Forest Floor Disturbance Research Articles

Cumulative effects of biomass harvesting and herbicide application on litter-dwelling arthropod communities in jack pine-dominated forests: 7th year postharvest assessment

Forest biomass harvest has the potential to provide feedstocks for energy production to offset fossil fuel consumption. However, concerns have been raised regarding the ecological sustainability of removing additional biomass from forests, in particular the impacts on biodiversity. In this paper, we used a suite of ground-dwelling arthropod taxa (ground beetles, spiders, and rove beetles) to measure community compositional changes along a gradient of biomass removal treatments 7 years postharvest, and compared against reference. Based on multivariate regression trees, changes in species composition reflected the intensity gradient of the biomass removal treatments or stand attributes associated with the level of forest floor disturbance across all arthropod groups. For each arthropod group, changes in composition were defined primarily by reductions or loss of abundant forest associated species and increases in the number and abundance of species associated with more xeric conditions and increased disturbance intensity. There were no differences between full-tree and tree-length treatments. Overall, results indicated a strong arthropod response to the removal of overstory, forest floor disturbance, and reductions in understory cover mostly resulting from the glyphosate applications. Arthropod recovery would benefit from overstory retention, reduction in forest floor disturbance, and judicious use of glyphosate.

Ground-dwelling arthropod response to fire and clearcutting in jack pine: implications for ecosystem management

We tested the response of species composition of three dominant litter-dwelling arthropod taxa (carabid beetles, spiders, and rove beetles) to wildfire and harvest. This study was conducted in north-central Ontario (47°42′N, 83°36′W) in jack pine (Pinus banksiana Lamb.) dominated stands in 2013 using pitfall trapping. Using 222 species (12 015 individuals), we compared the effects of disturbance using recently burned (3 years since fire) and clearcut sites (3 years since harvest; tree length, full tree, stump removal, and blading), as well as older, closed-canopy stands that have regenerated following clearcutting (51 years since harvest) and fire (92 years since fire), with multivariate regression trees. Taxa were more similar in the three controls (including recent fire) than between controls and harvest treatments, with increased forest floor disturbance in harvested plots being a likely explanation. In addition, taxa were different in the younger (51 years) harvest-origin plots than in the older (92 years) fire-origin plots, suggesting that communities had not yet recovered from the harvest disturbance possibly due to insufficient coarse woody debris in the younger stand. These results indicate that forest management practices that match natural forest floor disturbance could ameliorate short-term effects, whereas the maintenance of more coarse woody debris could reduce the recovery time of epigaeic communities.

Evidence of damage from exotic invasive earthworm activity was highly correlated to sugar maple dieback in the Upper Great Lakes region

Sugar maple (Acer sacharrum Marsh.) in the western Upper Great Lakes region has recently been reported with increased crown dieback symptoms, prompting investigation of the dieback etiology across the region. Evaluation of sugar maple dieback from 2009 to 2012 across a 120 plot network in Upper Michigan, northern Wisconsin, and eastern Minnesota has indicated that forest floor disturbance impacts from exotic invasive earthworms was significantly related to maple dieback. Other plot level variables tested showed significant relationships among dieback and increased soil carbon, decreased soil manganese, and reduced herbaceous cover, each of which was also be correlated to earthworm activity. Relationships between possible causal factors and recent growth trends and seedling counts were also examined. Maple regeneration counts were not correlated with the amount of dieback. The recent mean radial increment was significantly correlated with various soil features and nutrients. This study presents significant evidence correlating sugar maple dieback in the western Upper Great Lakes region with earthworm activity, and highlights the need for considering the impacts of non-native earthworm on soil properties when assessing sugar maple health and productivity.

Forest-Floor Disturbance Reduces Chipmunk (Tamiasspp.) Abundance Two Years after Variable-Retention Harvest of Pacific Northwestern Forests

Abstract We evaluated the two-year effects of variable-retention harvest on chipmunk (Tamias spp.) abundance () and habitat in mature coniferous forests in western Oregon and Washington because wildlife responses to density/pattern of retained trees remain largely unknown. In a randomized complete-block design, six treatments were applied to 13-ha units at three sites (blocks): four retention levels of original basal area (BA) in an aggregated tree pattern (100, 75, 40, and 15%) and two retention levels in a dispersed tree pattern (15 and 40%). Log-yarding method differed at each site (suspension cable, shovel-loader, or helicopter). We used an information-theoretic approach to compare six candidate regression models for their ability to predict treatment responses of chipmunk and associated habitat variables. Chipmunk had a positive linear relationship with retention level that predicted a 50% reduction in abundance as % BA retention decreased from 100 to 15% (R2 = 0.36). Disturbed soil cover was strongl...

