bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of fractures on reservoir deformation and flow modeling
Authors: Bagheri Mohammad Ali , Settari Antonin
Published: June 2006

Fracture opening and closure caused by changes in the effective stress on fracture planes is well known. This phenomenon happens in aquifers and hydrocarbon reservoirs where production or injection events change the applied effective stress. Modeling this phenomenon requires a rigorous coupled geomechanics and flow simulator as well as detailed information regarding fracture properties, spacing, and orientation. A method has been developed to account for the effects of fractures on deformation in coupled reservoir and geomechanics simulation. The equivalent continuum approach was used where the constitutive matrix of individual blocks was calculated by means of an analytical formula that considers both rock and fracture deformation properties. The rock material is assumed to be isotropic and the normal stiffness of fractures varies with the applied effective stress according to a law that is typical for joints. The shear deformation of the fractures can be incorporated easily in the future. The general pseudo-continuum model was verified by comparing it with an approach using explicit modeling of the fractures. The fractured rock geomechanics model is then coupled to a single porosity, multiphase flow model. The deformations produce changes in the permeability tensor in both magnitude and orientation, which in turn influences compaction behavior.Key words: fracture deformation, equivalent moduli, coupling, reservoir compaction, reservoir simulation.
Liquefaction analysis of Duncan Dam using strength ratios
Authors: Olson Scott M
Published: June 2006

B.C. Hydro performed extensive seismic safety studies for Duncan Dam in the late 1980s and early 1990s. The results of these studies indicated that Duncan Dam was reasonably safe from liquefaction-induced failure. A recently proposed liquefaction analysis procedure that uses strength ratios to assess liquefaction triggering and post-triggering stability was used to revisit the liquefaction analysis of Duncan Dam. When compared to the detailed field and analytical studies performed by B.C. Hydro, the proposed liquefaction analysis procedure predicts: (i) similar zones of liquefaction within a contractive unit of foundation sand; (ii) similar shear strengths at the triggering of liquefaction (yield shear strength) and at large strain (liquefied shear strength); and (iii) similar post-triggering factors of safety for slope stability. The good agreement suggests that the strength ratio based liquefaction analysis approach is relatively robust and is suitable for screening level studies for large projects or may serve as the primary analysis procedure for less complex projects.Key words: liquefaction, liquefied shear strength, yield shear strength, laboratory tests, penetration tests, Duncan Dam.
Pullout capacity of small ground anchors by direct cone penetration test methods and neural networks
Authors: Shahin Mohamed A , Jaksa Mark B
Published: June 2006

Marquees are temporary light structures that are connected to the ground by small anchors that act in tension and are designed to resist uplift forces. Due to the temporary nature of these structures, little, if any, attention is given to the pullout capacity of the anchors used to secure them. Failures of such structures are not rare and have resulted in deaths and tens of thousands of dollars of damage. This paper reports on a series of 119 in situ anchor pullout tests conducted on rough mild steel anchors of various lengths, cross-sectional shapes, and areas. Comparison tests are carried out to investigate the impact of the factors affecting the pullout capacity of small anchors. Six methods that determine the axial pile capacity directly from cone penetration test (CPT) data are presented and used to calculate the pullout capacity of small ground anchors. The capacities obtained from these CPT-based methods are compared with predictions from a recently developed artificial neural network (ANN) model. The actual pullout loads are compared with predictions from the CPT and ANN methods, and statistical analyses are carried out to evaluate and rank their performance. The results indicate that the ANN-based method provides superior predictions of the pullout capacity of small ground anchors, whereas the Schmertmann method provides the best performance of the CPT-based techniques examined.Key words: ground anchors, pullout capacity, cone penetration test, artificial neural networks.
Using disaggregation to link individual-tree and whole-stand growth models
Authors: Qin Jianhua , Cao Quang V
Published: June 2006

Data from 200 plots randomly selected from the Southwide Pine Seed Source Study of loblolly pine (Pinus taeda L.) were used to fit whole-stand and individual-tree equations. Another 100 plots, also randomly selected, were used for validation. Outputs from the individual-tree model were then adjusted to match observed stand attributes (number of trees, basal area, and volume per hectare) by four disaggregation methods: proportional yield, proportional growth, constrained least squares, and coefficient adjustment. The first three are existing methods, and the fourth is new. The four methods produced similar results, and the coefficient adjustment was then selected as the method to disaggregate predicted stand growth among trees in the tree list. Results showed that, compared to the unadjusted individual tree model, the adjusted tree model performed much better in predicting stand attributes, while providing comparable predictions of tree diameter, height, and survival probability. The proposed approach showed promise in the ongoing effort to link growth models having different resolutions.
A new spatial-attribute weighting function for geographically weighted regression
Authors: Shi Haijin , Zhang Lianjun , Liu Jianguo
Published: June 2006

