bluuebunny/crossref_metadata_2025 huggingface dataset:
Semiclassical variational calculation of energy levels of He@C70
Authors: Lee-Dadswell G R , Gray C G
Published: June 2006

Semiclassical variational methods are used to obtain estimates of the quantum mechanical energy levels for two simplified models of the potential seen by a helium atom trapped inside a C70 cage. We find that with the use of a simple trial solution, the calculations are simple. A more complicated trial trajectory, while improving some results of the calculation, makes the calculation prohibitively difficult. We also observe that as long as the precessional frequency of the orbits is small we can obtain very high accuracy in our results. However, the inability to accurately predict precessional frequencies results in poor prediction of energy levels when the precessional frequency is large.PACS No.: 5.45.Mt
Three-dimensional analysis of water infiltration into the Gouhou rockfill dam using saturatedunsaturated seepage theory
Authors: Chen Qun , Zhang L M
Published: June 2006

The Gouhou Dam was a concrete-faced rockfill dam built in a steep canyon that collapsed in 1993 due to internal erosion during the initial reservoir filling. In this paper, the process of water infiltration into the originally unsaturated rockfill dam is studied using three-dimensional saturatedunsaturated seepage theory. The three-dimensional characteristics of seepage through the dam bounded by steep abutments, the effect of material anisotropy, and the effect of rockfill stratifications are studied. The three-dimensional results are compared with those from two-dimensional analyses. The three-dimensional simulations show that seepage water flows faster and the hydraulic gradients are greater near the abutment boundary in the dam. As such, the evolution of the seepage failure in the three-dimensional cases is faster than that in the two-dimensional analyses, and the two-dimensional analyses will underestimate the risk of seepage failure, particularly near the abutment boundary. If the materials in the dam were uniform, the reservoir water would infiltrate into the dam along a downward flow path towards the riverbed, and not exit from the surface on the downstream slope. Increasing the horizontal coefficient of permeability of the rockfill increases the infiltration velocity, but the material anisotropy does not appreciably change the infiltration pattern. Stratifications in the rockfill, however, cause the seepage water to advance more quickly in the horizontal direction along the interface between the sandwich layer and the rockfill, thus increasing the possibility of seepage failure.Key words: seepage, seepage failure, rockfill dam, unsaturated soils, wetting front, numerical analysis.
Convergenceconfinement analysis of a bolt-supported tunnel using the homogenization method
Authors: Wong Henry , Subrin Didier , Dias Daniel
Published: June 2006

The behaviour of tunnels reinforced with radially disposed fully grouted bolts is investigated in this paper. Perfect bonding and ideal diffusion of bolt tension are assumed, so that the bolt tension can be assimilated to an equivalent uniaxial stress tensor. An analytical model of the convergenceconfinement type is proposed that accounts for the delayed action of bolts due to ground decompression prior to bolt installation. This factor leads to nonsimultaneous yielding, and more generally, a different stress history for each constituent, requiring special treatments in the incremental elastoplasticity calculations. Nonetheless, the resulting model remains sufficiently simple, and an analytical solution is still accessible. Charts are provided to allow for parametric studies and quick preliminary designs. Comparisons with 3D numerical calculations show that the model gives precise results if the correct convergence at the moment of bolt installation is used as an "external" input parameter, validating the homogenization approach. An approximate methodology based on previous works is proposed to determine this parameter to render the proposed model "self-sufficient." Its predictions are again compared to 3D numerical computations, and the results are found to be sufficiently accurate for practical applications.Key words: reinforcement, anisotropy, analytical, lining, yield, elastoplasticity.
New approach for analysis of cantilever sheet pile with line load
Authors: Choudhury Deepankar , Singh Shailesh , Goel Shubhra
Published: June 2006

Free-standing cantilever sheet pile walls in cohesionless soils subjected to horizontal line load have traditionally been analyzed assuming full active and passive earth pressure mobilization on the sides of the embedded portion of the wall. In the conventional analysis, the vertical equilibrium of forces is not checked and the effect of the wall friction angle is neglected because of the assumption of a smooth wall. In the present study, the limit equilibrium method has been used to estimate the minimum penetration depth required for a free-standing cantilever sheet pile wall subjected to horizontal line load, by considering the effect of wall friction angle, thereby satisfying all equilibrium conditions and considering the partial mobilization of earth pressures depending on the type and magnitude of the wall movement. The variation of earth pressure mobilization has been taken as a function of the displacement (rotation about both the top and the bottom) of the cantilever sheet pile wall, which in turn also governs the mobilized friction angles. A comparison has been made between the results of penetration depths obtained by the present study and those obtained by existing conventional solutions. New design values in nondimensional form are proposed.Key words: wall friction angle, partial earth pressure mobilization, cohesionless soil, penetration depth, equilibrium equations, displacement.
Limit analysis of anchored concrete soldier-pile walls in clay under vertical loading
Authors: Cardoso António S , da Costa Guerra Nuno M , Antão Armando N , Fernandes Manuel Matos
Published: June 2006

