Leaf survival of woody plants in deciduous broad-leaved forests. 2. Small trees and shrubs

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Abstract
Leaf survival of 29 species of small trees and shrubs was described in and around deciduous broad-leaved forests in Hokkaido, northern Japan. Twenty-four species had green leaves in the summer (summer green) and the other five species had green leaves in winter. Among the latter, three species were evergreen, one had green leaves in the winter and no leaves in the summer (winter green), and the other had two types of shoots: evergreen and summer green (heteroptosis). In summer-green species of the understory, both leaf emergence and leaf fall lasted only a short time. Duration of leaf emergence was long in open-site species and was intermediate in gap species. Leaf survival can be considered as part of the adaptive strategy of each species. The leaves of understory species emerged in a flush; that pattern could be adaptive to the strongly seasonal illumination of the forest floor. Evergreen and winter-green habits, as well as heteroptosis, were also assumed to be adaptive to life in the understory of deciduous broad-leaved forests, since full sunlight in early spring can be utilized by their overwintering leaves. Leaf survival of gap species was presumed to be more flexible than that of forest understory species. Leaf survival of open-site species was considered to be a strategy to occupy the available open spaces as widely as possible.