Tree crown ratio models for multi-species and multi-layered stands of southeastern British Columbia

Abstract

The ratio of live crown length to tree height (crown ratio; CR) is often used as an important predictor variable for tree level growth equations, particularly for multi-species and multi-layered stands. Also, CR indicates tree vigour and can be an important habitat variable. Measurement of CR for each tree can be time-consuming and difficult to obtain in very dense stands and for very tall trees where the base of live crown is obscured. Models to predict CR from size, competition and site variables were developed for several coniferous and one hardwood tree species growing in multispecies and multi-layered forest stands (complex stands) of southeastern British Columbia. Simple correlations indicated the expected relationships of CR decreasing with increasing height, and with increasing competition. A logistic model form was used to constrain predicted CR values to the interval [0,1]. Also, predictors were divided into tree size, stand competition, and site measures, and the contribution of each set of contributors was examined. For all models, height was an important predictor. The stand competition measure, basal area of larger trees, contributed significantly to predicting CR given that crown competition factor was also included as a measure of competition. Logical trends in CR versus size and competition variable groups were reflected by the models; site variable slightly improved predictions for some species. Much of the variability in CR was not accounted for, indicating that other variables are important for explaining CR changes in these complex stands.Key words: crown ratio, multi-species stands, multi-layered stands, basal area of larger trees RÉSUMÉ Le ratio entre la longueur de la cime vivante par rapport à la hauteur de l'arbre ( ratio de la cime; RC) est souvent utilisé en tant que variable importante de prédiction dans le cas d'équations de la croissance des arbres, spécialement pour les peuplements composés de nombreuses espèces et présentant plusieurs étages. De plus, le RC indique la vigueur de l'arbre et peut être une variable importante de l'habitat. La mesure du RC pour chaque arbre peut prendre beaucoup de temps et être difficile à obtenir dans des peuplements très denses et dans le cas d'arbres très grands pour lesquels la base de la cime vivante se retrouve dans l'ombre. Les modèles de prédiction du RC à partir des variables de diamètre, de compétition et de station ont été élaborées pour diverses espèces résineuses et pour une espèce feuillue retrouvées dans des peuplements composés de nombreuses espèces et présentant plusieurs étages (peuplements complexes) du sud-est de la Colombie-Britannique. Des corrélations simples ont démontré tel que prévu des relations de RC en décroissance avec l'augmentation de la hauteur et de l'augmentation de la compétition. Une forme de modèle logistique a été utilisée pour contraindre les valeurs prévues de RC selon un intervalle de [0,1]. De plus, les variables de prédiction ont été divisées selon le diamètre de l'arbre, la compétition au sein du ...

Development of height to crown base models for thirteen tree species of the North American Acadian Region

“…In multi-cohort, mixed species stands, like those that predominate in the Acadian Region, age is not very meaningful and SI is often difficult to accurately assess. Hasenauer and Monserud (1996) and Temesgen et al (2005) used additional geographical variables in their CR models; however, R 2 in both models were generally less than 0.6, while the site level Table 7. Estimated parameters for the final model a using nonlinear mixed effects (NLME) with a variance power function on diameter at breast height (DBH).…”

“…We categorized the covariates into three groups as used by Hasenauer and Monserud (1996) and Temesgen et al (2005). These were (a) size, (b) competition, and (c) site-specific covariates.…”

“…There are numerous studies modeling HCB and CR across a variety of regions and species such as Hasenauer and Monserud (1996) in Austria, Temesgen et al (2005) in British Columbia, Ritchie and Hann (1987) as well as Zumrawi and Hann (1989) in the US Pacific Northwest, and Liu et al (1995) in the US southeast. In the northeastern US, the forests are quite complex in terms of stand history, condition, structure, and management, but very little work has been done on crown size modeling in the region.…”

“…In order to calculate or estimate CR, we need to measure HCB or CL. However, measurements of HCB and CL are difficult in dense and/or multilayered stands (Temesgen et al 2005), prone to error due to conflicting definitions (McRoberts et al 1994), and time-consuming; therefore, measurements are often limited. Static HCB equations can be used to predict missing HCB measurements (Hann et al 1997), and also to estimate changes in crown ratio (Stage 1973).…”

Self-pruning of pedunculate oak (Quercus robur L.) stems and the diameter at breast height of trees in commercially managed stands

“…Wed³ug Hejnowicza (2002) starzenie siê i obumieranie ga³êzi bocznych odbywa siê w kilku etapach. Temesgen et al (2005) (za Kramer et Kozlowski 1979) uwa¿aj¹, ¿e ¿ywe ga³êzie pozostaj¹ na drzewach wówczas, gdy przyczyniaj¹ siê do produkcji netto fotosyntezy oraz ¿e wystêpowanie ulistnionych ga³êzi w ni¿szych partiach pnia drzew rosn¹cych w zwarciu zale¿y od ilooeci oewiat³a przepuszczonego przez sklepienie koron i cienioznooenooeci gatunku: u drzew rosn¹cych na otwartej przestrzeni zachowane s¹ ¿ywe ga³êzie do poziomu gruntu.…”