The vertical stability of anchored concrete soldier-pile walls is highly influenced by the complexity of the interaction between the different parts of the structure, i.e., wall, anchors, and supported soil mass. The problem is analyzed using upper bound limit analysis through published solutions and proposed closed-form equations. A comparison is made between these equations and numerical limit analyses. An estimate of the theoretical minimum pile resistance required to avoid excavation collapse is presented. Published finite element elastoplastic results are used for comparison.Key words: anchored retaining wall, concrete soldier-pile walls, vertical equilibrium, finite elements, limit analysis, soil-to-wall interface shear forces.
Centrifuge modeling of torsional response of piles in sand
Authors: Zhang L M , Kong L G
Published: June 2006

Centrifuge model tests were performed to investigate the torsional behavior of a well-instrumented model pile jacked into loose and dense sand. The whole process of pile jacking, torsional loading, and pile extraction was conducted in-flight at 40g using a four-axis robotic manipulator. The torsional response at the pile head, distributions of torque and shaft friction along the pile shaft, torsional load transfer, and loading rate effects were studied. The shaft resistances along the pile during torsional loading, compression loading, and tension loading were compared. The shear stress  local pile movement curves obtained from the present torsional load tests were found to be approximately hyperbolic and similar to those obtained from axial load tests reported in the literature. The torsional shear stress distribution along the pile shaft was influenced by stress degradation effects, particularly in the loose sand. A criterion was proposed to define pile failure under torsional loading. Torsional loading rates in the range of 18°/s had little effect on the torsional resistance of the pile. Depending on the initial state of the soil around the pile, the shaft resistance under torsional loading may be greater than that under axial loading when the horizontal stress is larger than the vertical stress, but smaller when the horizontal stress is smaller than the vertical stress.Key words: centrifuge modeling, compression test, loading rate, load transfer, pile foundations, tension test, torsional test.
Equivalent granular void ratio for characterization of Singapore's Old Alluvium
Authors: Ni Qing , Dasari G R , Tan T S
Published: June 2006

Characterization of the Old Alluvium (OA) Formation in Singapore is difficult due to its natural heterogeneity. The OA formation was deposited by a braided river system, and it exhibits a wide range of engineering properties. Its strength and stiffness at a given depth, within a few metres distance horizontally, may differ by an order of magnitude, and this cannot be explained by differences in void ratio alone. The formation consists of sand, silt, and clay particles in varying proportions with no consistent relation with depth. Since the majority of OA is sand mixed with fines (silt and clay), the concept of granular void ratio, which treats silt and clay particles as void, was first introduced to try to characterize the formation. Though the concept of the granular void ratio was more useful than that of the void ratio, it could not take into consideration the different contributions that nonplastic silt fines and plastic clay fines make to the shear strength and thus was found to be inappropriate for a natural soil such as OA. To deal with this problem, the relative contribution of different kinds of fines is incorporated through the concept of equivalent granular void ratio. The merit of equivalent granular void ratio for the characterization of mixed soil formations is demonstrated in this paper through the analysis of results from triaxial tests on in situ OA samples.Key words: natural soil, clayey sand, Singapore Old Alluvium, heterogeneity, granular void ratio.
Structure characteristics and mechanical properties of kaolinite soils. I. Surface charges and structural characterizations
Authors: Wang Y -H , Siu W -K
Published: June 2006

In this study on the surface charges and structural characterization of kaolinite clay, it is found that the highly pH dependent edge charges are important to the interparticle forces and associated fabric formations. When the pH is below the isoelectrical point of the edge surfaces, IEPedge, the Coulombian attraction between faces and edges dominates, which favors the formation of an opened edge-to-face (EF) association and a higher final sediment volume. At pH > IEPedge, the double-layer repulsion prevails at all surfaces to result in a deflocculated and dispersed fabric, which tends to form denser soil packing in the sediment. Increasing the ionic strength (with NaCl as the electrolyte) leads to the opposite behavior in clay suspensions below and above the IEPedge: the degree of fabric flocculation and the final sediment volume decrease with an increased ionic strength at pH < IEPedge but increase at pH > IEPedge. The measured pore-size distribution reveals a distinct dual-porosity characteristic in the pH 4 with salts (0.15 mol/L NaCl) specimen: it consists of inter-aggregate spaces (~1.10 µm) and intra-aggregate pores (~0.30 µm). Soils with a higher degree of EF flocculation due to the prevailing Coulombian or van der Waals attraction can render a higher liquid limit.Key words: pH, fabric associations, isoelectrical point, dual porosity, interparticle forces, liquid limit.
Structure characteristics and mechanical properties of kaolinite soils. II. Effects of structure on mechanical properties
Authors: Wang Y -H , Siu W -K
Published: June 2006

