bluuebunny/crossref_metadata_2025 huggingface dataset:
Early seedling establishment of Picea abies in small forest gaps in the Swiss Alps
Authors: Brang Peter
Published: April 2011

Early seedling establishment of Picea abies (L.) Karst. in small forest gaps was studied in drier, subalpine P. abies ecosystems in the Swiss Alps. Study sites were on steep south and north slopes. Average gap size was 15 m x 20 m on the south slope and 15 m x 70 m on the north slope. Sowing trials established on different microsites were observed for 2 or 3 years. Direct sunlight was assessed with hemispherical photography. Emergence was better on the north slope than on the south slope. On the south slope, emergence was higher on the mineral soil than on the organic layer and was negatively associated with direct sunlight, especially during the noon period. On both slopes, drought due to rainfall interception at the gap edge negatively affected emergence. The limiting factor for survival and growth on the south slope was drought (on the organic layer), whereas on the north slope lack of direct radiation and pathogenic fungi developing in the snowpack were limiting. The early regeneration niche on the south slope was narrower than on the north slope.
Phenolic predictors for Norway spruce resistance to the bark beetleIps typographus(Coleoptera: Scolytidae) and an associated fungus,Ceratocystis polonica
Authors: Brignolas Franck , Lieutier François , Sauvard Daniel , Christiansen Erik , Berryman Alan A
Published: April 2011

Changes in phloem phenolic content of Norway spruce (Picea abies (L.) Karst.) clones were followed during the first 12 days of the reaction induced by phloem artificial inoculation with Ceratocystis polonica Siem., a bark beetle (Ips typographus L.) associated fungus. The aim was to confirm our previous results concerning the mechanisms of this reaction and the possible predictors of Norway spruce resistance to bark beetles and their associated fungi. The induced reaction was characterized by a slight decrease of tanning ability and an increase of (+)-catechin concentration, which confirmed our previous observations. The relative resistance of the clones was first predicted using the predictors previously proposed. In addition, the first axis of the principal component analysis describing the phenolic content of all clones was used as a synthetic predictor (resistance axis). Related variables were also tested as predictors. Actual resistance of each clone was then measured, using mass inoculations of C. polonica, and was compared with the predictions. Four predictors were so validated: the resistance axis, tanning ability and isorhapontin concentration in uninoculated phloem, and (+)-catechin concentration in the phloem 6 days after its inoculation. Phloem phenolic composition could thus be used to predict Norway spruce resistance to bark beetles and their associated fungi.
Carbon and nitrogen transformations in New Zealand plantation forest soils from sites with different N status
Authors: Scott Neal A , Parfitt Roger L , Ross Des J , Salt Gareth J
Published: April 2011

Interactions between soil nutrient cycling processes are likely to influence N losses following disturbance in forest ecosystems. During a 340-day laboratory incubation, we examined C and N transformations in three sandy soils of different N status from Pinus radiata D. Don plantations before clear-cutting. The soils were a high N status Andisol (losing -N in streamwater) and a fertilized and unfertilized Entisol. In contrast to other forest ecosystems, -N accumulated readily in all mineral soils and in the Andisol forest floor but did not accumulate until day 63 and 210 in the fertilized and unfertilized Entisol forest floor, respectively. However, gross nitrification occurred from day 42 in both Entisol treatments. Net nitrification in the Entisol forest floor began when substrate C/N ratio declined to about 40, possibly because of decreased C availability and decreased competition for both -N and -N in conjunction with a lower microbial C/N ratio. Carbon and gross N mineralization rates (per unit of C or N, respectively) correlated positively (r2 = 0.93) in mineral soil but correlated negatively in the forest floor, probably because of major differences in C and N quality and potential differences in microbial community structure. The mean residence time of N in mineral-N pools was higher for soils from the N-rich site, in part because of lower microbial N demand. These results suggest that sudden removal of C inputs (such as at harvest) may cause greater disruption of internal soil N cycles on nutrient poor sites, increasing the proportional losses of N as compared to nutrient-rich sites.
Predicting and managing light in the understory of boreal forests
Authors: Lieffers V J , Messier C , Stadt K J , Gendron F , Comeau P G
Published: April 2011

This paper reviews current information relating to the dynamics of light in northern and boreal forests and discusses factors affecting overstory light transmission, seasonality of light, sunflecks, canopy gaps, and understory development, particularly with regard to tree regeneration. Techniques for measurement of light in forests such as radiometers, photosensitive paper or chemicals, hemispherical canopy photographs, the plant canopy analyzer, or visual estimators of canopy density are each discussed in terms of their accuracy, costs, ease of use, and conditions required during measurement. Predictive models of light transmission based on canopy architecture are also described in terms of their assumptions, accuracy, and input data costs. Lastly the paper discusses the relationship among overstory and understory densities, ground-level light, and "windows of opportunity" for regeneration of trees in the understory following management interventions.
Potential biases of incomplete linear models in heritability estimation and breeding value prediction
Authors: Lu P X , Huber D A , White T L
Published: April 2011

