Energy exchange within individual layers of a meadow

Abstract

Measurements of the radiation extinction in a meadow at Baumkirchen (Tyrol) show that the decrease in the photosynthetically active radiation (PhAR: 400–700 nm) is different to that of the total net-radiation in a characteristic way. The photosynthetically active radiation is distributed evenly to all vegetation layers, the “active surface” comprises practically the entire 90 cm high canopy. The total radiation energy (net-radiation) is absorbed and 45% is converted into sensible and latent heat only in a 25 cm wide layer, i.e., between 30 and 55 cm within the canopy. A second “active surface” lies in the lowermost 10 cm of the meadow and at the soil surface where additional 28% of the radiation energy is transformed into heat.