bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Ferric Citrate Transport Gene Promoter of
Escherichia coli
Authors: Enz Sabine , Mahren Susanne , Menzel Claudia , Braun Volkmar
Published: March 2003

FecI, an extracytoplasmic-function σ factor, is required for initiation of transcription of the ferric citrate transport genes. A mutational analysis of the
fecA
promoter revealed that the nonconserved −10 region and a downstream regulatory element are important for
fecA
promoter activity. However, nucleotide substitutions in the well-conserved −35 region also have an effect on the
fecA
promoter activity. Titration of FecI suggests that the FecI-RNA polymerase holoenzyme does not bind strongly to the downstream regulatory element, which is therefore probably involved in a subsequent step of transcription initiation.
River Ice Engineering / Ingénierie des glaces fluvialesA digital image processing system to characterize frazil ice
Authors: Doering John C , Morris Michael P
Published: March 2003

The detection, measurement, and characterization of frazil ice particles is a necessary first step in advancing our understanding of frazil ice processes as well as improving models. The detection of frazil ice has been accomplished in a number of ways. Herein, a digital image processing system to characterize frazil in a laboratory environment is described. The system is part of an ice research facility that uses a counter-rotating flume to generate frazil ice. Frazil ice is detected using a cross-polarized light technique. The system acquires digital gray-scale images of frazil ice that are analyzed and manipulated digitally to elucidate the temporal and spatial variation of frazil ice characteristics. For example, the system can be readily used to determine the size distribution of frazil ice particles, the vertical distribution of frazil, or the concentration of frazil ice.Key words: frazil ice characterization, progressive scan camera, frame grabber, digital image, gray scale, processing system, pixel, binary image.
Determining winter discharge based on hydraulic modeling
Authors: Hicks F E , Healy D
Published: March 2003

At present, the only accurate means of determining discharge under ice-affected conditions is by direct measurement, a costly undertaking that places field staff at personal risk. Consequently, winter discharge hydrographs are often based on interpolation between relatively infrequent direct measurements. This study explores the viability of using gradually varied flow hydraulic modeling to determine winter discharge. Based on an analysis of data obtained on the Mackenzie River near Fort Providence, Northwest Territories, and on the Athabasca River at Fort McMurray, Alberta, it appears that the errors associated with this approach could be as low as 3%. The potential applicability of stagefall models based on hydraulic model data is also explored as a means to facilitate automated winter discharge measurements. Indications are that the viability of stagefall modeling is highly dependent on identifying a suitable reach and establishing an adequate range of data. Hydraulic modeling has the potential to address both these issues.Key words: streamflow measurement, rivers, ice, hydraulic modeling, stagefall analysis.
Agencement de prises d'eau en région nordique
Authors: Morse Brian , Trudeau Guy
Published: March 2003

The great quantity of small rivers in proximity of Canadian communities provide an excellent source of potable water. However, in our northern climate, intake structures must be built in rivers that are infested with ice. Since ice and hydraulic structures do not cohabit very well, the intakes must be designed to account for the many forms of ice. Referring to specific case studies, we examine the advantages and disavantages of conventional designs for municipal and industrial intakes. Conventional designs often employ weirs to raise water levels, whereas percolation systems withdraw water through the river bed. Their intake capacity is presented, and the use of retention basins to increase efficiency is discussed. Based on lessons learnt, we propose a design that meets the challenge of supplying water to a ski resort in typical hostile ice conditions for the Jacques-Cartier River in the Quebec City region.Key words: water intake, potable water, percolation, frazil ice, northern rivers.
Ice breakup: a neglected factor in river ecology
Authors: Prowse Terry D , Culp Joseph M
Published: March 2003

To minimize environmental impacts that may result from any engineered modifications of stream or river systems, a basic understanding of river ecology is required. Most fundamental theories of river ecology have developed largely from studies of warm-temperate and tropical streams and rivers. As these theories evolved over the last few decades, floods were recognized increasingly as dominant hydrologic events that control numerous abiotic and biotic forms and processes, both within the channel and on the adjacent riparian floodplains. Over approximately the same time frame, river-ice breakup was shown to be a major, if not predominant, source of floods on cold-regions rivers. Despite this, rarely has the role of ice-induced flooding been considered by subsequent modifications to the original theories or in the extensive studies and literature that they spawned. This manuscript reviews the broad, although frequently anecdotal, information about the abiotic and biotic effects of breakup processes and flooding. Based on this, it argues for breakup to be incorporated in future advancements of river ecological theory. The extensive list of cited studies provides a valuable reference source for scientists and engineers assessing development-related impacts on cold-regions streams and rivers, or further researching ecological aspects of river-ice breakup.Key words: river ice, river ecology, freshwater ecology, flooding, breakup, ice jam.
Climatic change and river ice breakup
Authors: Beltaos Spyros , Burrell Brian C
Published: March 2003

