Variation in Photosynthetic Photon Flux Density on a Larch Forest Floor

抄録

　The field experiment was conducted in a larch forest to investigate temporal and spatial variations in photosynthetic photon flux density (PPFD) on the forest floor (PPFD_f) and the phenological pattern of PPFD_f. PPFD was measured at seven points on the forest floor at height of 1 m and at one point above the canopy (PPFD_c) at 10 Hz from 18 April to 30 September in 2002. PPFD_f was expressed as %PPFD, which is the percentage of PPFD_c. %PPFD decreased as PPFD_c increased and became almost constant over PPFD_c of 500 µmol　m^-2 s^-1 throughout the measurement period. The relationship was well fitted by a rectangular hyperbola. Temporal and spatial variations in %PPFD increased exponentially with PPFD_c and increased with LAI.