Abstract
To determine the invasion and growth processes of natural broadleaved trees in a conifer plantation, and to examine the influence of forest operations on these processes, we investigated the species composition, the number of annual rings at 0.3 m from the ground and annual diameter increments of natural broadleaved trees in an 80-year-old Abies sachalinensis plantation in Hokkaido, northern Japan. Species number and the density of broadleaved trees increased after thinning. The frequency of the number of annual rings at 0.3 m from the ground was apparently high in years following thinnings, except for the first thinning. Therefore, plantation thinning induced natural invasion of broadleaved trees. Furthermore, the diameter increments of many broadleaved trees apparently increased after thinning. Thinning positively influenced the growth of broadleaved trees in the plantation. Mean annual diameter increments differed between late-successional and gap-phase species. The mean diameter increment and increases in the increment after a thinning were larger in gap-phase species than in late-successional species. Additionally, the individual ratio and frequency of apparent increases in diameter increments after thinning were larger in older broadleaved trees. Consequently, we conclude that age and ecological characteristics of broadleaved trees in an Abies sachalinensis plantation influence their growth and the influence of thinning on growth.
