Nitrogen transformations and soil processes in a wastewater-irrigated,mature Appalachian hardwood forest

Wastewater bioremediation has been practised successfully in several forests without significant adverse effect on water quality of adjacent aquatic systems. However, long-term success of wastewater irrigation systems depends on an overall positive response of the forest ecosystem to substantial amounts of added water and nutrients over time. Municipal wastewater irrigation effects on the fate of added nitrogen in a mature Appalachian hardwood forest were investigated during the first 2 years of irrigation. Wastewater was secondarily treated, chlorinated, and sprayed on the study site at five rates. Forest litter N decreased on irrigated sites due to increased litter decomposition rates. Nitrogen mineralization potential (N₀) decreased greatly in soils irrigated at a rate of 140 cm year⁻¹ for 2 years. Net nitrification and relative nitrification (the amount of NO₃⁻-N as a proportion of the total mineral N) increased proportionally with irrigation rate. The highest irrigation rates increased denitrification activity and contributed significantly to the bioremediation process by removing nitrate that otherwise would have been subject to leaching. The increase in NO₃⁻ production in the soil and limited N sequestration by the forest system nevertheless resulted in a net loss of N via leaching. Nitrate concentrations of soil water increased owing to irrigation, with the highest rate at 11 mg 1⁻¹ on sites receiving 70 cm year⁻¹. During the 2-year period, the forest ecosystem experienced a net leaching loss of N that ranged from 14.8 to 105 kg N ha⁻¹ year⁻¹, depending on the application rate. It is likely that this mature hardwood forest will continue to lose N, and that little or no additional N will be sequestered.     

Environmental controls on sap flow in a northern hardwood forest

Our objective was to gain a detailed understanding of how photosynthetically active radiation (PAR), vapor pressure deficit (D) and soil water interact to control transpiration in the dominant canopy species of a mixed hardwood forest in northern Lower Michigan. An improved understanding of how these environmental factors affect whole-tree water use in unmanaged ecosystems is necessary in assessing the consequences of climate change on the terrestrial water cycle. We used continuously heated sap flow sensors to measure transpiration in mature trees of four species during two successive drought events. The measurements were scaled to the stand level for comparison with eddy covariance estimates of ecosystem water flux (Fw). Photosynthetically active radiation and D together explained 82% of the daytime hourly variation in plot-level transpiration, and low soil water content generally resulted in increased stomatal sensitivity to increasing D. There were also species-specific responses to drought. Quercus rubra L. showed low water use during both dry and wet conditions, and during periods of high D. Among the study species, Acer rubrum L. showed the greatest degree of stomatal closure in response to low soil water availability. Moderate increases in stomatal sensitivity to D during dry periods were observed in Populus grandidentata Michx. and Betula papyrifera Marsh. Sap flow scaled to the plot level and Fw demonstrated similar temporal patterns of water loss suggesting that the mechanisms controlling sap flow of an individual tree also control ecosystem evapotranspiration. However, the absolute magnitude of scaled sap flow estimates was consistently lower than Fw. We conclude that species-specific responses to PAR, D and soil water content are key elements to understanding current and future water fluxes in this ecosystem.     

Carbon resources,soil organisms,and nitrogen availability: Landscape patterns in a northern hardwood forest

The interactions among different components of detrital food webs are likely to influence carbon processing and linkages between C and nutrient cycling. Our objective was to identify potentially important interactions in detrital food webs at the Hubbard Brook Experimental Forest, NH, USA, by exploring relationships among C resources, microbial biomass, microarthropod abundance and nitrogen availability as they vary across the landscape. We found significant spatial variation in microarthropod abundance in the forest floor across elevation zones in two watersheds, with consistently higher abundance in low-elevation hardwoods and upper conifer zones and lower abundance in mid- and high-elevation hardwoods. The same pattern was observed in the Oe horizon for microbial biomass C and respiration but not for N transformations; however, no patterns were observed in the Oa horizon. Microarthropod abundance and microbial biomass C were significantly positively correlated, but neither were related to forest floor mass or to annual aboveground fine litterfall flux. Instead, a positive correlation with fine root biomass suggests that C supply from roots plays a key role in the fungal channel of the detrital food web of these forests. The lack of relationship between patterns of microarthropod abundance and net N mineralization leads us to hypothesize that spatial patterns of nitrogen availability are not closely linked to variation in carbon flow through the detrital food web, within this forested landscape. In contrast, microarthropod abundance and net N mineralization did exhibit similar interannual variation and may respond to the same temporal controls.     

