bluuebunny/crossref_metadata_2025 huggingface dataset:
Foliage and stand growth responses of semimature lodgepole pine to thinning and fertilization
Authors: Yang Richard C
Published: April 2011

The aim of this study was to quantify the interactive response of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) to thinning and nitrogen (N) fertilization in midrotation stands by assessing foliar and stand growth response relationships and determining the optimum fertilizer regime. The experiment design was a factorial arrangement of treatments with two thinning intensities (thinned and unthinned control) and four N levels (0, 180, 360, and 540 kg·ha-1). Foliage was sampled annually from trees in buffers for 4 years following treatment and plot trees measured at a 5-year interval. Results indicated that the effect of fertilization on fascicle length and needle dry mass disappeared 2 years after N treatment, while thinning effects on foliage emerged 3 years after fertilization. Both first year fascicle length and dry mass were reliable predictors (r2 = 0.87 and 0.82, respectively) of subsequent stand volume growth. Applications of N at 360 kg·ha-1 to thinned and unthinned plots, respectively, improved 10-year periodic height increment by 20 and 19%, diameter at breast height by 29 and 34%, basal area by 21 and 36%, and total volume by 25 and 28%. Fertilization of N at this level appears to be optimal based on foliar and mensurational responses. High N loadings increased tree mortality and accelerated stand development and so it could be advantageously used as a tool for managing overstocked stands.
Growth of five hybrid poplar genotypes exposed to interacting elevated CO2 and O3
Authors: Dickson R E , Coleman M D , Riemenschneider D E , Isebrands J G , Hogan G D , Karnosky D F
Published: April 2011

A wide variety of hybrid poplar clones are being introduced for intensive culture biomass production, but the potential clonal or genotypic response to increasing tropospheric carbon dioxide (CO2), ozone (O3), and their interactions are unknown. To study these effects, we exposed five different hybrid Populus clones to increased concentrations of CO2, O3, and CO2 + O3 in open-top chambers for one growing season and determined growth responses. Exposure to elevated CO2 increased height growth, dry mass, and basal area; exposure to O3 decreased all three of these growth responses. Exposure impact differed among the different plant parts (leaf, stem, and roots) and among the clones. These differences were associated with different growth strategies or carbon allocation patterns inherent in the different clones. The fastest growing clones had the greatest response to O3 treatment. The addition of CO2 to the O3 exposure counteracted the negative impact of O3 in all plant components except leaf mass (e.g., CO2 + O3 plant mass equaled control plant mass) in all of the clones. But correspondingly, added O3 negated increased growth from CO2. Genetic variation in response to atmospheric pollutants must be considered even in closely related genotypes found in Populus culture.
Foliar nitrogen dynamics in Liquidambar styraciflua saplings: response to nitrogen fertilization
Authors: Kuers Karen , Steinbeck Klaus
Published: April 2011

The nitrogen (N) content of mature leaves and recently abscised leaves representing different crown positions of sweetgum (Liquidambar styraciflua L.) saplings was measured to (i) quantify the effects of N fertilization on seasonal distribution of foliar N, (ii) determine if N availability affected the relationship between leaf N per unit leaf area (NA) and leaf light exposure, and (iii) project the proportion of N incorporated into developing leaves that could be supplied by N reabsorbed from leaves senescing during the growing season. Fertilizer approximately doubled the foliar N pool and increased NA at all crown levels. The NA generally increased from the base to the top of the tree and acropetally along the branch. Fertilization elevated the NA for a given light exposure level and increased the slope of the NA to light relationship. Litter NA increased during the season across all plots. Fertilized trees reabsorbed more N from senescing foliage than controls. Whereas N reabsorbed from leaves falling prior to July 14 could supply only 17% of the N needed for new leaf development during that period, all of the N needed for the small amount of foliage produced after mid-July could have been obtained through retranslocation from senescing foliage.
Nitrogen mineralization associated with birch and fir under different soil moisture regimes
Authors: Evans Celia A , Miller Eric K , Friedland Andrew J
Published: April 2011

We examined net nitrogen mineralization rates in forest floor beneath birch-dominated or fir-dominated canopy plots in a high-elevation mixed-species forest in New Hampshire during the 1995 and 1996 growing seasons. Soil moisture was significantly greater in 1996 than in 1995 (season averages were 2.1 times and 1.4 times dry soil mass, respectively). Net mineralization was significantly greater in both plot types in 1996 than in 1995. The magnitude of difference, however, was much greater in fir plots. Nitrification increased in birch plots and significantly decreased in fir plots from 1995 to 1996. Results of a three-way ANOVA showed significant year and species main effects for net mineralization and a significant species × year interaction for nitrification. There were no significant correlations between net N mineralization and measured soil chemistry variables in 1995. In 1996 there were significant positive correlations between total N, and net mineralization and nitrification in birch plots and between soil moisture and net mineralization in fir plots. These results support a growing body of research suggesting that species feedbacks influence rates of net N mineralization in mixed species forests. Further, this study provides novel evidence that rates of net N mineralization may respond differently to changing abiotic conditions depending on the local canopy species in a mixed-species forest.
Location of cones in the crown and along shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) and the influence of coning intensity and shoot size
Authors: Clarke G C , Malcolm D C
Published: April 2011