Potential biases associated with incomplete linear models in the estimation of heritability and the prediction of breeding values have been investigated. Results indicate that estimates of additive genetic variance and heritability as well as predicted parental breeding values from incomplete models will inevitably be biased as long as the true variance components of ignored effects are not zero. While models ignoring the interaction effect of males and females (SCA) × environment (E) interaction downwardly biased the estimates of additive genetic variance and heritability, models ignoring SCA and (or) the additive genetic effect (GCA) × E interaction yielded upward biases. The magnitudes of biases are functions of population genetic architecture, mating design, and field experimental design and can be precisely assessed with formulae derived for balanced data. Numerical simulations using unbalanced data of different mating and field experimental designs suggest that the formulae from balanced data can be used to approximate the minimum biases associated with unbalanced data. Because of the magnitudes of biases for some typical forest genetic scenarios, it is suggested that models ignoring SCA and (or) GCA × E should be avoided when the numbers of test sites and crosses per parent are small. However, incomplete model ignoring SCA × E interaction may be used to reduce computational demand with only negligible consequences.
Patterns and controls of ecosystem function in longleaf pine - wiregrass savannas. I. Aboveground net primary productivity
Authors: Mitchell Robert J , Kirkman L Katherine , Pecot Stephen D , Wilson Carlos A , Palik Brian J , Boring Lindsay R
Published: April 2011

Longleaf pine - wiregrass (Pinus palustris Mill. - Aristida stricta Michx.) woodlands occupy sites ranging from deep, xeric sandhills to the edge of wetlands in the southeastern United States. Aboveground net primary productivity (ANPP) of the overstory and understory were determined for three replicate sites of three site types (xeric, intermediate, and wet-mesic) that span a wide environmental gradient. In addition, soil moisture (at 30 and 90 cm) and N mineralization (in situ buried bag incubations) were measured through an annual cycle. Longleaf pine - wiregrass ecosystems varied by nearly twofold in ANPP across complex gradients. Overstory and understory and total (overstory and understory) ANPP were positively correlated to soil moisture at 30 and 90 cm. The proportion of understory ANPP relative to the total ANPP did not increase across the environmental gradient as predicted by hypotheses that invoke niche differentiation in rooting habits of grasses and trees. Contrary to expectations, cumulative net N mineralization was negatively related to soil moisture. All ANPP estimates were significantly and negatively related to cumulative N-mineralization. Further work is needed to explore the mechanisms by which soil moisture regulates productivity across space, time, and for individual species. Additional experimentation through resource addition would allow for investigations into multiple resource limitations and how resource limitations vary depending on gradient position.
Managing low-output agroecosystems sustainably: the importance of ecological thresholds
Authors: Brown Joel R , Herrick Jeffrey , Price David
Published: April 2011

Managing vegetation to achieve ecological, economic, and social goals is difficult. Inherent complexity among ecosystem components and unpredictable climate often limit opportunities for converting cultural inputs to harvestable products. In addition, the long lag time between treatment and financial return makes capital investment in vegetation management economically risky. One tool that can assist land managers in dealing with these constraints is the identification of ecological thresholds and elucidation of processes that signal undesirable change before it is entrained. This approach places a premium on early detection of degrading processes and implementation of management responses in the initial stages of land degradation. Managerial expertise and manipulation of naturally occurring processes, rather than cultural inputs, are key management decisions. In this paper we review current applications of the threshold concept as a management decision point and propose modifications for use in managing plant communities with low potential for annual economic return. We also propose that research and institutional programs for sustainable land management shift direction toward identifying ecological thresholds and focus on developing low-input responses to avoid, rather than restore, land degradation.
Root length and biomass in mixtures of broomsedge with loblolly pine or sweetgum
Authors: Zutter Bruce R , Mitchell Robert J , Glover Glenn R , Gjerstad Dean H
Published: April 2011

Root length density (RLD) and root biomass density (RBD) of fine roots (<2 mm) were examined in a factorial combination of loblolly pine (Pinus taeda L.) and broomsedge (Andropogon virginicus L.) and a factorial combination of sweetgum (Liquidambar styraciflua L.) and broomsedge to determine the extent to which competition may influence belowground plant response. Broomsedge and sweetgum seedlings were planted, grown for 1 year, and cut before planting of pine seedlings. Sampling occurred 1 year after planting of pine. Broomsedge had a significant negative effect (p < 0.10) on RBD and RLD of sweetgum and loblolly pine in the upper 30 and 45 cm of soil, respectively. RLD and RBD of broomsedge increased with increasing broomsedge density (p < 0.10) and decreased with addition of either tree species, with sweetgum having a greater effect. Patterns in the effects of competitors on RBD and RLD were similar to those noted for aboveground biomass. Specific root length (SRL) of broomsedge was three and five times greater than that of sweetgum or loblolly pine, respectively (p < 0.05). The addition of interspecific competitors reduced the percentage of total RLD of pine and sweetgum and RBD of broomsedge in the 0- to 15-cm soil depth with a corresponding increase in the 15- to 30-cm depth.
Distribution of epiphytic macrolichens in relation to remnant trees in a multiple-age Douglas-fir forest
Authors: Sillett Stephen C , Goslin Matthew N
Published: April 2011

