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The objective of this paper is to discuss approaches and issues related to modelling stand dynamics for multi-cohort forest management in eastern Canadian boreal forests. In these forests, the interval between wildfires can be rather long, and the development of natural forest stands may include the establishment, growth and mortality of several cohorts of trees. Later cohorts are characterised by increasing structural complexity, including spatial heterogeneity and irregular tree size distribution. A multi-cohort forest management framework has been proposed to maintain this complexity, and associated biodiversity, on the landscape. Multi-cohort forest management planning requires forecasts of the development of stands with complex structure in response to silvicultural treatment and to natural disturbance, but current stand dynamics models in the region are applicable mainly to even-aged mono-specific stands. Possible modelling approaches for complex stands include i) the adaptation of current whole-stand growth and yield models, ii) distance-independent, empirically-derived individual-tree models, such as the USDA Forest Service Forest Vegetation Simulator, and iii) distance-dependent, empirically-derived or process-oriented individual-tree models. We conclude that individual-tree models are needed because observational data for fitting whole-stand models are not available for the full array of silvicultural treatments and natural disturbances encompassed by multi-cohort forest management. Predictive accuracy is a concern with individual-tree models, and the incorporation of coarse-scale constraints into these models is a promising means to control error.

We used a hierarchical approach to examine patterns of black spruce and balsam fir wood density across Newfoundland. Wood density measurements were aggregated at ring, tree, and plot levels. Portions of the variance in wood density at the different levels were explained by predictor variables at multiple levels of a forest structural hierarchy (ring-, tree-, and plot-level variables). Hierarchical fixed effects models accounted for 39%, 61%, and 86% of the variance in wood density of black spruce at ring, tree, and plot levels, respectively, with RMSE values of 62.7, 34.6, and 19.4 kg x [m.sup.-3]. Corresponding models accounted for 31%, 38%, and 63% of the variance in wood density of balsam fir, with RMSE values of 62.4, 35, and 16.7 kg*[m.sup.-3]. The hierarchical analysis demonstrated consistent negative associations of wood density to radial growth rate at ring, tree, and plot levels of aggregation. Variables that act as surrogates for radial growth are thus important for understanding patterns of wood density at higher scales and for the practical application of mapping wood density across landscapes. Key words: wood density, black spruce, balsam fir, radial growth rate, hierarchy, mixed effects models. Nous avons utilise une approche hierarchique pour etudier les patrons de densite du bois de l'epinette noir (Picea mariana (Mill.) B.S.P.) et du sapin baumier (Abies balsamea (L.) Mill.) a Terre-Neuve. Les mesures de densite ont ete regroupees a l'echelle du cerne annuel, de l'arbre et de la placette. Des portions de la variance de la densite du bois aux differentes echelles etaient expliquees par des variables de prediction a plusieurs niveaux d'une hierarchie structurale de la foret (variables a l'echelle du cerne annuel, de l'arbre et de la placette). Les modeles hierarchiques a effets fixes expliquaient respectivement 39, 61 et 86 % de la variance de la densite du bois de l'epinette noire a l'echelle du cerne annuel, de l'arbre et de la placette avec des valeurs d'EQM de 62,7, 34,6 et 19,4 kg [m.sup.-3]. Chez le sapin baumier, les modeles correspondants expliquaient respectivement 31, 38 et 63 % de la variance de la densite du bois avec des valeurs d'EQM de 62,4,35 et 16,7 kg [m.sup.-3]. L'analyse hierarchique a demontre qu'il y avait une association negative constante entre la densite du bois et le taux de croissance radiale a l'echelle du cerne annuel, de l'arbre et de la placette. Les variables de substitution pour la croissance radiale sont par consequent importantes pour comprendre les patrons de densite du bois a plus grande echelle et pour l'utilisation pratique de la cartographie de la densite du bois dans le paysage. [Traduit par la Redaction] Mots-cles : densite du bois, epinette noire, sapin baumier, taux de croissance radiale, hierarchie, modeles a effets mixtes., Introduction Wood density is an important wood quality attribute, affecting the strength of manufactured lumber and paper products, as well as wood processing characteristics (Panshin and de Zeeuw 1980). Wood [...]

