bluuebunny/crossref_metadata_2025 huggingface dataset:
Cylindrocarpon and Fusarium root colonization of Douglas-fir seedlings from British Columbia reforestation sites
Authors: Axelrood Paige E , Chapman William K , Seifert Keith A , Trotter David B , Shrimpton Gwen
Published: April 2011

Poor performance of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantations established in 1987 has occurred in southwestern British Columbia. Affected sites were planted with 1-year-old container stock that exhibited some root dieback in the nursery. A study was initiated in 1991 to assess Cylindrocarpon and Fusarium root infection in planted and naturally regenerating (natural) Douglas-fir seedlings from seven affected plantations. Percentages of seedlings harboring Cylindrocarpon spp.and percent root colonization were significantly greater for planted seedlings compared with natural seedlings. A significant linear trend in Cylindrocarpon root colonization was observed for planted seedlings with colonization levels being highest for roots closest to the remnants of the root plug and decreasing at distances greater than 10cm from that region. This trend in Cylindrocarpon colonization was not observed for natural seedlings. Cylindrocarpon destructans (Zins.) Scholten var. destructans and C.cylindroides Wollenw. var. cylindroides were the only species isolated from planted and natural conifer seedlings. For most sites, percentage of seedlings harboring Fusarium spp.and percent Fusarium root colonization were less than for Cylindrocarpon. Recovery of Fusarium spp.from seedlings and root colonization levels were not significantly different for planted and natural seedlings from all sites.
Relationships between tree slenderness coefficients and tree or stand characteristics for major species in boreal mixedwood forests
Authors: Wang Yue , Titus Stephen J , LeMay Valerie M
Published: April 2011

The slenderness coefficients of trees, defined as the ratio of total height to diameter at 1.3m above ground, have been widely used as an index of the resistance of trees to windthrow. For many European coniferous species, slenderness coefficients have been intensively studied, but very little information is available for the tree species in boreal mixedwoods of Canada. By applying correlation analysis and graphical approaches to permanent sample plots data from Alberta, the relationships between slenderness coefficients and tree or stand variables were investigated for the five major species in boreal mixedwoods. Tree slenderness coefficients were found to be negatively correlated with tree diameter at breast height (DBH), height, crown length and age, but positively correlated with stand density level, species composition, and site index values. For three coniferous species, the results were consistent with those found for European coniferous species in literature. However, for the two deciduous species, no similar studies were found for comparison. The graphical results indicated that about 50% of the sampled stands of the data had a slenderness coefficient over 100 and may be at high-risk for windthrow. Models were also developed to predict slenderness coefficient values from (i) DBH only and (ii) DBH and stand variables combined. The negative decay function was found to be the best for this prediction purpose. Potential applications of these models include selecting windfirm residual trees in a partial cutting and developing windthrow hazard rating systems.
Long-term effect of forest drainage on the peat carbon stores of pine mires in Finland
Authors: Minkkinen Kari , Laine Jukka
Published: April 2011

The drawdown of the water level has been hypothesized to change peatlands from carbon (C) sinks to C sources to the atmosphere as a result of increased oxidation of organic matter. We measured the change in peat thickness (subsidence of peat surface) ca. 60 years after drainage in 273 peatland sites (875 points) representing three nutrient levels of pine fens and five macroclimatic regions from southern to northern Finland, and we calculated the changes in peat C densities and peat C stores using direct measurements and estimates drawn from regression models for C density derived in this study. On average, the peat surface had subsided ca. 22 ± 17 cm (mean ± SD), the C density had increased by 26 ± 15 kg·m-3, and the C stores had increased by 5.9 ± 14.4 kg·m-2 after drainage. Therefore, the hypothesis that drainage of peatland always makes them sources of C to the atmosphere is incorrect. We concluded that the post-drainage subsidence of peat surface was mainly caused by changes in the physical structure of peat after the removal of water while the oxidation of peat was of less importance. The changes in C density and C stores seemed to be dependent on the input of new C into the system through net primary production, especially through the fine roots of trees. Our results suggest that tree stand development plays an important role in the post-drainage C balance of peat soils.
Soil warming in a northern hardwood forest: trace gas fluxes and leaf litter decomposition
Authors: McHale Patrick J , Mitchell Myron J , Bowles Francis P
Published: April 2011

The response of trace gas fluxes (CO2, CH4, and N2O) and litter decomposition to increased soil temperature was evaluated in a northern hardwood forest. Four experimental plots (10 × 10 m) had heating cables installed within the forest floor. Temperatures at 5 cm were increased 2.5, 5.0, or 7.5°C in individual heated plots during the field season in 1993 and 1994. The fourth plot was a cabled, nonheated reference. Trace gas fluxes were monitored using closed chambers. Soil moisture was monitored using tensiometers and time domain reflectometry. Changes in leaf litter decomposition were quantified using litter bags for American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.) litter. Fluxes of CO2 increased exponentially with increased soil temperatures within treatments and were higher in heated plots than in the reference plot. Temperature coefficients (Q10) and mass remaining of American beech leaf litter decreased with the level of heating, suggesting a nonlinear microbial response to elevated temperatures. Soil water content exhibited the most influence on CH4 and N2O flux in the second season. The experimental manipulations showed the importance of evaluating the influence of soil temperature coupled with effects of N and moisture availability.
A spatial, climate-determined risk rating for Scleroderris disease of pines in Ontario
Authors: Venier L A , Hopkin A A , McKenney D W , Wang Y.
Published: April 2011

