To the beach: a story of Shonan Seaside Protection Forest 湘南海岸砂防林

As I haven’t experienced the condition of the forest 100 years ago in Tanzawa 丹沢, I cannot say in definite the scree-covered forest floor is due to the crash of Philippines Plate and Eurasian/North American Plates, or because of soil erosion brought by the more recent deer problems. One thing for sure. Forest volunteers are in action for forest management, and feel the absolute power of the nature no matter what. Yeah, humans can annihilate the eco-system by dropping an atomic bomb, or even massive deforestation will cause serious problems. We volunteers are not interested in such things. Ours is thinning, mowing, pruning, in a tiny scale compared with the size of Fossa Magna. What we are doing is like “Hello forest, do you mind us helping you to welcome lots of living creatures, humans included?” We know even after a deep-seated slope failure, the vegetation will come back in mountains. Forests are resilient ... Or, are they? In Kanagawa Prefecture, there is another kind of forests. They are Seaside Protection Forests.

Shonan Seaside Protection Forest 湘南海岸砂防林 on both side of the Route 134

The seaside road, National Route 134 running the opposite shore of Enoshima Island 江の島 (my post on June 30, 2017), was a part of Tokaido 東海道, the most important artillery route connecting Tokyo and Kyoto. (Due to heavy traffic, the 21st Century Tokaido, aka Route 1, uses only partially the ancient parts, and the majority is expressways. Auxiliary national roads running in parallel to Route 1, such as Route 134, were often the former Tokaido.) Historically, during the Tokugawa Shogunate Period 江戸時代, the entire Tokaido was provided with the facilities, such as frequent road maintenance services and post-towns. The route along the coast was pine tree-lined in order to control the tidal erosion and to provide resting places for travelers. The Route 134 joins with Route #1 in the Oiso Town 大磯 where there are the remnants of such system. Having said that, despite of frequent road maintenances, the coastal road, especially between Enoshima and Oiso, has a serious problem even today of salt damage and accereation of sand from the Pacific Ocean. Typhoons and seasonal strong south-west winds between October and April could cover the road with sand, or destroy the entire structure. Do you know the construction work at Seisho Bypass 西湘バイパス in Oiso Town, due to the high-tide damage by a typhoon in October 2017, could continue beyond 2020? Moreover, beach front is always popular for housing and tourism, which makes the Shonan Beach 湘南海岸 a series of big cities, such as Kamakura 鎌倉, Fujisawa 藤沢, Chigasaki 茅ヶ崎, Hiratsuka 平塚, … People demands their laundry salt-free even their condo is within 10 minutes’ walk from the Ocean. Thus, both national and prefectural governments keep on tending the seaside route with providing the measure, i.e. planting the vegetation. 

Construction work is continuing for Seisho Bypass 西湘バイパス

The forest along the beach

The current Seaside Protection Forest of Shonan Beach 湘南海岸砂防林 was first afforested by modern methodology in 1920. Since then, there were the Great Kanto Earthquake with massive tsunamis, World War II when the Japanese military deforested pine trees and made Chigasaki Beach a maneuvering ground, and several big typhoons. Whatever. People have kept on planting. Academics from University of Tokyo, and Yokohama National University chose the flora that could survive on sand. Groynes, sand fence of many kinds, windbreak nets, etc. have been built. At the beginning it was only Japanese black pines and bamboo fences, but for these 100 years, Japanese brains for botany and civil engineering introduced more diversified afforestation with Euonymus japonicas, Japanese cheesewood, and many other plants protected by permanent structure of wire nets as windbreaker. Now, the Seaside Protection Forest is 11.4km long for 85.2ha. Its average width is 80m where more than 15 kinds of plants are intentionally planted by humans.

