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White spruce and trembling aspen are two important commercial species in British Columbia. They often grow in association, particularly in the Boreal White and Black Spruce and Sub-Boreal Spruce biogeoclimatic zones. Site index conversion equations are useful for estimating the site index of one species from the site index of another species. This study fills a need for site index conversion equations for mixed spruce/aspen stands. Seventy 0.01 ha study plots were established in mixed spruce/aspen stands. One site tree of each species was selected from each plot. The height and breast height ages of the site trees were measured and the site index was estimated with these data. The correlation between the site index of spruce and aspen was 0.6. Geometric mean regression was used to estimate the parameters of a linear site index conversion equation. The analysis did not reveal any differences in the conversion equations across the three major biogeoclimatic units (BWBSmw1, BWBSmw2, and SBS) that were sampled. Therefore, only one conversion equation is required.

Stand age is often hard to measure accurately. Measurement error in age affects height estimates when height is projected from one age to another age. In this study, our objective was to derive an estimator for the variance of the component of projection error associated with the error in age. To evaluate the estimator, a simulation approach was employed and the results showed that the estimator worked well in most cases. When the variance of the error in age increases and the projection is forward, however, the estimator might not work as well as in other cases. Another objective was to examine how the error in age behaved under different height-age models and to what extent it affected height and site index estimates. The effect of the error in age depended on its magnitude, the height-age model, initial value of dominant height and age, and projection length. It was also shown that the effect was sometimes negligible, but it could be considerable in other cases. Data from 80 ponderosa pine (Pinus ponderosa Dougl. ex Laws.) trees in British Columbia, Canada, were used in an illustrative example. L'age d'un peuplement est souvent difficile a mesurer precisement. Les erreurs de mesure de l'age influencent les estimations de la hauteur lorsque la hauteur est projet ee d'une valeur d'age a une autre. Dans cette etude, notre objectif etait de calculer un estimateur de la variance de la composante de l'erreur de projection associ ee a l'erreur sur l'age. Une approche de simulation a et e utilis ee pour evaluer cet estimateur et les r esultats montrent qu'il est ad equat dans la plupart des cas. Cependant, lorsque la variance de l'erreur sur l'age augmente et que la projection est vers l'avant, l'estimateur pourrait ne pas fonctionner aussi bien que dans les autres cas. Un autre objectif etait d' etudier le comportement de l'erreur sur l'age pour diff erents modeles reliant la hauteur a l'age et de d eterminer dans quelle mesure cette erreur influence les estimations de la hauteur et de l'indice de qualit e de station. L'effet de l'erreur sur l'age d ependait de son ampleur, du modele reliant la hauteur a l'age, des valeurs initiales de la hauteur dominante et de l'age, ainsi que de la p eriode de projection. Les r esultats ont aussi montr e que l'effet de l'age etait parfois n egligeable, mais qu'il pouvait etre consid erable dans d'autres cas. Les donn ees de 80 tiges de pin ponderosa (Pinus ponderosa Dougl. ex Laws.) de la Colombie-Britannique, au Canada, ont et e utilis ees comme exemple. [Traduit par la R edaction], Introduction Dominant height is an important explanatory variable in forest growth and yield modeling systems (e.g., Pienaar and Shiver 1986; Borders 1989; Lynch and Murphy 1995). Site index, often defined [...]