We used historical distribution data of Scleroderris disease (caused by the fungus Gremmeniella abietina var. abietina (Lagerb.) Morelet) in Ontario to model its probability of occurrence as a function of climate factors. A logistic regression model of the probability of occurrence as a function of the mean temperature of the coldest quarter and the precipitation of the coldest quarter was a very good fit. The concordance (index of classification accuracy) of the model was 84%. We subsampled the data repeatedly, generated new parameter estimates, and tested the predictions against data not included in the model. Classification accuracy was similar for each subsample model; therefore, we concluded that the final model is stable. Gridded estimates of the climate variables were used to spatially extend the two-variable logistic regression model and produce a probability of occurrence map for Scleroderris disease across Ontario. The predicted map of probability of occurrence fits well with the map of the observed locations of the disease. These results lend credence to previous work that suggests that distribution of Scleroderris disease is strongly influenced by climate. The classification results also suggest that this model is a useful tool for assessing the risk of Scleroderris disease throughout Ontario.
Estimating top height with variable plot sizes
Authors: García O
Published: April 2011

Conventional top height estimates are biased if the area of the sample plot differs from that on which the definition is based. Sources of bias include a sampling selection effect and spatial autocorrelation. The problem was studied in relation to the use of data sets with varying spatial detail for modelling Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation growth. Improved top height estimators, developed taking into account the selection effect, eliminated the bias. Bias was reduced, but not eliminated completely, when the estimators were tested using more highly autocorrelated eucalypt data.
Temporal and genotypic variation of wound-induced gene expression in bark of Populus tremuloides and P. grandidentata
Authors: Thamarus Karen A , Furnier Glenn R
Published: April 2011

In two related experiments, total RNA was extracted from wounded and unwounded bark of young aspen ramets for Northern and dot blot analyses. Wound-inducible genes isolated from other plant species were hybridized to blots, and mRNA levels were estimated. Analyses of variance (ANOVA) were used to examine the significance of experimental factors (wounding, time after wounding, and genotype) affecting variation in mRNA levels. The first experiment examined the timing (0.5-96 h after wounding) of expression of wound-inducible genes in bark tissue of a single Populus tremuloides Michx. genotype. Wounding and variation among RNA samples significantly (p < 0.05) affected mRNA levels of two chitinases (win6, win8) and phenylalanine ammonia-lyase (PAL). The second experiment examined interclonal variation of wound-induced win6 and PAL expression in aspen bark. Ramets of four P. tremuloides and one Populus grandidentata Michx. genotypes were wounded and bark was collected 4, 8, or 12 h later. Genotype, wounding, and time after wounding all significantly affected win6 and PAL mRNA levels, with levels increasing as a result of wounding.
Early performance and nutrition of two willow species in short-rotation intensive culture fertilized with wastewater sludge and impact on the soil characteristics
Authors: Labrecque Michel , Teodorescu Traian I , Daigle Stéphane
Published: April 2011

Recycling wastewater sludge as fertilizer in short-rotation intensive culture of willows offers a viable opportunity to increase biomass productivity. Salix discolor Mühl. and Salix viminalis L. were planted at two densities (20 000 and 30 000 cuttings/ha), on two sites: a well and a poorly drained site. Three doses of dried and granulated sludge (100, 200, 300, and 0 kg/ha of "available" N) were applied in the spring of the first and the second seasons of growth. The aims of the experiment were to (i) investigate growth and nutritional plant response to fertilization and (ii) estimate the impact of sludge application on the soil. Over two seasons, aboveground biomass was similar for S. discolor and S. viminalis on both sites and for all sludge treatments. Every increment in the sludge dose applied induced an increase in willow productivity. Vector analysis of stem and branch nutrient concentration suggested that nitrogen was the most limiting nutrient. At the end of the second season, plots fertilized with the highest doses of sludge indicated soil enrichment in organic matter. However, nitrate concentration in the soil increased with increasing sludge doses. The accumulation of heavy metals from sludge was not hazardous to the environment according to provincial limits. A moderate dose of dried and pelleted sludge (100 kg/ha "available" N) may reduce nitrate leaching and appears to be a good fertilizer during the establishment of willows.
Leaf area dynamics in Liquidambar styraciflua saplings: responses to nitrogen fertilization
Authors: Kuers Karen , Steinbeck Klaus
Published: April 2011

