Friday, October 27, 2017

Landslide! A very short story for water source forests in Japan

On 11 July 2004, a slope near the peak of Mt. Gozen-yama 御前山 in Okutama 奥多摩, Tokyo, collapsed. At that time it rained heavily for sure, but the place had sustained itself till then with down-pouring. Nonetheless, the landslide of 2004 was huge and damaged the weir beneath the slope. It seriously affected the community of Okutama Town where the water from the weir was their life-line. Metropolis Government of Tokyo paid hundreds of millions of yen for the restoration. They also called for experts to investigate the reason why formerly stable mountain slope collapsed that time. Among the civil engineers for the study group, there was a zoologist, i.e. Dr. Seiki Takatsuki 高槻成紀who was then for Univ. of Tokyo. Reason? He is a leading expert for Japanese deer, and everybody knew the forest of the collapsed slope was eaten up by deer. The afforested coniferous forest had tall damaged trees only where starving deer gnawed at even the barks of such unappetizing stuff. There was no undergrowth or litter that could carry rain to the underground water system.

According to Dr. Yoshiharu Ishikawa 石川芳治 of Tokyo University of Agriculture and Technology, when deer gobble up the ground vegetation, the fallen leaves from the tree canopy can be easily washed away by rain, especially on a steep slope. Once litter has gone, the soil beneath can be swept away rapidly, 1000 times more in volume than a place with 200g of fallen leaves covering 1m2. It’s the recipe for landslides. Moreover, even when a slope holds somehow, the rain water running down the mountain slope pushes down anyway the soil and debris into streams that are often water source for metropolitan area. River water becomes muddy at best. In worst case scenario of the most fortunate no-landslide situation, the stream collects lots of fragments from forests, like fallen trees and unfortunate deer swept away by the torrent. Purifying such water for safe human consumption requires lots of work and, hence, money. … Huh, it’s really Minimax. Game theorist must rejoice to have a practical example for their equations ... That’s why there is a kind of silent consensus among forest volunteers around me: if you want to attract lots of public fund for forest maintenance, it’s better persuading Water Authorities, rather than Environmental Protection Offices.

After rain in Tanzawa, sometimes we can find petit Cappadocia
where a collapsing slope has lots of tiny soil pillars with a stone on each top.
If there is something to hold on its head,
soil resists to be washed away completely,
as famously found in Cappadocia.

I’ve sensed that the offices for water have unspoken power within any governmental buildings in Japan. Even though, aging Japan cannot provide enough man-power to sustain optimal management for water source forests. Kanagawa Prefecture, including the City of Yokohama, is damned happy to work with forest volunteers. I suspect it’s one of the reasons why the Kanagawa Forest Volunteer training course can provide us such a generous grants … Yeah, Kanagawa Green Trust works closely with Nature Conservation Society of Japan, but we have almost equal lecture hours for the maintenance of water source forests and for nature conservation. Some of my class mates who are more inclined to the nature protection seem like a bit frustrated … “Well, so, we have to thin that forest for water management, don’t we?” At the other end, there are veteran forest volunteers who are not satisfied with prefectural policy of water source management with forest volunteers. “OK, we are enthusiastic volunteers happy to enter deep forests to preserve mountain soil for water. But, it’s obvious our effort is not at all enough to achieve the better conditions for the forests. There must be larger fiscal measure to deploy professionals who can do the job more efficient than we.”

I personally support prefectural policy of water source management that works with civil society volunteers. For one thing, I’ve learned Japanese forest has been for millennia a place of collaboration between government and civil society. The reason would be technical difficulty in Japanese forests. Japan is a relatively substantial archipelago that can be covered by deep forests unless humans concrete the ground and maintain it as such with continuous mowing. Our ancestors knew it, or I would say far better-understood the situation than we do in the 21st century. There is a book written by Dr. Conrad Totman of Yale, “The Green Archipelago; forestry in preindustrial Japan” (University of California Press, 1989). It’s a book written by an academic for general public, almost for the first time, about historical forest management in Japan. Certainly, 30 years later now from its first publication, there have been accumulated counter-evidences against Totman’s description. Even though, the basic conclusion of him looks robust.

According to Totman, for ages Japanese government had to find ways to mobilize commoners for physically demanding long-term jobs in mountainous forests. Quasi-slavery of 1500 years ago may have been able to harvest trees for massive temple constructions in Nara and Kyoto. It denuded the forests in Kansai Area, but soon people in ancient cities had to think how to manage the soil erosion and devastating floods during seasonal monsoons. They always returned to the same conclusion: planting and nurturing forests for generations is the MUST. Coercion did not work for jobs in steep mountains requiring 100 years as one unit time. There is no better way than asking long-term commitment from communities near forests, which demanded attractive policy incentives. That’s the conclusion Tokugawa Shogunate government reached in the early 17th century. Hmmmm … yeah, Japan is not suitable for palm oil plantation of shorter time span. Our forest is not on a flat semi-arid land like in Europe or America … Even today, mechanization of Japanese forestry is not much practical as for Germany. Man-power is needed as before. If shrinking population in mountainous community brings problems for traditional community-based water source management, why not soliciting helping hands from city folks? Thanks to very good highway systems, it does not take much time to commute between urban condos and deep mountain-forests during weekends. It’s like a present-day community can have a wider area with the 21st century technology. Attractive incentive nowadays could be generous grant for adult-education program, and free weekend getaway to take care of water source forests. That’s not bad, at least for us forest volunteers. Then, how about the result volunteers can provide for water source forests? Is it inadequate as the frustration of our senior volunteers says?

