Workshop Developing natural forest edges in electrical corridors to ensure electrical safety and to enhance biodiversity in wooded areas

Vegetation management is a key issue when dealing with electrical safety of high-tension lines crossing forest areas. In order to avoid any problem, most Transmission System Operators (TSO) proceed to regular vegetation cuttings. These operations are costly and they impact landscape and biodiversity.

As an alternative to the regular vegetation destruction, the LIFE Elia-RTE project implemented 7 different methods to manage vegetation in a more biodiversity-friendly way. During 6,5 years, this project is implemented in Belgium (along 155 km of lines) and France (7 sites) to combine electrical safety and biodiversity. The project is financed by the European Commission, Elia (Belgian TSO), RTE (French TSO), and the Walloon Region.

The most important method concerned structured forest edges on both sides of the forest corridor created by the high-tension line, shifting from a U-shaped corridor to a V-shaped corridor.

The methodology followed depended on the presence of indigenous species in the surrounding forests. If they were present, the LIFE Elia-RTE project proceeded by selective felling into spontaneous vegetation : removing problematic trees (those with height at adult age that will threaten electrical conductors : oak, beech, birch, poplar…), and keeping low-height bushes and small trees (those with final height at adult age that will not threaten electrical conductors : hawthorn, hazel tree, cranberry bush, cornelian cherry dogwood) in favor of biodiversity. If there were no indigenous species in the surrounding forests, which happen sometimes in production forests, forest edges were planted. Plantation scheme was the following one : plantation every 1,5 m in a row, and having 2 m between each row. A soil preparation was carried out before plantation to make it easier. Indigenous species used were selected on several criteria : final height at adult age (below electrical conductors), potential for biodiversity and resistance to wild game grazing.

In total, 171 ha of structured edges have already been either restored or planted during the project, while the objective to reach is 210 ha. These edges are contributing to the ecological network by offering a biodiversity corridor for plants, insects, birds, bats… Their great interest lies in the fact that they are a transition between the forest and the grassland in the center of the electrical corridor.

For the Transmission System Operator, implementation of edges means less work in corridor, and therefore less costs. Long-term management of these edges is undertaken by selective felling of problematic trees, while indigenous low-eight bushes are promoted. The foliar surface of these bushes will end up covering the soil and making it very difficult for a problematic tree to develop in these shadow conditions.

But these edges also benefit to local stakeholders such as forest managers, landowners or hunters. Surrounding forests are more protected to strong winds, wild game find food in edges and the boarder trees have a better commercial quality. Compared to the bare land left after regular felling, edges offer a better impact on the landscape by softening the transition between forest and corridor, and by showing colors during flowering period.

Feedbacks on technical solutions to install and manage these edges will be developed, as well as their interests for all stakeholders.

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Electricity transmission, vegetation management, biodiversity, innovation, local stakeholders, forest corridors, biological and economical monitoring, Europe.