bluuebunny/crossref_metadata_2025 huggingface dataset:
An Approach to the Problem of Progressive Failure
Authors: Lo K. Y.
Published: May 2008

In this paper, the different factors that contribute to progressive failure are briefly reviewed, and the necessary conditions for its occurrence delineated.Experiments on specimens trimmed from block samples of several clays were performed to study the post-peak stress deformation behavior. It is shown that the stiffness of the testing system has an important influence on the post-peak characteristics. A method of obtaining the effective 'residual' angle of friction from drained triaxial tests is developed.Because of the localization of deformation in the failure zone, both in the laboratory and in the field, the laboratory nominal post-peak stress–strain relationship cannot be directly applied to field problems. Based on laboratory and field observations on the mechanism of deformation, the ratio of the shear modulus of the failure zone to that of the pre-peak range is proposed as a deformation parameter to be used in analysis of progressive failure.A simplified theory for the solution of the problem of progressive failure is then developed, and a case record of a first time slide in sensitive Leda clay is analyzed to illustrate the practical application of the approach.
Surface Settlement of a Deep Elastic Stratum Whose Modulus Increases Linearly with Depth
Authors: Brown P. T. , Gibson R. E.
Published: May 2008

An examination has been made of the behavior of a half space of elastic material of constant Poisson's ratio, whose Young's modulus increases linearly with depth, and which is subject to a strip or circle of uniform load. Poisson's ratio was considered in the range zero to one-half, and the surface modulus ranged from zero to the value corresponding to a homogeneous material.Numerical values are presented for vertical surface displacement due to a load uniformly distributed over a circular area for Poisson's ratio = 1/2, 1/3 and 0, and for a wide range of inhomogeneity.
The Determination of Young's Modulus from the Direct Shear Test
Authors: Noonan D. K. J. , Nixon J. F.
Published: May 2008

A method is developed for determining Young's Modulus from a direct shear test. The finite element method is employed to compute stresses in a sample of rock subjected to direct shear. From the results of the analysis, the relationship between the shear load, horizontal displacement and the Young's Modulus is established for different sample geometries. The use of the solution is illustrated. Since direct shear tests are often used for strength testing the necessity for conducting alternative tests to determine the deformability characteristics of a rock mass is reduced.
Some Observations at le Coteau Landslide, Gatineau, Quebec
Authors: Eden W. J.
Published: May 2008

In April 1971, landslide activity developed in a 100-ft (30.5-m) high clay slope in a housing development. This note describes the landslide and discusses the pore-water pressure measurements made at the site.
Pile load tests in saline permafrost at Clyde River, Northwest Territories
Authors: Nixon J. F. (Derick)
Published: May 2008

Significant salt content in the pore phase of permafrost causes dramatic reduction in strength or bearing capacity. Previous experience with laboratory tests and limited field testing discussed in the Soviet literature indicate that creep rates can be accelerated many times and foundation bearing capacities reduced by factors of 2–3 if pore water salinities exceed 10–20 ppt. At Clyde River on the northwest coast of Baffin Island, pile load tests were carried out in 1982. A combination of high salinities and significant excess ice contents at some locations suggested that a limited program of pile load testing should be carried out to confirm or modify the initial pile loadings based on previously published material. No fully documented case history was available to support initial pile design loads.Three piles were subjected to loads of five different magnitudes for different durations. Creep settlement was initiated and persisted in all cases. Continuous curve fitting was carried out by computer, and the resulting smoothed strain rate plotted with time. The minimum settlement rates were compared with earlier predictions. They were generally somewhat faster than results from previous laboratory saline creep testing combined with theoretical pile design based on creep settlement.The tests highlight the dramatic reductions in foundation bearing capacity and acceleration in pile creep rates that can be expected in permafrost exhibiting significant pore water salinity. A simplified testing procedure suitable for laboratory or field testing is described. Key words: permafrost, saline, piles, load tests, laboratory, field, in situ, capacity, creep, creep rate, salinity test.
Casagrande resistance envelopes for rock and rockfill slopes having circular slip surfaces
Authors: Baikie L. D.
Published: May 2008

A series of Casagrande resistance envelopes are presented for use in the preliminary design and evaluation of uniform rock and rockfill slopes. The influence of tension cracks on the safety factors for such slopes is examined. A comparison is also made between the safety factors obtained using the resistance envelope method and those obtained using published stability charts for rockfill slopes having nonlinear shear strength envelopes. Key words: rock, rockfill, slope, stability, Casagrande resistance envelope, safety factor.
Constant-volume friction angle of granular materials
Authors: Negussey D. , Wijewickreme W. K. D. , Vaid Y. P.
Published: May 2008

