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Large-area growth estimates can be obtained by coupling growth model predictions with wall-to-wall remotely sensed auxiliary variables through a generalized hierarchical model-based (GHMB) inferential framework. So far, most GHMB variance estimators do not account for the residual errors of the submodels and their spatial correlations. This likely induces an underestimation of the true variance of the point estimator. In this study, we provide an example of large-area growth estimation obtained through the GHMB framework. To do this, we developed a new variance estimator that accounts for residual errors as well as potential spatial correlations among them. We tested this variance estimator through a simulation study and then used it to estimate the annual volume increment for a forest management unit in Quebec, Canada. Our results show that, contrary to our expectation, neglecting the residual errors of the different submodels leads to overestimating the true variance of the point estimator. We observed increases in the overestimation with small populations and spatially correlated residual errors. Our developed variance estimator corrected this overestimation and made it possible to derive reliable confidence intervals for annual volume increments at the population level. Key words: generalized hierarchical model-based inference, growth models, Landsat 8, variance estimation, simulation study, 1. Introduction Forest management requires information on current forest attributes and future growth. In mostjurisdictions in Canada, current forest attributes have been traditionally estimated using photo-interpretation and a stratified random [...]

Landscape-level studies such as those on forest management planning and carbon accounting rely on large-area growth projections provided by forest growth models. Nowadays, most of these models are individual tree-based models. The detailed input they require and their complexity are a challenge for the integration into a landscape-level study. A possible alternative consists of approximating the complex model through a meta-model. A meta-model mimics the behaviour of the original model, while being simpler in terms of input and computation. In this study, we developed a Bayesian meta-modelling approach that can be used to obtain a simplified growth model from an individual tree-based model. The approach was exemplified through a real-world case study, namely a forest management unit in the province of Quebec, Canada. Using a Markov chain Monte Carlo method, we managed to fit meta-models based on the Chapman-Richards equation or its derivative for the main potential vegetation types. This meta-modelling approach has the advantages of (i) being an effective method of upscaling, (ii) providing simple meta-models suitable for landscape-level studies, and (iii) ensuring a proper error propagation from the original individual tree-based model into the meta-model. Key words: meta-model, Bayesian statistics, Markov chain Monte Carlo, Metropolis-Hastings algorithm, individual tree-based models, upscaling, forest growth models, forest management planning Les etudes au niveau du paysage, telles que celles portant sur la planification de la gestion forestiere et la comptabilisation du carbone, reposent sur des projections de croissance sur de grandes surfaces fournies par des modeles de croissance forestiere. Aujourd'hui, la plupart de ces modeles sont des modeles bases sur des arbres individuels. Les donnees detaillees qu'ils requierent et leur complexite constituent un defi pour leur integration dans une etude au niveau du paysage. Une alternative possible consiste a approximer le modele complexe par un meta-modele. Un meta-modele imite le comportement du modele original, tout en etant plus simple en termes de saisie et de calcul. Dans cette etude, nous avons developpe une approche de meta-modelisation bayesienne qui peut etre utilisee pour obtenir un modele de croissance simplifie a partir d'un modele base sur des arbres individuels. L'approche a ete illustree par une etude de cas reelle, a savoir une unite de gestion forestiere dans la province du Quebec, au Canada. En utilisant une methode de Monte Carlo par chaines de Markov, nous avons reussi a obtenir des meta-modeles bases sur l'equation de Chapman-Richards ou sa derivee pour les principaux types de vegetation potentielle. Cette approche de meta-modelisation presente les avantages suivants : (i) elle constitue une methode efficace de saut d'echelle, (ii) elle fournit des meta-modeles simples adaptes aux etudes a l'echelle du paysage et (iii) elle assure une propagation correcte des erreurs du modele original base sur les arbres individuels vers le meta-modele. [Traduit par la Redaction] Mots-cles: meta-modele, statistiques bayesiennes, Monte Carlo par chaines de Markov, algorithme de Metropolis- Hastings, modeles bases sur des arbres individuels, saut d'echelle, modeles de croissance forestiere, planification de la gestion forestiere, 1. Introduction Landscape-level studies rely on large-area growth projections to assess the sustainability of ecosystem services such as wood supply, carbon sequestration, and water filtering. In this context, growth models [...]

