bluuebunny/crossref_metadata_2025 huggingface dataset:
Mycorrhizal networks: a review of their extent, function, and importance
Authors: Simard Suzanne W , Durall Daniel M
Published: September 2004

It is well known from laboratory studies that a single mycorrhizal fungal isolate can colonize different plant species, form interplant linkages, and provide a conduit for interplant transfer of isotopic carbon, nitrogen, phosphorus, or water. There is increasing laboratory and field evidence that the magnitude and direction of transfer is influenced by physiological sourcesink gradients between plants. There is also evidence that mycorrhizal fungi play a role in regulating transfer through their own sourcesink patterns, frequency of links, and mycorrhizal dependency. Although it is plausible that connections are extensive in nature, field studies have been hampered by our inability to observe them in situ and by belowground complexity. In future, isotopic tracers, morphological observations, microsatellite techniques, and fluorescent dyes will be useful in the study of networks in nature. Mycorrhizal networks have the potential to influence patterns of seedling establishment, interplant competition, plant diversity, and plant community dynamics, but studies in this area are just beginning. Future plant community studies would benefit from concurrent experimental use of fungal network controls, isotopic labeling, direct observation of interplant linkages, and long-term observation in the field. In this paper, we review recent literature on mycorrhizal networks and interplant carbon transfer, suggest future research directions, and highlight promising scientific approaches.Key words: common mycorrhizal network, carbon transfer, sourcesink, establishment, competition, diversity.
A change in the concentration of NaCl in soil alters the rate of hyphal extension of some arbuscular mycorrhizal fungi
Authors: Juniper S , Abbott L K
Published: September 2004

This study investigated the effect of a rapid change in the concentration of the soil solution on hyphal growth from germinated spores of three arbuscular mycorrhizal fungi: isolates of Acaulospora laevis Gerd. & Trappe, Gigaspora decipiens Hall & Abbott, and Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders. Spores of either G. decipiens or S. calospora were incubated between millipore filters buried in sand that had been watered to field capacity with solutions of 0, 150, or 300 mmol/L NaCl. After 11 d, the intact pairs of filters were recovered, left undisturbed, or transferred into and further incubated in soil watered with one of the three solutions. Spores of A. laevis were incubated between filters in sand without NaCl and after 20 d were either left undisturbed or transferred to soil with 0, 50, 150, or 300 mmol/L NaCl in the soil solution for a further 11 d. The filter sandwiches were stained and opened, and determinations of spore germination, number of auxiliary cells, and length of hyphae on each were made. For G. decipiens and S. calospora, the effect of NaCl on hyphal growth was reversible. Hyphae from spores germinated in sand with 300 mmol/L NaCl showed markedly increased growth when transferred to a less saline environment. Hyphae from spores germinated in nonsaline sand continued to grow, but at a slower rate, when transferred to a saline environment. Hyphae of A. laevis continued to elongate after transfer to soil with 50 mmol/L NaCl but not 150 or 300 mmol/L NaCl. Morphological differences were observed between hyphae of G. decipiens grown in a highly saline as compared with a nonsaline substrate.Key words: soil salinity, arbuscular mycorrhizas, species and genera of arbuscular mycorrhizal fungi, hyphae.
Mycorrhizal fungi as drivers of ecosystem processes in heathland and boreal forest biomes
Authors: Read David J , Leake Jonathan R , Perez-Moreno Jesus
Published: September 2004

The importance of mycorrhizas in heathland and boreal forest biomes, which together cover much of the landmass of the Northern Hemisphere and store most of the global stocks of carbon, is reviewed. The taxonomic affinities of the organisms forming these symbiotic partnerships are assessed, and the distinctive structural features of the ericoid mycorrhizas of heathland dwarf shrubs and the ectomycorrhizas of boreal forest trees are described. It is stressed that neither in terms of the geographical distribution of the plants nor in terms of the occurrence of their characteristic mycorrhizas in the soil profile should these biomes be considered to be mutually exclusive. What unites them is their apparent affinity for acidic organic soils of inherently low accessibility of the major nutrients nitrogen (N) and phosphorus (P). These properties relate directly to the nature of the nutrient-poor recalcitrant litter produced by their host plants and through positive-feedback mechanisms that are reinforced by selective removal of labile nutrients by the mycorrhizas. We suggest that coevolution of these plant litter traits with mycorrhizal associations that are adapted to them has been one of the defining features of these ecosystems. Ericoid and ectomycorrhizal fungi have biochemical and physiological attributes that make them highly efficient at scavenging for organic sources of N and P in surface soil horizons. In so doing, they restrict supplies of these elements to the decomposer communities. Case studies involving exploitation of N and P in defined organic substrates are described. In both biomes the dominant plants depend upon the abilities of their fungal partners to recover nutrients, so the symbioses control nutrient cycles, productivity, species composition, and functioning of these ecosystems. It is in this context that the fungal symbionts are here considered to be drivers of nutritional processes in their respective biomes. Through their influences upon the quality of carbon residues mycorrhizal fungi must also affect the sink-source balance for this key element in soil. There is an urgent need for the evaluation of the relative contributions of symbiotic and saprotrophic components of the microflora to the processes of carbon storage and cycling in these biomes, particularly in the context of global climate change and impacts of anthropogenic pollutant N deposition.Key words: carbon sequestration, peatlands, C/N ratios, carbon and nutrient cycles.
Experimental investigation of pull loads and borehole pressures during horizontal directional drilling installations
Authors: Baumert Michael E , Allouche Erez N , Moore Ian D
Published: September 2004

