positively correlated with spring soil moisture conditions (R2 = 0.60). Seedling survival, on the other hand, differed greatly between clearcut and forest. In clearcuts, heat and drought injuries were the primary causes of seedling mortality. In the forest, seedlings had poor vigour and quickly succumbed to pathogens, herbivores, and rain splash. First-year survival rates were strongly correlated with minimum summer soil moisture levels (R2 = 0.71). Height growth of seedlings on clearcuts (2–5 cm after 1 year; 8–23 cm after 2 years) was much slower than rates typically described for red alder. Best establishment occurred on skid trails and landings, suggesting that young seedlings may suffer less from heat or moisture stress on these heavily disturbed microenvironments.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 7
    Publication Date: 1999-08-01
    Description: Ten-year response of plant communities to disk trenching, plowing, rotoclearing and windrow burning was studied on two contrasting sites to address concerns that mechanical site preparation reduces structural and species diversity. Cover and height of all species on randomly located subplots within 0.05- to 0.075-ha treatment plots were used to develop indices of volume, structural diversity, and species diversity; to ordinate the plots; and to correlate species diversity with crop-tree performance. At both sites, community response was strongly influenced by the severity of site preparation. On a boreal site dominated by willow (Salix L. spp.), green alder (Alnus crispa (Ait.) Pursh ssp. crispa) and trembling aspen (Populus tremuloides Michx.), site preparation increased structural diversity and had little effect on species diversity. High-severity treatments increased non-native species abundance 10- to 16-fold while only marginally enhancing growth of planted white spruce (Picea glauca (Moench) Voss) over medium-severity treatments. On a nutrient-poor sub-boreal site, species diversity declined with increasing treatment severity and with increasing lodgepole pine (Pinus contorta var. latifolia Engelm.) stem volume. Velvet-leaved blueberry (Vaccinium myrtilloides Michx.) was highly sensitive to mechanical disturbance. Moderate mechanical treatments appear to improve conifer performance while causing little change to plant communities, but high severity treatments can cause substantial change.
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    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 8
    Publication Date: 1993-07-01
    Description: Red alder (Alnusrubra Bong.) seed showing strong phytochrome activity in the laboratory was tested to determine whether the phytochrome effect could influence germination under light conditions experienced in the field. Seeds in sealed Petri dishes were placed beneath three types of overstory cover (clearcut (no overstory); Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) (coniferous evergreen overstory); and red alder (broad-leaved deciduous overstory)) and seven types of understory cover (control (complete darkness); uncovered; 1-cm mineral soil; leaf litter; moss; swordfern; and non-evergreen herbs). Germination was highest in clearcuts (68.6%), intermediate in Douglas-fir stands (47.4%), and lowest in red alder stands (11.7%). Covers of understory vegetation, leaf litter, and mineral soil significantly reduced germination, with the greatest reduction occurring where understory vegetation was dense enough to significantly reduce the ratio of red:far-red light. These findings concur with field studies of red alder seedling establishment and suggest that the phytochrome sensitivity of red alder seed plays an important role in this species' success on disturbed habitats.
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    Electronic ISSN: 1208-6037
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  • 9
    Publication Date: 2008-02-01
    Description: Stability and resilience of conifer-dominated vegetation communities following clear-cutting and slashburning in central British Columbia, were modeled across gradients of resource availability, fire return interval (FRI), and fire severity. We hypothesized that high resource availability and long fire-free intervals would enhance stability, whereas high resource availability and short fire-free intervals would confer resilience. Fire weather indices and pre- and post-burn fuel loads were recorded and vegetation regrowth monitored for 5–11 years at 12 sites. Stepwise regression was used to model rates of revegetation, increases in vascular species richness, and pre- and post-burn similarity of species composition as a function of the environmental variables. Predicted stability for four sub-boreal to subalpine vegetation communities with contrasting resource availability and FRI corresponded closely to our hypotheses. Rates of revegetation were more strongly correlated with resource availability, whereas composition-based response variables were more strongly correlated with the FRI. Based on revegetation rates, all ecosystems were predicted to have equal resilience. However, based on vegetation composition, mesic sub-boreal ecosystems were predicted to be more resilient than mesic subalpine ecosystems because the degree of change in species composition was less sensitive to increasing burn severity. More slashburned sites with a broader range of burn severities are needed to verify these preliminary models.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 10
    Publication Date: 2004-10-01
    Print ISSN: 0378-1127
    Electronic ISSN: 1872-7042
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Elsevier
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