High-elevation Spruce-fir Forests Research Articles

Influences of Succession and Biogeoclimate on Forage Resources for Elk in Northern Idaho

Natural disturbance shaped forest communities for millennia, but fire suppression and timber harvest declines have altered forest structure across the western United States, reducing the abundance of forage for ungulates. We evaluated quality and quantity of forage resources for lactating elk (Cervus canadensis) and their calves in relation to season, succession, and biogeoclimate, the latter indexed by potential vegetation (PV) zones, across 36,500 km2 in Idaho's Clearwater and St. Joe River basins. In 0.2-ha macroplots (n = 359), we measured characteristics of forest overstory, biomass of current annual growth of undergrowth vegetation (kg ha-1), and nutritional content of these plants. Using biomass, digestible energy (kJ g-1), digestible protein (DP, g per100 g forage), and prior knowledge of elk diet selection and nutritional constraints, we developed 8 forage resource metrics. The greatest abundance of undergrowth vegetation (500 to 1,000 kg ha-1) occurred during the first 20 years after stand-replacing disturbance and declined as the overstory closed in wetter PV zones. Digestible energy decreased, whereas DP increased as stands aged. Evidence of nutritional limitations for lactating elk increased markedly after mid-summer; early-seral, high-elevation spruce–fir forests on productive soils provided the best opportunity for lactating elk to satisfy their requirements in late summer. Our findings demonstrate the importance of disturbance regimes that maintain early-seral communities in mosaics with mid- and late-seral stages, and suggest that implementing stand-replacing disturbance in relatively moist forest zones at mid and high elevations provides the greatest improvement in forage resources for lactating elk and their calves in summer.

A NEW SPECIES OF FLEA (SIPHONAPTERA: CTENOPHTHALMIDAE) PARASITIZING VOLES AT HIGH ELEVATIONS IN THE GREAT SMOKY MOUNTAINS OF TENNESSEE AND NORTH CAROLINA.

Both sexes of Catallagia appalachiensis n. sp. are described from high elevation spruce-fir forests in Sevier County, Tennessee and adjoining Swain County, North Carolina in the Great Smoky Mountains National Park. The type host of the new flea is the southern red-backed vole, Myodes gapperi (Vigors) (25 flea specimens), although small numbers of specimens were also collected from a sympatric northern short-tailed shrew, Blarina brevicauda (Say) (2 fleas), a red squirrel, Tamiasciurus hudsonicus (Erxleben) (1 flea), and a North American deer mouse, Peromyscus maniculatus (Wagner) (1 flea). Infestation prevalences for these hosts are provided. The new species is compared morphologically with other known species of Catallagia, in particular with Catallagia borealis, the only other described congeneric flea in eastern North America. This is the first new species of flea to be described from the eastern United States since 1980.

Schadonia saulskellyana (Pilocarpaceae; Lichenized Ascomycetes) an unusual new species endemic to the southern Appalachian Mountains of eastern North America

Schadonia saulskellyana is described as new to science based on material from the southern Appalachian Mountains in the eastern United States. The species appears to be endemic to the region and mostly restricted to the bark of conifers. It is particularly abundant and frequent in the imperiled high-elevation spruce-fir forests of the region. The new species is distinguished from its congeners by its corticolous habit, minutely areolate thallus with areoles that erupt into soralia which dissolve the areoles and give the appearance of a leprose crust, epruinose, dark brown-black apothecia with a brown hypothecium, and monosporous asci with large, muriform ascospores. It is also compared with other genera of Pilocarpaceae, particularly Calopadia. Lopadium disciforme, a superficially similar species is also compared to the new species and photographs, as well as a distribution map for eastern North America, are provided for that species.

