The density of juveniles of broad-leaved woody species in young Cryptomeria japonica plantations bordering natural laurel forests on Yakushima Island.

Abstract

Inducing development of natural-forest-type stands or mixed forests of Cryptomeria japonica and evergreen broad-leaved trees may be an effective way of ecologically rehabilitating Cr. japonica plantations surrounding laurel forests. We compared the species composition and the population of seedling and sapling banks in young plantations to those in bordering laurel forests in Yakushima Island to judge the possibility of inducing the development of natural-forest-type stands and the necessity of artificial regeneration. The species composition of juveniles based on their presence in the plantations was similar, in many cases, to that in the bordering laurel forests, while community structure based on their stem density differed between the plantations and the laurel forests. Seedling density in the plantations was significantly lower than that in the laurel forests, especially in eight major component species of laurel forests, such as Distylium racemesum. Hence, artificial regeneration, such as planting and sowing for these species seems to be effective in inducing the development of mixed forests or laurel forests from young plantations. The juvenile density in the plantations did not depend on the distance from the adjacent laurel forest or the juvenile density in the laurel forests. The effectiveness of zoning of silvicultural treatment, such as planting, sowing, and gap creating, as a function of the distance from an adjacent laurel forest can not be corroborated with regard to the status of seedlings and sapling banks.