Simulations of Net CO2 Flux at Takayama (Central Japan) with BEPS Ecosystem Model

The ecosystem model BEPS (Boreal Ecosystem Productivity Simulator) is used to simulate net CO₂ flux observed from 1998 to 2002 at the Takayama site located in a temperate deciduous forest in central Japan. Given soil and biological properties at the site, BEPS is driven by meteorology (temperature, humidity, radiation and precipitation) and the leaf area index (LAI). The model is integrated with a time step of 1 hour, and calculates NPP and soil respiration to obtain the net CO₂ flux. In this way, processes governing the diurnal cycle of carbon emission and absorption can be identified at the site. Meteorological and LAI data to drive the model are obtained from measurements made on the flux tower at the site. BEPS has been used to estimate CO₂ flux at the BERMS site (a boreal forest ecosystem in northern Saskatchewan, Canada), as well as sites in Europe and China, with some success. It is found that the BEPS sensitivity to LAI results in its inability to properly simulate the early photosynthetic drawdown of CO₂ by the undergrowth (mainly Sasa bamboo grass) and the stoppage of photosynthesis by dead leaves in the fall that have not yet fallen from the trees. The model requires additional phenological parameters.