Afforested forest of Japanese black pines
 along Sodegahama Beach 袖ヶ浜,
 Hiratsuka 平塚

Japanese cheesewood near Nijigahama Beach 虹ケ浜, Hiratsuka 平塚

In addition to the above 3 kinds of trees, carefully chosen species were located along the beach. The list includes Carex kobomugi (ha ha, invasive plants for the USA), Beach morning, Autumn olive, Quercus phillyraeoides, Castanopsis sieboldii, Ilex integra, Machilus thunbergii, Daphniphyllum teijsmannii, Japanese cinnamon, Chinese bayberry, Japanese camellia, Dentropanax trifidus, Ligustrum japonicum, and Phaphiolepis umbellata. The way how they are planted is also controlled based on engineering. First, the grasses such as Carex kobomugi and Beach morning, are planted nearer to the shore to reduce the effect of acceration. Next, shrubby areas are created with Euonymus japonicas, Phaphiolepis umbellata and others. Together with the wind-breaking net behind the shrub, the structure acts as the frontline to protect houses from the shifting sand. Beyond the net is the forest of higher trees, including black pines, of at least 10m high. In the middle of the forest runs the Route 134, almost nestled in the forest. Moreover, planting is just the beginning.

I think they are dried Carex pumila,
 in Southern Beach, Chigasaki 茅ヶ崎.
 (Could you figure out Eboshi-iwa 烏帽子岩 over there?)
 It seems they were just surviving,
 but actually acted as a strong buffer for erosion.

The structure of windbreaker is like this.

Some old bamboo nets are remaining.
 According to Mr. Hiramoto of Kanagawa Prefecture,
 they think
 “It’s better leaving them as such to have as many fences as possible.”

Come to think of it,
 this photo may say something amazing
 about humans and the Ocean …

The next level is for shrubs like Euonymus japonicas. They are all slanted to the leeward
 due to continuously strong sea breeze.

Then there is a “forest” covered by windbreakers.
 Could you see the canopy
 forming a slope from the leeward to the Ocean?
 It’s thanks to the strategic planting.
 This part of the pines in Chigasaki is roughly 30 years old.

Next, people mow and cut the vines to make supposed-to-be tall trees to grow high enough for a better barrier. Also, as the entire Seaside Protection Forest runs along the busy (and fashionable) Route 134 and the residential area, tidying up the outer rim of the forest is the must to prevent the area from forest fires and “aesthetically problematic features.” Black pines are vulnerable to Monochamus alternatus (or pine wilt nematode which the beetle carries). Annual spraying of insecticide is the absolute minimum. Regular cleaning of the forest with fresh water is necessary to wash off the salt from the leaves. When a dry spell attacks, people irrigate the forest of 85 ha. Even with such efforts, die-outs and typhoon damages are not rare so that continuous supply of seedlings is important for replanting. Prefectural and contracted nurseries for the above 17 and more species are deployed within the prefecture. The researchers in Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター are busy creating more resilient black pines against salt, sand, wind, and pests … Supported by such painstaking efforts, the seaside afforestation can protect from salt and sand damage both several meters’ wide of beach spreading windward, and 2-3 hundred meters inland to the direction of leeward. Amazingly, these days some other kinds of broadleaved trees have naturally started to invade into the “80m-wide.” Together with such wild comers the artificially created forests guard the human settlement in Shonan 湘南.

The nursery for black pines at Fujisawa Civil Engineering Office at Shiomidai.
 The Office is actually facing to the Route 134, and circled by condos.
 Here, the officers collect pine cones from the nearby Seaside Protection Forest,
 and grow them to the seedlings, expecting the local pines have better DNA for survival.
 The ground is improved by manure and black soil for the babies which spend their first 5 years here.
 Mr. Hiramoto said
 “Well, they are pampered now, but have to endure far harsher environment later!” Indeed.

The Engineering Office also has an exhibition garden
 for the vegetation the Prefecture plants for the Protection Forest.
 Mr. Hiramoto:
 “This place becomes too much like inland,
 and it cannot receive shifting sand, which is problematic.
 Those grasses in the garden need regular covering by the sand to thrive.
 They are losing the momentum because of over-nutritious environment.”
 Hmmmmmmmmmmm.

Natural Environment Conservation Center has
 a nursery of new-breed of pines in Tanzawa.