In recent years, geographically weighted regression (GWR) has become popular for modeling spatial heterogeneity in a regression context. However, the current weighting function used in GWR only considers the geographical distances of trees in a stand, while the attributes (e.g., tree diameter) of the neighboring trees are totally ignored. In this study, we proposed a new weighting function that combines the "geographical space" and "attribute space" between the subject tree and its neighbors, such that (1) neighbors with greater geographical distances from the subject tree are assigned smaller weights, and (2) at a given geographical distance, neighboring trees with sizes that are similar to that of the subject tree are assigned larger weights. The results indicate that the GWR model with the new spatial-attribute weighting function performs better than the one with the spatial weighting function in terms of model residuals and predictions for different spatial patterns of tree locations.
Paternity analysis with microsatellites in a Danish Abies nordmanniana clonal seed orchard reveals dysfunctions
Authors: Hansen O K , Kjær E D
Published: June 2006

A paternity analysis using five microsatellite markers was conducted in a Danish clonal seed orchard with 13 Abies nordmanniana (Stev.) Spach clones. The purpose was to investigate potential seed-orchard dysfunctions, with special emphasis on nonequal pollen contributions and selfing. Male paternity was found for 232 seedlings germinated from seeds collected on three ramets, each of eight clones, and the relative contribution of each clone to the gene pool of male gametes was calculated. Furthermore, 49 ramets were genotyped to check for erroneous grafting. The effect of an unbalanced male contribution was quantified by means of two measures: (1) the status number (NS), which reflects buildup of coancestry in the seed-orchard crop as a result of a low number of clones and an unequal male contribution, and (2) the asymptotic variance effective population number (Ne(v)). The contributions by pollen donors from the 13 clones were highly skewed. Three clones were fathers to more than 75% of the progenies, while making up only 24% of the ramets in the seed orchard. Four clones sired no progenies at all. The unequal contribution on the male side corresponded to NS = 4.2 and Ne(v) = 5.8. Some selfing was observed, which may give rise to concern if clonal seed orchards with few clones are established. The estimated maximum pollen contamination from outside the seed orchard was 4.3%. No graftinglabelling errors were identified.
Fertilization and water stress interactions in young Eucalyptus grandis plants
Authors: Graciano Corina , Guiamet Juan J , Goya Juan F
Published: June 2006

We determined whether fertilization with N and P affects water relations, and thereby water-stress tolerance, in young Eucalyptus grandis plants. To assess whether fertilization enhances osmotic adjustment under drought, 3-month-old E. grandis were planted in pots and fertilized with either N (1 g of urea) or P (12 g of calcium super phos phate). The soil was watered to attain one of two conditions: field capacity and 0.8 MPa. P fertilization when plants were well watered conditions increased solute accumulation, which might confer better performance under water stress. However, under water-stress conditions, nonfertilized and N-fertilized plants showed osmotic adjustment, while P-fertilized plants did not. P fertilization increased dry-mass allocation to leaves and decreased allocation to roots even under water-stress conditions. N-fertilized plants increased allocation to roots and maintained allocation to leaves under water-stress conditions in comparison with control plants, so they were not affected by water stress as much as P-fertilized plants were. This may explain why P fertilization increased growth when water was not limiting but had no effect under drought conditions. In the long term, changes in dry-mass allocation caused by P fertilization might increase susceptibility to water deficit.
Clear-fell harvest impacts on biodiversity: past research and the search for harvest size thresholds
Authors: Pawson S M , Brockerhoff E G , Norton D A , Didham R K
Published: June 2006

Clear-fell harvesting has large aesthetic impacts and significantly alters ecosystem attributes at multiple spatial scales. Known abiotic changes include increased microclimatic variability, changes in regional water balance, and modified hydrological patterns that influence erosion processes. Biotic changes include increased species richness immediately post-clear-felling due to shifts in species composition resulting from changes in individual species abundance and colonization by disturbance-adapted or open-habitat species. Given the large ecological changes caused by clear-fell harvesting and the negative public perception of clear-felling, it is surprising that few studies have investigated whether reducing clear-fell harvest area may be a viable strategy to mitigate ecological change within individual clearcuts. Clear-fell size studies conducted to date rarely exceed a maximum harvest area of 10 ha, and biotic communities measured exhibit mixed responses with respect to species richness and other biodiversity attributes with increasing clear-fell size. Some postharvest ecological responses are nonlinear with respect to harvest area and suggest possible threshold sizes beyond which clear-fell impacts increase disproportionately to their size. Conceptual models of potential ecological thresholds in clear-fell harvest impacts are discussed, as is the need for rigorous empirical testing to ensure a solid foundation exists for forest harvesting guidelines.
Effects of precommercial thinning on tree growth and lumber quality in a jack pine stand in New Brunswick, Canada
Authors: Zhang S Y , Chauret Gilles , Swift D Edwin , Duchesne Isabelle
Published: June 2006

