bluuebunny/crossref_metadata_2025 huggingface dataset:
Résultats après 5 ans d'un essai de coupe de jardinage dans une érablière
Authors: Majcen Zoran , Richard Yvon
Published: February 2008

To study the effects of selection cutting and to determine the optimal residual basal area after such cuttings, an experimental area was established in Sainte-Véronique (Quebec) in 1983. Five-year results indicate that the gross rate of growth increases when residual basal area decreases. The best net annual basal area growth lies between 0.40 and 0.43 m2/ha in selection plots; this is almost twice the growth of control plots. Sugar maple regeneration is excellent no matter the residual basal area. Selection cuttings also resulted in a good yellow birch regeneration, and survival is better, after 5 years, in high residual basal area plots. Yellow birch regeneration is almost absent in control plots. When all factors (growth in basal area, regeneration, and tree injuries) are considered, block 2, with a residual basal area of 19.3 m2/ha, gives the best results after 5 years.
Abondance de la régénération 5 ans après la coupe à blanc mécanisée de peuplements d'épinette noire (Piceamariana)
Authors: Ruel Jean-Claude
Published: February 2008

Regeneration was studied 5 years after harvesting on 128 permanent blocks located before logging in black spruce (Piceamariana (Mill.) BSP) stands. Regeneration after 5 years was related to the abundance of advance growth, mainly black spruce layers. Regeneration also differed with the harvesting system used. Best results were obtained with the use of feller-forwarders while tree-length harversting gave the lowest softwood stockings. Regional climax and soil texture also had an effect, mostly by modifying the advance growth abundance. The better softwood stocking observed on thick humus and in the black spruce -moss climax zone was related to higher precutting regeneration levels. The regeneration problems observed on coarse textured soils were also associated with initial differences in the amount of advance growth. The duration of spruce budworm (Choristoneurafumiferana (Clem.)) infestations seemed to have an impact on the regeneration of the stands studied. Hardwoods regeneration, mostly white birch (Betulapapyrifera (Marsh.)), became established after logging or after defoliation by the spruce budworm. Their abundance was also dependent on regional climax and soil texture.
Ectomycorrhizae of Douglas-fir and western hemlock seedlings outplanted on eastern Vancouver Island
Authors: Roth A.L. , Berch S.M.
Published: February 2008

Ectomycorrhizal colonization of container-grown Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings was determined in a container nursery near Nanaimo, British Columbia, and after one growing season under a range of field conditions on eastern Vancouver Island. The percentage of Douglas-fir and western hemlock short roots colonized by ectomycorrhizal fungi in the nursery was highly variable, but over 99% of the ectomycorrhizae were formed by Thelephoraterrestris Ehrh.:Fr. Between 72 and 93% of the new roots were ectomycorrhizal after one field season, and Thelephoraterrestris remained the dominant fungus in most cases. Rhizopogonvinicolor like ectomycorrhizae were also common on new roots of Douglas-fir. Cenococcumgeophilum Fr. was less common. Douglas-fir seedlings formed 33 morphologically distinct ectomycorrhizae on eight sites within one growing season in the field. Western hemlock formed nine types on a single site.
Long shoot terminal bud development and the differentiation of pollen- and seed-cone buds in Pinuscaribaea var. hondurensis
Authors: Harrison Derek L.S. , Slee Mike U.
Published: February 2008

Bud type differentiation and development were investigated in early and late flowering grafted clones of Pinuscaribaea Morelet var. hondurensis Barr. & Golf. (Caribbean pine) growing at two sites in the tropical north of Australia. Regardless of the early and late flowering tendencies, pollen- and seed-cone buds began to differentiate in middle and late March, respectively. Unlike the cone buds of temperate pines, there was no apparent pause in development between pollination and differentiation. The long shoot terminal bud organogenic sequence resembled that described in temperate pines and led to an episodic, monocyclic shoot growth pattern. The formation of up to several long shoot terminal buds between the onset of seed-cone-bud differentiation and flowering frequently resulted in multiple sets of seed cones.
Bark temperature patterns in mountain pine beetle susceptible stands of lodgepole pine in the central Rockies
Authors: Schmid J.M. , Mata S.A. , Schmidt R.A.
Published: February 2008

Bark temperatures were recorded on five lodgepole pine (Pinuscontorta Dougl. ex Loud.) in stands of different growing stock levels in Colorado and Wyoming. Mean bark temperatures were significantly different among growing stock levels. Temperatures in the partially cut growing stock levels were significantly warmer than in uncut controls during diurnal hours, but temperatures were cooler during nocturnal hours. Bark temperatures correlated with ambient air temperature. Equations were developed for predicting north- and south-side bark temperatures for partially cut stands of three growing stock levels and an uncut control from air temperatures. Bark temperature patterns in lodgepole and ponderosa pine (Pinusponderosa Laws.) stands are compared. The relationship between growing stock level and mountain pine beetle (Dendroctonusponderosae Hopk.) infestation is discussed from the standpoint of bark temperatures.
Intra- and inter-clonal variation in gypsy moth larval performance on bigtooth and trembling aspen
Authors: Chilcote Charley A. , Witter John A. , Montgomery Michael E. , Stoyenoff Jennifer L.
Published: February 2008