This paper reports the effects of structure on the mechanical responses of kaolinite with known and controlled fabric associations. The dynamic properties and strength were assessed by resonant column tests and undrained triaxial compression tests, respectively. The experimental results demonstrate that interparticle forces and associated fabric arrangements influence the volumetric change under isotropic compression. Soils with different structures have individual consolidation lines, and the merging trend is not readily seen under an isotropic confinement up to 250 kPa. The dynamic properties of kaolinite were found to be intimately related to the soil structure. Stronger interparticle forces or higher degrees of flocculated structure lead to a greater small-strain shear modulus, Gmax, and a lower associated damping ratio, Dmin. The soil structure has no apparent influence on the critical-state friction angle (ϕ′c= 27.5°), which suggests that the critical stress ratio does not depend on interparticle forces. The undrained shear strength of kaolinite is controlled by its initial packing density rather than by any interparticle attractive forces, and yet the influence of the structure on the effective stress path is obvious.Key words: interparticle forces, shear modulus, damping ratio, stressstrain behavior, undrained shear strength, critical state.
Effect of weathering on the compressibility and shear strength of a natural clay
Authors: Gullà Giovanni , Mandaglio Maria Clorinda , Moraci Nicola
Published: June 2006

In situ, seasonal changes expose soils to frequent wettingdryingfreezingthawing cycles. Such processes can favour and trigger shallow instabilities controlled by the weathering process. This paper presents an experimental study carried out to investigate the effects of the weathering process, caused by the wettingdryingfreezingthawing cycles, on the compressibility and shear strength of a natural clay. Several specimens were trimmed from block samples of overconsolidated clays taken from a slope in south Calabria, Italy. Specimens were subjected to wettingdryingfreezingthawing cycles of different durations and then tested with standard equipment (oedometer and direct shear). Test results show that the wettingdryingfreezingthawing cycles caused a change in the initial microstructure that produced a decrease in the compression index and an increase in the swelling index. Moreover, the direct shear test results show a decrease in the peak shear strength and demonstrate that a larger reduction occurs in the first month of weathering cycles. The intense cycles performed in the laboratory produced a decay of compressibility and a shear strength approaching reconstituted values. The conclusions are important when choosing the shear strength parameters required when studying shallow landsliding in clay slopes.Key words: weathered clay, structure, cycle of degradation, shallow instability.
Large herbivores control the invasive potential of nonnative Austrian black pine in a mixed deciduous Mediterranean forest
Authors: Chauchard Sandrine , Pille Gaëlle , Carcaillet Christopher
Published: June 2006

The invasive potential of the nonnative Austrian black pine (Pinus nigra subsp. nigra Arn.) was analyzed in a 100-year-old Mediterranean mixed deciduous forest in the Massane Nature Reserve, eastern Pyrenees (France). The reserve holds approximately 120150 semiferal cattle (Bos taurus L.) that browse and trample the woody regeneration. Tree age structure was assessed by dendrochronology to reconstruct the pine population dynamics in grazed and nongrazed (fenced in 1954) portions of the forested reserve. The age structure of the pine population regenerating before 1960 was similar between the inside and outside of the enclosed reserve area. Since 1960, pine recruitment has occurred only in the nongrazed area. The diameter variability with age changed since the 19th century. For pines less than 20 years old, the diameter variability is low, whereas it is very high for individuals older than 100 years. Diverse forest structural changes (composition, canopy height, density, etc.) likely explain the variability in diameter at a given age. Cattle do not appear to affect tree growth as it is similar inside and outside the fenced area, but they control the regeneration of nonnative Austrian black pines, which can spread in the absence of cattle. If nonnative black pine poses a risk for forest conservation, large herbivores may play a useful role in maintaining this species at low abundance.
Comparing methods of reconstructing fire history using fire scars in a southwestern United States ponderosa pine forest
Authors: Van Horne Megan L , Fulé Peter Z
Published: June 2006

Fire scars have been used to understand the historical role of fire in ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) ecosystems, but sampling methods and interpretation of results have been criticized for being statistically invalid and biased and for leading to exaggerated estimates of fire frequency. We compared "targeted" sampling, random sampling, and grid-based sampling to a census of all 1479 fire-scarred trees in a 1 km2 study site in northern Arizona. Of these trees, 1246 were sufficiently intact to collect cross-sections; of these, 648 had fire scars that could be cross-dated to the year of occurrence in the 200-year analysis period. Given a sufficient sample size (approximately n ≥ 50), we concluded that all tested sampling methods resulted in accurate estimates of the census fire frequency, with mean fire intervals within 1 year of the census mean. We also assessed three analytical techniques: (1) fire intervals from individual trees, (2) the interval between the tree origin and the first scar, and (3) proportional filtering. "Bracketing" fire regime statistics to account for purported uncertainty associated with targeted sampling was not useful. Quantifying differences in sampling approaches cannot resolve all the limitations of fire-scar methods, but does strengthen interpretation of these data.
Predicting survival of lodgepole pine stands infected with western gall rust
Authors: Wolken J M , Blenis P V , Duncan I
Published: June 2006

