This (or another) side of a mountain 2: Afforested area in the Doshi Village 道志村

East African Rift Valley, Baikal Rift Zone, Rhine Valley, Death Valley … On this planet there are several gigantic grabens that the movements of Earth’s crust are creating. It may not be so-dramatic as its siblings, but Japan also has such physiographical feature. Kanagawa Prefecture happens to situate in the middle of it. The area is called Fossa Magna, named by German scholar, Heinrich Edmund Maumann, in the late 19^th century. He noticed in this small archipelago, there were two strikingly different strata. One is estimated to be created around 550 to 65 million years ago. Another, aka Fossa Magna, is of 25 million or younger years ago. The thickness of Fossa Magna is about 6km in planes, and 9km in mountains. Interestingly, younger stratum is sandwiched by older strata, and it’s bended that presents a characteristic bow-shape of Honshu Island 本州.

The northern border of this map is still hotly debated among scholars.

The scholars consider the area was first instigated by the crush of Eurasian and North American Plates. Such moving lithosphere produced a large fissure from north to south of the ancient Japanese archipelago that was then straighter and nearer to the Eurasian Continent. The crack formed a large U-shaped valley along the split and simultaneously pushed the islands to the east. The space between the moving island and the continent eventually became the Sea of Japan. Next, the Philippines Plate joined the melee from the south by bringing the seabed up and annexed at least 2 islands from the Pacific Ocean to the former seabed area. The islands are now Izu Peninsula 伊豆半島 and Miura Peninsula 三浦半島. All the collisions bent the Honshu Island. A gigantic pile-up of plate tectonics stimulated the magma oozing out from the core of the planet and gave the Honshu a beautiful chorus line of erupting volcanos in the middle. Mt. Fuji 富士山 and Mt. Hakone 箱根山 are a part of the troop. Volcanic ashes piled up over the bowed graben, and the current day Fossa Magna was created. That’s that … With this bookish knowledge, I simply thought the soil of Fossa Magna area is more or less the same. That was laughably wrong. I noticed it in Doshi Village 道志村.

Doshi River running in Fossa Magna

It would be better to check the location of Doshi and Tanzawa Mountains. Doshi Village is spreading over the northern slope of the Tanzawa Mountains 丹沢, down from the rim at approx. ASL 600 – 1580m. This ridgeway is also a border between Yamanashi 山梨 and Kanagawa Prefectures 神奈川. The scree-covered area I talked last week was in the southern slope of Tanzawa, on the south slope of Mt. Nabewari (ASL 1272m) 鍋割山 to be exact. From there, we can enter the main peaks of Tanzawa, starting from Mt. Tonodake (ASL 1491m) 塔ノ岳, then Mt. Tanzawasan (ASL 1567m) 丹沢山, Mt. Hirugatake (ASL 1673m) 蛭が岳, Mt. Hinokiboramaru (ASL 1601) 檜洞丸, Inugoeji Pass (ASL 1168m) 犬越路, and Mt. Omuroyama (ASL 1587m) 大室山 that is on the prefectural border. i.e. Between the last week’s forest and the forest of Doshi Village, there lies a block of mountains with lots of ridges and gorges. The characteristics of Tanzawa Mountains is, although they are not so high, they are very steep, and consequently they have deep valleys that can provide good water for us in Kanagawa Prefecture. I just recalled the reason for their sheerness is due to the collision of the Philippines Plate from the south with the North American and the Eurasian Plates. They are contesting each other, and pushing up the seabed of the Pacific Ocean even now. So the soil of south-side of Tanzawa Mountains is fragile mixture of marine sediments and volcanic rocks spewed from Mt. Hakone and Mt. Fuji. The tip of Philippines Plate is somewhere near Mt. Hakone, around Mt. Yagura 矢倉岳 (ASL 870m) we visited August last year. Lots of gravels we find last week would be a kind of features of the push by the Philippines Plate. But this becomes less evident after we cross the land mass of Tanzawa and go north of Doshi River 道志川, that’s what I’ve found.

