How to Keep Nature: 20th anniversary for Koajiro Forest 1 小網代の森

 

In 2025, Koajiro Forest 小網代の森, 70ha jewel for Kanagawa Prefecture as a nature reserve (; my post on July 15, 2016), is celebrating their 20th anniversary as designated Suburban Green Zone 近郊緑地保全区域. The title was issued by the Minister of Land, Infrastructure, Transport and Tourism based on the 1966 Act on the Conservation of Suburban Green Zones in the National Capital Region 首都圏近郊緑地保全法. The purpose of the system is the same for the philosophy of Urbanization Control Area (; my post on January 12, 2025), i.e. to stop uncontrolled bulldozing greenery around Tokyo. The difference between Suburban Green Zone and Urbanization Control Area is the latter is in the middle of a city, whereas the former resides in rural area. Yeah, to reach Koajiro Forest, we proceed Route 134 in the middle of cabbage fields ... Among Suburban Green Zones, Koajiro Forest has the distinctive label of “Special Conservation Zone 近郊緑地特別保全地区,” which is a designation where ecosystem is considered especially noticeable.

It is said that in the Kanto 関東 and Tokai 東海 Regions of Honshu Island 本州 the Koajiro Forest is the only remaining environment where the entire watershed is preserved with the minimum invasion of human construction. The area for the entrance to the forest from Route 134, with ASL 47.9m, is covered by a forest whose underground water system is the source for Uranokawa River 浦の川, a tiny 1.3km stream but the backbone of the ecosystem of drainage basin. From the entrance, a boardwalk goes down to Koajiro Bay. The wooden deck is the only artificial structure in the forest and does NOT nudge visitors to stray from the route. The path does not have much detour, and this is the key for the conservation of the area. It’s a familiar story ill-behaved tourists stomping precious natural resources and destroying nature. Stop such overtourism is important. That’s easy to understand, isn't it? 😉 Ho ho ho. The floor has another mission. It is a culvert preventing the area from aridification. Very important thing, and the source of uniqueness of Koajiro Forest.

 I’ve been walking on boardwalk

2025 is the 20th anniversary for Koajiro Forest for obtaining legal protection as a nature reserve. This year is also the 10th anniversary for the Forest to open to the public as a nature park. For celebrating the occasion, last February there was a symposium in which the players for protecting Koajiro Forest gathered and talked the “development” (oh, yes) of the place as a nature reserve. At that time, one of the players, Prof. Hiroichi Yanase 柳瀬博一 of Institute of Science Tokyo, showed us the backstage of Koajiro Forest. And he revealed to us the importance of boardwalk. To understand it, it’s better to start with the history of the place.

Route of Koajiro Forest is like this:
occasional trekking road with boardwalk.
Here, we can see the next beginnings
of the boardwalk over there.

Koajiro Forest is located in the west shore of Miura Peninsula 三浦半島. The peninsula was created by plate tectonics of Eurasian and Philippines plates. The sediments accumulated in the deep ancient sea was upthrusted by humongous push by Philippines Plate to Eurasian one. Eruptions of undersea volcanos frequented and provided scoria that is sandwiched between deposits. Piling up sediments, scoria from volcanos, piling up, then pushed upward … The process is continuing for millions of years and has formed coastal terrace, which is Miura Peninsula in this case. For Koajiro Forest, until 120 thousand years ago, the place was undersea. Then about 100 thousand years ago, the rising occurred. This means, the geological base structure for Koajiro Forest is fragile sandstone, mudstone and occasional scoria. After it became land, loam layer fell from many volcanos, including Mt. Fuji, for ONLY 100 thousand years. The topsoil of Koajiro Forest, and surrounding area of Miura Peninsula, is not thick, 15-30cm at best, and water retention of the soil is not good. That’s the reason even today, the agriculture of Miura Peninsula is mainly vegetable cultivation, not rice needing lots of water during growing season.

Koajiro Bay.
It remains under water after the tectonic thrust,
but very shallow sea.

When you walk Miura Alps (; my post for April 29, 2016), you may notice lots of trees can grow large due to warm climate, but their roots are almost exposed, clinging to sandy and steep slopes along the hiking course. Do you think they can stand for hundreds of years as such? Nope. It’s easy for trees in the area falling. Still, humans established their villages for millennia. People cultivated the place for veggies and rice when it was possible. In Koajiro Forest, for more than 1000 years local fishermen raised rice using Uranokawa River and in hillside planted jolcham oaks for fuel, chestnuts for preserved food, pines for constructing boats, and cherries for comfort. The size of rice harvest was small, and large trees could collapse easily. Not an easy life. When in the 1960s locals became possible to live a modern life of petrol, and did not have to depend on the forest and Uranokawa River, they quickly left the area. The forest was abandoned.