The postulate that the constant-volume friction angle [Formula: see text] of a granular material is unique and a function of mineral composition is verified experimentally. Granular materials comprised of particles ranging from minerals to metals are tested in a ring shear apparatus. Test samples are subjected to large shear displacements until a constant lower bound friction angle [Formula: see text] is mobilized. Possible effects of confining pressure, initial packing density, gradation, and particle shape on the value of [Formula: see text] are investigated. Friction angles mobilized in drained shear at the instant of maximum contraction and in undrained shear at phase transformation and steady state are compared with [Formula: see text] values. The experimental results confirm a broader fundamental significance of [Formula: see text] as a material parameter in that it is a consistent minimum drained friction angle equal to friction angles mobilized at phase transformation and steady state in undrained shear. Key words: granular materials, sand, friction angles, constant volume, steady state, phase transformation state, ring shear test.
Prediction of wick drain performance using piezometer cone data
Authors: Robertson P. K. , Campanella R. G. , Brown P. T. , Robinson K. E.
Published: May 2008

The technique of installing prefabricated wick drains is well established in Europe and Japan, but is relatively new to North America. This paper describes the use of piezometer cone data to predict the performance of wick drains in a soft clayey silt in Burnaby, British Columbia. A description of the testing procedures and the theory to calculate the rate of consolidation are briefly presented. The predicted rate of consolidation using the piezometer cone data and the measured performance is compared and discussed; good agreement between the two was found. Key words: wick drains, piezocone, prediction, preload, settlement.
Theoretical bearing capacity of clay under shallow footings: verifying whether it is realistic
Authors: Chapuis Robert P. , Silvestri Vincent , Soulié Michel
Published: May 2008

Traditionally, the bearing capacity and the settlement of footings on clay are determined independently by theoretical analyses: the bearing capacity for short-term conditions and the settlement for long-term conditions. Bearing capacity methods usually assume that the clay has a rigid-plastic behaviour and they neglect prefailure deformations. Conventional settlement methods ignore failure conditions. However, field load tests give load–settlement curves in which it is impossible to dissociate settlement and bearing capacity.This paper examines whether the calculated theoretical qult is realistic. A long-term load–settlement curve can be easily calculated using an oedometric equation. The curve of soed/B versus load is a good approximation of the true long-term settlement curve and can be used to determine whether the (short-term) bearing capacity qu is realistic: if soed/B has a high value for a load smaller than the computed qu, it means that this qu is not a valid evaluation of the bearing capacity, the true value of which remains unknown. To establish when conventional analyses give erroneous bearing capacities four cases are analyzed, encompassing the influence of the compressibility of the clay material and the influence of downward groundwater gradients on the compressibility. The results show that groundwater conditions have a major influence upon the bearing capacity of highly compressible, slightly overconsolidated clays but practically no influence upon the bearing capacity of clays of low compressibility. Key words: shallow foundations, clay, deformability, bearing capacity, settlement.
Effect of sample size on consolidation of a fissured clay
Authors: Garga Vinod K.
Published: May 2008

This paper describes an experimental investigation on the effect of sample size on consolidation characteristics of fissured London Clay. Pore pressure dissipation tests on 38, 100, and 300 mm diameter samples were undertaken in the laboratory. Constant-head in situ permeability tests were conducted in four boreholes at different depths in the clay. Conventional oedometer tests on 76 mm diameter samples recovered from the same depths at which in situ permeability tests were carried out were also undertaken. The results show that both the coefficient of compressibility mv and the coefficient of consolidation determined in the laboratory are not significantly affected by sample size. It is concluded that estimate of in situ coefficient of consolidation can best be made from mv determined in the laboratory, and from in situ permeability measurements. Key words: consolidation, compressibility, fissured clay, permeability, size effect, testing.
Tenth Canadian Geotechnical Colloquium: Recent developments in consolidation of natural clays
Authors: Leroueil Serge
Published: May 2008

A global analysis of the consolidation of natural clays is realized considering the consolidation process to be a combination of the effects of compressibility and of permeability. The compressibility or stress–strain curve followed is strongly influenced, both in the laboratory and in situ, by the strain rate. The self-boring permeameter appears to be an excellent tool for permeability measurement; however, in homogeneous clays direct measurement in the laboratory also gives representive results. The coefficients of consolidation determined graphically strongly underestimate the in situ coefficient. The consolidation must thus be analysed by considering compressibility and permeability parameters measured separately. Key words: consolidation, clay, compressibility, permeability.
Finite element analysis of the stability of a vertical cut using an anisotropic soil model
Authors: Banerjee P. K. , Kumbhojkar A. S. , Yousif N. B.
Published: May 2008

A finite element (FE) analysis of the field test excavation in Welland Clay is performed using an anisotropic soil behavior model. This paper describes the model, FE formulation, and transient effective stress stability analysis, and compares FE results with the field measurements. The analysis reflects the postexcavation decrease in the factor of safety with time and predicts the failure of the slope along the observed failure surface. The parametric study shows that the time to failure is a function of the pore pressure boundary conditions at the excavation surface and affects the transient factor of safety. Key words: constitutive relations, excavations, finite element, plasticity models, pore pressure, soil anisotropy, stability.
Seismic response of long-period sites: lessons from the September 19, 1985, Mexican earthquake
Authors: Finn W. D. Liam , Nichols Andrew M.
Published: May 2008

