Having Abandoned the Use of Herbicides in the Early 1980s, Fingrid Oyj, Finland's transmission system operator, controls the growth of vegetation on its rights-of-way (ROW) mechanically, at a frequency that varies between five and seven years. This vegetation management practice involves maintaining an area equivalent to 33,000 hectares (81,545 acres) in a geographical area of 338,000 sq km (130,503 sq miles).

Fingrid Oyj is a member of the Nordic electricity market and is responsible for the 110-kV to 400-kV transmission system that extends 14,000 km (8699 miles). As is common in many countries, one of the key reasons for opposing the construction of new transmission lines in Finland is that the ROW would create new corridors in forests, which would adversely disturb forest species. To meet this challenge, Fingrid Oyj has taken steps in the past decade to acquire scientific information on the impact of ROW on biodiversity and the procedures to adopt for ROW maintenance that would be most favourable for the natural environment.


Agriculture in Finland intensified during the 20th century, resulting in a rapid reduction of meadow areas and a decline in many meadow species. Regular clearance of vegetation from the ROW maintained by Fingrid resembled the traditional meadow management practice of mowing and pasturing.

In 2002, in response to Fingrid's initiative, the Finnish Environment Centre studied the significance of ROW as an alternative habitat for meadow plants and butterflies. The research results revealed that numerous plants and butterfly species that typically favoured lush and dry meadows were also encountered in the ROW. However, the favourable conditions within the ROW for meadow species were reduced by vegetation clearance that resulted in the fast growth of trees.


Studies have shown that ROW maintained at regular intervals are an important means of protecting some threatened species, as the area provides natural shielding. For example, small populations of the endangered butterfly False Heath Fritillary (Melitaea diamina) tend to inhabit ROW, using these areas as dispersal corridors, which reduces the risk of losing the species in the region.

This finding was further strengthened by a study conducted by the University of Helsinki that examined the impact of the heterogeneity of the landscape structure on the mobility behaviour of the Silver-bordered Fritillary (Boloria selene) butterfly in ROW. The results confirmed that ROW constitute a dispersal corridor for local butterfly populations.


Finland has an abundance of mires, or ditches, but most of them have been drained since the 1970s. Draining has led to a decrease in water levels, causing deterioration of typical mire vegetation and an increase in the growth of trees, which ultimately completely drains the mire. These changes in agriculture practices have led to the decline and, in some areas, the eradication of the butterfly species that previously inhabited the mires.

Fingrid sponsored the University of Jyväskylä to undertake a research study on the significance of vegetation clearance from ROW on the mire butterflies and flora in central Finland. Completed in 2004, the study assessed the impacts of ROW clearing on the occurrence of mire butterflies by comparing the species found in the cleared ROW with an adjacent uncleared control area and mires in pristine conditions. As a result of clearing, drained mires have remained moist, open and luminous in ROW; however, outside of these areas, mires have turned into forests of tall trees.

The research results confirmed that the number of butterfly species and butterfly population were the same, regardless of the state of the mires. In addition to mire butterflies, the research areas also were inhabited by other species of butterfly, whereas the control areas located adjacent to the ROW that had growing trees proved to be an unsuitable habitat for butterflies. Overall, these results indicated that the favourable conditions maintained by clearing the vegetation have enabled the continued existence of mire butterflies and mire flora in ROW.

The average number of butterfly species and individual butterflies in test plots located in ROW were much higher than in the adjacent control areas. As far as the number of butterfly species was concerned, ROW were actually better habitats than natural mires.

A follow-up study was performed in 2006 to 2008 to determine the optimum ROW clearing interval for maintaining the butterfly population. The results indicated that the optimum clearing interval should be every three to four years.


ROW provide a favourable nesting environment for many bird species that prefer low shrubbery and half-open ground. In 2002, Fingrid assigned one of Finland's leading ornithologists, Pertti Koskimies, to study bird species nesting in ROW in southern Finland.

The research locales were used for nesting by 53 different bird species, most of which were relatively common birds found in forests and thickets. According to the study, the nesting frequency of six bird species along the ROW was considerably higher than the average recorded in other Finnish habitats. In terms of their protection value, the most valuable species in ROW are the red-backed shrike (Lanius collurio) and the woodlark (Lullula arborea). The European Union Bird Directive identifies these two species as requiring particular attention, and a significant number of their total population in Finland is known to nest in ROW.

The suitability of transmission line towers for nesting by the common kestrel (Falco tinninculus), a small falcon, also has been studied in Finland by Fingrid's initiative in 2004.

In the mid-20th century, common kestrels were the most numerous falcons in Finland. However, the subsurface drainage of fields, use of control substances and other types of intensification of agriculture reduced the preying environments and preys of the common kestrel. In 2000, Finland classified this bird as an endangered species. Hence, the purpose of Fingrid's project was to increase the number of nesting common kestrels.

The field study undertaken by Koskimies involved the installation of 100 birdhouses installed on towers in six field areas in ROW in southern Finland. In year two of the study, nine pairs of common kestrels nested in the birdhouses. It now appears likely this number will increase as the common kestrels grow accustomed to their new type of nesting location.

In general, the nesting of birds on transmission towers is not a major problem in Finland. However, transmission towers erected in close proximity to lakes tend to attract gulls on the crossarms, polluting the insulators. In problem areas, Fingrid installs devices to prevent gulls from roosting on crossarms.


As a result of the research studies promoted and funded by Fingrid Oyj during the past six years, the transmission system operator has adopted a new policy for managing its ROW. The changes from past practice specify that in southern Finland, the interval between clearing ROW will be reduced from intervals of six to seven years to five-year intervals; in all other parts of Finland, the clearing of ROW will be reduced from intervals of six to nine years to five- to seven-year intervals.

Even though the growth of trees in mires is slower than on forest land, the same reduced clearing interval will be applied to mires, thereby completely clearing all vegetation from the transmission line ROW at the same time.

This change to the shorter clearance periods has not significantly increased maintenance costs, as the clearing work is now easier and there is no longer nearly as much of a need for urgent tree felling in advance of the normal clearing. The reduced clearing interval is naturally an advantage in terms of transmission system reliability, and it has reduced the need to regularly monitor the growth of vegetation.

The International Transmission Operations & Maintenance Study confirms that transmission line maintenance by Fingrid Oyj continues to be of the highest standard, even though the standards and policies for the vegetation management of ROW are environmentally friendly based on the results of field research studies funded by the utility.

Fingrid Oyj will continue to contribute to research studies focusing on the environmental impact of transmission lines, and it will enhance cooperation and information exchange with various authorities and organisations through a specific interaction forum established for this purpose.

Terhi Lensu (terhi.m.lensu@jyu.fi) works as a research scientist at the University of Jyväskylä in Finland. For her master's degree thesis, she studied the significance of ROW for mire butterflies and flora. The research work continues, now focusing on the role of ROW as a habitat for mire butterflies.

Ari Levula (ari.levula@fingrid.fi) is regional manager of Fingrid Oyj. During his 20-year career, Levula has been involved in developing maintenance management, inspections and vegetation handling for transmission lines including the related data systems. Levula has a bachelor's degree from the University of Jyväskylä and a forestry engineering degree from the Evo University of Applied Sciences, both in Finland.