A familiar forest scenery in Koajiro Forest

Abandoned forests were ubiquitous in Miura 三浦 -Hayama 葉山 -Zushi 逗子 area during the 1960s to the 1980s. They often spread along a small river just like Koajiro. But complete neglect includes forgetting water flows. As the topsoil is very shallow for the area, water quickly washed away the basin. The soil from the ridge soon filled up the remaining wetlands downstream. The small valleys were worn deeper and the entire water basin covered by dark forests. The climate of Miura Peninsula could reach its climax with broadleaved evergreens, i.e. dark forest. Such forests and shadowy streams lose their biodiversity quickly. People did not want to enter such places. In contrast, Koajiro was not forgotten completely. After private owners left the place, Keikyu Corporation 京急 bought the Forest to develop housing and resort facilities. Also, the area is warm and has lots of rain. Rainwater steadily goes underground and flows out to Uranokawa River. The water system of Koajiro Forest has a certain level of dependability. The municipality which traditionally had water supply problem maintained the water station at the ridge of Koajiro Forest near Route 134. These new arrangements for land ownership did a kind of “good thing.” Municipal water control prevented Uranokawa River from sweeping away the shallow topsoil of the forest to the downstream. Keikyu patrolled the place to plan their business. The wetland started where the slope from Route 134 ended, i.e. the place the soil from the higher place to be deposited, was survived, though not as it is for today. Let me tell you what happened to Koajiro Forest after that next week. Please stay tuned. 😊

Ridge Entrance for Koajiro Forest.
This particular point is not in the Special Conservation Zone.
 When we start descending from here,
we enter the nature reserve.
Then, what is this place?
 Could you see a fence in this photo?
 It’s the fence surrounding the water station of Miura City,
standing next to the entrance signboard of the Forest.
Though practically defunct these days,
the city office maintains the facility just in case.

If you find environmental issues in Koajiro Forest, please make a contact with

Greenery Section, Environment Division
Yokosuka-Miura Region Prefectural Administration Center
横須賀三浦地域県政総合センター環境部みどり課

2-9-19 Hinode-machi, Yokosuka 238-0006
〒238-0006　横須賀市日の出町２-９-19 

Phone: 046-823-0381

Goodbye Cherry Blossoms: Sakura this year around me

 

This year I did not intend to tell you about cherry blossoms. But … I could not resist. I have not been anywhere to admire particularly blossoms this year. Nevertheless, these are photos taken in familiar places for me.

Cerasus jamasakura in Niiharu Citizen Forest 新治市民の森. Late Mr. Nakamaru, the first chair for the Lovers Association of Niiharu Citizen Forest 新治市民の森愛護会, once said cherry blossoms must be seen from afar. Indeed.

This is also from Niiharu, in Ikebuchi Open Space. Personally, I think the beginning of April is the time when Niiharu Citizen Forest is the most beautiful ...

And we can find more cherry blossoms inside Niiharu Citizen Forest. This scenery is from the open space next to the Workshop.

This is the promenade for Satoyama Garden, Yokohama. These old Cerasus Jamasakura go strong.

Cherry blossoms, Someiyoshino, Street in front of the Forest Lab. Next to the venue for art show, there are two elderly care facilities whose buildings are surrounded by Someiyoshino trees … Hmmmm. Grandmas and Grandpas spend their final days with cherry blossoms. I think it’s not bad.

In Yadoriki Water Source Forest, we can spot wild cherry blossoms here and there on the slopes. I have not identified the one in this photo, but chances are, it is Fuji Cherry found especially around Mt. Fuji. Botanically, they are categorized as a species of Fossa Magna Element = endemic species for Fuji-Hakone-Izu National Park, and Tanzawa-Oyama Quasi-National Park. They are found only in deep mountains of the area. The petals of the beau are smaller than Someiyoshino, and the colors are paler. More ephemeral ...

Yadoriki Water Source Forest also has a series of cherry trees near the entrance. They are Someiyoshino planted intentionally 50 or so years ago when the place was a camping facility. Of course, now such an act is not welcomed for the Quasi-national park. Anyway, they are beautiful, aren’t they?

Just like the global stock market, this spring weather in our neighborhoods is jumping around. One day, it’s freezing cold and the next morning is hot requiring half sleeves. I guess plants are confused and decided to flower at once in Yokohama and Kanagawa, as for spring of the places in more northern area.

Chinese fringe flower in a garden next to the Forest Lab.
They are supposed to be full bloom after the cherries.
This year, on one go!

Cherry silver berry is also in full-bloom along Umeda River
 near Niiharu Citizen Forest.
They are also after cherry blossoms.

Lonicera gracilipes var. glabra open their flowers
 finally in April for Niiharu!
 They are supposed to be so before cherry blossoms.

