Boreal forests and peatlands are shaped by hydrological changes caused by both human activity and natural processes. In a recent study carried out in the Evo area in southern Finland, researchers examined how forestry drainage and beaver-induced flooding have transformed the landscape over the past 60 years. They combined historical maps, aerial imagery from different decades, current geospatial data and long-term field observations.

The study showed that between 1963 and 2023, the ditch network almost quadrupled in size and the proportion of drained peatlands increased from 23.8% to 72.5%. The substantial expansion of the ditch network reflects a long-term shift towards drier conditions.

The study also assessed, for the first time, the total extent of areas flooded by beavers in the Evo area. Altogether, 77 active and previously flooded sites form a wetland mosaic covering approximately 1.4 square kilometres. At the landscape level, drainage is clearly a more extensive hydrological change than beaver activity; locally, however, beavers create new wetlands and re-establish wetter conditions, particularly along the edges of bodies of water.

“A historical analysis helps us understand the scale of long-term changes occurring in the wetland landscape. At the same time, it provides an important basis for assessing how the environment may develop in the future,” says University Lecturer Sonja Kivinen of the University of Eastern Finland.

Historically, beavers have formed part of Finland’s boreal forest landscapes and, following introductions, they have also returned to the Evo area, where their landscape-shaping impact has gradually intensified.

“The results suggest that beavers can contribute to wetland restoration by re-establishing natural hydrological processes in drained landscapes. Beavers have the advantage of being able to re-establish wetter conditions without active restoration measures, which are often costly,” says Senior University Lecturer Petri Nummi of the University of Helsinki.

“Previous international studies have also shown that beaver ponds in headwater areas act like sponges, as wetlands generally do. They retain water and gradually release it downstream. In a changing climate, this may help mitigate the effects of events such as heavy rainfall and periods of drought.”