The implications for seismic design in Canada, of the acceleration data recorded at a number of sites in Mexico City during the September 19, 1985, earthquake, were investigated. The conditions for amplification of low-level incoming ground motions at deep sites were identified, in particular, the critical role of variation in shear modulus with shear strain. The current procedure for determining site-specific ground motions was evaluated and major sources of uncertainty in the results were identified. Criteria for selecting representative input motions for site response studies are recommended based on results of analyses of Mexico City sites. A comparative study of sites in the Fraser Delta area of British Columbia showed that offshore subduction earthquakes should be considered when developing design spectra for deep sites in the delta. Key words: earthquakes, seismic design, ground motions, shear modulus, design spectra.
Profiling of overconsolidation ratio in clays by field vane
Authors: Mayne Paul W. , Mitchell James K.
Published: May 2008

The field vane (FV) has traditionally been utilized to obtain profiles of undrained shear strength in soft to medium clays. After some 40 years of experience with FV results, it has been suggested that empirical correction factors be applied to the FV data to account for the effects of strain rate, anisotropy, and disturbance on measured shear strengths. As an additional use of the device, the FV may be calibrated at each site to develop profiles of overconsolidation ratio (OCR) with depth. A data base of oedometer test results and FV strengths from 96 different clays has been compiled to use as a basis for this calibration. Key words: field vane, undrained strength, clay, overconsolidation ratio, preconsolidation pressure, shear strength, vane shear.
Performance of piles with enlarged bases subject to uplift forces
Authors: Dickin E. A. , Leung C. F.
Published: May 2008

The influence of embedment, base diameter, and backfill density on the uplift behaviour of piles with enlarged bases embedded in sand was investigated in a centrifuge. Comparitive tests on straight-shafted piles are also reported. For piles in dense sand, sensible agreement was found with earlier research on anchor plates and published field data. However, uplift capacities in loose sand were considerably lower than previously observed for anchor plates. A number of theories for anchors considerably overpredict the observed capacity for belled piers in both dense and loose sand, although in the case of dense sand, reasonable values are obtained using an empirical equation derived from centrifuge tests on anchor plates and a finite element based design approach. The normally conservative vertical slip-surface model is alone in providing reasonable agreement with the surprisingly low observations for piles in loose sand. Key words: piles, uplift capacity, centrifuge tests, sand.
Development and use of an electrical resistivity cone for groundwater contamination studies
Authors: Campanella R. G. , Weemees I.
Published: May 2008

The evaluation of groundwater quality has become increasingly important as more industrial waste and solid domestic refuse come into contact with groundwater. One method of detecting contaminated groundwater is by noting the electrical resistivity of the contaminated soil. This method has been applied at the University of British Columbia by the development and use of a new resistivity cone. The resistivity cone consists of four circumferential surface electrodes contained in a separate module behind a 15 cm2 piezocone. The cone has a capability of providing a continuous record of resistivity with depth.Initially, a laboratory testing program was carried out using a simplified probe design to ensure the feasibility of the project. On the basis of favourable laboratory results the module was constructed, calibrated in the laboratory, and then field tested. The paper describes the design and operation of the resistivity cone, theory and laboratory calibration, and test results from three sites in the lower mainland of British Columbia. The results of the testing program provided evidence of the reliability of the instrument and illustrated its application in determining changes in groundwater quality. Factors affecting results and applications of the resistivity cone in contaminant site investigations are discussed. Key words: electrical, resistivity, cone, groundwater, contamination, plumes, mapping, in-situ testing, soil.
Liquefaction and ground failure induced by the 1988 Saguenay, Quebec, earthquake
Authors: Tuttle Martitia , Law K. Tim , Seeber Leonardo , Jacob Klaus
Published: May 2008

Ongoing geological and geotechnical investigations are under way for two sites in Ferland, Quebec, where sand boil deposits, ground fissures, and liquefaction-related damage to homes were documented immediately following the M = 5.9 Saguenay earthquake of November 25, 1988. Both sites are about 26 km from the epicentre. To date, the geological investigation of the sites suggests that (i) liquefaction and ground failure have occurred in this area in the past, (ii) lateral spreading was the principal mode of ground failure in 1988 and in the past, (iii) 1988 and earlier displacements due to lateral spreading were on the order of centimetres, and (iv) topography played an important role in the localization and characterization of ground failure. The geotechnical investigation suggests that (i) liquefaction at these sites is predictable using Seed's method, and (ii) the material that liquefied during the Saguenay earthquake is a gray, siltysand or sandy silt that is about 0.3 m thick and occurs at a depth ranging from 2.5 to 4.5 m below the surface. These preliminary results suggest that the potential for liquefaction and related damage may be higher than previously recognized in the Ferland–Boilleau valley in particular and in the Saguenay area in general. Key words: liquefaction, ground failure, earthquake, geological investigation, geotechnique, silty sand, damage.
Generalized stress-path-dependent soil behaviour with a new hollow cylinder torsional apparatus
Authors: Vaid Y. P. , Sayao A. , Hou Enhuang , Negussey D.
Published: May 2008