The probability of lodgepole pine (Pinus contorta Dougl. ex Loud.) having main-stem galls caused by western gall rust, Endocronartium harknessii (J.P. Moore) Y. Hiratsuka, surviving to rotation is unknown. To evaluate survival, 400 galled trees with at least one stem gall and 400 trees without stem galls were measured in 1992 in two precommercially thinned stands approximately 20 years old. The survival of trees was assessed in 2003. Nonlinear regression using iteratively reweighted least squares was employed to estimate the survival of galled trees as a function of the proportion of the main stem encircled by galls. Galls encircling >79% and >91% of the stem in the two stands increased the risk of mortality relative to non-galled trees, with the risk increasing steeply with percent gall encirclement; smaller stem galls did not cause tree mortality. The 11-year pattern of survival of galled trees was similar for infections that occurred on the main stem and those that had reached the stem from a nearby branch infection. Based on an earlier model of gall expansion, 38%–43% of stem-galled trees would be expected to survive until age 80. Scribing of stem galls to prevent their expansion does not appear to be a feasible management strategy.
Using bioeconomic models to assess research priorities: a case study on afforestation as a carbon sequestration tool
Authors: McKenney Daniel W , Yemshanov Denys , Fox Glenn , Ramlal Elizabeth
Published: June 2006

We have developed a spatial cost–benefit afforestation model that includes the tracking of five carbon pools. In this application we represent three possible afforestation strategies that could be implemented in Canada using plantations of hybrid poplar, hardwoods, and softwoods with average expected growth rates of 12–14, 5–7, and 5–7 m3· ha–1·year–1respectively. The model provides spatially explicit insights into the cost effectiveness of afforestation as a carbon sequestration tool. Here we develop an elasticity metric and experiment to assess model sensitivity and use the results to make recommendations about research priorities. The most important biological variables across all scenarios include site suitability, which is related to refining the spatial estimates of potential yields, biomass to carbon ratios, and wood density. The most important economic variables include refinement and lowering of establishment costs and agricultural opportunity costs. Parameters that have a low impact on the break-even carbon price, suggesting refinements in knowledge in these areas would be relatively less beneficial, include decay rates for forest products, stand senescence age (the age when stand mortality reaches its maximum), bioenergy and pulpwood prices, and mean residual time for leaf litter. Less importance was also placed on the proportions of forest products in the total harvest and refining a fossil fuel substitution coefficient.
The role of epiphytes in rainfall interception by forests in the Pacific Northwest. I. Laboratory measurements of water storage
Authors: Pypker Thomas G , Unsworth Michael H , Bond Barbara J
Published: June 2006

Old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests frequently contain large populations of epiphytic lichens and bryophytes. To determine the effect these epiphytes have on canopy hydrology we measured the maximum water fraction (f(x)max; maximum mass of internal and external water stored by an epiphyte divided by its tissue dry mass) of common lichens, bryophytes, and dead branches in the laboratory and the water storage and interception efficiency (pi) (the rainfall stored on a branch divided by the rainfall intercepted by the branch) of whole epiphyte-laden branches under a rainfall simulator at three intensities (11.3, 16.1, and 39.8 mm·h1). The f(x)max values for epiphytic fruticose lichens, foliose lichens, and bryophytes were 2.2 ± 0.4, 3.4 ± 0.6, and 10.0 ± 0.5, respectively. The water stored by an epiphyte-laden branch during and after exposure to simulated rainfall could be predicted if the biomass of epiphytic lichens and bryophytes on the branch was known (R2 = 0.8, p value < 0.0001). For all three rainfall intensities, the branches required >6 mm of rainfall to saturate. Values of pi averaged between 0.5 and 0.7 after 2 mm of rainfall and did not differ among the three intensities (all p values > 0.05). We conclude that epiphytes increase the canopy water storage of a typical old growth Douglas-fir forest by >1.3 mm.
Effects of forest roads on the growth of adjacent lodgepole pine trees
Authors: Bowering Michael , LeMay Valerie , Marshall Peter
Published: June 2006

The effects of roads on growth of adjacent lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees were studied in an area near Williams Lake, British Columbia. Plots were established in a range of stand ages, site qualities, stand densities (stems/ha), stand basal areas (m2/ha), edge aspects, and adjacent road widths. Plots were divided into five zones beginning at the road edge: 0–5 m (zone 1), 5–10 m, 10–20 m, 20–30 m, and 30–40 m (zone 5) from the edge. When the 5 years prior to road establishment were used to scale growth rates, relative tree basal growth rates for zone 1 differed significantly from those for the other zones, with zone 1 rates being 32.1% higher, on average, for 3 to 15 years after the road opening was established. Fewer dead standing trees were found nearest the road edge. Tree bole shapes at breast height were not significantly different among zones, and no significant increases in average basal area per tree or in average height were found. On average, zone 1 had a 31.3% greater stand basal area than zone 5. For a 23.4 m wide road, the increased stand basal area translates to 3.13 m (2 × 31.3% × 5 m for zone 1), or 13.4% recovery of timber losses, if both sides of the road were similarly impacted. This estimate can be improved by using stand basal area to reduce variability.
Landscape- and age-based factors affecting fungal colonization of conifer seedling roots at the alpine tree line
Authors: Germino Matthew J , Hasselquist Niles J , McGonigle Terence , Smith William K , Sheridan Peter P
Published: June 2006