Sustainability is central to forest management. To determine the sustainable annual harvest, practitioners rely on a simulation framework that combines inventory data, growth models, and optimization software. Because this standard simulation framework is based on model predictions aggregated into yield tables, it may not properly capture natural dynamics. In this paper, we designed an alternative simulation framework that does not require aggregated model predictions. However, the growth model must implement a harvest submodel and produce stochastic predictions. To showcase this alternative simulation framework, we used a forest management unit in southwestern Quebec, Canada, and compared our simulation results with those of the standard simulation framework. Our alternative simulation framework showed that the standing volume of most coniferous species would decrease, whereas that of maple species would increase over the 21st century. The annual harvest of one species as determined through the standard simulation framework was found to be unsustainable in the alternative simulation framework. Being much lighter in terms of computation, this alternative simulation framework can be used as a complement to the standard simulation framework, notably for checking if the optimization-based annual harvest is sustainable. Key words: sustainable annual harvest, annual allowance cut, growth model predictions, simulation, optimization, harvest model. La durabilite est un pilier central de la gestion forestiere. Pour determiner la recolte annuelle durable, les praticiens se fient au cadre de simulation qui combine les donnees de l'inventaire, les modeles de croissance et un logiciel d'optimisation. Parce que ce cadre de simulation standard est fonde sur des previsions du modele regroupees dans les tables de rendement, il est possible qu'il ne saisisse pas adequatement la dynamique naturelle. Dans la presente etude, nous avons concu un cadre de simulation de remplacement qui ne necessite pas de previsions regroupees du modele. Toutefois, le modele de croissance doit mettre en oeuvre un sous-modele de recolte et produire des previsions stochastiques. Pour presenter ce cadre de simulation de remplacement, nous avons utilise une unite d'amenagement forestier dans le sud-ouest du Quebec, au Canada, et nous avons compare les resultats de notre simulation avec ceux d'un cadre de simulation standard. Notre cadre de simulation de remplacement a montre que le volume sur pied de la plupart des especes de coniferes diminuerait alors que celui des especes d'erables augmenterait au cours du 21e siecle. La recolte annuelle d'une espece, de la maniere determinee dans le cadre de simulation standard, a ete jugee non durable dans le cadre de simulation de remplacement. Etant beaucoup plus souple en matiere de calcul, ce cadre de simulation de remplacement peut etre utilise comme complement du cadre de simulation standard, notamment pour verifier si la recolte annuelle fondee sur l'optimisation est durable. [Traduit par la Redaction] Mots-cles : recolte annuelle durable, reduction de l'indemnite annuelle, previsions du modele de croissance, simulation, optimization, modele de recolte., Introduction For more than a century, sustainability has been a central issue in the management of Canadian forests (Drushka 2003). Sustainable forest management can be defined as a concept that [...]

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The forests of North America have undergone important changes since European settlement, particularly in terms of stand composition and associated changes in soil properties. While soil nutrients availability is known to influence forest productivity, the causes and consequences of its variation through time remain poorly understood. This study investigates the effects of long-term changes in forest composition and soil properties on the radial growth of sugar maple (Acer saccharum Marsh.) and balsam fir (Abies balsamea (L.) Mill.), two important species of northeastern North America's forests. Using data from 130 plots measured in 1930 and in 2012-2014 and a mixed-effects modelling approach, we studied the links between radial growth, soil nutrients availability, current stand composition, and shifts in vegetation. The radial growth of balsam fir was found to vary with soil available nitrogen and present-day relative basal area of yellow birch in the stand, while that of sugar maple was found to be invariant to soil characteristics, but proportional to present-day spruce (Picea spp.) relative basal area. However, no direct effects of vegetation change on radial growth were detected. Our results suggest that prior stand composition had no influence on radial growth of both studied species, yet vegetation change could indirectly influence balsam fir growth through an improvement of litter quality with an increase in the abundance of yellow birch (Betula alleghaniensis Britton). Moreover, despite clear differences between the studied species, we conclude that maintaining a certain proportion of compositional diversity may enhance radial growth of both balsam fir and sugar maple. Key words: shifts in forest composition, soil properties, radial growth, balsam fir, sugar maple. Les forets d'Amerique du Nord ont subi d'importants changements depuis la colonisation europeenne, particulierement en termes de composition des peuplements et des modifications consecutives des proprietes du sol. Bien que l'influence de la disponibilite des