A new hollow cylinder torsional shear apparatus is described. The apparatus is suitable for investigating soil behaviour under generalized stress paths, including principal stress rotations, characteristic of earthquake and offshore-wave loadings. A new, more rational assessment of stress nonuniformity across the wall of the hollow cylinder specimen is made, and the "no go" regions of the stress space are delineated that limit stress nonuniformity to acceptable levels. Operation of the apparatus and experimental procedures for tests on reconstituted specimens of sand are described. Typical results of drained tests on loose and dense sand are presented to illustrate the capabilities of the apparatus as a general stress-path loading device and to highlight the stress-path dependence of soil behaviour, in particular, the deformation response to principal stress rotations. Key words: hollow cylinder apparatus, generalized stress paths, principal stress rotation, sand, deformations.
Modelling spatial variability of soil parameters
Authors: Soulié M. , Montes P. , Silvestri V.
Published: May 2008

The purpose of this study is to show that geostatistics can help in finding the structure of the spatial variability of the undrained shear strength within a clay deposit. The site under study, B-6, owes its name to the earth dam that will be constructed on it; the site is located on the shore of the Broadback River in the James Bay area of Quebec. The geostatistical analysis is carried out on the unaltered zone of the B-6 clay; it shows an anisotropic structure for the spatial variability. The knowledge of the structure (variogram) of the undrained shear strength is used in the kriging theory to compute estimations at points of the deposit where experimental measurements are not available. Kriging is also used to identify weak zones within the B-6 clay. The geostatistical analysis of the B-6 clay gives the opportunity to test the capability of the method. Even if the errors of measurements were small, the variogram has permitted detection and correction of a bias that affected a certain number of vane profiles. Key words: clay, geostatistics, undrained shear strength, variogram, measurements errors, kriging.
Quelques propriétés d'une argile sur la « ligne optimale de compactage »
Authors: Cabot Louis , Bihan Jean-Pierre Le
Published: May 2008

This paper deals with the evolution of the texture of the clay during compaction and with the importance of maintaining a close correlation between the degree of compaction and the water content to obtain a sealed fill with a homogeneous texture. The results of laboratory tests show the orderly evolution of some physical and mechanical properties of the compacted clay along this optimal correlation of compaction. Finally, the results of the control tests on the clay of the core of Kompienga dam compacted according to these specifications are presented. Key words : compacted clay, texture, macroporosity, optimal line of compaction, evolution of properties, specifications of compaction.
Whitebark pine and white pine blister rust in the Rocky Mountains of Canada and northern Montana
Authors: Smith Cyndi M. , Wilson Brendan , Rasheed Salman , Walker Robert C. , Carolin Tara , Shepherd Brenda
Published: May 2008

In 2003–2004, we examined 8031 whitebark pine ( Pinus albicaulis Engelm.) trees and 3812 seedling-establishment sites in 170 plots for mortality and incidence of white pine blister rust ( Cronartium ribicola A. Dietr.). We found blister rust in all but four plots (98%), and 57% of all trees assessed for blister rust were either already dead or showed signs of blister rust infection. Mean percentage of trees infected was highest in the southern Canada – United States border area (∼73%), decreasing to a low in the northern region of Banff National Park, Alberta (∼16%), and then rising (∼60%) in the northern end of the study area in Jasper National Park, Alberta. Stands with higher infection, mortality, and canopy kill of trees and higher presence of rust on seedlings tended to be located on the western side of the Continental Divide. In the eight stands in Waterton Lakes National Park, Alberta, that had been previously assessed in 1996, infection levels increased from 43% to 71%, and mortality increased from 26% to 61%, whereas no change was apparent in Glacier National Park, Montana, stands. The impacts of high mortality and infection levels, high crown kill, and reduced regeneration potential, suggest that the long-term persistence of whitebark pine in the southern part of the study area is in jeopardy.
The effect of age and sample position on eucalypt tree-ring width series
Authors: Brookhouse Matthew , Brack Cris
Published: May 2008