Ectomycorrhizal fungal community assembly on regenerating Douglas-fir after wildfire and clearcut harvesting

Wildfire severity in forests is projected to increase with warming and drying conditions associated with climate change. Our objective was to determine the impact of wildfire and clearcutting severity on the ectomycorrhizal fungal (EMF) community of Douglas-fir seedlings in the dry forests of interior British Columbia, Canada. We located our study within and surrounding the area of the McLure fire (August 2003). We hypothesized that disturbance would affect EMF community assembly due to reductions in fungal inoculum. Five treatments representing a range of disturbance severities were compared: high severity burn, low severity burn, screefed clearcut (manual removal of forest floor), clearcut, and undisturbed forest. EMF communities in the undisturbed forest were more complex than those in all disturbance treatments. However, aspects of community assembly varied with disturbance type, where the burn treatments had the simplest communities. After 4 months, regenerating seedlings in the burn treatments had the lowest colonization, but seedlings in all treatments were fully colonized within 1 year. EMF communities were similar among the four disturbance types, largely due to dominance of Wilcoxina throughout the study period. However, forest floor retention influenced community assembly as the EMF in the clearcut treatment, where forest floor was retained, had levels of diversity and richness comparable to the undisturbed forest. Overall, the results suggest that increasing forest floor disturbance can alter EMF community assembly in the first year of regeneration. A correlation between poorly colonized seedlings and seedling productivity also suggests a role for productivity in influencing community assembly.

Influences of Mechanized Thinning and Prescribed Fire on Natural Regeneration in an Uneven-Aged Jeffrey Pine Stand

Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types.

Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota, USA

We investigated the effects of skidder traffic intensity, soil disturbance intensity, and canopy removal intensity on the richness, diversity, composition, and cover of the entire ground flora (woody and herbaceous vegetation ≤2 m tall), various individual life forms, invasive/noxious species, and species with different requirements with respect to moisture, nutrients, heat, and light (synecological coordinates) in a mesic northern hardwood stand 6 years after a clearcut-with-reserves regeneration harvest removed 50–100% of the canopy. Skidder traffic was restricted to a network of trails and a global positioning system (GPS) tracked skidder movement to quantify the number of passes at pre-established sampling points along the anticipated soil disturbance gradient on and off skid trails. Soil disturbance intensity within the top 15 cm of soil was quantified by relativized resistance to penetration (RRP) compared to untrafficked plots; post-harvest increases in RRP ranged from 81 to 272%. Regression analysis and ordination revealed a pattern of increasing difference from pre-disturbance composition with increasing skidder traffic (i.e., forest floor disturbance), with increased RRP (i.e., soil compaction) and (less so) canopy removal intensity. The ground flora shifted from interior forest species such as Anemone quiquefolia, Aralia nudicaulis, Clintonia borealis, Maianthemum canadense, and Oryzopsis asperifolia to more ruderal, invasive/noxious, and disturbed-forest species such as Aster lateriflorus, Cirsium spp., Phleum pretense, Rubus idaeus, and Trifolium spp. The relative resistance of the initial ground flora to change (inverse of the distances between pre- and post-harvest samples in ordination space) was nonlinearly related to skidder traffic intensity and linearly related to RRP, indicating that the largest compositional changes occurred with the first few passes of the skidder. Mean plot scores for the synecological coordinates revealed that the post-harvest species were on average less demanding of water and nutrients; the opposite was true for light. Plots exposed to less skidder traffic and RRP had higher herb cover and higher nutrient scores; those with more skidder traffic and higher RRP levels had higher shrub cover and higher light scores. We conclude that protection of the ground flora from forest floor and soil disturbance requires careful planning of skid trail networks. Concentrating skidder traffic to a designated skid trail system can result in less area disturbed and spatially connected networks of larger, untrafficked remnant forest patches that may maintain species that are sensitive to forest floor and soil disturbance.