Response of bird communities to selection harvesting in a northern tolerant hardwood forest

We investigated the responses of forest birds to habitat changes following timber harvest by selection cutting in three northern tolerant hardwood forest stands using a before–after control-impact (BACI) type of experimental design. We observed only minor effects on the bird community associated with mature forests. Ovenbird (Seiurus aurocapilla) abundances declined by about 80–90% in two of the three harvested blocks. Black-throated blue warblers (Dendroica caerulescens) declined in abundance by about 70% on a single block 2 and 3 years post-harvest. Mechanical disturbance of the shrub layer [primarily Canada yew (Taxus canadensis)] was coincident to this decline. Several bird species that prefer early successional or shrubby habitats, such as veery (Catharus fuscescens), cedar waxwing (Bombycilla cedrorum), chestnut-sided warbler (Dendroica pensylvanica), magnolia warbler (Dendroica magnolia), American redstart (Setophaga ruticilla), mourning warbler (Oporornis philadelphia) and white-throated sparrow (Zonotrichia albicollis), benefited from selection cutting, with the timing of individual species’ responses related to changes in habitat structure and composition. Effects in one block were still evident 7 years after harvest. Guidelines that support a residual stocking target of 20 m²/ha should promote the retention of mature forest bird communities, including ovenbird, while still providing habitat for early successional bird species.     

Short-term effects of group-selection harvesting on breeding birds in a northern hardwood forest

We used a before-after, control-impact design (one year pre-harvest, two years post-harvest) and unlimited-radius point counts to study the effects of typical group-selection harvesting (0.5 gaps ha⁻¹ placed near seed trees within a standard single-tree selection harvest) and intensive group-selection harvesting (4 gaps ha⁻¹ placed on a grid with no harvesting between gaps) on the composition and abundance of breeding birds in tolerant hardwood forests in Algonquin Provincial Park, Ontario. Percent similarity between pre- and post-harvest bird communities was 5–9% lower in selection harvested stands than in reference stands. Differences in percent similarity among the three treatments were not significant, however, suggesting that the changes in the bird community in stands harvested with group selection were not substantially different than those in reference stands. Abundance of aerial foragers and tree-and-shrub nesters increased in response to typical and intensive group selection in the second year post-harvest. By contrast, bark foragers and cavity-nesters decreased in the first year post-harvest and then increased in the second year post-harvest in response to typical group selection. Abundance of 16 (73%) of 22 species was not affected by harvesting. Blue Jay (Cyanocitta cristata), Chestnut-sided Warbler (Dendroica pensylvanica), Least Flycatcher (Empidonax minimus), and White-throated Sparrow (Zonotrichia albicollis) increased in response to intensive group selection in the first or second year post-harvest, whereas Chestnut-sided Warbler, Hairy Woodpecker (Picoides villosus), and White-throated Sparrow increased in response to typical group selection in the first or second year post-harvest. Ovenbird (Seiurus aurocapilla) decreased slightly in response to typical group selection in the second year post-harvest. Our short-term data suggest that intensive, rather than typical, group-selection harvesting is preferred for maintaining densities of cavity-nesting birds and Ovenbird; whether these advantages continue through the remainder of the cutting cycle and beyond requires further investigation.     