Alternatives to clear-cutting are being implemented to increase biodiversity of managed forests in the Pacific Northwest. Lichens are an integral component of old growth, but lichen biomass develops slowly in forests. We evaluated the long-term potential of live tree retention for lichen conservation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. We sampled lichen litterfall in a 2-ha stand that contained 200- to 600-year-old remnant trees scattered in a forest composed mostly of 100-year-old trees that established following fire. We used association, principal components, and regression analyses to relate lichen litterfall biomass to the proximity of remnant trees. Two epiphytic lichens were strongly associated with remnant trees: the foliose cyanolichen Lobaria oregana (Tuck.) Müll. Arg. and the fruticose green algal lichen Sphaerophorus globosus (Hudson) Vainio. Biomass of both species was highest near remnant trees, and biomass was slightly higher within groves of remnant trees than it was at the edges of these groves or near isolated trees. Lichens appear to have persisted on remnant trees through the last fire and are slowly recolonizing younger trees from this source of propagules. Retention of live trees, maintenance of hardwoods, and longer rotation periods have great potential to maintain old-growth-associated lichens in at least some managed forests.
Production physiology and morphology ofPopulusspecies and their hybrids grown under short rotation. III. Seasonal carbon allocation patterns from branches
Authors: Scarascia-Mugnozza G E , Hinckley T M , Stettler R F , Heilman P E , Isebrands J G
Published: April 2011

Seasonal patterns of photosynthates export were followed on 1- and 2-year-old trees of four Populus clones, belonging to the species Populus trichocarpa Torr. & Gray, Populus deltoides Bartr., and their interspecific hybrids grown in the field under short rotation. Different types of branches (including sylleptic and proleptic) and cohorts of leaves on the main stem were exposed to14CO2at monthly and bimonthly intervals in the first and second growing season. Patterns of photosynthates export were influenced by phenology and differed markedly among clones. Differences of translocation patterns were also found among various portions of the crown. Sylleptic branches exported carbon mainly to the lower stem and the roots, whereas main stem leaves, before bud set, contributed much to the height growth of the tree. Sylleptic branches also had greater translocation efficiency than proleptic, contributing more, on a per unit mass basis, to the growth of the tree. Within branches of the same order and among branches of different order, export of assimilates followed patterns similar to those found in the main stem. There was little export of assimilates between adjacent branches of the same order or between branches and main stem leaves. Clones 11-11 and 1-12, which had the highest number of sylleptic branches, were also the most productive clones, respectively, for the hybrids and the parental species.
Changes in radial increment of host and nonhost tree species with gypsy moth defoliation
Authors: Muzika R M , Liebhold A M
Published: April 2011

Ring widths from 1458 trees from Massachusetts, New York, and New Jersey were measured to determine the influence of gypsy moth (Lymantria dispar L.) defoliation on both hosts (primarily oaks (Quercus spp.)) and nonhosts. Previous year's defoliation negatively influenced radial increment in all oak species. Defoliation also negatively affected radial growth of pitch pine (Pinus rigida Mill.), an intermediate host. There was little or no effect of defoliation on increment of trembling aspen (Populus tremuloides Michx.) and bigtooth aspen (Populus grandidentata Michx.), but both are preferred hosts. Defoliation of host trees in mixed stands resulted in increased increment in the nonhosts tulip-tree (Liriodendron tulipifera L.) and ash (Fraxinus spp.) in the year following defoliation. The effect of defoliation was also evident in the relative production of earlywood and latewood with a pronounced dominance of earlywood production in host trees during the same year as defoliation and often in the following year.
Evaluation of several measures of canopy openness as predictors of photosynthetic photon flux density in deeply shaded conifer-dominated forest understory
Authors: Machado José-Luis , Reich Peter B
Published: April 2011

The ability to accurately estimate light levels in shaded environments is important for understanding plant adaptations to shade. This study evaluates the effectiveness of three rapid methods of estimating the long-term integrated percentage of above-canopy photosynthetic photon flux density (PPFD) in a deeply shaded conifer-dominated forest understory. These methods included (i) hemispherical canopy photography, (ii) hemispherical sensors (LAI-2000), and (iii) instantaneous %PPFD. Transmitted PPFD was continuously measured starting in June and ending in November using photodiodes at 60 measurement points ranging from 1 to 50% PPFD. Measurements from all methods were positively and linearly related to the mean daily %PPFD measured for two different periods of the year (foliage on and foliage off). However, the strength of the relationship and closeness to a 1:1 fit was weaker for the hemispherical photograph technique. During the foliage-on period, the hemispherical sensor (LAI-2000) explained 90% of the variation in mean daily %PPFD, while the instantaneous %PPFD and hemispherical photography explained 88 and 67%, respectively. Moreover, when examining low-light conditions only (<6 %PPFD), hemispherical photographs failed to detect differences in %PPFD, while the other two techniques were nearly as effective in low light as across the entire light gradient.
Fine woody debris is important for species richness on logs in managed boreal spruce forests of northern Sweden
Authors: Kruys Nicholas , Jonsson Bengt Gunnar
Published: April 2011