Crown length is a key aspect of vertical structure in multi-aged, multistrata, mixed-species forests. Crown length, defined as the distance from the tree top to the lowest live branch whorl, was determined for 3169 mapped trees ≥4.0 cm in diameter, in four 0.25 ha plots in each of two old-growth Abies lasiocarpa (Hook.) Nutt.--Picea engelmannii Parry ex Engelm. stands. We randomly selected half the trees to build models and half for validation. Crown length was modelled as a function of tree height, incorporating modifiers to account for neighbouring trees. The inclusion radius and height threshold for competition were 3 m and 70%, respectively. The addition of two modifiers significantly improved the model for A. lasiocarpa; crown length decreased as the number of neighbours increased and as the height of surrounding trees increased. In contrast, none of the modifiers significantly improved the model for P. engelmannii. Except at high levels of competition, Abies crowns were longer than those of Picea. However, both species in these forests have long crowns, typically three-quarters of the tree height and rarely less than half. The tightly programmed conical crown architecture of these species likely contributes to long crowns and to the limited effects of neighbours on crown length. Resume: La longueur de la cime est un aspect cle de la structure verticale des forets composees de plusieurs especes, dont les arbres d'age variable occupent des strates multiples. La longueur de la cime, definie comme la distance entre le faite de l'arbre et le plus bas verticille de branches vivantes, a ete mesuree sur 3169 arbres cartographies, dont le diametre etait superieur ou egal a 4,0 cm, dans quatre parcelles de 0,25 ha dans chacune de deux vieilles forets composees d'Abies lasiocarpa (Hook.) Nutt. et de Picea engelmannii Parry ex Engelm. Nous avons choisi aleatoirement la moitie des arbres pour etalonner des modeles alors que l'autre moitie a servi a leur evaluation. La longueur de la cime a ete modelisee en fonction de la hauteur de l'arbre tout en incorporant des modificateurs pour tenir compte des arbres voisins. Le rayon d'inclusion et le seuil de hauteur de la competition etaient respectivement de 3 m et de 70 %. L'introduction de deux modificateurs a significativement ameliore le modele d'A. lasiocarpa. Dans ce cas, la longueur de la cime diminuait avec l'augmentation du nombre et de la hauteur des arbres voisins. A l'oppose, aucun modificateur n'a significativement ameliore le modele de P. engelmannii. Les cimes d'Abies etaient plus longues que celles de Picea, sauf lorsque la competition etait forte. Toutefois, les deux especes presentes dans ces forets ont de longues cimes qui atteignent typiquement les trois quarts et rarement moins de la moitie de la hauteur des arbres. L'architecture conique genetiquement programmee de la cime de ces especes contribue probablement a leur longue cime et a l'effet limite des voisins sur la longueur de leur cime. [Traduit par la Redaction], Introduction The structure of old, uneven-aged stands is often complex. Creating a multistrata canopy structure may be an important goal of management when considering biodiversity issues or trying to emulate [...]

Insect outbreaks, such as the current mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forests in British Columbia, are major disturbances in many forests. After an insect outbreak, the advance regeneration typically forms a new canopy, which may be adequate for timber objectives in some stands. Our purpose was to quantify and then model the abundance and spatial distribution of advance regeneration (trees Les epidemies d'insectes constituent une perturbation majeure dans beaucoup de forets, incluant l'epidemie actuelle du dendroctone du pin ponderosa dans les forets de pin tordu latifolie (Pinus contorta var. latifolia Engelm.) en Colombie-Britannique. La regeneration preetablie forme typiquement un nouveau couvert qui peut etre adequat pour satisfaire les objectifs de production de matiere ligneuse dans certains peuplements. Notre objectif consistait a quantifier puis a modeliser l'abondance et la distribution spatiale de la regeneration preetablie (arbres [Traduit par la Redaction], Introduction Many forests contain large numbers of small trees in the understory, which often fill small canopy gaps and can also form new stands following a major disturbance to the [...]

Abstract: Shade-tolerant trees that start in the understory but ultimately reach the canopy persist through different microhabitat conditions during their ontogeny. We evaluate how the height to diameter ratio and [...]

Growth response functions (GRFs) that relate the growth of a population to the climate of the sites in which it is tested are gaining attention for their ability to predict impacts of climate change on tree growth. However, nonclimatic site to site variation introduces error into GRFs. Using data from a large lodgepole pine (Pinus contorta Dougl. ex Loud.) provenance test in British Columbia and the Yukon, Canada, a technique is presented that accounts for the effect of nonclimatic variation in GRFs. The mean height of the 'local' provenances at each test site was used to predict 'site height' from site climate variables in multiple regression. Residuals from the site height equation provided an index of the nonclimatic effect for each site and were included as a covariate in quadratic GRFs that related provenance height at each test site to mean annual temperature at each test site. Inclusion of the nonclimatic index in the model resulted in a moderate or large displacement of GRFs for 25% of the provenances, while increasing mean [R.sup.2] values for 138 of 140 provenances and decreasing the root mean squared error for 113 of 140 provenances. These results suggest that inclusion of the nonclimatic index in GRF models could substantially affect height predictions for some provenances and reduce prediction error for most provenances. Les fonctions de reaction de la croissance (FRC) qui relient la croissance d'une population au climat des stations oh elles sont testees gagnent en popularity; a cause de leur capacity; a predire les impacts des changements climatiques sur la croissance des arbres. Cependant, les variations non climatiques entre les stations introduisent des erreurs dans les FRC. A partir des donnees d'un test de provenance de pin tordu latifolie (Pinus contorta Dougl. ex Loud.) de grande envergure en Colombie-Britannique et au Yukon, au Canada, nous presentons une technique qui tient compte de l'effet des variations non climatiques dans les FRC. La hauteur moyenne des provenances <> a chaque endroit oU le test a ete etabli a ete utilisee pour predire, a l'aide de la regression multiple, la <> a partir des variables climatiques de la station. Les residus de l'equation de la hauteur specifique a la station ont fourni un indice de l'effet non climatique dans chaque station et ont etes inclus comme covariable dans des FRC quadratiques qui reliaient la hauteur de la provenance dans chaque station a la temperature annuelle moyenne de la station. L'introduction de l'indice non climatique dans le modele a produit un dylplacement modere a grand des FRC chez 25 % des provenances, a augmente la valeur moyenne du [R.sup.2] de 138 des 140 provenances et a diminue l'erreur quadratique moyenne chez 113 des 140 provenances. Ces resultats indiquent que l'introduction de l'indice non climatique dans les modeles de FRC pourrait substantiellement affecter les predictions de hauteur pour quelques provenances et diminuer l'erreur de prediction pour la plupart des provenances. [Traduit par la Redaction], Introduction With climate change raising the spectre of significant changes to forest productivity due to altered adaptation, provenance tests have encountered a resurgence of interest, as modellers attempt to mitigate [...]

