bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact des changements climatiques sur les plans de gestion des lacs Saint-François et Aylmer au sud du Québec
Authors: Fortin Louis-Guillaume , Turcotte Richard , Pugin Stéphane , Cyr Jean-François , Picard François
Published: September 2007

This study presents the results of a pilot project, for the Saint-François and Aylmer lakes located in southern Quebec, aimed at developing a method to evaluate the adaptability of a current dam management plan to global climate changes. The hydrological simulations computed using available climate scenarios indicated modifications in annual water yields, from a 13% increase to a 30% decrease, and earlier spring floods. Peak flows, winter and summer low flows, and the level of increase in water yields vary depending on the studied climate scenario. The simulation of the current management plan shows that climate changes will affect the current trade-off between the various management objectives of the reservoirs. Adaptation solutions to the current management plan appeared to be feasible, but no unique solution applicable to all climate scenarios was found.Key words: climate change, dam, impacts, adaptation, hydrologic modeling, Quebec.
Phylogenetic diversity of bacteria isolates from the Qinghai-Tibet Plateau permafrost region
Authors: Zhang Gaosen , Niu Fujun , Ma Xiaojun , Liu Wei , Dong Maoxing , Feng Huyuan , An Lizhe , Cheng Guodong
Published: September 2007

The Qinghai-Tibet Plateau in east Asia is a unique and important permafrost environment. However, its microbiology remains largely unexplored to date. In this study, sediment samples were collected from the Qinghai-Tibet Plateau permafrost region, bacteria isolation procedures were performed 8 times, and the samples incubated at 4 °C for nearly 3 months. The number of colony forming units (cfu) ranged from 0 to 107/(g dry soil). The quantity of culturable bacteria grew exponentially within the first few weeks, and then slowed gradually to a plateau. Phylogenetic analyses indicated that all the isolates fell into 6 categories: high G+C Gram-positive bacteria, low G+C Gram-positive bacteria, α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, and Cytophaga–Flavobacterium–Bacteroides group bacteria. The isolates belong to 19 genera, but the genera Arthrobacter and Pseudomonas were predominant. With the increase in incubation time, the isolated populations changed in terms of both species and their respective quantities. Of the 33 analyzed isolates, 9 isolates related to 8 genera might be new taxa. These results suggest that the Qinghai-Tibet Plateau permafrost region is a specific ecologic niche that accommodates an original microbial assemblage.
Microbial surfactant activities from a petrochemical landfarm in a humid tropical region of Brazil
Authors: Maciel Bianca Mendes , Dias João Carlos Teixeira , Freire dos Santos Ana Cácia , Argôlo Filho Ronaldo Costa , Fontana Renato , Loguercio Leandro Lopes , Rezende Rachel Passos
Published: September 2007

The goal of this study was to assess the presence and surfactant potential of naturally occurring microbes from a tropical soil with petrochemical contamination. Microorganisms in a soil sample from a Brazilian landfarm were isolated and grown on petroleum as the sole carbon source. Of 60 isolates screened for petroleum-based growth, 7 demonstrated surfactant activities by the drop–collapse methodology over various types of oils. From their growth profiles in liquid culture during 132 h, all had their first detection of surfactant activity after 96 h. Little is currently known about biosurfactant-producing microorganisms in tropical environments contaminated by hydrophobic compounds, and the search for them is essential for bioremediation and for oil recovery enhanced by microbes. Our results indicate that different petroleum-grown microorganisms showing surfactant activity can be recovered from landfarm soil in a tropical environment.
Murine immunomodulation of IL-10 and IL-12 induced by new isolates from avian type 2 Lactobacillus acidophilus
Authors: Bleau Christian , Savard Roland , Lamontagne Lucie
Published: September 2007

Several bacterial and immunogenic factors are involved in the host response to probiotic strains of Lactobacillus . Here, we report the isolation of new intestinal lactobacilli from chicken, with different immunomodulating properties on lymphoid cells from SJL and C57BL/6 mice. Analysis of biochemical markers in the Lactobacillus acidophilus CBA4P, CBA3P, and TPA3P isolates reveal that these bacterial isolates belong to the type 2 prototype, although they differ from each other. The effect of conditioned media (CM) from SJL- and C57BL/6-derived peritoneal macrophages incubated with the 3 sonicated bacterial isolates from chicken, as well as with Lactobacillus rhamnosus 9595, Escherichia coli lipopolysaccharide, or Staphylococcus aureus peptidoglycan were compared. Our results show that the CM of macrophages from C57BL/6 and SJL mice treated with the CBA4P isolate stimulated syngeneic splenic lymphocytes at a level similar to the one induced with CM from peptidoglycan-stimulated macrophages. In contrast, the CM from TPA3P- and CBA3P-treated macrophages promoted low or no stimulation of lymphoid cells. Incubation of splenic cells with CM from macrophages treated with L. rhamnosus or TPA3P led to a relative decrease in the percentages of splenic CD4+ T cells, whereas the relative percentages of B cells increased. The CBA4P and CBA3P isolates induced higher levels of gamma interferon when compared with the TPA3P isolate. The effects of the lactobacilli isolates differed according to the mouse strain used but correlated with the production of macrophagic tumor necrosis factor alpha and interleukins 6, 10, and 12 and with the modulation of the p38 mitogen-activated protein kinase (MAPK). Taken together, these results indicate that the immunomodulating properties of the new L. acidophilus isolates depend on their capacity to induce production of interleukins 10 and 12 by macrophages, which is under genetic control and depends on the p38 MAPK pathway.
Land base models for forest resource supply analysis: a critical review
Authors: Parks Peter J. , Alig Ralph J.
Published: September 2007