Total leaf production, vertical foliage profiles, and the timing of leaf production and loss were compared in fertilized and unfertilized 3-year-old sweetgum (Liquidambar styraciflua L.) saplings. Nitrogen (N) fertilization increased total leaf area and mass through increased leaf size rather than changes in leaf number or specific leaf mass. Both the vertical and temporal distribution of foliage shifted in response to N. Fertilization increased leaf area primarily in the mid- to upper crown. The midheight of the tree crowns shifted upward throughout the season as leaf abscission occurred from the base to the top of the tree and acropetally along the branches. Peak leaf display occurred in July regardless of N supply. However, fertilized trees had twice the leaf area of the unfertilized trees by early autumn. Leaf area production and loss were modeled separately as a function of fertilization and crown height and the equations combined to model temporal changes in leaf area display.
A comparison of several methods for estimating light under a paper birch mixedwood stand
Authors: Comeau P G , Gendron F , Letchford T
Published: April 2011

In 1996 we initiated a study to evaluate several techniques for measuring light under broadleaf canopies. Hourly average photosynthetic photon flux density and percent transmittance were measured 1 m above the ground at four points in each of three canopy densities created by a spacing experiment in a 35-year-old paper birch (Betula papyrifera Marsh.) dominated stand located near Prince George, B.C. At each point, fisheye photographs were taken and LAI-2000 plant canopy analyzer (LAI-2000), spherical densiometer, and competition index (Lorimer's index) measurements were made. Percent transmittance measurements on an overcast day (1-h average), transmittance measured over periods of 3 h or longer on a clear day, LAI-2000 diffuse noninterceptance measurements, and gap light index determined from fisheye photographs were strongly correlated with growing season percent transmittance (r2>= 0.96) as was competition index (r2 = 0.928). Concave spherical densiometer measurements and midday percent transmittance measurements on clear days were also well correlated with measured percent transmittance (r2>= 0.89). Estimates of understory light by the LITE model were strongly correlated with growing season percent transmittance. Correlations improved with increasing length of the period simulated (r2 = 0.755 for a point measurement on a clear day; r2 = 0.936 for an entire sunny day; and, r2 = 0.953 for the entire growing season). However, this version of the model underestimated percent transmittance in these spaced birch stands by 34-90%.
Seasonal dynamics and effects of nitrogen supply rate on nitrogen and carbohydrate reserves in cutting-derived Salix viminalis plants
Authors: Bollmark Lars , Sennerby-Forsse Lisa , Ericsson Tom
Published: April 2011

Nutrient storage is an important aspect of resprouting potential and production of Salix viminalis L., a pioneer species used for biomass production in Sweden. Seasonal dynamics of nitrogen (N), protein, soluble carbohydrates, starch, and lipids were studied in roots, cuttings, stems, and leaves during a full growth cycle induced by varying photoperiod and temperature in a growth chamber. Nitrogen was supplied at two rates. Both season and N availability significantly affected storage of N and carbohydrates. Reserves peaked in dormancy, and plants grown at a higher N availability were able to build up larger N reserves, whereas carbohydrate reserves were similar in the two N treatments. All perennial plant organs functioned as storage sites for N. Roots were prominent in carbohydrate storage, in good agreement with the notion of a pioneer species adapted to recurring disturbance by a pronounced resprouting capacity. Roots differed from aboveground plant parts in their exceptionally high starch levels, and in that N storage in roots to a greater extent involved nonprotein compounds. Triglycerides contributed to carbon storage in aerial plant parts but not in roots. Our results suggest that an increased N supply enhance both the accumulation of nutrient reserves and early season growth.
Tree-ring analysis of yellow-cedar (Chamaecyparis nootkatensis) on Vancouver Island, British Columbia
Authors: Laroque Colin P , Smith Dan J
Published: April 2011

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) are the oldest known coniferous trees in Canada. This paper reports on the first dendrochronological investigation of yellow-cedar trees at montane sites on Vancouver Island. Mature yellow-cedar trees were selected for study at four sites along a 200-km northwest-southeast transect. Trees older than 500 years were common at three of the four sites, with numerous individuals older than 750 years identified. Carefully prepared cores proved well suited for ring-width measurement, with 220 cores from 156 trees included in our final four chronologies. The best replicated segment of the four chronologies (1800-1994 A.D.) show common intervals of reduced radial growth in the 1800s, 1840s, 1860s, 1920s, 1950s, and 1970s. While the relative strength of the between-site signals varies over this interval (r = 0.424-0.908), it is apparent that the chronologies share a common radial growth signal. Our efforts to identify the role climate played in this relationship were successful and the results appear to have a dendroecological basis within the annual yellow-cedar growth cycle. Six different temperature and precipitation variables explain 61% of the annual ring width variance. Our results suggest that further dendrochronological and dendroclimatological studies using this long-lived species are warranted.
Interactions between forest heterogeneity and surface fire regimes in the southern Sierra Nevada
Authors: Miller Carol , Urban Dean L
Published: April 2011