Installation loads during 19 commercial horizontal directional drilling (HDD) installations were monitored using new in-hole monitoring cell technology. Fifteen of these installations were part of an 8.3 km section of 203 mm diameter by 4 mm wall thickness steel gas distribution line. The predominant soil type was silty clay, and similar construction practices were employed for all installations. The resistance to pipe advancement within the bore was found to increase in an approximately linear manner, varying from 0.20 to 0.31 kN/m, with a mean of 0.26 kN/m and standard deviation σx = 0.03 kN/m. Local peaks caused by borehole curvature or borehole anomalies were found to dissipate, usually within 10 m, before the underlying linear trend resumed. The remaining four installations were evaluated to determine the relationship between measured pull head load and borehole pressure. The correlation observed provides new insight into the factors that contribute to pulling forces during HDD installations. Based on the findings, a conceptual framework is proposed for an improved HDD design model. The framework outlines two development stages: stage 1, based on tabulated measurements of pulling force per length of pipe inserted; and stage 2, involving significant modifications to an existing prediction model to better represent field conditions.Key words: pipelines, tensile loads, mud pressure, directional drilling, load monitoring, pressure monitoring.
Analysis of dispersion curves of Rayleigh waves in the frequencywavenumber domain
Authors: Lu Laiyu , Zhang Bixing
Published: September 2004

The method of spectrum analysis of surface waves (SASW) is discussed briefly. The analysis of the dispersion curves of Rayleigh waves in the frequencywavenumber (fk) domain is suggested due to the problems encountered in SASW. Three models of the layered media are considered according to typical situations in practice. All the modes that can be effectively excited are analyzed. The excitation and propagation characteristics of the Rayleigh waves are investigated by numerical simulation. The effects of some parameters such as number of channels and distance (s) between the source and the first receiver on the dispersion curves are investigated in detail for three models. Some important results about the number of receiver channels, relative error, mode jumping, and other aspects are obtained. It is found that reliable dispersion curves can be obtained by fk analyses when the distance between the first receiver and the source is greater than one half the wavelength (0.5λ).Key words: dispersion curves, Rayleigh waves, SASW, frequencywavenumber domain, mode jumping.
Numerical study of soil conditions under which matric suction can be maintained
Authors: Zhang L L , Fredlund D G , Zhang L M , Tang W H
Published: September 2004

The effect of negative pore-water pressure is often ignored in slope stability studies. There is a perception among geotechnical engineers that negative pore-water pressures will dissipate with rainfall infiltration and cannot be relied upon in design considerations. The objective of this paper is to illustrate that under certain conditions soil suction can be maintained. Based on the theory of infiltration and seepage through a saturatedunsaturated soil system, steady state and transient finite element seepage analyses were conducted using Seep/W on a 20 m high slope inclined at 30°. The results of the analysis showed that under steady state conditions, the most important factor influencing the permanency of matric suction in the soil is the magnitude of rainfall flux expressed as a percentage of the saturated coefficient of permeability of soil. For the analysis under transient seepage conditions, the results showed that the pore-water pressure profile depends on the magnitude of the rainfall flux, the saturated coefficient of permeability, the soil-water characteristic curve, and the water storage function. For a soil with a low coefficient of permeability and a large water storage capacity, the matric suction needs a substantial amount of time to dissipate and thus may be maintained over a longer time period than the rain is likely to fall, even if the ground surface flux is equal to or greater than the saturated coefficient of permeability. Engineers should address more appropriate engineering design assumptions that can be related to the permanence of matric suction in soil slopes based on the numerical analysis. Measures such as slope cover or surface recompaction can be taken into consideration to minimize the rainfall infiltration and thus maintain active matric suction in slopes.Key words: unsaturated soils, slope, rainfall infiltration, matric suction, permeability.
Static loading test on a 45 m long pipe pile in Sandpoint, Idaho
Authors: Fellenius Bengt H , Harris Dean E , Anderson Donald G
Published: September 2004

