Uncut Forest Research Articles

The effects of green tree retention and subsequent prescribed burning on ground beetles (Coleoptera: Carabidae) in boreal pine‐dominated forests

We studied how two methods to promote biodiversity in managed forests, i.e. green tree retention and prescribed fire, affect the assemblages of carabid beetles. Our experiment consisted of 24 study sites, each 3–5 ha in size, which had been prepared according to factorial design. Each of the eight treatment combinations determined by the two factors explored – tree retention level (0, 10, 50 m3/ha−1 and uncut controls) and prescribed use of fire (yes/no) – was replicated three times. We sampled carabids using pitfall traps one year after the treatments. Significantly more individuals were caught in most of the burned sites, but this difference was partially reflective of the trap‐catches of Pterostichus adstrictus. The fire did not increase no. of P. adstrictus in the uncut sites as much as in the other sites. Species richness was significantly affected by both factors, being higher in the burned than in the unburned sites and in the harvested than in the unharvested sites. Many species were concentrated in the groups of retention trees in the burned sites, but only a few were in the unburned sites. The species turnover was greater in the burned than in the unburned sites, as indicated by the NMDS ordinations. Greater numbers of smaller sized species and proportion of brachypterous species were present in the burned sites. Fire‐favored species, and also the majority of other species that prefer open habitats were more abundantly caught in the burned sites than in the unburned sites. Dead wood or logging waste around the traps did not correlate with the occurrence of species. We conclude that carabids are well adapted to disturbances, and that frequent use of prescribed fire is essential for the maintenance of natural assemblages of carabid beetles in the boreal forest. Small retention tree groups can not maintain assemblages of uncut forest, but they can be important by providing food, shelter and breeding sites for many species, particularly in the burned sites.

Effects of harvesting and soil disturbance on soil CO2 efflux from a jack pine forest

We measured organic matter removal and soil compaction effects on soil surface CO2 efflux (F) from a jack pine (Pinus banksiana Lamb.) forest and developed an analytical framework involving multiplicative response functions to interpret response. Treatments included stem-only harvest (OM0C0), full-tree harvest (OM1C0), full-tree harvest with surface soil removal (OM2C0), full-tree harvest with surface soil removal and soil compaction (OM2C2), and uncut forest (UF). Mean F and calculated F at 10 °C under nonlimiting soil moisture conditions (F10) were greatest in treatments with intact organic surfaces and often larger in the OM2C0 than in the OM2C2. F10 showed strong linear relationships with detrital production in harvested plots, with total near-surface carbon in all plots, and was positively correlated with understory cover. F increased exponentially with soil temperature, with the most and least pronounced responses found in the UF and OM2C0 treatments, respectively. F also responded in parabolic fashion to relative soil water content. In the UF, F was often low in May because of cold soils, but subsequently attained rates equivalent to those of the OM0C0 and OM1C0, despite lower soil temperatures. Three to five growing seasons after treatment, soil temperature and moisture, together with F10, explained 71%–87% of the plot-level variation in F.

Effects of green tree retention and prescribed burning on the crown damage caused by the pine shoot beetles (Tomicus spp.) in pine‐dominated timber harvest areas

Abstract: We explored how two recently introduced methods to promote biodiversity during the timber harvest in boreal forests – green tree retention and use of fire – may affect damages caused by pine shoot beetles (Tomicus piniperda and Tomicus minor; Col., Scolytinae) in the surrounding pine forests. The experimental design included 24 separate study sites, 3–5 ha each, which were assigned to different treatments according to factorial design. Retention levels included 0, 10, 50 m3/ha and uncut controls. Twelve of the sites were burned and thus there were three replicates of each treatment combination. Old and new fallen pine shoots were counted from transects in adjacent pine‐dominated forests 2 and 3 years after the treatments. Populations of Tomicus spp. in the sites were monitored using window traps before and after the treatments, and by examining felled sample trees. Numbers of fallen shoots returned to background levels around unburned and burned clearcuts with no retention trees in 3 years after the treatments, but remained still at increased level in burned harvested sites with 10 and 50 m3 of retained trees per hectare. Numbers of fallen shoots in burned uncut forests increased in one site only, where the fire was intense enough to kill large pine trees, but the damage did not extend outside the burned area. Shoot numbers remained at such low levels (<18 000 shoots/ha) in all treatment combinations that growth losses were not likely. Numbers of egg galleries of Tomicus spp. in trees killed by fire were low, indicating that burnings that take place after the swarming of Tomicus beetles create dead wood that is not optimal for the breeding of these pests. We conclude that green tree retention and prescribed use of fire do not automatically affect populations of Tomicus spp. more than traditional forestry operations (thinnings and clearcuttings) do.