Species richness of wood-inhabiting cryptogams was compared on fine woody debris (FWD; diameter 5-9 cm) and coarse woody debris (CWD; diameter [Formula: see text]10 cm) logs of Picea abies (L.) Karst. Data were collected from managed boreal forests of northern Sweden. Species richness was higher on CWD than FWD when equal numbers of logs were compared. When equal surface areas were compared, species richness on FWD and CWD did not differ. When equal volumes of CWD and FWD were compared, FWD had more species. This was an effect of surface area and log quantity, as a certain volume of FWD was composed of more logs and had greater surface area than the same volume of CWD. We varied woody debris volume and proportion of FWD in a simulation model of species richness on logs. At low volumes of woody debris, species richness increased with the proportion of FWD. At higher log volumes, species richness increased with the proportion of CWD. In managed forests where there are small amounts of woody debris, FWD is important for the total species richness on logs and should not be neglected despite the fact that species richness is generally positively correlated with log diameter.
Fractal dimension based features are useful descriptors of leaf complexity and shape
Authors: Borkowski Wojciech
Published: April 2011

An application of fractal dimensions as measures of leaf complexity to morphometric studies and automated plant identification is presented. Detailed algorithms for the calculation of compass dimension and averaged mass dimension together with a simple method of grasping the scale range related variability are given. An analysis of complexity of more than 300 leaves from 10 tree species is reported. Several classical biometric descriptors as well as 16 fractal dimension features were computed on digitized leaf silhouettes. It is demonstrated that properly defined fractal dimension based features may be used to discriminate between species with more than 90% accuracy, especially when used together with other measures. It seems, therefore, that they can be utilized in computer identification systems and for purely taxonomical purposes.
A simple model to examine the impact of changes in wood traits on the costs of thermomechanical pulping and high-brightness newsprint production with radiata pine
Authors: Chambers Paul GS , Borralho Nuno MG
Published: April 2011

A number of functions were investigated that related the costs of thermomechanical pulp (TMP) and high-brightness newsprint production, using Pinus radiata D. Don, to important pulp and paper quality (breeding objective) variables, including specific energy consumption and pulp handsheet tear and tensile strength, brightness, and opacity. Pulp handsheet quality traits were considered to be reasonable two-dimensional predictors of paper quality traits in this context. A specific production process that requires the use of a reinforcement kraft pulp and an artificial clay filler to improve the quality of paper produced from the bleached TMP fibres was investigated, similar to the production process used by Australian Newspaper Mills' Boyer Mill in Tasmania, Australia. Pulp and pulp handsheet quality variables could be explained by significant (P > 0.05) wood traits using multiple linear regression equations. This provided a method to predict the economic importance of each wood trait in relation to the thermomechanical production process investigated. The results showed that tracheid length, wood density, wood brightness, and tracheid coarseness were the best predictors of costs. Increases in tracheid length, wood density, and wood brightness and decreases in tracheid coarseness resulted in decreasing the total costs of TMP and high-brightness newsprint production.
Influence of fire on native nitrogen-fixing plants and soil nitrogen status in ponderosa pine - Douglas-fir forests in western Montana
Authors: Newland J A , DeLuca T H
Published: April 2011

Nitrogen fixing plants have been reported to play an important role in replacing N lost from soil in fire dominated ecosystems. Exclusion of fire from ponderosa pine (Pinus ponderosa Dougl. ex Laws.) - Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests of western Montana has lead to widespread changes in forest structure, composition, and function including a potential reduction in the occurrence of N-fixing plant species. We investigated the effect of fire exclusion and reintroduction of fire on the frequency, occurrence, and function of native N-fixing plant species at 11 paired burned and unburned sites in western Montana. These pairs had been either undisturbed since the early 1900s or had been repeatedly opened by logging and (or) fire over the last 80-100 years. Although the percent cover of N-fixing plants was low at all sites, the cover and frequency of N-fixing plants were significantly greater in sites exposed to fire than in the unburned sites and greater in repeatedly opened sites than in undisturbed sites. In contrast, levels of available N were significantly lower in burned sites compared with unburned sites and in repeatedly opened sites. Nitrogen-fixing plants may have played an important role in maintaining productivity in frequently burned ponderosa pine forests but now appear to be suppressed in fire-excluded forests.
Regional forest resource accounting: a northern Alberta case study
Authors: Haener M K , Adamowicz W L
Published: April 2011