Seasonal Activity Patterns of Bats in High-Elevation Conifer Sky Islands

In the southern Appalachian Mountains of the southeastern USA, bat communities in high-elevation habitats tend to be relatively under-surveyed. High-elevation habitats may provide important habitat to certain species (i.e., migratory tree bats), and may serve as climate refugia during droughts or high temperatures. We conducted an opportunistic acoustic survey of bat communities in ten survey areas in high elevation (1,585–1,920 m a.s.l.) montane Picea rubens (red spruce)-Abies fraseri (Fraser fir) forest in the southern Appalachian Mountains of western North Carolina. In each survey area, we randomly placed three full spectrum acoustic detectors (N = 30) during three seasons (spring, summer and fall) in 2015. We deployed each detector for two five-day periods during each season (n = 900 survey nights). Although we detected seven bat species/groups during the surveys, 73% of echolocation files were attributed to Lasiurus cinereus (hoary bat) and Lasionycteris noctivagans (silver-haired bat). Generally rare in the Appalachians and typically present only at low densities in the summer at mid- and low-elevations, both species were detected at all sites during all seasons. Overall, mean nightly activity of bats was higher in the summer than the spring or fall. We observed 3.7–5 times greater activity of L. cinereus in spruce-fir forests during the summer compared to spring and fall, whereas L. noctivagans had 1.3–5 times more activity in the summer compared to other seasons. After accounting for precipitation events, our finite mixture models showed that season, temperature, elevation, and canopy height influenced L. cinereus activity, whereas season and temperature affected L. noctivagans activity. Our observations suggest that high-elevation spruce-fir forests are providing summer foraging and possibly day-roosting habitat of tree bats not previously documented this far south in North America.

Acidic Deposition and Climate Warming as Drivers of Tree Growth in High-Elevation Spruce-Fir Forests of the Northeastern US

Acid rain in eastern North America contributed to the widespread decline of red spruce in high-elevation spruce-fir forests. With recent reductions in acid deposition and a warming climate, resurgence of red spruce growth has been reported in some mountain areas. Based on an extensive tree-ring sampling network established across elevations (600 to 1200 m above sea level) in spruce-fir forests on 10 mountains in the northeastern US (New York, Vermont, New Hampshire, and Maine), we investigated whether this resurgence was specific only to red spruce or if it occurred also in the codominant balsam fir. Furthermore, we tested if tree growth changes for both species were related to recent trends in acidic deposition and climate. Sharply increasing growth rates of red spruce were evident at all elevations and most closely correlated with increasing rainwater pH. Although climate of the previous year (cool July and warm November) explained higher spruce growth in certain years, recent trends in climate did not drive observed increases in spruce growth. In contrast, balsam fir exhibited no regional growth surge during the period of spruce recovery. Thus, spruce growth resurgence appears to be mediated primarily by declining acid deposition and not climatic changes or stand dynamics that would also impact fir growth. Although high-elevation forests may ultimately be at risk for future warming-related heat and drought stress, the observed recent dramatic resurgence of spruce growth illustrates the benefits of policy-driven reductions in acidic deposition for the health and productivity of northeastern US forests.

Climates on the move: Implications of climate warming for species distributions in mountains of the northeastern United States

Mountains contain steep but constricted climate gradients that can provide climate warming refugia often overlooked in coarse-scale models of species migrations. With continued climate warming, the potentially important role of mountains in maintaining suitable climate for migrating species is still not clear. To determine if mountains in the northeastern U.S. can continue to serve as refugia for species in high-elevation spruce-fir forests under warming climate, we studied climate and climate-vegetation relations along elevational gradients across 76 sites on 11 mountains in four states of this region. We calculated (a) fine-scale temperature lapse rates using in situ climate loggers on each mountain, and (b) regional long-term temperature trends using 36 meteorological stations, in order to determine (c) recent and expected future shifts in species temperature envelopes along elevational gradients by linking lapse rates with regional temperature trends and climate warming scenarios for 2100 (+1, 3, and 5°C). Since 1960, temperature regimes have shifted upslope on average by 377m and 133m for the monthly mean of daily minimum (Tmin) and maximum (Tmax) temperatures, respectively, although climate did not warm equally for all months. By 2100, mid-range warming of 3°C may shift monthly temperature regimes upslope relative to their 1960s locations on average by 986m for Tmin (580m for 1°C, and 1393m for 5°C scenario) and 588m for Tmax (285m for 1°C, and 891m for 5°C scenario). We confirmed that spruce-fir forest distribution in the northeastern U.S. is strongly related to temperature, particularly October Tmax that has surprisingly differed from the overall warming trend as it cooled slightly since the 1960s and thus possibly contributed to the recent downslope shifts in some species ranges documented across the region in other studies. However, the vast majority of monthly temperature variables suggest considerable climate warming since the 1960s, and, given the expected future warming, the temperature regimes characteristic of the lower range margin of spruce-fir forests are unlikely to be present on many mountains in the region by 2100. Consequently, mountains in the northeastern U.S. may not provide long-term climate refugia for species dependent on the climate currently found in spruce-fir forests unless they can adapt to warmer temperatures.