A field study on the effects of interclonal and intraclonal variations of aspens on the performance of gypsy moth, Lymantriadispar (L.), was conducted in Michigan during 1988 and 1989. Study species were trembling aspen, Populustremuloides Michx., and bigtooth aspen, Populusgrandidentata Michx. Larvae were caged on intact host trees in the field in fine mesh bags. We examined the leaf phenological development of aspen clones and its relationship to a number of insect parameters: larval weight, relative growth rates, survival, and pupal weights. Interclonal variations in larval growth on trembling aspen clones and bigtooth aspen clones were high in 1988 and 1989. Leaf phenological differences between clones also were highly significant. These differences in leaf phenology led to a window of vulnerability existing for each clone. While insects that initiated feeding on phenologically delayed clones had poorer survival and lower growth rates than did larvae on more phenologically advanced clones, later in the season these larvae were able to catch up as the phenology of delayed clones caught up to that of more advanced clones. Because of this, pupal weights did not show significant effects of clones. Intraclonal variation in larval growth was extremely low for all growth periods. While there were significant differences in phenology between ramets within clones, the variation was much less than the variation seen in phenological differences between clones. Phenology of caged branches within a tree did not vary significantly for either species.
Factors affecting the relationship between sapwood area and leaf area of balsam fir
Authors: Coyea Marie R. , Margolis Hank A.
Published: February 2008

The ratio between projected leaf area (LA) and cross-sectional sapwood area (SA) of dominant and codominant balsam fir trees (Abiesbalsamea (L.) Mill.) was determined in 24 forest stands across the province of Quebec. Various physical factors proposed in the Whitehead hydraulic model, and some of the easily measured surrogates of these factors, were tested for their influence on LA:SA ratios. Average growing season vapor pressure deficit, temperature, precipitation, and stand drainage class did not significantly influence LA:SA ratios. On the other hand, LA:SA ratios were positively influenced by sapwood permeability (k), tree height, and crown length. As suggested by the model, there was a positive correlation between sapwood permeability and LA:SA ratio and a negative correlation between tree height or crown length and LA/(SA k). Increases in sapwood permeability with tree age were associated with longer tracheids having larger lumen diameters. Of the various empirical factors tested, only site quality, 5-year basal area growth, and age had a significant influence on LA:SA ratios. Sapwood cross-sectional area at breast height by itself was a reasonable linear predictor of LA for all stands (LA = −0.158 + 0.709 SABH, R2 = 0.75). Using the variables that were previously determined to influence LA:SA ratios, stepwise regressions revealed that only crown length and 5-year basal area growth significantly improved linear predictions of LA based on sapwood area. However, the increase in R2 was relatively modest, i.e., 0.83 for all three independent variables versus 0.75 for SA alone. The results from this study will be useful in integrating physiologically based measurements, such as growth efficiency, into standard forest inventory practices for balsam fir and thus could be beneficial in developing new silvicultural strategies for protecting Quebec's forest resource.
Croissance de sapinières à bouleau blanc boréales issues de coupe avec protection de la régénération
Authors: Bertrand Lucie , Bélanger Louis , Beauregard Robert L.
Published: February 2008

Models of compatible volume and basal area growth and yield covering a period of 10 to 45 years after harvesting were developed for second growth boreal stands of balsam fir (Abiesbalsamea (L.) Mill.). The 131 permanent plots used for the study were located near Matane, in the Gaspé Peninsula, and are part of the balsam fir–white birch ecoclimatic domain. These stands were harvested in 1934, 1944, and 1953, using a manual cut-and-bunch harvesting method that protected advance growth, and measures were taken in 1954, 1964, and 1978. The stands were moderately affected by spruce budworm outbreaks between 1950–1957 and 1975–1978. Years elapsed since release rather than total age was used as the temporal variable. Even though the characteristics of the coniferous natural regeneration were quite variable, total basal area explained an important part of growth variations of young fir stands by integrating both density and dimensions of the regeneration. Results show, within the limits of the observed densities (< 15 000 stems/ha, 10 years after harvesting), that stands with a higher basal area will have higher total and merchantable volumes at a given age; rotation age for maximum volume production will decrease correspondingly. Abundance of saplings in the initial natural regeneration can thus have an important impact on stand production and rotation age. In the case of nonoverdense young fir stands (< 15 000 stems/ha, 10 years after harvesting with no height growth impediment), the use of spacing treatments that significantly reduce total basal area could be questioned when pursuing maximum fiber production.
Root- and stem-colonizing insects recovered from eastern white pines with procerum root disease
Authors: Nevill R.J. , Alexander S.A.
Published: February 2008