Is forest close to lakes ecologically unique?: Analysis of vegetation, small mammals, amphibians, and songbirds

We compared vegetation structure, flora, and fauna in forest stands at varying distances from small lakes in the boreal mixedwood zone of Alta., Canada, with that in the surrounding upland landscape. We tested the hypothesis that lakeside riparian forest is more structurally diverse, hosts different biotic communities, and has greater floral diversity and greater abundance and richness of other biota, as compared with similar forest in areas far from open water. Lakeside forest was characterized by greater canopy cover, and aspen height and diameter (breast height) than upland forest, but absolute differences were quite small and there was no evidence of greater structural diversity. Contrary to expectations, herb richness and diversity were lower in lakeside forests and the understory community there could not be differentiated from that of upland forests. Two species of anuran amphibians [wood frog ( Rana sylvatica) and boreal toad ( Bufo boreas boreas)] were more abundant in forest up to 100 m from lakes than in upland areas 400–1200 m away from open water. However, differences in abundance between trapping sites in the non-forested riparian zone and sites up to 100 m into the lakeside forest were small. Use of upland habitats by amphibians (juvenile wood frog in particular) was substantial during the latter part of their active season, possibly because they used upland areas for dispersal and overwintering. The two most abundant species of small mammal [red-backed vole ( Clethrionomys gapperi) and deer mouse ( Peromyscus maniculatus)] were trapped less often in the non-forested riparian zone, while the meadow vole ( Microtus pennsylvanicus), meadow jumping mouse ( Zapus hudsonicus), and shrews ( Sorex spp.) were more abundant in those areas. Abundance did not differ significantly among trap lines located in forest from 50 m to >600 m from open water. Songbird abundance and richness were higher near lakes, possibly because of the additional niches available at the forest/lake interface and increased food supply for insectivorous birds. Overall, our results did not strongly support our hypotheses concerning the ecological attributes of lakeside riparian forest. If any part of these lakeside riparian areas can be considered ecologically unique or species-rich it appears to be the non-forested riparian zone and, for birds, the natural lakeshore ecotone (∼50 m into the forest). We encourage those responsible for forest management to re-think prescriptive placement of fixed-width forested buffers around all lakes, and instead consider a landscape-scale planning approach that determines the appropriate placement of uncut forest on the landscape to meet broad conservation objectives.

Attributes of forest strips used by snowshoe hare in winter within clear-cut boreal landscapes

The snowshoe hare (Lepus americanus Erxleben) is an important prey for many predators in the boreal forest. In this biome, clear-cut landscapes are generally large and consist of aggregated cutting blocks separated by narrow forest strips (typically 60–100 m wide). To identify attributes of forest strips that are important for snowshoe hares, we measured the use of strips using track counts over two winters in six clear-cut landscapes (23–256 km2) in south-central Quebec. Surveys were conducted in 20 riparian strips (RS), 20 upland strips (US), and 15 control sites (CO) at the periphery of clear-cut landscapes. Overall, 392 signs of hare presence were recorded along 50 km of transects. Snowshoe hares were present in one-third of the strips surveyed and were five times less abundant in US and RS than in CO. The species avoided strip edges. Hares were more common in the wider strips (>100 m), in the strips adjacent to residual forest patches (≥25 ha), or in those having a denser shrub canopy, which is often associated with a greater basal area in balsam fir (Abies balsamea (L.) Mill.). To maintain snowshoe hare at moderate densities in large clear-cut landscapes, we suggest leaving uncut forest strips >100 m wide in areas having a good shrub cover with presence of balsam fir.