The Influence of Western Spruce Budworm on Fire in Spruce-Fir Forests

Western spruce budworm (Choristoneura freemani Razowski; WSBW) is the most significant defoliator of coniferous trees in the western United States. Despite its important influence on Western forests, there are still gaps in our knowledge of WSBW’s impact on fire, and little research has been done on this relationship in high-elevation spruce-fir forests. Although this species is native to western North America, current outbreaks have persisted for many years in some areas, leading to high mortality rates among host tree species. Using the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS), we examined the current and future impact of an ongoing WSBW outbreak on potential fire behavior in spruce-fir forests in northern New Mexico, USA. We found that this ongoing WSBW outbreak resulted in little to no difference in fire behavior under moderate fire weather conditions. Under high-severity fire weather conditions, stands enduring WSBW outbreaks experienced less severe fire behavior. We also found that WSBW outbreaks resulted in a decrease in fire behavior under severe fire weather conditions for 40 years following the outbreak.

High-Elevation Observations of Long-Tailed Weasel and Eastern Chipmunk in North Carolina

Abstract Observations of Mustela frenata (Long-tailed Weasel) are rare within the southern Appalachians, while observations of Tamias striatus (Eastern Chipmunk) are uncommon in high-elevation spruce-fir forests. We conducted camera-trap surveys at Roan Mountain Highlands, Mitchell County, NC, during summer 2016 in a Picea rubens (Red Spruce)—Abies fraseri (Fraser Fir) forest. During the survey, we observed a Long-tailed Weasel at 1893 m in elevation and an Eastern Chipmunk at 1703 m in elevation. These are the highest-elevation records for both species in the eastern United States outside of Great Smoky Mountains National Park, and the highest elevation record for Longtailed Weasel in North Carolina.

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.

Interspecific aggression by the Swainson's Thrush (Catharus ustulatus) may limit the distribution of the threatened Bicknell's Thrush (Catharus bicknelli) in the Adirondack Mountains

ABSTRACT Bicknell's Thrush (Catharus bicknelli) is a threatened species that inhabits high-elevation spruce–fir forests in the northeastern United States. Bicknell's Thrush populations are predicted to shift upslope in response to global warming, leading to local extinctions on mountains that lack the elevational extent to accommodate such shifts. However, biotic interactions may influence how montane species respond to changing abiotic conditions. In territorial songbirds, for example, aggression from dominant low-elevation species has been hypothesized to combine with warming temperatures to “push” populations of subordinate montane species upslope at a faster rate than in the absence of interspecific aggression. This “push” hypothesis could apply to Bicknell's Thrushes: the related Swainson's Thrush (Catharus ustulatus) inhabits lower elevations, Bicknell's Thrushes are largely confined to mountaintops, and interspecific aggression by Swainson's Thrushes toward Bicknell's Thrushes has been anecdotally ...

Little evidence for niche partitioning among ectomycorrhizal fungi on spruce seedlings planted in decayed wood versus mineral soil microsites

