Clearcut Plots Research Articles

Spatial and Temporal Variation in the Response of Understory Vegetation to Disturbance in a Central Appalachian Oak Forest

SMALL, C.J. AND B.C. MCCARTHY (Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701). Spatial and Temporal Variation in the Response of Understory Vegetation to Disturbance in a Central Appalachian Oak Forest. J. Torrey Bot. 129: 136-153. 2002.-Understory vegetation in stand-initiating (7 year clearcuts) and understory-reinitiating (> 125 year mature second-growth) oak-dominated forest stands in southeastern Ohio was examined relative to topographic aspect, micro-environmental conditions, and sampling season to explore patterns of understory dynamics and stand development following management disturbance. Plots were established on upper and lower slopes across a range of aspect positions and sampled in spring and summer to capture topographic and seasonal changes in herb layer dynamics. Micro-site light, temperature, and physical soil properties differed significantly with stand age whereas fertility and moisture varied with aspect. Species richness was greater in clearcut than mature forest stands, associated with greater resource availability and spatial heterogeneity. Herb richness and abundance were greater on NWand SE-facing slopes and lower slope positions, corresponding to greater soil moisture and fertility. Greater frequencies of non-native species were also found in resource rich, clearcut plots. Canonical correspondence analysis showed stand age, aspect, and fertility to strongly influence herb layer composition. Non-metric multidimensional scaling showed compositional divergence of spring vs. summer and clearcut vs. mature forest herb samples. Composition of clearcuts and mature forests differed markedly in June, suggesting that management influences may be more pronounced in summer herb communities. Most studies of understory dynamics in eastern forests fail to account for spatial and temporal variations in site and vegetation characteristics, however, understory disturbance response appears strongly linked to these ecosystem properties. A better understanding of these factors is needed to fully understand the effects of forest management on herb layer communities in our eastern forests.

Effect of clearcutting, selection cutting, shelterwood cutting and microsites on soil surface CO 2 efflux in a tolerant hardwood ecosystem of northern Ontario

The effect of clearcutting, selection cutting, shelterwood cutting and microsites on soil surface CO 2 efflux (SSCE) evolution was evaluated in a tolerant hardwood forest ecosystem in northern Ontario from May to November, 1998 using a LI-6200 dynamic, flow-through, portable, infrared CO 2 gas analyzer. Selection and shelterwood cutting had the greatest effect, decreasing SSCE in September and October compared to control. SSCE from clearcut plots were intermediate between the control and other treatments. SSCE correlated strongly with soil temperature and weakly with soil moisture. Comparison of microsites disturbed by harvesting with those left undisturbed showed that SSCE was significantly lower on scarified microsites than on undisturbed microsites. Our results emphasize the importance of microsite distribution within harvested or otherwise treated areas, and may explain some of the discrepancies between several studies on the effect disturbed ecosystems have on SSCE.

Does shelterwood harvesting have less impact on forest floor nutrient availability and microbial properties than clearcutting?

Chemical and microbial properties of the forest floor were measured in 4-year-old shelterwood treatment plots in the montane coastal western hemlock biogeoclimatic zone of British Columbia, Canada, and compared to those in adjacent old-growth and 4-year-old clearcut plots. Forest floor pH, exchangeable Mg, total C and total N concentrations were similar in all three treatments. Bray-extractable P was significantly lower in humus from shelterwood plots, exchangeable Ca was significantly lower in humus from clearcut plots, and exchangeable K was significantly higher in humus from old-growth plots. Indices of available C (basal respiration rate, microbial biomass and metabolic quotient) were significantly higher in old-growth plots than in the two harvested treatment plots. The relative increase in maximum microbial metabolic rate due to the addition of organic nutrients was significantly greater in clearcut plots. Principal component analysis (PCA) ordination of humus samples based on C source utilization patterns of microbial communities (i.e., Biolog assay) showed distinctive clustering by treatment, although indices of substrate richness, evenness and diversity were the same in all three treatments. The relative utilization rates of substrates with the highest factor loadings on PCA axes 1 and 2 were dissimilar in each treatment. We conclude that forest floors can develop under shelterwood harvested stands to exhibit chemical and microbial properties atypical of either clearcut or old-growth plots.

