Diverse Patterns of Vegetation Change after Upland Field Abandonment in Japan

Abstract

Vegetation changes in abandoned farmland that deviates from locally targeted states pose conservation and restoration problems in various parts of the world. Here, we review the patterns of vegetation change after upland field abandonment in Japan. Inconsistent invasiveness and weediness of exotic species such as Phyllostachys edulis and Leucaena leucocephala in rural habitats indicated that even if an exotic species is present in a focal area, its impacts on revegetation pathways vary depending on the local species pool, species recruitment order, and interspecific competition. Improved soil nutrients for crop production before abandonment decreased the presence of native grasses and forbs during early successional stages. Buried seeds and resprouting plants maintained under slash-and-burn cultivation led to the dominance of native tree species. After the recent abandonment of conventional farming in warm-temperate regions of Japan, competitive clonal native species such as a dwarf bamboo (Pleioblastus chino) and kudzu ( Pueraria lobata) became dominant and limited the seedling establishment of various native tree species. The drastic decrease of grassland areas in the past century suggests that many fewer seeds of Miscanthus sinensis , which serves as a facilitator of various plants in grassland systems, are dispersing into abandoned fields than in the past. Studies of wildlife in abandoned farmland in Japan indicated that herbivore damage by rodents, Japanese hare, and sika deer are potent factors affecting forest recovery. These results suggest that vegetation change after upland field abandonment occurs in diverse ways, reflecting historical differences in environmental factors such as local flora and fauna, agricultural technologies and practices, and landscape mosaics. This implies that revegetation pathways after upland field abandonment tend toward novel states and that deterministic predictions of upland field succession will be easily violated in many cases.