Stand-level response of breeding forest songbirds to multiple levels of partial-cut harvest in four boreal forest types

We investigated whether impacts on boreal forest songbird communities in northwestern Alberta could be mitigated through a harvesting system that attempts to emulate the local natural disturbance regime. The EMEND (Ecosystem Management by Emulating Natural Disturbance) project is a multidisciplinary experiment to compare clearcuts and partial-retention cuts in four upland cover types with uncut forest and with experimentally burned stands. We studied breeding birds at EMEND between 1998 (pretreatment) and 2000, focusing on their responses to partial harvesting. Partial cuts were generally intermediate (and varied in a linear fashion) between clearcuts and undisturbed forest for community and species measures. Species that declined in abundance in partial cuts were typically dependent on shrubs and trees, whereas species that benefited were typically ground nesters. While partial cutting offered some advantages over clear-cutting in conserving short-term avian diversity, we suggest that low retention levels (i.e., 10%, 20%) cannot be justified from this perspective. The benefits that accrued in these treatments were relatively small, and species that declined or disappeared were typically characteristic of mature forest habitats. Higher retention levels (i.e., 50%, 75%) may conserve some species of concern, but the extent to which these treatments offer productivity advantages over lower residuals requires further study.

Aspect modifies the magnitude of edge effects on bryophyte growth in boreal forests

Summary The increased length of forest clear‐cut edges is considered to be one of the main ecological consequences of silviculture. The effects vary over the landscape, and studies have shown that aspect is one important factor determining the extent of microclimatic edge effects across forest clear‐cut boundaries. However, little is known about the relationship between contrasts in microclimate at edges and responses of ecological processes and biodiversity, such as growth, decomposition and species distributions. A field experiment was conducted in the boreal forest of northern Sweden to assess the effect of aspect at north‐ and south‐facing edges using mosses as bioindicators. The growth of two species (Hylocomium splendens and Hylocomiastrum umbratum) was evaluated during one growing season. Samples of each species were planted in pots at eight north‐ and eight south‐facing forest clear‐cut edges. Growth increased exponentially with distance from the edge to the interior, and there was a significant effect both in north‐ and south‐facing edges. The percentage decline in growth at the edge was larger in the south‐ than in the north‐facing edges. The spatial extent of the edge effect, when measured at the point of 90% of interior growth, was similar between north‐ and south‐facing edges, although it differed between the two species evaluated. Synthesis and applications. The difference in exposure to sunlight between north‐ and south‐facing edges was shown to modify the magnitude of the growth of a poikilohydric organism at the very edge, but not the depth of the edge influence. Aspect should be taken into account in management plans for conservation of boreal forests. In the northern hemisphere, wider buffers of uncut forest should be left at the south side than at the north side of retained forest patches. Those forest interior species that are most sensitive to alterations in microclimate will, however, need equal protection from edge effects at all aspects.

Harvest retention patches are insufficient as stand analogues of fire residuals for litter-dwelling beetles in northern coniferous forests

We compared litter-dwelling beetle assemblages of <1- to 2-ha unharvested coniferous patches embedded in 1-year-old clearcuts with beetle assemblages from <1- to 10-ha unburned fire residuals within 15- and 37-year-old burned forests. Our primary objective was to determine whether unharvested patches retain biotic elements that are similar to those of the surrounding uncut forests and to those of patches of forest skipped by wildfires. Beetle assemblages of the harvest residuals were similar to those of the uncut forest, suggesting that harvest residuals retain elements of the mature forest. However, beetle assemblages of harvest residuals differed from those of fire residuals. Thus, harvest residuals sited without regard to microhabitat characteristics or stand structure in fire residuals are insufficient analogues for the late successional habitats provided by fire residuals. There was no relationship between size of harvest residuals and either beetle catch or diversity. Beetle catches were higher in round harvest residuals, and a number of forest species also appeared to be aggregated in round residuals. Forest managers may preserve biotic elements of young uncut forest by leaving round harvest residuals in clearcuts; however, a closer habitat match between harvest and fire residuals is likely required to preserve and maintain landscape-level forest biodiversity.

