A simple tropical ecosystem model of carbon, water and energy fluxes

A simple tropical ecosystem model (SITE) was developed to study the response of tropical ecosystems to environmental conditions. SITE fills the niche of an ecosystem model of intermediate complexity, sophisticated enough to be used to study the fast dynamics of tropical ecosystems, while simple enough to be used to introduce the ecosystem modelling concepts to students and inexperienced modellers. SITE is a dynamic model that incorporates several processes: canopy infrared radiation balance, solar radiation balance, aerodynamic processes, canopy physiology and transpiration, balance of water intercepted by the canopy, transport of mass and energy in the atmosphere, soil heat flux, soil water flux and carbon balance. It is structured with one canopy layer and two soil layers, and is forced by hourly data of temperature, radiation balance, precipitation, humidity and wind, and simulates the fluxes of CO2, water and energy, as well as the dynamics of carbon in the ecosystem. For calibration and validation, we used fluxes of CO2, water vapour and sensible heat, measured at a primary evergreen forest site in Eastern Amazonia, Brazil. Even though SITE is considerably less complex than other models of similar goals, it reproduces well the hourly variability of the fluxes of CO2 and water vapour, and simulates the seasonal scale balance of those elements properly. SITE is available as a 1200-line FORTRAN code, and as a computer spreadsheet. We believe the model will be useful to help train the next generation of tropical ecologists in the use of ecosystem models.