elements nutritifs du sol sur la productivite de la foret soit connue, les causes et consequences de sa variation a travers le temps demeurent obscures. Cette etude examine les effets des changements a long terme dans la composition de la foret et les proprietes du sol sur la croissance radiale de l'erable a sucre (Acer saccharum Marsh.) et du sapin baumier (Abies balsamea (L.) Mill.), deux especes importantes des forets du nord-est de l'Amerique du Nord. A l'aide de donnees provenant de 130 places echantillons mesurees en 1930 et de 2012 a 2014, et d'une approche de modelisation a effets mixtes, nous avons etudie les liens entre la croissance radiale, la disponibilite des elements nutritifs du sol, la composition actuelle du peuplement et les modifications de la vegetation. La croissance radiale du sapin baumier variait en fonction de la disponibilite de l'azote (N) dans le sol et de la surface terriere relative actuelle du bouleau jaune (Betula alleghaniensis Britton) dans le peuplement, tandis que celle de l'erable a sucre n'etait pas influencee par les caracteristiques edaphiques, mais etait proportionnelle a la surface terriere relative actuelle de l'epicea (Picea spp.). Cependant, aucun effet direct des modifications de la vegetation sur la croissance radiale n'a ete detecte. Nos resultats indiquent que la composition anterieure du peuplement n'a eu aucune influence sur la croissance radiale des deux especes etudiees. Par contre le changement dans la vegetation pourrait indirectement influencer la croissance du sapin baumier par le biais d'une amelioration de la qualite de la litiere due a une augmentation de l'abondance du bouleau jaune. De plus, malgre de nettes differences entre les especes etudiees, nous arrivons a la conclusion que le maintien d'une certaine proportion de diversite dans la composition peut augmenter la croissance du sapin baumier et de l'erable a sucre. [Traduit par la Redaction] Mots-cles: modifications de la composition de la foret, proprietes du sol, croissance radiale, sapin baumier, erable a sucre., Introduction Forests in North America have experienced significant disturbances since European colonization (Whitney 1994). Numerous historical and paleoecological studies have highlighted the role of human activities on forests such as [...]

The sampling intensity of a national forest inventory is usually low. Forest dynamics models can be used to update plots from past inventory campaigns to enhance the precision of the estimate on smaller areas. By doing this, however, the inference relies not only on the sampling design, but also on the model. In this study, the contribution of model predictions to the variance of enhanced small-area estimates was assessed through a case study. The French national forest inventory provided different annual campaigns for a particular region and department of France. Three past campaigns were updated using a forest dynamics model, and estimates of the standing volumes were obtained through two methods: a modified multiple imputation and the Bayesian method. The update greatly increased the precision of the estimate, and the gain was similar between the two methods. The sampling-related variance represented the largest share of the total variance in all cases. This study suggests that plot updating provides more precise estimates as long as (i) the forest dynamics model exhibits no systematic lack of fit and was fitted to a large data set and (ii) the sampling-related variance clearly outweighs the model-related variance. Key words: hybrid inference, multiple imputation, forest dynamics model, growth model, Bayesian method. L'intensite d'echantillonnage d'un inventaire forestier national est generalement faible. Des modeles de dynamique forestiere peuvent etre utilises pour mettre a jour les placettes de campagnes d'inventaire precedentes afin d'ameliorer la precision de l'estimation sur des surfaces plus petites. Cependant, en procedant ainsi, l'inference repose non seulement sur le plan d'echantillonnage, mais aussi sur le modele. Dans cette etude, on a evalue la contribution des predictions du modele a la variance des estimations ameliorees pour de petites surfaces au moyen d'une etude de cas. L'inventaire forestier national francais a fourni differentes campagnes annuelles pour une region et un departement de la France. Trois campagnes anterieures ont ete mises a jour a l'aide d'un modele de dynamique forestiere et des estimations des volumes sur pied ont ete obtenues par deux methodes : l'imputation multiple modifiee et la methode bayesienne. La mise a jour a considerablement augmente la precision de l'estimation et le gain etait similaire avec les deux methodes. Dans tous les cas, la variance liee a l'echantillonnage representait la part la plus importante de la variance totale. Cette etude suggere que la mise a jour des placettes fournit des estimations plus precises pourvu : (i) que le modele de dynamique forestiere ne presente aucun manque de concordance systematique et qu'il a ete ajuste a un grand ensemble de donnees et (ii) que la variance liee a l'echantillonnage l'emporte clairement sur la variance liee au modele. [Traduit par la Redaction] Mots-cles: inference hybride, imputation multiple, modele de dynamique forestiere, modele de croissance, methode bayesienne., 1. Introduction Because of international agreements on climate change, countries now need to assess the state of their forests annually (McRoberts et al. 2009; Vidal et al. 2016). This need [...]