The flow hydrograph, thickness of the winter ice cover, and stream morphology are three climate-influenced factors that govern river ice processes in general and ice breakup and jamming in particular. Considerable warming and changes in precipitation patterns, as predicted by general circulation models (GCMs) for various increased greenhouse-gas scenarios, would affect the length and duration of the ice season and the timing and severity of ice breakup. Climate-induced changes to river ice processes and the associated hydrologic regimes can produce physical, biological, and socioeconomic effects. Current knowledge of climatic impacts on the ice breakup regime of rivers and the future effects of a changing climate are discussed.Key words: breakup, climate change, global warming, greenhouse effect, hydrology, ice, ice jam, impacts, prediction, river ice.
Review of prediction methods for breakup ice jams
Authors: White Kathleen D
Published: March 2003

Breakup ice jams often occur suddenly, with little warning. Severe flooding or ice-related damage can result from rapid rises in upstream water levels associated with breakup ice jams. Breakup jam prediction methods that can be used to increase response time are desirable to minimize flood damage, including potential loss of life. A variety of hydrologic and hydraulic models exist to predict open-water flooding, whether resulting from rainfall, snowmelt, or catastrophic events such as dam breaches. However, breakup ice jams result from a complex series of physical processes that cannot currently be described with analytical or deterministic models, hindering the development of prediction methods. Those which do exist are highly site specific and range from simple empirical models to an artificial intelligence formulation. To date, no one model exhibits a clear advantage over the others. This paper provides examples of existing breakup ice jam prediction methods and discusses their potential advantages and disadvantages.Key words: ice jam, breakup ice jam, flood prediction, flood warning, ice jam mitigation.
Midwinter breakup and jamming on the upper Saint John River: a case study
Authors: Beltaos Spyros , Ismail Sayed , Burrell Brian C
Published: March 2003

Changing climates will likely result in more frequent midwinter ice jams along many Canadian rivers, thereby increasing the likelihood of flood damage and environmental changes. Therefore, the possibility of more frequent ice jams has to be considered during the planning of flood damage reduction measures, the design of waterway structures, and the enactment of measures to protect the environment. As a case study of midwinter jamming, four winter breakup and jamming events that occurred along an upper stretch of the Saint John River during the 1990s are described and the implications of similar midwinter jamming are discussed.Key words: breakup, river ice, climate change, ice jamming, ice thickness, winter, winter thaw.
Ice jam release surges, ice runs, and breaking fronts: field measurements, physical descriptions, and research needs
Authors: Jasek Martin
Published: March 2003

Surges or flood waves made up of ice and water resulting from the release of ice jams can be destructive to life and property and are also one of the more complicated problems in river ice engineering. The interaction between the ice mechanics and unsteady flow leads to results that are often unpredictable with open water unsteady flow models. There are considerable differences of opinion on the degree of significance of this waterice interaction. There have also been recent developments in two-phase unsteady flow modelling which are capable of handling these complicated situations. It is the aim of this paper to present both quantitative data and qualitative observations on ice runs and breaking fronts to provide insight to the physical processes involved as and possible sources of model calibration data.Key words: ice jam, surge, unsteady flow, ice run, ice jam release, breaking front, break-up, breakup, break-up front.
Semi-automated classification of river ice types on the Peace River using RADARSAT-1 synthetic aperture radar (SAR) imagery
Authors: Weber Frank , Nixon Dan , Hurley Jeff
Published: March 2003

The winter regime of the Peace River in northern British Columbia and Alberta is a determining factor for the operation of the British Columbia Hydro and Power Authority Williston Reservoir. Therefore, fine beam RADARSAT-1 synthetic aperture radar (SAR) satellite images were acquired in winter and spring 2000 and 2001 and analyzed for ice cover types. Video footage of the ice conditions on the Peace River was obtained from aerial ice observations that were conducted simultaneously with the image acquisitions. The analysis of the images was done (i) visually and (ii) using an unsupervised Fuzzy K-means classification. To streamline the process in an operational environment, the unsupervised ice classification was semi-automated. The unsupervised classification broke the data into seven classes, which represent the major ice cover types observed on the Peace River. The spatial distribution of ice cover types as generated by the ice classification generally coincides well with air-truth information and backscatter signatures from SAR images. The location of the boundaries between the ice types appears to be accurate, but it may not be precise. The ice maps can be used for ice monitoring, decision-making purposes, or the verification of ice models.Key words: river ice, remote sensing, RADARSAT-1, Peace River, semi-automated classification.
Numerical models of the exchange flows between Hamilton Harbour and Lake Ontario
Authors: Hamblin P F , He C
Published: March 2003