Soil and litter organisms in Pacific northwest forests under different management practices

Soil and litter organisms are important indicators of stress and disturbance to forest ecosystems. In this study, soil and litter organisms were monitored for their response to different forest management practices. Litter and soil cores (0–10, 10–20 cm) were collected at approximately 8 week intervals over a 19 month period from a low elevation 110–140-year-old Douglas-fir forest and adjacent 8-year-old clearcut and from a high elevation 200–250-year-old Douglas-fir forest and adjacent 5-year-old clearcut. The low elevation clearcut had been broadcast burned and replanted with Douglas-fir trees and a grass–legume mixture whereas the high elevation clearcut was not burned, large woody debris was left, and it was replanted with Douglas-fir, Noble-fir, Grand-fir, and western white pine. The litter and soil cores were analyzed for types of microarthropods and numbers of nematodes, fungi, culturable, aerobic bacteria, spore-forming bacteria, and chitin-degrading bacteria. Microbial community metabolic profiles, using the Biolog™ method, were also generated for the 0–10 cm soil samples. Populations of Pseudomonas spp. were analyzed in the litter and soil samples using 16S rDNA fingerprints. Plant surveys were conducted to identify potential relationships of soil organisms to plant community composition. At both elevational field sites, there were significantly ( P<0.05) higher levels of nematodes and microarthropods in litter and soil in forest plots than in clearcut plots. Bacterial and fungal populations were also significantly higher in litter in forest plots than in clearcut plots at the high elevation site. In the litter and soil at the low elevation site and the soil at the high elevation site, however, microbial levels were higher in clearcut plots than in forest plots. The Pseudomonas spp. populations and the microbial community metabolic profiles in the 0–10 cm soil differed significantly between the forest and clearcut plots at the low elevation site but not at the high elevation site. At both elevational field sites, the plant cover (%) and plant density were significantly higher in clearcut plots than in forest plots. These observed differences in the population size and composition of organisms between mature forests and both low management and high management clearcuts demonstrated the impacts forest management practices may have on the soil ecosystem.

Woody Species Composition of Disturbed Forests in Intermittent Stream Bottomlands of Southern Indiana

JENKINS, M. A. (Twin Creeks Natural Resources Center, Great Smoky Mountains National Park, Gatlinburg, TN 37738) AND G. R. PARKER (Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907). Woody species composition of disturbed forests in intermittent stream bottomlands of southern Indiana. J. Torrey Bot. Soc. 128: 165-175.-Between 1993 and 1995 we sampled understory and overstory woody vegetation on 84 plots in Platanus/Asarum Wet-Mesic Bottomland forests to determine how these forests have responded to human disturbance. Four different types of disturbed stands were sampled (abandoned agricultural areas, clearcuts, group selections, and single-tree selections), and 80-100 year-old reference stands were sampled for comparison. Overstory vegetation differed in composition among these 5 stand types with abandoned agriculture, clearcut, and group selection plots exhibiting compositions very different from single-tree selection and reference plots. This was largely due to shifts in dominance by Acer saccharum and Liriodendron tulipifera across the five stand types. Although abandoned agricultural areas experienced more severe site disturbance from years of cultivation, they were similar in composition to clearcuts and group-selection openings. The mean species richness of abandoned agriculture, clearcut, and group-selection plots was generally greater than that of single-tree selection and reference plots. Abandoned agricultural areas and clearcuts had greater overstory species richness (summed across all plots), suggesting that larger canopy openings have allowed more shade-intolerant species to establish. Total species richness was greatest on abandoned agriculture plots due to an influx of drysite, disturbance, and exotic species. However, these species did not tend to dominate sites. The dominance of A. saccharum in single-tree selection openings has led to the exclusion of other species, resulting in greatly reduced overstory species richness and diversity.