Lots of fertile stems of Field Horsetail (; my post for April 13, 2018).
Er … you’re late!
You should be like that before cherry blossoms!

Violet orychophragmus in Niiharu Citizen Forest.
They are designated as “Invasive Species” to Japan.
 In any case, beautiful …

Mmmmmmmmmmmmm! It’s spring. Though, cold rain this weekend will disperse cherry blossoms, and summer is coming. Goodbye, this year’s cherries. Well, next week, I’ll return photos I’ve taken during this winter. The brown scenery again. Reason? I tell you my recent adventure in Koajiro Forest 小網代の森. To explain it, it’s better using photos taken during winter. Please stay tuned!

Stachyurus praecox in Yadoriki Water Source Forest

If you find environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121
〒243－0121　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 http://www.pref.kanagawa.jp/div/1644/

Our water from Sakawa River: water silk is gone from Yadoriki Stream

 

This week, we’ve been drenched with cold rain for April … It would do something good, though, for Yadoriki Water Source Forest. Here are photos I’ve taken before this rain.

You see? Dry, dry, dry. At least apparent water silk were not there. Maybe, water flow becomes so thin even for water silk …

Then, I saw this scenery in front of Iizumi Water Intake Weir 飯泉取水堰 at the downstream of Sakawa River.

Yap, the weir always keeps water inside the weir. That’s for sure. But don’t you think the flow of released water are too thin? This week, weather forecasters said the climate was like for February. But, at least it rained. I hope it would have done some good for water of Kanagawa Prefecture.

Then, after rain has gone,
cherry blossoms are in full-bloom in Yokohama
this weekend.

If you find environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121
〒243－0121　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 http://www.pref.kanagawa.jp/div/1644/

What to keep: Retention forestry for Hiromachi Ryokuchi Forest 広町緑地

 

Let’s return to the crossing where we entered Kotakegaya Valley 小竹ヶ谷 at the forest of Japanese lacquer tree. This time we take the road to the south. This route brings us Takegaya Valley 竹ヶ谷. In Japanese, prefix “ko” can mean “small.” So, I surmise Takegaya Valley was thought larger than Kotakegaya Valley when people named the place millennium years ago. Indeed, the size of the valley to this direction is definitely bigger and the stream we walk along is longer than that for Kotakegaya. After a bit of stroll on an ordinary country pass, we enter a well-maintained boardwalk. The Vally is a good-sized wetland in which casual visitors need elevated route to ramble. The walk is roughly 150m long and both sides of it show various kind of vegetation changing its face from season to season. Beneath the board, there are streams and ponds where aquatic creatures, like larva of fireflies, live.

The beginning of the Takegaya Valley

The stream in Takegaya Valley has a good amount of flow.

Especially during winter,
volunteers do repair work for ponds in Takegaya Valley.

The well-maintained boardwalk

The bog seen from the boardwalk in winter

When we enter the forest from this direction, it becomes clearer the impression of “lots of trees” we had when we proceed along the farming area (; my post last week). Of course, the ecosystem of natural wetland gives us more diverse living things compared with dry-land forests. But I think it’s not only for this reason, but also from the surrounding forest itself. Strangely, even comparing with celebrated Koajiro Forest (; my post on July 15, 2016), the forest of Hiromachi Ryokuchi looks having more mixture of vegetations. Geologically speaking Koajiro and Hiromachi stood on the same Miura Group. At least the dryland part of the environment for both Koajiro and Hiromachi forests could be more or less the same. But …

The forest surrounding the Valley
looks biodiverse in Hiromachi Forest.

The recent scenery from Koajiro Forest.
During winter we can easily notice
 some places of the forest is getting dry,
and sasa bamboos easily start dominating the site.

Yeah, I do not know scientific research done for these places measuring biodiversity. My intuition in this post is purely from my subjective feeling. To be fair for Koajiro, it is still suffering the aftereffects of 3.11. tsunami that attacked the place 14 years ago. The killer wave entered deep inside the wetland of Koajiro, swept some vegetations stood at the rim of the marsh. In addition, the Koajiro is damaged by rampant oak tree wilt that has made gaps in the forest spreading along the boardwalk. Still, it might not explain everything. The keeper of Koajiro Forest, NPO Koajiro Field Activity Coordination Conference 小網代野外活動調整会議, heavily engineers the water flow of the Koajiro in order to maintain the size of wetland. Their way of keeping the ground wet is manual constructions of numerous small dams and banks that control the flow of water. Such human intervention prevents the ground from aridification. Why do they do so? When the volunteers came in more than 10 years ago for reconstructing the place, their rice paddies were abandoned, and the place was showing rapid drying. In contrast, Hiromachi’s wetlands are smaller and even today showing previous usage as rice paddies, i.e. not showing possible collapse as a swamp. Probably it allows the Kamakura Hiromachi Forest Citizen Association 鎌倉広町の森市民の会, the keeper of the forest, hands-off approach, such as their “complete” organic farming. The end result is a rich forest of broadleaved trees thriving amid the sea of suburban landscape of houses.