Enhanced forest resources inventory systems delineate and define polygons based on fundamental ecological units such as ecosites, which are standard combinations of vegetation and substrate types. Our study objective was to model wood quality characteristics of individual black spruce (Picea mariana (Mill.) B.S.P.) trees across a representative boreal forest landscape in northeastern Ontario, Canada, based on relationships to ecosite and other stand-level variables. A total of 127 large (12 mm) increment core samples were extracted at breast height from dominant or co- dominant black spruce trees in forest stands representing a gradient from dry sandy to wet mineral and organic ecosites. Sample cores were prepared, processed, and analyzed using standard SilviScan protocols. Hierarchical classification models were then fitted using Random Forests to predict density and latewood percentage for black spruce stems at a reference age of 50 years. These models each explained over 32% of variance, with estimated root mean squared errors of 40.4 kg x [m.sup.-3] and 5.6% for density and latewood percentage, respectively. Among tree-, site-, and stand-level covariates, ecosite group was the most important predictive variable. Knowledge of ecosite - wood quality relationships could support efficient planning for black spruce management by including an indication of potential use as a modeled variable in a forest inventory system. Key words: black spruce, earlywood-latewood ratio, juvenile wood, mature wood. Les systemes sophistiques d'inventaire des ressources forestieres delimitent et definissent des polygones sur la base d'unites ecologiques fondamentales telles que les ecosites qui representent des combinaisons standards des types de vegetation et de substrat. L'objectif de notre etude consistait a modeliser les caracteristiques de la qualite du bois de tiges individuelles d'epicea noir (Picea mariana (Mill.) Britton, Sterns, Poggenb.) dans un paysage representatif de la foret boreale du nord-est de l'Ontario, au Canada, en fonction de l'ecosite et d'autres variables de peuplement. Au total, 127 grosses carottes (12 mm) ont ete prelevees a hauteur de poitrine sur des epiceas noirs dominants et codominants dans des peuplements forestiers qui representaient un gradient allant d'ecosites caracterises par un sol sablonneux xerique a mineral humide puis organique. Les carottes ont ete preparees, traitees et analysees selon les protocoles standards de SilviScan. Des modeles de classification hierarchique on ensuite ete ajustes a l'aide du logiciel' Random Forests' pour predire la densite et le pourcentage de bois final pour des tiges d'epicea noir a un age de reference de 50 ans. Chacun de ces modeles expliquait plus de 32 % de la variance avec un ecart-type estime de respectivement 40,4 kg-m-3 et 5,6 %. Parmi les covariables a l'echelle de l'arbre, de la station et du peuplement, le groupe d'ecosites etait la plus importante variable predictive. La connaissance des relations entre l'ecosite et la qualite du bois pourrait servir de base a une planification efficace pour amenager l'epicea noir en incluant dans un systeme d'inventaire forestier une indication de l'usage potentiel en tant que variable modelisee. [Traduit par la Redaction] Mots-cles: epicea noir, rapport entre bois initial et bois final, bois juvenile, bois mature., Introduction Models used to predict growth and yield of forest stands depend on reliable inventory data of known accuracy as the starting point for simulating forest production over time (Weiskittel [...]