Tree recruitment is affected by numerous biotic and abiotic factors, including climate. However, the relative importance of climate variables in empirical models of tree recruitment remains to be evaluated. We fitted models of tree recruitment to 26 species in the province of Quebec, Canada. For a better understanding of the recruitment process, we used a two-part model to distinguish recruitment occurrence from abundance. The relative importance of the different variables was assessed using Akaike weights. Our main hypothesis was that climate is one of the major drivers of tree recruitment. Our results showed that growing degree-days counted among the major drivers of recruitment occurrence but not of recruitment abundance. Stand variables, such as the presence and abundance of adult trees of the species, and broadleaved and coniferous basal areas were found to be relatively more important than all the climate variables for both recruitment occurrence and abundance. Species occupancy within a 10-km radius also had a significant effect on recruitment occurrence for two-thirds of the species, but it was less important than growing degree-days and other stand variables. Climate change is expected to improve the suitability of habitats located at the northern edge of species distributions. However, our model predictions point to a low probability of colonization in newly suitable habitats in the short term. [ABSTRACT FROM AUTHOR]

Studying intra-annual growth dynamics through a modelling approach has proved useful for characterizing differences in wood phenology between species and deviations from the expected tree growth due to climate change. The aim of this paper was to determine the climatic factors and the inter- and intra-specific competition traits that drive intra- annual secondary growth dynamics in three Mediterranean tree species that naturally co-exist in the Spanish Northern Plateau (Pinus pinea L., Juniperus thurifera L., and Quercus ilex subsp. ballota (Desf.) Samp.). For this purpose, we obtained girth increment data from band dendrometers installed on 58 trees from May 2012 to April 2015. Half of them were located in a high-density plot and half were in a low-density plot. These data were analysed through a nonlinear multifactorial model considering daily and cumulative climatic effects together with inter- and intra-specific competition indices. Our results provide evidence of a spatiotemporal niche separation between species. Compared with other species, Q. ilex subsp. ballota showed a wider thermal amplitude, a higher mean optimum temperature for growth, and a milder effect of drought on its secondary growth. Under current climate change projections, simulations based on our model predict a secondary growth reduction for P. pinea and a growth enhancement for Q. ilex subsp. ballota in these Mediterranean mixtures. Key words: dendrometers, mixed stands, climate change, nonlinear mixed models, Mediterranean species. L'etude de la dynamique de la croissance intra-annuelle par une approche de modelisation s'est averee utile pour caracteriser les differences de phenologie du bois entre les especes et les ecarts de croissance des arbres par rapport aux previsions en raison du changement climatique. L'objectif de cette etude etait de determiner les facteurs climatiques et les caracteristiques de la competition inter- et intra-specifiques qui expliquent la dynamique de la croissance secondaire intraannuelle de trois especes mediterraneennes arborescentes qui coexistent de facon naturelle sur le plateau septentrional en Espagne (Pinus pinea L., Juniperus thurifera L. et Quercus ilex subsp. ballota (Desf.) Samp.). A cette fin, nous avons obtenudes donnees d'accroissement circonferentiel provenant de dendrometres a bande installes sur 58 arbres de mai 2012 a avril 2015. La moitie de ces dendrometres etait situee dans une placette a forte densite et l'autre moitie dans une placette a faible densite. Ces donnees ont ete analysees a l'aide d'un modele multifactoriel non lineaire en tenant compte des effets climatiques journaliers et cumules de meme que des indices de competition inter- et intra-specifiques. Nos resultats attestent d'une separation spatio- temporelle de niche entre les especes. Comparativement aux autres especes, Q ilex subsp. ballota avait une plus grande amplitude thermale, une temperature moyenne optimale plus elevee pour la croissance et l'effet de la secheresse sur sa croissance secondaire etait moins prononce. En considerant les projections actuelles de changement climatique, les simulations provenant de notre modele prevoient une reduction de la croissance secondaire pour P. pinea et une amelioration de la croissance pour Q. ilex subsp. ballota dans ces peuplements mixtes mediterraneens. [Traduit par la Redaction] Mots-cles: dendrometres, peuplements mixtes, changement climatique, modeles mixtes non-lineaires, especes mediterraneennes., 1. Introduction Mixed-species forests have gained significant attention in recent years as many studies have shown that tree species richness is a key feature for most forest functions and services [...]

