Maintaining plant species composition and diversity of understory vegetation under strip-clearcutting forestry in conifer plantations in Kyushu, southern Japan

Abstract

We investigated the understory vegetation in sugi ( Cryptomeria japonica) and hinoki ( Chamaecyparis obtusa) plantations, including a mature hinoki plantation in which strip-clearcutting had been carried out 30 years previously. Plant species composition and diversity in uncut strips (US), cut strips (CS), and strip edges (SE) were compared with a 20-year-old even-aged sugi plantation (CC) and nearby young sugi plantations (YN) which had undergone large-scale, conventional clearcutting. Vegetation cover was highest in YN (100.0%), dominated by Miscanthus sinensis, followed by US (85.3%) and SE (55.2%), while CS and CC had much lower cover (30.1% and 25.2%, respectively). Vegetation height in CC treatments (0.58 m) was significantly lower than in the other stand types. Species richness and diversity indices ( H′) in the cut strips (CS) were the lowest but were similar to the clear-cut plantation of similar age (CC). However, cluster analysis and DCA ordination indicated important differences in species composition, with CS vegetation being characterized by species more typical of semi-natural forest, while that of CC vegetation had more disturbance-related species able to colonize open sites. These results suggest that strip-clearcutting may be more effective in conserving plant species of natural forests compared with standard clearcutting practice. The lack of significant difference between the light environments of SE, CS and CC treatments suggests that the promotion of trees and shrubs associated with semi-natural forest conditions in the cut strips is probably dependent on seed dispersal and competition with forbs during the establishment stage of stand regeneration.