This study outlines the development of a resource accounting system for a region of public forestland in northern Alberta. The purpose of this exercise is to provide a clearer picture of the market and nonmarket benefits provided by the forest. The services valued include commercial activities such as forestry, trapping, and fishing plus noncommercial or nonmarket activities. Nonmarket services include recreational activities (fishing, hunting, and camping), subsistence resource use, and environmental control services (carbon sequestration and biodiversity maintenance). The case study provides the basis for future estimates that when tracked over time can provide information regarding the sustainability of income flows from the region. Many of the complexities of resource accounting at this finer resolution parallel those of resource accounting at the national level. The case study also illustrates constraints and challenges unique to the regional and forestry context.
Comparison of direct and indirect estimation of leaf area index in mature Norway spruce stands of eastern Germany
Authors: Küßner Ralf , Mosandl Reinhard
Published: April 2011

IIn three mature Norway spruce (Picea abies (L.) Karst.) stands of the Erzgebirge (Ore Mountains) in eastern Germany, the performance of the LAI-2000 plant canopy analyzer (LI-COR instruments) was tested for indirect estimation of leaf area index (LAI). The LAI-2000 calculates effective leaf area index (LAIe, m2/m2) resulting from radiation measurements and subsequent model calculations. LAIe underestimated directly estimated half the total leaf area index (LAI0.5t, m2/m2) by 37-82% as determined from allometric relationships derived from subsample harvesting. The degree of underestimation was dependent upon stand density in two of three spruce stands examined; it was the highest in sparsely stocked plots. The relationship of LAIe to allometrically determined LAI0.5t for one of the three stands differed significantly from the other two spruce stands and the underestimation of LAI0.5t was less distinct. This was explained by stand structure, i.e., higher amounts of nonassimilating surfaces relative to LAI0.5t. These results indicate that the LAI-2000 is not generally applicable for estimation of LAI in mature spruce stands of the Erzgebirge because of effects of stand structure on LAIe-LAI0.5t relationships, which are stand specific.
Succession après épidémie de la tordeuse des bourgeons de l'épinette (Choristoneura fumiferana) dans des sapinières boréales pluviales de seconde venue
Authors: Déry Stéphane , Bélanger Louis , Marchand Stéphane , Côté Sylvie
Published: April 2011

Following spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks, Baskerville's model (G.L. Baskerville. 1975. Spruce budworm: super silviculturalist. For. Chron. 51: 138-140), referred to as the cyclic model, is generally accepted as one of the best established regeneration models in wet boreal fir stands typical of northeastern America. According to that model, old virgin fir stands killed by the insect are replaced by other fir stands. In this study, we wanted to check if the cyclic model would work with wet boreal fir stands originating from harvest and having reached the felling age (50-60 years old) observed in Quebec. The study set up after the last budworm outbreak (1974-1987) shows that, although coniferous regeneration is abundant, the seedling bank is obviously immature: young and small seedlings, empty microsites. In most cases, the regeneration is codominated or dominated by deciduous species, which may bring about the development of a deciduous stand. Thus, the cyclic model does not seem suited to describe dynamics of second-growth boreal fir stands when it is kept in a premature state (<50-60 years old). These stands may not be as resilient as virgin ones, which are characterized by ecological rotations longer than 90 years.[Translated by the Journal]
Liquid water content of wood tissue at temperatures below 0°C
Authors: Sparks Jed P , Campbell Gaylon S , Black R Alan
Published: April 2011

Time domain reflectometry (TDR) offers an opportunity to measure the liquid water content of otherwise frozen plant material. We applied TDR technology to the examination of freezing in three types of wood represented by Robinia pseudoacacia L. (ring porous), Populus trichocarpa Torr. & A. Gray (diffuse porous), and Pinus contorta Dougl. ex Loud. and Larix occidentalis Nutt. (conifer wood). Gravimetric analysis revealed similar water contents of all wood types during the summer. In contrast, winter data showed that R. pseudoacacia wood exhibited a lower total (liquid and ice) water content (0.250 m3·m-3) than that of Populus trichocarpa (0.600 m3·m-3) or of the two conifer species' wood (0.510 m3·m-3). Additionally,R. pseudoacacia wood contained more air by volume during the winter than all other wood types (air-filled porosity 0.34 m3·m-3 compared with 0.12-0.22 for all other species). At all temperatures below 0°C, R. pseudoacacia wood contained less liquid water than the other wood types, as revealed by TDR measures. The TDR analysis further demonstrated that more than 25% of the water in wood of all species was liquid even at temperatures of -15°C. This liquid water is likely found within the cell wall and is potentially transportable at temperatures well below 0°C.
The effect of habitat type and rock type on individual tree basal area growth response to nitrogen fertilization
Authors: Shen Guanghong , Moore James A , Hatch Charles R
Published: April 2011

Individual tree basal area increment models for nitrogen fertilized stands were developed using data from permanent research plots located throughout the Inland Northwest. Results show that tree size, stand density, habitat type, and rock type significantly interact to affect individual tree basal area growth response to nitrogen fertilization. Suppressed trees growing on moist habitat types and all rock types, except metasedimentary, exhibited greater relative response than did dominant or codominant trees growing in the same stand. However, suppressed trees growing on dry sites or on soils derived from granite rocks did not show different relative response than dominant or codominant trees growing in the same stand. This study quantitatively demonstrates that individual tree competitive relationships are significantly affected by rock type. Rock types proved to be useful in representing broad differences in a site's nutrient environment. Incorporating the new equations into individual tree growth and yield simulators would provide better representation of N fertilization response differences within a stand.
Allozyme genetic diversity amongFagus grandifoliatrees resistant or susceptible to beech bark disease in natural populations
Authors: Houston Daniel B , Houston David R
Published: April 2011