Fire is a major agent of spatial pattern formation in forests, as it creates a mosaic of burned and unburned patches. While most research has focused on landscape-level patterns created by crown fires, millions of hectares of forests in North America are subject to surface fire regimes. A spatially explicit forest gap model developed for the Sierra Nevada was used to evaluate the influence of surface fire regimes on the heterogeneity of forest structure and composition within forest stands. Forest pattern was evaluated for a wide range of topographic positions in Sequoia National Park, California, to determine if repeated surface fires amplify existing spatial patterns. The spatial heterogeneity of some forest characteristics increased under a simulated fire regime relative to scenarios without fire. Although a distinct and regular fire-generated spatial pattern was not detected with an analysis of spatial autocorrelation, simulated surface fires did alter the spatial heterogeneity within a forest stand, primarily by degrading a regular structure that is imposed by competition for light in the absence of fire. The interaction between surface fires and forest pattern may be qualitatively different from that which occurs in forests subject to crown fires. As such, what has been learned about forests dominated by crown fires may not apply to forests subject to surface fire regimes.
Red maple dynamics in Appalachian hardwood stands in West Virginia
Authors: Tift Brian D , Fajvan Mary Ann
Published: April 2011

The growth strategies red maple (Acer rubrum L.) used to attain current overstory canopy positions were investigated in two West Virginia Appalachian hardwood stands. In both stands, red maple comprised a small percentage of overstory basal area but was the most abundant understory species. The stands originated after a stand-replacing disturbance around 1930. During stand initiation, red maple invaded the sites for 10-15 years longer than most other species; however, all of the codominant red maples sampled were similar in age to other codominant species. Twenty-seven percent of stem-analysed codominant maples were 1-4 years older than the disturbance and may have originated as advanced reproduction. One sampled codominant maple had been overtopped for 20 years. Other codominant maples had height growth rates similar to codominant oaks (Quercus sp.). Even at advanced ages, understory maples showed increased height growth rates in response to small canopy disturbances. Red maple's understory persistence suggests that partial harvesting may release these individuals and promote greater proportions of overstory maples in the future.
Wood-inhabiting cryptogams on dead Norway spruce (Picea abies) trees in managed Swedish boreal forests
Authors: Kruys Nicholas , Fries Clas , Jonsson Bengt Gunnar , Lämås Tomas , Ståhl Göran
Published: April 2011

We surveyed the quantity and quality of dead Norway spruce (Picea abies (L.) Karst.) trees and wood-inhabiting cryptogams in a managed boreal forest landscape in northern Sweden. Size and decay of dead trees was related to substrate utilization by wood-inhabiting species. Coarse woody debris (CWD) was surveyed along 34 strip transects. CWD and wood-inhabiting cryptogams were surveyed in eight circular plots at each site. A total of 6195 spruce CWD units occurred along strip transects and 809 spruce CWD units in circular plots. On average 2.2 m3/ha spruce CWD was found on the plots. The majority (63%) of the transect CWD units were <10 cm diameter and in early to intermediate decay stages. Sixty-eight wood-specific species of fungi, lichens, mosses, and hepatics occurred on the plots. Of these, 13 occurred on [Formula: see text]5% of the 809 CWD units surveyed for wood-inhabiting species. Eight species occur on the Swedish red lists, indicating that such species are indeed uncommon in managed forests. Red-listed species showed strong preferences for large diameter CWD and CWD in late decay stages, i.e., substrates that are poorly represented in managed forests. Frequently occurring species, however, showed utilization patterns that correspond with the distribution of the substrate types.
Modelling recruitment of Populus tremuloides, Pinus banksiana, and Picea mariana following fire in the mixedwood boreal forest
Authors: Greene D F , Johnson E A
Published: April 2011

We examined the relationship between the post-fire regeneration density of Populus tremuloides Michx., Pinus banksiana Lamb., and Picea mariana (Mill.) BSP and their pre-fire basal area density at the spatial scale of 70 m (the width of the stands studied) in four fires in central Saskatchewan and one in Quebec. For these three species with mechanisms for in situ reproduction, there were highly significant relationships between regeneration density and pre-fire basal area density (basal area per area). Given equal source basal area densities, Populus tremuloides has an advantage, relative to the other two species, in initial regeneration densities, but the advantage is not great because the asexual stems thin rapidly. The overriding conclusion is that, for these three species, there is little change in species composition following fire. Simple predictive equations performed reasonably well for Pinus banksiana and Picea mariana: FD = 806BD0.95 and FD = 593BD0.86, where FD is regenerative stem density (no./m2), and BD is basal area density (m2/m2). For asexual reproduction by Populus tremuloides, the thinning begins immediately following fire, and the regeneration model was FD = 11 600BD0.79(t + 1)-1.64, where t is years since fire.
Allometric crown relations in three northern Idaho conifer species
Authors: Monserud Robert A , Marshall John D
Published: April 2011

Allometric equations predicting individual branch and total crown leaf area, leaf mass, and branch wood mass were developed for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca), ponderosa pine (Pinus ponderosa Dougl. ex Laws.), and western white pine (Pinus monticola Dougl. ex D. Don) on the Priest River Experimental Forest in northern Idaho. Whole crowns were weighed fresh in the field by crown quarter. Two antithetic random branches were sampled from each crown quarter, weighed fresh in the field, and returned to the laboratory for detailed analysis. Nonlinear weighted regression with the general allometric equation was used to estimate all parameters. For the branches, branch diameter and length, foliated length, and position in the crown explain 82-97% of the variation. Specific leaf area (leaf area/mass) differs significantly among species and increases with distance from the tree top. For whole trees, sapwood area at breast height, crown ratio and length, and crown competition factor (CCF) explain 94-99% of the variation. The assumption of linearity and constant ratio between leaf area and sapwood area held rather generally. Differences between two alternative estimators (branch summation vs. crown weighing) of total crown biomass and leaf area were not statistically significant. For stands, stand totals were estimated from the whole-tree equations and stand-inventory data. Generally, these stand estimates were intermediate between coastal forests west of the Cascades and drier forests in the rain shadow of the Rocky Mountain crest.
First-year growth response of four Populus trichocarpa × Populus deltoides clones to fertilizer placement and level
Authors: van den Driessche R
Published: April 2011

