Figure 2-2-11 Distribution of Forestation Rates in Japan and an Image of a Green Corridor

Distribution of forest rate within pixels in the case of 500x500 pixels

Distribution of forest rate within pixels in the case of 4,000x4,000 pixels

[Image of a green corridor]

Source: Forestry Agency Montreal Process Second Report by Country and an image of a green corridor (available in the website)

(Hynobius tokyoensis) inhabit forests, but, during their larval stage they move to moist environment such as rice paddies and mountainous wetlands and lay their eggs in water. The distance of movement for their egg laying is approximately 50-130 meters, and they need interaction between forest and water ecosystems such as rice paddies within a relatively narrow range.

As another example, Japanese giant salamander (Andrias japonicus) spends most of their lives in the water of a river. During their breeding season, they move several hundred meters or several kilometers upstream and downstream in the river. It is difficult for them to move back upstream if there is an obstruction of approximately 80cm in height lying across the river. So they rely on a river environment with few obstructions in their habitat.

River ecosystems have been affected significantly by various impacts such as water shortage, changes of river course, fragmentation of river flow, reduction of sand and gravel supply, reduction of flood disturbance and river water pollution. These are because of residential housing and other infrastructural development around riverside and of conversion of floodplains, wetlands and riverfront forests into agriculture land.

According to the United Nations Environment Programme - World Conservation Monitoring Center (UNEP-WCMC), fragmentation due to dams and river deposits can be seen in two-thirds of the world's large rivers. Rivers tend to be highly fragmented in dry areas or in countries with extremely large populations, such as the United States, Europe and China. On the other hand, rivers in areas with low population density, such as Alaska, Canada, and Russia, tend to be not fragmented, and flow freely in their original state (Figure 2-2-12).

In Japan as well, fragmentation caused by dams can be seen since around 1930s. In the 1990s, Ministry of the Environment had a survey about the range of river flows in which it is possible for fish, such as cherry salmon and sweetfish with strong ability for swimming up, to swim up freely from river mouth to upstream. The 41% of main rivers in Japan (46 of the 113 rivers) are fragmented rivers in which the range possible for fish to swim up from the river mouth is half or less of the river flow. The 15% of main rivers (17 of 113 the rivers) are highly fragmented rivers in which the range is only a quarter or less (Figure 2-2-13).

It was also reported that change of river basin environments impacts on the ocean environments. Here is an example of the relationship between Sagami River and Sagami Bay in Kanagawa Prefecture.

In the Sagami River, which flows into Sagami Bay, various human activities such as erosion control, construction of dams, and gravel extraction have been carried out. These human activities have various benefits for people's everyday lives, but they also change the dynamics of sediment transport, which recently causes the reduction of dam's capacity for water storage and the impacts on ecosystem of the river basin.

The dams in Sagami River are affected by these changes of sediment transport. In Sagami Dam, sand deposition in the dam is proceeding and the water storage capacity is declining. From Shiroyama Dam to the mouth