In forest inventories, there are many variables of interest that are difficult to measure. Practitioners have to rely on auxiliary variables and models to obtain predictions of these variables. In such contexts, design-based or model-dependent inferences are often ineffective and hybrid estimators are required. Because most models now contain mixed effects, we investigated how the random effects and residual errors affected the inferences in a context of hybrid estimation. We first developed hybrid estimators for the different mixed models. We then tested these estimators through a simulation study. Finally, the estimators were applied to a real-world case study: stone pine (Pinus pinea L.) cone production in central Spain. It turned out that the contributions of the random effects and the residual errors to the variance were constant regardless of the sample size. In our case study, these contributions were rather small when compared with those of the sampling and parameter estimates. The greatest impact came from the underestimation of the variance of the parameter estimates when random effects were not taken into account in the model. As the variance estimators make it possible to distinguish different variance components, they can be useful for identifying the greatest sources of uncertainty. Key words: hybrid estimators, mixed-effects models, Horvitz-Thompson estimator, variance components, Monte Carlo simulation. Dans les inventaires forestiers, il y a plusieurs variables d'interet qui sont difficiles a mesurer. Les forestiers doivent compter sur des variables auxiliaires et des modeles pour obtenir des previsions de ces variables. Dans de tels contextes, des inferences fondees uniquement sur le modele ou sur le plan de sondage sont souvent inefficaces, ce qui necessite d'avoir recours a des estimateurs hybrides. Parce que la plupart des modeles contiennent maintenant des effets mixtes, nous avons etudie comment les effets aleatoires et les erreurs residuelles influencent les inferences dans un contexte d'estimation hybride. Nous avons d'abord mis au point des estimateurs hybrides pour les differents modeles mixtes. Nous avons ensuite teste ces estimateurs a l'aide d'une etude de simulation. Finalement, les estimateurs ont ete appliques a une veritable etude de cas : la production de cones de pin parasol (Pinus pinea L.) au centre de l'Espagne. Il est apparu que les contributions des effets aleatoires et des erreurs residuelles a la variance etaient constantes pour toutes les tailles d'echantillon. Dans notre etude de cas, ces contributions etaient plutot petites comparativement a celles de l'echantillonnage et des estimations des parametres. Le plus gros impact provenait d'une sous-estimation de la variance des estimations des parametres lorsque les effets aleatoires n'etaient pas pris en compte dans le modele. Puisque les estimateurs de la variance permettent de distinguer les differentes composantes de la variance, ils peuvent etre utiles pour identifier les plus grandes sources d'incertitude. [Traduit par la Redaction] Mots-cles : estimateurs hybrides, modeles a effets mixtes, estimateur de Horvitz-Thompson, composantes de la variance, simulation de Monte-Carlo., 1. Introduction Forest resources usually cover areas so large that a ground census is impossible, making it necessary for foresters to rely on sampling to evaluate them. Even in a [...]