Land base models in regional forest resource supply analyses project area changes in forest vegetation and land use. Models of forest vegetation dynamics are classified according to the basic modeling unit (canopy gap and forest); land use dynamics models are classified according to technique (inventory–descriptive, normative, and positive). Relationships among models used in analyzing timber supply are reviewed, including necessary links between models of forest vegetation dynamics and land use dynamics.
Estimating the accuracy of volume equations using taper equations of stem profile
Authors: Biging Greg S.
Published: September 2007

Comparisons of log volume estimation techniques are performed using the equations of Smalian, Huber, and Newton, and a numerical technique using cubic splines. The data utilized were obtained by predicting diameters at various points along the stem from two paper equations for white fir. Results indicate that Newton's and Huber's equations were the most accurate, followed by the cubic spline and Smalian's equation, respectively. This technique facilitated partitioning of the total error in volume estimation into measurement error and error due to model misspecification arising when the taper of logs could not be exactly described by a simple model such as a frustum of a paraboloid. For the taper relationships analyzed it was shown that the error due to the selection of an inappropriate mensurational model is less than 5% for a measurement distance of 16 ft (4.9 m) for all models tested and can be substantially reduced by applying the formulae only to logs positioned above basal swell. Systematic measurement error was assessed analytically and found to range between 1 and 4%. Thus, total error in volume estimation was less than 9% for all methods tested.
Reflectance characteristics of cumulative defoliation of balsam fir
Authors: Leckie D. G. , Teillet P. M. , Fedosejevs G. , Ostaff D. P.
Published: September 2007

Knowledge of the spectral characteristics of trees with varying degrees of needle loss is essential for developing remote sensing techniques for assessing defoliation. Spectra covering the range 400–2400 nm were acquired for single tree crowns suffering varying degrees of cumulative defoliation due to the spruce budworm (Choristoneurafumiferana (Clem.)), using a spectrometer mounted in the bucket of a boom truck. Spectra over the range 360–1100 nm were also obtained for the components of defoliated trees (i.e., needles, bare branches, and lichen), using a separate spectrometer and integrating sphere. Estimates of defoliation symptoms of each tree were made from the ground and above the tree. Changes in reflectance had a close and simple relationship with the defoliation symptoms measured. The spectral differences due to cumulative defoliation that were observed were broad-band features. The best spectral regions for differentiating levels of cumulative defoliation symptoms were the blue, red, shorter near-infrared wavelengths, and middle-infrared. Although currently available satellite and airborne sensors operate in these spectral regions, defoliation assessment may be improved by the use of optimized spectral bands.
An intraregional economic analysis of production structure and factor demand in major Canadian softwood lumber producing regions
Authors: Meil J. K. , Nautiyal J. C.
Published: September 2007

Cross-sectional time-series data were employed to estimate four intraregional models of production structure and factor demand over the time period 1968–1984. Lumber, tie, and pulp chip information was incorporated into the restricted, single-output, variable cost transcendental logarithmic function. Results indicate that aggregate sectoral studies do not adequately reflect regional production behaviour in the industry. Additional tests for aggregation bias demonstrated that different mill sizes within a region also portray differing production behaviour. Factor demand decomposition analysis indicated that demand for production inputs is not static, but is governed by offsetting dynamic effects. With few exceptions, all mills across regions exemplify material- and energy-using and labour-saving biases in technical change. Larger mills consistenly registered the greatest labour-saving technical change, which countered their lack of attaining significantly large cost-reducing scale economies. Mid-sized mills consistently exhibited the largest returns to scale. The data suggest that small mills are leaving the industry in some regions and production capacity is becoming concentrated in the larger mills.
Heritability and C effects in a 3-year-old balsam poplar clonal test
Authors: Farmer Jr. Robert E. , Garlick Karen , Watson Steven R.
Published: September 2007

A 20-clone population of Populusbalsamifera L. was grown for 3 years in a field test which allowed evaluation of variance due to clones and to primary ramets within clones, the source of cuttings. Primary ramets did not influence rate of summer shoot elongation, which had a broad-sense heritability of 0.24 and 0.16 in the 2nd and 3rd years, respectively. By the end of the 2nd year, height variation associated with primary ramets (i.e., C effects) was nonsignificant, and broad-sense heritability for height was about 0.50.
Decline in old-growth red spruce in western Maine: an analysis of wood density and climate
Authors: Conkey Laura E.
Published: September 2007

