Challenges of planted forests and the introduction of the Ohashi road network

In Japan, more than 40% of forests have been converted to planted forests through expansion of afforestation. However, due to the decline in timber prices, an increasing number of forests are being left in disrepair due to poor management.

The development of work roads is essential for the regeneration and sustainable use of these forests. However, until now, most forest roads in the country have been paved with concrete, which is expensive and in harmony with nature.

In this respect, the Ohashi road network is a method of building paths without using concrete, which reduces the impact on nature while also making it less likely to break down and can be constructed at low cost.

Kosuge Village introduced this method in 2007 and has achieved inexpensive and durable road network maintenance.

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Expanded water spreading method: harnessing the power of nature

The Ohashi method of road networking observes the natural terrain and makes the most of its power. According to Dr Keisaburo Ohashi, the instructor, the strongest and most stable place in the mountain is the 'ridge'. Therefore, the road network takes a route that climbs all the way up to the mountain ridge (ridge line) and selects a path with a gentle slope.

Dr Ohashi also talks about the importance of observing how water flows during heavy rainfall, saying that problems occur when people and water gather. If water concentrates in one place, it can scrape the ground and cause landslides, so paths are designed to be lower on the valley side to disperse the water as it flows. The method based on this idea is known as the 'water spreading method'.

Mechanism and potential of the Ohashi road network

The distinctive feature of this road network is its simple and functional design, which follows the natural topography.

 The main road is routed over a rounded, flat and stable ridge, and makes use of hairpin bends to reach the ridge at a stretch. The branch lines that extend from there are built horizontally along contour lines and are designed to be resistant to collapse even on slopes.

Branch lines are designed to pass through topographically stable areas known as 'tanas'. This is a point on the map where the contour lines are slightly wider apart, and is a relatively calm and safe point on the slope.

Such a structure is the result of Dr Ohashi's years of observation and practice of nature at Ohashiyama, which he owns in Chihaya Akasaka Village, Minamikawachi County, Osaka.

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Reforestation and sustainable management with the Ohashi style road network

Working on the steep slopes of the mountain is demanding and dangerous, and this has been a contributing factor to the neglect and degradation of the forest. The owners of the mountains in Kosuge Village have also given up on road maintenance because they believe that putting a road on a slope destroys the mountain.

However, with the Ohashi road network, it is possible to construct a work road at a density of 200 m per ha, which can be used by a 2-tonne truck, at a low cost. As one person can carry out everything from felling to transport, this also extends the working age of the workforce in the ageing forestry industry. For Kosuge Village, where 95% of the village is forested, the introduction of this method is a major step towards regeneration.

Low-cost reforestation and sustainable environmental improvement with the Ohashi road network

The Ohashi road network is based on a road width of 2.5 m and a cut height of 1.4 m (the height of a human shoulder). As the paths are built on steep slopes, the shoulders need to be well reinforced.

To this end, the road is constructed by laying logs as a foundation, nailing horizontal timbers on top of them at 1 m intervals, stacking logs for earth retaining, and covering them with soil to harden them. A typical forest road in Kosuge Village would have cost about 250,000 yen per metre, whereas the Ohashi road network can be constructed for about 7,000 yen per metre. As paths are cleared, light pours in, grass grows on the slopes, and eventually bushes and shrubs grow up. The forest, which was once an artificial forest, is gradually transformed into a rich forest with a diverse ecosystem.

The future of forestry regeneration guided by Ohashi's road network and nature observation

Dr Ohashi says: ""The state of the inside will always appear on the outside. See nature as it is. If you look at a mountain and see that it is round, calm and thick, the inside is also stable. If the mountain is steep, sharp, crooked, sharp, thin or disturbed, it is unstable and not good"".

When he actually visited Kosuge Village, he went up and down the site again and again to check the road network in order to decide where to put it through. We were really deeply impressed by his sincere attitude.

The use of trees can bring back vitality to headwater villages. However, until now, trees have remained unused because there was no way to transport them out of the area even after they had been cut down. The Ohashi road network has shown us the means to overcome these challenges.

We hope to spread this initiative to other areas that have similarly given up on forestry regeneration, and eventually develop it into a nationwide movement.

Exemplary forestry in Japan - winner of the Emperor's Trophy at the Agriculture, Forestry and Fisheries Festival

Ohashiyama Forestry was awarded the Emperor's Cup at the 1993 Agriculture, Forestry and Fisheries Festival for its exemplary forestry work in Japan.

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Beautiful sea and mountains, rich in nature Kaizuka

The timber from Kaizuka, Osaka, comes from 100-year-old forests in the foothills of the Izumi-Katsuragi Mountains and beech forests, which are a national natural monument.

 Kaizuka has been known as a 'forest country' producing timber since the Nara period (710-794), and it is recorded that when the high priest Gyoki built 49 temples in the Kinai region, including Suima-ji Temple, timber was provided from the domain of the imperial family, the Tachibana family, Mount Soma.

Kaizuka is also a sacred site of Katsuragi Shugendo and is registered as a Japanese Heritage Site. The cedar timber used in this project was also taken from one of the sites, BUTSUNENZAN FUDOTAKI.

The forests nurture mudflats and a beautiful marine environment, and the Kaizuka coastline was the first in Osaka Prefecture to receive the international environmental certification 'Blue Flag Beach' in May 2024.

 Furthermore, the ""Kaizuka Project Connecting the Sea and the Mountains"" is working to nurture the next generation.