Meta-analysis of the effects of rice-field abandonment on biodiversity in Japan.

Farmland abandonment is increasing worldwide. Concurrently, some conservationists view this as an opportunity for biodiversity restoration (i.e., rewilding). Due to a lack of data, however, it remains unclear whether farmland abandonment increases biodiversity in different farmland types and surrounding environments. Information is particularly scarce for Asia, home to one-third of identified biodiversity hotspots and where dominant farmlands (i.e., rice fields) are often viewed as substitutes for natural wetlands. We conducted the first meta-analysis of the impacts of rice-field abandonment on biodiversity, in which we considered multiscale factors, such as taxon surveyed, landscape context, and climate. Species richness and abundance after abandonment decreased to 56-72%. This reduced biodiversity was unlikely to recover, at least for plant species richness, even after 10-15 years. These results suggest rewilding will not necessarily be achieved by rice-field abandonment. Moreover, there was a pronounced biodiversity decline under dry conditions (e.g., low precipitation), especially for organisms closely associated with aquatic environment, such as amphibians and fish. Biodiversity reduction was least pronounced for birds and mammals. Such context dependency may suggest that impacts of farmland abandonment can be predicted by considering biological features of organisms and their associations with human-modified environments.