The location of female cones in the crowns of rooted cuttings and mature forest-grown trees of Sitka spruce (Picea sitchensis (Bong.) Carr.) was recorded. When cones were allocated to crown sections there were clear patterns of bearing, with the majority of cones on second-order distal shoots on whorls 2 and 3. As total cone production increased, the bearing zone progressed onto more proximal shoots on upper whorls and distal shoots on lower whorls. On individual branches of clonal grafts, female cones tended to be borne on more distal shoots than male cones. Female cones, on all sample sets, tended to be borne primarily on second-order shoots and male cones, on the clonal grafts, on third-order shoots. On the clonal grafts there was a weak, though significant, relationship between the number of original buds and female, but not male, cones on a shoot. Cones were also described by position on bearing shoots. There was a tendency for the proportion of progressively more proximal cone positions to increase on lower-order shoots and vice versa. Cone position was also influenced by the dimensions of the bearing shoot independent of its position with a distal shift in cone-bearing position as shoot dimensions decreased.
Catastrophic disturbance in the presettlement forests of the Upper Peninsula of Michigan
Authors: Zhang Quanfa , Pregitzer Kurt S , Reed David D
Published: April 2011

The General Land Office (GLO) survey notes (1840-1856) were used to examine the interaction among natural disturbance, vegetation type, and topography in the presettlement forests of the Luce District, an ecological unit of approximately 902 000 ha in the Upper Peninsula of Michigan, U.S.A. The surveyors recorded 104 fire and 126 windthrow incidences covering 3.1 and 2.8% of the total length of the surveyed lines, respectively. The rotation periods over the entire landscape were 480 years for fire and 541 years for windthrow, but these varied with vegetation type and topographic position. Fire occurred more frequently on southerly aspects and at elevations where pinelands were concentrated. The density of windthrow events increased with elevation and slope, with the highest occurrence on westerly aspects. Based on the estimated rotation periods, we calculated that 7.5, 24.4, and 68.1% of the presettlement forest were in the stand initiation, stem exclusion, and old forest (including both understory reinitiation and old growth) stages, respectively. Pinelands and mixed conifers were the major components in both the stand initiation (34.5 and 31.1%) and the stem exclusion stage (20.9 and 39.8%), while mixed conifers (39.3%) and northern hardwoods (34.7%) were the major old-forest cover types. The diverse mosaic of various successional stages generated by natural disturbance suggests a "shifting-mosaic" landscape in this region.
Scale-dependent patterns of soil enzyme activity in a forested landscape
Authors: Decker Kelly LM , Boerner Ralph EJ , Morris Sherri Jeakins
Published: April 2011

We evaluated the patterns of variation in the activity of four soil enzymes in oak forests soils at spatial scales from 10s of km to <3 m. The four enzymes (β-glucosidase, chitinase, phenol oxidase, and acid phosphatase) are specific for substrates that vary widely in lability or recalcitrance. Significant variations in enzyme activity were observed at the regional (among forested areas), topographic (along elevation gradients within a watershed), and single-tree (1 m upslope and downslope of an individual tree) scales, but not at the local scale (contiguous watersheds within forested areas). However, the specific patterns of variation in relation to spatial scale were unique to each enzyme system. Detrended correspondence analysis (DCA) ordination of the activity of the four enzymes in each soil sample suggested a strong nutrient availability gradient underlying these spatial scale differences. Exploratory path analysis produced relatively strong predictive models based on soil nutrients, organic matter, and moisture for all the individual enzymes except phenol oxidase. However, path analysis produced an even stronger model for the activity of all four enzymes together, using the DCA axis scores as the dependent variable. The results indicate that the four enzyme systems could help resolve spatial dependencies at a range of scales and could also be used to develop a scale-independent metric to be used for regional analyses in a geographic information system environment.
Testing a new competition index for Maritime pine in northwestern Spain
Authors: Schröder Jörg , Gadow Klaus von
Published: April 2011

A distance-independent competition index is derived from the basal area in larger trees (BAL) index combining individual tree's basal area percentiles with a relative-spacing stand-density measure. Empirical increment data from Maritime pine trees (Pinus pinaster Ait.) sampled from regular, naturally regenerated stands in the province of Pontevedra, northwestern Spain, are used to compare the performance of the two competition indices in the context of basal area growth modelling. The basal area increment of individual trees was first predicted exclusively as a response to competition using a two-parameter exponential function and then as a function of potential growth reduced by competition. For the criteria evaluated in this paper, the new competition index has shown superior qualities. The main improvement over BAL is the incorporation of the relative spacing measure.
Biomass, thermal inertia, and radiative freeze occurrence in leafless forests
Authors: Potter Brian E , Zasada John C
Published: April 2011

Using field measurements of air temperature, wind, and relative humidity from a clear-cut site and two wooded sites in northern Wisconsin, we used a radiative transfer model to simulate temperatures on seven calm, clear nights similar to those on which freezes typically occur. Each night was simulated twice for the wooded sites. One simulation ignored the presence of vegetation, the other approximated the vegetation's heat storage capacity and its influence on air temperatures. The simulations including biomass heat storage showed smaller mean absolute temperature errors and decreased magnitude of systematic model error when compared with the simulations ignoring vegetation. The results suggest that the thermal inertia of forest biomass may play a significant role in controlling forest temperatures on calm, clear nights and, hence, in controlling freeze occurrence.
Spring changes in water relations, gas exchange, and carbohydrates of white spruce (Picea glauca) seedlings
Authors: Wang Yingfang , Zwiazek Janusz J
Published: April 2011