Accurate simulations of the flow and the transport of water quality constituents in such coastal zones of large lakes as the western end of Lake Ontario and Hamilton Harbour are needed to assess the impact on pollutant levels of cleanup operations and sewage diversions. Coastal models in temperate zone lakes are classified in terms of density stratification, uniform in winter and stratified during summer. During the winter period a 1-D model of the flow between a lake and adjacent harbour is shown to agree favourably with advanced acoustic measurements of the flow in the connecting passage, but does not account for the observed winter buildup of salinity in the harbour. A calibrated 2-D hydrodynamic and salt transport model is used to show that significant exchange does not take place unless the excursion of the inflow is several times greater than the length of the connecting channel, an infrequent occurrence. The exchange is also shown to depend on the flow field at the entrances of the channel. In summer a 1-D vertical model illustrates the dramatic effect of the inflow from Lake Ontario on hypolimnetic temperatures of the harbour. Three-dimensional hydrodynamic and temperaturesalt transport models are validated by extensive field observations taken in 1996. The stratified exchange is much stronger than its winter counterpart and more steady. Winter exchange is forced by short-term water level fluctuations, whereas summer or stratified exchange by slowly fluctuating density contrasts between the two water bodies.Key words: exchange flows, hydrodynamic and transport modelling, lakes, harbours, water quality.
Static ice loads on dams
Authors: Comfort G , Gong Y , Singh S , Abdelnour R
Published: March 2003

A 9 year field program was undertaken from 19911992 to 19992000 to (i) measure the loads in the ice sheet near a dam, (ii) measure the load distribution between a gate and a pier, and (iii) compare the loads on wooden and steel stoplogs. Parallel work was conducted to develop analytical predictors for ice loads. Much progress has been made. One of the most significant findings has been to identify the importance of water level changes on the resulting ice loads. Ice loads are much higher and more variable (compared to purely thermal loads) when significant, but not excessive, water level changes occur. Methods have been developed to predict the ice load. The algorithms predict thermal loads well. They are less accurate for loads produced by a combination of water level and ice temperature changes. An environmental model was developed, and the predictions using the model compare well with the measured data. Hindcast analyses were carried out to evaluate the distribution of expected ice temperature changes and thermal events. With respect to the loads on gates and stoplogs, an analytical method was developed to extend the results obtained in this project to other stoplog or gate configurations (i.e., spans, flexural rigidities, etc.) and pier lengths.Key words: ice loads, dam(s).
Modelling creep deformation in floating ice
Authors: Steenis K van , Hicks F E , Hrudey T M , Beltaos S
Published: March 2003

The ability to predict the response of an ice sheet to long-term loading is important in many situations. In northern regions, ice sheets have been used as construction platforms, drilling rig platforms, airfields, parking lots, and festival platforms. Numerical models can be used to predict the deflection of an ice sheet over time and, together with a failure criterion based on allowable deflection, can facilitate the safe use of an ice cover under long-term loading situations. In this study, a two-dimensional axisymmetric finite element model was developed to model the behaviour of a homogeneous, transversely isotropic, infinite ice cover under long-term loading. The model was validated using 33 sets of long-term load test data from large-scale field experiments performed on lake, bay, and reservoir ice and was shown to be capable of reliably predicting deflections under a variety of loading scenarios.Key words: bearing capacity of ice, long-term loading, ice platforms.
Validation en temps réel des données hydrométriques
Authors: Faouzi Berrada , Malika Khalili , Saad Bennis
Published: March 2003

The managers of hydrological systems take real-time level and discharge measurements on several reservoirs and river reaches. The measurements are frequently tainted with errors that are reflected by uncertainties in decision making and by non-optimal resource management. This article aims at developing a methodology for the validation of levels in real-time. The proposed approach is based on material and analytical redundancy, and uses two models. The first one is spatial and enables linking of the measurements carried out at different stations with the help of a multiple regression equation. The second one is temporal, which enables the determination of variation trend at the different stations with the help of an auto-regressive model. These two models are incorporated into a diagnosis system for breakdowns based on a logic vote principle. Among the values that are measured and estimated by the linear regression model, the one which is the most consistent with the variation trend indicated by the auto-regressive model is selected. The Kalman filter is used to filter the measurements and identify the parameters of the models used in real-time. The proposed methodology turned out to be conclusive when applied to both measured data and synthetic hydrographs.Key words: validation, real-time, material redundancy, analytical redundancy, regressive, auto-regressive, Kalman filter.
Lateral resistance of bolted wood-to-concrete connections loaded parallel or perpendicular to grain
Authors: Mohammad M , Karacabeyli E , Quenneville J H.P
Published: March 2003