Snowpack recovery in regenerating coastal British Columbia clearcuts

A study was undertaken to define curves of snowpack recovery for coastal B.C. forests. The study was conducted using repeated snow course sampling techniques under regenerating stands with a range of canopy heights, and old growth. Measurements were made over five seasons from 1992-1993 to 1996-1997. For each season, recovery factors due to both peak accumulation and post-peak ablation rate were calculated for the regenerating stands. These factors were calculated using linear interpolation between extremes defined by the peak accumulation or ablation rate of old growth and clear-cut equivalent plots. An asymptotic exponential model was found to provide a reasonable fit to the data of recovery as a function of either canopy height or canopy density. The results suggest that there is a hydrologic recovery threshold at a level where the tallest trees in the stand are at a height roughly equal to the mean peak snow depth for open sites. Recovery proceeds rapidly; at a height of 4 m or canopy density of 20%, expected recovery is about 50%. At a height of 8 m, or a canopy density of 45%, expected recovery is about 75%, and by the time the trees have reached a height of 20 m, or more than 95% canopy density, the stand approaches full recovery. These results demonstrate how clear-cut harvesting and subsequent regeneration affect snow accumulation and ablation at the site level, but do not address the important issue of how those changes affect streamflow at the watershed scale.

Snowpack recovery in regenerating coastal British Columbia clearcuts

A study was undertaken to define curves of snowpack recovery for coastal B.C. forests. The study was conducted using repeated snow course sampling techniques under regenerating stands with a range of canopy heights, and old growth. Measurements were made over five seasons from 1992-1993 to 1996-1997. For each season, recovery factors due to both peak accumulation and post-peak ablation rate were calculated for the regenerating stands. These factors were calculated using linear interpolation between extremes defined by the peak accumulation or ablation rate of old growth and clear-cut equivalent plots. An asymptotic exponential model was found to provide a reasonable fit to the data of recovery as a function of either canopy height or canopy density. The results suggest that there is a hydrologic recovery threshold at a level where the tallest trees in the stand are at a height roughly equal to the mean peak snow depth for open sites. Recovery proceeds rapidly; at a height of 4 m or canopy density of 20%, ...

The response of herbaceous-layer vegetation to anthropogenic disturbance in intermittent stream bottomland forests of southern Indiana, USA

Between 1993 and 1995 we sampled herbaceous layer vegetation on 84 plots in Platanus/Asarum Wet-Mesic Bottomland forests to determine how these forests have responded to human disturbance. Four different disturbance types were sampled (abandoned agricultural are as, clearcuts, group-selection openings, and single-tree selection openings), and uncut 80–100 year-old reference stands were sampled for comparison. Detrended Correspondence Analysis (DCA), distance analyses (chord distance and normalized Euclidean distance) and similarity analysis (Bray-Curtis similarity coefficient) suggest that agricultural use has shifted herbaceous-layer vegetation composition away from that typical of the reference forests, but that clearcutting, group-selection harvest, and single-tree selection harvest have not greatly shifted herbaceous composition. This shift in vegetation on abandoned agricultural land resulted from a loss of indicator species, such as Cardamine concatenata (Michx.) Sw., Stellaria pubera Michx., and Laportea canadensis (L.) Weddell and an influx of disturbance, exotic, and nonforest species (e.g., Lycopodium complanatum L., Lonicera japonica Thunb. and Senecio aureus L.). However, only two species found in reference stands, Erigenia bulbosa (Michx.) Nutt. and Sphenopholis obtusata (Michx.) Scribn., were missing from clearcuts, group-selection openings, and single-tree selection openings. The species richness values of abandoned agriculture, clearcut, and group-selection plots were generally greater than those of single-tree selection and reference plots. Abandoned agricultural areas had much greater total species richness because of the influx of dry-site, exotic, disturbance, and non-forest species.

