Examining the possibility of introducing broadleaved tree species in warm-temperate old coniferous planted forests in sika deer habitat based on a four-year change in understory vegetation

We observed the change in understory vegetation over a period of four years after thinning within an old coniferous planted forest in the southern Boso peninsula where sika deer inhabit. Based on our observations, we examined the possibility of introducing broadleaved tree species through thinning. Number of tree species, tree cover rate, species richness and number of individuals with ≥ 1.3 m height tended to be higher in fenced plots than in non-fenced plots. In plots with severe disturbance during logging, numbers of tree species in the first and second year were larger, however, the increase of tree cover rate was slow, causing smaller tree cover rate in the fourth year than in less-disturbed plots. In terms of abundance, only Maesa japonica, a low tree species, and a few other species were dominant. Pionees species Idesia polycarpa and Broussonetia monoica grew well in fenced plots, which may tentatively achieve introduction of broadleaved tree species. Among high tree species, Neolitsea sericea, not a canopy tree species of climax forest, was abundant and grew well in both fenced and non-fenced plots, which may achieve multistory forest without fences. However, it was suggested to have large difficulties to prompt introduction of evergreen top-layer tree species, including frugivore seed dispersal species whose seeds may reach relatively easily, into old coniferous planted forest in warm-temperate zone through thinning.