Shoot water relations, gas exchange, and carbohydrate content and composition were studied from March 30 to May 11, 1995, in white spruce (Picea glauca (Moench) Voss) seedlings growing in nursery beds. The seedlings exhibited reduced shoot osmotic potentials at turgor loss point and at full hydration from March 30 to April 27 followed by an increase until May 11. Shoot relative water contents also showed a marked increase after April 27. Bulk modulus of elasticity of shoots gradually increased from early to late April indicating a decrease in cell wall elasticity. Net photosynthesis of seedlings recovered rapidly in mid-April. Both net photosynthesis and stomatal conductance showed a significant linear relationship with minimum air and soil temperatures, and there was a significant linear relationship between net photosynthesis and stomatal conductance. Needle starch content increased, but total sugar content was relatively constant. The composition of soluble carbohydrates changed in early spring with an increase in sucrose accompanied by a decrease in raffinose and other soluble carbohydrates. The results suggest that white spruce seedlings develop characteristics associated with the optimum drought stress resistance in early spring.
Calcium and magnesium in wood of northern hardwood forest species: relations to site characteristics
Authors: Arthur M A , Siccama T G , Yanai R D
Published: April 2011

Improving estimates of the nutrient content of boles in forest ecosystems requires more information on how the chemistry of wood varies with characteristics of the tree and site. We examined Ca and Mg concentrations in wood at the Hubbard Brook Experimental Forest. Species examined were the dominant tree species of the northern hardwood forest and the spruce-fir forest. The concentrations of Ca and Mg, respectively, in lightwood of these species, mass weighted by elevation, were 661 and 145 µg/g for sugar maple (Acer saccharum Marsh.), 664 and 140 µg/g for American beech (Fagus grandifolia Ehrh.), 515 and 93 µg/g for yellow birch (Betula alleghaniensis Britt.), 525 and 70 µg/g for red spruce (Picea rubens Sarg.), 555 and 118 µg/g for balsam fir (Abies balsamea (L.) Mill.), and 393 and 101 µg/g for white birch (Betula papyrifera Marsh.). There were significant patterns in Ca and Mg concentrations with wood age. The size of the tree was not an important source of variation. Beech showed significantly greater concentrations of both Ca (30%) and Mg (33%) in trees growing in moist sites relative to drier sites; sugar maple and yellow birch were less sensitive to mesotopography. In addition to species differences in lightwood chemistry, Ca and Mg concentrations in wood decreased with increasing elevation, coinciding with a pattern of decreasing Ca and Mg in the forest floor. Differences in Ca and Mg concentration in lightwood accounted for by elevation ranged from 12 to 23% for Ca and 16 to 30% for Mg for the three northern hardwood species. At the ecosystem scale, the magnitude of the elevational effect on lightwood chemistry, weighted by species, amounts to 18% of lightwood Ca in the watershed and 24% of lightwood Mg but only 2% of aboveground biomass Ca and 7% of aboveground Mg.
A stochastic characterisation of the natural disturbance regime of the boreal mixedwood forest with implications for sustainable forest management
Authors: Armstrong Glen W
Published: April 2011

The annual area burned on an 8.6 × 106 ha study area in the boreal mixedwood forest of northeastern Alberta, Canada, was characterised as a serially independent random draw from a lognormal distribution. This characterisation was applied in Monte Carlo simulations, which showed that estimates of the mean annual burn rates, even with long sample periods, are highly imprecise. Monte Carlo simulation was also used to simulate the development of a forest subject to lognormally distributed annual burn rate in an attempt to characterise the equilibrium age-class structure. No equilibrium age-class structure could be identified from the simulation results. The validity of equilibrium age-class distribution models (e.g., the negative exponential and Weibull) and analysis that relies on these models is questioned for forests where the annual burn rate is highly variable.
Effects of genetic selection for growth on frost hardiness in western hemlock
Authors: Hannerz Mats , Aitken Sally N , King John N , Budge Sonya
Published: April 2011

Fall and spring frost hardiness was determined from electrolytic leakage of artificially frozen needle segments in 22 full-sib families of western hemlock (Tsuga heterophylla (Raf.) Sarg.) from British Columbia and Washington State representing different levels of genetic gain, and of four provenance materials (stand progenies from the Queen Charlotte Islands, Vancouver Island, and Oregon Cascades, and seed-orchard progenies from the northern Oregon Coast Range). Samples for freeze testing were collected in a 5-year-old trial at Jordan River on southwestern Vancouver Island. Height and date of bud flush were recorded in the field. Genetic gain among the full-sib families was not correlated with fall frost hardiness, but high-yielding families displayed a lower spring frost hardiness and an earlier bud flush than low-yielding families. Both fall and spring frost hardiness increased and height growth decreased with the latitude of provenances. The highest growth, earliest bud flush and lowest fall and spring frost hardiness was demonstrated by the Oregon provenances, while the lowest growth, latest bud flush and highest hardiness was found for the Queen Charlotte Islands provenance.
Point accuracy of combined pseudorange and carrier phase differential GPS under forest canopy
Authors: Næsset Erik
Published: April 2011