Short-term impact of forest soil compaction and organic matter removal on soil mesofauna density and oribatid mite diversity

This study examines the short-term impact of forest soil compaction and organic matter removal on soil mesofauna, in general, and oribatid mite species, in particular. Both soil compaction and organic matter removal reduced the density of soil mesofauna. Stem-only harvesting reduced total mesofauna densities by 20% relative to uncut forest values. A combination of whole-tree harvest and forest floor removal with heavy soil compaction significantly reduced total soil mesofauna densities by 93% relative to the uncut forest control. Removal of the forest floor represents a substantial loss of habitat for most soil mesofauna. The forest floor apparently buffered the mineral soil by limiting both the impact of soil compaction and fluctuations in soil temperature and moisture. The relative abundance of Prostigmata and Mesostigmata increased with treatment severity, whereas that of Oribatida decreased. Species richness of the oribatid mite fauna was reduced as the severity of treatments increased. The number of rare oribatid species (those representing <1% of the total oribatid mite sample) decreased by 40% or more relative to the uncut forest control. Evenness also decreased as treatment severity increased. Oppiella nova and Suctobelbella sp. near acutidens were the dominant oribatid species in both the forest floor and mineral soil, regardless of treatment. Soil compaction and organic matter removal significantly impacted the density and diversity of soil mesofauna and oribatid mite fauna in the short term at these study sites.

Effects of forest management practices on red-shouldered hawks in Ontario

The red-shouldered hawk (Buteo lineatus) is a species of special concern throughout its northern range. It is considered to be sensitive to forest management practices because it requires dense mature hardwood forest for nesting. In Ontario, guidelines that prescribe spatial and temporal buffers were developed in about 1990 to mitigate the potential impacts of harvesting. We monitored 84 nesting areas of red-shouldered hawks in central and southeastern Ontario from 1988 to 1995 to describe the effects of forest management practices on the occupancy and productivity of nesting areas, to evaluate the effectiveness of the guidelines, and recommend modifications as appropriate. The number of years nesting areas had been used previously had a significant negative effect on activity status, but not on nest success. Nesting areas harvested with application of the guidelines had a similar probability of being active to those in uncut forest but nesting areas harvested without application of the guidelines did not. Neither the area nor proximity of selection cuts with a moderate to high residual basal area ( ≥18 m2/ha) affected the activity status of nesting areas. In contrast, the area and proximity of heavy cuts (shelterwood cuts or selection cuts with a residual basal area of 14–16 m2/ha) appeared to have a negative effect on activity status. When nesting areas were active, the proximity and amount of harvesting did not influence nest success. We concluded that the impact of harvesting on the activity status of nesting areas could be mitigated by prohibiting heavy cuts within 300 m of active nests and retaining ≥20 ha of forest dominated by tolerant and mid-tolerant hardwood trees, ≥18 m tall, with ≥70% canopy closure around nests. Key words: Buteo lineatus, effectiveness monitoring, habitat guidelines, nest success, Ontario, red-shouldered hawk, forest management, selection, shelterwood, tolerant hardwoods

Leaving forest strips in large clearcut landscapes of boreal forest: A management scenario suitable for wildlife?

Riparian forest strips (RS) along lakes and streams have been incorporated in regulations on clearcuts to protect water quality and fish habitat. As well, upland strips (US) are used to limit the size of clearcut patches. We conducted a three-year study to evaluate if RS and US between adjacent cutovers in large clearcut landscapes could be useful for certain terrestrial wildlife. Our study was conducted in southcentral Québec on six landscapes (23–256 km2) originating from black spruce (Picea mariana) forests that were recently logged (≤ 9 years). Residual uncut forest, mostly strips (width = 51–132 m), made up 31% of the productive forest area within these landscapes. RS and US were suitable habitat for red squirrel (Tamiasciurus hudsonicus) and many species of birds including spruce grouse (Falcipennis canadensis). They provided marginal habitat for snowshoe hare (Lepus americanus) and were not preferred by moose (Alces alces) over clearcut areas in winter. One bird species, bay-breasted warbler (Dendroica castanea), was absent in forest strips during the last year. We concluded that leaving RS and US is a management scenario that enables maintaining certain wildlife species within clearcut landscapes, but that larger residual forest patches are needed to accommodate area-sensitive and forest-interior species. A portion of these patches should be allowed to develop into mature and overmature stages for old-growth forest species. Green tree and dead tree retention should also be incorporated in logging practices to accommodate species that need snags for nesting or feeding. In areas where wildlife use has a high priority, large clearcuts should be intermixed with dispersed patch cutting in order to gain social acceptance. Key words: black spruce, forest strip, clearcutting, ecosystem management, Picea mariana, riparian strip

