Predicting tree mortality from diameter growth: a comparison of maximum likelihood and Bayesian approaches

Abstract

Ecologists and foresters have long noted a link between tree growth rate and mortality, and recent work suggests that interspecific differences in low growth tolerance is a key force shaping forest structure. Little information is available, however, on the growth-mortality relationship for most species. We present three methods for estimating growth-mortality functions from readily obtainable field data. All use annual mortality rates and the recent growth rates of living and dead individuals. Annual mortality rates are estimated using both survival analysis and a Bayesian approach. Growth rates are obtained from increment cores. Growth-mortality functions are fitted using two parametric approaches and a nonparametric approach. The three methods are compared using bootstrapped confidence intervals and likelihood ratio tests. For two example species, Acer rubrum L. and Cornus florida L., growth-mortality functions indicate a substantial difference in the two species' abilities to withstand slow growth. Both survival analysis and Bayesian estimates of mortality rates lead to similar growth-mortality functions, with the Bayesian approach providing a means to overcome the absence of long-term census data. In fitting growth-mortality functions, the nonparametric approach reveals that inflexibility in parametric methods can lead to errors in estimating mortality risk at low growth. We thus suggest that nonparametric fits be used as a tool for assessing parametric models. Resume : Les ecologistes et les forestiers ont depuis longtemps note le lien entre le taux de croissance et la mortalite des arbres. En outre, des travaux recents suggerent que la structure de la foret serait determinee principalement par les differences interspecifiques dans la capacite de survie a une faible croissance. Cependant, il y a peu d'information sur la relation entre la croissance et la mortalite pour la plupart des essences. Nous presentons trois methodes pour estimer les fonctions de croissance et de mortalite a partir de donnees de terrain facilement disponibles. Toutes les methodes utilisent le taux annuel de mortalite et le taux de croissance recent des arbres vivants et morts. Le taux annuel de mortalite est estime a la fois par 1'analyse de survie et 1'approche bayesienne. Le taux de croissance est obtenu par les carottes de sondage. Les fonctions de croissance et de mortalite sont ajustees a 1'aide de deux methodes parametriques et d'une methode non parametrique. Les trois methodes sont comparees a 1'aide des intervalles de confiance amorce et des tests du rapport de vraisemblance. A litre d'exemple, les fonctions de croissance et de mortalite montrent une difference substantielle entre I'Acer rubrum L. et le Cornus florida L. dans leur capacite a survivre a une faible croissance. L'estimation du taux de mortalite par 1'analyse de survie ou 1'approche bayesienne conduit a des fonctions de croissance et de mortalite semblables. L'approche bayesienne permet cependant de pallier 1'absence de donnees d'inventaire a long terme. Pour 1'a...

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