Forest floor temperature and relative humidity following timber harvesting in southern New England, USA

Forest amphibians, especially salamanders, prefer forests with shaded, cool, and moist forest floors. Timber harvesting opens the forest canopy and exposes the forest floor to direct sunlight, which can increase forest floor temperatures and reduce soil moisture. These microclimatic changes can potentially degrade the harvested stand for amphibian habitat or affect other biotic resources or ecological processes at the forest floor and in the understory. The degree of forest floor disturbance is directly related to the intensity of harvesting, however, the duration of this effect is unknown. We conducted a study of forest floor temperature and relative humidity over a 12-year chronosequence (1993–2004) of timber harvests. We compared simultaneous, paired measurements of temperature and relative humidity at three positions (soil, forest floor, air) in harvested and control sites over three seasonal survey sessions. Vegetation composition and structure were measured at each survey location. Ambient weather conditions were recorded at three open-field locations across the study area.We recorded over 23,000 paired measures of temperature and relative humidity at all 12 harvested and control sites during each survey session. While we found significant effects of time-since-harvesting on differences in temperature between harvested and uncut sites, the average differences were generally small (<1°C). We observed no temporal pattern in temperatures with time-since-harvest in the harvested sites compared to uncut conditions. Time-since-harvest had no effect on differences in relative humidity between cut and uncut sites. The variation in forest floor microclimate among sites was large, likely due to small-scale differences in cutting intensity (retained canopy), understory vegetation growth, and microtopography or aspect. We conclude that timber harvesting, within the range of intensities assessed in this study, would have only minimal and short-term effects on forest floor microclimate. We suggest that the small differences we observed in forest floor temperatures and moisture between cut and uncut forest parcels would likely have minor effects on climatic aspects of forest amphibian habitat, and on climatic influences on other forest floor biota and ecological processes.

Effects of forest floor disturbances by mechanical site preparation on floristic diversity in a central Ontario clearcut

The effects of forest floor disturbance by six mechanical site preparation (MSP) treatments on structural and compositional diversity of early successional communities were examined in a clearcut in central Ontario. Periodic assessment of floristic diversity and abundance was performed to quantify treatment effects on species richness and abundance of three discrete plant life forms (cryptogam, herbaceous and woody) in the first five growing seasons after MSP. Botanical surveys of the surrounding uncut forest provided an estimate of pre-harvest forest species composition of the clearcut study site. Intensity of forest floor disturbance differed significantly among MSP treatments, creating a variety of microsites. The percentage of mineral soil exposure and abundance of downed woody material ranged from 7% to 52% and 18% to 1%, respectively, from the least to most severe treatments. Five years after MSP, 134 species (50 cryptogams, 47 herbaceous, 37 woody) were present in the clearcut study site, compared with 102 species (54 cryptogams, 25 herbaceous, 23 woody) in the uncut forest. Species richness and abundance of cryptogam, herbaceous and woody plant species increased with time after MSP, except for herbaceous species richness. MSP treatment significantly influenced species richness of cryptogams, herbaceous and woody plants, and abundance (percent cover) of woody plants. Treatment differences in richness and abundance were strongly correlated with intensity of forest floor disturbance. Scalping treatments that created the most mineral soil exposure and removed the most downed woody material typically supported the lowest species diversity and lacked several native forest species. Cryptogams were most affected by MSP, with higher richness and abundance where forest floor disturbance was relatively low. MSP did not affect the incidence of alien plant species: only two alien species were observed on the study site, representing less than 1% of total cover. Evaluation of MSP effects on early successional plant communities based on beta diversity in an ordination analysis revealed several distinct species groups associated with specific treatments. The relative amount of forest floor disturbance and downed woody material among treatments were strong predictors of species groupings within the ordination. Plant communities in slash piles were distinct from those resulting from MSP and contained several remnant forest species. Examination of species’ autecology provided supporting evidence that the displacement of downed woody material and forest floor organic layers was the leading cause of changes in species richness and abundance on this site.