Design of piled foundations for bridge structures for the realignment of US95 in Sandpoint, Idaho, required a predesign static loading test on an instrumented, 406 mm diameter, closed-toe pipe pile driven to 45 m depth in soft, compressible soil. The soil conditions at the site consist of a 9 m thick sand layer on normally consolidated, compressible, postglacial alluvial deposits to depths estimated to exceed 200 m. Field explorations included soil borings and CPTu soundings advanced to a depth of 80 m. The clay at the site is brittle and strain-softening, requiring special attention and consideration in geotechnical design of structures in the area. Effective stress parameters back-calculated from the static loading test performed 48 days after driving correspond to beta coefficients of about 0.8 in the surficial 9 m thick sand layer and 0.15 at the upper boundary of the clay layer below, reducing to 0.07 in the clay layer at the pile toe, and a pile toe bearing coefficient of 6. The beta coefficients are low, which is probably due to pore pressures developing during the small shear movements during the test before the ultimate resistance of the clay was reached. The analyses of the results of the static loading test have included correction for residual load caused by fully mobilized negative skin friction down to 10 m depth and fully mobilized positive shaft resistance below 30 m depth, with approximately no transfer of load between the pile and the clay from 10 m depth through to 30 m depth.Key words: pile loading test, residual load, strain-gage instrumentation, load distribution, setup, pile modulus.
Network model for hydraulic conductivity of sand-bentonite mixtures
Authors: Abichou Tarek , Benson Craig H , Edil Tuncer B
Published: September 2004

A network formulation was used to model the hydraulic conductivity of sandbentonite mixtures (SBMs) as a function of bentonite content. The sand particles were assumed to be spheres, and their arrangement was defined using a discrete element model simulating sand particle interactions. Pores between the spheres were approximated as a network of straight capillary tubes. The space defined by the spheres was divided into a collection of neighboring tetrahedrons, and the geometry of the tetrahedrons was used to define tube diameters and lengths in the network. Hydraulic heads throughout the network were computed by solving a system of equations describing flow through the tubes. Hydraulic conductivity of the network was calculated as the rate of flow per unit area for a given network of tubes driven by a one-dimensional hydraulic gradient. Bentonite was introduced into the network in several schemes to simulate SBMs. SBMs prepared with powdered bentonite were modeled as a packing of sand, where the sand particles are coated with bentonite (grain coating model and pipe blocking model), whereas SBMs prepared with granular bentonite were modeled as a packing of sand with bentonite occupying pores between the sand particles (junction blocking model). The relationship between hydraulic conductivity and bentonite content obtained from the grain coating model was similar to that measured on sand  powdered bentonite mixtures. A comparable relationship was also obtained for hydraulic conductivities predicted with the junction blocking model using a size-based filling approach and hydraulic conductivities measured on sand  granular bentonite mixtures.Key words: sandbentonite mixtures, network models, hydraulic conductivity, degree of bentonation, bentonite distribution.
Consolidation analysis for unsaturated soils
Authors: Conte Enrico
Published: September 2004

This paper deals with the multidimensional consolidation of unsaturated soils when both the air phase and water phase are continuous. Following the approach proposed by D.G. Fredlund and his coworkers, the differential equations governing the coupled and uncoupled consolidation are first derived and then solved numerically. The solution is achieved using a procedure that depends on the transformation of the field equations by using the Fourier transform. This transformation has the effect of reducing a two- or three-dimensional problem to a problem involving only a single spatial dimension. The transformed equations are solved using a finite element approximation that makes use of simple one-dimensional elements. Once the solution in the transformed domain is obtained, the actual solution is achieved by inversion of the Fourier transform. The time integration process is formulated in a stepwise form. Results are presented to point out some aspects of the consolidation in unsaturated soils. Moreover, it is shown that the results obtained using the simple uncoupled theory are of sufficient accuracy for practical purposes.Key words: coupled consolidation, uncoupled consolidation, unsaturated soils, Fourier transform.
Coupled hydromechanical modeling of rock fractures under normal stress
Authors: Bart M , Shao J F , Lydzba D , Haji-Sotoudeh M
Published: September 2004

In this paper, a nonlinear poromechanical model is developed for a single rock fracture under normal stress. The fracture is represented by a set of voids, and the progressive fracture displacement is considered as a modification process of void space. Based on experimental data obtained from three representative rock fractures, the constitutive model is formulated through an extension of Biot poroelasticity theory to a saturated fracture. A generalized poroelastic coupling coefficient is introduced to describe the interaction between pore fluid pressure and fracture deformation. This coefficient is expressed as a function of fracture aperture. Five parameters involved in the model have been determined from mechanical and poromechanical compression tests. The validity of the model is checked on fluid flow tests under different normal stresses. Comparisons between numerical simulations and experimental data are provided.Key words: hydromechanical coupling, interfaces, joints, poroelasticity, rock mechanics, fractures.
Disturbance effects in pressuremeter tests in clay
Authors: Silvestri Vincenzo
Published: September 2004