Survival of seedlings is a demographic bottleneck for tree populations in alpine tree-line ecotones (ATE) and may play a pivotal role in determining the elevation of timberlines and tree lines. We evaluated (1) fungal colonization of root surfaces of natural seedlings of Picea engelmannii Parry ex Engelm. and Abies lasiocarpa (Hook.) Nutt. in an ATE, (2) the relative importance of soil versus microclimate variation to differences in colonization in the ATE, determined using a reciprocal soil transplant experiment, and (3) ecophysiological responses of seedlings to natural and experimental variation in colonization. Many root systems lacked ectomycorrhizae but had extensive quantities of white mycelium attached to root surfaces. This mycelium was composed of a group of species referred to as the "alpine white complex" (AWC), and included Mortierella parvispora Linneman, Trichoderma viride Pers.:Fr., and a basidiomycete. Nearly all seedlings that survived beyond the first year of growth were colonized by AWC, whereas <10% of emergent seedlings had AWC where they commonly do not survive, in microsites distant from trees. No relationships of AWC and microclimate, photosynthesis, or water relations of seedlings were detected, and low colonization levels likely resulted from scarcity of AWC in ATE soils. Determining if and how AWC or emergent conifer seedlings benefit from their symbiosis in ATEs will require further inquiry.
The effects of partial cutting on the Rose-breasted Grosbeak: abundance, food availability, and nest survival
Authors: Smith Lyndsay A , Burke Dawn M , Nol Erica , Elliott Ken A
Published: June 2006

Periodic partial harvesting of trees is an important economic activity within the highly fragmented woodlands of southern Ontario. We studied the population density, age structure, food abundance, productivity, and nest survival of Rose-breasted Grosbeaks (Pheucticus ludovicianus) nesting in 35 deciduous woodlots with varying intensities of harvest. Heavily cut woodlots contained higher densities of territorial males and greater abundances of fruit-bearing shrubs compared with standard cut and reference sites (uncut for >13 years). Results based on insect sampling were mixed, depending on the sampling technique and sample date. All treatments were demographic sinks, with populations in this landscape showing annual declines of 19%24%. Though the proportion of parasitized nests tended to be higher in heavily cut sites, harvesting had little effect on nest survival, nest initiation dates, clutch size, age structure, or the number of young fledged from a successful nest. Our results indicate that within the fragmented woodlots of southern Ontario, partial harvesting does not further degrade breeding habitat for Rose-breasted Grosbeaks. However, further research is needed to determine the underlying causes of population declines.
Population structure and parentage analysis of black poplar along the Morava River
Authors: Pospíšková Markéta , Šálková Ivana
Published: June 2006

Twelve nuclear microsatellite markers were used to assess the population genetic structure of the riparian pioneer tree species Populus nigra L. along the Morava River in the Czech Republic. Parentage analysis of 30 seedlings was performed to examine the extent of hybridization between P. nigra and introduced hybrid poplars and to determine the distances of pollen and seed movement. Additionally, spatial genetic structure was analysed and gene dispersal was estimated indirectly. In spite of the limited size of our studied population (65 adult trees), the apparent overall genetic diversity was high (expected heterozygosity He = 0.82) and comparable to the known diversity of P. nigra in southern Europe, where its glacial refugia were located. Introgression of Populus deltoides Bartr. ex Marsh. genes to P. nigra was confirmed, since 13% of tested seedlings descended from a Populus ×canadensis Moench female. The results of parentage analysis showed that a low percentage (20%) of offspring originated from parents located outside the study site. Dispersal distances for pollen and seeds movement ranged from 10 to 230 m and from 163 to 370 m, respectively. The study revealed significant spatial genetic structure (regression slope 0.0158), which was probably caused by limited gene flow.
Fire history of a naturally fragmented landscape in central Oregon
Authors: Arabas Karen B , Hadley Keith S , Larson Evan R
Published: June 2006

We examined the fire history of 11 forest isolates surrounded by lava flows (kipukas) in central Oregon to determine historical differences in fire regimes between kipukas and the surrounding forest, and the role of spatial and environmental variables in fire occurrence. Tree-ring analysis and statistical comparisons show that historical agency records underestimate the number of fires based on the incidence of fire scars. Fires occurred more frequently on kipukas, were typically smaller, and were predominantly lightning-initiated. Except for three widespread fires, fires on kipukas and in the surrounding forest were largely asynchronous. The mean fire-return interval (MFRI) in the surrounding forest decreased following Euro-American settlement and increased on the kipukas with spot-fire removal. This suggests either that forest management and fire exclusion in the surrounding forest decreased fire spread to the kipukas, or that most fires originated on the kipukas. MFRI correlates strongly with distance to the nearest kipuka and a distance-weighted isolation index. The number of fires correlates with elevation change and distance to the nearest kipuka. Fire in naturally fragmented landscapes is influenced by the spatial arrangement of patches, environmental conditions, and human activities. Reconstructing fire histories from forest isolates in the context of their mainland counterparts may have methodological advantages and theoretical implications for forested landscapes characterized by human-imposed insularity.
Compatible taper function for Scots pine plantations in northwestern Spain
Authors: Diéguez-Aranda Ulises , Castedo-Dorado Fernando , Álvarez-González Juan Gabriel , Rojo Alberto
Published: June 2006