Partial and clear-cut harvesting of high-elevation spruce–fir forests: implications for small mammal communities

Subalpine spruce (Picea) – fir (Abies) forests occur throughout the Cordillera of western North America. A variety of alternative silvicultural systems to clear-cutting are being investigated in these high-elevation forests in terms of their impacts on ecosystem components. We tested the hypotheses that abundance, reproduction, and survival of populations of (i) southern red-backed voles (Clethrionomys gapperi Vigors) will decline, (ii) long-tailed voles (Microtus longicaudus Merriam) and northwestern chipmunks (Tamias amoenus J.A. Allen) will increase, and (iii) deer mice (Peromyscus maniculatus Wagner) will be similar, with respect to decreasing levels of tree retention. Small mammal populations were live-trapped from 1994 to 1998 in replicated sites of uncut forest, single tree selection, 0.1-ha patch cuts, 1.0-ha patch cuts, a 10.0-ha clearcut, and edges in an Engelmann spruce (Picea engelmannii Parry ex Engelm.) – subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forest near Sicamous, British Columbia, Canada. Clethrion omys gapperi dominated the small mammal community, reaching a peak abundance of 80 animals/ha with mean values ranging from 31 to 50 animals/ha. Over the 4 postharvest years, abundance, reproduction, and survival of C. gapperi populations were consistently similar among uncut forest, single tree selection, and patch cut treatments compared with clear-cut sites where this species declined to extirpation. Microtus longicaudus and T. amoenus occurred predominantly in clearcut sites, whereas P. maniculatus was present in low numbers on all sites. With respect to small mammals, partial harvesting systems appear to provide a means for combining timber extraction with maintenance of mature forest habitat in these subalpine ecosystems.

Effect of gap size on litter decomposition and soil nitrate concentrations in a high-elevation spruce–fir forest

Possible mitigation of nitrate losses associated with clearcuts through harvesting smaller gaps was tested in a high-elevation forest of Engelmann spruce (Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.). We measured concentrations of ammonium and nitrate after 6-week buried bag incubations of forest floor and mineral soil samples in replicated plots of uncut forest and gaps of 10, 1.0, and 0.1 ha and single-tree removal for 7 years after harvest. Nitrate concentrations in forest floor and mineral soil were elevated 3–7 years after harvesting in gaps of 0.1 ha and larger. Removal of the same proportion of trees as single trees did not result in increased nitrate concentrations, suggesting that nitrate losses could be reduced by harvesting single trees rather than creating gaps. Greater N availability was not associated with faster rates of decomposition of litter and forest floor, which were similar in gaps of all sizes (0–10 ha). Reciprocal transplant of forest floor and soil from the 10-ha gaps and the uncut forests indicated that changes in the nature of the forest floor or soil following harvest had a greater influence on nitrate concentrations than the changes in environmental conditions in the gaps.

Should riparian buffers be part of forest management based on emulation of natural disturbance?

Riparian communities (those near open water) have often been shown to display high structural and compositional diversity and they have been identified as potentially serving a keystone role in the landscape. Thus, they are the focus of specific management guidelines that attempt to protect terrestrial and aquatic ecosystems. We used a digital forest inventory database for a portion of the boreal mixed-wood forest in Alberta, Canada, to examine whether proximity to a lake affects forest composition, age, or configuration. Two analyses were employed: (1) forest composition (dominant canopy species, proportional composition of different species) and age (decade-of-origin) in bands of 50 m width and varying distance from small lakes were compared to forest in a similar spatial configuration but away from open water and (2) forest composition, dominant canopy species, age, and stand shape metrics were examined along transects emanating out from lakes in two regions, which varied in topography and dominant forest cover. We found no effect of distance from lake on forest age. The proportion of the landscape covered by forest of the predominant canopy species increased with distance from lake, but this was largely due to a corresponding decline in cover of non-forest vegetation rather than a change in forest canopy composition. At the spatial resolution of forest management planning, riparian forests in this region are of similar age and composition as those away from lakes. Since there is no natural analogue for riparian buffer strips around lakes, they may not be justified in the context of ecosystem management following the natural disturbance paradigm. Management of riparian forests should focus on meeting defined management and conservation objectives through, for example, protection of finer scale features of riparian zones and landscape-level planning for allocation of uncut forest.