This paper analyzes the effect of borehole disturbance, caused by installation of pressuremeter probes in clays, on the derived stressstrain curves. Both overpushing- and overcutting-induced disturbances are considered. It is shown that overpushing results in underestimation of the undrained shear resistance. In general, the degree of underestimation cannot be determined. As for overcutting, the derived stressstrain curves are characterized by high peak strengths. The degree of overestimation of the undrained shear strength may reach 100% for the case of a strain-hardening material. Determination of the strain that corresponds to the peak shear strength allows determination of the true stressstrain curve from the expansion test. Analysis of four well-documented case histories serves to illustrate the proposed approach.Key words: pressuremeter, borehole disturbance, clay, stress-strain curves, case histories, undrained shear strength.
A study of infiltration on three sand capillary barriers
Authors: Yang Hong , Rahardjo H , Leong E C , Fredlund D G
Published: September 2004

The capillary barrier effect was investigated by conducting infiltration tests on three soil columns of fine sand over medium sand, medium sand over gravelly sand, and fine sand over gravelly sand. The barrier effect was verified in the underlying layer of coarser material, and the water-entry values of the coarser layers were confirmed to be nearly equal to the residual matric suctions of the soils. The coarser layer of gravelly sand, which had a lower water-entry value, was more effective in forming a barrier than the coarser layer of medium sand, which had a higher water-entry value. When the capillary barrier was comprised of a coarser layer of gravelly sand, there was more water stored in the finer layer at the end of the drying stage than when the capillary barrier was comprised of a coarser layer of medium sand. Non-equilibrium static conditions of pore-water pressure profiles were observed in the three soil columns, and a generalized ultimate pore-water pressure profile of a capillary barrier system was proposed. In addition, the final volumetric water contents versus matric suctions of the soils as measured from the soil columns were reasonably consistent with the soil-water characteristic curves (SWCCs) of the soils, suggesting that the drying SWCC of a soil could also be obtained from the drying process in a soil column (or a capillary open tube). The drying SWCC could be established from measurements in the soil column up to a height corresponding to two times the residual matric suction head of the soil.Key words: capillary barrier, soil column, soil-water characteristic curve, pore-water pressure, water content, matric suction.
The prediction of one-, two-, and three-dimensional heave in expansive soils
Authors: Vu Hung Q , Fredlund Delwyn G
Published: September 2004

The prediction of heave in unsaturated, expansive soils has historically been studied primarily as a one-dimensional type analysis. This paper proposes a methodology that can be used for the prediction of one-, two-, or three-dimensional heave. It is suggested that negative pore-water pressures (i.e., soil suctions) can be estimated through a saturatedunsaturated seepage analysis. The results of the seepage analysis are then used as input for the prediction of displacements in a stressdeformation analysis. The formulation of the governing partial differential equations for both seepage and stressdeformation is based on the general theory of unsaturated soils using two independent stress state variables. The elasticity parameter functions required for a stressdeformation analysis can be calculated from various tests, including conventional one-dimensional oedometer tests. The proposed method is studied and tested against data collected on a case history involving a slab-on-ground floor on Regina clay. The predicted results from the two-dimensional analysis agree well with the measured data in terms of both total vertical displacements and final water contents in the soil. The results of a parametric study are also presented to show the effect of measured soil parameters (i.e., swelling index and initial void ratio) and assumed parameters (i.e., Poisson's ratio and coefficient of earth pressure at rest) on the predicted displacements.Key words: heave prediction, unsaturated soil, expansive soil, seepage analysis, stress analysis.
Time-dependent behavior of pile groups by staged construction of an adjacent embankment on soft clay
Authors: Jeong Sangseom , Seo Donghee , Lee Jinhyung , Park Joogbai
Published: September 2004

A series of centrifuge model tests were performed to investigate the behavior of pile groups subjected to lateral soil movements by surcharge loading from approach embankments. The emphasis was on quantifying the time-dependent response in terms of deflections, bending moments, and earth pressures acting on pile groups during embankment construction and over short- and long-term periods after embankment construction. A variety of instruments were used to examine the soilpile interaction for pile groups adjacent to surcharge loads. Through these studies, it is found that pile cap deflections and bending moments developed to their maximum values under the short-term surcharge loading and decreased gradually to minimum values under the long-term loading. The ground settlement reached its maximum value under long-term loading, however, due to the consolidation of soft clay. It is also found that the lateral mean pressure acting on the pile is about 0.75 and 0.35 times the surcharge load q (= γH, where γ is the unit weight of the soil and H is the height of the embankment) under short- and long-term loading, respectively.Key words: time-dependent response, lateral soil movements, pile groups, centrifuge model tests, surcharge loads, soft clay.
A new elastoplastic constitutive model for coarse granular aggregates incorporating particle breakage
Authors: Salim Wadud , Indraratna Buddhima
Published: September 2004

