On Location: Yakushima – The Jomon Sugi (Dating a Tree)

The Jomon sugi (縄文杉) is the name given to a Yakusugi tree, which is a sub-species of sugi, a Japanese cedar or Cryptomeria japonica. Standing 25.3 metres high and with a girth of 16.4 metres, it is the largest known specimen of its kind. Its age, however, is a mystery.

IF

During the feudal age in Japan, citizens of the country were expected to pay taxes usually in rice or some other produced goods. There was little farmland on Yakushima, so the locals endeavoured to pay their taxes in cedar wood. They climbed up the mountainsides where the largest of the cedar trees grew and using axes only, they cut down some of the great trees and chopped the wood into logs. It was during these days that a giant among giants of a tree was known to exist up the slopes of Miyanouradake, at about 1,300 metres elevation. However, as time went on, the tree became forgotten.

In 1914, Ernest Henry Wilson, an English botanist who spent much time in China, introduced to the world a massive tree stump on Yakushima. This stump (to be written about in detail later) became known as the Wilson Stump. Had Wilson continued his trek 300 metres up the mountainside he might have encountered the enormous Jomon sugi. But the re-discovery of the tree would not happen until 1966 when a Mr. Teiji Iwakawa found it after following rumours of an ancient giant of a tree said to exist beyond the Wilson Stump. His discovery was nationally publicized in 1968. At the time, the tree was called the Ohiwa sugi (Bigrock – Big because of its size and Rock from Iwakawa’s name, Rockriver). At the time, the tree was believed to be about 4,000 years old, and a contemporary newspaper article stated that the tree was a relic from the Jomon Period in Japan (about 10,500-ca. 300 B.C.). The sensation of the article gave rise to the new name of Jomon sugi.

In 1976, Kyushu University researchers examined the tree and based on the size and girth of the trunk and tree ring count from trees in the area, the tree’s age was estimated to be over 7,000 years old. The tree’s age was decided at 7,200 years. If this were the true age, the Jomon sugi would be even older than the bristlecone pines of the White Mountains of California. But was the tree really that old?

A drill sample was carbon dated and the age came out to be 2,700 years. That could not possibly be the accurate age though because the centre of the tree was hollow. All the old sugi rot from the centres as the trees continue to grow big and old outwards. The bigger and older the tree, the more of the old wood that has rotted away. There were possibly dozens of centuries of lost data, which meant that there was no reason to believe the Jomon sugi was not 7,200 years old.

Enter the Kikai Caldera. On Yakushima one can find a thick layer of red clay almost anywhere on the island, be it in the sub-alpine area or deep down in the valleys. The red layer of clay, known as the Akahoya, is anywhere from about 40 to 100 centimetres thick and in many places it contains chunks of pumice, some as large as a hand. If Yakushima is not a volcanic island, then where did this volcanic ejecta originate?

Looking north northwest of the island, two small island sit rather innocently among the waves. One island, Satsuma Iwojima (usually just called Iwojima but not to be confused with the famous one from WWII) bears a volcano that frequently sends up plumes of smoke. The other island, Takejima, is nothing remarkable except that there is a small settlement there. Near Iwojima’s east flank is a very small island composed entirely of lava rock. This is Showa Iwojima, so named because it emerged from the ocean during the early Showa Period days, between September 1934 and September 1935. The island grew from an undersea eruption, was destroyed by an eruption, and grew again before finally reaching its present size, minus the square metres lost to erosion in the intervening years.

These three small islands are all that remain of a great volcano that once occupied this corner of ocean. Now known as the Kikai Caldera, the great volcano collapsed with a cataclysmic explosion, originally believed to have occurred 6,300 years ago.  The evidence of the blast suggests that it was a 7 on the VEI – Volcanic Explosivity Index – making it one of the four most powerful and devastating eruptions in the last 10,000 years. The VEI grading system works like the magnitude scale for earthquakes with each number grade representing ten times more power than the previous number. The Mt. Saint Helens eruption of May 1980 was rated 5. That makes the Kikai eruption 100 times more powerful.

The blast sent out a pyroclastic flow, a moving current of hot gases, ash, and volcanic rock that can race along at up to 200 metres per second, and the more powerful ones can travel up to 200 kilometres from their source. Archaeological evidence in southern Kagoshima shows that human occupation ceased after the eruption and did not resume for some 700 years, an indication that the devastation from the blast may have annihilated life in the area.

How did Yakushima fare, being located so near? The Akahoya layer covers much of the island and a blast of that magnitude is believed to have taken a significant toll on the island’s biosphere. It is perhaps the mountainous terrain that saved a few pockets of life from complete obliteration. This was incredibly fortunate for Yakushima’s ecology since many of the species had migrated there during the ice ages and would not have been able to replenish their populations now that Yakushima was an island.

But if the island’s biosphere was devastated nearly but not quite to extinction 6,300 years ago, then is seems virtually improbable that the Jomon sugi could be 7,200 years old. Once again, updated research strolls onto centre stage: the eruption is now believed to have taken place 7,300 years ago. If that is the case, then the Jomon sugi may well be the last survivour of the earliest individuals to reclaim the island.

Still though, the tree’s true age cannot be stated with any certainty. It is surely over 3,000 years old, and very likely to be over 4,000 years old. It could be over 6,000 years old and may be as old as 7,200 years. We simply don’t know. But as my guide Kikuchi-san said, does it really matter? The tree is magnificent no many how many thousands of years we ascribe to it.

IF

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2 responses to “On Location: Yakushima – The Jomon Sugi (Dating a Tree)

  1. Thoroughly enjoyable post, absolutely publication quality! Looking forward to further updates…

  2. Many thanks for this fascinating enquiry into the real age of the Jomon Sugi – so it may actually be as old as a bristlecone pine. An inspiring thought. Equally amazing to read that the tree was “re-discovered” as recently as 1966. One wonders what else might be lurking within the unexplored forests of Yaku-shima…

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