Key-factors and key-stages that determine the leaf longevity of an evergreen broad-leaved tree, Neolitsea sericea (Lauraceae) at different growing sites in southern Japan

Chronological distribution pattern of leaves is an important factor to determine plant productivity in relation to photosynthesis. Therefore, intensive studies of leaf longevity are essential in plant ecology. Leaf longevity of Neolitsea sericea (Lauraceae) was surveyed from 1972 to 1995. Mean leaf longevity varied from 5.6 to 53.8 months among different year classes of leaf emergence. To detect factors and stages determining the leaf longevity, we adopted the method of key-factor/key-stage analysis. We categorized N. sericea trees into four groups; short and tall trees in an evergreen broad-leaved forest, short trees along the forest edge, and short trees in a Moso bamboo forest, where N. sericea grows as an understory plant. This categorization enabled us to realize how the factors and stages differently influenced leaf longevity at different sites. Four groups of factors (growing site, cecidomyiid gall induction, stem boring by a cerambycid, typhoon) and eight stages (every 6 month after leaf emergence until a leaf age of 48 months) were distinguished in the analysis. Effects of annual precipitation and annual mean temperature were evaluated separately. In a bamboo forest, cerambycid negatively affected leaf survival in the first year. In an evergreen broad-leaved forest, cerambycid and typhoon affected leaf survival of short and tall trees but cerambycid damage was compensated in later stages. Short trees along the forest edge suffered severe leaf fall from typhoon but were positively affected by annual precipitation. This study gives suggestions for better understanding of chronological distribution patterns of leaves.