Soil carbon release along a gradient of physical disturbance in a harvested northern hardwood forest

Changes in soil respiration associated with forest harvest could increase net loss of CO₂ to the atmosphere relative to pre-harvest values. By excavating quantitative soil pits across a gradient of physical disturbance in a harvested northern hardwood forest, this study examines C release from mineral soil. Mineral soil samples were analyzed for pH, percent organic matter (%OM), C and N concentration, δ¹³C, and total C per unit area. Results show a relationship between degree of disturbance and C concentration in soil 10-30 cm beneath the O-horizon. Highly disturbed sites show C depletion, with horizons from disturbed sites containing 25% less total C than the least disturbed sites. δ¹³C signatures of soil profiles at these sites show vertical mixing of plant-derived material into deeper mineral horizons. Mixing, as a result of physical disturbance, could have led to the observed C depletion by physical or chemical destabilization, or through the promotion of microbial respiration in deep mineral soil. Regardless of the mechanism, these results suggest elevated CO₂ emissions from soil following harvest, and, thus, have implications for the validity of wood biomass as a carbon neutral energy source.     

Organic matter composition and dynamics in a northern hardwood forest ecosystem 15 years after clear-cutting

Soil organic matter (SOM) plays an important role in governing soil properties and nutrient cycling in forest ecosystems. Clear-cutting alters the SOM cycle by changing decomposition rates and organic matter (OM) inputs to the forest ecosystem. We studied the 15-year clear-cutting response on the properties and composition of SOM at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. Solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to study the structural chemistry of SOM in whole soils and extracted humic substances. Overall, alkyl C and O-alkyl C were the dominant C fractions in soils and humic substances. Alkyl C accounted for 38–49% of the total NMR signal intensity in soils and 33–56% in humic substances. O-alkyl C accounted for 32–45% of the signal intensity in soils and 20–31% in humic substances. Following clear-cutting, the contribution of O-alkyl C increased in whole soils and humic acids of the Oa horizon, while alkyl C decreased in whole soils and humic acids of Oa and Bh horizons. Thus, the ratio of alkyl C to O-alkyl C, an index of the degree of decomposition of SOM, decreased in whole soils and humic acids after clear-cutting, indicating that the SOM in post-harvest soils is less decomposed relative to pre-harvest soils. On average, humic substances accounted for 47% of SOM. The concentration of humic acid decreased by up to 25% in Oa, E and Bh horizons after clear-cutting, while the concentration of fulvic acid decreased by more than 40% in the Oa and E horizons. Together, these results indicate that clear-cutting resulted in the loss of humic substances from the forest floor and upper mineral horizons, which was replaced by less decomposed OM in the post-clear-cut soils under the regrowing forest.     

Nitrogen immobilization by wood-chip application: Protecting water quality in a northern hardwood forest

Forest harvesting disrupts the nitrogen cycle, which may affect stream water quality by increasing nitrate concentrations, reducing pH and acid neutralizing capacity, and mobilizing aluminum and base cations. We tested the application of wood chips derived from logging slash to increase immobilization of N after harvesting, which should reduce nitrate flux to streams. In August 2004, a stand of northern hardwoods was patch-clearcut in the Catskill Mountains, NY, and four replicates of three treatments were implemented in five 0.2-ha cut patches. Wood chips were applied to the soil surface at a rate equivalent to the amount of slash smaller than eight inches in diameter (1× treatment). A second treatment doubled that rate (2×), and a third treatment received no chips (0×). Additionally, three uncut reference plots were established in nearby forested areas. Ion exchange resin bags and soil KCl-extractions were used to monitor nitrate availability in the upper 5–10 cm of soil approximately every seven weeks, except in winter. Resin bags indicated that the wood chips retained 30% or 42% of the nitrate pulse, while for KCl extracts, the retention rate was 78% or 100% of the difference between 0× and uncut plots. During the fall following harvest, wood-chip treated plots had resin bag soil nitrate concentrations about 25% of those in 0× plots (p = 0.0001). In the first growing season after the cut, nitrate concentrations in wood-chip treated plots for KCl extracts were 13% of those in 0× treatments (p = 0.03) in May and about half those in 0× treatments (p = 0.01) in July for resin bags. During spring snowmelt, however, nitrate concentrations were high and indistinguishable among treatments, including the uncut reference plots for resin bags and below detection limit for KCl extracts. Wood chips incubated in litterbags had an initial C:N of 125:1, which then decreased to 70:1 after one year of field incubation. These changes in C:N values indicate that the wood-chip application can potentially immobilize between 19 and 38 kg N ha⁻¹ in the first year after harvesting, depending on the rate of wood-chip application. Our results suggest that the application of wood chips following harvesting operations can contribute to the protection of water quality and warrant additional research as a new Best Management Practice following cutting in regions that receive elevated levels of atmospheric N deposition.     