A naturally regenerated jack pine (Pinus banksiana Lamb.) trial established in 1966 in New Brunswick was studied to determine how three precommercial thinning intensities (1.22 m × 1.22 m, 1.52 m × 1.52 m, and 2.13 m × 2.13 m) and a control (154 trees in total) affected tree growth and lumber quality. Mild (thinned to 1.22 m) and moderate (1.52 m) thinning had a modest impact on tree growth after 34 years (stand age 59). However, intensive thinning (2.13 m, or 2212 stems/ha) increased tree height by 13.1% compared with the control, whereas tree diameter and merchantable stem volume per tree increased by >20% and >75%, respectively. Yields of No. 2 and Better increased slightly with increasing thinning intensity, but lumber bending properties decreased with increasing thinning intensity. There was, respectively, >20% and >15% difference in lumber strength (modulus of rupture) and stiffness (modulus of elasticity) between the mild (1.22 m) and intensive (2.13 m) thinnings. Intensive precommercial thinning (2.13 m) is recommended for increased volume growth, but rotation age (>59 years) should not be reduced if lumber bending properties are of concern.
Tree seedling growth and survival over 6 years across different microsites in a temperate rain forest
Authors: Bellingham P J , Richardson S J
Published: June 2006

We investigated whether canopy tree seedlings have different growth and mortality rates on different microsites in montane rain forests of the western South Island, New Zealand. Seedling relative height growth rates of three species, Podocarpus hallii, Quintinia acutifolia, and Weinmannia racemosa, were very low (mean = 0.037 cm·cm–1·year–1). Seedling growth rates were higher on logs than on the ground at high light levels, but the probability of seedling death on logs was also greater at high light levels. Seedling foliar N and P concentrations were generally not different between logs and the ground. Growth rates and foliar N concentrations of Quintinia and Weinmannia were greater for seedlings on tree fern trunks than for seedlings on the ground. Mortality rates did not differ between seedlings on tree fern trunks and seedlings on the ground. Seedling densities of Quintinia and Weinmannia were greater on logs and tree ferns than on the ground. Podocarpus densities were not different between logs and the ground, and this species did not occur on tree ferns. Quintinia and Weinmannia benefit from establishment on elevated microsites but this is not clearly the case for Podocarpus. Tree regeneration niches for such slow-growing species can only be determined through long-term studies.
Ectomycorrhizal fungal communities of black spruce differ between wetland and upland forests
Authors: Robertson Susan J , Tackaberry Linda E , Egger Keith N , Massicotte Hugues B
Published: June 2006

Ectomycorrhizal (ECM) communities of black spruce (Picea mariana (Mill.) BSP) seedlings were characterized from three habitats spanning a moisture gradient in central British Columbia: black spruce dominated wetlands, black spruce  tamarack wetlands, and black spruce  lodgepole pine uplands. Morphological and molecular (PCR-RFLP) analyses indicated a diverse community of root-associated ECM fungi consisting of 33 morphotypes and 65 genotypes. ECM abundance varied significantly between habitats for six morphotypes. Although many occurred in all three habitats, some occurred in only one or two, and some genotypes had distributions that suggested habitat specificity across the moisture gradient. Intraspecific variation (defined as genotype variation within morphotypes) ranged from one to seven genotypes, depending on ECM morphotype. Both morphological and molecular analyses showed that ECM diversity was greater in upland than in wetland habitats and greater in black spruce  tamarack wetlands than in black spruce dominated wetlands (α ≤ 0.05). Morphological assessment captured contributions to diversity by both abundant and less abundant ECM morphotypes, whereas molecular analysis revealed patterns of genetic variation and habitat distribution at a finer resolution. The study presents the first comprehensive information on black spruce ECM and suggests that ECM community composition and richness varies across the moisture gradient in response to soil heterogeneity and alternate hosts (tamarack and lodgepole pine).
Height growth determinants and adaptation to temperature in pines: a case study ofPinus contortaandPinus monticola
Authors: Chuine Isabelle , Rehfeldt Gerald E , Aitken Sally N
Published: June 2006

In this study we aimed to compare and explain the height growth performance of two contrasting pine species: lodgepole pine (Pinus contorta Dougl. ex. Loud) and western white pine(Pinus monticola Dougl. ex D. Don.). We compiled measurements of total height growth at different ages and shoot elongation phenology realized in several provenance test trials for 109 provenances of lodgepole pine and 54 provenances of western white pine. The response of shoot elongation to temperature was assessed using a phenological model fitted on provenance mean growth curves. Although total height growth followed the same geographic trends in both species, the response of shoot elongation to temperature was different between the two, with few (lodgepole pine) or no differences among provenances (western white pine) from diverse geographic regions. The temperature for which potential cell growth rate is 50% was 10.8 ± 0.13 °C (mean ± standard error) for western white pine compared to 5.26 ± 0.075 °C for lodgepole pine. Phenology did not explain growth performance differences among geographical regions in both species, which instead were explained by differences in the number of internodes set the preceding summer; provenances originating from stressful environments produced the fewest internodes, possibly due to reallocation of carbohydrates to stress resistance.
Decomposition of green foliage in eastern hemlock forests of southern New England impacted by hemlock woolly adelgid infestations
Authors: Cobb Richard C , Orwig David A , Currie Steve
Published: June 2006

