APPLICABILITY OF THE RADIATION-USE EFFICIENCY CONCEPT FOR SIMULATING GROWTH OF FOREST STANDS

The aim of the study was to estimate the radiation-use efficiency (RUE ) and investigate its suitability as a tool to simulate growth of mixe d forest stands. We applied a mechanistic forest growth model (FORGRO) , (1) to investigate differences between RUE of deciduous broadleaved trees (beech) and evergreen conifers (Douglas-fir), and (2) to analyze the effects of stand structure and stand composition on RUE in mixed species forests. With FORGRO, RUE under optimum growing conditions was calculated. Based on comparison of net primary production (NPP) rates estimated by FORGRO with data from the literature, we concluded that using FORGRO to estimate RUE was legitimate. Sensitivity analysis show ed that RUE is relatively insensitive to changes in values of photosyn thetic parameters. Temperature had some effect, depending on the speci es. Hence, species-specific responses to temperature can be expected t o affect competitive interrelationships in case of climate change. Tho ugh RUE showed large daily variability, RUE derived from cumulative ab sorbed photosynthetically active radiation (APAR) and NPP was virtuall y constant throughout the year and over a 10-yr period, in both monosp ecies and mixed-species stands. It was concluded that the RUE-concept is a useful tool in simulating forest growth. (C) 1997 Elsevier Scienc e B.V.