Continuing my spring adventure last week in in Hakone Sengokubara National Treasure site 箱根仙石原, the Botanical Garden is currently the only place for Sengokubara wetland open to the public. Immediately to the west along Shitsugen Street is more or less developed for vacation houses and commercial facilities. Between such places and the national treasure site, there is a forest. It is closed off, open only for the permit holders. The 2.33 ha of the forest was donated to Hakone Town from the previous owner, and the rest 6.83 ha was bought by Kanagawa Trust, Kanagawa version of English-style National Trust. The purchase was funded by a broad donation from the public. The legal process to close off the National Treasure with the surrounding forest was completed in 2021. From 2022 a scheme was started to protect and improve the biodiversity for the wider Sengokubara wetland area. The very first yearly project cycle is being completed now. We had a chance to enter the off-limit site how it goes. For me, the difference in scenery between autumn and spring was astonishing in Sengokubara. The open space of the wetland in spring gave us the opportunity to understand the actual working of the project easily. Let me explain.
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| The border line |
For centuries people managed Sengokubara by open burning in March. The burnt reeds and pampas grass return nutritional base such as potassium to the soil that helped rice cultivation. The remaining roots soon sprout new shoots that were harvested in early summer for roofs of thatched houses and raincoats (yes!). Such circular management began collapsing during the industrialization in the late 19th century. In the middle of the previous century, the ferocious “nature protection” movement was popular that drove in 1970 the public opinion to halt completely open burning in Sengokubara. On the other hand, with rapid mass tourism development of the area by paved car roads and heavy usage of ground water for hotels, the wetland was pushed quickly to aridification. Natural succession kicked in, which meant for this area the invasion of taller trees, beginning with Japanese alders. When the wetland was designated for the National Treasure in 1934, the place was graced by elegant wild Japanese water irises. They rapidly disappeared during the 1970s. It affected the bottom line of the local tourism industry. Confused people started in 1985 research for managed protection of the wetland. The place for trial was the experimental area of present-day Hakone Botanical Garden which was till then rice paddies. In 1991, they concluded from the study returning the traditional way, i.e. open burning and early summer mowing, was the most effective for restoring biodiversity of the area. The tradition resumed. The new plan from 2022 with deer fence is the extension from here.
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| If we
leave the Sengokubara wetland to its own devises, it becomes like this within 10-20 years. |
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| And
this is the experimental area of Botanical Garden. In Hakone, Sengokubara is the only place where the wetland remains (; my post on October 29, 2021). |
In 1991, open burning returned but the surrounding forest where aridification started was left as-was. During the 1990s, the role of adjacent environment for the wetland was not yet clear for humans. People wondered what to do in this place. Besides, it was a private property. Legally, only the landlord can decide for the matter, even if that person was clueless. I guess the previous owner was wondering if it was profitable to bulldoze the forest for new cafés or something for tourists. Luckily, Japan entered “the lost 30 years” after the burst of the Bubble economy. Developmental pressure was not so strong for the area. The forest was sold as a “national trust area.” Eventually the understanding of the importance of ecosystem became mainstream. Pros, including the people for the National Park management, began to consider the entire area for the wetland management. Let’s start with water. Supply of water for the swamp comes from Mt. Daigatake 台ヶ岳 and from one of the water sources for River Hayakawa 早川. (In addition, beyond the Sengokubara Street, there is Itari Pond イタリ池 whose water is pumped up to Oakudani 大涌谷 to be heated and distributed to the hotels as “hot spring water.”) To maintain the wetland, the Offices secured water supply from these places by public works. Do you remember the ditch we washed our boots before entering the closed-off place (my post on November 5th, 2021)? The gutter was one of such result of public works. Next, monitoring devices for ground water level were situated here and there of the Sengokubara to make it sure the water supply is OK. The basics for maintaining wetland water have done. Next is to manage the natural succession.