In this study, we examine within-tree variance in proportionate tree-ring width (prw) and correlation between radii (rwt), samples (rbh), and trees (rbt) in four eucalypt species common throughout eastern Victoria, Australia. In all species and sites studied, rwt and rbh differ significantly between cambial-age and sample-height classes. Differences between rwt and rbh are nonsignificant between tree-age or radial-azimuth classes. Significant differences in prw exist between cambial-age, tree-age, and sample-height classes and between radii on different compass bearings. Whilst differences in rwt and rbh between cambial-age classes appears to be the result of variation in mechanical demands with increasing stem size, stem deformation may account for differences between sample-height classes. Variation in prw appears to be due to stem geometry, stem eccentricities associated with root buttressing, and tree-age dependent variation in the rate of radial growth. No significant differences in rbt exist between sample-height classes. Analysis of the expressed population signal statistic indicates that site-level and species differences are far more significant than sample position on variance within tree-ring width series collected from eucalypts. We discuss the implications of the current work for eucalypt dendroclimatology.
Beyond “fire temperatures”: calibrating thermocouple probes and modeling their response to surface fires in hardwood fuels
Authors: Bova Anthony S. , Dickinson Matthew B.
Published: May 2008

The maximum temperatures of thermocouples, temperature-sensitive paints, and calorimeters exposed to flames in wildland fires are often called “fire temperatures” but are determined as much by the properties and deployment of the measurement devices as by the fires themselves. Rather than report device temperatures that are not generally comparable among studies, we show that maximum and time-integrated temperatures of relatively thick (4.8 mm diameter) type-K thermocouple probes (TCPs) can be calibrated to estimate fuel consumption and fire line intensity in surface fires. Although reporting standard fire characteristics is an improvement over reporting device temperatures, TCPs are not ideal instruments for monitoring surface fires, because they provide only point estimates of fire behavior and must be calibrated for different fire environments, TCP characteristics, and deployments. To illustrate how TCPs respond to fires and to point the way towards a more general calibration method, we report results from a numerical model that accurately simulated TCP response to a spreading surface fire.
Lichens on down wood in logged and unlogged forest stands
Authors: Bunnell Fred L. , Spribille Toby , Houde Isabelle , Goward Trevor , Björk Curtis
Published: May 2008

Lichen communities of forests often appear to be negatively affected by timber harvest presumably because of reduction of suitable substrate and increased desiccation. We examined species richness and composition of lichens on wood of logs of the same decay class in unlogged stands (>140 years old) and logged, 20- to 30-year-old stands. There was no significant difference in species richness or mean lichen cover between logged and unlogged stands, but species composition differed, including species that were unique to either logged or unlogged stands. Crustose lichens accounted for 71% of rare species and all of the species occurring more commonly in unlogged stands; macrolichens accounted for 82% of common species and 60% of the species occurring more commonly in logged stands. Diameter at breast height and decay characteristics of down wood were the best predictors of lichen richness. Among lichen-rich, decay class 3 logs, relatively small amounts of retained down wood sustained lichen richness equivalent to unlogged stands. It appears important to ensure that decay classes favourable to lichens are retained after harvest.
Effects of weed and erosion control on communities of soil mites (Oribatida and Gamasina) in short-rotation willow plantings in central New York
Authors: Minor Maria A. , Norton Roy A.
Published: May 2008

Several pre-emergent herbicides (azafenidin, oxyfluorfen, and imazaquin–pendimethalin mixture), used for weed control during the establishment of short-rotation willow plantings, were tested for their impact on population density, species richness, and community structure of predaceous (Gamasina) and saprophagous and (or) mycophagous (Oribatida) soil mites. The experimental control was hand-weeded (no herbicide). Two site preparation treatments were used: conventional (disked) and erosion controlled (no-till with cover crop of winter rye). The influence of herbicide application on non-target organisms (soil mites) cannot be generalized, with groups being differentially affected. Overall, Oribatida were most affected by herbicides. Among specific herbicides, azafenidin and oxyfluorfen had a negative effect on density and species richness of soil mites. The response of Oribatida and Gamasina to herbicides was species-specific. Two species of Oribatida ( Sellnickochthonius immaculatus (Forsslund) and Liochthonius lapponicus (Trägårdh)) declined significantly in all herbicide-treated plots. The cover crop residue had positive effect on both Oribatida and Gamasina; the negative effect of herbicides on Oribatida was greatly mitigated by cover crop. Herbicides appear to reduce mite diversity and alter community structure, but they do not always affect abundance. We speculate that the sensitivity of Oribatida to herbicides can reflect the indirect impacts of herbicides on soil microflora.
Fire history and the establishment of oaks and maples in second-growth forests
Authors: Hutchinson Todd F. , Long Robert P. , Ford Robert D. , Sutherland Elaine Kennedy
Published: May 2008