A compatible system for estimation of individual tree volume was developed for Scots pine (Pinus sylvestris L.) in northwestern Spain. The system comprises a merchantable volume equation, a total volume equation, and a taper function. The use of the volume equation allows rapid estimation of tree volume, and stand volume by summing individual tree volumes, which is equal to the volume obtained by integrating the taper equation. The volume equation is very easy to use and is therefore preferred when classification of the products by merchantable sizes is not required. Data from 228 destructively sampled trees were used for model development. Fourteen compatible volume equations were evaluated, 13 of these equations were taken from the available literature, and the other was developed in the present study. A modified second-order continuous autoregressive error structure was used to correct the autocorrelation of the hierarchical data used. The model developed by Fang et al. (Z. Fang, B.E. Borders, and R.L. Bailey. 2000. For. Sci. 46: 112) best described the data. There model is therefore recommended for the estimation of diameter at a specific height, merchantable volume, and total volume of Scots pine stems in the area of study.
Changes in bird communities throughout succession following fire and harvest in boreal forests of western North America: literature review and meta-analyses
Authors: Schieck Jim , Song Samantha J
Published: June 2006

Within boreal forests of western North America, the dominant large-scale natural disturbance is wildfire. Thus, harvesting that is as similar as possible to fire is expected to best maintain natural bird communities. We reviewed studies of birds (mainly grouse, woodpeckers, and songbirds) from boreal forests of western North America and conducted meta-analyses to compare the similarity of bird communities occurring postfire versus postharvest. We compared the bird communities at five seral stages and also summarized the effects of retaining large live trees at harvest. Bird communities immediately postharvest differed greatly from those postfire. Differences between disturbance types disappeared as the forest regenerated, and both disturbance types became dominated by relatively few bird species in 31- to 75-year-old forests. During the period 76125 years postdisturbance, old-forest birds became present and bird species richness increased. However, the trajectory of forest succession during this period influenced bird communities; old aspen (Populus tremuloides Michx.), old mixedwood, and old white spruce (Picea glauca Moench (Voss)) forests all had different bird communities. Retention of large live trees in cutblocks resulted in their use by many old-forest birds, but results were not consistent among studies. Although most bird species had clear peaks in abundance in a specific forest type, no species with more than five detections was limited to a single forest type.
Bayesian inference for normal multiple-trait individual-tree models with missing records via full conjugate Gibbs
Authors: Cappa Eduardo P , Cantet Rodolfo JC
Published: June 2006

In forest genetics, restricted maximum likelihood (REML) estimation of (co)variance components from normal multiple-trait individual-tree models is affected by the absence of observations in any trait and individual. Missing records affect the form of the distribution of REML estimates of genetics parameters, or of functions of them, and the estimating equations are computationally involved when several traits are analysed. An alternative to REML estimation is a fully Bayesian approach through Markov chain Monte Carlo. The present research describes the use of the full conjugate Gibbs algorithm proposed by Cantet et al. (R.J.C. Cantet, A.N. Birchmeier, and J.P. Steibel. 2004. Genet. Sel. Evol. 36: 4964) to estimate (co)variance components in multiple-trait individual-tree models. This algorithm converges faster to the marginal posterior densities of the parameters than regular data augmentation from multivariate normal data with missing records. An expression to calculate the deviance information criterion for the selection of linear parameters in normal multiple-trait models is also given. The developments are illustrated by means of data from different crosses of two species of Pinus.
Development of a basal area growth system for maritime pine in northwestern Spain using the generalized algebraic difference approach
Authors: Anta Marcos Barrio , Dorado Fernando Castedo , Diéguez-Aranda Ulises , Álvarez González Juan G , Parresol Bernard R , Soalleiro Roque Rodríguez
Published: June 2006

A basal area growth system for single-species, even-aged maritime pine (Pinus pinaster Ait.) stands in Galicia (northwestern Spain) was developed from data of 212 plots measured between one and four times. Six dynamic equations were considered for analysis, and both numerical and graphical methods were used to compare alternative models. The double cross-validation approach was used to assess the predictive ability of the models. The data were best described by a dynamic equation derived from the Korf growth function using the generalized algebraic difference approach (GADA) by considering two parameters to be site specific. The equation was fitted in one stage using the base-age-invariant dummy variables method. In addition, the system incorporates a function for predicting initial stand basal area, in which the site-related variable was expressed as a power function of site index. This function can be used to establish the starting point for the projection equation when no inventory data are available. The two equations are compatible. The effect of thinning on basal area growth was examined; the results showed that there was no need to use a different equation to reliably predict postthinning basal area development. The nonlinear extra sum of squares method indicated differences in the model parameters for the two ecoregions (coastal and interior) defined for this species in the area of study.
Using multispectral satellite imagery to estimate leaf area and response to silvicultural treatments in loblolly pine stands
Authors: Flores Francisco J , Allen H Lee , Cheshire Heather M , Davis Jerry M , Fuentes Montserrat , Kelting Daniel
Published: June 2006

