The Kobushi Biosphere Reserve encompasses most of the Kanto Mountains, including the main Okuchichibu ridge of 20 peaks rising above 2,000 metres. It is a watershed and source for major rivers, notably the Ara, Tama and Fuefuki rivers and Chikuma, or Shinano, River. The Biopshere Reserve features a wealth of geological formations and rock types with fauna that includes almost 40% of Japan recorded butterfly species, 24 of which are endangered. The area has traditionally been a centre for the cultivation of grapes, persimmons, peaches and other delicacies collectively described as the “eight rare fruits of Koshu.”
The Kobushi Biosphere Reserve is characterized by the fact that, despite its steeply sloping mountainous terrain, it is densely wooded up to the vicinity of the ridgeline, with less denuded and barren land than found in the mountains of the Japan Alps. This is because it has a number of conditions conducive to forest establishment: few mountains higher than the tree line; little debris, due to there being few faults or fractures in the strata; and well-developed soil, due to the weathering of the bedrock on slope surfaces into a variety of particle sizes, both large and small. The climate also promotes forest growth, as there is comparatively abundant rainfall, mainly during summer.
The fauna inhabiting this diverse environment are just as abundant as the flora; in addition to species at the top of the food chain, such as large mammals and raptors, a variety of other species can be seen, including those favoring frigid, warm, alpine, and lowland climates. For example, the presence of 126 species of butterfly — just under 40% of Japan’s approximately 320 species — has been confirmed, distributed from the subalpine zone to grasslands and semi-natural satochi-satoyama habitats. This figure includes 24 endangered species, making the nominated area a treasure trove of rare species.
In addition to large mammals such as Asian black bear (Ursus thibetanus japonicus), Japanese deer (Cervus nippon), and Japanese serow (Capricornis crispus), which is a nationally designated special natural monument, raptors such as mountain hawk eagle (Nisaetus nipalensis) and common buzzard (Buteo buteo) can be seen.
Mountains in the 2,000 m range run through the nominated area, so much of the land is sloping and therefore topographically unfavorable from the perspective of agriculture, but local people have managed to overcome the disadvantages and even use them as a symbol of the local scenery. In the Tochimoto district of Chichibu City, the entire settlement is located on a steep slope without any level ground, so dwellings and farmland appear to hang from the slope, positioned between the valley below and the mountain forest above. Arable land has been carved out in narrow steps that follow the line of the slopes and farming techniques tailored to the local natural environment have traditionally been used, such as sakasa-ugari, which involves tilling the fields in a way that prevents the soil from spilling over the sides.
While being protected under the Natural Parks Act to ensure that it is used appropriately, the buffer zone is also a place where people can enjoy exploring nature through such activities as mountain climbing at a relatively undemanding level, as well as hiking along the valleys, camping, and hot spring bathing in the mountains. In addition, there are many natural monuments designated by Yamanashi Prefecture and the nominated buffer zone provides a venue for sustainable ecotourism and environmental learning activities, which leverage these monuments, while conserving natural resources.