We used dendrochronology to examine the influence of past fires on oak and maple establishment. Six study units were located in southern Ohio, where organized fire control began in 1923. After stand thinning in 2000, we collected basal cross sections from cut stumps of oak (n = 137) and maple (n = 204). The fire history of each unit was developed from the oaks, and both oak and maple establishment were examined in relation to fire history. Twenty-six fires were documented from 1870 to1933; thereafter, only two fires were identified. Weibull median fire-return intervals ranged from 9.1 to 11.3 years for the period ending 1935; mean fire occurrence probabilities (years/fires) for the same period ranged from 11.6 to 30.7 years. Among units, stand initiation began ca. 1845 to 1900, and virtually no oak recruitment was recorded after 1925. Most maples established after the cessation of fires. In several units, the last significant fire was followed immediately by a large pulse of maple establishment and the cessation of oak recruitment, indicating a direct relationship between fire cessation and a shift from oak to maple establishment.
Epidemiology of Phytophthora ramorum in Oregon tanoak forests
Authors: Hansen E. M. , Kanaskie A. , Prospero S. , McWilliams M. , Goheen E. M. , Osterbauer N. , Reeser P. , Sutton W.
Published: May 2008

We followed the local intensification and dispersal of Phytophthora ramorum Werres, De Cock, & Man In’t Veld in Oregon tanoak ( Lithocarpus densiflorus (Hook & Arn.) Rehd.) forests from its initial detection in 2001 through 2006, coincident with a continuing eradication effort. The initial infested area included nine scattered sites below 400 m elevation, close to the Pacific Ocean near Brookings, Oregon. In subsequent years, one-half of new infections were within 122 m of a previous infection, and 79% of the newly detected trees occurred within 300 m of a previously identified tree. Dispersal up to 4 km was occasionally recorded. Initial infection occurred in the upper crowns of tanoak trees. The pathogen was recovered in rainwater collected beneath diseased tanoak trees in every month from November 2006 through October 2007. Twenty-four multilocus microsatellite genotypes were identified among 272 P. ramorum isolates collected from Curry County. Genotypic analysis provided independent estimates of time of origin of the Oregon infestation, its clustered distribution, and dispersal distances. In all sampling years, 60%–71% of the isolates belonged to the same multilocus genotype. In 2001, 12 genotypes were detected and new genotypes were identified in each of the subsequent years, but all isolates belonged to the same clonal lineage. Knowledge of local intensification of the disease and long-distance dispersal should inform both Oregon eradication efforts and national quarantine regulations.
Demographic history and interspecific hybridization of fourShoreaspecies (Dipterocarpaceae) from Peninsular Malaysia inferred from nucleotide polymorphism in nuclear gene regions
Authors: Ishiyama Hiroko , Inomata Nobuyuki , Yamazaki Tsuneyuki , Shukor Nor Aini Ab , Szmidt Alfred E.
Published: May 2008

Shorea acuminata Dyer, Shorea curtisii Dyer ex King, Shorea leprosula Miq., and Shorea parvifolia Dyer are dominant tree species in the tropical rainforest of Peninsular Malaysia, which experienced several climatic changes during Pleistocene. To investigate the current population structure and demographic history of these species, we analyzed levels and patterns of nucleotide polymorphism of the nuclear gene region PgiC. We also used sequence data of the GapC gene region obtained in our previous study. Negative Tajima’s D values observed in both investigated gene regions for S. curtisii, S. leprosula, and S. parvifolia implied that all three species have experienced population expansion events. Little to moderate levels of population differentiation in S. acuminata and S. curtisii suggested recent divergence of the investigated populations after postglacial colonization of the Peninsular Malaysia. In addition, some haplotypes were similar or identical to haplotypes of the other species. The existence of such haplotypes could be partially explained by interspecific hybridization. Indeed, we found some putative hybrid individuals. Interspecific hybridization among closely related species might have contributed to the polymorphism of the investigated species.
Assessing effects of laser point density, ground sampling intensity, and field sample plot size on biophysical stand properties derived from airborne laser scanner data
Authors: Gobakken Terje , Næsset Erik
Published: May 2008

Canopy height distributions were created from small-footprint airborne laser scanner data with an average sampling density of 1.13 points·m–2 collected over 132 sample plots and 61 forest stands. Field measurements of each plot were carried out within two concentric circles corresponding to fixed areas of 200 m2 and 300 or 400 m2. The laser point clouds were thinned to approximately 0.25, 0.13, and 0.06 point·m–2. For all comparisons, the maximum values of the first as well as last return canopy height distributions differed significantly between the full density and the thinned data. The combined effects of number of field plots, field plot sizes, and point densities on the accuracy of mean tree height, stand basal area, and stand volume predicted at stand level using a two-stage procedure combining field training data and laser data, were assessed using Monte Carlo simulation randomly selecting 75% and 50% of the field plots. The average standard deviation showed only a minor increase by decreasing point density and increased when the number of sample plots was reduced. The effects of field plot size varied with canopy structure and stem density.
Reconstructing spatial tree point patterns from nearest neighbour summary statistics measured in small subwindows
Authors: Pommerening Arne , Stoyan Dietrich
Published: May 2008