Changes in soil properties, tree growth, and nutrition over a period of 10 years after stump removal and scarification on moderately coarse soils in interior British Columbia

Silvicultural site preparation treatments that involve severe soil and forest floor disturbance may, in the long-term, reduce soil productivity and negate the initial increased forest productivity obtained by controlling root diseases or vegetation. The effect of a range of stump removal treatments on selected soil chemical and physical properties, and growth of planted lodgepole pine ( Pinus contorta) and hybrid spruce ( Picea glauca (Moench) Voss × Picea engelmanii Parry), was examined at three sites in the Interior Cedar–Hemlock (ICH) zone of British Columbia. Changes in forest floor and mineral soil chemistry and bulk density were measured 1 year after treatment and again 9 years later. Tree growth and foliar nutrient status of planted seedlings were measured 3, 5 and 10 years after planting. Forest floor mass and depth were altered by treatment, and decreased significantly between years 1 and 10. Mineral soil bulk density was greater in all stump-removal treatments than in the non-stumped treatment in year 1; however, 10 years after treatment, bulk densities had decreased and no treatment effects were apparent. Changes in forest floor chemistry that were measured in year 1 had largely disappeared by year 10. Mineral soil chemical concentrations were not affected by treatment at any time, except for a significant increase in carbon (C) concentration between years 1 and 10. Lodgepole pine height and diameter were increased over the measurement period by the most intense, scarified treatment, whereas spruce growth was largely unaffected by stump removal treatment. Both tree growth and soil measurements suggest that, on the moderately coarse soils within the climatic regime of the present study, soil limits to tree growth have not been exceeded.

Reconstitution floristique et structurale d’une forêt de lauracées après coupe rase: une chronoséquence de 60 ans à La Palma (Îles Canaries)

We analyzed a post-clearcut chronosequence (0.5 to 60 years after harvesting) in the laurel forest of La Palma island (Canarian Archipelago) to determine the recovery of the stands with respect to species composition, richness, life strategies and structural parameters of the canopy. Multivariate analysis showed that exotic species, as well as annual ruderal species were confined to early-successional stages, while native perennials, typical of laurel forests, dominated the late-successional stages. Total species richness decreased significantly with time after clear-cutting. The relative fast recovery of understory native species may be due to low forest floor disturbance during harvesting. Shade-intolerant pioneer, pioneer-remnant and shade-tolerant late-successional species were the main life strategies of native tree species. Most structural parameters showed a continuous and monotonic increase (basal area, biomass) or decrease (density, percentage of photosynthetic biomass) during succession. Once clear-cutting, here performed with an interval of 8 years, is abandoned, the recovery of the laurel forest seems possible due to careful logging that protects the soil and a rapid asexual regeneration of native tree species, revealing this to be a sustainable management practice.

Regeneration Strategies, Disturbance and Plant Interactions as Organizers of Vegetation Spatial Patterns in a Pine Forest

To determine how vegetation pattern in early successional forests may be related to plant traits and types of disturbance, we measured percent cover of individual taxa annually in a South Carolina Pinus elliottii forest, starting one year before, and ending four years after harvest and tree girdling disturbances were applied. The 17 most important taxa surveyed were grouped into four regeneration strategies chosen a priori, and the spatial patterns of these groups and of the soil were investigated using global variability, semivariograms and kriged maps. We also examined spatial correlations across years, across taxa, and between species and soil disturbance. Seed bank taxa represented by Dichanthelium spp. increased rapidly and formed large patches, and then quickly declined. Taxa that regenerate by newly dispersed seeds, represented by Rhus copallina and Rubus spp. occurred at first in a few patches, and became widespread later. Stump sprouters, represented by Quercus spp. and Myrica cerifera, had rapid increases in cover, but their spatial patterns were largely determined by their pre-disturbance patterns. Prunus serotina, which relies on both sprouting and dispersed seed, had moderate cover and a random distribution. Within-species temporal correlation of spatial pattern was lower in girdled than in harvested plots, and was not clearly related to regeneration strategy. Forest floor disturbance was patchy and affected the pattern of Dichanthelium spp. in the harvested plots. Negative correlations between herbs and woody plants in harvested plots reflected the role of biotic (i.e., successional) filters on vegetation pattern. Surprisingly, no spatial correlations were detected between the nitrogen fixer, Myrica cerifera and other taxa in this N-limited system. In comparing the spatial and temporal patterns, we found kriged maps more informative than analysis of semivariograms alone. The maps and correlation statistics demonstrated that regeneration traits, spatial patterns of soil disturbances, and interactions among taxa influence dynamics of the spatial patterns of the plants. We also demonstrated that disturbance types affected the importance and interactions among these three factors, and caused different spatial patterns of the plant taxa.