The relationship between leaf area index (LAI) of loblolly pine plantations and the broadband simple ratio (SR) vegetation index calculated from Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data was examined. An equation was derived to estimate LAI from readily available Landsat 7 ETM+ data. The equation developed to predict LAI with Landsat 7 ETM+ data was tested with ground LAI measurements taken in 12 plots. The root mean square error of prediction was 0.29, an error of approximately 14% in prediction. The ability of Landsat 7 ETM+ data to consistently estimate SR over time was tested using two scenes acquired on different dates during the winter (December to early March). Comparison between the two images on a pixel-by-pixel basis showed that approximately 96% of the pixels had a difference of <0.5 units of SR (approximately 0.3 units of LAI). When the comparison was made on a stand-by-stand basis (average stand SR), a maximum difference of 0.2 units of SR (approximately 0.12 units of LAI) was found. These results suggest that stand LAI of loblolly pine plantations can be accurately estimated from readily available remote sensing data and provide an opportunity to apply the findings from ecophysiological studies in field plots to forest management decisions at an operational scale.
The impact of differential success of somatic embryogenesis on the outcome of clonal forestry programs. I. Initial comparison under multitrait selection
Authors: Lstibůrek Milan , Mullin TJ (Tim) , El-Kassaby Yousry A
Published: June 2006

A breeding program where clones or clone mixtures are deployed through somatic embryogenesis of superior genotypes produced from elite-parent crosses was evaluated by simulation. A recurrent-selection scheme for general combining ability was considered with a breeding population size of 100 individuals. The population was assortatively pair-crossed with offspring cloned in a progeny test to facilitate forward selection of the next generation. Apart from crosses for the population advancement, "elite" crosses were made among 10 top-ranking individuals in each generation. These crosses differed in their propensity to produce somatic embryos (defined as induction success rate); the impact of this variable propensity on genetic response for two traits in selected 10-clone deployment mixtures was evaluated. The two traits considered in this study can be regarded as "productivity" and "quality". The results revealed that variation in success of clonal propagation does not necessarily lead to a reduction in potential genetic gains from selected clonal mixtures. This can be explained by the relatively small variation that exists among elite crosses, as opposed to large within-family variation. This large within-family variation provides ample potential for selecting superior offspring genotypes, even though they may have not originated from crosses among the very best of the elite parents. This conclusion holds for a range of heritability, correlations between traits, and their relative economic importance.
Comparing productivity of pure and mixed Douglas-fir and western hemlock plantations in the Pacific Northwest
Authors: Amoroso M M , Turnblom E C
Published: June 2006

We studied pure and 50/50 mixtures of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) plantations to compare attained total yields between mixed-species stands as opposed to monocultures of equal densities. Whether overall stand density influences this outcome has not been adequately investigated, and to address this we included three density levels (494, 1111, and 1729 trees/ha) in the analysis. At age 12, as components of the mixed stands, Douglas-fir exhibited greater height, diameter, and individual-tree volume than western hemlock at all densities. At 494 and 1111 trees/ha the monocultures had a higher volume per hectare than the mixed stand, but at 1729 trees/ha the mixed stand appeared to be just as productive as the pure stands. The increase in productivity by the mixture at high densities seems to have resulted from the partial stratification observed and most likely also from better use of the site resources. Because of this, less interspecific competition was probably experienced in the mixed stand than intraspecific competition in the pure stands. This study shows the important role density plays in the productivity of mixed stands and thus in comparing mixed and pure stands.
Price linkages in the North American softwood lumber market
Authors: Baek Jungho
Published: June 2006

This paper examines structural changes and the dynamics of price relationships in the United States (US), British Columbia, Quebec, and Ontario lumber markets. With monthly price series from 1981 to 2002, I used Perron's method to identify structural shifts and the Johansen cointegration analysis and vector-error correction model to determine both short- and long-run price relationships. I found that because of restrictions on federal timber harvests in the Pacific Northwest, price instability experienced in 1992 has caused structural shifts for the US and Canadian lumber prices. I also found that the North American lumber market is indeed integrated, with the US price significantly affecting Canadian prices in both the short and long run. This further indicates that the US market plays a dominant role in price setting in the North American lumber market, as Canadian prices respond to the US price change, but the reverse situation does not occur.
Does aerial spraying ofBacillus thuringiensissubsp.kurstaki(Btk) pose a risk to nontarget soil microarthropods?
Authors: Addison Janet A , Otvos Imre S , Battigelli Jeffrey P , Conder Nicholas
Published: June 2006