This study examined the impacts of hemlock woolly adelgid (Adelges tsugae Annand) (HWA), a small, invasive insect, on foliar chemistry, forest floor microclimate, and subsequent green foliage decomposition in eastern hemlock (Tsuga canadensis (L.) Carrière) forests. We investigated the direct effects of HWA feeding and indirect changes in microclimate on foliar decomposition by incubating HWA-infested and uninfested foliage across eight eastern hemlock dominated stands in southern New England that had different histories of HWA infestation. Infested stands had much poorer average crown health (3.4 versus 1.4 crown loss ratings), higher percent open sky (10.9 ± 2.4 vs. 5.3 ± 0.5 gap light index), and lower organic soil moisture (0.83 ± 0.02 g·g1 vs. 1.06 ± 0.05 g·g1) than uninfested stands. There were no significant differences in percent C, percent N, or percent lignin for the excised foliage at the start of the study. However, after 120 days, decomposing foliage from infested trees had significantly higher N concentrations (1.83% ± 0.05% vs. 1.69% ± 0.02 %) and lower C/N ratios (29.9 ± 0.8 vs. 31.6 ± 0.2) than uninfested foliage, suggesting that HWA herbivory resulted in alterations of litter chemistry as decomposition progressed. Mass loss of common uninfested foliage was lower in uninfested hemlock stands than in infested ones (30.9% ± 0.7% vs. 34.2% ± 0.1%). These rates of mass loss were significantly correlated with microclimate factors and indicate that organic soil moisture levels are controlling decomposition in HWA-infested forests. Infestation by HWA causes virtually no direct feeding damage to foliage, but it does lead to several indirect and significant ecological and functional changes over the 10- to 20-year course of infestation and stand decline.
Genetics of wood stiffness and its component traits inPinus radiata
Authors: Dungey Heidi S , Matheson A Colin , Kain Dominic , Evans Robert
Published: June 2006

The potential for breeding Pinus radiata D. Don to improve wood stiffness (modulus of elasticity, MoE) was examined by obtaining pith-to-bark cores from trees at breast height in two independent genetic trials. The effectiveness of early selection for stiffness and indirect selection on the component traits, microfibril angle (MfA) and wood density, was determined as well as the age-related changes in the genetic variation of these traits. The first trial comprised 50 open-pollinated families in the central North Island, New Zealand. The second trial comprised 20 control-pollinated families in New South Wales, Australia. The genetic control of MfA, density, and MoE was found to be high in the corewood and moderate in the outerwood. Estimated genetic correlations suggested that early selection for most traits would be successful but could be carried out slightly earlier at the New Zealand site than at the Australian site. To maximize gain in the corewood, selection for MoE and MfA would be most effective around rings 4-8. There were no adverse correlations between MoE and MfA or density, implying that selection for MoE would also improve MfA and density.
The dynamics of coarse woody debris in boreal Swedish forests are similar between stream channels and adjacent riparian forests
Authors: Dahlström Niklas , Nilsson Christer
Published: June 2006

Although numerous studies have focused on the dynamics of coarse woody debris (CWD) in boreal Fennoscandian forests, information on CWD in streams remains limited. To achieve a better understanding of CWD dynamics in streams we compared amounts and characteristics of CWD between streams and adjacent riparian forests in old-growth and managed forest sites, respectively. We also identified distances to the sources of CWD and evaluated these in relation to the lateral zonation of riparian trees. CWD volumes found in the stream channels were related to, but exceeded, the volumes found in the adjacent forest. In-channel volumes separated by species were better correlated with terrestrial volumes of CWD than with volumes of living trees. Tree species appeared to be zoned across the riparian zone, with slightly higher abundances of deciduous trees and lower abundances of Scots pine trees close to the stream. Similar to upland forests, riparian forests were dominated by coniferous tree species, mainly Norway spruce (Picea abies (L.) Karst.). These findings suggest large similarities in CWD input between streams and riparian forests and substantially slower decomposition rates in stream channels compared with those in riparian forest. The results provide an improved basis for creating reliable models of CWD supply and maintenance in streams based on knowledge of forest development and CWD dynamics in the terrestrial environment. Site productivity could potentially be used to predict CWD volumes in stream channels under pristine conditions.
Modeling seed dispersal of black cherry, an invasive forest tree: how microsatellites may help?
Authors: Pairon Marie , Jonard Mathieu , Jacquemart Anne-Laure
Published: June 2006