Natural regeneration comprises different subprocesses, each of them driven by specific climatic and stand-related factors, which determine the success of natural regeneration. The objective of this study was to investigate the seed availability of maritime pine (Pinus pinaster Aiton). To meet this objective, seed rain was monitored for four different levels of stand density at the experimental site of Cuellar, Spain, during a 10-year period. A generalized linear mixed-effects model was fitted to test the effects of climatic variables and stand density on the annual seed production and seed rain. The climatic covariates were chosen among those that are thought to affect the key physiological phases governing these subprocesses: minimum temperature in October 2 years before dispersal (cone growing), April precipitation 1 year before dispersal (cone growing), and October-November precipitation 1 year before dispersal (cone maturation). No climate variable related to flowering or seed rain process was significant. Moreover, stand density was considered through a spatially explicit index called the seed-source index. Primary cone growth was limited by extreme cold events. Absence of precipitation limits secondary growth and hinders final cone ripening. It turns out that seed production and seed rain may be a bottleneck for natural regeneration of P. pinaster under low stand densities, especially under extreme climatic scenarios. Key words: climate change, generalized linear mixed model, Mediterranean ecosystem, natural regeneration, seed limitation. La regeneration naturelle comporte differents sous-processus, chacun d'eux influences par des facteurs specifiques relies au climat et au peuplement, qui determinent le succes de la regeneration naturelle. L'objectif de cette etude etait d'examiner la disponibilite des semences du pin maritime (Pinus pinaster Aiton). Pour atteindre cet objectif, la pluie de graines a ete suivie pour quatre niveaux de densite de peuplement a la station experimentale de Cuellar, en Espagne, pendant une periode de 10 ans. Un modele lineaire mixte generalise a ete ajuste pour tester les effets des variables climatiques et de la densite du peuplement sur la production annuelle de semences et sur la pluie de graines. Les covariables climatiques ont ete choisies parmi celles qui sont censes influencer les phases physiologiques cles regissant ces sous-processus: la temperature minimale en octobre deux ans avant la dispersion des graines (croissance des cones), les precipitations en avril un an avant la dispersion des graines (croissance des cones) et les precipitations en octobre et novembre un an avant la dispersion des graines (maturation des cones). Aucune variable climatique n'a ete significativement reliee aux processus de floraison ou de pluie de graines. De plus, on a tenu compte de la densite des peuplements a l'aide d'un indice spatialement explicite nomme indice semence-source. La croissance primaire des cones a ete limitee par des evenements de froid extreme. L'absence de precipitation a limite la croissance secondaire et a semble empecher la maturation finale des cones. Il semble donc que la production de semences et la pluie de graines peuvent constituer un goulot d'etranglement pour la regeneration naturelle du pin maritime dans des peuplements de faible densite, particulierement lors de scenarios climatiques extremes. [Traduit par la Redaction] Mots-cles: changements climatiques, modele lineaire mixte generalise, ecosysteme mediterraneen, regeneration naturelle, manque de semences., Introduction It is well established that natural regeneration methods contribute to effectively and economically perpetuate natural ecosystems in the long term (Barnes et al. 1998). As a result, silviculture treatments [...]

Tree classification systems are generally designed to predict the supply of high-quality logs for the wood processing industries and to mark defective trees for removal with the aim of improving both the vigor and quality of future stands. Although these two objectives are generally inversely related, their joint consideration could enable the development of robust criteria for improved tree selection in partial cuttings of northern hardwood stands by targeting low-vigor (LV) trees of high quality (HQ). In this study, we used a copula approach to model the joint probability distribution of trees characterized by both vigor and quality, which accounts for the statistical dependence between the different classes of both classification systems. The relationships between the probability of occurrence of a tree in each joint category and tree diameter at breast height (DBH) were quite similar among the three studied species: yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.), and American beech (Fagus grandifolia Ehrh.). In particular, the probability of occurrence of LV-HQ trees was characterized by a parabolic curve with a maximum value attained at the mid-DBH range, whereas that of LV and low-quality (LQ) trees increased with increasing DBH. This suggests that instead of harvesting large and mostly LV-LQ trees, partial cutting should target smaller LV-HQ trees, so that the volume of harvested HQ trees would increase without compromising the silvicultural objective of improving the vigor of future stands. Resume: Les systemes de classification des arbres sont generalement concus pour prevoir l'approvisionnement en bois de haute qualite des industries de transformation et pour marquer les arbres defectueux a prelever dans le but d'augmenter la vigueur et la qualite des futurs peuplements. Bien que ces deux objectifs soient generalement contradictoires, leur prise en compte simultanee pourrait permettre de definir des criteres robustes visant a ameliorer la selection des arbres a prelever lors de coupes partielles dans des peuplements de feuillus nordiques en ciblant les arbres de faible vigueur (FV) et de haute qualite (HQ). Dans cette etude, nous avons utilise une approche par copule pour modeliser la distribution de la probabilite conjointe des arbres caracterises par leur vigueur et leur qualite qui tient compte de la dependance statistique entre les classes des deux systemes de classification. La relation entre la probabilite qu'un arbre se situe dans chaque categorie conjointe et son diametre a hauteur de poitrine (DHP) etait assez similaire pour les trois especes etudiees: le bouleau jaune (Betula alleghaniensis Britt.), l'erable a sucre (Acer saccharum Marsh.) et le hetre a grandes feuilles (Fagus grandifolia Ehrh.). De facon particuliere, la probabilite d'occurrence des arbres FV-HQ etait caracterisee par une courbe parabolique dont la valeur maximale etait atteinte pres du milieu de la gamme des DHP, alors que celle des arbres FV et de faible qualite augmentait avec le DHP. Ces resultats indiquent qu'au lieu de recolter les gros arbres qui sont souvent de faible vigueur et de faible qualite, les coupes partielles devraient cibler des arbres plus petits caracterises par une faible vigueur et une haute qualite. Ainsi, on augmenterait la proportion du volume recolte constituee d'arbres de haute qualite sans compromettre l'objectif sylvicole d'ameliorer la vigueur des futurs peuplements., Introduction Valuable tree species from the northern hardwood forests of North America have traditionally been harvested to supply the 'appearance' wood products industries. The demand and market prices are particularly [...]

