Introduction / Chapter 6

Processing & Civil Works

Logs cannot be used as they are. They must be split, sawn or laminated. This chapter follows how wood has been processed from the Edo period to today, and how it has been used in civil works such as utility poles and land reclamation.

Working the wood

Splitting: older than the saw

Cedar grows straight and splits easily along the grain. It can be split as thin as about 5 mm and was used for barrels and tubs.^[1] Old Japanese saws were crosscut tools, poorly suited to sawing wood lengthwise.^[2] That is why easily split wood was so valued.

Sawing: the oga and the maebiki-oga

The oga, a saw for ripping wood lengthwise, came from China in the 14th–15th centuries (mid-Muromachi period). Its blade, about 2 m long and 5 cm wide, was stretched in a frame and worked by two people.^[2] It made it easy to cut wide, thin boards, transforming board making and woodworking.^[2]

In the early Edo period the one-person maebiki-oga appeared and spread.^[2] Craftsmen who sawed logs into boards and squared timber were called kobiki, sawyers.

Single-piece slabs sawn from large trees remain popular. In July 2026, a slab sale was held in the event space beneath JR Shinjuku Station, with boards still bearing their bark-side edges (live edges) and boards with holes where knots had fallen out lined up as tabletops.

Laminating: glulam and CLT

Today's timber buildings are supported by laminated materials. The National Stadium's roof frame uses glulam of larch and cedar, and athletes' facilities use domestic CLT (panels of boards layered crosswise).^[3] In Nagano Prefecture, a "glued stacked beam" made from small and medium larch logs under 30 cm in diameter has received ministerial certification.^[4] Being able to turn slender trees into structural members for large buildings is what made timber buildings in central Tokyo possible (Chapter 5).

Showing it off: furniture that makes use of cracks and rot

Cracks, rot holes and edges with bark left on are the parts usually cut away in ordinary sawmilling. Set in clear resin, they become furniture that shows those shapes as they are.

There were also solid-wood stools carved from blocks of log, without resin. The cracks running from the heart of the growth rings and the marks of the cutting tools are left as they are.

Even without making furniture, the shapes of branches and roots themselves can be put on show. In a clothing store in Shibuya, a huge tangle of dried branches and vines hung from the ceiling, spreading over the sales floor.

Split firewood, once stacked, becomes decoration in itself. In the lounge of the Conrad Tokyo in Shiodome, small conifer ornaments were lined up on a partition of firewood stacked like a wall.

The resin blocks and solid-wood stools were photographed on the sales floor of a department store in Tokyo with the store's permission. I did not record what kinds of wood and resin were used.

The city's foundations, and where felled trees go

Wooden utility poles

Japan's first utility poles were erected in 1869 to carry an official telegraph line between the Yokohama lighthouse office and the court. From early Meiji to the Taisho era, poles were made of wood.^[5]

Wooden poles rot from where they meet the ground. A Hokkaido study describes poles pressure-treated with creosote oil, mainly of Yezo spruce and Sakhalin fir, with larch used for small poles. Poles erected in 1958 had lost their preservative 22 years later and were badly decayed, especially at ground level.^[6] The report, from 1981, notes that concrete poles were already common in urban areas.^[6]

When and how Tokyo's wooden poles were replaced by concrete is still being researched. The species and treatment above are examples from Hokkaido.

Reclaiming Tokyo Bay

Much of Tokyo's land was made by filling in the sea. Soon after entering Edo, Tokugawa Ieyasu began filling in the Hibiya Inlet, turning it into land between 1593 and 1614. He also cut down Kanda Hill and used its soil to fill the area from Nihonbashi-Hamacho to Shinbashi. The center of Edo's port was placed at Nihonbashi.^[7]

East of the Sumida River, reclamation began in 1596. Between 1615 and 1629 reclaimed land increased rapidly in today's eastern Chuo ward, including Reiganjima. Each piece of land was surrounded by canals and became a kashi, a landing for boats.^[7]

Timber storage overlaps with this history of reclamation. Genroku-era Kiba was built by timber wholesalers who filled in the Fukagawa marshes themselves (Chapter 1). Shin-Kiba, where it moved in the Showa era, also stands on reclaimed land in Tokyo Bay.