Ectomycorrhizal fungal (EMF) communities vary among microhabitats, supporting a dominant role for deterministic processes in EMF community assemblage. EMF communities also differ between forest and clearcut environments, responding to this disturbance in a directional manner over time by returning to the species composition of the original forest. Accordingly, we examined EMF community composition on roots of spruce seedlings planted in three different microhabitats in forest and clearcut plots: decayed wood, mineral soil adjacent to downed wood, or control mineral soil, to determine the effect of retained downed wood on EMF communities over the medium and long term. If downed and decayed wood provide refuge habitat distinct from that of mineral soil, we would expect EMF communities on seedlings in woody habitats in clearcuts to be similar to those on seedlings planted in the adjacent forest. As expected, we found EMF species richness to be higher in forests than clearcuts (P ≤ 0.01), even though soil nutrient status did not differ greatly between the two plot types (P ≥ 0.05). Communities on forest seedlings were dominated by Tylospora spp., whereas those in clearcuts were dominated by Amphinema byssoides and Thelephora terrestris. Surprisingly, while substrate conditions varied among microsites (P ≤ 0.03), especially between decayed wood and mineral soil, EMF communities were not distinctly different among microhabitats. Our data suggest that niche partitioning by substrate does not occur among EMF species on very young seedlings in high elevation spruce-fir forests. Further, dispersal limitations shape EMF community assembly in clearcuts in these forests.

Carex fumosimontana (Cyperaceae), a new endemic from the Great Smoky Mountains National Park, North Carolina and Tennessee

Carex fumosimontana (Great Smoky Mountain Sedge), a new and narrowly endemic species of section Phacocystis, is described from the southern Appalachian Mountains of North Carolina and Tennessee, in the southeastern United States. It differs from the closely related C. gynandra in its dark reddish-brown pistillate scales that are strongly retuse apically, shorter spikes, narrower leaves, and strongly red-scabrous proximal sheath faces. It is locally abundant and sometimes the dominant sedge where it occurs in spite of being completely restricted to high-elevation spruce-fir forests and associated environs of Great Smoky Mountains National Park.

Microbial community diversity and composition across a gradient of soil acidity in spruce–fir forests of the southern Appalachian Mountains

Anthropogenic deposition of sulfur (S) and nitrogen (N) contributes substantially to soil acidity in some forest regions and hence studies have focused on modeling and quantifying depositions in landscapes. The resulting acidity can change the soil chemical balance, nutrient availability, microbial communities, and at a broader scale, ecosystem functioning. In this study, a 16S PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) approach was used to measure the bacterial diversity and identify the dominant bacterial species along a soil acidity gradient in high elevation spruce–fir forests of Great Smoky Mountains National Park (GSMNP). Sample sites were selected based upon modeled S deposition class (6–14, 15–23, 23–32, and 33–41kgha−1). Collected soils were analyzed for pH, C, N, Ca, Al, S, CEC, and base saturation. Average soil pH in the O, A, and B horizons were 3.6, 3.6 and 3.9, respectively. Modeled S deposition was found to be an unreliable predictor of soil S content as well as most other soil chemical properties. DGGE profiles of bacterial partial 16S rRNA genes revealed minor differences in bacterial diversity while communities were similar, dominated by members of phylum Actinobacteria, Acidobacteria, Planctomycetes, Proteobacteria, and Chloroflexi. Dominance of acidophilic bacterial species, often found in highly acidic environment such as acid-mine drainage and sphagnum bogs, suggests that the poorly buffered soils that are endemic to southern Appalachian spruce–fir forests are saturated with acidity. Our results suggest that stricter air quality standards have not resulted in shift to less acid-tolerant bacteria.

Armillaria species distribution on symptomatic hosts in northern hardwood and mixed oak forests in western Massachusetts

Armillaria spp. are some of the most important forest pathogens in mixed hardwood forests of southern New England, yet their role as prominent disturbance agents is still not fully appreciated. We investigated the distribution of Armillaria species across eight separate stands of northern hardwood and mixed oak forests in western Massachusetts. We were specifically interested in the Armillaria species distribution from live, symptomatic hosts and not in determining overall incidence in the forest. From 32 plots (16 within each forest type), 320 isolates were collected. Armillaria was routinely encountered causing disease of live trees. In total, 89% (286/320) of all isolations came from live hosts exhibiting symptoms of root and butt rot. Overall, A. gallica was the dominant species in each forest type, making up 88/160 (55%) isolates from northern hardwood and 153/160 (96%) of all isolations from mixed oak stands. However, northern hardwood forests showed much greater species diversity, as A. calvescens, A. gemina, A. ostoyae, and A. sinapina were all found. At one site, a northern hardwood forest surrounding a high elevation spruce-fir forest, A. ostoyae was the most abundant species encountered. All five Armillaria species were found causing disease of live hosts, including A. gemina, a species considered by some as weakly virulent. Armillaria gallica was found on 22/23 tree species’ sampled, and was found most often causing butt rot.