We used empirical models and three dispersal functions (Weibull, lognormal and 2Dt) to model seed distributions derived from the black cherry (Prunus serotina Ehrh.) understorey of a pine-dominated stand. Two different approaches were used to disentangle the overlapping seed shadows: the traditional inverse modeling approach and the genetic approach that uses microsatellite markers to assign a dispersed seed to its maternal parent. The distinction was made between the seeds passively dispersed by gravity (fruits with mesocarp) and those dispersed by birds (fruits without mesocarp). Our main objectives were to compare the three dispersal functions and assess the differences between the two approaches used. The functions performed equally well, but the lognormal function often showed a better data correlation. The best dispersal curves obtained by both traditional and genetic approaches were quite similar for the seeds dispersed by gravity, and 95% of these seeds were predicted to fall 5 and 3 m away from the parent tree for the traditional and genetic approaches, respectively. Differences were more important for the seeds dispersed by birds. The traditional approach predicted a lower number of seeds near the parent plant and a higher dispersal distance. Microsatellites provided accurate information on individual dispersal events and led to a better insight into the dispersal process.
Nitrogen mineralization in short-rotation tree plantations along a soil nitrogen gradient
Authors: Lee Kye-Han , Jose Shibu
Published: June 2006

We measured soil nitrogen (N) mineralization along an N fertilization gradient (control; irrigation only (I + 0 N); irrigation with 56 (I + 56 N), 112 (I + 112 N), and 224 (I + 224 N) kg N·ha1·year1, respectively) in 7-year-old cottonwood (Populus deltoides Marsh.), cherrybark oak (Quercus falcata Michx. var. pagodifolia Ell.), American sycamore (Platanus occidentalis L.), and loblolly pine (Pinus taeda L.) plantations established on a well-drained Redbay sandy loam (a fine loamy, siliceous, thermic Rhodic Paleudult), in Florida, USA. Nitrogen mineralization was measured monthly for 1 year, beginning in April 2001, with the buried bag incubation technique. Irrigation alone or fertigation (irrigation + N) affected annual net N mineralization rates under hardwood species, but no effect was found under loblolly pine. Overall, the rates were higher under cherrybark oak (108 kg N·ha1·year1) and cottonwood (101 kg N·ha1·year1) than under sycamore (82 kg N·ha1·year1) and loblolly pine (75 kg N·ha1·year1). Significant correlations were observed between N mineralization and stem volume in all species but loblolly pine. These results suggest that N mineralization response to irrigation or fertigation (irrigation + N) is heavily dependent on species-specific feedback mechanisms. Our results also support the hypothesis that the N mineralization versus productivity relationship is a fundamental feature of forests, resulting from the impact of N availability on productivity and the long-term feedback effects of vegetation on N availability.
Patterns of initial versus delayed regeneration of white spruce in boreal mixedwood succession
Authors: Peters Vernon S , Macdonald S Ellen , Dale Mark RT
Published: June 2006

The timing of white spruce regeneration in aspen (Populus tremuloides Michx.)  white spruce (Picea glauca (Moench) Voss) boreal mixedwood stands is an important factor in stand development. We examined boreal mixedwood stands representing a 59-year period of time since fire and determined (1) whether and when a delayed regeneration period of white spruce occurred, (2) whether the relative abundance of initial (<20 years) versus delayed (≥20 years postfire) regeneration is related to seed availability at the time of the fire, and (3) what are the important regeneration substrates for initial versus delayed regeneration. Initial regeneration occurred primarily on mineral soil or humus, while delayed regeneration established primarily on logs and peaked 3844 years after fire. Of the 20 stands investigated, seven were dominated by initial regeneration, six were dominated by delayed regeneration, and seven were even mixtures of both. The dominance of a site by initial or delayed regeneration could not be simply explained by burn timing relative to mast years or distance to seed source; our results suggested that fire severity and the competitive influence of initial regeneration on delayed regeneration were important at fine scales. Based on our results we describe several possible postfire successional pathways for boreal mixedwood forests.
Restoration of floral diversity through plantations on abandoned agricultural land
Authors: Newmaster Steven G , Bell F Wayne , Roosenboom Christopher R , Cole Heather A , Towill William D
Published: June 2006

Plantations have been claimed to be "monocultures", or "biological deserts". We investigated these claims in the context of a long-term study on plant diversity within plantations with different indigenous tree species, spacings, and soil types that were compared with 410 native stands. Soil type had no influence on plantation species diversity or abundance, and wider spacing resulted in higher richness, lower woody plant abundance, slightly higher cover of herbaceous plants, and large increases in cryptogam cover. We also found a canopy species × spacing interaction effect, where the impact of increased spacing on understory vegetation was more pronounced in spruce than in pine plantations. The dynamic community interactions among species of feathermoss appear to be in response to the physical impediment from varying amounts of needle rain from the different tree species. High light interception and needle fall were negatively correlated with understory plant diversity, as was lack of structural diversity. This study indicates that through afforestation efforts agricultural lands can be restored to productive forests that can harbour nearly one-half of the plant species found in equivalent natural forests within the same geographic region in as little as 50 years. We recommend applying afforestation using indigenous conifer species as a first step towards rehabilitating conifer forests that have been converted to agriculture and subsequently abandoned.
Riparian tree fall directionality and modeling large wood recruitment to streams
Authors: Sobota Daniel J , Gregory Stanley V , Sickle John Van
Published: June 2006