Data in forestry are often spatially and (or) serially correlated. In the last two decades, mixed models have become increasingly popular for the analysis of such data because they can relax the assumption of independent observations. However, when the relationship between the response variable and the covariates is nonlinear, as is the case in generalized linear mixed models (GLMMs), population-averaged predictions cannot be obtained from the fixed effects alone. This study proposes an estimator, which is based on a five-point Gauss-Hermite quadrature, for population-averaged predictions in the context of GLMM. The estimator was tested through Monte Carlo simulation and compared with a regular generalized linear model (GLM). The estimator was also applied to a real-world case study, a harvest model. The results showed that GLM predictions were unbiased but that their confidence intervals did not achieve their nominal coverage. On the other hand, the proposed estimator yielded unbiased predictions with reliable confidence intervals. The predictions based on the fixed effects of a GLMM exhibited the largest biases. If statistical inferences are needed, the proposed estimator should be used. It is easily implemented as long as the random effect specification does not contain multiple random effects for the same hierarchical level. Resume: Les donnees forestieres sont souvent correlees dans le temps ou dans l'espace. Au cours des 20 dernieres annees, les modeles mixtes sont devenus de plus en plus populaires pour analyser de telles donnees parce qu'ils permettent d'assouplir le postulat d'independance des observations. Cependant, lorsque la relation entre la variable reponse et les covariables est non lineaire, comme c'est le cas dans les modeles lineaires generalises mixtes (MLGM), des previsions de la moyenne de la population ne peuvent etre obtenues des seuls effets fixes. Cette etude propose un estimateur base sur une quadrature Gauss-Hermite a cinq points pour predire de la moyenne de la population dans un contexte de MLGM. Cet estimateur a ete teste a l'aide d'une simulation de Monte-Carlo, compare a un modele lineaire generalise (MLG) regulier et applique a une etude de cas reel, un modele de prelevement. Les resultats indiquent que les previsions du MLG sont non biaisees, mais que leurs intervalles de confiance n'atteignent pas leur couverture nominale. Par ailleurs, l'estimateur propose produit des previsions non biaisees avec des intervalles de confiance fiables. Les biais les plus grands etaient associes aux previsions basees sur les effets fixes d'un MLGM. Si des inferences statistiques sont necessaires, l'estimateur propose devrait etre utilise. Sa mise en oeuvre est facile dans la mesure ou la specification des effets aleatoires ne contient pas d'effets aleatoires multiples pour un meme niveau hierarchique., Introduction Mixed-effects (both random and fixed) models are widely used in forestry. The reasons for their popularity are twofold. First, sample plot data in forestry are often spatially and (or) [...]