Volunteers are learning
how to hand-mow grass in water source forest.

Simply comparing the available number of men for forests between now and 100 years ago, it’s true the forests of the yesteryears definitely had a leg-up. But, it seems to me, the consequence for the forest itself was not that simple. The concept of land ownership and user rights, established 350 years ago with economic incentives from Shogun, is still very important in the 21st century Japan. (Oh, how difficult it is to take away goodies once it was given …) It means, when there lived more people in mountainous area, our grandpas did whatever they wanted to extract rents as much as possible from mountains and forests. According to Joe Suga 須賀 , Atsushi Ushimaru 丑丸 敦史, and Toru Okamoto 岡本 in “Grassland and Japanese: a journey of 10000 years in Japanese green field” (2012, Tsukiji Shokan,「草地と日本人―日本列島草原1万年の旅」, ISBN-13: 978-4806714347), Japanese were crazy to cut trees until very recently, say the 1950s. First of all, Japan had a long period of population growth that required more ag-land. People “developed” the forests for farms and rice paddies. Subsistence agriculture in Japan required lots of inputs from forest … leaf litters for fertilizer and logs for energy and tools. Such demand created intensive exploitation of forests. Moreover, the technology of Japanese agriculture was not much different from the present day thrush-and-burn. Even mountainous areas could not have enough time for establishing a thriving forest of lots of undergrowth. The 3 scholars had found many archeological evidences and old travelogues that showed the present day deep mountain forests were grasslands for hundreds of years. The authors said the majority of Japanese afforested area now (some 40% of the entire forests) returned to be a forest during the 1950s almost for the first time in a couple of millennia. Why people suddenly agreed to plant trees then? Government gave lucrative subsidies for afforestation, and the price of cedars and cypresses were phenomenal due to the post-war reconstruction boom. Money, money, money … The massive human intervention, being professional or not, is not necessarily useful to maintain reliable water source forests. Although juries are still out to give final evaluation about activities of forest volunteers, I think it would be better than abandoning the mountains all together as it has been so until the 1980s. Especially for securing clear and safe water from mountain forests …

A grassland
expected to be a broad-leaved forest in 20 years’ time

When we think such history of Japanese forestry, Kanagawa Prefecture scores relatively well. During Tokugawa Shogunate, 2/3 of the area was directly governed by Shogun in Edo, and the remaining 1/3 that was around Odawara City and Hakone was the domain of the Lord of Odawara who directly reported the Shogun the security situation of strategically important Hakone Checkpoint. The majority of the forests in Kanagawa were once the property of Shogun, and, after the Meiji Restoration in 1868, of the Imperial Family. The continuous protection by the central government spared many forests in Kanagawa from clear-cutting for about 500 years. We have preserved afforested areas of different ages, from roughly 450 years’ old forest of Daiyusan Saijoji Temple 大雄山最乗寺 to about 60 years’ old forest of Niiharu. (Oh, yeah, our Niiharu forest is a baby forest.) In addition, due to the proximity to many research institutes in metropolitan Tokyo, forests and mountains of Kanagawa are the most scientifically studied and monitored nature in Japan. Actually Dr. Ishikawa confirmed the importance of leaf litters from his experiments of soil erosion in Tanzawa 丹沢. Their research became the basis of collaboration between local governments and civil society in Kanagawa. Kanagawa Forest Instructor scheme is the oldest and the best in Japan with lots of public money. Admitting it is not sufficient for the entire forests of the prefecture, volunteers at least engage in responsible maintenance for several water source forests. It’s a kind of popular belief we, people of Kanagawa, do not have much water crisis as Tokyo or any other areas in Kanto Region because water source forests are relatively well-taken care of. Water system in Kanagawa does not have to go far as the other prefectures of Kanto, including Tokyo. The dams for water supply are in the forest of Kanagawa itself, and weirs are well-protected. All are at least partly because of historical reason and the measures taken from the lessons learnt. From next week, I tell you my adventure with dams and water source forests in Kanagawa Prefecture. They are beautiful nature spots worth a visit. 😊  Oh, by the way, the historical reasons for good maintenance of water source forests in Kanagawa is not exclusive for Shogun, but with international geopolitics and colonialism. I return to it in my later post. Stay tuned!

A water pipe joint once used for the City of Yokohama

Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター can follow up if you find something unusual during your hiking in water source forests in Kanagawa. The contact address is

657 Nanasawa, Atsugi City, 243-0121 2430121 厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at

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