Removal of competitive native species combined with tree planting can accelerate the initial afforestation process: an experiment in an old field in Japan invaded by dwarf bamboo and kudzu

Restoring natural forests after field abandonment is a land management objective that fosters the recovery of forest biodiversity. We performed seeding and transplanting of native tree species 40 years after the abandonment of an arable field that became dominated by a dwarf bamboo (Pleioblastus chino (Franch. et Sav.) Makino) and by kudzu (Pueraria lobata (Willd.) Ohwi). By permutation tests, the removal of competing vegetation (gap creation) significantly increased the survival of three seeded species of Fagaceae and of eight transplanted species. In contrast, intact vegetation prevented most individuals of all species from surviving for 1 year after planting. The lack of natural recruitment of Fagaceae in the nonseeded subplots indicated that seed limitation was a cause of the slow afforestation. Although litter accumulation in gaps at the time of seeding slightly increased survival for late-germinating Quercus myrsinifolia Blume and Castanopsis sieboldii (Makino) Hatus. ex T. Yamaz. et Mashiba, the effect was not consistent among plots and was not statistically significant. Our results suggest that for successful afforestation using native trees in abandoned fields, it will be necessary to remove competitive native species to avoid severe limitations on microsite availability and that simultaneous tree establishment by seeding or transplanting should be implemented to accelerate the establishment of native tree species.