Ten-year response of the herbaceous layer to an operational herbicide-shelterwood treatment in a northern hardwood forest

Shelterwood seed cutting in conjunction with herbicide site preparation has proven effective at regenerating Allegheny hardwood forests, but the long-term impact of this silvicultural system on herbaceous vegetation has not been determined. From 1994 to 2004, we studied the impacts of operational herbicide site preparation using glyphosate plus sulfometuron methyl herbicides in the context of a shelterwood seed cut. Our study took place on 10 partially cut sites on the Allegheny National Forest in northwestern Pennsylvania. Half of each site received herbicide and half did not in a split-plot design with repeated measures. Fences were erected after year six because deer impact had increased. Resilience of individual species and the community were determined using measures of percent cover by species or species groups and indices of diversity and similarity comparing post-treatment to pre-treatment conditions and controls. In the short term, abundance of all species was reduced and there were four fewer species on average in treated areas. No species was eliminated by herbicide across all sites in the long term. Graminoids were more abundant on treated plots after year six. Targeted ferns remained less abundant on treated than control plots after 10 years. Species richness recovered within 4 years following treatment. Shannon Diversity and Shannon Evenness were greater in treated than in control plots over the full study period, but the differences were not significant in any single year. The richness-based Jaccard index of similarity did not differ between control and treatment plots after year two, while relative abundance influenced indices showed significant differences through year eight. Results suggest that herbaceous layer vegetation is resilient to the disturbance created by herbicide-shelterwood treatments.     

Short- and long-term responses of total soil organic carbon to harvesting in a northern hardwood forest

The long-term response of total soil organic carbon pools (‘total SOC’, i.e. soil and dead wood) to different harvesting scenarios in even-aged northern hardwood forest stands was evaluated using two soil carbon models, CENTURY and YASSO, that were calibrated with forest plot empirical data in the Green Mountains of Vermont. Overall, 13 different harvesting scenarios that included four levels of aboveground biomass removal (20%, 40%, 60% and 90%) and four different rotation lengths (60 year, 90 year, 120 year, and No Rotation (NR)) were simulated for a 360 year period. Simulations indicate that following an initial post-harvest increase, total SOC decreases for several decades until carbon inputs into the soil pool from the re-growth are greater than losses due to decomposition. At this point total SOC begins to gradually increase until the next harvest. One consequence of this recovery pattern is that between harvests, the size of the SOC pool in a stand may change from −7 to 18% of the pre-harvest pool, depending on the soil pool considered. Over 360 years, the average annual decrease in total SOC depends on the amount of biomass removed, the rotation length, and the soil pool considered. After 360 years a stand undergoing the 90yr-40% scenario will have 15% less total SOC than a non-harvested stand. Long-term declines in total SOC greater than 10% were observed in the 60yr-60%, 60yr-90%, and 90yr-90% scenarios. Long-term declines less than 5% were observed in scenarios with 120 year rotations that remove 60% or less of the aboveground biomass. The long-term decreases simulated here for common management scenarios in this region would require intensive sampling procedures to be detectable.     