Revegetation and Nitrate Leaching from Lake States Northern Hardwood Forests Following Harvest

The sugar maple (Acer saccharum Marshall)–red oak (Quercus rubra L.) and sugar maple–basswood (Tilia americana L.) ecosystems are Lake States forests that differ in net nitrification (5 and 15 g N m−2 yr−1, respectively), but experience equivalent rates of NO−3 leaching following clear‐cut harvest (≈5 g N m−2 yr−1). Our objectives were to determine whether high rates of N leaching are sustained following harvest and whether ecosystem‐specific patterns of biomass accumulation influence NO−3 loss. We studied two stands in each ecosystem and established four research plots in each stand; two plots were clear‐cut in 1991 and two were controls. In 1996, we measured soil solution NO−3 concentration (1‐m depth) and calculated areal losses by a water balance method. We used allometric equations to estimate woody biomass in clearcut plots; herbaceous biomass was clipped. In the sugar maple–red oak ecosystem, NO−3 leaching from 5‐yr‐old clear‐cut plots (0.56 g N m−2 yr−1) was significantly greater than leaching from control plots (0.05 g N m−2 yr−1). In contrast, NO−3 leaching did not differ between control (0.41 g N m−2 yr−1) and 5‐yr‐old clear‐cut (0.02 g N m−2 yr−1) in the sugar maple–basswood ecosystem; however, loss from these clear‐cut plots was significantly lower than that from clear‐cut sugar maple–red oak plots. Five years after harvest, 7.1 Mg ha−1 of aboveground biomass accumulated in clear‐cut sugar maple–basswood plots, almost twice that of clear‐cut sugar maple–red oak plots (3.9 Mg ha−1). Five years after harvest, the highest rates of NO−3 loss occurred in the sugar maple–red oak ecosystem, in which aboveground biomass accumulation was least.

SOIL MICROBIAL CONTROL OF NITROGEN LOSS FOLLOWING CLEAR-CUT HARVEST IN NORTHERN HARDWOOD ECOSYSTEMS

Establishing the relationship among the spatial distribution of forest ecosystems, N cycling processes, and N loss following harvesting could enable land managers to anticipate and predict the potential for N loss at the scale of local and regional landscapes. In the Great Lakes region, northern hardwood forests with distinct floristic, edaphic, and physiographic characteristics vary predictably across the landscape in N cycling processes, especially in rates of nitrification. Although their landscape distribution and patterns of N cycling are well established, it is uncertain whether this type of information could be used to predict landscape-level patterns of N loss following overstory harvest or other types of disturbance. We studied the microbial processes in soil that control the retention and loss of N following clear-cutting in two northern hardwood ecosystems that are widely distributed in the upper Great Lakes states and differ floristically, edaphically, and in N cycling processes. The overstory of one hardwood ecosystem is dominated by Acer saccharum and Quercus rubra, and the other is dominated by A. saccharum and Tilia americana. These ecosystems differ in annual rates of net nitrification (5 vs. 15 g NO3−-N·m−2·yr−1), and we studied paired intact and clear-cut plots within them to understand whether spatial patterns of nitrification could be used to predict N loss following harvest. We measured microbial biomass, NO3− leaching, denitrification, and microbial N transformations for one year following a clear-cut harvest. Clear-cut harvest led to significant loss of N through NO3− leaching in both ecosystems, averaging 4.9 g N·m−2·yr−1 in clear-cut plots and 0.2 g N·m−2·yr−1 in intact plots. Denitrification was low in both ecosystems (0.08–0.42 g N·m−2·yr−1) and did not increase significantly following clear-cutting (0.16–0.29 g N·m−2·yr−1). Averaged across ecosystems, annual net N mineralization increased by a factor of 2 in clear-cut plots (14.2 g N·m−2·yr−1) relative to intact plots (7.3 g N·m−2·yr−1); net nitrification similarly increased after harvest (11.4 g N·m−2·yr−1 clear-cut vs. 5.5 g N·m−2·yr−1 intact). Gross rates of N mineralization and nitrification displayed a response similar to that of net rates. Although gross rates of N immobilization increased following clear-cutting, microbial biomass did not change. Thus, increased turnover of N through microbial biomass ([biomass N]/[gross N immobilization]) resulted in the observed increase in net N mineralization rates. Our results indicate that microbial immobilization of N was not an important process of N retention following clear-cut harvest in sugar maple-dominated northern hardwood forests. Rather, increases in net N mineralization following harvest increased substrate availability to nitrifying bacteria, which eventually resulted in substantial losses of N through leaching. Regardless of initial differences in net nitrification, harvesting led to similar rates of rates NO3− leaching from both northern hardwood ecosystems. We conclude that N loss following clear-cutting in these forests cannot be predicted by rates of nitrification prior to harvest. Rather, N loss depends on high initial rates of net N mineralization and on the effects of changes in microclimatic conditions and heterotrophic activity on NH4+ availability to nitrifying bacteria following overstory removal.