Fertilizer (18:40:0, N:P:K) was applied by two methods, each at different levels, following establishment of a hybrid poplar (Populus trichocarpa Torr. & Gray × Populus deltoides Bartr. ex Marsh.) plantation, containing four clones, on central Vancouver Island. Nitrogen and P were supplied at 0, 100, and 200 kg·ha-1 by banding, and at 0, 25 and 50 kg·ha-1 by placing in holes adjacent to cuttings. After one season, response to placed treatments (mean height 182 cm) was greater than to banded treatments (mean height 149 cm). The 50 kg·ha-1 placed treatment increased stem volume 4.3-fold above control, and the 200 kg·ha-1 banded treatment increased stem volume 2.4-fold above control. Uptake of N and P was about 10-fold greater per kilogram of fertilizer nutrient for placed than banded treatments. Fertilizer increased leaf N concentration, but concentrations of most other nutrients declined despite increased uptake. Significant increases in stem volume occurred when leaf N concentration was about 29 g·kg-1 in clone 1, but 23-25 g·kg-1 in the other clones. Clone 2 tolerated foliage P concentrations below 1.4 g·kg-1 at the greatest growth rates. Stem volume was positively correlated with soil total N% and organic C% in the 16-30 cm horizon.
Effect of drainage and microtopography in forested wetlands on the microenvironment and growth of planted black spruce seedlings
Authors: Roy Vincent , Bernier Pierre-Y. , Plamondon André P , Ruel Jean-Claude
Published: April 2011

Black spruce (Picea mariana (Mill.) BSP) seedlings were planted on eight drained forested wetland cutblocks to study the effects of soil type, distance from drainage ditch, and microtopography on the physical conditions of the rooting zone and on seedling growth, survival, and physiology. After two growing seasons, providing a raised planting spot had a greater impact on seedling growth than locally intensive drainage. Less saturated, better aerated, and warmer rooting zone on hummocks increased foliar N and Ca concentrations, which led to significantly greater relative growth rate, terminal shoot height growth, diameter, and survival compared with the seedlings in hollows. The effect of drainage on seedling growth is not conclusive. Depth of the aerobic layer and soil water content at 10 cm depth were similar at all distances to the ditch despite a significantly lower water table level in the 5-m plot. Thus, no significant differences were observed as a function of distance to drainage ditch for water relation and growth parameters except for better height growth in the 5-m plot the second year after planting. Water table levels were identical for both soil types and consequently growth was similar on wet mineral and organic soil types.
A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine, Norway spruce, and birch
Authors: Peltola H , Kellomäki S , Väisänen H , Ikonen V -P
Published: April 2011

A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula spp.) is presented. The model predicts the critical turning moment and wind speed at which the trees will be uprooted or break at forest margins. The resistance to uprooting is predicted using the estimate of the root-soil plate weight to derive a resistive moment, while the resistance to stem breakage relies on values for the modulus of rupture determined for different species of timber. A tree is assumed to be uprooted if the total turning moment exceeds the support provided by the root-soil plate anchorage. Similarly, a tree is assumed to break if the breaking stress acting on the stem exceeds a critical value of the modulus of rupture. The model is in general quite sensitive to parameter changes, which partly results from the location in the forest to which it was designed to apply (the stand edge). The predictions of the critical turning moments needed to uproot and break trees nevertheless give a good agreement on average with the Finnish tree-pulling data for Scots pine, Norway spruce, and birch.
Woody and herbaceous competition effects on stand dynamics and growth of 13-year-old natural, precommercially thinned loblolly and shortleaf pines
Authors: Cain Michael D
Published: April 2011

Stand dynamics of naturally regenerated, even-aged, loblolly pines (Pinus taeda L.) and shortleaf pines (P. echinata Mill.) were examined on the Upper Coastal Plain of southeastern Arkansas, U.S.A., following four levels of competition control. Treatments included a check (Ck) with no competition control, woody control (WC), herbaceous control (HC), and total control (TC) of nonpine vegetation. After pines became established from natural seeding, herbicides were used to control herbaceous plants for four consecutive years and woody plants for five consecutive years. At age five, 1235 crop pines/ha were retained and all noncrop pines >1.5 m tall were precommercially hand thinned. Although 93% of crop pines on Ck plots were judged free-to-grow 13 years after establishment, crop pines on vegetation control plots were larger (P [Formula: see text] 0.001) in mean diameter at breast height, total height, and volume per tree. From age 5 through 13 years, crop pine diameter growth increased on WC plots and decreased on HC plots because of hardwood competition in the latter treatment. At age 13, mean pine volume production was 48% greater (P < 0.01) on plots that received competition control than on Ck plots (160 m3·ha-1); TC resulted in 31% more (P < 0.01) volume (282 m3·ha-1) than the mean of WC and HC plots; and there was no difference (P = 0.15) between the latter two treatments.
Understory vegetation, resource availability, and litterfall responses to pine thinning and woody vegetation control in longleaf pine plantations
Authors: Harrington Timothy B , Edwards M Boyd
Published: April 2011