: In most large-scale inventories, volume models rely on predicted heights instead of measured heights. The effect of height predictions over volume estimate uncertainty is therefore a crucial issue. In this study, we designed a statistical estimator that enables the propagation of tree height prediction errors into a general volume model. The proposed estimator relies on the assumption that both the volume model and the height-diameter model that provides the height predictions do not exhibit any lack of fit. This estimator was tested against a Monte Carlo simulation for 90 plots from three typical forest types in Quebec, Canada (hardwood, mixedwood, and softwood). The results show that the estimator provides plot volume predictions with error variances that fit those estimated using the Monte Carlo simulation. The estimator developed in this study may be useful to quickly provide the uncertainty associated with plot volume predictions in large-scale inventories. Resume: Dans la plupart des inventaires a grande echelle, les modeles de volume sont bases sur des hauteurs predites plutot que mesurees. L'effet des previsions de la hauteur sur l'incertitude des estimations du volume a donc une grande importance. Dans cette etude, nous avons formule un estimateur statistique qui permet la propagation des erreurs de prevision de la hauteur des arbres dans un modele general de volume. L'estimateur propose est base sur l'hypothese quil ny a aucun manque d'ajustement du modele de volume et de la relation hauteur-diametre qui fournit les estimations de la hauteur. Cet estimateur a ete teste a l'aide d'une simulation de Monte Carlo pour 90 parcelles provenant de trois types forestiers typiques (feuillu, mixte et resineux) du Quebec, au Canada. Les resultats indiquent que l'estimateur fournit des previsions du volume des parcelles dont la variance de l'erreur est similaire a celle qui a ete estimee par la simulation de Monte Carlo. L'estimateur qui a ete mis au point dans cette etude peut etre utile pour fournir rapidement l'incertitude associee aux previsions du volume des parcelles des inventaires a grande echelle. [Traduit par la Redaction], Introduction The availability of commercial wood volumes is central to forest management in most jurisdictions. However, in practice, measuring stem volume is almost impossible without felling the tree. In fact, [...]

Modelling volumes by log grades in standing hardwood trees is often hindered by the nature of the response variable. In this paper, we used a two-part conditional model to account for the excess of zero responses for some log grades. Moreover, this approach was used as a framework to compare three different tree classifications in their ability to predict volumes by log grades in standing yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh.) trees. A tree grade classification was compared with two preharvest tree classifications based on mortality risk assessment. A cross-validation was also tamed out to evaluate the two parts of the model. The results showed that the twopart conditional approach was efficient in this case study. Compared with a general model, the three classifications improved the maximum likelihood. According to the Akaike and Bayesian information criteria, the tree grade classification was the 'best' one. All three classifications proved to be better able to distinguish log grade occurrence than log grade volume. Although it implies additional cost, the implementation of the tree grade classification into the preharvest inventories would improve the prediction of volumes by log grades for yellow birch and sugar maple trees. La modelisation des volumes par classes de qualite des billes des tiges feuillues sur pied est souvent rendue difficile par la nature de la variable reponse. Dans cet article, nous utilisons un modele conditionnel constitue de deux parties pour their compte de la surabondance de reponses nulles pour certaines classes de qualites. De plus, cette approace a ete utilisee comme cadre conceptuel pour comparer trois classifications differentes des tiges sur la base de leur capacite a predire les volumes par classes de qualite des billes des tiges sur pied de bouleau jaune (Betula alleghaniensis Britton) et d'erable a sucre (Acer saccharum Marsh.). Une classification de la qualite des tiges a ete comparee a deux classifications des arbres avant la recolte sur la base de (evaluation des risques de mortality. Une validation croisee a egalement ete effectuee pour evaluer les deux parties du modele. Les resultats montrent que l'approche conditionnelle constituee de deux parties etait efficace dans cette etude de cas. Comparativement au modele general, les trois classifications ont ameliore le maximum de vraisemblance. Selon les criteres d'information d'Akaike et Bayesian, la classification de la qualite des tiges etait la meilleure. Les trois classifications ont demontre qu'elles distinguaient mieux (occurrence que le volume des classes de qualite des Mlles. Meme si cela implique un tout additionnel, l'implantation de la classification de la qualite des tiges dans les inventaires prerecolte ameliorerait la prediction des volumes par classes de qualite des Mlles pour les tiges de bouleau jaune et d'erable a sucre. [Traduit par la Redaction], Introduction In forest management, decision-making is often based on total merchantable volume predictions, whereas industrial needs are expressed as volumes of particular log grades. The need to separate logs into [...]

Abstract: In this study, a diameter increment model was calibrated for individual trees in hardwood stands in Quebec, Canada. Two random effects, a first one for the plot and a [...]