Tests were carried out to determine the lateral resistance of bolted lumber-to-concrete connections. Specimens were made of hemlockfir and sprucepinefir lumber and bolted to concrete blocks using anchor bolts. Three sizes of anchor bolts were used, with nominal diameters of 12.7 mm (1/2 in.), 15.8 mm (5/8 in.), and 19.1 mm (3/4 in.). The minimum strength of the connections loaded parallel to grain with a single bolt exceeds the characteristic strength specified in the 1994 edition of the Canadian Standards Association (CSA) standard O86.1 by a factor of 1.6 for 12.7 mm (1/2 in.) diameter bolts and 2.0 for 19.1 mm (3/4 in.) diameter bolts. Results on connections loaded perpendicular to grain showed that the 5th percentile strength of a connection with a single bolt was greater than the characteristic strength specified in the CSA standard by a factor of 1.42.5. The reasons for this underestimation of the strength values in the standard are attributed to a low estimate of the embedment strengths of wood and concrete, a low estimate of the yield strength of the bolts, and the lack of a design method that accounts for the axial tensioning effect. Changes to the CSA standard O86.1 provisions were proposed and have been accepted to improve the strength predictions of bolted wood-to-concrete connections. The 2001 edition of standard O86.1 reflects those changes.Key words: wood, anchor bolts, concrete, strength, parallel to grain, perpendicular-to-grain embedment, connections.
Regular papers / Articles ordinairesReceiver operating characteristic (ROC) curve analysis of the effectiveness of construction planning efforts in Australia and the United Kingdom
Authors: Faniran O O , Proverbs D G
Published: March 2003

This paper presents the results of a receiver operating characteristic (ROC) curve analysis of the effectiveness of construction planning efforts, based on samples of building projects in Australia and the United Kingdom. The results of the study provide an evaluation of the extent of the effort that must be invested in planning and control activities to achieve success in the performance of construction projects. The study also illustrates the potential application of ROC curve analysis in construction engineering and management research. Planning efforts in a sample of 52 building projects in Australia and 37 building projects in the United Kingdom were evaluated and compared. This study builds on work done in an earlier study in which the concept of optimal planning of construction projects was explored. The ROC curve analysis offers several advantages over the regression methodology employed in the previous optimal planning study. The graphical representation of the relationship between sensitivity and specificity over all possible diagnostic cutoff points provides an insight into the interactions of the variables that was not apparent in the original methodology.Key words: construction planning, project planning, project management, ROC curve analysis, Australia, United Kingdom.
Behaviour of hollow concrete masonry walls with one-course bond beams subjected to concentric and eccentric concentrated loading
Authors: Yi Junyi , Shrive Nigel G
Published: March 2003

Three-dimensional finite element models of unreinforced hollow concrete masonry walls with one-course bond beams subjected to concentrated loading have been analyzed. The walls were modelled with different loading plate sizes, different loading locations along the wall (at the midpoint of the wall, at the end of the wall, and between these points), and different out-of-plane eccentricities (e = 0, t/6, and t/3). The hollow block units, mortar, grout, and bond beam blocks in the walls were modelled separately. Both smeared and discrete cracking methods have been utilized for predicting cracking under load. Geometric and material nonlinearities and damage due to progressive cracking were taken into account in the analyses. The predicted failure modes and ultimate capacities of the walls with the concentric concentrated load applied at the midpoint or at the end of the wall compared very well with the experimental results. When the load was between the midpoint and the end of the wall, the predicted ultimate capacity was between those for the load at the midpoint and at the end. The strength of the walls decreases with increasing out-of-plane eccentricities.Key words: finite element models, hollow masonry, smeared and discrete cracking models, concentrated load, loading locations, out-of-plane eccentricities.
Behaviour of partially grouted hollow concrete masonry subjected to concentrated loads
Authors: Yi Junyi , Shrive Nigel G
Published: March 2003

An experimental programme was performed to study the behaviour of hollow concrete masonry wallettes with bond beams and vertical columns of grout subjected to concentrated loads. Forty-three wallettes were tested, with concentrated loads being applied either concentrically or eccentrically, through various-sized loading plates above the grout columns or on the bond beams above the hollow blocks. When the concentrated load was applied above the grout columns, the face shells of the hollow block units attached to the grout columns split and the columns subsequently crushed. When the load was applied on the bond beams, wallettes failed similarly to hollow masonry walls without vertical columns of grout, with web splitting and vertical cracking in line with the load, followed by face-shell spalling and (or) mortar crushing. When the eccentricity was one third of the wall thickness, failure was dominated by local spalling beneath the loading plate. The testing programme and mechanisms of failure are described, together with strength variation with increasing eccentricity, and dispersion of the concentrated load through the bond beam. General implications for the design of hollow concrete masonry with bond beams and vertical columns of grout subjected to concentrated loads are discussed.Key words: hollow concrete masonry, bond beam, grout columns, concentrated load, concentric, eccentric.
Design rules for hollow concrete masonry walls subjected to concentrated loads
Authors: Yi Junyi , Shrive Nigel G
Published: March 2003