Clearcuts, Salamanders, and Field Studies

Environmental impact assessment is an extremely difficult area in which to conduct field research studies. There are many design problems due to difficulties in finding controls and in randomization and replication of study plots. Often, the need for results in a short time and with little expenditure poses practical difficulties. Currently, examining effects of clearcutting and other forest management techniques on herpetofauna is a very active field. The studies in question deal specifically with Plethodontid salamanders of the Southern Appalachians. We note that there are (at least) two fundamentally different approaches considered in the literature for the estimation of salamander population recovery following clearcutting. One approach, used by Ash (1988, 1997), is a direct longitudinal approach. Matched control and treated (clearcut) plots at different locations are followed over time-ideally from before clearcutting until many years later-to monitor the recovery of the salamander populations. This is an example of the well-known beforeafter-control-impact (BACI) design (e.g., Green 1979; Eberhardt & Thomas 1991). Assuming that the control and treated plots (in absence of clearcutting) would have had the same time trends since clearcutting, recovery can be measured directly, provided that the different sites are measured over a long enough time period. At intermediate time points, extrapolation of trends forward in time is necessary and requires the additional assumption that past recovery trends will hold in the future. Ash (1997) assumes that the recovery trends can be extrapolated linearly. Another approach, used by Petranka and coworkers (Petranka et al. 1993, 1994), is a time-specific approach. Sites of different ages since clearcutting are all sampled at one specific point in time to monitor the current status of salamander populations. Recovery of clearcut

Effect of subalpine canopy removal on snowpack, soil solution, and nutrient export, Fraser Experimental Forest, CO

Research on the effects of vegetation manipulation on snowpack, soil water, and streamwater chemistry and flux has been underway at the Fraser Experimental Forest (FEF), CO, since 1982. Greater than 95% of FEF snowmelt passes through watersheds as subsurface flow where soil processes significantly alter meltwater chemistry. To better understand the mechanisms accounting for annual variation in watershed streamwater ion concentration and flux with snowmelt, we studied subsurface water flow, its ion concentration, and flux in conterminous forested and clear cut plots. Repetitive patterns in subsurface flow and chemistry were apparent. Control plot subsurface flow chemistry had the highest ion concentrations in late winter and fall. When shallow subsurface flow occurred, its Ca 2+ , SO 4 and HCO 3 - concentrations were lower and K + higher than deep flow. The percentage of Ca 2+ , NO SO 4 2- , and HCO 3 - flux in shallow depths was less and K + slightly greater than the percentage of total flow. Canopy removal increased precipitation reaching the forest floor by about 40%, increased peak snowpack water equivalent (SWE) > 35%, increased the average snowpack Ca 2+ , NO 3 - , and NH 4 + content, reduced the snowpack K + content, and increased the runoff four-fold. Clear cutting doubled the percentage of subsurface flow at shallow depths, and increased K + concentration in shallow subsurface flow and NO 3 - concentrations in both shallow and deep flow. The percentage change in total Ca 2+ , SO 4 2- , and HCO 3 - flux in shallow depths was less than the change in water flux, while that of K + and NO 3 - flux was greater. Relative to the control, in the clear cut the percentage of total Ca 2+ flux at shallow depths increased from 5 to 12%, SO 4 2- 5.4 to 12%, HCO 3 - from 5.6 to 8.7%, K + from 6 to 35%, and NO 3 - from 2.7 to 17%. The increases in Ca 2+ and SO 4 2- flux were proportional to the increase in water flux, the flux of HCO 3 - increased proportionally less than water flux, and NO 3 - and K + were proportionally greater than water flux. Increased subsurface flow accounted for most of the increase in non-limiting nutrient loss. For limiting nutrients, loss of plant uptake and increased shallow subsurface flow accounted for the greater loss. Seasonal ion concentration patterns in streamwater and subsurface flow were similar.