Directionality of tree fall in riparian forests can strongly influence predictions of large wood recruitment to streams, yet accuracy of this model parameter has rarely been assessed with field data. We measured fall directions of 1202 riparian trees distributed among 21 stream sites across the Pacific Northwest, USA. Fall directions were oriented towards the stream at 16 sites, upstream at four sites, and not distinguishable from random at one site. Average tree fall direction across sites was correlated with valley constraint (Spearman r = 0.53; p = 0.02), but variability of fall directions was not correlated with this variable. When grouped by species (six conifers and one deciduous), individual trees exhibited stronger tendency to have fallen towards the channel on steep hillslopes (>40%) than on moderately sloped landforms (<40%). Integration of field data into an established recruitment model indicated that 1.5 to 2.4 times more large wood (by number of tree boles) would be recruited to stream reaches with steep hillslopes than to reaches with moderate side slopes or flat banks, if riparian forest conditions are assumed to be constant. We conclude that stream valley topography should be considered in models that use tree fall directions in predictions of large wood recruitment to streams.
Economic analysis of stand establishment for Scots pine
Authors: Hyytiäinen Kari , Ilomäki Sakari , Mäkelä Annikki , Kinnunen Kaarlo
Published: June 2006

Experimental data, a process-based forest growth model, and stand-level economic optimization were combined to investigate financial returns from investments for establishing Scots pine (Pinus sylvestris L.) stands in southern Finland. Four regeneration methods (planting, sowing, and natural regeneration with 25 or 100 seed trees·ha1) and three intensities of soil preparation (unprepared, conventional harrowing, intensive harrowing) are compared. At a 1% interest rate, artificial regeneration by planting or sowing and high investment in soil preparation yielded the highest net present values. Natural regeneration involves low material and labor costs and becomes the optimal regeneration method at a 3% interest rate. Sowing and natural regeneration yielded equally good economic outcomes at a 5% interest rate. Owing to overlapping rotation periods, natural regeneration with a high number of seed trees yielded a long-run timber supply comparable to that obtained with artificial regeneration. However, constraints limiting density and retention time for seed trees involve additional costs with natural regeneration. Optimal thinning aimed at artificial regeneration may provide an attractive option for converting the stand to natural regeneration.
On the formation of dense understory layers in forests worldwide: consequences and implications for forest dynamics, biodiversity, and succession
Authors: Royo Alejandro A , Carson Walter P
Published: June 2006

The mechanistic basis underpinning forest succession is the gap-phase paradigm in which overstory disturbance interacts with seedling and sapling shade tolerance to determine successional trajectories. The theory, and ensuing simulation models, typically assume that understory plants have little impact on the advance regeneration layer's composition. We challenge that assumption by reviewing over 125 papers on 38 species worldwide that form dense and persistent understory canopies. Once established, this layer strongly diminishes tree regeneration, thus altering the rate and direction of forest succession. We term these dense strata recalcitrant understory layers. Over half of the cases reviewed were linked to increases in canopy disturbance and either altered herbivory or fire regimes. Nearly 75% of the studies declared that competition and allelopathy were the likely interference mechanisms decreasing tree regeneration, yet only 25% of the studies used manipulative field experiments to test these putative mechanisms. We present a conceptual model that links the factors predisposing the formation of recalcitrant understory layers with their interference mechanisms and subsequent impacts on succession. We propose that their presence constricts floristic diversity and argue for their explicit inclusion in forest dynamics theory and models. Finally, we offer management suggestions to limit their establishment and mitigate their impacts.
The relationship between site and tree characteristics and the presence of wet heartwood in black spruce in the boreal forest of Quebec, Canada
Authors: Krause Cornelia , Gagnon Réjean
Published: June 2006

