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In this study, compatible height and diameter increment models were fitted for lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), trembling aspen (Populus tremuloides Michx.), and white spruce (Picea glauca (Moench) Voss), using the relationship between diameter and height growth. It was assumed that tree diameter increment is directly proportional to height increment, and the proportionality constant is a function of competition and site productivity. The results showed that the fit statistics are comparable with results of other studies, with adjusted R2 ranging from 30% to 50%. A validation test of the models, using independent permanent sample plots data, showed that the short-term predictions of the models for both pure and mixedwood stands are fairly unbiased. The models also gave reasonable average height growth and diameter growth trajectories for pure stands of the three species and also projected long-term mixedwood (aspen – white spruce mixture) volume growth dynamics reasonably well. The models also projected reasonably well (i) the effect of increasing initial stem density on average diameter and height, and (ii) the stand volume compared with an older version the Mixedwood Growth Model (ver. 2000A). It was concluded that explicitly linking tree height and diameter increment models does not only have a solid ecological basis, but it also results in a compatible prediction of tree growth and stand dynamics. [ABSTRACT FROM AUTHOR]

The mechanisms governing tree mortality in surface fires are poorly understood, owing in large part to the absence of a process-based framework for defining and evaluating these mechanisms. This paper begins the development of such a framework by deriving a first-order process model of tree mortality in surface fires (intensities less than approximately 2500 kW·m–1). A buoyant line-source plume model is used to drive heat transfer models of vascular cambium and vegetative bud necroses, which are linked to tree mortality using an allometrically-based sapwood area budget. Model predictions are illustrated for white spruce (Picea glauca), lodgepole pine (Pinus contorta), and trembling aspen (Populus tremuloides) and are compared with independent mortality data for Engelmann spruce (Picea engelmannii Parry ex Engelm.) and Pinus contorta Dougl. Results help define first-order mortality mechanisms and suggest second-order mortality mechanisms that should be incorporated into future modeling efforts. Les mécanismes qui régissent la mortalité des arbres à la suite d’un feu de surface sont peu connus, surtout à cause de l’absence de cadre théorique basé sur les processus permettant de définir et d’évaluer ces mécanismes. Cet article jette les bases d’un tel cadre théorique en dérivant un modèle de premier ordre de mortalité des arbres basé sur les processus à la suite d’un feu de surface (intensité inférieure à environ 2500 kW·m–1). Un modèle de panache flottant dont la source est linéaire est utilisé pour faire fonctionner des modèles de transfert de chaleur du cambium vasculaire et de nécrose des bourgeons foliaires, laquelle est reliée à la mortalité des arbres grâce à un bilan de surface d’aubier basé sur des relations allométriques. Les prédictions du modèle sont illustrées pour l’épinette blanche (Picea glauca), le pin tordu (Pinus contorta), et le peuplier faux-tremble (Populus tremuloides) et sont comparées à des données indépendantes de mortalité pour le l’épinette d’Engelmann (Picea engelmannii Parry ex Engelm.) et Pinus contorta Dougl. Les résultats aident à définir les mécanismes de premier ordre et à suggérer des mécanismes de second ordre à l’origine de la mortalité. Ces mécanismes devraient être retenus lors de tentatives futures de modélisation. [ABSTRACT FROM AUTHOR]

Sustainable forest management that employs the emulation of natural disturbance paradigm develops plans based on disturbance-driven forest succession. However, most research on forest succession has focused primarily on postdisturbance species change, often ignoring predisturbance legacies. We used the FORECAST ecosystem management model and a newly created natural regeneration submodel to examine the interaction of fire severity, fire frequency, and natural regeneration to produce multicycle dynamics of white spruce (Picea glauca (Moench) Voss), lodgepole pine (Pinus contorta Dougl. ex Loud.), and trembling aspen (Populus tremuloides Michx.) in a western Canadian boreal forest. We simulated 19 different scenarios in a factorial disturbance experiment of three severities and six frequencies and a no-disturbance scenario. Our simulations resulted in a wide diversity of boreal forest community types, including trembling aspen dominated mixedwoods with high-frequency (75 year), high-severity (100% mortality) fires, and nearly pure lodgepole pine stands at midfrequency (100–125 year) and high-severity fires. With the unvarying disturbance regimes we used, a variety of different but recurring temporal patterns emerged. We show that the loss of seed source legacies reinforces the disturbance-driven species dominance, demonstrating community inertia. This study provides a long-term perspective to boreal forest management that demonstrates the role of disturbance and legacies in long-term dynamics. [ABSTRACT FROM AUTHOR]