A new elastoplastic stressstrain constitutive model is developed for granular coarse aggregates incorporating the degradation of particles during triaxial shearing. Coarse granular aggregates are subjected to breakage during excessive stress changes. Most of the available constitutive models do not consider the degradation of particles during shearing. In the current model, a plastic flow rule has been developed incorporating the energy consumption due to particle breakage during shear deformation. A non-associated flow and a kinematic type yield locus have been adopted in the model. A general formulation for the rate of particle breakage during shearing has been developed and incorporated in the plastic flow rule. The effects of particle breakage on the plastic distortional and volumetric deformations are incorporated in the current model. The stressstrain formulations are developed within the general critical state framework. The model can accurately predict the stressstrain and volume change behaviour of coarse granular aggregates. The plastic dilation and contraction features of coarse aggregates at various confining pressures are well captured, and the strain-hardening and post-peak strain-softening behaviour of coarse granular media is adequately represented. A particular feature of the model is its capability to predict the degree of particle breakage at any stage of shear deformation.Key words: constitutive modelling, coarse granular aggregates, particle breakage, dilatancy, non-associated flow, plasticity.
Changes in ectomycorrhizal communities and nutrient availability following prescribed burns in two upland pineoak forests in the New Jersey pine barrens
Authors: Tuininga Amy R , Dighton John
Published: September 2004

Forests in the New Jersey pine barrens are frequently prescribed burned to reduce fuel loads and risk of wildfire. To acquire baseline data for effects of prescribed burns on ectomycorrhizal diversity and nutrient uptake, field studies were undertaken in two upland pineoak forests in the New Jersey pine barrens subjected to different burn regimes. Ectomycorrhizal diversity was assessed by extraction of roots from soil cores and separation according to morphological characters. Nutrient availability to plant roots was measured using root bioassays. Relative to unburned plots, plots exposed to a fire at Greenwood, where burning was more frequent, had decreased total abundance of ectomycorrhizal tips, richness of ectomycorrhizal types, and Simpson's diversity in the L and F horizons, but increased Simpson's diversity in the deeper A horizon. At Lebanon, under a less frequent burn regime, richness was lower in whole cores and in the A horizon of burned versus unburned plots. Nitrogen, phosphorus, and potassium uptake by root bioassays indicated higher field availability of nutrients to roots in burned plots than roots in unburned plots, indicating a fertilization effect of the fire. Prescribed burning primarily impacted ectomycorrhizal community structure in the L and F horizons at these sites. Changes in function of ectomycorrhizae (nutrient uptake) in response to the burns was associated with decreased ectomycorrhizal diversity.
Influence of initial chemistry on decomposition of foliar litter in contrasting forest types in British Columbia
Authors: Prescott C E , Vesterdal L , Preston C M , Simard S W
Published: September 2004

We compare rates of decay of foliar litters of British Columbia tree species in two field studies, and assess which initial litter chemistry parameters best predict the decay rates. Nutrient concentrations, tannins, and carbon fractions (based on proximate analysis and nuclear magnetic resonance spectroscopy) were measured in fresh litter of 14 tree species in one experiment and seven species in a second experiment. Each study was replicated in a different site in order to assess the transferability of results. Broadleaf litters decayed faster than needle litters only during the first year; thereafter, they decayed slower. Lignin concentration was a good predictor of mass loss only during the first year and only in one of the two experiments, which may have resulted from all foliar litters having high lignin concentrations (>170 mg·kg1). Litter chemistry effects on first-year decay were consistent and transferable among sites. None of the initial litter chemistry parameters were good predictors of mass remaining after 4 or 5 years, because mass loss of most litters was similar by this time. The convergence in mass losses of litters after 45 years despite initial differences indicates that decomposition estimates extrapolated from early rates or initial chemistry may not accurately predict long-term decay.
Prediction of 2 × 2 tables of change from repeat cluster sampling of marginal counts
Authors: Magnussen Steen
Published: September 2004

Repeat cluster sampling of a binary (0,1) attribute at time 1 (Y1) and time 2 (Y2) in a finite population of discrete units is considered. All clusters contain m units and a cluster provides the marginal count of ones and zeroes at the two time points only. From these counts, we seek to predict a 2 × 2 table of the rates of no change (π11 = E[Y1Y2], π00 = E[(1  Y1)(1  Y2)]) and change (π10 = E[Y1(1  Y2)], 01 = E[(1  Y1)Y2]). Two predictors are proposed; one is derived from the temporal correlation of marginal counts and the second from the odds ratio of no change that maximizes a (pseudo-) likelihood of a non-central, hypergeometric distribution. The bias of the first is positive when there is a positive intracluster correlation of Y1, Y2, and Y1Y2, while the bias of the second is negative when the odds ratio of no change is >1. A proposed combined estimator worked well in three examples of change analysis with paired, classified Landsat images of forest cover type and cluster sampling with 3 × 3 arrays of 30 m × 30 m units (pixels). 2 × 2 tables obtained from marginal counts were superior, in terms of mean absolute error, to estimates based on a direct unit-by-unit count when the time 2 image had a root mean square registration error of 0.5 pixel relative to the time 1 image. The proposed method is intended for settings where a direct unit-by-unit estimation of the 2 × 2 table is either compromised or when data (by design) consist of marginal counts from a repeat cluster sampling.
Sphagnum invasion after clear-cutting and excavator mounding in a hypermaritime forest of British Columbia
Authors: Asada Taro , Warner Barry G , Banner Allen
Published: September 2004

