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Generally, the effects of climate change on tree growth focus on changes in one dimension of a tree. However, diameter increment along the main stem reacts differently to climatic variables, which in turn influences tree form. These differences can thus have important implications on stem volume, which could induce biases in future forest biomass estimation. A stem taper model including climatic variables was fitted to stem analysis data of five different species (Abies balsamea, Betula papyrifera, Picea glauca, Picea mariana, Populus tremuloides) distributed along a gradient from the temperate to the boreal forest of Eastern Canada. The effects of shifts in stem form on tree volume between different climatic scenarios were then estimated and related to different functional traits. Changes in stem form with climatic variables were observed for four of the five species, with up to 5% differences in stem volume between different climatic situations. Changes in stem volume were found to decrease with increasing waterlogging and shade tolerance. The most important differences in stem volume can induce changes of 3–4% in the biomass of a single tree. Not taking into account shifts in stem form could have implications in forest biomass estimations.

Five non-segmented taper functions were modeled for Tectona grandis, which has increased significantly their planted area in Coastal Ecuador were formulations of this type are unknown. A process of nonlinear regression (maximum likelihood) was performed to a sample of 125 trees with fit evaluation. Subsequently, an independent validation process were performed, non parametric tests and a relative height analysis in order to identify strengths and weaknesses in each part of the shank was also applied. The fifth grade polynomial function showed the best fit (Absolute Bias = 1.009, Fit Index = 0.962), for that reason, the integrated form of this equation was calculated. It is expected that these developed models and their application benefits could be useful for the forestry comunity in Ecuador. Se modelaron cinco funciones no segmentadas de conicidad para Tectona grandis, especie forestal que ha incrementado notoriamente su área plantada en la zona costera ecuatoriana y donde se desconocen formulaciones de este tipo. Se realizó un proceso de regresión no lineal por el método de máxima verosimilitud a una muestra de 125 árboles y se evaluó su ajuste. Posteriormente, se hizo un proceso de validación independiente, se aplicaron pruebas no paramétricas y un análisis por altura relativa, para identificar fortalezas y debilidades en cada parte del fuste. La función polinomial de quinto grado presentó el mejor ajuste (Sesgo Absoluto = 1.009, Índice de Ajuste = 0.962), por ello se calculó la forma integrada de esta ecuación. Se espera que estos modelos desarrollados y sus bondades de aplicación puedan ser de utilidad para la comunidad forestal ecuatoriana.

International audience; Studies on stem profile of teak (Tectona grandis) hardly exist. This can be possibly attributed to the occurrence of forks that is prevalent on teak trees. Stem profile model was therefore developed for teak in West Africa, which took into account the occurrence of forks. Trees were destructively sampled from Moist Evergreen Forest (MEF), Moist Semi-deciduous Forest (MSDF), Dry Semi-deciduous Forest (DSDF) and Savannah ecological zones in both Ghana and Côte d’Ivoire for the study. A single set of parameters could be used explicitly to predict stem profileof any teak tree, irrespective of country, eco-climatic zone, edaphic variables, site index, tree age, stand density and tree competition. The model efficiency and root mean square error (in relative diameter) were calculated to be 0.97 and 0.053, respectively. The relative position of the forks along the stem bole, with respect to total tree height, was highly variable and did not follow any particular trend, except higher value for the first fork in the Moist Evergreen Forest zone. However, average tree height to the first fork decreased along the ecological gradient from MEF, MSDF and DSDF to Savannah. The extent of diameter reduction due to the forks could be predicted. Relative tree form for zero-forked, one-forked and two-forked trees was calculated to be 0.39, 0.36 and 0.33, respectively. Relative loss of stem volume due to one fork and two forks was estimated to be 6.5 and 13.9%, respectively. The measured stem volume when related to the corresponding predicted value yielded coefficient and intercept not significantly different from unity and zero, respectively, with an r2 value of 0.97.

Compatible systems of merchantable total tree cubic volume and stem taper equations are derived by integrating an existing volume equation. The systems are developed to yield volume at any merchantable length, total volume and for any merchantable top diameter. It is also demonstrated that the most common types of volume equation can be converted to compatible taper equation. Key words/phrases: Merchantable volume, compatible volume, taper equations SINET: Ethiopian Journal of Science Vol. 28 (1) 2005: 15–22

Different taper equations for Pseudotsuga menziesii (Mirb.) Franco plantations were evaluated in the Argentina Patagonian Andes. Functions fitted by Bruce et al. (1968), Real and Moore (1986), Kozak (1988) and Pérez et al. (1990) were tested. Data were collected from 268 trees scattered throughout 68 stands. The models were compared based on their bias and error when predicting volume, diameter and height. The validation was performed on a separate set of data. The best models were those developed by Kozak (1988) and Bruce et al. (1968)., Se evalúan distintos modelos fustales para ser utilizados en Pseudotsuga menziesii (Mirb.) Franco en la Patagonia Andina Argentina. Los modelos evaluados corresponden a los propuestos por Bruce et al. (1968), Real y Moore (1986), Kozak (1988) y Pérez et al. (1990), utilizando para el ajuste información de 268 árboles provenientes de 68 rodales distribuidos en el área geográfica donde se foresta con esta especie en el país. La validación de la estimación de volúmenes, diámetros y alturas, se realizó utilizando medidas de error y sesgo, empleando una base de datos independiente a la utilizada en el ajuste de cada uno de los modelos. Se analizó el comportamiento de cada uno de ellos para el total del fuste y para diferentes porciones del mismo. Finalmente, la evaluación realizada indica que los mejores modelos correspondieron a los de Kozak (1988) y Bruce et al. (1968).

Different taper equations for Pseudotsuga menziesii (Mirb.) Franco plantations were evaluated in the Argentina Patagonian Andes. Functions fitted by Bruce et al. (1968), Real and Moore (1986), Kozak (1988) and Pérez et al. (1990) were tested. Data were collected from 268 trees scattered throughout 68 stands. The models were compared based on their bias and error when predicting volume, diameter and height. The validation was performed on a separate set of data. The best models were those developed by Kozak (1988) and Bruce et al. (1968). Se evalúan distintos modelos fustales para ser utilizados en Pseudotsuga menziesii (Mirb.) Franco en la Patagonia Andina Argentina. Los modelos evaluados corresponden a los propuestos por Bruce et al. (1968), Real y Moore (1986), Kozak (1988) y Pérez et al. (1990), utilizando para el ajuste información de 268 árboles provenientes de 68 rodales distribuidos en el área geográfica donde se foresta con esta especie en el país. La validación de la estimación de volúmenes, diámetros y alturas, se realizó utilizando medidas de error y sesgo, empleando una base de datos independiente a la utilizada en el ajuste de cada uno de los modelos. Se analizó el comportamiento de cada uno de ellos para el total del fuste y para diferentes porciones del mismo. Finalmente, la evaluación realizada indica que los mejores modelos correspondieron a los de Kozak (1988) y Bruce et al. (1968).