1999 Volume 49 Issue 1 Pages 1-10
We studied the relationship between the light environment and distribution patterns of understory woody species in a natural beech forest in Japan. Stem locations and diameter at breast height (dbh) of 2,039 understory trees comprising of 30 species (1 cm≦dbh<cm) were investigated in a 0.4-ha plot. Relative photosynthetic photon flux density (rPPFD) at 0,2 and 4 m above ground was measured at 189 points in the plot in September and November. The understory vegetation was covered with heavy snow until early June, when the overstory trees had already leafed out. Using the rPPFD data at 4m height in September, the light condition above each stem was evaluated for the understory trees. The rPPFD value varied within a wide range, 5.4〜65.7%. Higher rPPFD values were related to the presence of canopy gaps of ≧100 m2. Two types of understory species were recognized from their distribution patterns, according to the relationship between stem locations and rPPFD distribution. The Prunus grayana type was distributed widely throughout the plot without any change in its local density, irrespective of the rPPFD level. The Corylus sieboldia type showed an aggregated distribution at sites with a high rPPFD value, although it also appeared throughout the plot. These results suggest that the varied light environment resulting from a heterogeneous canopy structure is an important factor affecting local density for some components of the understory community.