Expansion and intensification of agriculture have led to an immense decrease in biodiversity. However, the area of abandoned farmland has been increasing globally in recent years and is expected to provide novel habitats for various organisms. Despite the promising potential for biodiversity conservation in agricultural landscapes, few studies have compared biodiversity among multiple land use types, including abandoned farmland. We examined the effects of major land use types (wetland, grassland, forest, farmland, abandoned farmland) and the surrounding landscape openness (proportion of wetland/grassland in the surrounding area) on the abundance and species richness of bird communities and four functional groups (wetland, grassland, farmland, and forest species) in the agricultural landscape of central Hokkaido in northern Japan. The abundance of wetland/grassland species in abandoned farmland tended to be intermediate between those of their original habitats (wetland and grassland) and other land uses (forest and farmland), and to be positively associated with the landscape openness. The abundance of forest species tended to be higher in forest areas than in areas with other land use types and was not associated with the landscape openness. The abundance and species richness of the bird community were predicted to be high in large abandoned farmland areas surrounded by open land. For wetland species, whereas total abundance was predicted to be primarily mediated by landscape openness, species richness was predicted to be primarily mediated by the farmland abandonment area. The abandoned farmland in our study area would not currently have a high conservation value for forest birds. However, the-3-/ 36 abandonment of farmland surrounded by open land would significantly improve the conservation of wetland/grassland birds in the agricultural landscape. Given the decline in the area of grassland, wetland, and low-intensity farmland, farmland abandonment provides an opportunity to conserve and restore the declining populations of wetland and grassland birds.

While wetlands have been converted into farmlands, large amounts of farmlands are now being abandoned, and this novel habitat is expected to be inhabited by species which depend on wetlands. Here we examined the effects of habitat and landscape variables on the densities of wetland bird species in abandoned farmlands. We surveyed birds in abandoned farmlands with varied patch area, habitat, and landscape variables in Kushiro district, eastern Hokkaido, northern Japan. We also surveyed birds in 15 ha of the remaining wetlands as a reference habitat. We used abundance-based hierarchical community model (HCM) to estimate patch-level estimates of abundance of each species based on sampling plots data that only partially covered the studied patches. We observed 14 wetland species and analyzed them with HCM. Abandoned farmland patch areas had significant positive effects on the densities of two species. Tree densities and shrub coverage exerted positive and negative effects on some species. Amounts of surrounding wetland/grassland had positive effects on many species. Ensemble of species-level models suggested that 24.7 ha and 10.6 ha of abandoned farmlands would be needed to harbor a comparable total abundance and species richness in 15-ha wetlands, respectively. These required amounts can be increased/decreased depending on the covariates. The use of HCM allows us to predict species-and community-level responses under varied conditions based on incomplete sampling data. A quantity of 1.6 times larger areas of abandoned farmlands may be required to restore wetland bird communities in eastern Hokkaido.

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Land cover change for agriculture is thought to be a major threat to global biodiversity. However, its ecological impact has rarely been quantified in the Northern Hemisphere, as broad-scale conversion to farmland mainly occurred until the 1400s–1700s in the region, limiting the availability of sufficient data. The Ishikari Lowland in Hokkaido, Japan, offers an excellent opportunity to address this issue, as hunter–gatherer lifestyles dominated this region until the mid-nineteenth century and land cover maps are available for the period of land cover changes (i.e. 1850–2016). Using these maps and a hierarchical community model of relationships between breeding bird abundance and land cover types, we estimated that broad-scale land cover change over a 166-year period was associated with more than 70% decline in both potential species richness and abundance of avian communities. We estimated that the abundance of wetland and forest species declined by greater than 88%, whereas that of bare-ground/farmland species increased by more than 50%. Our results suggest that broad-scale land cover change for agriculture has led to drastic reductions in wetland and forest species and promoted changes in community composition in large parts of the Northern Hemisphere. This study provides potential baseline information that could inform future conservation policies.

Abandoned farmland area has been expanding globally for decades. Studies showed that conservation value of abandoned farmland has differed among studies and regions and thus is difficult to predict. However, predicting the effects of farmland abandonment on biodiversity remains vital to the development of appropriate conservation strategies. Here, we compared the species-, community-, and functional group-level habitat suitability of abandoned farmland for birds by comparison with active farmland (pasture, cropland, and rice paddy) and natural wetland on Hokkaido, Japan, over a study area of 400 km × 500 km. Results differed markedly between functional groups. The abundance and species richness of grassland species in abandoned farmland were higher than that in active farmland, and comparable to that in wetland. In contrast, abundance and richness of bare-ground species was highest in active farmland. For most species, interactive effects between climate variables and abandoned farmland were not significant, suggesting a consistent habitat suitability of abandoned farmland irrespective of varied climatic conditions. Our results suggest that abandoned farmland plays an important role as habitat for grassland and forest species at large scales; farmland abandonment provides a valuable alternative habitat for species whose primary habitats have been lost to agricultural expansion. Especially, abandoned farmland in warmer areas in Hokkaido would represent a potential mitigation to the negative effects of wetland loss. A functional group approach synthesizes varied species-level responses and allows for a comprehensive understanding of the habitat suitability of abandoned farmland.Adopting this approach will contribute to establishing appropriate conservation strategies.