A scenery from a slope for Takegaya Valley

We proceeded on the boardwalk, and soon the road rapidly climbing up for the ridge way. If we continue straight from the point we reached the ridge, it leads us to Johka Centre Entrance 浄化センター入口that is the nearest gate of the forest for Shichirigahama Station 七里ガ浜駅. To the east, we head for Kamakurayama Iriguchi Entrance 鎌倉山入口. To the west, we can go down to Kamakura Highschool Station 鎌倉高校前駅 via Shichirigahama Entrance 七里ガ浜入口. It is also very interesting strolling the ridge way of Hiromachi Ryokuchi. We notice there is a variety of large broadleaved trees, evergreen and deciduous. Many have name plate placed by the volunteers, a show of love to the place. The road is sometimes narrow, but well-maintained and difficult to lose direction. Even though, the bushes of, say, sasa bamboos and Japanese laurel, often remained intact. Thanks to such forest maintenance, the place is famous for little wild birds needing bushes for their home and refuge. Japanese bush warbler, black-faced bunting, red-flanked bluetail, Siberian blue robin, blue and white flycatcher … Where small birds and mammals thrive, there are birds of prey at the peak of food chain. Eastern buzzard, Eurasian goshawk, owl, … It tells something of success for maintaining biodiversity through human intervention.

The ridge way to the direction of Shichirigahama Entrance

Shichirigahama Entrance.
The route dives straight into a suburbia of houses.

Passing the Shichirigahaa Entrance,
and going to the direction of Johka Centre Entrance,
we walk through bush of sasa bamboos.
The road is clear,
i.e. the volunteers control the invasion of sasa into the route.
Such an environment is loved by small birds as their home.

Mixture of Japanese laurel and large broadleaved trees.
Beautiful.

This is a large Cerasus jamasakura in winter.

During winter, we can easily notice
fat trunks of large trees in the ridge way of Hiromachi.

Going down to Johka Centre Entrance

The other day, I attended a zoom session done by Dr. Yuichi Yamaura of Forestry and Forest Products Research Institute (FFPRI) of Japan. He said retention forestry is currently the most understandable tool for maintaining biodiversity of a forest. Forestry is in the end the way to use forest for human business. The best method for cost minimization is clear-cut logging = deforestation = damage to biodiversity. In retention forestry, human intervention to a forest is done by strategically selecting trees to be retained. Those preserved trees then act as mother trees. The environment around them is not disturbed even if it might be a small area. They also spread their seeds, which makes the germination rate higher. Gene level contamination can be avoided for the environment, in contrast to the method of planting seedlings brought from some other places. Nature is a strong creature. If a sufficient condition is met, notwithstanding human money-making activities, a forest and biodiversity can recover rather sooner in such retention forestry. Humans can also achieve a successful forestry business by harvesting the trees. The issue in this approach for Japan is our highly diverse geography. Our forest can show different ecosystems even between minute valleys locating side-by-side sandwiching a ridge. A way of selecting mother trees on this side of valley may not be optimum for another side. Inevitably, the Japanese way of retention operation is the process of trials and errors …

I love this scenery in the ridge way of Hiromachi.
Bushes and large trees consist of many kinds of vegetation.
Yet, the road is well-maintained.

I think the enthusiastic “organic operation” Kamakura Hiromachi Forest Citizen Association is very successful so far for biodiverse forest. It would be an example of effective retention forestry for urban forest park. But it may not be suitable for Koajiro Forest that has larger wetland and directly facing sea. Or how about for Niiharu Citizen Forest? It’s difficult to have a conclusion … Still, please visit Hiromachi Ryokuchi Forest where lots of living creatures including enthusiastic organic volunteer farmers are calmly busy all year round. It’s just another side of the noisy tourism melee of Slam Dunk.

The management office which is what we’ve found at the entrance is

Kamakura Hiromachi Ryokuchi Management Office 鎌倉広町緑地管理事務所
1133 Tsu, Kamakura, 248-0032
〒 248-0032 鎌倉市津1133番地
Phone/FAX：0467-32-5112

The city office who oversees the place is

Parks and Green Spaces Section, Kamakura Cityscape Division 都市景観部みどり公園課　
18-10 Onarimachi, Kamakura, 248-8686
〒248-8686鎌倉市御成町18-10 本庁舎3階
Phone: 0467-61-3491 

park@city.kamakura.kanagawa.jp