In 1988, eastern white pines (Pinusstrobus L.) from four southwestern Virginia Christmas tree plantations symptomatic of infection by Leptographiumprocerum (Kendr.) Wingf. were assigned to one of four symptom categories based on crown color and resin exudation at the root collar. A fifth category was added in 1989 and 1990. From each plantation, the root system and the lower stem of one tree in each symptom class was excavated monthly and examined for fungi and insects from June to September in 1988 and 1989 and from April to September in 1990. Larvae of two weevil species, Hylobiuspales (Herbst) and Pissodesnemorensis Germ., were recovered with L. procerum from 23, 17, and 21% of the trees in all symptom classes in 1988, 1989, and 1990, respectively. Pre-emergent adults of both weevil species contaminated with L. procerum were also recovered from excavated stems. Bark beetle genera (family Scolytidae), including Pityogenes, Xyleborus, Orthotomicus, Ips, and Pityophthorus, were recovered with L. procerum from 10, 11, and 8% of diseased trees with advanced symptoms in 1988, 1989, and 1990, respectively. The association of these insects, especially H. pales and P. nemorensis, with L. procerum throughout the decline of the host adds further evidence that they may act as vectors of the fungus.
Respiratory cost of leaf growth and maintenance in white oak saplings exposed to atmospheric CO2 enrichment
Authors: Wullschleger Stan D. , Norby Richard J.
Published: February 2008

Atmospheric CO2 enrichment reportedly reduces respiration of mature leaves in a number of woody and herbaceous perennials. It has yet to be determined, however, whether these reductions reflect changes in maintenance respiration alone or whether CO2 might affect growth respiration as well. This possibility was examined in white oak (Quercusalba L.) seedlings that had been planted directly into the ground within open-top chambers and exposed to ambient, ambient +150 μL•L−1, and ambient +300 μL•L−1 CO2 concentrations over a 3-year period. In the spring of 1992, respiration rates were measured repeatedly during leaf expansion, and the growth and maintenance coefficients were determined using a two-component model. Specific respiration rates (mg CO2•g−1•h−1) were consistently lower for leaves of CO2-enriched saplings than for leaves of ambient-grown saplings. Partitioning these reductions in leaf respiration to either the growth or maintenance coefficients indicated a strong effect of CO2 on both components. The growth coefficient for leaves exposed to the ambient CO2 treatment was 964 mg CO2•g−1 compared with 849 and 664 mg CO2•g−1•for leaves from the two elevated CO2 concentrations, respectively. The maintenance coefficient was similarly reduced from a control rate of 114 mg CO2•g−1•d−1 to below 65 mg CO2•g−1•d−1 for leaves exposed to CO2 enrichment. Our results quantitatively describe the magnitude by which growth and maintenance respiration are affected by CO2 enrichment and as such should provide useful information for the future modeling of this phenomenon.
Past and future climate change: response by mixed deciduous–coniferous forest ecosystems in northern Michigan
Authors: Solomon Allen M. , Bartlein Patrick J.
Published: February 2008

During the 21st century, global climate change is expected to become a significant force redefining global biospheric boundaries and vegetation dynamics. In the northern hardwood–boreal forest transition forests, it should, at the least, control reproductive success and failure among unmanaged mixed forest stands. One means by which to predict future responses by the mixed forests is to examine the way in which they have responded to climate changes in the past. We used proxy climate data derived from Holocene (past 10 000 years) pollen records in the western Upper Peninsula of Michigan to drive forest gap models, in an effort to define regional prehistoric vegetation dynamics on differing soils. The gap models mimic forest reproduction and growth as a successional process and, hence, are appropriate for defining long-term tree and stand dynamics. The modeled period included a mid-postglacial period that was warmer than today's climate. Model failures, made apparent from the exercise, were corrected and the simulations were repeated until the model behaved credibly. Then, the same gap model was used to simulate potential future vegetation dynamics, driven by projections of a future climate that was controlled by greenhouse gases. This provided us with the same "measure" of vegetation in the past, present, and future, generating a continuously comparable record of change and stability in forest composition and density. The resulting projections of vegetation response to climate change appear to be affected more by the rate than by the magnitude of climate change.
Predicting effects of global warming on growth and mortality of upland oak species in the midwestern United States: a physiologically based dendroecological approach
Authors: LeBlanc David C. , Foster Jeffrey R.
Published: February 2008