Ten-year response of bird communities to an operational herbicide-shelterwood treatment in a northern hardwood forest

Use of herbicides in forestry to direct successional trajectories has raised concerns over possible direct or indirect effects on non-target organisms. We studied the response of forest birds to an operational application of glyphosate and sulfometuron methyl herbicides, using a randomized block design in which half of each 8 ha block received herbicide and the other acted as a control, on shelterwood seed-cut Allegheny hardwood stands in northwestern Pennsylvania. We monitored birds using 50 m radius point counts in two pretreatment years and for 10 years post-treatment (1992-2004). Fences were erected six years after herbicide treatment in response to increased deer browsing at a subset of sites. Avian responses to herbicide treatment varied by nesting guild: we detected no response by cavity-nesters, but documented declines in the shrub-, ground- and canopy-nesting guilds. Responses were short-lived (2-4 years post-treatment), but shrub-nesters did not recover until fencing provided regenerating vegetation respite from browsing. Thus, apparent responses of birds to herbicide were confounded with deer browsing in this study. High species turnover, even within control plots, suggests that avian communities may be assessed more appropriately assessed at larger spatial scales than those used in this study (6.5-8 ha).     

Short-term community-level response of arthropods to group selection with seed-tree retention in a northern hardwood forest

We examined the short-term effects of group-selection harvesting with seed-tree retention on ground-dwelling and bark-dwelling arthropod communities in a northern hardwood forest in the Upper Peninsula of Michigan. Arthropods were sampled in 16 group-selection openings and 8 closed canopy reference plots. Two opening sizes were examined—radii of 0.5 (320 ± 27 m², n = 8) and 1.0 (1217 ± 62 m², n = 8) times the mean canopy height (22 m). Each opening and reference plot was centered on a single Betula alleghaniensis Britt. (yellow birch). Ground-dwelling arthropods were sampled using pitfall traps that were opened for two 1-week periods (rounds 1 and 2), and bark-dwelling arthropods were sampled with sticky traps attached to the centrally located B. alleghaniensis trees. Family-level diversity of ground-dwelling arthropods was lower in reference plots than in the openings, but the only significant difference occurred during round 2, between the matrix and large openings (P < 0.01). During both sampling periods, the ground-dwelling community exhibited a distinct clustering of family-level composition along environmental gradients such as opening size. Families such as Staphylinidae (rove beetles) and Trombidiidae (red velvet mites) were not favored by higher canopy openness while families such as Acrididae (grasshoppers) and Lycosidae (wolf spiders) were captured more in openings than in the forest matrix. Landing rates of wood-boring insects such as Buprestidae (metallic wood-boring beetles) and Xiphydriidae (wood wasps) were significantly higher on seed trees in group-selection openings than in reference plots (P < 0.05). Our results suggest that integrating group-selection openings within northern hardwood forests can lead to an increase in the family-level diversity of ground-dwelling arthropods, at least in the short term. Furthermore, seed trees left in such openings may be more attractive to bark- and wood-boring insects, which warrants further investigation into the susceptibility of these seed trees to damage by certain insect pests.     

Maximum entropy modeling of mature hardwood forest distribution in four U.S. states

In the eastern United States, mature hardwood forest provides habitat for many species of native flora and fauna, but is much less common now than historically. This study examined the utility of maximum entropy modeling and spatial application to identify ecosystem types like mature hardwood forest. I performed pilot modeling in Charles County, Maryland, where I compared fine-scale geographic data available locally to coarse-scale data available nationally. As expected, a model constructed with the best locally available data, including LiDAR-derived canopy height and fine-scale soil maps, outperformed a model constructed with nationally consistent data. However, the model using national data nevertheless accurately identified most mature hardwood forest sites and excluded most young forest. I then applied the coarse-scale approach to four states: Pennsylvania, Ohio, Kentucky, and Tennessee. Average test AUC (area under the receiver operating curve) based on 10 replicates varied from 0.76 to 0.80 when comparing mature hardwood forest locations to general forest locations. The maximum training or test sensitivity plus specificity threshold, depending on the state, captured 78-79% of positive locations while rejecting 74-81% of negative locations. The maximum entropy approach is versatile, and can be applied to other ecosystems and species.     