The effect of shelterwood harvesting and site preparation on eastern red-backed salamanders in white pine stands

We studied the effects of the regeneration cut of the shelterwood system and four site preparation options on populations of eastern red-backed salamanders in 90–100-year-old white pine forests in central Ontario, Canada. We established the study in 1994 using a randomized complete block design with three replicates and five treatments: (1) no harvest, no site preparation; (2) harvest, no site preparation; (3) harvest, mechanical site preparation; (4) harvest, chemical site preparation; (5) harvest, mechanical and chemical site preparation. We applied harvest and site preparation treatments from fall 1995 to fall 1997. We collected pre-treatment data in spring and summer of 1995 and post-treatment data from 1998 to 2002. We monitored salamander abundance using a grid of 20 cover boards surveyed 10 times per year within each of the 15 treatment plots. We also quantified changes in overstory and understory cover, supply of downed woody debris, and disturbance to the forest floor. Our data suggest that shelterwood cutting and site preparation can have immediate negative effects on the abundance of red-backed salamander populations in pine forest. However, effects are relatively short lived (<5 years). Changes in abundance appeared to be related to overstory and understory cover, and forest floor disturbance.

Initial response of understorey vegetation to fire severity and salvage‐logging in the southern boreal forest of Québec

Abstract. In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage‐logging (clear‐cutting after fire). All 61 400‐m2 sampling sites were controlled for overstorey composition (Deciduous, Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem‐only and Whole‐tree Harvesting). Percent‐cover data of vegetation and post‐disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous‐Mixed sites, due to the release of the understorey from Sphagnum spp. dominance, this pattern being a function of FIS. On Deciduous‐Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage‐logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage‐logging was introduced. Salvage‐logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade‐tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.

Initial response of understorey vegetation to fire severity and salvage-logging in the southern boreal forest of Québec

Abstract. In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage-logging (clear-cutting after fire). All 61 400-m2 sampling sites were controlled for overstorey composition (Deciduous, Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem-only and Whole-tree Harvesting). Percent-cover data of vegetation and post-disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous-Mixed sites, due to the release of the understorey from Sphagnum spp. dominance, this pattern being a function of FIS. On Deciduous-Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage-logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage-logging was introduced. Salvage-logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade-tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.

The influence of partial harvesting and forest floor disturbance on nutrient availability and understory vegetation in boreal mixedwoods

The impacts of partial cut systems on nutrient availability and understory vegetation are poorly understood. To examine these responses, white spruce dominated stands in the boreal mixedwood of Alberta were clear-cut or partial-cut and the forest floor treated by slash burning, mixing, mounding, or scalping in a split-plot design. Soil nutrient availability (ion exchange resin), net N mineralization (in situ incubations), and vegetation (density and cover) responses were assessed. With the exception of higher Mg availability in the clearcuts, differences in nutrient availability were driven by forest floor disturbance and not harvest method. Relative to controls, burning increased availability of NH4+, NO3–, and P, and scalping increased Ca and Mg but diminished K. Controls had low levels of NO3–. The mixing treatment substantially reduced net N mineralization. In terms of vegetation, partial cuts reduced root suckering by Populus spp. (Populus tremuloides Michx., Populus balsamifera L.) relative to clearcuts. Burning and mounding stimulated fireweed (Epilobium angustifolium L.) cover, while scalping increased Populus spp. sucker density. In contrast, mixing largely reduced vegetation establishment, likely because of the destruction of roots and rhizomes and reduced N supply. Nutrient availability and vegetation establishment were more strongly controlled by forest floor disturbance than by partial canopy retention.

Changes in forest floor bryophyte (moss and liverwort) communities 4 years after forest harvest

Forest harvest presents a potential threat to forest floor bryophyte communities primarily through alteration of the microclimate and disturbance of substrates on the forest floor. Management, including harvest, applied at the landscape scale creates patches of disturbance of differing severities at the spatial scale experienced by bryophytes. Presumably, bryophyte diversity in managed landscapes is best conserved by forest harvest techniques that minimize community change, thereby allowing disturbed communities to reassemble to approach predisturbance composition. We monitored bryophyte community reassembly by sampling quadrats established in a 54-ha management block of Acadian forest in New Brunswick, before and after harvest. Quadrats were either in unharvested areas, or experienced a range of disturbance severities from removal of some or all canopy, to forest floor disturbance with complete canopy removal. Bryophyte communities showed compositional change over 4 years, even in areas that were not harvested. Although species richness was maintained or recovered 4 years after harvest, changes in species composition were significant in all disturbance classes with greatest change related to forest floor disturbance. In particular, liverworts were lost in areas with forest floor disturbance. We suggest that the simplest method to reduce immediate species loss, and presumably promote conservation of bryophyte communities within managed forest landscapes, is to utilize techniques that reduce the area of forest floor and associated substrates that are physically disrupted.Key words: bryophyte, community change, disturbance, forest harvest, monitoring.