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| We wash our feet first there in the gutter. |
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| Measuring the underground water level |
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| The result of water management |
The main approach for stopping natural succession in Sengokubara was clear: open burning in March, and mowing in early summer. The issue was how to treat the surrounding forest. From purely practical point of view, the role of forest for open burning was to seal the man-made structures in the area from the burning. But after studying the ecology in the semi-dried forest, researchers have noticed the system there was to buffer the direct impact from touristic development on the ecosystem of wetland. In addition, for Kanagawa Prefecture, Sengokubara is the only wetland and its surrounding forest with Japanese alders is more and more rare in the urbanized cities and towns. The wet forest itself has a rich biodiversity that is to be protected. So, in the new management plan, the adjacent forest is also the place whose ground water level is monitored to be maintained as is.
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| The
border between the forest and the wetland. After open burning, reeds will sprout from the wet ground on the rim of the forest. To begin burning, people first hand-mow these reeds adjacent to the forest, then ignite fire. The open space after mowing becomes a buffer against direct fire. The shrubs at the hedge of forest protect the life in deeper part of the forest. |
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| After
burning, new shoots of reeds are coming, but not overwhelming to cover the groundof Sengokubara proper. Potentilla freyniana won’t miss this opportunity of sunshine and flowering here and there. |
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| Cirsium sieboldii were
thriving this year in Sengokubara. There are many species of Asteraceae in Sengokubara. Some of them are in the Red List for endangered species. So, I don’t show you the photo of them today … Sorry. |
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| Actual place designated for
National Treasure is within the area surrounded by wood fences. It’s not much, really. |
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| Carex thunbergii Steudel that is common in Sengokubara in spring. In general, they thrive in wet soil and sunshine on footpaths between rice fields. Footpath is often mowed for easier access to the rice paddies that makes a happy environment for them. In contrast, in Sengokubara, once the tall reeds dominate the place, Carex thunbergii cannot win the game. Spring is a rare chance for them. |
As we’ve completed only the first year of the first phase of the project, no one knows how this approach for the management of Sengokubara turns out. The people, including Mr. Katsuyama, hope once the stabilization is completed for the ecosystem of Sengokubara, Hakone town may be able to extend the pedestrian deck from the Botanical Garden to the Sengokubara for experiencing the wider wetland ecosystem. At such a stage, the wild irises should return with lots of cool purple flowers dotting the large space. It can attract more entrance fee that will support the maintenance of fragile ecosystem ... Anyway, that’s the idea. We’ll see how it goes. I realized the things for Sengokubara are similar to the Satoyama management in Niiharu Citizen Forest 新治市民の森. In the climate of Kanagawa Prefecture, without human intervention, the village forest around us will be dominated by large evergreen Quercus myrsinifolia. With its broadleaves, the forest floor of the place is dark with smaller biodiversity. If we control the tree by mowing, thinning, pruning …, forest becomes brighter with more species here and there. Our great-great grandparents utilized the mowed grass, thinned and pruned tree trunks and boughs for daily use and for fuel. That’s the circular economy of rich Satoyama. Rich wetland is the same in our Prefecture … Mr. Katsuyama said “In terms of climate, Kanagawa Prefecture is not suitable for low or high moor. Having Sengokubara is a sort of miracle, and probably the passing scenery in the process of shrinking Lake Ashinoko 芦ノ湖 and aridification of the area for these 60 thousand years. Even so, with the wetland, the number of species dwelling in our home is definitely higher. It’s worthwhile to do our best to protect the fragile National Treasure.” OK. It would be another way for us to talk with the nature in this age of global warming …
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| Inside the surrounding forest of Japanese alders |
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| The ground was swampy and there were colonies of Carex dispalata with which people make sedge hats. |
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| They also flower in spring! |
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| There were lots of Viola verecunda in the forest. |
If you find environmental issues in Hakone, please make a contact with Hakone Visitor Centre 環境省箱根ビジターセンター
164 Motohakone, Hakone Town, Ashigarashimo-gun, Kanagawa Prefecture 250-0522
250-0522 神奈川県足柄下郡箱根町元箱根164
TEL：0460-84-9981
FAX：0460-84-5721
https://hakonevc.sunnyday.jp/
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