Evaluation of the light interception by non‐photosynthetic organs in a Larix leptolepis plantation

Vertical changes in relative light intensity within the canopy of a 19‐year‐old (as of 1982) plantation of Japanese larch were investigated before and after defoliation. The relative light intensity at 1.3m above the ground was 6% before defoliation, while it was about 20% after defoliation. The leaf area index and the total longitudinal section area of such non‐photosynthetic organs as stems and branches were in the range 4.84 to 5.61 ha/ha and 0.788 to 0.798 ha/ha, respectively. An equation of I′(z)/I 0 =exp[‐( K F F(z) + K c C(z) ], which gives a description of light attenuation within a canopy, was proposed on the assumption that the relative light intensity I′(z)/I o at a depth z from the canopy surface is affected by both the cumulative densities of leaf area F(z) and the longitudinal section area of non‐photosynthetic organs C(z) existing above that depth. The value of the extinction coefficient for the leaves K F was computed to be 0.31–0.36 ha/ha, while that for the non‐photosynthetic organs K c was computed to be 1.4–1.7 ha/ha. The function C(z) was proportional to F(z) , or C(z)=aF(z) where the constant a was 0.11–0.13. The proposed equation led to the formula, I′(z)/I 0 =exp[‐ KF(z) ]. The apparent extinction coefficient K was partitioned into two terms as follows, K=K F + aK c . The value of K was estimated to be 0.46–0.59 ha/ha, and was about 1.5 times larger than of K F .