One 6-channel and two 12-channel single frequency GPS receivers observing C/A (course/acquisition) code and carrier phase were tested to determine positional point accuracies under conifer and deciduous tree canopies. Positional accuracies were determined for 38 subcanopy sites by differential processing of C/A code observations only and combined use of C/A code and carrier phase. Observation periods of 2.5-30 min were evaluated. Mean positional accuracy ranged from 1.17 to 3.70 m for the 12-channel receivers based on 2.5-30 min of observation of C/A code. Mean accuracy ranged from 0.79 to 2.25 m for combined use of C/A code and carrier phase. The accuracy was 7.34 m with 30 min of C/A code observations with the 6-channel receiver. With combined use of C/A code and carrier phase the mean accuracy of the 6-channel receiver increased to 0.98-2.44 m. The accuracy increased with decreasing basal area and improving geometric satellite distribution. The mean accuracy was significantly higher for the 12-channel receivers than for the 6-channel receiver and significantly higher by combined use of C/A code and carrier phase than use of C/A code only.
Growth, suppression, death, and self-pruning of branches of Scots pine in southern and central Finland
Authors: Mäkinen Harri
Published: April 2011

Branch development of Scots pine (Pinus sylvestris L.) was studied in 19 thinning experiments in southern and central Finland. Data were collected from 229 trees on sites of different fertility with different stand density, age, and canopy position. Stem sections that included the thickest branch or knot of the whorl were sawn out from the whorls below the lowest living and dead whorl. The stem sections were dissected and the years of birth, suppression, death, and occlusion of the branches were determined. Diameter growth of the branches continued for a longer time in older trees. Branch growth was also prolonged by rapid radial growth of the stem. On average, branches died 7 years after their growth cessation. The number of years that branches stayed alive after growth cessation was independent of the tree or stand characteristics. After the death of a branch, more than 40 years elapsed before the branch was occluded. Large branch diameter and rapid radial growth of the stem increased the width of the loose knot zone in the stem. The results showed that there are limited possibilities of using delayed thinnings to reduce the knottiness of timber, and artificial pruning is needed to produce timber of high quality.
Development of structural root architecture and allometry of Quercus petraea
Authors: Drexhage Michael , Chauvière Marc , Colin Francis , Nielsen Christian NN
Published: April 2011

Root growth direction, radial distribution of roots, and biomass partitioning within the root system were examined on fifty-five 20 and 28-year-old sessile oak (Quercus petraea (Matt.) Liebl.) trees. The root systems were spatially subdivided into three concentric cylinders. Diameters and compass direction of roots were recorded at each point where they crossed one of the cylinders. Analysis of the distribution of root cross-sectional area (Ar) at 30 cm radius from the stem showed clustering in a preferred direction only for 10 small trees (diameter at breast height (DBH) < 9 cm). A classification of four incline growth types was used to describe differences in root architecture associated with the different age stands. Approximately 75% of all roots kept their orientation throughout the root-soil plate on both plots. Equations were developed to describe allometric relationships between basal area, DBH, sum of Ar, and root biomass. With increasing stem diameter, the root biomass was allocated predominantly to and evenly distributed within the surface root system, effectively increasing tree stability. Results from this study support the idea that root system architecture is inherently determined and that DBH or proximal root diameter measurements are sufficient to predict root biomass of young sessile oak when soil properties are nonrestrictive.
An intervention analysis of Hurricane Hugo's effect on South Carolina's stumpage prices
Authors: Yin Runsheng , Newman David H
Published: April 2011

Using intervention analysis and Timber Mart-South price data, we test hypotheses concerning the impact of Hurricane Hugo on regional stumpage prices. In both the hardwood sawtimber and pine pulpwood markets, a gradual die-down price effect was detected, but a persistently higher or lower price was not found. In the hardwood pulpwood market, we could not even identify a significant price drop immediately followed the occurrence of Hugo. Only in the pine sawtimber market were we able to detect a higher price of $6.00 per thousand board feet in the long run. However, our examination of an average price series for pine sawtimber across the southern United States suggests that this effect could have come from structural shifts in the regional market, rather than from Hugo's impact. Our empirical evidence thus rejects the hypothesis of a persistently higher or lower price in favor of the alternative that Hugo caused only a gradual die-down price effect.
Influence of partial cutting on site microclimate, soil nitrogen dynamics, and microbial biomass in Douglas-fir stands in western Washington
Authors: Barg Amy K , Edmonds Robert L
Published: April 2011