In six 8- to 11-year-old plantations of longleaf pine (Pinus palustris Mill.) near Aiken, S.C., responses of understory vegetation, light, and soil water availability and litterfall were studied in relation to pine thinning (May 1994), herbicidal treatment of nonpine woody vegetation (1995-1996), or the combined treatments (treatment responses described below are in absolute units). Treatment differences in fifth-year (1998) herbaceous species density were as follows: pine thinning > woody control = combined treatments > untreated (33, 30, 30, and 25 species per 40 m2, respectively). Forb and grass covers were 13 and 8% greater, respectively, after pine thinning and 7 and 9% greater after woody control. Pine thinning stimulated a large increase in third-year gap fraction (0.26), short-term increases in soil water content (1%), and a reduction in pine litterfall by half (-120 g·m-2 per year). Woody control had no effect on gap fraction, decreased litterfall of nonpine woody vegetation (-32 g·m-2 per year), and stimulated season-long increases in soil water content (1-2%). The ranking of factors affecting herbaceous vegetation responses was as follows: light > soil water > herbicides > litterfall. Herbaceous species density and cover can be promoted in longleaf pine plantations by intensive thinning of pines and herbicidal control of non-pine woody vegetation.
Effects of timber harvesting on coarse woody debris in red pine forests across the Great Lakes states, U.S.A.
Authors: Duvall Matthew D , Grigal David F
Published: April 2011

Coarse woody debris (CWD) chronosequences were developed for managed and unmanaged red pine (Pinus resinosa Ait.) stands across the Great Lakes states. Throughout stand development, there is less CWD in managed than in unmanaged forests, and effects of management are strongest in young forests (0-30 years old). At stand initiation, CWD is 80% lower in managed than unmanaged forests, 20 200 versus 113 200 kg·ha-1, while at 90 years, CWD is 35% lower, 6600 versus 10 400 kg·ha-1. Timber management especially affects snags. In young managed forests, snag biomass is less than 1% of that in unmanaged forests, 150 versus 58 200 kg·ha-1, while log biomass is 80% lower, 5000 versus 22 800 kg·ha-1. This trend continues in mature forests (91-150 years old), where snag biomass is 75% lower in managed than in unmanaged forests, 1700 versus 6400 kg·ha-1. Management has relatively little impact on total log biomass of mature forests but increases the biomass of fresh logs nearly 10-fold, to 1400 versus 150 kg·ha-1. CWD in managed forests is highly variable, primarily related to thinning schedules in individual stands.
Vegetation changes through time on islands of Lake Duparquet, Abitibi, Canada
Authors: Larocque I , Bergeron Y , Campbell I D , Bradshaw RHW
Published: April 2011

Succession after fire has mainly been studied by chronosequence, which does not allow study of pre- and post-fire communities at the same site. By using palynology and anthracology, we recovered vegetation communities and fire histories through time on islands of Duparquet Lake, Canada. We show that succession after fire is dependent on interval between two fires (evaluated with depth of humus between subsequent fires). Sites with high fire occurrence show a cyclic succession (same species reappearing after fire), while sites with low fire occurrence show a directional succession. Different fire intervals lead to different pre- and post-fire pollen assemblages. During longer fire intervals, pollen assemblages change from Pinus banksiana Lamb. domination to Pinus strobus L. and Picea mariana (Mill.) BSP domination. When fire intervals are short, Pinus banksiana dominates both pre- and post-fire assemblages.
The changing landscape of Canada's western boreal forest: the current dynamics of permafrost
Authors: Vitt Dale H , Halsey Linda A , Zoltai Stephen C
Published: April 2011

This paper examines the impact that climatic change over the last millennium has had on aggradation and degradation of permafrost peatlands and the associated change in organic matter accumulation. Permafrost reached its southernmost Holocene extent in boreal continental western Canada during the Little Ice Age with 28 800 km2 of permafrost peatland present within a sensitive zone demarcated by permafrost degradation. Subsequent degradation of permafrost has occurred in response to warming, with forested bogs changing to nonforested poor fens, associated with rising water levels. In conjunction with this ecosystem change, long-term net organic matter accumulation increases. As permafrost is in disequilibrium with climate, much of the permafrost that remains is in a relict state. Mapping of past and present permafrost distribution from peatland landforms indicates only 9% has degraded since the Little Ice Age, resulting in a 5% increase in long-term net organic matter accumulation. Of the permafrost that remains, 22% is in disequilibrium, located largely in the northern part of the sensitive zone. Additional loss of forested lands will occur in the future in boreal continental western Canada under present-day climatic conditions as permafrost approaches equilibrium, with a further 11% increase in long-term net organic matter accumulation predicted.
Effects of adventitious roots on age determination in Balsam fir (Abies balsamea) regeneration
Authors: Parent Sylvain , Morin Hubert , Messier Christian
Published: April 2011