Design rules are proposed for assessing the bearing strengths of hollow concrete masonry walls subjected to in-plane concentrated loads. These are derived from numerical and experimental studies of this problem. Two possible zones of failure are considered: the solidgrouted masonry directly beneath the concentrated loads, and the hollow masonry beneath the grouted portion. The important factors influencing the bearing strength are taken into account: loading eccentricity across the wall width, effective loading area, loading plate length, and loading location along the wall. An angle of 22° or slope (vertical to horizontal) of 2.5:1 is chosen for a safe estimate of the dispersion of concentrated load through the solidgrouted masonry. For partial grouting patterns, at least two courses downward should be grouted to a length compatible with the loading plate. When compared with the available numerical and experimental results, conservative estimates of ultimate strength are obtained in all cases.Key words: design rules, hollow concrete masonry wall, in-plane concentrated load, out-of-plane eccentricities, loading plate length, loading locations, dispersion angle.
Realizing opportunities in forest growth modelling
Authors: Vanclay Jerome K
Published: March 2003

The world is continually changing; the emergence of new technology and new demands for pertinent information pose new challenges and possibilities for forest management. Are forest growth models keeping up with client needs? To remain relevant, modelers need to anticipate client needs, gauge the data needed to satisfy these demands, develop the tools to collect and analyze these data efficiently, and resolve how best to deliver the resulting models and other findings. Researchers and managers should jointly identify and articulate anticipated needs for the future and initiate action to satisfy them. New technology that offers potential for innovation in forest growth modelling include modelling software, automated data collection, and animation of model outputs. New sensors in the sky and on forest machines can routinely provide data previously considered unattainable (e.g., tree coordinates, crown dimensions), as census rather than sample data. What does this revolution in data availability imply for forest growth models, especially for our choice of driving variables?
Calibrating predicted diameter distribution with additional information in growth and yield predictions
Authors: Kangas Annika , Maltamo Matti
Published: March 2003

Diameter distribution of the growing stock is essential in many forest management planning problems. The diameter distribution is the basis for predicting, for example, timber assortments of a stand. Usually the predicted diameter distribution is scaled so that the stem number (or basal area) corresponds to the measured value (or predicted future value), but it may be difficult to obtain a distribution that gives correct estimates for all known variables. Diameter distributions that are compatible with all available information can be obtained using an approach adopted from sampling theory, the calibration estimation. In calibration estimation, the original predicted frequencies are modified so that they respect a set of constraints, the calibration equations. In this paper, an example of utilizing diameter distributions in growth and yield predictions is presented. The example is based on individual tree growth models of Scots pine (Pinus sylvestris L.). Calibration estimation was utilized in predicting the diameter distribution at the beginning of the simulation period. Then, trees were picked from the distribution and their development was predicted with individual tree models. In predicting the current stand characteristics, calibrated diameter distributions proved to be efficient. However, in predicting future yields, calibration estimation did not significantly improve the accuracy of the results.
Predicting basal area increment in a spatially explicit, individual tree model: a test of competition measures with black spruce
Authors: Mailly Daniel , Turbis Sylvain , Pothier David
Published: March 2003

A current trend in the development of forest stand models is to use spatially explicit, individual-tree information to simulate forest dynamics with increased accuracy. By adding spatial information, such as tree coordinates, crown shape, and size, it is hypothesized that the computation of the model's driving function is improved over traditional competition indices, especially when simulating multistoried stands. In this paper, we want to test whether computationally demanding competition indices outperform traditional indices in predicting mean basal area increment. The study was undertaken in old, uneven-aged black spruce (Picea mariana (Mill.) BSP) stands in northeastern Quebec, Canada. The predictability of individual tree growth rates was related to crown dimensions and other stand and tree variables measured in the field. Data were collected from 90 trees coming from stands of varying site quality (range 9.616.5 m height at 50 years, age taken at 1 m) and age (range 66257 years). Hegyis's distance-dependent competition index was found to be the most strongly correlated competition measure (r = 0.57) with mean basal area growth of the last 20 years. This value, 12% higher than the value obtained from the best distance-independent competition index (r = 0.45), clearly shows that precision gains can be achieved when estimating basal area increment with spatial indices in black spruce stands. Using indices computed from virtual hemispherical images did not prove superior to simpler distance-dependent indices based on their individual correlations with basal area increment. When included in a basal area increment model for the last 20 years of growth, however, the gains in precision were comparable to Hegyi's competition index. This indicates that indices derived from a hemispherical approach have some value in spatially explicit forest simulations models but that further tests using younger stands are needed to confirm this result in black spruce stands.
Modelling forest ecosystems: state of the art, challenges, and future directions
Authors: Landsberg Joe
Published: March 2003