Wet heartwood in black spruce (Picea mariana (Mill.) BSP) causes considerable problems during the drying process. Forest companies try to avoid harvesting stands with wet heartwood, but no relationship has been yet established between the incidence of wet heartwood and tree or site characteristics. To characterize areas containing a significant proportion of black spruce affected by wet heartwood, a total of 635 black spruce trees were sampled in eighteen 400 m2 study plots under management in the central boreal forest of Quebec. A total of 18 study sites were analysed and classified as wet, intermediate, or dry, based on the proportion of individuals with wet heartwood. Thirteen of the study sites were classified as wet, two as intermediate, and three as dry. The average age calculated for trees on wet sites was significantly (p = 0.0001) higher than that of the other two classes, whereas growth rate was significantly lower on wet sites. No difference was noted in the average height or diameter of the individuals from all three classes. The wet sites contained organic soil, whereas Podzols characterized two of the three dry study sites. An additional sampling of black spruce (n = 509) revealed a significant relationship between the groundwater level and heartwood moisture content classification (i.e., dry, intermediate, or wet). Trees in the dry heartwood class grew on sites with the lowest groundwater levels (p = 0.002) compared with trees in the wet or intermediate classes.
Native American influences on the forest composition of the Allegheny Plateau, northwest Pennsylvania
Authors: Black Bryan A , Ruffner Charles M , Abrams Marc D
Published: June 2006

We integrate witness tree distribution, Native American archaeological sites, and geological and topographic variables to investigate the relationships between Native American populations and pre-European settlement forest types on the Allegheny Plateau, northwest Pennsylvania. Detrended correspondence analysis of witness tree data separated the presettlement forests into oakhickorychestnut and beechhemlockmaple communities. Oak, hickory, and chestnut forests were centered on Native American village sites. Using archaeological data, an index of Native American influence (NAI) was derived to reflect the intensity of Native American land use across the landscape. In a comparison among species, mean NAI value of oak, hickory, and chestnut trees was significantly higher than that of beech, maple, and hemlock. Logistic regression demonstrated that among geology type, landform, elevation, aspect, slope, and NAI, NAI was by far the most significant predictor of oak, hickory, and chestnut distribution. Although cause and effect of this relationship cannot be tested, we suggest that long-term Native American activity selected for the disturbance-adapted oak, hickory, and chestnut. We contend that Native American agriculture, burning, and resource extraction could have converted maplebeechhemlock to oakhickorychestnut, or at least reinforced the dominance of this forest type.
Site classification of afforested arable land based on soil properties for forest production
Authors: Wall A , Westman C J
Published: June 2006

We used discriminant analysis to identify the key soil properties that discriminate among 30 forest sites representing a floristic site-type fertility gradient. Thereafter we classified 24 sites on afforested arable land into forest site types using these discriminant functions. The most important soil properties of the E horizon separating different forest site types were pH and the densities of Ca, P, and silt. Using properties of soil from the 010 cm depth to represent the current level of site productivity, we classified all soils from afforested arable land into forest site types of high productivity. Among these soils, the most fertile were those with high clay and silt densities. Again, using properties of soil from the 3040 cm depth to emulate the site productivity that prevailed before soil-formation processes and agricultural land use altered the upper soil horizon, we classified most of the soils from afforested arable land into forest site types of medium productivity. This implies that agricultural land use had increased the densities of basic elements at the 010 cm soil depth and, consequently, site productivity. The high productivity of former arable lands was attributed to their previous agricultural use and to the inherent properties of fine-grained soils.
Elevated mortality of residual trees following single-tree felling in northern hardwood forests
Authors: Caspersen John P
Published: June 2006

In this paper, I examine tree mortality in northern hardwood forests subjected to single-tree felling. Mortality risk was estimated as a function of growth prior to harvest and time since harvest. This allowed me to separately quantify mortality due to (1) natural processes, (2) intentional felling, and (3) stress and (or) felling damage (postcut mortality). The long-term rate of mortality due to natural causes was 1.5% per year. The intentional felling of trees increased the average mortality to 3.1%, and postcut mortality of residual trees increased the average an additional 0.2%3.3% (the latter reflects both the direct negative effects of harvesting and the indirect positive effect of releasing residual trees from suppression). Thus, from a population-level perspective, the increased mortality caused by stress and (or) felling damage to residual trees was small compared to that caused by both natural mortality and tree felling. However, the long-term population average obscures more dramatic (though transient) effects of felling on small trees (DBH <10 cm), for which mortality rates increased by as much as 5% immediately after felling. This increase is several times greater than the natural mortality rate for small trees and may therefore have a substantial impact on stand structure and community dynamics.
Impacts of repeated fertilization on components of the soil biota under a young lodgepole pine stand in the interior of British Columbia
Authors: Berch Shannon M , Brockley Robert P , Battigelli Jeff P , Hagerman Shannon , Holl Brian
Published: June 2006

