林床

The purpose of this paper is to elucidate the light environments of forest floor, and to provide fundamental data on their natural regeneration. This investigation was carried out in natural forests of Momi (Abies firma) and Tsuga (Tsuga sieboldii) in a 44-year-old Sugi (Cryptomeria japonica) stand distributed in the Kyushu University Forest of MIYAZAKI. Light environments of the forest floor are characterized by sun flecks. We studied the relationship between intensity and distribution of sun flecks, solar radiation, and distribution of Suzutake (Pseudosasa ρurpurascens). The results obtained are summarized as follows: Sun flecks varied in light intensity. Sometimes, the light intensity of sun flecks was only about 70% of that of the open. And the duration of sun flecks of a fixed point was short. Judging from the relationship between the duration of sun flecks and integrated solar radiation, 62000 Lux solar radiation for 10 minutes was equivalent to that of as un fleck for aw hole day at any given point. Accordingly, even if ephemeral, the sun flecks seem to have an important role in contributing to the total amount of solar radiation on the forest floor. Minimum relative light intensity in the stand was constant and not influenced by weather conditions. Judging from the result of the distribution analysis by the 1δ index, sun flecks were contagious distribution. Moreover, Suzutake distributed in the stand decreased with increasing canopy closure, and it survived in small groups in good light conditions. When relative solar radiation fell below 3%, Suzutake disappeared from the stand. From the above results, it is considered that frequency of Suzutake is an index of the light environment of the forest floor in the stand.