Criterion for the Need to Weed on Sugi (Cryptomeria japonica) Plantations Varies according to Competing Vegetation Types

Abstract

We investigated the height and suppression status of planted trees in young sugi (Cryptomeria japonica) plantations that were weeded every year in Yame, Fukuoka, Japan, to develop a criterion to determine the need for weeding. Plantations with varying competing vegetation types were studied, and the height of competing vegetation that had recovered one year after weeding differed with variation in the dominate species. Miscanthus (Miscanthus sinensis) exhibited high recovery values, while the recovery heights of three major component species of the competing vegetation (M. sinensis, Rhus chinensis and Mallotus japonicus) were almost the same within each species irrespective of the number of times of weeding (i.e., years after planting). The planted sugi trees tended to be released from suppression according to their height. However, the degree of the release was different for the different vegetation types; generalized linear models demonstrated that sugi needed to be taller in the miscanthus-dominated type than other vegetation types to achieve the same degree of release from suppression. These results suggest that there is no depression of the recovery height for major weeds or trees caused by repeat weeding, and that the weeding criterion should vary with vegetation types, according to their respective post weeding recovery potential. With the assumption that weeding is needed when 90％ of planted sugi tree are taller than surrounding competing vegetation, the critical height of sugi trees is 2.2 m for the miscanthus-dominated type and 1.4 m for the other vegetation types.