Maximum ring densities from an old-growth red spruce stand in western Maine are well correlated with climate over the period of comparable record, but they show evidence of an unusual decrease in recent decades, one that is not as marked in ring widths from the same trees. Regressions between spring temperature and maximum wood density are significant and quite similar in the two halves of the time period, 1899–1945 and 1946–1984, but a regression in 1965–1984 is not significant. Correlations between predictions of density from spring temperature and actual densities are high, positive, and significant until the mid-1960s, when they become nonsignificant and very small in value. The cause of such an unprecedented change in the relationship between maximum density of red spruce and climatic conditions has not been identified.
Isozyme variation in balsam poplar along a latitudinal transect in northwestern Ontario
Authors: Farmer Jr. R. E. , Cheliak W. M. , Perry D. J. , Knowles P. , Barrett J. , Pitel J. A.
Published: September 2007

Isozyme characteristics were examined for eight enzyme systems in five 50-tree populations of balsam poplar (Populusbalsamifera L.) collected at longitude 90°W, from latitudes 45 to 55°N. Fifty-four percent of the trees were polymorphic at one or more loci, and 8 of the 17 loci examined were polymorphic in one or more populations. Average heterozygosity was low (0.037) and varied little among populations (0.025–0.043). No significant departure of multilocus genotypic proportions from those expected under random mating was observed. Genetic distances and F-statistics indicated that there is little genetic differentiation among populations in terms of the observed enzyme systems.
Fine-resolution analysis of stem form and its implication to the mechanism of plant self-thinning
Authors: Osawa Akira
Published: September 2007

Stem forms of trees were examined in detail using a fine-resolution analysis. The results were then used to examine the use of stem form in explaining mechanisms of self-thinning in even-aged tree populations. The analysis indicated that stems of forest trees generally consist of four segments of variously shaped parts. The stems have forms that change from a cylinder, to a cone, to a paraboloid, and then to a solid of revolution that tends to diverge toward infinite stem area at the base. A scale-dependent structure of stem form was also noted. At coarse scale, stems can be approximated by the generalized form with changing shapes along the axes. At fine scale, however, stems (excluding the top and the base of a tree) have a pagoda-like structure that is determined by piling blocks of paraboloid frusta of various sizes, and there are jumps in stem diameter at boundaries of the stem segments. Therefore, there is little evidence that the widely used elastic similarity model portrays stem forms accurately.
Comparative growth and yield of layer- and seed-origin black spruce (Piceamariana) stands in Quebec
Authors: Morin Hubert , Gagnon Réjean
Published: September 2007

Stem analysis was used to compare the height, diameter at breast height, and volume growth of seven merchantable black spruce (Piceamariana (Mill.) B.S.P.) stands regenerated after harvesting from advance growth of layer origin with the growth of three merchantable black spruce stands regenerated after fire from seed. The year of harvesting in the second-growth stands was precisely determined using synchronous growth release after logging, scars left by the logging operation, and historical records. The year of the fires in seed-origin stands was determined using fire scars and historical records. Fire-origin stands showed typical even-aged structure, and logged, second-growth stands showed an uneven-aged structure associated with an asymmetric curve. When compared with seed-origin stands, layer-origin stands showed a significantly greater total height 30 years after the stand origin because of the initial height of the layers. However, annual height increments were similar between the two origin types at 30 years. The mean diameter increment at 30 years was significantly higher in the second-growth stands. The mean annual specific volume increment values for the entire period of growth were slightly higher for the fire-origin stands. Layers that were small at the time of logging (<1 m) had a higher specific volume increment after logging compared with the medium (1–2 m) and tall layers (>2 m). There was a significant negative correlation between the height, diameter, and age of the layers at the time of logging and both the mean specific volume increment and the mean annual height increment 30 years after logging. In the second-growth stands, the number of merchantable trees and volume increment increased gradually because of the uneven structure of the stands. In contrast, in the seed-origin stands, the trees attained merchantable size at around 30 years after the fire, and the merchantable volume rose rapidly after this. The layer-origin populations had a significant advantage over the seed-origin populations because of the initial height and diameter of the layers at the time of logging. All seven layer-origin stands achieved, or were predicted to achieve, higher merchantable volumes than the seed-origin stands at 40 years. Our results indicate that the second-growth stands growing on mesic sites have the potential to produce merchantable forests comparable to the yield tables available for black spruce provided that the number of stems per hectare is adequate.
Optimal timber harvest scheduling under harvest volume constraints: a comparison of two opportunity cost criteria
Authors: Armstrong Glen W. , Phillips William E. , Beck Jr. James A.
Published: September 2007