We studied elements of the soil biota in a 24-year-old lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stand in interior British Columbia 10 years after initiation of annual fertilizer treatments. The treatments included an unfertilized control, ON1 (650 kg nitrogen (N), 400 kg phosphorus (P), 400 kg potassium (K)), and ON2 (1350 kg N, 400 kg P, 400 kg K). In the forest floor, the C/N ratio was lower in ON1 and ON2 than in the unfertilized control, while available P and exchangeable magnesium were higher; NO3was higher only in ON2. In the upper mineral soil, available P was higher in ON1 and ON2, while NO3was higher only in ON2. In both the forest floor and upper mineral soil, microbial activity was higher in ON1 than in the unfertilized control or ON2. In the forest floor and mineral soil, Acari density, especially Oribatida and Prostigmata, was higher in ON2 than in ON1 and the unfertilized control. In contrast, Collembola density, especially Hypogastruridae, increased in ON2 relative to that in other treatments. ON2 had less lodgepole pine fine-root length, fewer ectomycorrhizal roots, fewer active fine roots, more nonmycorrhizal fine roots, and a different ectomycorrhizal community structure than ON1 and the unfertilized control. These dynamic changes to the soil biota appear to reflect changes to the plant community in response to fertilization.
Response of soil microbial biomass, activities, and community structure at a pine stand in northeastern Germany 5 years after thinning
Authors: Maassen Sebastian , Fritze Hannu , Wirth Stephan
Published: June 2006

A thinned and an unthinned treatment were compared in a 62-year-old pine stand located in northeastern Germany (Brandenburg, Ost-Prignitz, Revier Beerenbusch) (year of thinning: 1999, degree of canopy opening: 0.4). Samples of the organic layer (O) and the mineral horizon (Aeh) of an acid brown earth were collected along a transect at each treatment in November 2003 and April 2004. Substrate induced respiration, basal respiration, and a suite of enzymes involved in the degradation of lignocellulose (endocellulase, exocellulase, β-glucosidase, endoxylanase, exoxylanase, phenoloxidase, peroxidase) were assayed. Microbial community structure and relative biomass of bacteria, actinomycetes, and fungi were assayed by phospholipid fatty acid analysis. Five years after thinning, microbial biomass, basal respiration, and enzyme activities in both soil layers did not differ significantly between thinned and unthinned treatments. However, the analysis of soil microbial community structure revealed a significant difference between the thinned and unthinned treatment at both sampling dates. Thus, it was concluded that thinning had not yet resulted in any response in soil microbial activities at the site under study, but since early evidence of change in the microbial community was detected, long-term monitoring and additional studies on mineralization activities are required.
Evidence for competition and facilitation trade-offs: effects of Sitka alder density on pine regeneration and soil productivity
Authors: Simard Suzanne W , Radosevich Steven R , Sachs Donald L , Hagerman Shannon M
Published: June 2006

We suggest that the net outcome of interactions between regenerating conifers and early seral deciduous species depends on trade-offs between competition and facilitation over time. Vegetation management treatments that dramatically reduce competitive effects of deciduous species may constrain the ability of conifers to optimize resource trade-offs (e.g., increased growth response to light at the expense of increased drought mortality), potentially affecting long-term productivity. In a 15-year study in southern interior British Columbia, we investigated whether lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) survival, growth, and resource availability differed among manipulated stand compositions, from pure pine stands to mixtures with native N2-fixing Sitka alder (Alnus viridis subsp. sinuata (Regel) Á. Löve & D. Löve) or herbs. We found that pine growth increases were sustained only in pure stands, where alder and herbs were completely removed, corresponding with short-term increases in light, soil and air temperature, and soil nitrate. However, this came at a significant cost to survival (through loss of protection from browsing, desiccation, and sun scald), as well as dramatic depletions in soil nitrogen mineralization over the longer term. Our results support a competitionfacilitation trade-off hypothesis, suggesting that treatment-imposed shifts in resource availability over time could negatively affect forest productivity.
Twenty years of community dynamics in a mixed conifer  broad-leaved forest under a selection system in northern Japan
Authors: Yoshida Toshiya , Noguchi Mahoko , Akibayashi Yukio , Noda Masato , Kadomatsu Masahiko , Sasa Kaichiro
Published: June 2006

Single-tree selection has been employed widely in northern Japanese mixed forests, but management-induced changes in forests are not well understood. This study examined demographic parameters of major tree species during a 20-year study of a 68 ha stand in which single-tree selection has been conducted since 1971. Results showed that growth and survival of conifers (mostly Abies sachalinensis (Fr. Schm.) Masters) was the most strongly positively affected by the treatment. Nevertheless, recruitment of conifers was not sufficiently improved, suggesting their decreased dominance over the longer term. Instead, shade-intolerant broad-leaved species (mainly Betula ermanii Cham.) will gradually increase because of their higher recruitment rates after the treatment. Shade-tolerant broad-leaved species (mainly Acer mono Maxim. and Tilia japonica (Miq.) Simonkai) appeared to experience the most distinct negative effects, especially on survival. These trends differed markedly from those reported in previous papers concerning partial harvesting systems, which predicted an increase in dominance of shade-tolerant species. The results shown here should be generalized carefully because we have investigated only one stand without repetition of the control area. Nevertheless, trends described in this large-scale, long-term study could provide a basis for simulating stand dynamics. We discussed possible reasons for the observed patterns and provided implications for sustainable management in the region.