Forest models should in future combine the predictive power and flexibility of process-based models with the empirical information and descriptive accuracy of conventional mensuration-based models. Progress is likely to be rapid if model developers identify the potential users of their models and the needs of those users. Users include operational forest managers, planners, bureaucrats, politicians, community and environmental groups, scientists, and academics. Extant models that could be used immediately or could be adapted for use by these groups are reviewed. Currently available process-based models can provide good estimates of growth and biomass productivity at various scales; combined with conventional models they can provide information of the type required by managers and planners. Climate-driven models can provide good estimates of potential plantation productivity, while detailed process models contribute to our understanding of the way systems function and are essential for future progress. Technical challenges for the future include continued research on carbon-allocation processes, nutrient availability in soils, and nutrient uptake by trees. It is important that we have models that can be used to predict and analyze the effects of technologies such as clonal forestry and possible genetic manipulation, as well as intensive management in relation to nutrition, weed control, and disease control. Large-scale analysis of forest productivity is already possible using models driven by remote sensing; inclusion of nutrition should be a goal in this area. Moves towards active collaboration and the implementation of mixed models in operational systems, as well as improving communication between model developers and users, should ensure that practical problems are identified and fed back to modellers, which should lead to rapid progress.
Process-based modelling of tree and stand growth: towards a hierarchical treatment of multiscale processes
Authors: Mäkelä Annikki
Published: March 2003

A generally accepted method has not emerged for managing the different temporal and spatial scales in a forest ecosystem. This paper reviews a hierarchical-modular modelling tradition, with the main focus on individual tree growth throughout the rotation. At this scale, model performance requires (i) realistic long-term dynamic properties, (ii) realistic responses of growth and mortality of competing individuals, and (iii) realistic responses to ecophysio logical inputs. Model development and validation are illustrated through allocation patterns, height growth, and size-related feedbacks. Empirical work to test the approach is reviewed. In this approach, finer scale effects are embedded in parameters calculated using more detailed, interacting modules. This is exemplified by (i) the within-year effect of weather on annual photosynthesis, (ii) the effects of fast soil processes on carbon allocation and photosynthesis, and (iii) the utilization of detailed stem structure to predict wood quality. Prevailing management paradigms are reflected in growth modelling. A shift of emphasis has occurred from productivity in homogeneous canopies towards, e.g., wood quality versus total yield, spatially more explicit models, and growth decline in old-growth forests. The new problems emphasize the hierarchy of the system and interscale interactions, suggesting that the hierarchical-modular approach could prove constructive.
Communities of soil mites (Acarina) in planted birch stands compared with natural forests in central Finland
Authors: Huhta Veikko , Niemi Ritva
Published: March 2003

The aim of the study was to compare the soil mite communities in anthropogenous birch stands of different origin with each other and with natural forests at the same latitude. Nine sites were investigated: three birch stands (Betula pendula Roth) planted ca. 30 years prior to the study after clear-cutting of spruce stands ("birch after spruce"), three birch stands planted ca. 30 years earlier on arable soil that had been under cultivation until reforestation ("birch after field"), and three natural deciduous forests. These were sampled twice, and microarthropods were extracted, counted, and identified. There were clear differences between birch stands established after spruce forest and after cultivation and between these and natural deciduous forests. The communities of birch after spruce were rather similar to those of natural spruce forests, but the population densities were lower. The populations in birch after field were generally very low. There were also conspicuous differences among replicates of the same kind of forests. All the dominant species in the study sites are common members of the forest soil fauna. The communities of birch after field could be characterized as impoverished forest communities. Soil pH and the removal of the litter layer by earthworms were regarded as the most important factors explaining the observed differences.
FVSBGC: a hybrid of the physiological model STAND-BGC and the forest vegetation simulator
Authors: Milner Kelsey S , Coble Dean W , McMahan Andrew J , Smith Eric L
Published: March 2003

The physiological model STAND-BGC was linked to the forest vegetation simulator (FVS) as a system extension. With the linked model, an FVS user can invoke STAND-BGC to obtain tree- and stand-level physiological output in addition to standard FVS mensurational output. An FVS user may choose to have increments in diameter, height, crown ratio, and mortality from STAND-BGC replace those generated by FVS. This option essentially replaces the empirical growth engine of FVS with the physiological engine from STAND-BGC. Physiological and mensurational outputs were generated for an existing, fully stocked, Pinus contorta Dougl. ex Loud. stand, with and without thinning, using the hybrid model. The STAND-BGC engine produced results similar to FVS for the unthinned stand but predicted more rapid tree growth than FVS following thinning. Simulations for a newly regenerated stand using the linked model allowed assessment of the predicted effects of grass competition and drought on stand production. Comparisons of model predictions to remeasured permanent plot data showed the empirical and process growth engines had similar precision, but that STAND-BGC substantially overpredicted growth, while FVS slightly underpredicted growth. The need for model calibration and opportunities for more sophisticated communication between models is discussed.
Estimating individual tree growth with nonparametric methods
Authors: Sironen S , Kangas A , Maltamo M , Kangas J
Published: March 2003