American beech (Fagus grandifolia Ehrh.) trees resistant (R = 760) and susceptible (S = 681) to beech bark disease were located and mapped in nine natural stands in West Virginia (WV), Massachusetts (MA), Maine (ME), Nova Scotia (NS), and Prince Edward Island (PEI). Dormant bud tissue collected from each tree was examined by isozyme analysis to characterize the population genetic structure of R and S subpopulations mapped in each of four intensively sampled (R/S) stands, and five additional populations in which only R trees were sampled. Seventeen enzymes (with 9 polymorphic and 14 monomorphic loci) were analyzed to estimate variation across the spatial range of disease occurrence. All populations possessed significant levels of inter- and intra-population diversity; several parameters appeared to increase in magnitude from southwest to northeast across the range. In the R/S stands, percent polymorphic loci averaged 38%, average number of alleles/locus was 1.8 (3.0 for polymorphic loci), and mean expected heterozygosity was 0.165. Most genetic variation resided within populations (97%; GST= 0.03). Analyses of pooled R and S subpopulations demonstrated that observed heterozygosities were up to 26% higher in S trees, i.e., R tree populations exhibited consistent heterozygote deficits.
Effects of aphids and moth caterpillars on epiphytic microorganisms in canopies of forest trees
Authors: Stadler Bernhard , Müller Thomas
Published: April 2011

Different types of herbivores were investigated for their effects on microorganisms in the phyllosphere of forest trees during the growing season. Aphids on spruce, beech, and oak produced honeydew, which was readily consumed by microorganisms and resulted in two to three orders of magnitude higher densities (colony forming units) of bacteria, yeasts, and filamentous fungi on leaves of infested trees. The amounts of honeydew excreted by different aphid species and their mode of excretion (large droplets, tiny droplets scattered over leaves, production of wax wool) affected the degree to which honeydew could be processed by epiphytic microorganisms. All groups of microorganisms appeared to be energy limited. These results were consistent for different growth media offered to the microorganisms. Leaf-feeding moth caterpillars also positively affected the growth of microorganisms on leaves of beech and oak. The effects were more pronounced for bacteria and yeasts especially on oak. Thus, different functional groups of herbivores positively affected the growth of microorganisms in the phyllosphere of trees. It is suggested that the population dynamics of herbivores and their feeding characteristics are important features, which should be considered when the population dynamics of microorganisms in the canopies of trees is studied.
The effects of paclobutrazol, abscisic acid, and gibberellin on germination and early growth in silver, red, and hybrid maple
Authors: Marshall John , Beardmore Tannis , Whittle Carry Anne , Wang Ben , Rutledge Robert G , Blumwald Eduardo
Published: April 2011

Silver maple (Acer saccharinum L.) seeds were used to examine the mechanisms regulating recalcitrant seed germination aiming towards the development of a biochemical method to temporarily inhibit germination without refrigeration. Treatment of fresh silver maple seeds with the cytochrome P450inhibitor paclobutrazol delayed germination and reduced root and shoot extension. The inhibitory effect of paclobutrazol plus abscisic acid (ABA) on the shoots of silver maple could not be overcome by a brief treatment with gibberellic acid A3(GA3). Red maple seeds (Acer rubrum L.) were almost completely inhibited by the treatment with paclobutrazol alone, and this inhibition could not be overcome by a brief treatment with GA3. In the red × silver hybrid, root growth was little affected by paclobutrazol plus ABA; however, shoot growth was markedly inhibited by paclobutrazol, and this inhibition was sharply increased by the combination with ABA but partially alleviated by GA3. Treating fresh silver maple seeds with paclobutrazol for 12 h followed by storage under ideal germination conditions, in the presence of 1 mM ABA, completely prevented germination for 1 week. Root extension was completely restored by the continuous provision of GA3along with the ABA.
Heterogeneity in ponderosa pine/Douglas-fir forests: age and size structure in unlogged and logged landscapes of central Colorado
Authors: Kaufmann Merrill R , Regan Claudia M , Brown Peter M
Published: April 2011