A simple model is developed to determine the economically optimal combination of stands to harvest in a period when there are periodic maximum harvest volume constraints. The model is formulated using concepts developed in the Faustmann optimum forest rotation model. The objective function minimizes the net opportunity cost of delayed harvest. For each stand in the forest, the model is used to determine if the stand should be harvested this period or if the harvest decision should be deferred to the next period. In the typical exposition of the Faustmann model, the opportunity costs of delayed harvest are expressed per unit area. Because of this, and the spatial orientation of forest management, it is tempting to use costs per hectare to set harvest priority. However, when harvests are constrained by some maximum harvest volume, costs per unit volume are the appropriate criterion to use. The purpose of this paper is to demonstrate the economic losses resulting from the use of the inappropriate priority criterion. The model is applied to a study area in Saskatchewan. As well as demonstrating the economic losses, the study shows that a much wider variety of species associations and site classes are scheduled for harvest when the volume-based ranking criterion is used. This mix of harvested species and sites is consistent with the observed behaviour of firms. It has been argued elsewhere that this behaviour is due largely to government-imposed behaviour (e.g., operating ground rules) or to the spatial considerations of forest management. We suggest here that at least some of this behaviour can be attributed to optimal response to harvest volume constraints.
Denitrification in forest soils of Oregon
Authors: Vermes Jean-François , Myrold David D.
Published: September 2007

Denitrification represents a potential loss of N from forest soils as well as a source of N oxides to the atmosphere; however, this process has not been closely examined in forest ecosystems of the Pacific Northwest. The objectives of this study were to survey insitu denitrification rates in a range of forest ecosystems and to assess the importance of selected soil properties as controlling factors of denitrification in forest soils. Soils from eight mature conifer stands, three recently clear-cut sites, and four Alnusrubra Bong, stands were sampled in spring, summer, and autumn. Denitrification potentials (anaerobic soil slurries), insitu denitrification rates, soil respiration rates, soil water contents, and soil NO3− concentrations were measured. Denitrification potentials ranged from <1 to 1900 ng N•g−1•h−1, and insitu denitrification rates varied from 0.1 to 40 g N•ha−1•day−1. Denitrification potentials were highly correlated with soil NO3− concentrations and soil water contents; these two soil variables explained more than 90% of the variation in denitrification potentials. Field denitrification rates were best correlated with soil water contents: using multiple regression, up to 79% of the variation in field denitrification rates was explained by soil water contents. Experiments on the short-term dynamics of denitrification following water addition confirmed the importance of soil water content as a regulator of denitrification and suggested that active denitrification requires formation of anaerobic microsites. Extrapolation of seasonal denitrification measurements suggests that relatively little N (<10 kg N•ha−1•year−1) is lost from Oregon forest soils as N gases.
Changes in enzyme activity and protein patterns during the maturation phase of somatic embryogenesis in hybrid larch (Larix × eurolepis)
Authors: Pitel J.A. , Yoo B.Y. , Klimaszewska K. , Charest P.J.
Published: September 2007

Changes were monitored in the activity of 10 enzymes and in the protein patterns revealed by one-dimensional SDS–PAGE gels during the maturation phase of hybrid larch somatic embryos up to the globular stage of the embryogenic cell line L2. For all the enzymes tested, activity increased up to 15 days after transfer of the proembryogenic calli on maturation media and then gradually decreased. In the globular somatic embryos, enzyme activity increased. Analyses of total protein patterns on SDS–PAGE indicated a decrease in the amount and number of detectable protein bands. As expected, mature globular embryos showed a different protein pattern. The decrease in calli metabolism, as demonstrated by enzyme activity and protein patterns, is consistent with the phenotypic observation of calli degeneration during the maturation phase. No differences in the protein pattern were observed between the embryogenic line L2 and another nonembryogenic line, L1. From these results, protein patterns specific to time in the maturation phase have been identified, but further investigation is required to determine if they are causes or effects of the process.
Use of selection indices to increase tree height and to control damaging agents in 2-year-old balsam poplar
Authors: Riemenschneider Don E. , McMahon Bernard G. , Ostry Michael E.
Published: September 2007

Cuttings were collected from balsam poplars (Populusbalsamifera L.) representing 21 populations in Minnesota, Wisconsin, and Michigan, and a replicated nursery trial containing 153 clones was established. Tree height, phenology, leaf morphology, and resistance to damaging agents were evaluated during the second growing season, and genetic and phenotypic variances and covariances among traits were estimated. Clones differed significantly in all traits. However, populations differed only in tree height, number of leaves produced after August 31, bud-set date, number of sylleptic branches (i.e., branches that arise from buds the same year that the buds formed), and severity of Septoria leaf spot symptoms. Tree height was positively correlated with number of leaves, bud-set date, most measures of leaf size, and resistance to Melampsora leaf rust. Predicted responses to index selection for 2nd-year tree height using leaf area or leaf length as secondary selection criteria were not significantly greater than predicted response to univariate selection for tree height alone. However, results supported use of restricted selection indices to curb increased susceptibility to damaging agents that would otherwise result from selection for tree height.
Treating Scots pine seedlings with the herbicide atrazine does not affect shoot chemistry or feeding and oviposition by Lygusrugulipennis
Authors: Holopainen Jarmo K. , Tuhkalainen Jaana , Kainulainen Pirjo , Satka Heli
Published: September 2007