Responses of available soil nitrogen and litter decomposition to openings of different sizes in dry interior Douglas-fir forests in British Columbia

Selection of an appropriate silvicultural system that maintains productivity requires an understanding of the effects of harvest type on post-harvest changes in nitrogen availability. The effects on inorganic nitrogen availability and litter decomposition of various harvesting systems, including partial canopy removal and a range of clearcut opening sizes, were investigated in a dry Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) forest in southern British Columbia. We measured concentrations of ammonium and nitrate after 6-week buried bag incubations of forest floor and mineral soil samples in replicated plots within uncut forest, within partially harvested forest, and in openings of 1.7, 0.4, and 0.1 ha, from two to seven growing seasons after harvest. Post-incubation nitrate and the proportion of inorganic N as nitrate in forest floor and mineral soil were elevated from 2 to 7 years after harvesting in the 1.7 ha openings. There was no consistent trend of higher ammonium concentration in either uncut forest or 1.7 ha openings. The proportion of inorganic N as nitrate was consistently the lowest in the uncut forest, and often significantly different from any opening treatment, including partial cutting. The increased proportion of inorganic N as nitrate occurred within 11 m of the uncut forest edge. At very low moisture contents, nitrate concentrations tended to zero only in the uncut forest. Leaching of the increased available nitrate is unlikely because of the large increase in grass biomass that occurs after harvesting, and the dry soil moisture conditions during the growing season. Decomposition of Douglas-fir, lodgepole pine and trembling aspen litters, or forest floor was inconsistently, or not affected by any harvest treatment or by distance from, or aspect of, the edge of the forest. The post-harvest increases in nitrate concentrations cannot be attributed to faster decomposition.

Aspen Regeneration in Riparian Management Zones in Northern Minnesota: Effects of Residual Overstory and Harvest Method

Abstract We examined aspen regeneration under different riparian management zone (RMZ) treatments in aspen forests in northern Minnesota. We also compared aspen regeneration in partially harvested RMZs to adjacent upland clearcuts. The four RMZ treatments included: (1) full control (no cutting in RMZ or upland; (2) riparian control (RMZ uncut; upland clearcut); and partially harvested RMZs cut to 54 ft2/ac, with upland clearcut using (3) cut-to-length (CTL), or (4) tree-length harvesting. Three years after harvest, aspen sucker densities in the tree-length and CTL treatments were significantly higher than the full control, but did not differ from each other or the riparian control. Mean individual sucker heights (63–73 in) and aboveground biomass (2.4–3.4 oz) varied among the riparian treatments, but not significantly. Sucker densities were 62% higher in the adjacent clearcuts than in the partially harvested RMZs. Mean suckers heights did not differ between the two locations (71 in.), but aboveground biomass of suckers did differ significantly, averaging 3.4 oz in the partially harvested RMZs and 4.5 oz in the clearcuts. Our results indicate that 60% removal of basal area within RMZs increases density and size of aspen regeneration significantly, compared to uncut forest, but stocking is still below what is considered adequate for 3-yr-old stands. Suckering responses were similar with cut-to-length and tree-length harvesting, suggesting that harvest system has little effect on sucker development. While aspen likely will be a component of partially harvested RMZs, density and biomass increment will be much lower than in single-cohort stands and lower than what is considered desirable for commercial production. North. J. Appl. For. 20(2):79–84.

Effects of different soil treatments on growth and net nitrogen uptake of newly planted Picea abies (L.) Karst. seedlings

