Strategy for the reallocation of plantations to semi-natural forest for the conservation of endangered riparian tree species

Abstract

Riparian forests provide habitat for rare or infrequent plant species (Sakio 1997; Suzuki et al. 2002; Sakio & Yamamoto 2002) including several endangered trees (Ito et al. 2003, Ito et al. 2004; Ito & Nogami 2005), and therefore have high conservation value. However, mountainous riparian forests in Japan, particularly in the warmtemperate region, have been heavily exploited or converted to plantations of evergreen conifers such as sugi (Cryptomeria japonica D. Don) or hinoki (Chamaecyparis obtusa Sieb. et Zucc.) because of their high site productivity (Ito et al. 2003). This has resulted in a severe decline in habitat for rare riparian trees (Ito et al. 2004; Ito & Nogami 2005). Most of the rare tree species dependent on riparian habitat cannot complete their life history beneath the dense canopy of planted conifers because their reproduction (flowering and fruiting) usually requires bright crown conditions. Thus, in addition to maintaining remnant populations in natural forest patches, an important strategy for conserving these rare riparian trees is to restore habitat by re-converting suitable portions of the conifer plantations to semi-natural forest (Ito et al. 2004).