This study combined an ecophysiological model and dendroecological analyses to evaluate potential effects of global warming on the physiology, growth, and mortality of white oak (Quercusalba L.) and black oak (Quercusvelutina Lam.) in the Ohio River region. The model integrated data for ecophysiology of oak species, site attributes, and daily temperature and precipitation to model nonlinear responses of stomatal conductance (gs), net photosynthesis (Pnet), and woody respiration (Rw) to variations in temperature and soil water content. Relationships between modeled physiological response indices and actual white and black oak annual radial growth indices were evaluated by regression analyses, using growth and weather data for the period 1900–1987 for seven upland oak–hickory forests. Modeled physiological response indices explained 40–60% of variation in radial growth indices. To evaluate the effects of global warming, daily temperature values for the period 1900–1987 were increased by 2 or 5 °C, without changing precipitation values, and physiological response indices were computed. Model indices generated in warming simulations were entered into dendroclimatic regression models calibrated under conditions without any warming to predict radial growth under warming scenarios. Under the warming scenarios, OAKWBAL predicted a substantial increase in growing season Rw, but little change in growing season Pnet. Warming merely shifted the period of near-maximal Pnet earlier in the growing season, without changing its duration. However, this result was somewhat dependent upon the ability of leaf-out phenology to track changes in temperature regime. The net effect of increased Rw, with little change in Pnet, was a reduction in radial growth and a higher frequency of years with climatic conditions stressful to oaks on upland sites. A historical association between severe drought and increased incidence of oak growth decline and mortality indicated that global warming could increase the incidence of decline and mortality in oak populations on upland sites similar to those in this study.
Foliar sulfur and nitrogen along an 800-km pollution gradient
Authors: Pregitzer Kurt S. , Burton Andrew J. , Mroz Glenn D. , Liechty Hal O. , MacDonald Neil W.
Published: February 2008

Emissions of sulfur (S) and nitrogen (N) oxides in the midwestern and northeastern United States result in pronounced regional gradients of acidic deposition. The objective of this study was to determine the extent to which atmospheric deposition alters the uptake and cycling of S and N in five analogous northern hardwood forests located along one of the most pronounced regional gradients of SO42−-S and NO3−-N deposition in the United States. We tested the hypothesis that acidic deposition would alter foliar S and N ratios and nutrient cycling in aboveground litter fall. Sulfate in both wet deposition and throughfall increased by a factor of two across the 800-km deposition gradient. The July concentration of S in sugar maple (Acersaccharum Marsh.) leaves increased from about 1600 μg•g−1 at the northern research sites to 1800–1900 μg•g−1 at the southern sites. Differences in leaf litter S concentration were even more pronounced (872–1356 μg•g−1), and a clear geographic trend was always apparent in litter S concentration. The 3-year average S content of leaf litter was 63% greater at the southern end of the pollution gradient. Nitrate and total N deposition were also significantly greater at the southern end of the gradient. The concentration of N in both summer foliage and leaf litter was not correlated with N deposition, but the content of N in leaf litter was significantly correlated with N deposition. The molar ratios of S:N in mid-July foliage and leaf litter increased as atmospheric deposition of SO42−-S increased. Ratios of S:N were always much greater in leaf litter than in mid-July foliage. The molar ratios of S:N retranslocated from the canopies of these northern hardwood forests were less than those in mid-July foliage or litter fall and showed no geographic trend related to deposition, suggesting that S and N are retranslocated in a relatively fixed proportion. Significant correlations between SO42−-S deposition and foliar S concentration, S cycling, and the molar ratio of S:N in foliage suggest that sulfate deposition has altered the uptake and cycling of S in northern hardwood forests of the Great Lakes region.
ForestHealth, an expert advisory system for assessing foliar and crown health of selected northern hardwoods
Authors: Nash B.L. , Saunders M.C. , Miller B.J. , Bloom C.A. , Davis D.D. , Skelly J.M.
Published: February 2008

Assessment of tree health requires accurate estimates of crown condition and identification of specific biotic and abiotic agents that may affect crowns, stems, or roots. ForestHealth, an expert advisory system written in C language for the Macintosh™ platform, provides a diagnostic module and two training modules. The diagnostic module provides guidance in identifying foliar symptoms and the common insects, diseases, and abiotic disorders found on leaves of: sugar maple (Acersaccharum Marsh.), red maple (Acerrubrum L.), black cherry (Prunusserotina Ehrh.), northern red oak (Quercusrubra L.), and white oak (Quercusalba L.). Graphical user interfaces are central to both training modules. The Foliar Severity routine trains users to categorize injury (percent leaf area) on single leaves using a modified Horsfall–Barratt scale. The Crown Dieback routine displays different types and degrees of crown injury that users must identify and classify. Each crown is unique, generated in "real time" using tree–branch parameters selected by the user. Since the crowns are created on a three-dimensional basis, multiple views are possible. Written output from training sessions or periodic checks provide quantitative information for quality assurance and quality control. ForestHealth provides diagnostic assistance, training, quality assurance and quality control data, and standardization for research or survey projects involving forest health.
Temporal change (1988–1990) in sugar maple health, and factors associated with crown condition
Authors: Allen Douglas C. , Barnett Charles J. , Millers Imants , Lachance Denis
Published: February 2008

