How much abandoned farmland is required to harbor comparable species richness and abundance of bird communities in wetland? Hierarchical community model suggests the importance of habitat structure and landscape context

Abstract

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.

Drivers of land-use changes in societies with decreasing populations: A comparison of the factors affecting farmland abandonment in a food production area in Japan

“…It may be difficult to restore forest ecosystems to a composition resembling that of natural forests if there are no seed sources in the surrounding areas [82,83]. However, open-land vegetation (e.g., grassland and wetland) can be restored due to the high seed dispersal ability of grass species [84][85][86][87][88].…”

“…On Sado island, abandoned paddies function as foraging habitats of the reintroduced Crested Ibis, Nipponia nippon [ 89 ], and in the Lake Inbanuma watershed, abandoned paddies on small valley bottoms have potential for multipurpose usages such as flood control, water purification, and wetland biodiversity [ 90 ]. In Hokkaido, the abandoned farmlands could be used to harbor organisms of wetland ecosystems [ 84 – 87 ] and provide wetland green infrastructure [ 91 ]. Natural recovery of vegetation in abandoned farmlands will proceed in the future, although the government would prefer to maintain the present farmlands through subsidies and land management policies.…”

Adaptation to climate change and conservation of biodiversity using green infrastructure

“…Regarding vegetation, the original back marsh community dominated by P. australis tends to recover after the abandonment of pastures (Morimoto et al, 2017). Additionally, abandoned farmland can serve as an alternative habitat for wetland ground beetles (Yamanaka et al, 2017) and wetland and grassland birds (Hanioka et al, 2018). Thus, if we can use abandoned farmlands as GI-2, there is a high possibility that these areas may function as wetland ecosystems, which we have lost through land conversion for agriculture.…”

“…The wetlands that existed in Japan in the early twentieth century (approximately 2110 km 2 ) have been reduced to less than half (821 km 2 ) their area at that time, with more than 60 % of the wetlands having been lost during the last 100 years (Geospatial Information Authority of Japan, 2000). Fortunately, recent studies in Hokkaido revealed that abandoned farmlands in backwater marshes (mesic sites) may become wetlands and continue to provide suitable habitats for wetland/grassland vegetation (Morimoto et al, 2017), insects (Yamanaka et al, 2017), and birds (Hanioka et al, 2018). These abandoned farmlands are distributed along streams and rivers.…”

Long-term declines in common breeding seabirds in Japan

“…The parameter log r mean,j was drawn from a normal distribution with hyperparameters log r global (mean) and σ r 2 (variance). This hierarchical model structure increases parameter estimate accuracy, as data-poor species can borrow information from data-rich species (Gelman and Hill 2007, Hanioka et al 2018).…”