Average annual precipitation in Doshi Village is 1677mm (1982-2012), while that’s for Yadoriki Community is 1545mm. Yeah, Doshi definitely has more rain than in the slope of Nabewari. So it may explain the difference in the forests. As long as historical aspects of the treatment of the forest, Tanzawa and Doshi are basically the same. Both were Goryo-rin 御領林, properties of the central government and protected by the Shogunate Government 江戸幕府 since the 17^th century, and then from the middle of the 19^th century by the Emperor. But during the first half of the 20^th century, Tanzawa experienced substantial deforestation for military expansion of Japanese Imperialist government. In contrast, Doshi Village kept their trees as water source forests for the international port of Yokohama. That may have made the disparity between the trees, but if the time of afforestation was more or less the same for the both forests, as the size of the trees suggested, the forests in Doshi and Yadorki would have toed the mark equally. The remoteness from the population center? It takes roughly 3 hours from Shinjuku 新宿 to a forest in Doshi Village. It’s about 2 hours to a slope of Nabewari. In terms of the availability of foresters, the forests in Tanzawa could receive human cares more easily. But …

Mountains of Doshi Village,
 far from the crowds in Shinjuku …

With a fresh memory of the scree-covered floor for a forest in Tanzawa, this September I entered in a forest spreading over the south slope of Mt. Nabatakeura (ASL 1283m) 菜畑山, Doshi Village. Even for my inadequately trained eyes, the cedars and cypresses in the afforested slope of the Village were … beautiful. They stood straight, and the cut ends of logs were almost always so clean. Probably their age is the same as for the forest in the slopes of Nabewari … But the number of gnarling trees was definitely larger in Mt. Nabewari. The reason of the difference I could think of was, the soil. I was surprised to step on that so-soft soil, although the steepness of the mountain was more or less the same as in the south slope of Mt. Nabewari. Unlike the ridgeway of Mt. Nabewari, not much scree was there. The mixture of cypresses and cedars let the soil abundantly covered by leaves and branches of coniferous trees. It must be preventing the soil from erosion. But the same thing could have happened in Tanzawa if they would have had the same kind of soil as Doshi … Come to think of it, Doshi Village does not have deer problem as in Tanzawa. It must have made the biodiversity of the forest much richer in Doshi than in Tanzawa. Hmmmmmmmmmm …

An angle-wise,
 this photo of a forest in Doshi Village is the same as

this photo taken on the south slope of Mt. Nabewari.
 Could you figure out the difference in forest floor here,
 compared with the above photo?

Soft forest floor in Doshi Water Source Forest

A close shot.
 The place is covered with the leaves and branches
 of cedars and cypresses.

And lots of small-sized broad leaved shade trees,
 including Lindera umbellata.
 Doshi forests do not have deer problem so that
 the forest floor can keep many plants
 that might have been eaten up by the animal
 if their population exploded as in Tanzawa.

This is the forest floor of Mt. Nabewari.
 The place is dominated by
  Boenninghausenia albiflora var. japonica which deer hate to eat.

In terms of higher category of strata, Doshi and Tanzawa belong to the same Fossa Magna area. But probably Tanzawa’s feature would be more unique due to the Philippines Plate and the deer. Predictably, the southern part of Fossa Magna around Tanzawa has a unique ecology with a group of flora called Fossa Magna elements. They are typically found in Tanzawa, Hakone, Izu Peninsula, the southern slope of Mt. Fuji, and Izu Islands 伊豆諸島. These plants are so tough that can survive and thrive in rocky and steep soil of Tanzawa Mountains ... I don’t know Doshi Village is the place for the Fossa Magna elements … but at least Tricyrtis affinis (not Fossa magna element) are definitely more vigorous in Doshi than in Yadoriki. There would be more to learn about Fossa Magna. That’s for sure ...

Cirsium microspicatum Nakai,
 a thistle endemic in Fossa Magna of Japan.

Hosta longipes var. longipes, a hosta and ditto!

Tricyrtis affinis in Doshi Village.
 They are simply abundant even along a commuter road
 to schools and clinic.

The highest peak behind
 the Doshi elementary and junior-high is Mt. Nabatakeura.

Doshi Village Office 道志村役場

6181-1 Doshi Village, Minamitsuru-gun, Yamanashi, 402-0209

〒402-0209 山梨県南都留郡道志村6181-1

Phone: 0554-52-2111

FAX: 0554-52-2572

http://www.vill.doshi.lg.jp/