Polyphagous Lygus (Heteroptera: Miridae) bugs, which have one of the widest documented host-plant ranges, have accepted nursery-grown conifer seedlings as host plants only recently. One explanation for this adaptation to the conifer nursery environment could be the increased attractiveness of conifer seedlings due to herbicide treatments. In three laboratory experiments, we tested whether atrazine treatments (2 or 4 kg•ha−1) affected shoot chemistry of pine seedlings and the feeding and oviposition behaviour of the European tarnished plant bug, Lygusrugulipennis Popp. Shoot growth of the pine seedlings was decreased by the atrazine treatment (2 kg•ha−1) in only one experiment. The number of feeding lesions caused by Lygus bugs and the number of eggs laid per seedling were not affected by herbicide treatments, nor was the proportion of seedlings damaged. Concentrations of total amino acids were not affected by the herbicide in any of the experiments. In one experiment, the level of lysine was increased in the atrazine treatment. Terpenes and resin acids were analysed only in one experiment, and total concentrations of these defence compounds were not affected by atrazine. Dominant monoterpenes were α-pinene and 3-carene, the latter varying strongly between individual seedlings. Abietic acid and neoabietic acid were the dominant abietane and pimarane resin acids. The results suggest that applications of atrazine are not likely to reduce the resistance of pine seedlings to Lygus bugs. Herbicides may have an indirect effect by reducing the availability of alternative host plants for bugs. Other potential causes for increased numbers of Lygus bugs on nursery-grown conifer seedlings are discussed.
Availability of nitrogen and phosphorus in the forest floors of Rocky Mountain coniferous forests
Authors: Prescott Cindy E. , Corbin John P. , Parkinson Dennis
Published: September 2007

Nutrient supply rate and limitation were measured in forest floors of lodgepole pine, white spruce–lodgepole pine, and Engelmann spruce–subalpine fir (pine, spruce, and fir forests, respectively) forests in the Kananaskis Valley of southwestern Alberta. Earlier analyses of the nutrient content of foliage and litter indicated low N and P supply in the pine forest, high P supply in the spruce forest, and high N–low P supply in the fir forest. Measurements of nutrient supply (insitu rates of net mineralization, extractable P, and uptake of N and P from the forest floor in pot trials) confirmed the differences in N and P supply among the forests and indicated that nutrient concentrations in needle litter were useful as an index of nutrient supply rate. Subtractive tests were useful in identifying the most limiting nutrients in each forest: lodgepole pine seedlings grown in forest floor material from the pine and spruce stands responded with increased growth to the addition of N; those in fir forest floor material responded to P addition. Vector analysis of N and P concentrations and contents in needles from trees fertilized with ammonium phosphate sulphate showed responses to both N and P in the pine site, no response at the spruce site, and response to P at the fir site.
Isolation of inhibitor-free poly(A+) RNA from Pinusmonticola and Pinuslambertiana seedlings
Authors: Baker S.M. , White E.E. , Misra S.
Published: September 2007

Inhibition of invitro translation by material(s) that co-purifies with RNA obtained from 6- to 12-week-old western white pine (Pinusmonticola Dougl. ex Lamb.) and sugar pine (Pinuslambertiana Dougl.) seedlings was demonstrated. A method that consistently produces inhibitor-free poly(A+) RNA from small amounts of total RNA isolated from these seedlings is described.
How the pollination mechanism and prezygotic and postzygotic events affect seed production in Larixoccidentalis
Authors: Owens John N. , Morris Sheila J. , Catalano Glenda L.
Published: September 2007

The pollination mechanism of western larch (Larixoccidentalis Nutt.) is described in relation to the optimal time of pollination. Five stages of conelet receptivity were recognized and stages two to four had the greatest pollination success. Four categories of seed were recognized by X-ray and dissection of seeds from mature cones. The causes of degenerated, empty, and rudimentary seeds are discussed and recommendations are made for increased seed production through supplemental pollination. Light microscope and ultrastructural observations were made of the pollination mechanism and of pollen from 0 to 72 h after pollination, during pollen engulfment, during shedding of the exine, and during penetration of the nucellus. Pollen attachment to stigmatic hairs and pollen engulfment are described. Pollen hydration and ultrastructural changes began about 72 h after pollination. The exine was shed but the pollen remained just inside the sealed micropyle for 5–6 weeks. A pollination drop secreted from the nucellus then carried the pollen to the nucellus. There a pollen tube formed and penetrated the nucellus. Two male nuclei formed in a common body-cell cytoplasm when the pollen tubes reached the archegonia.
Effect of population, environment, and maturation on the frost hardiness of yellow-cedar (Chamaecyparisnootkatensis)
Authors: Hawkins B.J. , Russell J. , Shortt R.
Published: September 2007

Three 2-year-old experimental plantations of yellow-cedar (Chamaecyparisnootkatensis (D. Don) Spach.) seedlings and stecklings (rooted cuttings) from 4- and 12-year-old hedges were analyzed periodically for frost hardiness between September 1991 and May 1992. The plantations were at different elevations and latitudes, and seedlings and stecklings of three geographically diverse populations were represented. Frost hardiness was assessed using the freeze-induced electrolyte leakage method on upper, primary branches. Air temperature at the low elevation sites was monitored. Frost hardiness of all plants increased from September to the end of January, and then decreased. Plants grown at high elevation were consistently more hardy than those grown at low elevation; however, no obvious differences in hardiness between the two latitudes were evident. Seedlings and stecklings of parents from certain families and populations developed greater hardiness than stock of parents from other areas, showing that frost hardiness of yellow-cedar plants has a genetic component. The three stock types did not show any consistent, significant differences in hardiness; however, stecklings from 12- and 4-year-old hedges were, on average, slightly more hardy than seedlings.
Red spruce seedling gas exchange in response to elevated CO2, water stress, and soil fertility treatments
Authors: Samuelson L.J. , Seiler J.R.
Published: September 2007