Partial cutting as an alternative to clear-cutting is being practiced in many Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands in the Pacific Northwest United States. The objectives of this study were to determine the influence of (i) partial cutting (dispersed green-tree retention) and clear-cutting on air and soil temperatures and soil moisture, on surface mineral soil net ammonification, nitrification, and total N mineralization rates, and on soil microbial biomass and (ii) the proximity to trees in the green-tree retention areas on these factors. The study was conducted in 60- to 70-year-old stands in the Cedar River Watershed, about 70 km southeast of Seattle, Wash., between July 1994 and August 1995. Air and soil temperatures and soil moisture in the green-tree retention treatments were generally intermediate between the uncut forest and the clearcut treatments. There were no significant differences in net ammonification, nitrification, and total N mineralization rates and in soil microbial biomass among treatments. Soil moisture influenced net ammonification and total N mineralization rates and microbial biomass. Nitrogen dynamics were generally not influenced by nearness to trees in the green-tree retention treatment. Average microbial biomass, however, was higher near to green trees (1 m) than far (6 m).
Effects of shelter and competition on the early growth of planted white spruce (Picea glauca)
Authors: Groot Arthur
Published: April 2011

Overstory manipulation and vegetation control treatments were applied at three experimental locations in northern Ontario, Canada, to examine shelter and competition effects on planted white spruce (Picea glauca (Moench) Voss). Overstories were nearly pure trembling aspen (Populus tremuloides Michx.) or aspen-conifer mixedwoods. Overstory treatments included clear-cutting, uniform shelterwood (40% canopy removal), strip shelterwood (widths from 0.5 to 1.0H, where H is the height of dominants), patch shelterwood (diameter about 1.0H), narrow strips (width 0.25H), and intact overstory. Vegetation-control treatments included herbicide and no-herbicide treatments. Second-year seedling growth was poorest under intact overstories and in 0.25H strips, and vegetation control had little effect on growth in this situation. Vegetation control in clearcuts increased seedling diameter but not height growth. In shelterwood treatments, however, vegetation control often increased both diameter and height growth. Greatest diameter tended to occur in clearcuts with vegetation control, whereas greatest height growth tended to occur in shelterwoods with vegetation control. These differing responses likely occur because diameter growth is influenced primarily by light availability, but height growth is additionally affected by other environmental factors. Combining early vegetation control along with shelterwood treatments appears to provide the optimum environment for establishing white spruce.
Changes in the herbaceous and vine communities at the Bisley Experimental Watersheds, Puerto Rico, following Hurricane Hugo
Authors: Chinea Jesus D
Published: April 2011

While herbaceous species and vines constitute a minor portion of the biomass in tropical closed forest ecosystems, they account for a substantial portion of the diversity of these ecosystems and become more conspicuous after natural disturbances. This study describes the changes in abundance and diversity of the herbs and vines during 5 years following Hurricane Hugo at the Bisley Experimental Watersheds, Puerto Rico. The cover of herbs, ferns, and vine species was sampled within a 5-m2 area in 25 randomly chosen circular permanent plots within the 13 ha of these watersheds. Sampling was done 12, 18, 36, 48, and 60 months after the hurricane. One year after the hurricane the overall mean herbaceous cover in the watersheds was 55%. Four years later, the cover and species richness of herbs and vines, but not ferns, had been significantly reduced. The only change in species diversity (H') was a significant increase in ferns. These changes are explained in terms of the extent and spatial variability of the hurricane damage, as well as changes in the tree component of this ecosystem.
Point relascope sampling of downed coarse woody debris
Authors: Gove Jeffrey H , Ringvall Anna , Ståhl Göran , Ducey Mark J
Published: April 2011

This paper presents a method based on angle-gauge sampling useful for inventorying downed coarse woody materialin forest stands. The method is closely related to transect relascope sampling, except that sample points are used rather than line transects. Theestimators for the total and per unit area are given along with theestimators of their variances. Methods for handling both borderline material and boundaryoverlap situations are also presented.
Understory responses to fire and artificial seeding in an eastern Cascades Abies grandis forest, U.S.A.
Authors: Schoennagel Tania L , Waller Donald M
Published: April 2011

To mitigate erosion after fire, land managers often seed non-native grasses onto burned slopes. To assess how post-fire seeding affects plant recovery, we compared areas that were either unseeded or artificially seeded after high-intensity fire in a dry Abies grandis (Dougl.) Lindl. forest in the northeastern Cascades. Seeding with a mix of non-native grasses and a legume significantly reduced the cover of native plants and shifted patterns of relative abundance after 2 years. Although seeding did not significantly affect total cover or native species richness, it reduced overall native plant cover by 47%. Species that recolonize via wind-dispersed seeds (e.g., Epilobium angustifolium L., Lactuca serriola L., and Arenaria macrophylla Hook.), species with long-lived seeds that germinate after fire (e.g., Ceanothus velutinus Dougl.), and species with wide successional amplitudes that resprout after fire (e.g., Apocynum androsaemifolium L. and Salix scouleriana Barratt) all declined steeply in cover on seeded plots. In addition, conifer seedlings were only half as abundant on seeded plots. As seeding after fire does not boost total plant cover and limits conifer tree establishment on the study area, it appears to do little to reduce the risk of soil erosion. It also appears to inhibit native shrub and herb re-establishment. These substantial effects on native species appear to alter plant communities well beyond the life of the seeded species.
Effects of gall age, gall size, and rust severity on incidence of the mycoparasite Scytalidium uredinicola
Authors: Moltzan B D , Blenis P V
Published: April 2011