Gap disturbances in northern old‐growth forests of British Columbia, Canada

Abstract. We characterized the abundance, size and spatial patterning of canopy gaps, as well as gap‐forming processes and light availability in boreal, sub‐boreal, northern temperate and subalpine old‐growth forests of northwestern British Columbia. The proportion of area in canopy gaps ranged from 32% in northern temperate forests to 73% in subalpine forests. Evenly distributed developmental gaps were dominant but permanent openings created by edaphic components and by shrub communities were also common, particularly in subboreal forests. Abundant gaps, large gap sizes, high numbers of gap makers per gap and frequent gap expansion events suggest that gaps have long tenure in these forests. Snapped stems and standing dead mortality were the most common modes of mortality in all forest types resulting in little forest floor disturbance, creating few germination sites for seedling establishment. We found high mean light levels (16–27% full sun) and little difference between non‐gap and gap light environments. Our results suggest that gap dynamics in these forests differ fundamentally from those in temperate and tropical forest ecosystems.

Gap disturbances in northern old-growth forests of British Columbia, Canada

We characterized the abundance, size and spatial patterning of canopy gaps, as well as gap-forming processes and light availability in boreal, sub-boreal, northern temperate and subalpine old-growth forests of northwestern British Co- lumbia. The proportion of area in canopy gaps ranged from 32% in northern temperate forests to 73% in subalpine forests. Evenly distributed developmental gaps were dominant but permanent openings created by edaphic components and by shrub communities were also common, particularly in sub- boreal forests. Abundant gaps, large gap sizes, high numbers of gap makers per gap and frequent gap expansion events suggest that gaps have long tenure in these forests. Snapped stems and standing dead mortality were the most common modes of mortality in all forest types resulting in little forest floor disturbance, creating few germination sites for seedling establishment. We found high mean light levels (16-27% full sun) and little difference between non-gap and gap light environments. Our results suggest that gap dynamics in these forests differ fundamentally from those in temperate and tropical forest ecosystems.

Early response of the herbaceous layer to harvesting in a mixed coniferous–deciduous forest in New Brunswick, Canada

We studied plant communities before and after two types of clearcutting to determine their response and their relationships to disturbance intensity and to make management recommendations. Permanent plots sampled before and for 2 years after harvesting were used to compare changes in the herbaceous layer for 2 years after harvest in three treatments: clearcutting with natural regeneration (C), clearcutting with mechanical site preparation and planting (CS) and uncut control (UC). The greatest compositional changes occurred in the CS treatment, where 16 species were lost and 20 new species were gained compared to 14 lost and 16 gained in the C treatment. The number of forest habitat species decreased 20–24% by the second year after harvest in both treated areas. Species that were lost included Cypripedium acaule, Monotropa hypopithys, Orthilia secunda, Ribes lacustre, Streptopus amplexifolius, Thelypteris noveboracensis and Vaccinium vitis-idaea. The number and cover of disturbance-adapted species increased about 250% in the CS treatment compared to 200% for the C treatment. Mean total species richness per plot, Shannon–Wiener, Simpson and evenness diversity indices were significantly greater ( P<0.05) the second year after harvest than before harvest in the two harvest treatments. Richness of forest species significantly declined in both treated areas. Sørensen’s similarity index (each post-harvest year versus pre-harvest) increased with time in all treatments and was lowest in the CS treatment. Cover of most growth forms, especially bryophytes, decreased after harvesting in the two harvest areas, whereas small trees/shrubs and graminoids increased, particularly in the CS treatment. Cover of conifer seedlings and bryophytes greatly decreased in the C treatment where coniferous stand types dominated before harvest. Four non-native taxa ( Plantago major, Ranunculus acris, Taraxacum officinale and Veronica officinalis) were encountered in the study. In 1997, total cover of non-natives was 0.2% in the CS treatment and <0.05% in the C and UC treatments. We conclude that the more dramatic changes in species composition and diversity in the CS treatment are the result of greater forest floor disturbance caused by site preparation. Protection of forest understory plants can be improved by minimizing forest floor disturbance, maintaining shade cover and leaving uncut strips or patches in areas containing species that are sensitive to harvesting.