Tree age and size structures were compared within and among topographic categories in portions of a 35-km2 unlogged landscape and a comparable adjacent logged landscape. Tree density was generally higher in the logged landscape. One fifth of plots in the unlogged landscape had trees older than 400 years, but no trees older than 400 years remained in the logged landscape plots. Ten recruitment pulses were identified for the unlogged study area, accounting for 49% of all trees measured during 26% of the 421-year survival record. Recruitment pulses in the logged area accounted for fewer trees during a larger amount of time. Most recruitment periods in the unlogged landscape coincided with known past major fires. The mixed-severity historical fire regime created openings that persisted for as long as 148 years. The following components exist in the unlogged landscape: (i) forest patches having a distinct age cap reflecting regeneration following an earlier stand-replacing fire, (ii) uneven-aged forest patches having no evidence of an age cap, (ii) openings created by fire, and (iv) riparian areas. Results suggest that the logged landscape is poised to regain an old-growth age distribution, and tree removal in the logged landscape could restore the size distribution found in the unlogged landscape. However, the unlogged landscape has openings not found in the logged landscape that should be considered in restoration efforts at a landscape scale.
Interaction of vasomotor and exocrine neurons in bullfrog paravertebral sympathetic ganglia
Authors: Ford Christopher P , Ivanoff Alexander Y , Smith Peter A
Published: April 2011

A 2 min sample of an intracellular recording of in vivo synaptic activity from a vasomotor C-neuron in a bullfrog sympathetic ganglion was converted to a series of stimulus pulses. This physiologically derived activity was used to stimulate preganglionic C-fibres of similar ganglia studied in vitro. Intracellular recordings were made from exocrine B-cells within the ganglia. Although they do not receive fast, nicotinic synaptic input from preganglionic C-fibres, B-cell excitability was profoundly increased by stimulation of C-fibres with physiologically derived activity. Also, subthreshold depolarizing current pulses that failed to generate action potentials in B-cells under control conditions almost always generated action potentials whilst C-fibres were activated. These effects were attenuated or prevented by the luteinizing hormone releasing hormone antagonist, [D-pyro-Glu1,D-Phe2,D-Trp3,6]-LHRH (70 µM). The physiological release of luteinizing hormone releasing hormone from C-fibres therefore causes an interaction between vasomotor and exocrine outflow within a paravertebral sympathetic ganglion.Key words: ganglionic transmission, hypertension, autonomic nerve, m-current, neuropeptide.
Radiotelemetric monitoring of blood pressure and mesenteric arterial bed responsiveness in rats with streptozotocin-induced diabetes
Authors: Tatchum-Talom Rabelais , Gopalakrishnan Venkat , McNeill J Robert
Published: April 2011

We investigated the changes in arterial blood pressure (BP) and of mesenteric arterial bed (MAB) responsiveness that accompany streptozotocin (STZ)-induced diabetes. BP was recorded by radiotelemetry in conscious animals before and during a 4-week period following induction of the diabetic state with STZ. At the end of this period, the MAB was isolated and perfused under constant flow conditions: perfusion pressure (PP, mmHg) was taken as an index of arteriolar tone. BP was lower (P < 0.05) in STZ-treated diabetic rats (82.9 ± 5.0 mmHg) than in vehicle-treated rats (108.9 ± 6.3 mmHg). Basal perfusion pressure of the MAB was lower in STZ-treated rats than in control rats and inhibition of nitric oxide (NO) synthesis with NG-nitro-L-arginine-methyl-ester and NG-nitro-L-arginine (100 µM each) failed to change this relationship. Increases in PP of MAB to phenylephrine (Phe), norepinephrine (NE), and potassium chloride (KCl) were reduced in STZ-treated rats compared with control rats. Inhibition of NO synthesis reduced responses to Phe, NE, and KCL in both STZ and control rats. The reduced responsiveness of STZ rats to Phe, NE, and KCl persisted after inhibition of NO synthesis. Acetylcholine (ACh) evoked relaxation of the MAB in a dose-dependent fashion. Maximal responses to ACh, but not sodium nitroprusside, were lower in STZ rats than in vehicle treated rats. Inhibition of NO synthesis reduced responses to ACh in both STZ and control rats. The reduced responsiveness of STZ rats to ACh persisted after inhibition of NO synthesis. The data demonstrate that STZ-induced diabetes is associated with a fall in blood pressure when pressure is recorded with radiotelemetry. The fall in blood pressure may be related to a non-specific decrease in responsiveness to vasoconstrictor stimuli mediated at least in part by NO-independent mechanisms. A decrease in responsiveness to endothelial dependent vasodilator mechanisms appeared insufficient to restore responsiveness to vasoconstrictor stimuli.Key words: radiotelemetry, blood pressure, mesenteric arterial bed reactivity, acetylcholine, norepinephrine, STZ-diabetic rat.
The negative inotropic action of catecholamines: Role of β3-adrenoceptors
Authors: Gauthier Chantal , Leblais Véronique , Moniotte Stéphane , Langin Dominique , Balligand Jean-Luc
Published: April 2011

There is now evidence for the involvement of four β-adrenoceptor populations in the regulation of cardiac function by catecholamines. β1- and β2-adrenoceptor stimulation classically produces an increase in contractility. A fourth β-adrenoceptor, as yet uncloned and designated provisionally as a β4-adrenoceptor, also mediates a positive inotropic effect. β3-adrenoceptors, which had been cloned at the end of the eighties, has been extensively studied as a potential target for antiobesity and antidiabetic drugs. Its characterization in the heart has opened new fields of investigations for the understanding of the cardiac adrenergic regulation. This review describes the cardiac electrical and mechanical effects induced by β3-adrenoceptor stimulation in different species (including human), as well as the signaling pathway. It also analyzes the role of these receptors in the abnormal responsiveness of catecholamines in heart failure.Key words: beta-adrenoceptor, heart, contractility, signaling pathway, heart failure.
Effect of hypertension on the development of diabetic cardiomyopathy
Authors: Mathis David R , Liu Stephanie SL , Rodrigues Brian B , McNeill John H
Published: April 2011