Eighteen lodgepole pine (Pinus contorta Dougl. ex Loud.) stands, 19-32 years in age, were surveyed for Scytalidium uredinicola Kuhlman et al. in west-central Alberta. The purpose of the study was to determine how hyperparasite incidence was affected by gall age, gall size, and the occurrence of western gall rust caused by Endocronartium harknessii (J.P. Moore) Y. Hiratsuka (Peridermium harknessii J. P. Moore). Such information was deemed valuable for evaluating the likelihood that S. uredinicola was functioning as a density-dependent constraint in the pathosystem and assessing the potential for using this fungus as a biological control agent. The hyperparasite was present in all stands, albeit at generally lower levels than previously reported, but there was little evidence that its incidence increased with increasing incidence of gall rust. The odds of hyperparasitism increased by a factor of 1.3 for each year of gall growth, following adjustment for gall size effects, and by a factor of 2.1 for each 1 cm increase in gall size, following adjustment for gall age effects. Since gall age and gall size were positively correlated, there was a strong positive relationship between the unadjusted effects of both age and size and the incidence of S. uredinicola. However, although the incidence of S. uredinicola consistently increased as galls became older and larger, low levels of the hyperparasite on small and young galls may limit the effectiveness of S. uredinicola as a biological control agent.
Automatic individual tree based analysis of high spatial resolution aerial images on naturally regenerated boreal forests
Authors: Brandtberg Tomas
Published: April 2011

Individual tree based forest surveys are feasible using modern computer technology. The presented approach for analysing high spatial resolution (pixel size 10 cm) aerial images of naturally regenerated boreal forests is based on visible significant trees. Sunlight patches on the ground are suppressed, followed by optimal image smoothing. The problem with inclined illumination is handled by adapted thresholding. Each connected threshold segment (a collection of one or more trees) is further smoothed. A selection of the resulting convex edge segments is used for identifying significant tree crown circles. Six complementary image variables are estimated and used for regression analysis. An evaluation of the ground-truth data in central Sweden gives good results on the stem position estimate (a root mean square (RMS) error of 108 cm) and the stem number estimate (a relative RMS error of 11%). The complementary variables contribute significantly to the stem diameter prediction, resulting in the following experimental values: Scots pine (Pinus sylvestris L.) (R2 = 59.5%, s = 4.9 cm, N = 157), Norway spruce (Picea abies (L.) Karst.) (R2 = 21.9%, s = 6.4 cm, N = 398), birch (Betula pubescens Ehrh.) (R2 = 35.4%, s = 5.3 cm, N = 133), and European aspen (Populus tremula L.) (R2 = 61.4%, s = 4.6 cm, N = 13). The results indicate strong species dependence.
Nutrient availability and plant gender influences on the short-term compensatory response of Salix planifolia ssp. planifolia to simulated leaf herbivory
Authors: Houle Gilles
Published: April 2011

Males and females of dioecious plants often differ in their biochemistry, physiology, morphology, and (or) ecology. For example, growth rates often are higher for males than for females. Because the ability of plants to compensate for herbivory frequently varies with growth rate, we may expect males and females of dioecious plants to differ in their compensatory ability (hypothesis 1). However, environmental factors such as nutrient availability may influence the expression of such a response (hypothesis 2). For example, low nutrient availability may reduce growth rate and thus restrict compensation. To test these hypotheses, I cloned male and female genets of Salix planifolia Pursh ssp. planifolia from a natural population in northeastern Canada. I then submitted the plants of each sex to two levels of simulated leaf herbivory in combination with two levels of nutrient availability. Contrary to the first hypothesis, plant gender had no significant effect on the compensatory response to simulated leaf herbivory. However, nutrient availability modulated the compensatory ability of plants of both sexes, therefore supporting hypothesis 2. Herbivory may thus be more detrimental to the performance of S. planifolia individuals in low-nutrient environments, such as on dunes or rock outcrops.
Ectomycorrhizal colonization of Picea engelmannii × Picea glauca seedlings planted across cut blocks of different sizes
Authors: Hagerman Shannon M , Jones Melanie D , Bradfield Gary E , Sakakibara Stacey M
Published: April 2011

The purpose of this study, carried out at the Sicamous Creek Silvicultural Systems Trial located in the southern Interior of British Columbia, was to investigate the effects of cut block size and distance from the forest edge on patterns of ectomycorrhizal colonization and diversity at a subalpine forest. Non-mycorrhizal Picea engelmannii Parry ex Engelm. × Picea glauca (Moench) Voss seedlings were planted across cut blocks of three sizes (0.1, 1.0, and 10 ha) and in the uncut forest. In 1996 and 1997, seedlings were harvested after 13 weeks and examined for mycorrhizae. In 1996, diversity and richness of ectomycorrhizal types were significantly greater at forest plots and at plots located 2 m from the forest edge as compared with plots located >16 m into the cut block. In 1997, richness was again significantly reduced beyond 2 m. No differences in any of the diversity measures were detected between the different cut block sizes. The results of this study suggest that proximity to overstory trees may be more important than cut block size for patterns of ectomycorrhizal diversity and colonization. Additionally, polymerase chain reaction - restriction fragment length polymorphism (RFLP) analysis was used to assess the accuracy of morphotyping and, in some cases, to identify the associated fungus by comparison with RFLP patterns generated by sporocarps.
Provenance variation in carbon isotope discrimination of mature ponderosa pine trees at two locations in the Great Plains
Authors: Cregg Bert M , Olivas-García J Miguel , Hennessey Thomas C
Published: April 2011