The interactive influences of ambient (374 μL•L−1) or elevated (713 μL•L−1) CO2, low or high soil fertility, well-watered or water-stressed treatment, and rooting volume on gas exchange and growth were examined in red spruce (Picearubens Sarg.) grown from seed through two growing seasons. Leaf gas exchange throughout two growing seasons and growth after two growing seasons in response to elevated CO2 were independent of soil fertility and water-stress treatments, and rooting volume. During the first growing season, no reduction in leaf photosynthesis of seedlings grown in elevated CO2 compared with seedlings grown in ambient CO2 was observed when measured at the same CO2 concentration. During the second growing season, net photosynthesis was up to 21% lower for elevated CO2-grown seedlings than for ambient CO2-grown seedlings when measured at 358 μL•L−1. Thus, photosynthetic acclimation to growth in elevated CO2 occurred gradually and was not a function of root-sink strength or soil-fertility treatment. However, net photosynthesis of seedlings grown and measured at an elevated CO2 concentration was still over 2 times greater than the photosynthesis of seedlings grown and measured at an ambient CO2 concentration. Growth enhancement by CO2 was maintained, since seedlings grown in elevated CO2 were 40% larger in both size and weight after two growing seasons.
Temporal and spatial shift within the Nectria pathogen complex associated with beech bark disease of Fagusgrandifolia
Authors: Houston David R.
Published: September 2007

Beech bark disease occurs when either Nectriagalligena Bres., or Nectriacoccinea var. faginata Lohman, Watson, and Ayers kills bark that is or has been infested and altered by the beech scale, Cryptococcusfagisuga (Lind.). Introduced to Nova Scotia around 1890, this insect now occurs as far southwest as Ohio, West Virginia, Virginia, and North Carolina. I determined the relative occurrence of the two pathogens in forests affected for varying times and the temporal changes in their relative occurrence in recently affected stands of the Monongahela National Forest, West Virginia (MNF). Stands in the Canadian Maritimes, New England, New York, and Pennsylvania were sampled in 1985–1986; and in the Catskill Park, New York in 1988 and 1991. Stands on the MNF were sampled in 1982, 1983, 1984, 1986, 1988, and 1991. The following trends were indicated: N. galligena dominated recently affected stands in Pennsylvania and West Virginia, and N. coccinea var. faginata dominated long-affected stands in Canada, New England, and New York. On the MNF, only N. galligena was isolated in 1982; by 1988, N. coccinea var. faginata was isolated from 8 of 16 stands and from all 16 stands in 1991. Stands where N. galligena persisted had higher proportions of tree species highly susceptible to N. galligena than stands dominated quickly by N. coccinea var. faginata. Once present, however, N. coccinea var. faginata eventually will replace N. galligena as the dominant pathogen.
Formation and vertical distribution of juvenile and mature wood in a single stem of Cryptomeriajaponica
Authors: Yang K.C. , Chen Y.S. , Chiu C.
Published: September 2007

A single tree stem was used to study the formation and vertical distribution of juvenile and mature wood in Cryptomeriajaponica D. Don. The sample tree was collected from a 45-year-old plantation with 1.5 × 3.0 m spacing at Maio-li, Taiwan. Nine diametric wood strips were cut from the tree trunk from both the east and the west aspects, starting from 0.3 m by increments of 2.5 m to the top of the tree. The widths of juvenile and mature wood were recorded with two measures, i.e., the number of rings and the width in millimetres. The relationships between both the width of juvenile and mature wood and the height and age at each level of the tree were obtained by regression methods. The relationships between the age of the cambial initial and the period of juvenile wood formation at the various height levels were also determined. It was found that juvenile wood has a conical shape with a wide base at the bottom of the tree. There is no significant difference in the ratio of juvenile to mature wood width between the east and west aspects of the tree. The impact of both the height and age at each level of the tree on the width of juvenile wood appears to differ, and a similar observation must be made for mature wood. A high proportion of the total wood volume (64%) was found to be juvenile wood. No mature wood was observed at the top of the tree. The width of juvenile wood is highly correlated with the age of formation of cambial initials counted from the year of seed germination. The older the cambial initial, the narrower is the width of juvenile wood in terms of ring count.
Impact of spacing on tracheid length, relative density, and growth rate of juvenile wood and mature wood in Piceamariana
Authors: Yang K.C. , Hazenberg G.
Published: September 2007