Competition in forest stands has long been of interest to researchers. However, much of the knowledge originates from empirical studies that examined the effects of competition. For instance, many studies were focused on the effects of the presence of herbaceous species on the development of tree seedlings or the decrease in individual tree growth with increases in stand density. Several models that incorporate competitive effects have been developed to predict tree and stand growth, but with simplified representations of competitive interactions. While these studies provided guidance useful for forest management, they contributed only partially to furthering our understanding of competitive mechanisms. Also, most competition studies were conducted in single-species stands. As competitive interactions occurring in mixed stands are characterized by a higher degree of complexity than those in single-species stands, a better understanding of these mechanisms can contribute to developing optimal management scenarios. The dynamics of forest stands with at least two species may be affected not only by competition, but also by facilitation or complementarity mechanisms. Thus, knowledge of the mechanisms may provide insight into the relative importance of intra- versus inter-specific competition and whether competition is symmetric or asymmetric. Special attention to the implementation of field experimental designs is warranted for mixed stands. While traditional spacing trials are appropriate for single-species stands, the examination of competitive interactions in mixed stands requires more complex experimental designs to examine the relative importance of species combinations. Forest productivity models allow resource managers to test different management scenarios, but again most of these models were developed for single- species stands. As competitive interactions are more complex in mixed stands, models developed to predict their dynamics will need to include more mechanistic representations of competition. Key words: competition, facilitation, complementarity, experimental designs, site resources, modelling. Resume : Les chercheurs s'interessent depuis longtemps a la competition dans les peuplements forestiers. Cependant, la majeure partie des connaissances provient d'etudes empiriques n'examinant que les effets de la competition. Par exemple, plusieurs etudes se sont concentrees sur les effets de la presence d'especes herbacees sur le developpement des plantules d'arbres ou sur la diminution de la croissance des arbres individuels avec l'augmentation de la densite. Plusieurs modeles incorporant les effets de la competition ont ete developpes pour predire la croissance des arbres et des peuplements, avec cependant des representations simplifiees des interactions competitives. Bien que ces etudes fournissent des pistes utiles pour l'amenagement forestier, elles contribuent seulement partiellement a ameliorer notre comprehension des mecanismes competitifs. De plus, la plupart des etudes sur la competition ont ete conduites dans des peuplements monospecifiques. Puisque les interactions competitives survenant dans les peuplements mixtes se caracterisent par un degre de complexite plus eleve que celles des peuplements monospecifiques, une meilleure comprehension de ces mecanismes pourra contribuer au developpement de scenarios d'amenagement optimises. La dynamique des peuplements comportant au moins deux essences peut se voir affectee non seulement par la competition, mais aussi par des mecanismes de facilitation ou de complementarite. Ainsi, la connaissance des mecanismes peut jeter un nouvel eclairage sur l'importance relative de la competition intra- vs inter-specifique et determiner s'il s'agit de competition symetrique ou asymetrique. Une attention speciale lors de la conception de plans experimentaux est essentielle pour les peuplements melanges. Alors que les essais d'espacement traditionnels conviennent pour les peuplements monospecifiques, l'examen des competitions interactives necessite des plans experimentaux plus complexes pour evaluer l'importance relative des combinaisons d'especes. Les modeles de productivite forestiere permettent a l'amenagiste des ressources de verifier divers scenarios d'amenagement, mais encore une fois la plupart de ces modeles ont ete developpes pour des peuplements monospecifiques. Les interactions competitives etant plus complexes dans les peuplements mixtes, les modeles developpes pour predire leur dynamique devront desormais inclure de plus fortes representations des mecanismes de competition. [Traduit par la Redaction] Mots-cles: competition, facilitation, complementarite, plans experimentaux, ressources des sites, modelisation., Introduction Although competition is a widespread phenomena [sic] exhibited by organisms from microbes to mammals, empirical evidence is elusive. Controlled laboratory experiments usually involve simplified competitive systems whose results cannot [...]

The PSRA (process safety risk assessment) is the most important element of an effective process safety management program. A PSRA is an organized and systematic effort but there are also highly complex tasks related to it. The effort is to create a complete identification of causes and consequences and subsequently set of effectiveness of barriers to manage the risk to acceptance level. The critical task is that the information to be compiled about the chemistry needs to be comprehensive enough for an accurate assessment of the reactivity hazards, fire and explosion characteristics and toxic releases. A successful PSRA also requires an unambiguously Risk Assessment Metric or risk graph, the availability of reliable clean (failure) data and must be organized properly. The organizational part of the PSRA's have to deal with demanding circumstances like time pressure, culture, workload, costs, motivation, procedures of classification and competent resources to complete the risk assessment in time. These elements together are typical ingredients introducing the human factor in PSRA's and the presence of so-called cognitive biases. These biases can have a negative influence on the validity of the risk assessment and can lead to incorrect and hence ineffective recommendations. Cognitive biases are defined by Kahneman as the tendency of systematic deviations when assessing risk instead of objective and rational judgment. The occurrence of these cognitive biases can be clarified by the understanding the dual-system of thinking (system 1 and system 2), Kahneman. The objective of this paper is to identify what kind of human factors and organisational factors are present in a PSRA and what can be done to prevent them? To identify these biases, we have evaluated multiple PSRA's from our company. The results of this evaluation show that human and organisational factor can be avoided, and more important incorrect conclusions and implementation of ineffective recommendations can be prevented. [ABSTRACT FROM AUTHOR]

An uneven-aged silviculture experiment was established in second-growth peatland black spruce (Picea mariana [Mill.] B.S.P.) stands in the boreal forest of northeastern Ontario, Canada in 1994. Three harvest treatments along with an unharvested control were applied in three replications. Fifteen-year results indicate that light- and medium-intensity harvest treatments maintain stand structure suitable for the continued application of uneven-aged silviculture treatments. Based on basal area growth trends and the development of stand structure, a cutting cycle of 20–25 years appears to be feasible for these treatments. Future harvests will likely yield a higher proportion of larger diameter trees with a greater value. The heavy harvest intensity treatment will result in a greater fluctuation of the growing stock and a longer cutting cycle. Without cutting treatments, the control treatment may eventually develop a stand structure that is unsuitable for the implementation of uneven-aged silviculture. [ABSTRACT FROM PUBLISHER]