Allometric models defining the relationship between stem diameter and total tree height in the Amazon basin are important because they refine the estimates of tree carbon stocks and flow in the region. This study tests different allometric models to estimate the total tree height from the stem diameter in an ecotone zone between ombrophilous and seasonal forests in the Brazilian state of Roraima, in northern Amazonia. Stem diameter and total height were measured directly in 65 recently fallen trees (live or dead).Linear and nonlinear regressions were tested to represent the D:H relation in this specific ecotone zone. Criteria for model selection were the standard error of the estimate (S yx ) and the adjusted coefficient of determination (R² adj ), complemented by the Akaike Information Criterion (AIC). Analysis of residuals of the most parsimonious nonlinear models showed a tendency to overestimate the total tree height for trees in the 20-40 cm diameter range. Application of our best fitted model (Michaelis-Menten) indicated that previously published general equations for the tropics that use diameter as the independent variable can either overestimate tree height in the study area by 10-29% (Weibull models) or underestimate it by 8% (climate-based models). We concluded that our site-specific model can be used in the ecotone forests studied in Roraima because it realistically reflects the local biometric relationships between stem diameter and total tree height. Studies need to be expanded in peripheral areas of northern Amazonia in order to reduce uncertainties in biomass and carbon estimates that use the tree height as a variable in general models. Modelos alométricos para estimar altura de árvores em florestas ecotonais do norte da Amazônia RESUMOModelos alométricos que definem o relacionamento entre diâmetro do tronco e a altura total da árvore na bacia amazônica são importantes porque refinam as estimativas de fluxo e estoques de carbono arbóreo na região. Este estudo testou diferentes modelos alométricos para estimar a altura total de árvores a partir do diâmetro do tronco em uma zona de ecótono entre florestas ombrófilas e sazonais no estado de Roraima, norte da Amazônia. Diâmetro do tronco e altura total foram medidos de forma direta em 65 árvores tombadas recentemente (vivas e mortas). Regressões linear e não-linear foram testadas para representar a relação D:H nesta zona específica de ecótono. Os critérios de seleção dos modelos foram o erro padrão da estimativa (S yx ), o coeficiente de determinação ajustado (R² adj ) e o Critério de Informação de Akaike (AIC). A análise dos resíduos dos modelos não-lineares mais parcimoniosos mostrou uma tendência de superestimar a altura total para árvores entre 20-40 cm de diâmetro do tronco. A aplicação do modelo melhor ajustado (Michaelis-Menten) indicou que equações gerais publicadas previamente para os trópicos que usam diâmetro como variável independente podem superestimar em 10-29% (modelos Weibull) ou subestimar em 8% (modelos baseados no clima) a altura da...

RESUMENLa floración de los bambúes es poco frecuente, tiende a ser esporádica cuando algunos culmos de la población florecen o gregaria, donde todos los individuos florecen al mismo tiempo y en diferentes zonas. Algunas especies de bambúes leñosos mueren después de florecer y otras no. Chusquea scandens Kunth es un bambú leñoso muy abundante en zonas de alta montaña cercanas a Bogotá. En cada población se evaluaron las etapas fenológicas y la tasa de crecimiento de diez culmos en estado vegetativo y diez en inicio de la floración. En la población que presentó un área extensa de flores, se indagó qué le sucedió a C. scandens después de la floración. La asociación de C. scandens con otras especies tanto de bosque nativo como exóticas, pudo ser uno de los factores que indujo su floración. El parche florecido presentó secamiento y posterior colonización por especies pioneras. Durante el tiempo de estudio C. scandens, presentó evidencias de ser una especie monocárpica. La estrategia de floración de C. scandens fue diferente a otras especies del género Chusquea, respecto al menor tiempo que duró un culmo en pasar de botones a frutos con semillas y en que presentó características de floración esporádica.Palabras clave. Fenología, bambú, sucesión, monocarpía. ABSTRACTFlowering of bamboos is rare, it tends to be sporadic when some culms flower or gregarious, when all the individuals in the population flower at the same time and in different areas. Some species of woody bamboos die after flowering while others do not. Chusquea scandens Kunth is a woody bamboo very abundant in high mountain ecosystems and populations in the study area were flowering. To determine the characteristics of the flowering of C. scandens, we selected two populations located in a rural area of Bogotá. On each population we evaluated the phenological stages and growth rate often vegetative culms and ten in the beginning of flowering. In the population that presented a wide area of flowers, it was investigated what happened to C. scandens after flowering. The association of C. scandens with other species of both native and exotic forests, could be one of the factors influencing its flowering. The flowered patch showed drying and subsequent colonization by pioneer species. During the study period C. scandens showed evidence of being a monocarpic species. The strategy of flowering C. scandens, was different from other species of Chusquea,