Characterization of light climate under canopies of intensively-cultured hybrid poplar plantations

Abstract

Photosynthetically active radiation (PAR) was measured by quantum sensors in the open and in young hybrid poplar plantations. On clear summer days the incoming PAR approached 2000 μEm −2 s −1. From May to October, daily PAR in the open averaged 30–33 E m −2. Fully-foliated canopies transmitted only a fraction of 1% of the incoming PAR and leafless canopies transmitted less than 50%. Foliated canopies depleted the blue and red portions of the spectrum and allowed more green and near-infrared light to reach the forest floor. Sunflecks provided 66–89% of the total PAR under foliated canopies and may be important for the survival and longevity of the shaded leaves. During the growing season (May–September), hybrid poplar plantations may convert up to 8.5% of the incident PAR into dry matter.