Stand dynamics and tree quality response to precommercial thinning in a northern hardwood forest of the Acadian forest region: 23 years of intermediate results

In the late 1980s, large forest companies began precommercial thinning (PCT) operations in young northern hardwood cutovers in New Brunswick, Canada. To provide supporting growth and yield information, an industrial experiment was established at residual stand densities of 1300, 1600, 1900, and 2200?stems?ha^?1. Stand responses were examined for measurements recorded at 0 (1987), 5 (1992), 10 (1997), 16 (2003), and 23 (2010) years after establishment. Average diameter at breast height, quadratic mean diameter, stand basal area, and stand total volume growth increased as stem density decreased from PCT. There were significant linear differences for many of these variables between treatments and time periods (year). No significant differences were detected in tree height between treatments. In 2010, the four PCT thinning treatments did not exhibit any differences in potential sawlogs at 2.4?m (8?ft) and 3.6?m (12?ft) lengths. Significant differences were observed for 4.9?m (16?ft) sawlogs that were produced at the least dense spacing (1300?stems?ha^?1). Results from this study and recommendations from the European literature suggest that value-added timber products may be produced from more intense PCT treatments than are currently being practiced on sites dominated by yellow birch (Betula alleghaniensis Britt.).     

Leaf turnover and growth responses of shade-grown saplings of four Shorea rain forest species to a sudden increase in light

We tested the hypothesis that sapling growth following a sudden increase in solar irradiance is related to recovery from photoinhibition and the balance between rate of production of new leaves and rate of abscision of old leaves. Leaf gas exchange, chlorophyll fluorescence and relative growth rate (RGR) of stem basal area were measured following the sudden exposure of shade-grown (7% of full sunlight) saplings of four Shorea species to full sunlight. Sudden exposure to full sunlight resulted in an immediate and substantial reduction in dark-adapted quantum yield of photosystem II (Fv/Fm), followed by a gradual recovery in all species. Near light-saturated net assimilation rate (A max) and area-based leaf chlorophyll concentration ([Chl area]) also declined immediately after exposure. Eleven days after exposure, A max had recovered to pre-exposure values in all species, whereas [Chl area] had not recovered. Across species, RGR of stem basal area increased with increasing RGR of the number of leaves following exposure to full sunlight. The interspecific variations in RGR of stem basal area suggest that new leaf production is crucial for determining the potential growth of saplings following gap formation.     

The relation of harvesting intensity to changes in soil, soil water, and stream chemistry in a northern hardwood forest, Catskill Mountains, USA

Previous studies have shown that clearcutting of northern hardwood forests mobilizes base cations, inorganic monomeric aluminum (Al_im), and nitrate (NO₃⁻-N) from soils to surface waters, but the effects of partial harvests on NO₃⁻-N have been less frequently studied. In this study we describe the effects of a series of partial harvests of varying proportions of basal area removal (22%, 28% and 68%) on Al_im, calcium (Ca²⁺), and NO₃⁻-N concentrations in soil extracts, soil water, and surface water in the Catskill Mountains of New York, USA. Increases in NO₃⁻-N concentrations relative to pre-harvest values were observed within a few months after harvest in soils, soil water, and stream water for all three harvests. Increases in Al_im and Ca²⁺ concentrations were also evident in soil water and stream water over the same time period for all three harvests. The increases in Al_im, Ca²⁺, and NO₃⁻-N concentrations in the 68% harvest were statistically significant as measured by comparing the 18-month pre-harvest period with the 18-month post-harvest period, with fewer significant responses in the two harvests of lowest intensity. All three solutes returned to pre-harvest concentrations in soil water and stream water in the two lowest intensity harvests in 2-3 years compared to a full 3 years in the 68% harvest. When the results of this study were combined with those of a previous nearby clearcut and 40% harvest, the post-harvest increases in NO₃⁻-N concentrations in stream water and soil water suggest a harvesting level above which the relation between concentration and harvest intensity changes; there was a greater change in concentration per unit change in harvest intensity when basal area removal was greater than 40%. These results indicate that the deleterious effects on aquatic ecosystems previously demonstrated for intensive harvests in northern hardwood forests of northeastern North America that receive high levels of atmospheric N deposition can be greatly diminished as harvesting intensity decreases below 40-68%. These results await confirmation through additional incremental forest harvest studies at other locations throughout the world that receive high levels of atmospheric N deposition.     

