Spectral Quality and Absorption of Solar Radiation in a Mountain Birch Forest, Abisko, Sweden

Abstract

Field measurements of the spectral (300–1100 nm) distribution of the incoming and reflected solar radiant energy above and below the canopy of mountain birch (Betula pubescens ssp. tortuosa) carried out at Abisko, during 1989 and 1990, in the subalpine/subarctic region above the Arctic Circle in northern Scandinavia are used to analyze the solar radiation balance of the birch canopy and the undergrowth, respectively. Complementary laboratory measurements of the optical properties of mountain birch leaves and the woody biomass make it possible to estimate the radiant energy absorbed separately by the leaves and the woody biomass. Depending on forest density, the leaves absorb about 52 to 65% of the incoming photosynthetically active radiation (PAR) above the birch canopy, whereas the woody biomass absorbs 9 to 18%. For the near infrared radiation (NIR, 700–1100 nm) case, the leaves absorb 14% and the woody biomass 19–34%