A SIMPLE PROCESS-BASED XYLEM GROWTH-MODEL FOR DESCRIBING WOOD MICRODENSITOMETRIC PROFILES

A mechanistic model of xylem production based on physiological and ana tomical assumptions is proposed. It focuses on tracheids and on the ma in phases of cell development: cell division, enlargement and wall thi ckening. For each phase, the most limiting environmental factors are a ssessed and their effect is modeled with a weekly time step. Combined with simple process-based stand growth and yield models, which take th e mean monthly climatic data into account, the xylem production model provides simulations of infra-annual density profiles along stem radiu s. Simulations are performed for two sites in northeastern France, usi ng past climatic data. The outputs are qualitatively discussed and vis ually compared with the observed microdensitometric profiles of Pinus sylvestris and Picea abies in these two sites. These models provide a basis for integrating timber quality features into process-based model s. They also point to new sources of data that could be used to valida te process-based models, and suggest some biological assumptions to un derstand the infra-annual variability of wood basic density. (C) 1998 Academic Press.