Individual growing conditions that affect diameter increment of tree saplings after selection harvesting in a mixed forest in northern Japan

We analyzed temporal patterns in diameter growth of saplings following selection harvesting in an uneven-aged mixed stand dominated by Abies sachalinensis, Acer mono, Quercus crispula, and Betula ermanii in Hokkaido, northern Japan. We examined interspecific differences in growth responses to local growing conditions including harvesting intensity, crowding, stem size, and past duration of the small growth period. Consistent with expectations based on shade tolerance of the species, the age at which the individual reached a diameter at breast height (DBH) of 12.5 cm was highest for A. sachalinensis and lowest for B. ermanii. The interspecific growth differences between saplings that had or had not experienced local harvesting increased gradually for A. sachalinensis and B. ermanii, but peaked at around 4–6 years after harvesting for Q. crispula. Generalized linear mixed model analysis clearly suggested that individual growth conditions required to enhance diameter growth of saplings differed considerably among species. For Q. crispula and B. ermanii, local harvesting intensity was most strongly and positively associated with diameter growth rate, whereas for A. sachalinensis and A. mono, stem size had the strongest negative effect. Abies sachalinensis saplings responded more to surrounding harvesting when they were relatively small, whereas A. mono showed a weak opposite response. The duration of the small growth period before harvesting had negative effect for A. sachalinensis, but not for the other species. Our study indicated that the influence of selection harvesting on growth of shade-tolerant species depends upon pre- and post-harvest growing conditions.     

Riparian trees,shrubs, and forest regeneration in the coastal mountains of Oregon

Riparian trees and shrubs are important providers of shade, bank stability, and woody debris needed for optimal stream quality and fish habitat in the coastal mountains of Oregon, but more data are needed to relate this woody vegetation to environmental variables. Trees, shrubs, and forest regeneration were studied in 22 riparian environments to provide those data. Conifer basal area increased with elevation, stream gradient, time since disturbance, and distance from the stream; it decreased with stream width. Salmonberry (Rubus spectabilis Pursh) cover and stink currant (Ribes bracteosum Dougl. ex Hook.) cover were highest near the streams. Dwarf Oregon grape (Berberis nervosa Pursh) cover and salal (Gaultheria shallon Pursh) cover were lowest near the streams. Although forest regeneration was poor everywhere, it decreased with total shrub cover and increased with stream gradient. Existing riparian conifer stands should be maintained wherever a continuing supply of coarse woody debris is required.     

Demographic and height growth response of native broad-leaved deciduous tree saplings to overhead canopy release in a coastal Pinus thunbergii forest in Hokkaido, northern Japan

Prevention efforts to combat pine wilt disease must be instituted to avoid destruction of coastal forests in Hokkaido, northern Japan. We examine an alternative method involving the conversion of Pinus thunbergii forests to native broadleaf species through advancing their growth, but we have little knowledge about the response of advanced growth to overhead canopy release. To demonstrate the demographic and height growth response of advanced growth to the light change in a coastal Pinus thunbergii forest, canopy trees were removed and the sapling populations were monitored for 6?years. Inhibition in height growth caused by light increase was observed in Cerasus sargentii and Kalopanax septemlobus saplings. Especially in Kalopanax septemlobus, a remarkable decline was observed in the saplings growing in the darker positions which experienced light change. Therefore, large light changes should be carefully avoided for this species especially in the darker positions. In contrast, relative height growth rates of Quercus crispula and, especially, Quercus dentata increased with increasing light, and saplings tended to die in the darker positions. No dead trees of Sorbus commixta were observed during the study period. The saplings also showed good height growth even when under closed canopy. This species seems to be adaptive to a dark environment. Since Quercus dentata and Kalopanax septemlobus are the major components of the natural coastal forests in Hokkaido, gradual canopy release is available to foster advanced growth in coastal Pinus thunbergii forest, in accordance with the concept of density control in coastal forests.