This field study was carried out to investigate whether application of an aerial spray containing Bacillus thuringiensis subsp. kurstaki (Btk) to control the western spruce budworm (Choristoneura occidentalis Freeman, 1967) had any measurable effects on aspects of the abundance, distribution, diversity, and feeding behaviour of nontarget soil microarthropods. Although total abundance and species richness (N0) of Collembola declined significantly in samples taken 3 weeks after spraying, this decline occurred in the control plots as well as in plots sprayed with Btk. Values for the diversity indices N1and N2were not affected by the treatment. Correspondence analysis did not identify changes in collembolan communities following the aerial application of Btk. Total abundance of mites and populations of different suborders (Prostigmata, Mesostigmata, and Oribatida) were not significantly affected by application of Btk, or by the time of year that the samples were collected. There was no evidence of a selective reduction in the surface-dwelling portions of the collembolan and mite communities following exposure to Btk. Similarly, the experimental spray did not cause a decline in the abundance of the guild of Collembola known to feed on bacteria, and the proportion of bacteria in the diet of these Collembola following application of Btk was also unchanged.
Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation
Authors: Eschtruth Anne K , Cleavitt Natalie L , Battles John J , Evans Richard A , Fahey Timothy J
Published: June 2006

Hemlock woolly adelgid (HWA; Adelges tsugae Annand) infestations have resulted in the continuing decline of eastern hemlock (Tsuga canadensis (L.) Carrière) throughout much of the eastern United States. In 1994 and 2003, we quantified the vegetation composition and structure of two hemlock ravines in the Delaware Water Gap National Recreation Area. This is the first study to use pre-adelgid disturbance data, annual monitoring of infestation severity, and annual records of hemlock health to assess forest response to HWA infestation. In 2003, 25% of monitored hemlock trees were either dead or in severe decline. Measures of hemlock decline (crown vigor, transparency, density, and dieback) were correlated with HWA infestation severity and changes in light availability over the study period. Average percent total transmitted radiation more than doubled at these sites from 5.0% in 1994 to 11.7% in 2003. The total percent cover of vascular plants increased from 3.1% in 1994 to 11.3% in 2003. Species richness increased significantly, and more species were gained (53) than lost (19) from both ravine floras over the 9-year study period. Though exotic invasive plants were absent from these ravines in 1994, our 2003 resurvey found invasive plants in 35% of the permanent vegetation plots.
MEMBERSHIP AND FINITENESS PROBLEMS FOR RATIONAL SETS OF REGULAR LANGUAGES
Authors: AFONIN SERGEY , KHAZOVA ELENA
Published: June 2006

Let Σ be a finite alphabet. A set [Formula: see text] of regular languages over Σ is called rational if there exists a finite set [Formula: see text] of regular languages over Σ such that [Formula: see text] is a rational subset of the finitely generated semigroup [Formula: see text] with [Formula: see text] as the set of generators and language concatenation as a product. We prove that for any rational set [Formula: see text] and any regular language R ⊆ Σ* it is decidable (1) whether [Formula: see text] or not, and (2) whether [Formula: see text] is finite or not. Possible applications to semistructured databases query processing are discussed.
A KLEENE THEOREM FOR LANGUAGES OF WORDS INDEXED BY LINEAR ORDERINGS
Authors: BÈS ALEXIS , CARTON OLIVIER
Published: June 2006

In a preceding paper, Bruyère and Carton introduced automata, as well as rational expressions, which allow to deal with words indexed by linear orderings. A Kleene-like theorem was proved for words indexed by countable scattered linear orderings. In this paper we extend this result to languages of words indexed by all linear orderings.
COMBINATORIAL PROPERTIES OF STURMIAN PALINDROMES
Authors: DE LUCA ALDO , DE LUCA ALESSANDRO
Published: June 2006

We study some structural and combinatorial properties of Sturmian palindromes, i.e., palindromic finite factors of Sturmian words. In particular, we give a formula which permits to compute in an exact way the number of Sturmian palindromes of any length. Moreover, an interesting characterization of Sturmian palindromes is obtained.
UNAMBIGUOUS MORPHIC IMAGES OF STRINGS
Authors: FREYDENBERGER DOMINIK D. , REIDENBACH DANIEL , SCHNEIDER JOHANNES C.
Published: June 2006

We study a fundamental combinatorial problem on morphisms in free semigroups: With regard to any string α over some alphabet we ask for the existence of a morphism σ such that σ(α) is unambiguous, i.e. there is no morphism τ with τ(i) ≠ σ(i) for some symbol i in α and, nevertheless, τ(α) = σ(α). As a consequence of its elementary nature, this question shows a variety of connections to those topics in discrete mathematics which are based on finite strings and morphisms such as pattern languages, equality sets and, thus, the Post Correspondence Problem.

Our studies demonstrate that the existence of unambiguous morphic images essentially depends on the structure of α: We introduce a partition of the set of all finite strings into those that are decomposable (referred to as prolix) in a particular manner and those that are indecomposable (called succinct). This partition, that is also known to be of major importance for the research on pattern languages and on finite fixed points of morphisms, allows to formulate our main result according to which a string α can be mapped by an injective morphism onto an unambiguous image if and only if α is succinct.