Spatial tree data are required for the development of spatially explicit models and for the estimation of summary statistics such as Ripley’s K function. Such data are rare and expensive to gather. This paper presents an efficient method of synthesizing spatial tree point patterns from nearest neighbour summary statistics (NNSS) sampled in small circular subwindows, which uses a stochastic optimization technique based on simulated annealing and conditional simulation. This nonparametric method was tested by comparing tree point patterns, reconstructed from sample data, with the original woodland patterns of three structurally different tree populations. Analysis and validation show that complex spatial woodland structures, including long-range tree interactions, can be successfully reconstructed from NNSS despite the limited range of the subwindows and statistics. The influence of the NNSS varies depending on the woodland under study. In some cases, the sampling results can be improved by reconstruction. Furthermore, it is clearly shown that it is possible to estimate second-order characteristics such as Ripley’s K function from small circular subwindows through the reconstruction technique. The results offer new opportunities for adding value to woodland surveys by making raw data available for further work such as growth projections, visualization, and modelling.
Decreased fire frequency and increased water levels affect riparian forest dynamics in southwestern boreal Quebec, Canada
Authors: Denneler Bernhard , Asselin Hugo , Bergeron Yves , Bégin Yves
Published: May 2008

The relative importance of fire and flooding on the population dynamics of eastern white-cedar ( Thuja occidentalis L.) and black ash ( Fraxinus nigra Marsh.) was evaluated in eight old-growth riparian stands of southwestern boreal Quebec, Canada. Rising water levels and decreasing fire frequency since the end of the Little Ice Age (ca. 1850) were expected to have favoured an inland migration of the riparian forest fringe, with the flood-tolerant black ash colonizing the lower parts of the shore terraces and eastern white-cedar the upper parts. Black ash was found to be restricted to the riparian zone (<200 cm elevation), whereas eastern white-cedar trees did not occur below 100 cm above lake level. Gaps of postfire eastern white-cedar recruitment were noted in stands exposed to riparian disturbances, whereas relatively continuous recruitment occurred at protected sites. Black ash, more tolerant to flooding and ice push, invaded the shore terrace sites left vacant by eastern white-cedar. The riparian forest fringe surrounding Lake Duparquet is currently migrating upland and this trend is expected to continue as water levels continue to increase and fire frequency continues to decrease during the 21st century.
Canadian national biomass equations: new parameter estimates that include British Columbia data
Authors: Ung Chhun-Huor , Bernier Pierre , Guo Xiao-Jing
Published: May 2008

National allometric equations covering the most common tree species of Canada’s forests were produced based on tree mass data acquired in the early 1980s during the ENergy from the FORest (ENFOR) program. The equations allow us to calculate the mass estimate of four tree components (foliage, branches, stem bark, and stem wood) using either diameter at breast height or a combination of diameter at breast height and height. Missing from that data set, however, were the data from British Columbia. A usable British Columbia data set was finally found and has now been incorporated into the national data set. Here, we present revised allometric equations for six species covered in the previous work and also found in the British Columbia data set as well as for the “hardwoods”, “softwoods”, and “all species” equations. New equations are also provided for eight species specific to the British Columbia data.
Effects of stand, landscape, and spatial variables on bird communities in larch plantations and deciduous forests in central Japan
Authors: Yamaura Yuichi , Katoh Kazuhiro , Takahashi Toshimori
Published: May 2008

We examined the effects of stand, landscape, and spatial variables on bird communities in deciduous forests and Japanese larch ( Larix leptolepis (Sieb & Zucc.) Gord.) plantations in a montane region of Nagano Prefecture, central Japan. We used plot-transect methods at 97 sites: 33 in winter 2003 and 18 sites were added in the 2004 breeding season in deciduous forests, and 32 in winter 2004 and 14 sites were added in the 2005 breeding season in larch plantations. Bird–environment relationships were explored using partial redundancy analysis and partial regression analysis. We used spatial variables derived from principal coordinates of neighbor matrices as explanatory variables to detect nonrandom spatial structure of bird communities. Variation in bird communities was mainly explained by stand and spatial variables for both forest types, whereas the effects of landscape variables were small. In plantations, important stand variables for both seasons included stand height, elevation, and the basal area of vines, whereas shrubs, dwarf bamboo ( Sasa senanensis (Franch. & Savat.) Rehd.), and larch snags were important in the breeding season. In deciduous forests, the most important stand variable for both seasons was the basal area of northern Japanese hemlock ( Tsuga diversifolia (Maxim.) Mast.) and Nikko fir ( Abies homolepis Sieb. & Zucc.) trees. Spatial variables showed that bird communities had large-scale (>10 km) spatial variation that could not be explained by stand or landscape variables.
Climate sensitivity of trembling aspen radial growth along a productivity gradient in northeastern British Columbia, Canada
Authors: Leonelli Giovanni , Denneler Bernhard , Bergeron Yves
Published: May 2008