Ten 38-year-old trees of Piceamariana (Mill.) B.S.P., grown at each of three spacings (1.8 × 1.8, 2.7 × 2.7, and 3.6 × 3.6 m), at Stanley, 30 km west of Thunder Bay, Ont., were used to study the impact of spacing on growth rate, relative density, and tracheid length of juvenile and mature wood. Increment cores of 12 mm diameter were extracted from the south aspect of each tree at breast height. The boundary of juvenile and mature wood was demarcated by the variation in tracheid length, which varied among trees from ring 11 to 21. Average growth rate, relative density, and tracheid length were obtained between the pith and boundary point (juvenile wood) and beyond the boundary point (mature wood). Differences between the levels of spacing for the three response variables in both juvenile and mature wood were tested using contrasts. Properties of juvenile and mature wood were found to be affected differently by the plantation spacing. Juvenile wood has a faster growth rate and shorter fibres than mature wood. Relative density was similar in both wood zones. The growth rate in juvenile wood was found to be significantly different among the spacing levels. For mature wood, only the growth rate at the 3.6 × 3.6 m spacing was significantly different from the other two spacing levels. The highest relative density, 0.39, in both juvenile and mature wood was found at the 1.8 × 1.8 m spacing. No significant difference in the relative density between the two wider spacings was observed. At the widest spacing, the relative density was 8% lower than that at the 1.8 × 1.8 m spacing. The longest fibre lengths were found at the intermediate 2.7 × 2.7 m spacing, 2.05 mm in juvenile wood and 2.94 mm in mature wood. Tracheid lengths of the 3.6 × 3.6 m spacing were significantly shorter than those of the other two spacings. The relative density and tracheid length of plantation grown wood were lower than those of natural grown wood by at least 5% for relative density and 33% for tracheid length.
A 1397-year tree-ring chronology of Thujaoccidentalis from cliff faces of the Niagara Escarpment, southern Ontario, Canada
Authors: Kelly P.E. , Cook E.R. , Larson D.W.
Published: September 2007

Living and dead Thujaoccidentalis L. (eastern white cedar) on cliff faces and in the talus of the Niagara Escarpment, southern Ontario were sampled and measured for dendrochronological analyses. One hundred and forty-two tree-ring series were cross-dated and a 1397-year tree-ring chronology was produced spanning the period 594–1990 A.D., making it the longest in Canada. An additional 784-year floating chronology was constructed from dead debris at the base of the cliff. Radiocarbon dates indicate that the floating chronology begins approximately in 580 B.C. Correlations between the tree-ring indices and 51 climate variables indicate that growth in T. occidentalis is negatively correlated with the previous growing season's temperature. The strongest correlation was between radial tree growth and maximum temperature in the previous July and August. Extremely hot summer conditions will negatively impact tree growth in the following year. These temperature correlations are very similar to those observed for T. occidentalis growing in western Quebec. This consistent climate response and the extreme longevity of T. occidentalis means that it is now an important species to exploit for dendroclimatological reconstructions of regional climate. The close proximity of these sites to the industrial heartland of eastern North America suggests that this, and future Thuja chronologies under development from the Niagara Escarpment, will provide an important ecological data base for exploring the human component of climate change.
Thermoregulation in two free-ranging subtropical insectivorous bat species: Scotophilus species (Vespertilionidae)
Authors: Jacobs D.S. , Kelly E.J. , Mason M. , Stoffberg S.
Published: September 2007

Little is known about the thermal regulatory behaviour of free-ranging subtropical bats. We studied torpor use in two free-ranging subtropical sibling species of insectivorous bat, Scotophilus dinganii (A. Smith, 1833) and Scotophilus mhlanganii , during the austral autumn. All S. dinganii (mass 28.9 ± 2.6 g (mean ± SD)) roosted in buildings, whereas all S. mhlanganii (28.0 ± 0.4 g) roosted in the foliage of trees or in a tree cavity. Contrary to what has been seen in other subtropical species, both Scotophilus species used only one bout of torpor per day. Bats entered torpor 2 h after returning from foraging and aroused passively as the roost was heated by the sun the following day. There was a negative correlation between duration of foraging and duration of torpor, probably because bats that foraged longer had less time for torpor. Despite physical differences between roosts, foliage and building roosts appeared equally thermally labile, resulting in torpor bouts of similar depth and duration between individuals of the two species that used such roosts. Cavity-roosting female S. mhlanganii, on the other hand, used torpor bouts that were longer and shallower than those used by its female conspecifics in foliage roosts and female S. dinganii in buildings. Thus, thermal regulatory behaviour was determined more by the type of roost used than by interspecific differences in physiology.
Site- and sex-level differences in adult feeding behaviour and its consequences to offspring quality in tree swallows (Tachycineta bicolor) following brood-size manipulation
Authors: Ardia D.R.
Published: September 2007

