### 1. Security in Everyday Life Provided by Biodiversity

Biodiversity regulates drastic environmental changes and keeps the environment in a good status. This function is referred to as biodiversity's regulating services, and a well-known example is the water regulating function of forests. Here we will take a look at the example of the Bekanbeushi River Basin and Obetsu River Basin in eastern Hokkaido.

The Bekanbeushi River Basin consists of planted forest, natural forest and wetlands. The ratio of area of agricultural land is no more than 7.6 percent. Meanwhile, most part of the Obetsu River Basin, which is a branch river of the Bekanbeushi River, consists of agricultural land. The ratio of agricultural land is two-thirds of the river basin.

Comparing the amounts of rainwater inflow into these river basins during three days after rainfall, the amount of rainfall in the Bekanbeushi River Basin is only about 10% of the amount of rainfall and the amount of rain fall in the Obetsu River Basin is approximately 70% of the amount of rainfall flows. This shows that the rainfall stays longer within the Bekanbeushi River Basin because forests in Bekanbeushi River Basin remain more than in Obetsu River Basin (Table 2-1-1).

Further, a past event of logging in Japan shows that large-scale logging affected flood regulating functions. There is a report on the relationship between large-scale logging of forests and flood of the Oi River in the northern region of Shizuoka Prefecture during the Edo Period (from $ 17^{th} $ to $ 19^{th} $ century). In order to obtain timber for the Edo government, approximately 3,600

Figure 2-1-2 Area of Cut-Down Forests and Position of Hanebashi Bridge

hectares of forests around the upper course of the Oi River were cut down during the nine years from 1692 to 1700 (Figure 2-1-2). After 1692, large-scale floods began to strike the areas and they washed downstream bridges away.

The state of the floods at that time can be estimated from old records of changes of the length of the Ikawa Hanebashi Bridge (rare type of wooden cantilever bridge) that spanned the Oi River, which flows from the logging area. After the Ikawa Hanebashi Bridge was built in the beginning of the 1600s, even after it was repaired several times, the length of the bridge, approximately 73-meter, did not change until around the end of the 1600s. However, the bridge had become approximately 30 meters longer after the upstream logging from 1700 until 1825 (Figure 2-1-2). This was because the water-retaining capacity of the forests declined and this caused the amount of river flow to increase and the width of the riverbed to expand after large scale logging in the upstream areas of the Oi River.

As seen by these examples, the environment’s regulating functions of biodiversity have provided the foundation for our stable everyday life, and still play an important role today.

Table 2-1-1 Amounts of Rainwater River Flows in Obetsu River and Bekanbeushi River

Obetsu River	Bekanbeushi River
Area of river basin	38.68km²	378.97km²
Ratio of agricultural land	65.7%	7.6%
Total amount of rain in river basin	2,530,000t	24,830,000t
Amount of flow within 24 hours	23.5%	3.2%
Amount of flow within 48 hours	53.4%	8.2%
Amount of flow within 72 hours	66.0%	12.8%

Source: Study of Associations among Forests, Countryside, and the Sea, edited by Field Science Education and Research Center, Kyoto University, Chief Editor Yo Yamashita

Figure 2-1-3 Extension of the Length of Ikawa Hanebashi Bridge

Source: Illustration by the Ministry of the Environment, based on The Relationship between the Length of Hanebashi Bridge in the Oi River in the Edo Period and Cut Down Forests, by Kazuhiro Takao and Yutaka Omura (2008), Journal of Forest Research Issue 90: 190-193