Responsible Forestry: Modular Bridge for Stream Crossing

Tomorrow’s Forest is about more things than reforestations. For our common future, we need to protect existing forests and the communities who depend on the nature’s benefits – air, waters, biodiversity, and the timber from the trees as well. The first project in the sustainable forestry programme of the Foundation is a mobile, modular bridge, designed to improve forest infrastructure and to protect mountain waters.

We build a bridge over the river Tarnava Mare

When the mist lifts, in a late October morning, we needle our way through the woods in Harghita Mountains.

We arrive at Zetea Forest Management Unit, where we’ll witness the first wooden modular bridge built with support from Tomorrow’s Forest Foundation.

The purpose of the bridge is to protect a stream often crossed by forest machinery. “The forest management unit is FSC-certified, like most of Romania’s forests,” says project manager Kádár Tibor-Sándor, an engineer at the Zetea FMU. “Forest certification includes an important criterion – protection of the waters that are frequently crossed by forest roads.”

Crossing the riverbed with heavy machinery and timber dragged by the tractor is forbidden by law. The machines and logs undermine the banks, they dislodge rocks and sediments on the bottom and produce turbidity. The water becomes muddy, unfit for animals and plants living there as well as human consumption.

“Streams and rivers are amongst the most vulnerable terrestrial ecosystems,” says Demeter László. A biologist, he manages the National Agency for Protected Areas (Harghita County). „In the mountains there are hundreds of species associated with these habitats. We have to consider both the aquatic environment as well as the riparian habitats, the areas adjacent to the banks.”

We follow the forest road until we get to a stream less than two meters across. To our surprise, we find out it is the Tarnava Mare River. “We are about three kilometres from its source,” says András Róbert, manager of the Zetea FMU.

Wiggling between rocks, Tarnava Mare flows rapidly to the Zetea dam – the water source for tens of thousands of homes in Harghita and Mures Counties.

After taking a few measurements, we begin unloading the modular bridge.

Locally produced modular bridge, from sustainable materials

The bridged was built using local materials by a company in the village. “The technical project was designed by the professors at Transylvania University of Brasov,” says Ionut Apostol, executive director of the Tomorrow’s Forest Foundation. “The production itself was supervised by Zetea FMU, and they will continue testing it on the ground.”

The prototype is composed of 20 spruce beams, 6 meters long. The wood is not treated with chemicals, to prevent releasing toxins in the water. The only parts that are not biodegradable are the metal rods and bolts which ensure the bridge is sturdy. It supports loaded machinery with a mass of up to 10 tonnes!

The bridge is easy to move about. It is composed of three modules which can be sandwiched on the truck and are fast assembled. Including minor banks reinforcing and levelling, the installation and the first crossings with the articulated tractor took less than two hours.

“I like it a lot,” says with a big grin András Róbert, president of the neighbouring Nicolesti Composesorate, who is closely watching the project. In the meantime, the articulated wheeled tractor passes the bridge a second time. The bridge shows no signs of dislodging or deforming under the heavy load.

“It’s a very important project,” says Mr. Andras. “On the long term, these bridges can preserve everything – how we work, the nature around us, it’s a very good thing and very, very important. We all need this kind of projects.”

Apart from protecting waters and biodiversity, such a bridge is useful for the companies who offer forestry services. It helps to maintain the machinery in good conditions. This means reduced costs for repairs and increased efficiency.

And, when the works are done in a specific area, the bridge can be disassembled and moved to the next plot.

The alternative: concrete tubes who change the water flow

Despite that all around the world such bridges have been used for decades, modular wooden bridges are still rare in Romania. The most frequent water crossing solution deploys concrete tubing in the waterbed, just like gutter crossings near roads.

But these tubes are not environment-friendly at all.

On the one hand, at each freezing and defreezing, they deteriorate and slowly release chemicals in the water.

On the other hand, the tubes change the water flow such that local wildlife is impacted, quite severely. “These tubes have smooth surfaces that change the water speed,” explains biologist Demeter László. “Thus, the waterbed is eroded below the tube and steps are created, which are unpassable by the smaller species of fish. Trout can jump quite high, but for other species such obstacles are too difficult, and ecological problems ensue.”

There are about ten species of fish in the area, says Demeter László. All travel surprisingly long distances in the breeding season, to lay their roe in the cleanest waters.

“With this project, we help protect the water and biodiversity,” says Ionut Apostol. “At the same time, we support forest owners and managers, as well as forestry companies who aim to reduce their environmental impact when performing various forest services.”

Do you want to support the sustainable forestry programmes of Tomorrow’s Forest Foundation? Send your ideas for projects at or consider making a donation: for every 5 lei you donate, we plant a seedling!

The modular bridge helps protect waterways and biodiversity, but also benefits forestry companies