The aim of the study was to demonstrate the use of nonparametric methods in estimating tree-level growth models. In the nonparametric methods the growth of a tree is predicted as a weighted mean of the values of neighboring observations. The selection of the nearest neighbors is based on the similarities between tree- and stand-level characteristics of the target tree and the neighbors. The data for the models were collected from Kuusamo in northeastern Finland. Models for the 5-year diameter growth were constructed for Scots pine (Pinus sylvestris L.) with three different nonparametric methods: the k-nearest neighbor regression, k-most-similar neighbor, and generalized additive model.
Using miniature-scale plantations as experimental tools for assessing sustainability issues
Authors: Amateis Ralph L , Sharma Mahadev , Burkhart Harold E
Published: March 2003

Decisions concerning ecosystem management, forest certification, and sustainable management require stand- and tree-level information that reflects current silvicultural and management practices. Typical forest stands, however, take years to mature making timely data collection, analyses, and reporting difficult. Further, collecting and evaluating certain forest stand information that affects sustainability such as belowground biomass response or response to changing climatic factors is often intractable. One modeling tool that may be useful for supplying future informational needs at the tree and stand level is the use of miniature scale plantations. Data from a miniature scale spacing trial for loblolly pine (Pinus taeda L.) that was established at 1:16 scale to an operational study suggest that important stand characteristics associated with forest productivity develop similarly at the two scales. Once models are formulated that relate the size of trees (spatially scaled models) and the rates of growth (temporally scaled models) grown at miniature scale to their operational scale counterparts, it may become feasible to conduct experimentation in miniature and make inferences to operational scales.
Coppicing ability of 20 Eucalyptus species grown at two high-altitude sites in South Africa
Authors: Little Keith M , Gardner Robin AW
Published: March 2003

In the 1980s, Eucalyptus macarthurii and E. nitens were planted in the colder, higher altitude areas of South Africa to meet the increased demand for pulpwood. To find possible alternatives, six site × species interaction trials were planted in 19901991. Based on volume performance and pulping properties, E. badjensis, E. benthamii, E. oreades, E. nobilis, E. smithii, and E. fraxinoides were identified as having good commercial potential. Although the performance of the parent crop is important, the ability to coppice is advantageous because of lower reestablishment costs. To determine this, the ability for these species to coppice was assessed at 10 months after felling at two of the trial sites with widely different growing conditions (Broadholms in Mpumalanga province and Draycott in KwaZulu-Natal province). More than 80% of the living stumps of E. benthamii, E. smithii, E. quadrangulata, E. macarthurii, E. badjensis, E. dunnii, E. cypellocarpa, E. saligna, and E. elata had coppiced at both sites. At Draycott, an exposed, dry site, both E. smithii and E. benthamii could be considered as potential alternative species to E. nitens, because besides having good volume, both species coppiced well. At Broadholms, a more protected and slightly wetter site, the significantly better volume of E. fraxinoides (which did not coppice well) when compared with the other species would mean that a substantial saving in reestablishment costs via coppice regeneration would have to be made before one could consider this method of reestablishment.
Effets de différentes régies d'irrigation sur la croissance, la nutrition minérale et le lessivage des éléments nutritifs des semis d'épinette noire (1+0) produits en récipients à parois ajourées en pépinière forestière
Authors: Lamhamedi Mohammed S , Margolis Hank , Renaud Mario , Veilleux Linda , Auger Isabelle
Published: March 2003

To reduce the quantity of irrigation water used and the amount of mineral nutrients lost because of leaching, we used time domain reflectometry to monitor and maintain four irrigation regimes (15, 30, 45 and 60%, v/v) during the first growing season for 1+0 black spruce (Picea mariana (Mill.) BSP) seedlings. The seedlings were produced in air-slit containers (IPL 25350A), filled with a peat substrate and were grown under a polyethylene tunnel at a forest nursery. Similar fertility levels were maintained in all four irrigation regimes even though the water content of the substrate could be very low (15 and 30%). Irrigation regime did not affect growth, root architecture or tissue nutrient contents at the end of the growing season. Monitoring water use over the course of the growing season clearly showed that the amount of irrigation water could be reduced by 62 to 76% without compromising seedling quality relative to the 60% irrigation regime. Leachate losses varied exponentially as a function of irrigation regime. The mean amount of water leached, relative to the quantity of water applied during the sampling period, was 10, 7.1, 28.4, and 62.2% for the 15, 30, 45, and 60% irrigation regimes, respectively. The losses of mineral nitrogen at the beginning of August were 49.7, 35.9, 55.2, and 88.2%, respectively, for the 15, 30, 45, and 60% irrigation regimes. To optimize irrigation and decrease leaching, a dynamic model for irrigation management is proposed that accounts for the phenological development of black spruce seedlings grown under tunnel conditions in forest nurseries.
Responses to mechanical wounding and fire in tree species characteristic of seasonally dry tropical forest of Bolivia
Authors: Schoonenberg Tim , Pinard Michelle , Woodward Stephen
Published: March 2003