Change in the health of sugar maple (Acersaccharum Marsh.) and associated northern hardwoods was evaluated for 3 years (1988–1990) in seven states and four provinces. Generally, levels of crown dieback and crown transparency (a measure of foliage density) in 165 stands decreased during this period. In 1990, less than 7% of all dominant–codominant sugar maples (n = 7317) exhibited crown dieback ≥ 20%. Significantly (p = 0.05) fewer of these maples were classified as having high crown transparency (≥ 30%) in 1990 compared with 1988. Crowns of maples that received moderate (31–60%) or heavy (> 60%) pear thrips (Taeniothripsinconsequens (Uzel)) damage for 1 year recovered the following year. Crowns of maples exposed to severe drought in 1988 (Wisconsin) continued to show the effects (high transparency) of this stress in 1990. A majority (69–71%) of the dominant–codominant sugar maples with high (≥ 20%) crown dieback had bole and (or) root damage. Of those maples with crown dieback ≥ 50%, 86% had bole and (or) root damage. The condition of sugar maple in operating sugar bushes and undisturbed stands was similar. The condition of sugar maple crowns was similar in locations presumably exposed to low, medium, and high levels of sulfate deposition.
Growth and biomass allocation of symptomatic and asymptomatic Populustremuloides clones in response to seasonal ozone exposures
Authors: Karnosky D.F. , Gagnon Z.E. , Reed D.D. , Witter J.A.
Published: February 2008

The effect of single-season ozone exposures on growth and biomass production of numerous trembling aspen (Populustremuloides Michx.) clones was studied, using open-top chambers, in the Upper Peninsula of Michigan. All clones studied had previously been ranked according to foliar sensitivity to short-term, high-dose ozone exposures. For this study, comparisons were made between plants grown in charcoal-filtered, nonfiltered, and ozone-added (consisting of 80 ppb ozone for 6 h per day, 3 days per week) chambers and in open-air plots. For the plants grown in ozone-added chambers, as compared with those grown in the charcoal-filtered air, stem biomass decreases were 0% for the 18 ozone-tolerant clones and 46.4% for the 18 ozone-sensitive clones, in 1988. In 1989, they were 5% for the tolerant clones and 74% for the sensitive clones. Thus, our results suggest that ozone can have either a negative effect on growth or no effect, depending on the clones tested. However, it is clear from this study that ozone consistently affected biomass production in sensitive clones in a negative manner. These results strengthen the case for ozone being a strong selective force, even at relatively low total doses.
Sensitivity of four hardwood species to ambient ozone in north central Pennsylvania
Authors: Simini M. , Skelly J.M. , Davis D.D. , Savage J.E. , Comrie A.C.
Published: February 2008

Studies were performed to determine the injury and growth response of four native tree species to ambient ozone on ridgetop sites of the Allegheny Plateau of north central Pennsylvania. Open-top chambers were established at each of three sites located in Clear Creek State Park, Jefferson County (41°9′39″N, 79°02′35″W), Elliott State Park, Clearfield County (41°07′02″N, 78°31′40″W), and Tiadaghton, Lycoming County (41°20′05″N, 77°26′57″W). Seedlings of black cherry (Prunusserotina Ehrh.), yellow-poplar (Liriodendrontulipifera L.), red oak (Quercusrubra L.), and red maple (Acerrubrum L.) were exposed to ambient air or to charcoal-filtered air containing approximately 95, 60, or 40% of ambient ozone in randomized, complete blocks in 1988 and 1989. Black cherry seedlings were also exposed in 1990. Ozone was greatest in 1988 at all sites, and total ozone during the 3-year study was greatest at the westernmost sites (Clear Creek and Elliott). Foliar stipple injury of black cherry and yellow-poplar were correlated positively (p < 0.0001) with ozone within and among sites throughout the study. Premature leaf abscission of both species was significantly (p < 0.005) greater with higher ozone levels at the Elliott site in 1988 and 1989. Ozone stipple was not observed on red maple and red oak seedlings. Ambient ozone did not significantly decrease height, basal diameter, or leaf surface area of any species. Possible explanations for temporal and spatial ozone variation and subsequent plant response are discussed.
Plant species diversity on even-aged harvests at the Hubbard Brook Experimental Forest: 10-year results
Authors: Gove Jeffrey H. , Martin C. Wayne , Paul Ganapati P. , Solomon Dale S. , Hornbeck James W.
Published: February 2008

Comparisons of plant species diversity were made on two separate watersheds treated by a block clearcut and progressive strip cut in the Hubbard Brook Experimental Forest in New Hampshire. Intrinsic diversity profiles were used to make diversity comparisons. A jackknifing technique was used on the diversity profiles for bias correction and to test for intrinsic diversity orderings. Comparisons were made within treatments over time and between treatments at 1 and 10 years after cutting. The results suggest that plant species diversity was lowest the year following treatment on both watersheds, and that it was at its highest 10 years after cutting on the progressive strip cut; however, diversity was found to be decreasing after 10 years on the block clearcut. In addition, the data suggest that the overall diversity of the progressive strip cut was higher than that of the block clearcut both immediately and 10 years after treatment.
Economic and tree diversity trade-offs in managed northern hardwoods
Authors: Niese Jeffrey Neal , Strong Terry F.
Published: February 2008

Forest ecologists have long believed that greater tree species diversity in hardwood forests reduces biological risk, but researchers have not yet linked diversification with economic returns for managed hardwood forests. This paper shows how management of northern hardwood forests affects tree species diversity and economic returns. Shannon's index is used to measure regeneration diversity for eight even- and uneven-aged cutting methods from a 40-year study on the Argonne Experimental Forest. These indices of tree species diversity are compared with the potential economic returns for the research sites.
Scots pine needles as bioindicators of sulphur deposition
Authors: Manninen Sirkku , Huttunen Satu
Published: February 2008