We analyzed genotypic variation in carbon isotope discrimination (Δ), photosynthetic gas exchange, and needle morphology of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) trees from four seed sources growing in two 26-year-old provenance plantings near Plattsmouth, Neb., and Norman, Okla. The populations studied were from South Dakota, New Mexico, Wyoming, and Nebraska. Net photosynthesis (A) and needle conductance to water vapor (gwv), were measured during the growing season of 1994. Specific leaf area, stomatal density, and Δ were analyzed in needles grown from 1991 to 1994. The southernmost source (New Mexico) had the highest intrinsic water-use efficiency (A/gwv) among the sources studied. Carbon isotope discrimination was correlated with growth (r = -0.81, P < 0.05), A/gwv (r < -0.54, P < 0.001), and gwv (r > 0.46, P < 0.05) but not A. Variation in Δ was significant among seed sources and years (P < 0.001). We observed a strong genotype × environment interaction in Δ resulting from geographic location but not moisture availability within locations. We hypothesize that the genotype × environment interaction is related to variation in growth phenology among the seed sources. Improving water-use efficiency or growth of ponderosa pine via Δ will require an understanding in genotypic variation in growth rhythms.
Flurothyl le mice: seizure, post-convulsive behavior, and interactions with psychotropic drugs
Authors: Boissier J. R. , Simon P. , Villeneuve A. , Larousse C.
Published: April 2011

Flurothyl (Indoklon®), a convulsant hexafluorinated ether utilized in psychiatry in indications similar to those of electroshock, induced in mice a seizure of the same observed type as pentylenetetrazol and bemegride. This seizure was followed by a particular post-convulsive state consisting of catalepsy, hyperreflexia, and automatic movements. These phenomena resemble very much those observed after electroshock, pentylenetetrazol, and bemegride. Reserpine, chlorpromazine, atropine, biperiden, and amphetamine lowered the convulsive threshold to flurothyl and increased the lethality of it. Haloperidol decreased the latter whereas caffeine and procyclidine augmented it. Diethazine, profenamine, chlordiazepoxide, and diazepam raised the convulsive threshold and decreased the lethality. Prenylamine acted similarly although more weakly. Imipramine and its derivatives also had the same effect: they modified the tonic seizure or prevented its appearance, and diminished the lethality. Meprobamate raised the convulsive threshold. The monoamine oxidase inhibitors iproniazid, pargyline, tranylcypromine, and harmaline bad no apparent effect. All the drugs studied either did not affect or very little affected the post-convulsive phenomena.
The activity of carnitine palmitoyl transferase in the liver mitochondria of rats fed thrombogenic diets
Authors: Simard-Duquesne Nicole
Published: April 2011

Four groups of rats fed high-fat diets of reported different thrombogenic capacities were found similar with respect to their weight gain, and their liver weight and lipid content. Compared with a control group receiving laboratory chow, liver mitochondrial carnitine palmitoyl transferase activity was found to be increased in all four groups but this increase was unrelated to the reported thrombogenic potency of the diets.
Pharmacodynamic study of DDT in cockerels
Authors: Ecobichon D. J. , Saschenbrecker P. W.
Published: April 2011

White Leghorn cockerels were fed commercial DDT at levels of 250, 500, and 1000 μg/day in the diet. The absorption, distribution, and metabolism of DDT in plasma, brain, liver, kidney, heart, breast muscle, intestinal tract, skin, and fat were investigated, using gas–liquid chromatography in the quantitation of the residues. To aid in assessing chlorinated hydrocarbon toxicity in wild birds, correlations between observed symptoms and the residue levels in possible target tissues were studied in conjunction with the mechanism of action of DDT. The results indicate that the sum of the residues of p,p′-DDD, o,p′-DDT, and p,p′-DDT (toxic residues) in the brain was the best parameter for diagnosing DDT poisoning in birds. Signs of DDT toxicity were observed in all birds with brain levels in excess of 35 p.p.m. The lowest level of toxic residues in the brains of dead birds was 27.7 p.p.m. The mean brain level of toxic residues in tremoring and dead birds was 54.2 p.p.m. Metabolism and the significance of the levels of DDT and metabolites detected in other tissues are discussed in relation to the physiological function and metabolic activity of the particular tissue.
A manometric determination of nitrogen in small samples of blood. Application to measurement of arterial–alveolar nitrogen difference in man
Authors: Kabe Junzaburo , Beaudry Pierre H.
Published: April 2011

Arterial–alveolar nitrogen [Formula: see text] gradients in man can be obtained from a 3- to 4-ml sample of venous blood. The method described measures the nitrogen content in a 1-ml sample of blood by use of a slightly modified Natelson microgasometer equipped with automatic shakes. The values obtained are accurate and confirm those reported by others using macro-volumetric or gas chromatography techniques.
Active state prolongation associated with depolarization in frog's skeletal muscle
Authors: Clinch N. F.
Published: April 2011