Sphagnum invasion 8 years after an experimental clear-cut and mounding field trial was examined in a mesic western redcedar (Thuja plicata Donn ex D. Don)  western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest on the outer north coast of British Columbia. Sphagnum invasion was prominent in wet hollows in the mounded blocks. Pioneer species, Sphagnum pacificum Flatb. and Sphagnum angustifolium (C. Jens. ex Russ.) C. Jens., were common despite being minor components in the precut forest. Sphagnum girgensohnii Russ., a species of forests, showed expanding colonies and contained some Sphagnum capillifolium (Ehrh.) Hedw. Comparisons of vertical growth and decomposition rates of Sphagnum in the experimental field site and in a nearby natural peatland suggest that peat accumulation potential in the Sphagnum colonies in the mounded blocks is similar to that in the natural peatland. These observations suggest that open peatland-type plant communities become established and paludification processes are beginning. Mounding may be an effective strategy for silvicultural management to improve tree growth in the short term but may initiate paludification and negatively impact forest productivity in the long term in hypermaritime lower productivity forests.
An optimization model for annual harvest planning
Authors: Karlsson Jenny , Rönnqvist Mikael , Bergström Johan
Published: September 2004

The problem we consider is annual harvesting planning from the perspective of Swedish forest companies. The main decisions deal with which areas to harvest during an annual period so that the wood-processing facilities receive the required amount of assortments. Each area has a specific size and composition of assortments, and the choice of harvesting areas affects the production level of different assortments. We need to decide which harvest team to use for each area, considering that each team has different skills, home base, and production capacities. Also, the weather and road conditions vary during the year. Some roads cannot be used during certain time periods and others should be avoided. The road maintenance cost varies during the year. Also, some areas cannot be harvested during certain periods. Overall decisions about transportation and storage are also included. In this paper, we develop a mixed integer programming model for the problem. There are binary variables associated with harvesting, allocation of teams, and road-opening decisions. The other decisions are represented by continuous variables. We solve this problem directly with CPLEX 8.1 within a practical solution time limit. Computational results from a major Swedish forest company are presented.
Forest ecotone survey by line intersect sampling
Authors: Corona Piermaria , Chirici Gherardo , Travaglini Davide
Published: September 2004

Given their ecological relevance, the survey of ecotones is of considerable interest in forest multiresource inventory. To this end, it is useful to set up survey procedures to provide efficient and reliable information about the length of such elements within the landscape mosaic. This note demonstrates a procedure based upon line intersect sampling on remotely sensed imagery. The estimate of ecotone length per unit area is obtained by visual interpretation of the changes from forest to other land use classes along each sampling line. The experimentation carried out in two test areas within forest landscapes of central Italy proves the operative soundness of the proposed procedure, which is more efficient than the classical approach by forest polygon delineation and perimeter mensuration in a GIS environment. Under the examined conditions, samples based on a moderately high number of lines characterized by relatively long length prove to be more efficient than those based on shorter survey units.
Black spruce seedlings in a KalmiaVaccinium association: microsite manipulation to explore interactions in the field
Authors: Thiffault Nelson , Titus Brian D , Munson Alison D
Published: September 2004

We established a field trial on an ericaceous-dominated clearcut in Quebec to determine the effect of Kalmia angustifolia L., Vaccinium angustifolium (Ait.), and V. myrtilloides (Michx.) on the growth and physiology of black spruce (Picea mariana (Mill.) BSP) seedlings and on soil characteristics over the first two growing seasons. Plots undergoing one of three treatments (shrub removal, humus removal, or undisturbed control) were planted with black spruce seedlings that were either unfertilized or spot fertilized at time of planting. In some of the undisturbed control plots, we also used 15NH415NO3 to compare uptake of broadcast N fertilizer by vegetation. The ericaceous shrubs had a significant negative impact on seedling growth. Growth reductions were not related to water stress, soil temperature, or soil moisture. Extractable NH4-N and P concentrations in mineral soil tended to decrease in the presence of ericaceous shrubs, but effects were not significant. Seedling foliar N concentration was also reduced in the presence of ericaceous shrubs. Of the total amount of 15N fertilizer found in vegetation, 64% was immobilized in Vaccinium spp., 31% in Kalmia, and 5% in black spruce, but spruce took up more 15N per unit of root biomass than the ericaceous shrubs. Kalmia had consistently higher predawn xylem water potentials than black spruce.
Creating land allocation zones for forest management: a simulated annealing approach
Authors: Boyland Mark , Nelson John , Bunnell Fred L
Published: September 2004

