Simulation of forest carbon dynamics based on a dry-matter production model

Effects of dry season upon a tropical rainforest ecosystem are analysed by employing the microcomputer model developed in a previous paper (Oikawa, 1985). Surplus production (P _s) illustrated in a three-dimensional figure linearly decreases with the length of dry season (λ). Simulation experiments demonstrate that all the three strata constituting the tropical rainforest ecosystem model are able to exist stably and perpetually unless λ exceeds four months. However, it is suggested that the dry season lasting five months brings about a transition from a tropical rainforest to a subtropical deciduous forest, because the upper story fails in a stable and perpetual occurrence at λ =5 months. Though the total living phytomass gradually decreases with prolonged dry season within four months, supplementary increase of living phytomass is observed in the middle story. A considerable amount of soil organic dead accumulated is also observed with increasing dry season, so that fairly constant ecosystem biomass including soil organic dead is predicted independent of the length of dry season so long as it is less than five months.