Effects of planted tree species on biodiversity of conifer plantations in Japan: a systematic review and meta-analysis

Natural forests were increasingly replaced by plantations globally. While plantations support less biodiversity compared to natural forests, they can serve as an important habitat for forest-dependent species. Understanding the key drivers of the habitat function of plantations is necessary to reconcile both forestry and biodiversity. Planted tree species is one of the important factors determining biodiversity of plantations. Here, we systematically collected studies comparing the biodiversity between conifer plantations and natural forests, and conducted meta-analyses to quantify the effects of planted tree family/species (cypress family: Japanese cedar Cryptomeria japonica, Hinoki cypress Chamaecyparis obtuse; pine family: Japanese larch Larix kaempferi, Japanese red pine Pinus densiflora, Todo fir Abies sachalinensis) on abundance and species richness of a wide range of taxa (all taxa, vertebrates, birds, invertebrates, terrestrial arthropods, plants, and understorey plants) in plantations in Japan. Abundance and species richness in plantations relative to natural forests differed among planted tree family/species. In plantations of pine family (mainly larch), abundance or richness did not significantly differ from those in natural forests for many taxa, suggesting the important role as habitats. By contrast, in cypress family (mainly cedar), abundance or richness was significantly lower than in natural forests for all analysis groups except understorey abundance. These results indicate that the habitat function of plantations and its management should be considered for each planted tree species, separately. Nevertheless, since our literature review identifies some research gaps, e.g. studies on vertebrates in western Japan were scarce, more comprehensive research efforts should be made in the future