If the K+ content of normal Ringer solution is increased, the duration of the plateau of the active state begins to rise at 8–10 mM [K]out. If the Cl− of the Ringer solution is replaced by NO3−, the active state duration begins to rise at 4–5 mM [K]out, and increases markedly with further depolarization. The observed dependence of active state duration on [K]out is similar to the known relation between resting metabolism and [K]out and is taken as evidence in support of the concept of subthreshold activation of the excitation–contraction coupling system by depolarization.
Lipid composition of the subcellular elements, and mitochondrial respiration of the heart and liver in hypercholesterolemic rabbits
Authors: Huang C. C. , Kako K.
Published: April 2011

Rabbits were fed a diet containing 3% cholesterol for 2–6 months. Total cholesterol, cholesterol ester, phospholipids, and triglycerides were increased in the plasma. Total cholesterol and cholesterol ester were also increased in the heart mitochondria and supernatant, and liver mitochondria, microsomes, and supernatant, but triglycerides and phospholipids in all cell fractions studied remained within the normal ranges. The respiratory control ratio, P/O ratio, and oxygen consumption of the cardiac and hepatic mitochondria were not affected by the increase in cholesterol content. Possible mechanisms responsible for the altered lipid composition in the cells of rabbits on a high-cholesterol diet, as well as that for the unchanged mitochondrial respiratory function are discussed.
Enhanced RNA and protein synthesis in adipose tissue of rats adapted to periodic hyperphagia
Authors: Kazdová L. , Braun T. , Fábry P. , Poledne R.
Published: April 2011

RNA synthesis measured by the incorporation of orotic acid-6-14C into RNA was investigated in isolated adipose tissue of control rats and of rats adapted to periodic hyperphagia, evoked by meal-feeding (a single 2-h meal per day). Both groups were fasted for 22 h and subsequently fed a measured test meal for another 2 h. It was revealed that 2 and 4 h after feeding there was no significant change in comparison with values during fasting, whereas in tissue of meal-fed rats the specific activity of RNA gradually increased by 22% and 41% respectively. The difference between controls and meal-fed rats was even much more marked if the specific activity of RNA in fat cells, isolated after incubation of the tissue, was measured. A significantly greater response of meal-fed rats was found when protein synthesis and lipogenesis in adipose tissue were assessed under the same experimental conditions. The possibility is discussed that the enhanced RNA and protein synthesis in adipose tissue of meal-fed rats is associated with de novo synthesis of enzymes involved in adaptive hyperlipogenesis.
Hemodynamic responses to dopamine and to isoproterenol following acute myocardial injury
Authors: MacCannell Keith L.
Published: April 2011

Severe myocardial injury was produced in eight anesthetized dogs by the injection of microspheres into the coronary circulation. Cardiac output and renal blood flow were monitored continuously with electromagnetic flow probes around the ascending thoracic aorta and left renal artery respectively. Intravenous infusions of isoproterenol and of dopamine (0.01–0.64 and 0.4–32.0 μg/kg per minute respectively) produced an increase in the cardiac output. Renal blood flow increased with small doses of isoproterenol but tended to decrease with higher doses; in contrast, all doses of dopamine increased renal blood flow. Dopamine was more effective in raising the systemic arterial blood pressure, but also increased cardiac work. Occasional extrasystoles were induced at higher doses of both amines. In three unanesthetized dogs sensitized by prior ligation of a coronary artery, the largest doses of dopamine tested (24–64 μg/kg per minute) did not produce cardiac arrhythmias. However, when dopamine was given to anesthetized dogs during vagal-induced cardiac slowing (a condition conducive to the emergence of ventricular automaticity), arrhythmias were induced. These data suggest that dopamine can increase both cardiac output and renal blood flow after severe myocardial injury, and may be a rational agent in the treatment of cardiogenic shock. Its arrhythmogenic properties would not appear to restrict its use.
Renin activity in aortic tissue of rats
Authors: Rosenthal J. , Boucher R. , Rojo-Ortega J. M. , Genest J.
Published: April 2011

Plasma renin activity, aortic tissue renin, and plasma renin substrate concentrations were measured simultaneously and sequentially in groups of rats after (1) bilateral nephrectomy, (2) water deprivation, and (3) bilateral adrenalectomy. Following nephrectomy, plasma renin activity and aortic tissue renin fell in parallel fashion to undetectable or very low levels after 18 h, whereas the substrate concentration in plasma increased markedly. Rats deprived of water for 3 days, but receiving Purina Chow, showed a significant increase in plasma renin activity and in aortic tissue renin and a marked decrease in plasma substrate concentration. Bilateral adrenalectomy resulted in a. very marked augmentation of plasma renin activity and of aortic tissue renin with a concomitant suppression of plasma substrate concentration. These findings suggest that arterial tissue renin reacts to the same stimuli which modify renin activity in plasma.
Canine gastric and pancreatic secretion during intestinal distension and intestinal perfusion with choline derivatives
Authors: Sum P. T. , Schipper H. L. , Preshaw R. M.
Published: April 2011

Balloon distension of the duodenum in conscious dogs increased gastric acid secretion, but had no effect on external pancreatic secretion. Duodenal infusion of solutions of acetylcholine chloride did not stimulate pancreatic secretion. Duodenal infusion of solutions of bethanechol stimulated both gastric acid secretion and pancreatic secretion, but the same doses of bethanechol were more effective secretory stimulants when introduced intravenously.