When we stroll along the Shonan Beach, the forest on the leeward looks “natural.” But the reality is something of human creation. Yeah, after 100 years of struggle, we can now find some “natural invaders” in the forest, including vines, but its conditions are very different from the afforested but “natural” coniferous forests of Tanzawa. One September weekend, I had a chance to volunteer vine cutting at one of those forest blocks in Chigasaki City. Mr. Hiramoto for the Prefecture told us the engineers added black soil and fertilizer before planting to the sand some 50 years ago. Now the pines are taller than 20m. Good, good … but I found the ground inside the forest was sandy nonetheless, and annual spraying inevitably limits the biodiversity with a smaller range of vegetation. I had a conflicting feeling of cutting Paederia scandens and Pueraria montana var. lobata … Oh they were so resilient that can start to grow on yet very sandy soil. But if we allow them to form mantle vegetation by choking off the afforested trees, relentless winds from the Ocean can quickly cover them with lots of sand and salt. They will be killed off soon. The point of forest management in this case is, just let the planted trees to grow, and keep the forest floor modestly populated with the plants that do not hamper the growth of human-introduced plants. Er, well …

Pueraria montana var. lobata is covering
 the artificially planted vegetation
 at this part of the Protection Forest.

The outer rim of the forest shows lots of
 invading Vitis coignetiae and Farfugium japonicum wrapping the afforested Euonymus japonicas.

From outside,
 the Protection Forest looks having a rich forest floor …

But actually the inside is like this.
 It’s far from a “jungle.”

Vines here.
 I found they tend to be vigorous at the edge of the Protection Forest.
 It would be due to enough sunshine …

Volunteers exchanged the gossip about the Shonan Seaside Protection Forest. I learned the City of Hiratsuka and Oiso Town has a problem of homeless housing within the Seaside Forest. The authorities want to let them out, but especially during winter it’s a popular refuge … When I first heard the story, I imagined the forest floor of Tanzawa with vampire leeches … Wrong. Inside of the Seaside Protection Forest has still a limited biodiversity. It’s like a very artificially created park where boulevards are intentionally omitted by planting the trees closely. Yeah, the place would be comfortable to sleep outdoors during winter … It’s a very synthetic, vulnerable man-made forest. Can it survive without heavy human intervention? Another gossip among us was about progression of coastlines. The sandy beach in front of Enoshima Aquarium 江ノ島水族館 was at least more than 20m wider 20-or-so years ago, some locals say. Beaches in Chigasaki and Hiratsuka are regularly receiving sands from Sagami Lake 相模湖, some 30km away in a deep mountain, when the Water Authority of the Prefecture dredges Sagami Dam 相模ダム. The endeavor does not stop the narrowing of Sodegahama Beach 袖ヶ浜 or Southern Beach. When the authority dredges the Oiso Fishing Port 大磯漁港, gigantic pipes are passed over the wall to the neighboring Oiso Beaches. The divers vacuum the bottom of the Port and the gathered sand is spewed off from the pipe to the Beach for sunbathers to relax … Concreted estuary of rivers, in order to prevent floods in the coastal cities, changed the supply route of sands from Tanzawa Mountains via the rivers. People put groynes off the rivers to control the flow. It did not contribute much against the encroaching sea … 

“Over there years ago,
 groyens were built to control the flow of sediments from Sagami River.
 Now we know the tidal structure was changed in definite,
 but there is not much effect for stopping beach erosion.
 Beaches in Hiratsuka these days are shrinking.”

This is Sodegahama Beach, Hiratsuka, now.
 Come to think of it the place looked far wider
 when I was an elementary school kid …

I a kind of understood why the people living along the Shona Beach, next to the Protection Forest, were so “urbanized” This forest is not the forest of Mother Nature. Rather, it’s to resist the force of nature from the Pacific Ocean ... extremely inner-city situation in the guise of “natural forest.” Does human effort win the contest? I doubt it. Rather, rising sea level could overwhelm Japanese tradition of coastline afforestation sooner or later. Global warming ... Not all the forests are resilient, I guess. Though, the planet Earth is almighty.

If you find a problem in Shonan Seaside Protection Forest, please make a contact with

Fujisawa Civil Engineering Office at Shiomidai 藤沢土木事務所汐見台庁舎
1-7 Shiomidai, Chigasaki, 253-0033 〒253-0033　茅ヶ崎市汐見台１－７
Phone: 0467(58)1473
Fax: 0467-58-4953

The Office has an exhibition garden to show the vegetation they plant in the Seaside Protection Forest. The place is open to the public, 24/7. 😄