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (<2 m height) were harvested in whole from closed forest stands located in the province of Quebec, Canada. Seedling age was determined by (i) counting the number of annual growth rings at the presumed shoot-root interface, and (ii) counting all terminal bud scars from the apex to the base of the hypocotyl (true collar). For all seedlings with adventitious roots, the number of terminal bud scars on the entire trunk was higher than the number of growth rings at the shoot-root interface. The formation of adventitious roots on the belowground trunk was accompanied by a reverse taper phenomenon, i.e., the number of annual growth rings decreased from the presumed shoot-root interface to the true collar. Counting annual growth rings at any level on the trunk of balsam fir seedlings that form adventitious root systems would not be reliable, underestimation's exceeding 20 years are possible and the resulting age structures could lead to erroneous interpretations of regeneration dynamics.
Diet and body weight loss in the rat during calorie restriction
Authors: Karch Peter B. , Beaton John R.
Published: April 2011

With adult male rats, experiments were carried out to ascertain the different effects, if any, of isocaloric diets high in carbohydrate, fat, or protein fed in restricted amounts of 9 g per rat per day on body weight loss and composition. It was observed that the nature of the diet did not alter rate, amount, or composition of body weight loss when fed in restricted amount for a period of 12 days. Further, the nature of the diet did not alter significantly the following parameters during restriction: water intake, urine volume, resting metabolic rate, spontaneous activity, urine and feces calorie values. In an experiment with hypothalamic-obese rats, the body weight loss and composition were not significantly different among the dietary-restricted groups. An important observation in this experiment was that as body fat decreased markedly owing to restricted feeding, body water increased markedly and counterbalanced approximately 60% of the potential weight loss due to the decrease in body fat. Our reported observations do not support the hypothesis that the composition of the diet may determine the rate and amount of body weight loss as a consequence of restricted food intake. They do support the hypothesis that the calorie intake, not the nature of the source of calories, determines the rate and amount of weight loss, at least for relatively short periods of food restriction.
The effect of chymotrypsin on the gastrointestinal absorption, tissue penetration, and pharmacological activity of drugs. I. Penetration of penicillin through the blood–brain and blood–retinal barriers
Authors: Wohlman Alan , Syed M. , Ronchi M.
Published: April 2011

The administration of penicillin G plus the proteolytic enzyme chymotrypsin to rabbits and guinea pigs yields significantly higher serum, eye, and brain levels of penicillin than does the administration of the antibiotic alone. It is suggested that chymotrypsin exerts an effect on both the membrane permeability of cells constituting the blood–brain and blood–retinal barriers and the binding of penicillin to serum proteins. Chymotrypsin may be of considerable value in the enhancement of penicillin penetration into reiatively inaccessible tissues, such as the brain and eye, thereby making it possible to eliminate penicillin-sensitive bacteria which have become localized in these areas.
The use of a binding agent, polyvinylpyrrolidone, in the treatment of experimental barbiturate intoxication in rabbits
Authors: Ruedy John , Chernecki Walter
Published: April 2011

The binding of phenobarbital and secobarbital by polyvinylpyrrolidone (PVP) was studied by equilibrium dialysis and ultrafiltration techniques. Significant quantities of both barbiturates were bound at concentrations of PVP comparable to those which were attained in the serum and urine by dosing rabbits with 2 g/kg per hour of PVP of molecular weight 10 000 (PVP-10). Treatment of rabbits intoxicated with phenobarbital and secobarbital with PVP-10 enhanced the renal clearance of the barbiturates and ameliorated the toxic state more rapidly than did treatment with dextran of the same molecular weight. This effect was probably due to binding by PVP of a portion of the barbiturate in a non-reabsorbable form in tubular urine as well as binding of the barbiturate in a nondiffusible form in the extracellular space.
Regional myoglobin concentration in the myocardium of the dog
Authors: Anderson Naomi M. , Brandi Giorgio
Published: April 2011

It has been demonstrated previously that chronic hypoxia leads to an increase in myoglobin concentration. Evidence of differences in [Formula: see text] and blood flow in deep and superficial layers of cardiac muscle suggest that there might be a corresponding difference in myoglobin concentration in the myocardium. Results showed an even distribution of myoglobin concentration in inner and outer layers of the left ventricular wall, right ventricle, and septum, suggesting that [Formula: see text] in inner layers of the left ventricular wall is not sufficiently diminished to stimulate an increase in myoglobin concentration.
Studies on the cardiotoxicity of ouabain
Authors: Reynolds A. K. , Horne Margot L.
Published: April 2011