A New Vole (Cricetidae: Arvicolinae: Proedromys) from the Liangshan Mountains of Sichuan Province, China

Abstract In 2000, 2002, and 2006 we captured small mammals in the Liangshan Mountains, Mabian Dafengding National Nature Reserve and Meigu Dafengding National Nature Reserve, Sichuan Province, China. Among the collected specimens we identified a new species of the genus Proedromys. Its identifying characteristics are its relatively long tail, broad upper incisors without grooves, comparatively short lower incisors, and features of the molar teeth. The glans penis of the new species also is distinctive, the proximal and distal bacula are bony, whereas the lateral bacula are only slightly ossified. The proximal baculum is flask-shaped, the distal baculum is cap-shaped, and the lateral bacula are stick-shaped. This species is associated with high-elevation spruce–fir forest habitat, an unusual setting for Proedromys across its geographic range.

Carbon sources and sinks in high-elevation spruce–fir forests of the Southeastern US

Abstract This paper examines carbon (C) pools, fluxes, and net ecosystem balance for a high-elevation red spruce–Fraser fir forest [Picea rubens Sarg./Abies fraseri (Pursh.) Poir.] in the Great Smoky Mountains National Park (GSMNP), based on measurements in fifty-four 20 m × 20 m permanent plots located between 1525 and 1970 m elevation. Forest floor and mineral soil C was determined from destructive sampling of the O horizon and incremental soil cores (to a depth of 50 cm) in each plot. Overstory C pools and net C sequestration in live trees was estimated from periodic inventories between 1993 and 2003. The CO2 release from standing and downed wood was based on biomass and C concentration estimates and published decomposition constants by decay class and species. Soil respiration was measured in situ between 2002 and 2004 in a subset of eight plots along an elevation gradient. Litterfall was collected from a total of 16 plots over a 2–5-year period. The forest contained on average 403 Mg C ha−1, almost half of which stored belowground. Live trees, predominantly spruce, represented a large but highly variable C pool (mean: 126 Mg C ha−1, CV = 39%); while dead wood (61 Mg C ha−1), mostly fir, accounted for as much as 15% of total ecosystem C. The 10-year mean C sequestration in living trees was 2700 kg C ha−1 year−1, but increased from 2180 kg C ha−1 year−1 in 1993–1998 to 3110 kg C ha−1 year−1 in 1998–2003, especially at higher elevations. Dead wood also increased during that period, releasing on average 1600 kg C ha−1 year−1. Estimated net soil C efflux ranged between 1000 and 1450 kg C ha−1 year−1, depending on the calculation of total belowground C allocation. Based on current flux estimates, this old-growth system was close to C neutral.

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.

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.

Soluble organic nitrogen in forests and adjacent clearcuts in British Columbia, Canada

Soluble organic N (SON) is recognized to be a source of N for plants, but the few studies of the effects of clear-cut harvesting on SON levels have reported inconsistent results. SON and soluble inorganic N (SIN) contents were measured in 1 mol/L KCl extracts of soil from forests and clearcuts in coastal cedar–hemlock forests near Port McNeill, B.C., and in high-elevation spruce–fir forests near Sicamous, B.C. To characterize the seedling root environment, sampling was confined to the top 20 cm of soil (consisting of forest floor at Port McNeill and forest floor plus mineral soil at Sicamous). Amino acid N and microbial N were determined on subsets of the samples. At both sites, SON content tended to be lower in clearcuts than in forests. Lower SON contents in clearcuts were caused by the removal of F-layer forest floor at Port McNeill and by reduced SON concentrations in the forest floor at Sicamous. Correlation analyses indicated close relationships between moisture content, SIN, SON, and microbial N. Changes in SON, SIN, and microbial N concentrations during buried bag incubations could not be explained simply by exchange among these three N pools. Free amino acid N accounted for 1–1.5% of the total SON content.