Effects of Clear-Cutting and Plant Competition Control Methods on Carabid (Coleoptera: Carabidae) Assemblages in Northwestern Ontario

Total captures, species richness, diversity, and assemblages of adult carabids (Coleoptera: Carabidae) in a boreal mixed-wood ecosystem study were compared among unharvested, and clear-cut plots untreated or treated with herbicides (Vision® and Release®), mechanical treatments (brush saw and Silvana Selective). Carabids were sampled using unbaited pitfall traps for one growing season 7 and 9 years after clear-cutting, in the second growing season after competition control was applied. A total of 5032 individuals representing 30 species were collected between June 1 and September 25, 1995. Total catches were not affected by the harvest or the conifer release alternatives applied. Species richness and diversity increased following conifer release alternatives. Ten species showed habitat preferences after treatment whereas the remaining 20 species were not significantly affected by treatment.

Nitrification and denitrification in soil from a clear-cut norway spruce ( Picea abies) stand

Laboratory measurements of nitrification and denitrification were made on samples of the humus layer from a Norway spruce ( Picea abies L.) experimental site that was clear-cut 2 y before this study. For 30 y before the clear-cutting, the stand had been repeatedly fertilized with nitrogen and/or limed. In addition to the nitrogen-fertilized and/or limed experimental plots, there was also a clear-cut control plot and a forested reference plot that was not clear-cut. Aerobic incubation experiments were used to study net production of (NO 2+NO 3)-N, and an aerobic soil-suspension technique was used to study the nature and pH-dependency of nitrification. The numbers of nitrifiers were determined by a MPN method. Nitrification, which was active only in clear-cut plots, was acid-sensitive (no production at pH 4) and autotrophic, as it was inhibited by 2.5 Pa of acetylene. When the amount of NH 4-N was not limiting, as in soil suspension, the pH controlled nitrification: in a pH gradient from 4.2 to 6.2, higher pH values resulted in higher production of (NO 2+NO 3)-N. The soils from the clear-cut plots had an abundant community of nitrifiers, whereas in the forested reference soil, less than 10 NH 4-oxidizers cm −3 of soil were observed. Denitrification occurred in soils from all the clear-cut plots, and the main product was N 2. Denitrification started in the forested reference soil only after the addition of NO 3-N in the laboratory, and the main product was N 2O. In the soils from the clear-cut plots, denitrification was limited first by a lack of NO 3-N and second by pH.

Effects on erosion of two post-fire management practices: clear-cutting versus non-intervention

The different erosion responses derived from two contrasting post-fire management approaches were evaluated: the clear-cutting and immediate removal of the burnt trees and; the non-intervention, that is, leaving the vegetation untouched and the burnt trees standing. Erosion rates were obtained from 200 m 2 experimental plots, large enough to include the complete processes of rill and inter-rill erosion. Erosion rates of the clear-cut plot were very similar to those of the non-modified plot. Part of the burnt trees was still economically usable. The trees left in situ gradually decayed and were tumbled by the wind; the fire risk incremented. The opening of timber track networks without conservation measures was one of the most important erosion problems associated with clear-cutting. The complementary practice of brushwood dike-construction would need a preliminary study before being applied.