Pretreatment with reserpine in a catecholamine-depleting dosage schedule greatly increased the arrhythmic and lethal dose of ouabain in cats. Pretreatment with reserpine immediately before the administration of ouabain also increased these doses significantly but the effect was less marked than that produced by 24-h pretreatment. Tetrabenazine provided protection comparable to that of reserpine when the latter was given immediately before ouabain. This finding suggests that the protective action of reserpine may be partially of central origin. The initial effect of bretylium was to reduce the toxic dose, but this was not the case if pronethalol was also administered. Pronethalol alone significantly increased tolerance to ouabain. Adrenaline in doses that did not induce arrhythmias markedly reduced the toxic dose of ouabain. Acetylcholine and eserine both increased the toxic dose, and the effect was atropine-resistant. Atropine itself did not exert a significant effect. Compound P-286 had no effect on the arrhythmic dose of ouabain, but it did increase the lethal dose. Halothane anesthesia did not markedly alter the arrhythmic dose but definitely delayed cardiac arrest. Procaine infiltration of the superior atriocaval junction provided significant protection. The most marked protection, however, was seen with hypothermia. Although numerous agents were found capable of markedly altering the mean amount of ouabain required to evoke ectopic rhythm, very few significantly altered the additional amount required to cause death, once sinus dominance was lost.
Response differences in some steroid-sensitive hepatic enzymes in the fasting rat
Authors: Yuwiler Arthur , Geller Edward , Schapiro Shawn
Published: April 2011

The activities of the glucocorticoid-inducible enzymes, tryptophan pyrrolase, tryptophan and tyrosine α-ketoglutarate transaminases, and phenylalanine and tryptophan hydroxylases, were measured during fasting and realimentation. Of these, only tryptophan pyrrolase activity increased during the fasting period, despite sustained elevations in adrenocortical activity as evidenced by increased levels of corticosteroids. The increase appeared to reflect increased synthesis and resembled substrate induction. Total liver transaminase activity was unaltered by fasting whereas hydroxylase activity decreased. The results demonstrate the non-equivalence of exogenous glucocorticoid administration and the endogenous adrenal activation accompanying this stress in eliciting enzyme induction.
A simple rate meter and oscilloscope intensity modulator for single cell recording
Authors: Graystone Peter , Owen Neville , McLennan Hugh
Published: April 2011

A simple circuit has been described which gives a meter reading proportional to the rate of cell firing. The circuit will trigger reliably on any signal exceeding 100 mV, and a trigger-level control is provided to enable triggering to be suppressed below a threshold level. An external recorder may be driven from the circuit. In addition the circuit provides a pulse which may be used to modulate the intensity of an oscilloscope trace each time the threshold is exceeded.
The effect of vasoactive drugs on local coronary flow
Authors: Torres Edilberto C. , Brandi Giorgio
Published: April 2011

A method is described by which it is possible to study the selective effects of vasoactive drugs on the small vessels of the coronary circulation of the dog. We incorporated xenon-133 with different drugs and derived the flow/volume ratios from the rate of fall of radioactivity at the injection site. Ratios were consistently reduced by angiotensin (−37%), pitressin (−40%), and propranolol (−13%), and were increased by dipyridamole (+23%), nitroglycerine (+14%), isoproterenol (+30%), adrenaline (+30%), and noradrenaline (+25%), indicating that these agents have an effect on the small coronary vessels. Ratios were unaltered by phenylephrine and by combinations of propranolol with adrenaline or noradrenaline, suggesting that alpha receptor sites may be absent from the small vessel bed under study.
The effect of local anesthetics on the transmural potential difference of the small intestine of the rat
Authors: Dinda P. K. , Beck Ivan T.
Published: April 2011

It has been postulated that intestinal transmural potential difference (PD) depends on active transport of Na+ and glucose. Since local anesthetics are known to interfere with Na+ and K+ movement through nerve and red cell membranes, the effect of local anesthetics on PD was investigated. An apparatus for in vitro study of transmural PD and absorption in the small intestine of rats was described. In this system the isolated gut was found to remain viable for at least 90 min. Dibucaine HCl (0.04%) and tetracaine HCl (0.15%) depressed the negative polarity of the mucosal surface. Procaine (1.0%) depressed further and finally reversed the PD to a positive polarity. In the concentration used, procaine increased the osmolarity of the mucosal solution. In the control preparation a similar increase in osmolarity, achieved by the addition of mannitol, also resulted in a fall of PD. It is thought that the total effect produced by procaine was the sum of the osmolar and pharmacological actions of the drug. A possible relationship between Na+ and glucose transport in relation to the depressing effect of local anesthetics on the PD was discussed.
Hemodynamic responses to glycols and to hemolysis
Authors: MacCannell Keith
Published: April 2011

Ethylene and propylene glycol both decrease renal blood flow in dogs while increasing flow through the superior mesenteric artery. The decrease in renal blood flow is not a passive response to dilatation of major vascular beds since it precedes the increment in superior mesenteric arterial flow and since it can be duplicated by direct injection of glycols into the renal artery. These rheological changes in response to glycols are at least partly due to hemolysis since intravenous injection of plasma from hemolyzed blood or of crystalline hemoglobin produces the same pattern of response, which is not blocked by phenoxybenzamine. However, the production of hemoglobinemia may not be the sole explanation for the vascular responses to the glycols, since a concentration of 2 %, which does not induce detectable hemolysis, still produces the characteristic increase in superior mesenteric artery blood flow.