Five soil treatments in a 4-year-old clearcut in southern Sweden affected biomass increase and net nitrogen uptake by planted Norway spruce ( Picea abies (L.) Karst.) seedlings through their on net mineralisation and root growth. The patch soil treatments studied were: (i) soil inversion in an old clearcut; (ii) mineral soil from the clearcut remaining, (iii) mineral soil from the clearcut with fertiliser application during the first season; (iv) mineral soil from a nearby uncut forest replacing the clearcut mineral soil; and (v) an untreated control. Growth increased in seedlings in treatments (i) and (iii), but growth in soil treatments with humus removal was not better than that of seedlings in untreated soil. High N uptake early in the first growing season resulted in increased growth during this season in contrast to late N uptake that resulted in a high N concentration in the seedlings after the first growing season. This in turn led to a high growth rate during the next growing season. Generally, both root growth and net N mineralisation were positively correlated to N uptake in the soil treatments. Therefore, a combination of low net N mineralisation and poor root growth as a result of high soil density appears to explain the low N uptake in seedlings in undisturbed soil. The importance of competition with field vegetation for N and water was not clear. Net mineralisation was larger in soil treatments where the humus layer was retained than where it was removed. Net N mineralisation in soil from old clearcuts was the same as in soil from fresh clearcuts.

SOIL AND NUTRIENT LOSSES FOLLOWING SITE PREPARATION BURNING IN A HARVESTED LOBLOLLY PINE SITE

Soil loss and nutrient concentrations in runoff were evaluated to determine the effects of site preparation burningon a recently harvested loblolly pine (Pinus taeda L.) site in east Texas. Soil and nutrient losses prior to treatment wereapproximately the same from control plots and pretreatment burn plots. Nutrient analysis of runoff samples indicated that theprescribed burn caused increased losses of N, P, K, Ca, and Mg from treatment plots. Results also indicate a significantincrease in sediment concentration and soil loss from plots following the prescribed burning application. The data indicatea gradual decline in soil loss and nutrient concentration over time from treatment plots with respect to control plots. Soil lossfollowing treatment was within the normal range of soil loss for an uncut forest in the south.

Pre-dispersal seed predation of white spruce cones in logged boreal mixedwood forest

Predation of white spruce (Picea glauca (Moench) Voss) cones by red squirrels (Tamiasciurus hudsonicus Erxleben) was quantified in the mixedwood boreal forest of Alberta in cutblocks with seed tree retention and in adjacent uncut forest, during 3 years with varying levels of cone crop (1998, 1999, 2000). Percent cone loss was quantified by comparison of paired pre- and post-caching photographs of tree crowns. Cone loss from seed trees in cutblocks was significantly lower than from control trees in adjacent uncut forest (48.5 vs. 54.9%). Although the number of cones produced per tree declined by 42% and the percentage of trees producing cones declined by approximately 48% between 1998 and 2000, there was no corresponding increase in the percentage of cones harvested by squirrels. Percent cone loss was significantly lower from single seed trees in cutblocks, as compared with seed trees left in patches of more than 20 trees (33.4 vs. 50.5%). Cone predation significantly reduced the amount of seed available for natural regeneration using a seed tree system. Although blowdown may be reduced if seed trees are left in patches, leaving white spruce seed trees as singles in cutblocks may reduce the level of cone predation.

Carbon sequestration in trees and regrowth vegetation as affected by clearcut and partial cut harvesting in a second-growth boreal mixedwood

Ecosystem biomass and C sequestration and cycling were measured in a mature, budworm-ravaged, second-growth boreal mixedwood stand subjected to clearcut and partial cut harvest treatments. Ninety permanent sample plots, distributed among fifteen 10 ha blocks, were established in 1993 and remeasured shortly after harvest and, again, 5 years later to ascertain C removals, as well as post-harvest ingrowth and upgrowth. In addition, litter bags and litter traps were installed and ground vegetation and forest floor samples were collected to monitor changes in ecosystem C pools and fluxes as affected by harvesting. The harvested blocks were quickly reoccupied by a thriving ground species regrowth, followed by a prolific trembling aspen thicket. Despite this, 5-year growth per area on control plots exceeded that on either partial cut or clearcut plots. Annual C assimilation rates in the post-harvest period were similarly significantly higher on control (3.1 Mg ha −1 per year) than on partial cut (1.8 Mg ha −1 per year) or clearcut (0.3 Mg ha −1 per year) plots. When growth was expressed as a function of biomass, the order reversed indicating the young growth to be the more vigorous. The forest floor lost little mass during the post-harvest period. Further, leaf litter decomposition was slower on clearcut plots than in uncut forest. Results suggest that ecosystem C pools and fluxes are rapidly reconstituted following harvest. If harvesting were to occur, ecosystem C assimilation in boreal mixedwood forest would be maximized under partial cutting.