The ranges of total S content in the two youngest needle age-classes of Scots pine (Pinussylvestris L.) in the vicinity of an oil refinery were 1120–2267 μg•g−1 in December 1980, 902–2003 μg•g−1 in January 1986, and 1120–1820 μg•g−1 in December 1989, and annual mean SO2 concentrations were 20–68, 14–34, and 2–32 μg•m−3, respectively. A statistically significant correlation (p < 0.001) was found between needle total S content and the estimated SO2 load, i.e., the total monthly mean SO2 concentrations (r = 0.815) and the highest or second highest daily SO2 concentrations of each month (r = 0.910 or 0.849). It seems that, under conditions of SO2 pollution stress, the needle S content is greatly affected by the high short-term (24 h) SO2 concentrations and newly flushed young needles may absorb S very effectively. The erosion of needle surface waxes typical of areas polluted by SO2 and particle emissions was observed. The results indicate that in areas where the climate is similar to that in southern Finland, the United Nations Economic Commission for Europe draft critical levels of 70 μg SO2•m−3 as a daily mean and 20 μg SO2•m−3 as an annual and winter mean, especially in combination with other air pollutants, may result in enhanced S accumulation and needle damage.
Influence of microclimate on decomposition in loblolly pine stands: a field microcosm approach
Authors: Hornsby D.C. , Lockaby B.G. , Chappelka A.H.
Published: February 2008

The effect of climatic variation on decomposition was studied in a field experiment. Plexiglas microcosms were used to elevate temperatures and allow implementation of varied precipitation rates. The study was conducted in a loblolly pine (Pinustaeda L.) stand near Auburn, Alabama. Temperatures were elevated (1–8 °C depending on the season) and precipitation was varied (±30% of ambient). A litterbag approach was used to examine decomposition dynamics within the microcosms. Elevated temperatures significantly increased decomposition rates within microcosm treatments. Enhanced moisture stimulated decomposition above that associated with ambient levels of precipitation while decreased precipitation produced no significant decrease in decomposition within our temperature range. In general, litter N concentrations increased, carbon content decreased, and C/N ratios decreased over time, and these effects were accelerated when temperature was increased. Within our range of environmental factors, increases in temperature could result in accelerated decomposition and alterations in nutrient cycling regardless of the precipitation change. However, should precipitation increase as well, litter decomposition will be further stimulated.
Assessing measures of tree competition using fixed-area, variable-radius, and horizontal-line plot sampling
Authors: Schreuder H.T. , Williams M.S.
Published: February 2008

Fixed-area plot sampling, variable-radius plot sampling, and horizontal-line plot sampling performed similarly in estimating competition from adjacent trees if only plots were considered that had an adequate number of sample trees to compute the estimated indices. The percentage of plots for which the indices can be computed tends to be largest for variable-radius plot sampling, then line sampling, and last for fixed-area plot sampling. Variable-radius plot sampling performs about as well as fixed-area plot sampling in computing the competition measures used in the distance-dependent tree models evaluated in this analysis.
Contrasting patterns of resource limitation in tree seedlings across a gradient in soil texture
Authors: Knox Robert G. , Harcombe P.A. , Elsik I. Sandra
Published: February 2008

Resource competition theory for terrestrial plant communities explains gradients in species composition among various habitats as the outcome of differential supply and demand for limiting resources. To examine one group of assumptions of this theory, for forest vegetation in southeastern Texas, we grew seedlings of three broadly distributed tree species, Acerrubrum L. (red maple), Liquidambarstyraciflua L. (sweetgum), and Pinustaeda L. (loblolly pine), in intact soil cores collected from three sites located along a gradient in soil texture. We tested resource limitation in a temperature-controlled greenhouse with nutrient fertilization, light, and moisture treatments applied in a resource-minus or screening design. This design provided most resources at levels not limiting for growth while simulating (potentially limiting) field conditions for a single resource or group of related resources. Light was most limiting with clay-rich floodplain soil cores under simulated floodplain forest conditions. Soil nutrients were most limiting in sandy upland soil cores under upper slope forest conditions. Both light and soil nutrients were strongly limiting with loamy intermediate soil cores under simulated mesic forest conditions. The most limiting soil resource was phosphorus. The pattern of reciprocal limitation by aboveground or belowground resources in extreme habitats and joint limitation in intermediate habitats was consistent with requirements of the theory.
Soil microbial biomass and microbial and mineralizable N in a clear-cut chronosequence on northern Vancouver Island, British Columbia
Authors: Chang Scott X. , Weetman Gordon F. , Preston Caroline M.
Published: February 2008

