We examined the transition in the grassland areas and vegetation changes over time based on land use types and management in the grasslands of Kanpu-zan, Oga Peninsula, Akita Prefecture. Farmers harvested to utilize grassland resources until the 1960’s in Kanpu-zan. In the 1970's, grassland utilization gradually declined, and it has become an area for tourism. The grassland area in Kanpu-zan changed along with this transformation in usage. The grassland in our study area was 319 ha in 1975, but it had decreased to 138 ha by 2014. This result shows that extensive grassland management had ceased.
We conducted vegetation surveys in three types of areas to clarify vegetation changes because of the abandonment of grassland management. We had two types of management areas: high frequency, where mowing occurred more than twice a year, and low frequency, where mowing occurred once a year or only once over several years. The last type was areas where grassland management had been abandoned.
Our results showed that the vegetation varied depending on the management frequency. Indicator species that continuously appeared in management areas were grassland plants, and the frequency of occurrence of these plants declined in the abandonment area. In particular, the frequency of occurrence of endangered species, including Erigeron thunbergii A. Gray subsp. Thunbergii, Aeginetia sinensis G. Beck, and Vincetoxicum pycnostelma Kitag., was greatly diminished. However, grasslands were conserved in the abandoned management area, and did not transition into forest. Nonetheless, although it remained a grassland, it did not preserve high species diversity because the vegetation was altered, and grassland species were reduced or absent. In summary, when grassland management frequency and area is reduced, it is predicted that the grassland species that characteristically inhabit the Kanpu-zan may become extinct. Therefore, to maintain abundant grassland ecosystems in Kanpu-zan, it is necessary to initiate and continue new management methods that are not dependent on the policy of local governments, and grassland management should continue.
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