This paper describes the Zone Allocation Model (ZAM) that uses the simulated annealing algorithm to create forest management zones. ZAM partitions the landscape into the Timber, Habitat, and Old Growth zones by allocating small land tiles into contiguous areas. The zone allocation process is guided by landscape-level targets and size and shape objectives. An ecological representation objective proportionally distributes all ecosystem types into each of the three zones. Priority objectives control allocation of identified lands that are targeted for specific zones. All objectives are combined within an objective function, with a penalty-weighting system specifying relative importance of each objective. The ZAM model found 1.7%4.4% of theoretical optimum scores from small to large problems, respectively. A demonstration on a 1.2 × 106ha landscape from coastal British Columbia illustrates the iterative exploration of compromises between objectives that leads to informed zone allocation decisions.
Relating flame radiation to home ignition using modeling and experimental crown fires
Authors: Cohen Jack D
Published: September 2004

Wildlandurban fire destruction depends on homes igniting and thus requires an examination of the ignition requirements. A physicaltheoretical model, based on severe case conditions and ideal heat transfer characteristics, estimated wood wall ignition occurrence from flame radiation heating and piloted ignition requirements. Crown fire experiments provided an opportunity for assessing model reliability. The crown fire experiments were specifically instrumented with wood wall sections and heat flux sensors to investigate direct flame heating leading to home ignition during wildland fires. The experimental results indicated that the flame radiation model overestimated the structure-to-flame distance that would result in wood wall ignition. Wall sections that ignited during the experimental crown fires did not sustain flaming after crown fire burnout. The experiments also revealed that the forest canopy attenuated the flame radiation as the crown fire spread within the forest plot. Ignition modeling and the associated crown fire experiments described the flame-to-structure distance scale associated with flame heating related to wall ignition.
Population variation in growth and 15-year-old shoot elongation along geographic and climatic gradients in black spruce in Alberta
Authors: Wei Run-Peng , Han Sang Don , Dhir Narinder K , Yeh Francis C
Published: September 2004

Twenty black spruce (Picea mariana (Mill.) BSP) populations from Alberta were tested at one trial to study the variation of shoot elongation at ages of 15 years, height growth at 10 and 15 years, and breast-height diameter (DBH) at 14 years. Significant difference among populations was found for all of the growth traits and some of the shoot elongation traits investigated. Population means for shoot elongation and cumulative growth traits of significant difference were further regressed against the geographic coordinates and climates of seed origins to study patterns of genetic variation in relation to geography and climate. Both linear and quadratic regressions were investigated, but the one with better fit (lower P and standard error) was chosen and further analyzed. Geographic and climatic gradients explained 20%62.9% of the population variation in regressions that were statistically significant. Shoot elongation and cumulative growth traits were closely related to frost-free periods, but diverged in their relationships to geographic and all other climatic variables considered. While shoot elongation was associated exclusively with latitude, longitude, day length, and negative temperature variables, growth traits were associated with elevation and positive temperature and moisture variables. Climate factors were more effective than geographic coordinates in describing differentiation in shoot elongation and growth traits. The most effective factors in predicting growth traits were mean annual precipitation and summer moisture index of the seed origin.
Comparing line-intersect, fixed-area, and point relascope sampling for dead and downed coarse woody material in a managed northern hardwood forest
Authors: Jordan G J , Ducey M J , Gove J H
Published: September 2004

We present the results of a timed field trial comparing the bias characteristics and relative sampling efficiency of line-intersect, fixed-area, and point relascope sampling for downed coarse woody material. Seven stands in a managed northern hardwood forest in New Hampshire were inventoried. Significant differences were found among estimates in some stands, indicating a potential for difference in bias in field implementation of the methods. In terms of relative sampling efficiency, results for each method varied among stand. However, point relascope sampling had comparable or better time efficiency than the other methods in most stands.
Combustion aerosol from experimental crown fires in a boreal forest jack pine stand
Authors: Payne N J , Stocks B J , Robinson A , Wasey M , Strapp J W
Published: September 2004

Combustion aerosol particles from boreal forest fires were quantified to facilitate investigation of the potential effects of increased fire activity caused by global warming, by providing data inputs for global and regional climate modelling of the direct and indirect effects. Aerial sampling was carried out in smoke plumes from 1-ha prescribed burns in mature jack pine stands. The three sampled burns resulted in crown fires, with fuel consumption from 4.2 to 5.8 kg·m2. Accumulation and coarse mode aerosol (>0.1 µm) was quantified using a passive cavity aerosol spectrometer probe and cascade impactor. The number median diameter of particles in the smoke plume was 0.29 µm, and the peak number and cross-sectional area density occurred around a particle size of 0.4 µm. More than 99% of particles sized had diameters <1.2 µm. Aerosol from flaming combustion was coarser than that from the smouldering phase, with number median diameters of 0.3 and 0.2 µm, respectively.
Crown fire behaviour in a northern jack pine  black spruce forest
Authors: Stocks B J , Alexander M E , Wotton B M , Stefner C N , Flannigan M D , Taylor S W , Lavoie N , Mason J A , Hartley G R , Maffey M E , Dalrymple G N , Blake T W , Cruz M G , Lanoville R A
Published: September 2004