We studied the dynamics of microbial biomass and nitrogen in old-growth forests and in 3- and 10-year-old plantations established after clear-cutting and slash burning of old-growth western red cedar (Thujaplicata Donn ex D. Don)–western hemlock (Tsugaheterophylla (Raf.) Sarg.) stands on northern Vancouver Island. Ten-year-old plantations, after initially growing well, were experiencing declining growth rates. Three forest floor layers: F (fermentation), woody F (Fw), and H (humus) were sampled four times in May, July, August, and October of 1992. Moisture content was significantly greater in the old-growth forests than in the plantations for F on July 16 (p < 0.05) and Fw (p < 0.10), but was not significantly different for H. Microbial biomass C and N were relatively constant throughout the sampling period, resulting in nonsignificant date effects. Microbial C content was in the order: old-growth forests > 10-year-old plantations > 3-year-old plantations. Microbial N content was significantly greater in the old-growth forest than in the young plantations for both F (p < 0.001) and H (p < 0.05) but was not different between the plantations. Therefore, the hypothesis that the microbial biomass acted as a net sink in the 10-year-old plantations by immobilizing N into the microbial N pool is rejected. Microbial C/N ratios were greater (p < 0.05) in the 10-year-old plantations than in the old-growth forests and in the 3-year-old plantations in H and on July 16 in F, indicating that microbial competition for N was probably a factor in the growth declining in the 10-year-old plantations. Extractable C and N and mineralizable N were generally higher in the old-growth forests than in the 3-year-old plantations and higher in the 3-year-old than in the 10-year-old plantations. As a result of better nutritional conditions, tree and understory foliage in the 3-year-old plantations had higher N concentrations and lower C/N ratios than in the 10-year-old plantations. Trees in the 10-year-old plantations displayed chlorotic symptoms and slow growth which were not observed in the 3-year-old plantations.
Inverse relationship of crown fractal dimension to self-thinning exponent of tree populations: a hypothesis
Authors: Osawa Akira
Published: February 2008

The self-thinning rule describes in overcrowded even-aged plant monocultures a consistent relationship of mean mass to the approximately −3/2 power of plant density. Recent analyses revealed cases of statistically significant departures of the exponent from −3/2, confirming earlier suggestions. Shade tolerance, crown structure, and stand conditions have been suggested to influence variation in the self-thinning exponent; however, quantitative relationships of the species' traits to thinning exponent have been unclear. I examined patterns of crown fractal dimension, a quantitative measure of crown structure, and their relationship to the self-thinning exponent in four tree species, Nothofagussolandri var. cliffortioides (Hook. f.) Poole, Pinusbanksiana Lamb., Pinusdensiflora Sieb. et Zucc., and Cryptomeriajaponica (Linn. fil.) D. Don. Only stands at maximum crowding were used for analysis. Crown fractal dimension of monocultures is hypothesized to be a factor determining the species-specific variation in the self-thinning exponent of tree populations and is inversely proportional to the thinning exponent. Species-specific change in foliage packing through development of overcrowded populations is suggested to be closely related to variation in crown fractal dimension and the self-thinning exponent. Implications to possible effects of leaf shape and structural characteristics of crowns to crown fractal dimensions are discussed.
Heuristic procedures for solving mixed-integer harvest scheduling–transportation planning models
Authors: Weintraub Andrés , Magendzo Adrian , Magendzo Ariel , Malchuk Daniel , Jones Greg , Meacham Mary
Published: February 2008

Modeling both road construction and land management activities as 0–1 variables greatly enhances the spatial aspect of linear programming models dealing with harvest scheduling and transportation planning. In previous work we developed a heuristic procedure that modeled only road construction as 0–1 variables. We have expanded this past procedure to also consider land management decisions as 0–1 variables. This paper outlines the heuristic procedure developed for modeling both road building and land management decisions as integer variables in light of adjacency constraints. The heuristic procedure allows economic or physical objectives to be maximized or minimized. A wide variety of side constraints can be accommodated and these constraints can include both road construction and land management decision variables. These heuristic procedures have performed well on models tested thus far.
Effects of gap size on nutrient release from plant litter decomposition in a natural forest ecosystem
Authors: Zhang Qishui , Liang Yuwu
Published: February 2008

