Species diversity of woody recruits within Japanese cedar (Cryptomeria japonica) plantations established on grasslands: the effects of site conditions and landscape

Abstract

ABSTRACTPlantations established on grasslands have low recruitment of broadleaved trees and therefore may require particular attention when developing biodiversity-oriented management practices. In this study, we tested four hypotheses concerning woody recruits in Japanese cedar (Cryptomeria japonica) plantations established on grasslands with respect to their distance from the nearest Konara oak (Quercus serrata) forest. Our four hypotheses were as follows: (1) both species richness and occurrence frequency (the number of subplots in which recruits were present) decline with increasing distance; (2) the strength of the effect of distance differs depending on the growth form, seed dispersal type, or life history trait; (3) the species richness of recruits does not increase in response to a disturbance or other site conditions; (4) and species composition of recruits also changes with distance. Our results showed that species richness and occurrence frequency generally declined with increasing distance. This result supports the first hypothesis. The effect of distance was stronger in wind-dispersed species than in bird-dispersed species, as predicted by the second hypothesis. Disturbances such as thinning or wind throw did not increase but rather did decrease species richness, as predicted by the third hypothesis. Furthermore, distance had the strongest impact on species composition, as predicted by the fourth hypothesis. These findings show that, in biodiversity-oriented management, it may be more challenging to increase biodiversity using stand-level management in plantations established on grasslands than in plantations established after clear-cutting of broadleaved forests. Thus, landscape-level management may be required for these cases.