Wood inside the reclaimed land

Wood itself is buried inside the reclaimed land. In postwar Tokyo Port, the sea was filled with garbage, and from 1957 to 1967 garbage was brought to Landfill No. 14—later known as "Yumenoshima" (Dream Island). In a Tokyo Metropolitan Bureau of Port and Harbor survey, "wood, bamboo and straw" made up 13% of the garbage at No. 14.^[8] The wood waste of the time was not burned but became part of the material that turned sea into land.

Wood that holds up soft ground: pine piles

On soft, waterlogged ground, wooden piles have long been driven beneath buildings to support them. Beneath the Marunouchi building of Tokyo Station, completed in 1914, about 10,000 pine piles were driven at 0.5 m intervals.^[9] Wood rots when exposed to air, but below the groundwater table no oxygen reaches it, so it does not rot and keeps its form for a long time.^[10]

Using logs for ground improvement today

Making use of this property, a liquefaction countermeasure that drives thinned logs into the ground has been developed. Logs of sugi, larch and the like—simply debarked and sharpened—are driven into sandy ground to compact it and prevent liquefaction in earthquakes.^[11] Because logs placed below the groundwater table do not rot and keep storing carbon, the method is also described as "creating a new forest underground."^[10] In a case introduced in a Forestry Agency competition, 570 m³ of thinnings were used.^[11] The Tokyo Bay shore, with its many reclaimed areas, is also land at risk of liquefaction, so this is a possible use for Tama thinnings as well.

For "soil improvement" of the surface soil, chips and compost made from pruned branches of street and park trees are used (see "Green recycling" in the next section).

I have not confirmed any case of log-driving liquefaction countermeasures in Tokyo, or any use of Tama timber for them. Nor have I confirmed how Tokyo Station's pine piles were treated in the preservation work.

Where felled wood goes

Tama has long been known as the "Ome forestry district," producing mainly posts and scaffolding poles.^[12] Today, besides building timber, its wood also goes into plywood (Chapter 7) and fuel. Here we look separately at wood cut in the mountains and wood cut in the city.

Mountain wood as fuel: Hinohara Village

Hinohara Village continues to turn its own wood into heat.^[13][14]

The village subsidizes felling and hauling so that thinned wood, previously left lying in the mountains, can be brought out.^[14] Using wood as fuel gives a use even to the thin and crooked parts of felled trees.

Returning city trees to the city: green recycling

Branches and leaves from pruning parks and street trees can also be used. Since FY1990, Koto City has returned branches and fallen leaves from its greenery back to its own green spaces instead of burning or burying them.^[15]

Tokyo has more than one million street trees (Chapter 8). How to use their prunings is a kind of "urban forestry" challenge.

Laid on park paths: wooden paving of Tama timber

Tama wood is also used underfoot in metropolitan parks. According to a sign by the Tokyo Metropolitan Eastern Park Office that I saw in Ueno Park, the Tokyo government has used Tama timber, including thinnings, for road guard fences, the "Memorial Benches" in metropolitan parks and more, to conserve Tama's deteriorating forests and help prevent global warming. The sign explains that wooden paving will eventually rot and need replacing, but that this keeps thinnings in use and so helps protect the Tama forests.

It is a way of counting rot not as a defect but as a reason to keep using wood. The sign does not say, however, how much wood went into the paving, or whether Tama timber is used again each time it is replaced.

The sign's content is as of October 2021, when the photo was taken. I have not checked the current state of the paving.

Wood crossing the prefectural border: the Otsuki biomass power plant

Felled wood is sometimes carried out of Tokyo. The Otsuki Biomass Power Plant in Otsuki, Yamanashi, has an output of about 14,500 kW, enough electricity for about 30,000 households. It burns about 150,000 tonnes a year of chips made from unused thinnings and pruned branches, mainly from Yamanashi and the wider Kanto region.^[16] It began commercial operation in summer 2018.^[17]

When the author saw it from a train window in October 2020, logs were piled high in the plant's yard. They were "obstructing trees" (trees felled because they stand in the way of construction) from the building of the Shin-Tomei Expressway (the Second Tomei). Trees cut to build a road were being turned into electricity.