The taper equations used by the Ministry of Forests, Lands and Natural Resource Operations in British Columbia (BC), Canada, date back to the mid-1950s. Very little work has been done on examining the effect of climate on taper, particularly for BC but elsewhere as well. The objective of our research was to determine whether climate has an effect on tree taper for lodgepole pine (Pinus contorta Dougl. ex Loud.) in BC. The data for this project consisted of multiple diameter inside bark measurements along the stems of 270 trees across eight biogeoclimatic zones. In addition, 20 climate variables for the sample sites were predicted from the ClimateWNA model. Kozak's variable-exponent taper model was refitted with the climate variables in the exponent of the model. The single temperature- and precipitation-related variables that provided the best fit were incorporated into the final taper model. The model was analysed as a mixed-effects model, with spatial correlation and heteroscedastic errors being explicitly modelled. Mean annual precipitation and the Julian date of the first frost after the summer growing period were the best predictors of taper. Further work is required to understand why these variables are important predictors of taper, but a possible linkage is through the tree's crown. [ABSTRACT FROM PUBLISHER]

Non-linear mixed effects (NLME) models are now common in the forestry literature. The fixed effects parameters are estimated in the model fitting stage. For new individuals, the random effects parameters are predicted when the model is used to predict the response variable. Predicting both the random effects parameters and the response variable requires the underlying model to be linearized using a Taylor series expansion. This is done by expanding around the expected or predicted value of the random effects parameters. Whichever way is chosen, it should be consistent. However, mismatches between the predictors for the random effects and predictors for the future response are sometimes made in forestry growth and yield applications. We consider the implications of using mismatched predictors on a single-level NLME model. We analyzed and empirically compared a total of four combinations of two types of predictors for both the random effects and the response variable. Diameter at breast height was predicted for 140 loblolly pine trees using these four combinations of predictors. The predictors were evaluated with the mean squared error. Model accuracy was best when the predictors for the random effects and the response variables were based on the same expansion method. [ABSTRACT FROM AUTHOR]

Empirical growth and yield models for forest management are evolving toward individual-tree models that are capable of simulating the growth of mixed and uneven-aged stands. Spatially explicit (i.e., distance-dependent) models usually modify the growth of trees by means of competition indices; however, these competition indices rarely simulate the light available for tree growth explicitly. We used tree growth data from an even-aged, unthinned, 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand in British Columbia to test the hypothesis that the amount of absorbed light is a good predictor of diameter at breast height, height, and bole volume growth of an individual tree. We also explored the relationships between these variables. A spatially explicit light model was used to simulate photosynthetically active radiation absorbed by individual trees during a growth period (APAR) based on detailed canopy architecture information. For the purpose, we used a weighted leaf area (WLA) that is linearly related to APAR. Because of the integration of light absorption by a tree crown, estimates of WLA were highly correlated with leaf area for dominant trees. For suppressed trees, leaf area was a poor estimator of WLA. The relationship between WLA and bole volume growth was nonlinear, indicating a higher light-use efficiency in suppressed trees than in dominant trees. This relationship was strong enough to be useful for growth modeling. Only height growth of suppressed trees was affected by WLA. We conclude that single-tree WLA can be used as a process-oriented competition index in growth models for forest management. [ABSTRACT FROM PUBLISHER]