In species with biparental care, males tend to invest less in offspring than do females, likely because of differences in the costs and benefits associated with parental effort. Here I test for sex differences in the response of tree swallows ( Tachycineta bicolor (Vieillot, 1808)) to a brood-size manipulation at two locations differing in food resources, Alaska and New York. I tested sex and habitat differences in how swallows responded to changes in offspring demand. At both sites, both sexes increased effort when feeding enlarged broods, although Alaskan males increased feeding less than Alaskan females. Males decreased feeding effort more to reduced broods than females, but only in Alaska. Food abundance was higher in Alaska than in New York, and Alaskan tree swallows made more feeding visits than New York tree swallows. In New York, food availability did not predict feeding rate and there was no sex difference in the response to brood manipulation. In both sites, male feeding effort was linked with nestling residual body mass, while female feeding effort was correlated with nestling growth rate. This study demonstrates that male tree swallows differ from females by being the first to reduce feeding effort under certain conditions and that male and female feeding rate affects offspring quality differently.
UNCERTAINTY AVERSION, ROBUST CONTROL AND ASSET HOLDINGS WITH A STOCHASTIC INVESTMENT OPPORTUNITY SET
Authors: VARDAS GIANNIS , XEPAPADEAS ANASTASIOS
Published: September 2007

We formulate the portfolio choice problem as a robust control problem under uncertainty or ambiguity aversion. By considering a stochastic investment opportunity set, we derive optimal robust portfolio rules in the cases of one and two risky assets. With two risky assets and ambiguity structure determined by economy-wide factors, we show that the robust portfolio rule could lead to an increase in the total holdings of risky assets as compared to the holdings under the Merton rule, which is the standard risk aversion case. This result goes against the general belief that uncertainty aversion and robust control methods lead to conservative behavior. We also show that the investor is more likely to increase the holdings of the asset for which there is no ambiguity, and reduce the holdings of the asset for which there is ambiguity, a result that might provide an explanation for the home bias puzzle.
THE INFLUENCE OF SOCIAL TIES AND SELF-EFFICACY IN FORMING ENTREPRENEURIAL INTENTIONS AND MOTIVATING NASCENT BEHAVIOR
Authors: SEQUEIRA JENNIFER , MUELLER STEPHEN L. , MCGEE JEFFREY E.
Published: October 2007

Theoretical models of entrepreneurship suggest that an individual's intention to start an enterprise is a strong predictor of eventual entrepreneurial action. Less understood are factors that influence the likelihood of entrepreneurial intentions and nascent behavior. In this study, we develop and test several hypotheses about how social network ties and self-efficacy affect entrepreneurial intentions and nascent behavior. We found that a personal network of supportive strong ties coupled with high entrepreneurial self-efficacy increases the likelihood of entrepreneurial intentions and nascent behavior. A personal network of weak ties with practical business knowledge and experience also increases the likelihood of entrepreneurial nascent behavior but not entrepreneurial intentions. In contrast, a personal network of strong ties with practical business knowledge and experience has little effect on either intentions or nascent behavior and may, in fact, suppress both. The contribution of this study to nascent entrepreneurship research and implications for future research are discussed.
GHANAIAN AND KENYAN ENTREPRENEURS: A COMPARATIVE ANALYSIS OF THEIR MOTIVATIONS, SUCCESS CHARACTERISTICS AND PROBLEMS
Authors: CHU HUNG MANH , BENZING CYNTHIA , MCGEE CHARLES
Published: October 2007

Three hundred and fifty-six entrepreneurs from Kenya and Ghana were surveyed to determine their motivation for business ownership, variables contributing to their business success, and the problems they encountered. Kenyan and Ghanaian entrepreneurs indicated that increasing their income and creating jobs for themselves were leading factors motivating them to become business owners. Hard work and good customer service were cited by both Kenyan and Ghanaian business owners as critical for their success. But, compared to the Kenyan entrepreneurs, Ghanaians weighed support from family and friends and external relationship building as more important. A weak economy is the most important problem preventing entrepreneurs of both countries from achieving their goals. Ghanaian entrepreneurs were more concerned about the inability to obtain capital, while Kenyan entrepreneurs were more concerned about government regulations and problems related to business location.
STRUCTURAL DAMAGE QUANTIFICATION BY SYSTEM IDENTIFICATION
Authors: KOH C. G. , PERRY M. J.
Published: October 2007

After a disaster such as an earthquake has struck, the damage assessment of the affected buildings, bridges and other forms of structures is often urgently required for follow-up action. Research in using system identification for damage assessment in a quantifiable and non-destructive way has rapidly increased in recent years, due to advances in computing power and sensing technology. Though considerable progress has been made, many challenges still remain in achieving robust and effective identification of large structural systems using incomplete and noisy measurement signals. In this paper a novel strategy to tackle this problem is presented. A modified genetic algorithm (GA) strategy incorporating a search space reduction method, progressively and adaptively reduces the search space for each unknown parameter. By concurrent evolution of multiple species, it provides an excellent balance between exploration of the search space and exploitation of good solutions. The modified GA is incorporated into a damage detection strategy that works by comparing identified parameters for the undamaged and damaged structures and quantifies damage as a relative change in the stiffness of a member or a group of members. The additional information obtained from the analysis of the undamaged structure is used to greatly improve speed and accuracy in the identification of the damaged structure. Numerical studies on 10 and 20 degree-of-freedom (DOF) systems and an experimental study of a 7-storey small-scale steel frame are presented to illustrate the applicability of the method in accurately identifying even small amounts of damage.