Growth–climate relationships were analyzed for 15 stands of trembling aspen ( Populus tremuloides Michx.) along a productivity gradient in northeastern British Columbia. Productivity was evaluated with a site index model whose values varied between 6.65 and 26.93 m height at age 50 years. To assess the role of climate on radial growth, we built a tree-ring chronology for each site and then performed a dendroclimatic analysis by means of bootstrapped correlation functions using monthly and annual climatic variables. We found that trembling aspen sensitivity to climate varied across stands with different productivities in the study area. At the more productive sites, trees were more sensitive to climate, and ring widths were positively correlated, particularly with summer month precipitation prior to the year of growth. The different responses to climate along the productivity gradient are likely related to the differences in substrate properties; substrates at the more productive sites are richer in nutrients and have a better water holding capacity than those of the less productive sites. Our study suggests that the effects of future climate change on tree growth may not only increase towards the limit of a species distribution, but also towards richer and wetter stands.
Carbon cycling along a gradient of beech bark disease impact in the Catskill Mountains, New York
Authors: Hancock Jessica E. , Arthur Mary A. , Weathers Kathleen C. , Lovett Gary M.
Published: May 2008

Exotic pests and pathogens, through direct and indirect effects on forest structure and species composition, have the potential to significantly alter forest ecosystem processes, including C cycling. Throughout the northern hardwood forest, beech bark disease (BBD) is causing widespread disruption in forest structure and composition. In the Catskill Mountains of New York, some forests formerly codominated by American beech ( Fagus grandifolia Ehrh.) and sugar maple ( Acer saccharum Marsh.) are shifting to sugar maple dominance. The effects of BBD and a subsequent shift in species composition on annual aboveground net primary production and soil CO2 efflux were examined in eight forest plots selected to represent a gradient of BBD impact. There were no significant trends in aboveground net primary production across this gradient. However, growing season soil CO2 efflux decreased linearly along the BBD gradient, declining by 40%. Although the mechanism controlling this decline is uncertain, the decrease in soil CO2 efflux with BBD impact and a shift to greater composition of sugar maple in litterfall could significantly alter C cycling in northern hardwood stands in the Catskill Mountains.
Response of the cover of berry-producing species to ecological factors on the Kenai Peninsula, Alaska, USA
Authors: Suring Lowell H. , Goldstein Michael I. , Howell Susan M. , Nations Christopher S.
Published: May 2008

Land managers on the Kenai Peninsula have responded to recent extensive infestations of forests by spruce beetles ( Dendroctonus rufipennis (Kirby)) and associated increased fire risk with a variety of management approaches. To provide additional ecological information upon which to base these management prescriptions, we evaluated the response of the cover of berry species to variations in landscape factors and environmental conditions, including crown closure. Data were sufficient to describe the response of cover of bunchberry dogwood ( Cornus canadensis ), black crowberry ( Empetrum nigrum ), false toadflax ( Geocaulon lividum ), strawberryleaf raspberry ( Rubus pedatus ), lingonberry ( Vaccinium vitis-idaea ), and a combination of 24 other species through multinomial logistic regression. Crown closure and forest overstory type significantly influenced the cover of all berry species. Increasing crown closure had a negative effect on all berry species except strawberryleaf raspberry. Level of infestation by spruce beetles was significantly related to the cover of all species except lingonberry. Our findings indicate that spruce forests may be managed to enhance berry cover and that choice of management technique (e.g., timber harvest, prescribed fire) will likely result in different outcomes.
Response of small mammals to alternative stand structures in the mixed-conifer forest of northeastern CaliforniaThis article is one of a selection of papers from the Special Forum on Ecological Studies in Interior Ponderosa Pine — First Findings from Blacks Mountain Interdisciplinary Research.
Authors: Maguire Chris C. , Maguire Douglas A. , Manning Tom E. , Garber Sean M. , Ritchie Martin W.
Published: May 2008

A common, but largely untested, strategy for maintaining forest biodiversity is to enhance stand structural complexity. A silvicultural experiment was implemented from 1996 to 1998 at Blacks Mountain Experimental Forest, California, to test the efficacy of two levels of structural diversity (high versus low) and two levels of prescribed underburning (burn versus no burn) for maintaining or restoring biodiversity. Small mammals were trapped and tagged in experimental units for 2 noncontiguous weeks in fall 2003 and 2004. Total number of captures and number of captured individuals varied by year (P < 0.002). No treatment effects were detected for all species lumped together or for the three most frequent species analyzed separately ( Tamias amoenus J.A. Allen, 1890, Peromyscus maniculatus (Wagner, 1845), and Spermophilus lateralis (Say, 1823)), with the exception that T. amoenus was captured more often in burned units in 2004 (P = 0.004 for year × burn interaction). Mixed-effects regression models indicated that the number of captures and captured individuals of T. amoenus and P. maniculatus decreased with increasing residual basal area of overstory trees, but opposite results were obtained for S. lateralis. After accounting for residual stand density differences, T. amoenus was captured more frequently in units of low structural diversity and S. lateralis in units of high structural diversity.