Comparative soil CO 2 evolution, litter decay, and root dynamics in clearcut and uncut spruce-fir forest

An investigation was conducted in a northern spruce-fir forest to examine the impact of forest clearcutting on soil CO 2 efflux, litter decay, and root dynamics in the first year following harvesting. During a 6-month sampling period from May-November, clearcut plots released 16% more carbon dioxide than did uncut spruce-fir reference plots. Aboveground litterfall was much greater in the uncut site; however, unit decay rates for O i horizon surface litter in cut and uncut sites were similar. Thus, excess CO 2 efflux from the harvested site did not result from increased decomposition of litter and forest floor organic matter. Fine root (≤ 3 mm) biomass and necromass varied over the sampling period between cut and uncut sites, and live root biomass declined steeply over the growing season in the clearcut plots. Fine root decomposition in the O horizon of harvested plots equalled 35% of the initial standing crop of fine root biomass + necromass in the forest floor of the cut site, and accounted for about one-third of total soil CO 2 efflux from the clearcut site during the study period.

Inhibition of nitrification in forest soil by monoterpenes

Nitrate production was detected in untreated soil of a Norway spruce (Picea abies L.) stand only after clear-cutting the stand. The aim of this study was to determine whether allelochemical inhibition of nitrification by monoterpenes played any role in inhibiting nitrification in the stand. Therefore, soils from a clear-cut plot and from a forest plot were studied. In the field, monoterpenes (mostly α- and β-pinenes), measured by soil microair diffusive samplers, were intensively produced in the forest plot, but not in the clear-cut plot. In the laboratory, soil samples taken from the forest plot produced only small amounts of monoterpenes, indicating that monoterpenes were mainly produced by the roots and not to great extent by the soil microbial population. The effect of a mixture of monoterpenes (seven major monoterpenes detected in the field) on net nitrification, net N mineralization and denitrification activities of soil from the clear cut plot, and on carbon mineralization of soils from both the forest and clear-cut plots, was studied in the laboratory. In both aerobic incubation experiments and in soil suspensions with excess NH4-N, nitrification was inhibited by exposure to the vapours of monoterpenes at similar concentrations at which they had been detected in forest plot. This indicates direct inhibition of nitrification by monoterpenes. Exposure to monoterpenes did not affect denitrification. However, it increased respiration activity of both soils. This could also indicate indirect inhibition of nitrification by monoterpenes, due to immobilization of mineral N. Thus it seems that monoterpenes could play a role in inhibiting nitrification in the forest soil.

REGENERATION OF NORTHERN RED OAK: POSITIVE AND NEGATIVE EFFECTS OF COMPETITOR REMOVAL

The decreased ability of northern red oak (Quercus rubra) to regenerate throughout its range in the eastern United States has important ecological and economic implications. We studied regeneration of northern red oak in oak and pine stands on moderately productive sites in northern Lower Michigan. Our objectives were (1) to investigate the hypothesis that regeneration of northern red oak is more successful in pine than in oak stands and (2) to test whether removal of potential overstory and understory competitors increases regeneration success on moderately productive sites. Northern red oak acorns and 2-yr-old nursery seedlings were planted in spring 1991 in three natural oak stands and three red pine (Pinus resinosa) plantations on comparable, moderately productive sites. Each stand contained four canopy cover treatments: clearcut, 25% cover (50% the first year), 75% cover, and uncut. Each canopy cover treatment contained four understory treatments: herb-layer removal, shrub-layer removal, litter removal, and control. Seedling survival, performance, and damage due to deer and late spring frosts were quantified along with vegetation characteristics, light, soil moisture, air temperature, soil temperature, and precipitation during the 1991 and 1992 growing seasons. Survival of seedlings was significantly lower in the pine than in the oak stands; the pine stands had a higher incidence of white-tailed deer browsing and lower levels of belowground resources than the oak stands. Canopy cover treatments produced a gradient from high stress (low light and soil moisture) and low disturbance (slight browsing and frost damage) in uncut plots to low stress (high light and soil moisture) and high disturbance (high browsing and frost damage) in clear-cut plots. Understory vegetation development and soil temperature were low in uncut plots, high in clear-cut plots, and intermediate in plots with partial overstory removal. Despite poor growth, the mortality of seedlings planted in uncut plots was low. In contrast, mortality was high and surviving seedlings exhibited good growth in clearcuts. Understory treatment effects were slight compared with overstory treatment effects. Results on our sites (1) do not support the hypothesis that regeneration success of northern red oak may be greater in pine than in oak stands and (2) indicate that the positive effects of removing potential competitors on seedling growth and physiological status may be compromised by simultaneous negative effects of browsing and frost damage.