The effect of hypertension on the progression of diabetic cardiomyopathy was examined by attempting to induce a similar level of diabetes in both spontaneously hypertensive rats (SHR) and Wistar rats. Streptozotocin (STZ) was injected into SHR (45 mg/kg) and Wistar rats (55 mg/kg) before (eight weeks of age) and after (twelve weeks of age) the development of hypertension in the SHR. For both groups of animals, induction of diabetes resulted in depressed weight gain, increased food and fluid consumption, hypoinsulinemia, hyperglycemia, and hypertriglyceridemia. For the rats injected at eight weeks of age, an oral glucose tolerance test (OGTT) demonstrated that although the SHR were significantly less diabetic than Wistar rats, the degree of cardiac dysfunction was equivalent in both strains. These results suggest that hypertension was interacting with the diabetic condition to impair cardiac performance. Injecting SHR at twelve weeks of age increased the severity of diabetes but interestingly did not depress heart function compared with the non-diabetic SHR group. Injecting Wistar rats at this age also increased the severity of diabetes, but unlike the SHR diabetic animals, these rats still had impaired cardiac performance. These results suggest that hypertension exacerbates the cardiac dysfunction seen during diabetes, especially when SHR rats are injected with STZ prior to the elevation of blood pressure. Moreover, in the SHR, the development of LV hypertrophy at the time of STZ injection may have compensated for the damaging effects of diabetes on the myocardium, thereby enabling the heart to perform normally.Key words: diabetes, hypertension, streptozotocin, cardiac dysfunction, spontaneously hypertensive rat.
The effect of age and gender on the relative fatigability of the human adductor pollicis muscle
Authors: Ditor D S , Hicks A L
Published: April 2011

The purpose of this study was to examine the relative influence of such factors as age, gender, and absolute force on the fatiguability of the human adductor pollicis muscle. 12 young males (YM, 25.3 ± 2.1 y), 12 young females (YF, 23.5 ± 2.1 y), 12 older males (OM, 71.7 ± 5.6 y) and 12 older females (OF, 69.5 ± 4.6 y) participated. Three minutes of intermittent (5 s contraction, 2 s rest) maximal voluntary contractions (MVC) were used to fatigue the adductor pollicis muscle; the ulnar nerve was also stimulated in each 2 s rest period to evoke a maximal twitch. Males were stronger than females in both voluntary and evoked force (PT) in the young age group (MVC: YM, 10.0 ± 2.7 kg vs. YF, 6.6 ± 1.1 kg, P < 0.05) (PT: YM, 0.99 ± 0.21 kg vs. YF, 0.71 ± 0.12 kg, P < 0.05). In the older adults, however, males were stronger only in the evoked twitch (OM, 0.73 ± 0.24 kg vs. OF, 0.48 ± 0.07 kg, P < 0.05). There was no significant effect of gender or absolute muscle force on relative fatigability; the only variable found to significantly affect fatigability was age. Older adults were significantly less fatigable than young adults as indicated by the voluntary fatigue index (FI) (percentage of force reduction from baseline; FI-young, 40.2 ± 12.6% vs. FI-old, 25.2 ± 12.3%). This age effect, however, was more prominent in males than females (FI-YM, 44.7 ± 10.5% vs. FI-OM, 24.2 ± 10.7%, P < 0.01; FI-YF, 37.8 ± 14.1% vs. FI-OF, 26.3 ± 14.5%, P = 0.13). In conclusion, age was found to be the strongest single predictor of fatigability during short duration, intermittent exercise in human adductor pollicis muscle.Key words: neuromuscular fatigue, gender, age, muscle membrane excitability, absolute force.
De la peroxydation lipidique radioinduite : les facteurs déterminant l'oxydabilité des lipides
Authors: Rémita Samy
Published: April 2011

Lipids are the essential components of cell membranes and lipoproteins. Their peroxidation plays an important role in numerous pathologies in which oxidative stress is involved. Lipid peroxidation occurs through a chain reaction that contributes to membrane damage in cells. It results in the conversion of fatty acids to polar hydroperoxides and leads to the breakdown or malfunction of the membrane. Lipids are amphiphilic molecules that aggregate in aqueous solutions into micelles and liposoms. The effect of this structural organization is significant in studies of radiation-induced peroxidation damage in highly ordered biological systems such as biological membranes. In this paper, a synthesis of the data concerning radioinduced lipid peroxidation is completed by an original review of the different parameters that determine lipid oxidizability. In addition, the influence of lipid aggregation and the effect of molecular packing are discussed.Key words: radiolysis, peroxidation, lipids, fatty acids.