This paper reports on the behaviour of 10 experimental crown fires conducted between 1997 and 2000 during the International Crown Fire Modelling Experiment (ICFME) in Canada's Northwest Territories. The primary goal of ICFME was a replicated series of high-intensity crown fires designed to validate and improve existing theoretical and empirical models of crown fire behaviour. Fire behaviour characteristics were typical for fully developed boreal forest crown fires, with fires advancing at 1570 m/min, consuming significant quantities of fuel (2.85.5 kg/m2) and releasing vast amounts of thermal heat energy. The resulting flame fronts commonly extended 2540 m above the ground with head fire intensities up to 90 000 kW/m. Depth of burn ranged from 1.43.6 cm, representing a 25%65% reduction in the thickness of the forest floor layer. Most of the smaller diameter (<3.0 cm) woody surface fuels were consumed, along with a significant proportion of the larger downed woody material. A high degree of fuel consumption occurred in the understory and overstory canopy with very little material less than 1.0 cm in diameter remaining. The documentation of fire behaviour, fire danger, and fire weather conditions carried out during ICFME permitted the evaluation of several empirically based North American fire behaviour prediction systems and models.
Measurements of radiant emissive power and temperatures in crown fires
Authors: Butler B W , Cohen J , Latham D J , Schuette R D , Sopko P , Shannon K S , Jimenez D , Bradshaw L S
Published: September 2004

This study presents spatially and temporally resolved measurements of air temperatures and radiant energy fluxes in a boreal forest crown fire. Measurements were collected 3.1, 6.2, 9.2, 12.3, and 13.8 m above the ground surface. Peak air temperatures exceeded 1330 °C, and maximum radiant energy fluxes occurred in the upper third of the forest stand and reached 290 kW·m2. Average radiant flux from the flames across all experiments was found to be approximately 200 kW·m2. Measured temperatures showed some variation with vertical height in the canopy. Equivalent radiometric temperatures calculated from radiant heat flux measurements exceeded thermocouple-based temperatures for all but the 10-m height, indicating that fire intensity estimates based on thermocouple measurements alone may result in underestimation of actual radiant intensity. The data indicate that the radiative energy penetration distance is significantly longer in the forest canopy than in the lower levels of the forest stand.
Charcoal production, dispersal, and deposition from the Fort Providence experimental fire: interpreting fire regimes from charcoal records in boreal forests
Authors: Lynch Jason A , Clark James S , Stocks Brian J
Published: September 2004

The relationship between charcoal production from fires and charcoal deposition in lakes is poorly understood, which limits the interpretation of sediment charcoal records. This calibration study assessed charcoal particle production, size, and transport during the International Crown Fire Modelling Experiment (ICFME) and compared fossil charcoal particle accumulation from 16 lakes in boreal forests of North America. Particle accumulation averaged 20.1 mm2·cm2 inside the ICFME fire; accumulation declined sharply outside the fire, with only 1% of the measured particles transported beyond 20 m from the burn edge. Fossil charcoal accumulation during the past 9000 years was much lower than observed deposition in traps located within the ICFME fire but similar to airborne deposition in traps located 1060 m from the burn edge. A higher fraction of large diameter particles (>1 mm) was present in fossil charcoal accumulation from historical fires and charcoal peaks that exceeded background accumulation by 1.4 times, suggesting large particles are characteristic of nearby fires. On the basis of a charred-particle production of ~2% of the total fuel consumed by the ICFME fire, we estimate a potential long-term carbon sequestration of 58.2 ± 12 g C·m2 as charred particles from this fire stored in soils or lake sediments.
Jack pine regeneration and crown fires
Authors: de Groot W J , Bothwell P M , Taylor S W , Wotton B M , Stocks B J , Alexander M E
Published: September 2004

The effect of crown fires on Pinus banksiana Lamb. regeneration was studied in separate forest- and cone-burning experiments. Nine plots (0.562.25 ha) of jack pine trees near Fort Providence, Northwest Territories, were burned using crown fires to determine the effects of fire intensity, rate of fire spread, depth of burn, and postfire duff depth on seed viability and regeneration. Fire intensities were 36 902  93 476 kW/m, and fire spread rates were 2470 m/min. Depths of burn were low (2.03.6 cm), and postfire duff depths averaged 2.05.5 cm. Postfire seed rain was highly variable (64634 seeds/m2), but seed viability was near 67% on all plots. Jack pine regeneration was also highly variable (779 seedlings/m2). In the cone-burning experiment, the germination rate increased from 41% (unheated cones) to 64% after 10 s of burning but decreased sharply after 30 s. Flame temperature did not significantly affect viability. Cone-burning results suggest that the postfire seed rain originated from the upper canopy, where flame duration was 515 s, and seed in the lower canopy was consumed by fire. Seed rain and regeneration were primarily influenced by understory fine fuel consumption (and therefore, fire intensity), tree height, and live crown base height.