Regeneration of Northern Red Oak: Positive and Negative Effects of Competitor Removal

The decreased ability of northern red oak (Quercus rubra) to regenerate throughout its range in the eastern United States has important ecological and economic implications. We studied regeneration of northern red oak in oak and pine stands on moderately productive sites in northern Lower Michigan. Our objectives were (1) to investigate the hypothesis that regeneration of northern red oak is more successful in pine than in oak stands and (2) to test whether removal of potential overstory and understory competitors increases regeneration success on moderately productive sites. Northern red oak acorns and 2-yr-old nursery seedlings were planted in spring 1991 in three natural oak stands and three red pine (Pinus resinosa) plantations on comparable, moderately productive sites. Each stand contained four canopy cover treatments: clearcut, 25% cover (50% the first year), 75% cover, and uncut. Each canopy cover treatment contained four understory treatments: herb-layer removal, shrub-layer removal, litter removal, and control. Seedling survival, performance, and damage due to deer and late spring frosts were quantified along with vegetation characteristics, light, soil moisture, air temperature, soil temperature, and precipitation during the 1991 and 1992 growing seasons. Survival of seedlings was significantly lower in the pine than in the oak stands; the pine stands had a higher incidence of white-tailed deer browsing and lower levels of belowground resources than the oak stands. Canopy cover treatments produced a gradient from high stress (low light and soil moisture) and low disturbance (slight browsing and frost damage) in uncut plots to low stress (high light and soil moisture) and high disturbance (high browsing and frost damage) in clear-cut plots. Understory vegetation development and soil temperature were low in uncut plots, high in clear-cut plots, and intermediate in plots with partial overstory removal. Despite poor growth, the mortality of seedlings planted in uncut plots was low. In contrast, mortality was high and surviving seedlings exhibited good growth in clearcuts. Understory treatment effects were slight compared with overstory treatment effects. Results on our sites (1) do not support the hypothesis that regeneration success of northern red oak may be greater in pine than in oak stands and (2) indicate that the positive effects of removing potential competitors on seedling growth and physiological status may be compromised by simultaneous negative effects of browsing and frost damage.

Organic sulfur and the retention of nutrient cations in forest surface soils

Sulfur and cation transformations were studied in A-horizon soils from 9 plots in Deer Run State Forest (DRSF) in southeastern Missouri on two dates, and from 27 plots of the Missouri Ozark Forest Ecosystem Project (MOFEP) near DRSF, seasonally for three years. The DRSF plots were chosen based on history of timber harvest; 2–3 yr and 8–10 yr post clear-cut, with controls about 40 yt post cut. Total C and S, organic sulfur (OS), exchangeable K+ and Mg2+, and rates of microbial OS production varied by season and year in surface soils from MOFEP plots. Exchangeable K+ concentrations were correlated with total C, total S, and OS. In clear-cut DRSF A-horizon soils, OS production was greatly reduced (p < 0.05) compared with controls. Exchangeable K+ and Mg2+ also were much lower in soils from clear-cut plots than in soils from control plots (p < 0.01). Cation exchange for OS compounds with sulfhydryl groups was only marginally greater than for organic matter of similar structure with no sulfhydryl groups. Overall, litter input appears to be a key to maintaining long-term surface soil OS, K+, and Mg2+ concentrations.