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The Lake States variant of the FVS (Forest Vegetation Simulator) model (LS-FVS), also known as the LS-TWIGS variant of FVS, was validated for black spruce (Picea mariana (Mill.) BSP), white spruce (Picea glauca (Moench) Voss), jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.) forests in northern Ontario. Individual-tree data from 537 remeasured sample plots were used. This dataset included different combinations of site index, stand density and age. It was possible to compare observations and predictions for different projection length periods. The validation exercise included a biological consistency analysis, the computation of mean percent difference (MPD) for stand density, stand basal area, top height and quadratic mean diameter (QMD) and the comparison of observed and predicted individual-tree dbh. The biological consistency analysis indicated that LS-FVS logically predicted the effect of site index on top height, stand basal area and QMD for black spruce and jack pine. However, the decrease in stand basal area at young ages was inconsistent with the normal development pattern of the forest stands under study and was attributed to deficiencies in the prediction of mortality. LS-FVS was found to underpredict stand density, stand basal area and top height and to overpredict QMD. Even though there were large errors in the prediction of change in stand density, LS-FVS was nevertheless consistent in the prediction of the shape of the dbh size distribution. pour la densité, la surface terrière, la hauteur maximale et le diamètre moyen quadratique (QMD) et la comparaison des diamètres à hauteur de poitrine (dhp) observés et prédits d'arbres individuels. L'analyse de cohérence biologique a indiqué que LS-FVS a prédit de façon cohérente les effets de l'indice de site sur la hauteur maximale, la surface terrière et le QMD pour l'épinette noire et le pin gris. Cependant, la diminution en surface terrière en bas âge s'est avérée inconsistante avec la tendance normale de développement des types forestiers sous étude. Cette situation a été attribuée à une faiblesse de LS-FVS au niveau de la prédiction de la mortalité. Il a été trouvé que LS-FVS a sous-estimé la densité des peuplements, la surface terrière et la hauteur maximale et surestimé le QMD. Même s'il y avait de larges erreurs dans la prédiction du changement dans la densité des peuplements, LS-FVS était néanmoins cohérent dans la prédiction de la forme de la distribution des classes de dhp.

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. and Lacerte, V. 2006. Assessing a new soil carbon model to simulate the effect of temperature increase on the soil carbon cycle in three eastern Canadian forest types characterized by different climatic conditions. Can. J. Soil Sci. 86: 187-202. The predictive capacity of process-based models on the carbon (C) cycle in forest ecosystems is limited by the lack of knowledge on the processes involved. Thus, a better understanding of the C cycle may contribute to the development of process-based models that better represent the processes in C cycle models. A new soil C model was developed to predict the effect of an increase in the temperature regime on soil C dynamics and pools in sugar maple (Acer saccharum Marsh.), balsam fir [Abies balsamea (L.) Mill.] and black spruce [Picea mariana (Mill.) B.S.P.] forest types in Eastern Canada. Background information to calibrate the model originated from the experimental sites of the ECOLEAP project as well as from a companion study on laboratory soil incubation. Different types of litter were considered in the model: foliage, twigs, understory species, other fine detritus and fine roots. A cohort approach was used to model litter mineralization over time. The soil organic C in the organic (F and H) and mineral layers (0-20 cm) was partitioned into active, slow and passive pools and the rates of C transfer among the different pools and the amount of CO 2 respired were modelled. For each forest type, there was a synchrony of response of the C pools to soil temperature variation. The results of the simulations indicated that steady state conditions were obtained under current temperature conditions. When mean annual soil temperatures were gradually increased, the litter and active and slow C pools decreased substantially, but the passive pools were minimally affected. The increase in soil respiration resulting from a gradual increase in temperature was not pronounced in comparison to changes in mineralization rates. An increase in litter production during the same period could contribute to reducing net C losses. La capacité de prédiction des modèles mécanistes du cycle du carbone (C) dans les écosystèmes forestiers est limitée par le manque de connaissances sur les processus impliqués. Par conséquent, une meilleure compréhension du cycle du C peut contribuer à développer des modèles mécanistes basés sur une meilleure représentation des processus. Un nouveau modèle du cycle du carbone du sol a été développé pour prédire l'effet d'une augmentation du régime de température sur la dynamique et les réservoirs de C du sol dans des érablières, sapinières et pessières de l'est du Canada. L'information de base nécessaire au calibrage du modèle provenait des sites expérimentaux du projet ECOLEAP et d'une étude complémentaire d'incubation de sol en laboratoire. Différents types de litière ont été considérés dans le modèles : feuillage, ramilles, espèces de sous-bois, autres résidus fins et racines fines. Une approche par cohorte a été utilisée pour modéliser la minéralisation de la li...