Evaluation of the light interception by non-photosynthetic organs in aLarix leptolepis plantation

Abstract

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 ofI′(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 intensityI′(z)/I _o at a depthz from the canopy surface is affected by both the cumulative densities of leaf areaF(z) and the longitudinal section area of non-photosynthetic organsC(z) existing above that depth. The value of the extinction coefficient for the leavesK _F was computed to be 0.31–0.36 ha/ha, while that for the non-photosynthetic organsK _c was computed to be 1.4–1.7 ha/ha. The functionC(z) was proportional toF(z), orC(z)=aF(z) where the constanta was 0.11–0.13. The proposed equation led to the formula,I′(z)/I ₀=exp[-KF(z)]. The apparent extinction coefficientK was partitioned into two terms as follows,K=K _F +aK _c . The value ofK was estimated to be 0.46–0.59 ha/ha, and was about 1.5 times larger than ofK _F .