Short-term responses to stem wounding were measured over a 60-day period on six tree species found in seasonally dry tropical forest in Bolivia. Three types of wounds were inflicted to simulate mechanical bark damage and bark damage caused by low- and high-intensity fires. Extent of wood discoloration associated with wounding varied with wound type and severity, with high-intensity burns associated with the greatest amount of discoloration, low-intensity burns the least, and mechanical wounds intermediate. Two thin-barked species produced a distinct ligno suberised boundary zone in the bark earlier than thicker barked species; however, all species produced a distinct wound periderm by 60 days postwounding. The amount of wood discoloration associated with wounding appeared to be independent of the thickness of the lignosuberized boundary zone. Bark thickness provided a useful measure of species' resistance to wood discoloration with low-intensity burns but not with high-intensity burns where bark occasionally separated from the cambium or developed cracks and fissures. Variability in short-term responses to wounding and other factors may result in differences in the composition and abundance of microorganisms that colonize the wounds, with implications for reductions in wood quality and decay development.
Impact of plot size on individual-tree competition measures for growth and yield simulators
Authors: Hynynen Jari , Ojansuu Risto
Published: March 2003

The study addresses the effect of sample plot size on the bias related to measured stand density. We analyzed the effect of plot size on model coefficients and model performance in the simulation. Alternative growth models were developed for Norway spruce (Picea abies (L.) Karst.) on the basis of data obtained from permanent inventory sample plots of varying size. The competition measures were estimated from small plots with an average radius of 6 m, large plots with an average radius of 10 m, a cluster of three small plots within a stand, and a cluster of three large plots within a stand. The response of the models to competition varied depending on the plot size. Increasing the plot size increased the sensitivity of the models to the variation of overall stand density and the competitive status of a tree. The development of repeatedly measured, unthinned and thinned Norway spruce sample plots was simulated with the models, and the predictions were compared with the observed development. In the unthinned stand, the model with competition measures based on small plots resulted in a higher and more biased prediction of growth and mortality than the models based on larger plots. In the thinned stand, the differences between the models were negligible.
A model of wind-influenced leaf litterfall in a mixed hardwood forest
Authors: Staelens Jeroen , Nachtergale Lieven , Luyssaert Sebastiaan , Lust Noël
Published: March 2003

Litterfall is an important ecological process in forest ecosystem functioning. Some attempts have been made to develop spatially explicit models of litterfall, but wind influence has never been included. Therefore, we studied the effect of wind on litterfall in an intimately mixed birch-oak forest using tree diameter and position as input data. After testing a litterfall model that assumed isotropic leaf dispersal, an anisotropic dispersal module was developed to account for wind influence. Using leaf fall data of 104 litter traps, isotropic and anisotropic models were optimized for silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and red oak (Quercus rubra L.) and model quality was compared. The anisotropic leaf litterfall model proved to be relevant because (i) the estimated litterfall directions corresponded very well to prevailing wind directions during leaf fall and (ii) including directionality significantly increased the goodness of fit of the models for both oak species but not for birch. Consequently, prevailing wind directions during leaf fall affected leaf dispersal in a broad-leaved deciduous forest. Insight into the spatial variability of the litter layer in forest ecosystems can benefit from the improved understanding of small-scale litterfall processes.
The U-approach to forest modeling
Authors: Zeide Boris
Published: March 2003

So far, process-based models use largely the bottom-up approach. They start by describing physiological processes in a single plant element and then integrate the constituent processes to predict growth and dimensions of the tree and stand. Although bottom-up process models are praised for their contribution to knowledge of growth processes, their predictions are poor. The complementary top-down approach begins where the bottom-up model ends: with measurable variables such as height or diameter. This approach intends to uncover the ecophysiological processes responsible for the observed tree dimensions rather than to provide growth information for forest management. As foresters, we would like to utilize measurable variables to uncover inner mechanisms of growth in hope of predicting future diameter, number of trees, volume, and other practical variables. This means that we need to combine the top-down and bottom-up approaches. Examples of the united U-approach (so called because of its descending and ascending branches) are described. They demonstrate that growth models can be both meaningful and accurate.