The acceptance of obstructing trees is based on what the author saw and heard on site; it has not been checked against materials from the power plant or the expressway company.

Wood stove smoke: US regulation and Japan

Wood stoves, which burn felled wood as fuel, are being reconsidered as a use for wood. But burning makes smoke, and how countries deal with the fine particles (PM2.5) in that smoke differs greatly.

In the United States, standards under the Clean Air Act set limits on particle emissions from new residential wood stoves offered for sale. The 2015 standard was 4.5 g per hour; from May 2020 it became stricter, at 2.0 or 2.5 g per hour depending on the test method. Stoves that do not meet the standard cannot be sold new.^[18] There are also local rules. In the San Francisco Bay Area, burning wood in fireplaces, wood stoves, pellet stoves or outdoor fire pits is illegal on days when a winter air-pollution alert is issued, with fines of $100 for a first violation and $500 for a second.^[19] "Changeout" programs that subsidize replacing old stoves with certified ones are also run in many areas. The EPA explains that just 20 old non-certified stoves can emit more than a ton of fine particles during the cold months.^[20]

In Japan, there is no law or ordinance regulating smoke or odor from household wood stoves. Neighbor complaints about smoke are treated as civil matters that local governments say they cannot handle. All they can do is "ask" users to burn well-dried wood, not to burn garbage or construction waste, to be considerate of the time of day and surroundings, and to clean their chimneys.^[21] With no emission standard for products either, which stove to choose and how to burn it is left to the user.

If you use a wood stove in densely built Tokyo, the lack of a Japanese standard does not mean anything goes. How much smoke you produce depends greatly on whether your firewood is well dried and whether your stove burns as cleanly as the US standard requires.

I have not confirmed guidance on wood stoves issued by the Tokyo Metropolitan Government or Tokyo's municipalities, or the number of complaints in Tokyo.

Sources

1. 東京都 木育関連リーフレット(令和5年度) PDF
2. コトバンク「大鋸」 Link
3. 日本スポーツ振興センター「国立競技場について」 PDF
4. 長野県林業総合センター 研究トピックス(接着重ね梁) PDF
5. 国土交通省 無電柱化に関する資料 PDF
6. 北海道立林産試験場『林産試月報』1981年4月号(クレオソート油処理木柱) PDF
7. 国土交通省 関東地方整備局 東京港湾事務所「江戸の港」(原典:鈴木理生『江戸の川・東京の川』ほか) PDF
8. 東京都港湾局「東京港のごみ埋立地盤の安定化調査について」(平成13年5月) PDF
9. 日立製作所「東京駅丸の内駅舎」(日立の技術誌Foresight) PDF
10. 日本建設機械施工協会『建設機械施工』Vol.66 No.5「新工法紹介 丸太打設液状化対策工法」(2014年5月) PDF
11. 林野庁「Forest Good 2015 間伐・間伐材利用コンクール」(丸太打設液状化対策&カーボンストック工法) PDF
12. 東京都「林業・木材産業循環成長対策 変更事業構想」 PDF
13. 林野庁『平成28年度 森林・林業白書』事例(檜原村 数馬の湯) Link
14. 環境情報センター(EIC)「首長に聞く」檜原村 Link
15. 江東区「緑のリサイクル」 Link
16. 大林組 ニュースリリース「大月バイオマス発電所の建設に着手」(2016年8月4日) Link
17. 大林組 ニュースリリース(2018年6月1日、大月バイオマス発電所の営業運転開始) Link
18. 米国環境保護庁(EPA)「EPA Certified Wood Stoves」 Link
19. ベイエリア大気質管理地区(BAAQMD)「Winter Spare the Air」(2024年11月30日) Link
20. EPA「Implementing Wood-Burning Changeout Campaigns and Examples of Programs」 Link
21. 柏市「家庭用薪ストーブの使用」(2026年1月16日更新) Link