The rates of nutrient release were investigated during the Castanopsiskawakamii (Hayata) leaf, branch, and bark litter decomposition processes over a 360-day period within five different size classes of forest gaps that comprise a gap size gradient. Five different size classes of gaps were gap 1, under the closed canopy of pure C. kawakamii vegetation; gap 2, small gaps with a diameter of less than 5 m; gap 3, small to intermediate gaps with a diameter of 5–15 m; gap 4, intermediate to large gaps with a diameter of 15–30 m; gap 5, large gaps with a diameter of bigger than 30 m. After 360 days, decomposing plant litter under canopy condition or small gaps lost weight more rapidly than those in large gaps. Loss of K was highest among all nutrients measured for all three types of litter in all five size classes of gaps. Net immobilization of N and P occurred for all three types of litter in the first 2 or 4 months. Litter residue concentrations of N and P then declined until the end of this study, decreasing to 47% and 70%, respectively, of initial amounts. Loss of Ca and Mg averaged 60 and 40%, respectively, during the period of this study; loss of S averaged 50% and was continuous. Loss of nutrients measured were highest in leaves, intermediate in bark, and lowest in branches under the same size class of gaps, and were highest in gaps 1 and 2, intermediate in gap 3, and lowest in gaps 4 and 5 for the same type of litter. Cellulose and lignin components showed the similar patterns of mass loss as nutrients with highest in gaps 1 and 2, intermediate in gap 3, lowest in gaps 4 and 5 (P ≤ 0.001). Annual decomposition rate was correlated to the microclimatic factors for all types of litter within five different gap size conditions. Soil moisture content was the best predictor of annual decay rate (R2 = 0.922, P ≤ 0.001) among the microclimatic factors. The results indicated that small scale of natural disturbance do not influence the nutrient dynamics during plant litter decomposition; however, rates of nutrient release are strongly inhibited with the increase of scales of disturbance. In this study, gap size of 15 m in diameter is critical in determining the rates of nutrient release from plant litter decomposition processes.
Germination, survival, and early growth of red alder seedlings in the central Coast Range of Oregon
Authors: Haeussler Sybille , Tappeiner II John C. , Greber Brian J.
Published: February 2008

Effects of forest disturbance and soil moisture levels on establishment of red alder (Alnusrubra Bong.) seedlings were studied at four sites representing a climatic moisture gradient within the central Coast Range of Oregon. On average, there was no difference in seedling emergence between recent clearcuts and second-growth forests, but emergence was much higher on mineral soil than on organic seedbeds. Emergence, on both types of seedbed, was positively correlated with spring soil moisture conditions (R2 = 0.60). Seedling survival, on the other hand, differed greatly between clearcut and forest. In clearcuts, heat and drought injuries were the primary causes of seedling mortality. In the forest, seedlings had poor vigour and quickly succumbed to pathogens, herbivores, and rain splash. First-year survival rates were strongly correlated with minimum summer soil moisture levels (R2 = 0.71). Height growth of seedlings on clearcuts (2–5 cm after 1 year; 8–23 cm after 2 years) was much slower than rates typically described for red alder. Best establishment occurred on skid trails and landings, suggesting that young seedlings may suffer less from heat or moisture stress on these heavily disturbed microenvironments.
Alders increase soil phosphorus availability in a Douglas-fir plantation
Authors: Giardina Christian Paul , Huffman Steve , Binkley Dan , Caldwell Bruce A.
Published: February 2008

The effect of red alder (Alnusrubra Bong.) on soil phosphorus (P) availability in conifer forests of the Pacific Northwest has been the focus of several recent studies. One study at the Thompson Research Center in Washington State, found Bray No. 2 extractable P to be lower in soils under pure alder than in soils under adjacent stands of pure conifer. The Thompson study, and others in forests of the Northwest, have also found that the quantity of P in aboveground litter fall is greater for conifer stands mixed with alder than in adjacent pure conifer stands, suggesting equal or greater soil P availability under the influence of alder. We assessed the effect of low densities of red alder on soil P, using a modified Hedley sequential P fractionation scheme, in a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantation in coastal Oregon. We determined that soils under plots with 190 alder stems/ha and 740 Douglas-fir stems/ha had greater inorganic P availability than pure Douglas-fir plots (740 stems/ha). Inorganic P fractions, sequentially extracted from soils at 0–0.15 m depths by anion exchange resins, by sodium hydroxide, and by hydrochloric acid, were 65–225% greater in plots with alder. Soil phosphatase activity was nearly three times greater in plots mixed with alder. No significant pH differences between the treatments were found. We conclude that red alder appears to increase the availability of soil P at our site, but note that increased P supplies may not prevent a P limitation on productivity for either alder or conifers.
Early postharvest succession in relation to site type in the southern boreal forest of Quebec
Authors: Harvey Brian D. , Leduc Alain , Bergeron Yves
Published: February 2008

Early vegetation development following harvest was evaluated for nine common site types in the southern clay belt of northwestern Quebec. Stocking of broadleaf tree and high shrub stems less than 1 m tall was either stable or declined on all sites over a period of 8 years following harvest, whereas stocking of stems over 1 m displayed increases on all but mesic clay sites. These latter sites had the lowest broadleaf and high shrub stocking but a high cover of raspberry (Rubusidaeus L.), low shrubs, and herbs. Mesic to hydric clays and hydric organic site types had considerably higher cover of ruderal and introduced species than sand and till sites, TWINSPAN indicator species analysis was used to explore phytosociological associations of postharvest vegetation. The distribution of 11 phytosociological groups among the nine site types was analysed using contingency analysis to test the specificity of species groups to site types and the floristic amplitude of the latter. With the exception of one phytosociological group that displayed a broad spectrum of site type occupation, these groups tended to be associated with sites of similar soil moisture regimes and (or) parent material types. While site type may be improved upon as a stratifier by integrating other environmental, biotic, and operational variables, it does appear to provide a good initial basis for stratification in studies of postdisturbance vegetation dynamics.