Lake Cerknica is one of the largest intermittent lakes in Europe and a true natural gem of Slovenia. Its unique flooding and drying dynamics attract numerous naturalists, photographers, nature lovers, and other visitors each year. However, preserving this natural treasure requires careful and thoughtful management.
Why do we mow Lake Cerknica?
When the water recedes from the surface of the Cerknica Plain and remains only in underground cave systems and a few springs, vast areas of wet meadows, kravine (traditional mown pastures), and dense reedbeds are revealed. On the edges, there are also large areas of bogs and other wetlands, which are among the most endangered habitats in Europe and are rarely found elsewhere.
The landscape as we see it today is the result of long-standing human activity, especially mowing and grazing. Without this, much of the Cerknica Plain would gradually be overgrown by floodplain forest. Mowing at Lake Cerknica has a long tradition, as locals have always carefully managed their meadows and maintained an open grassland ecosystem. In the past, this was done with scythes and horse-drawn equipment; today, it is done with motor mowers and tractors.
Over time, as agriculture declined, mowing became less frequent, leading to the overgrowth of some parts of the lake. As a result, certain bird species that depend on open landscapes have begun to disappear.
What do we gain by mowing Lake Cerknica?
Mowing helps prevent the overgrowth of grassland areas, which would otherwise gradually turn into forest—a natural process known as ecological succession. By mowing, we maintain vital habitats for bird species such as the Corncrake, Eurasian Curlew, and Common Snipe, as well as butterflies like the Meadow Fritillary and the Dusky Large Blue, along with many other organisms.
In addition, mowing influences the structure of the habitat, creating a mosaic of open areas and hiding places. This affects the behavior of both predators and prey, including species not directly dependent on meadows. The result is a dynamic landscape with alternating mown and unmown patches, which supports greater biodiversity.
Why is it essential to leave some areas uncut?
Hedgerows, groves, riparian strips, forest islands, individual shrubs, and other such structures are crucial elements of a preserved cultural landscape. Although they may be considered undesirable in some respects, it is important that they remain part of the ecosystem. Certain species, such as the red-backed shrike, are dependent on such habitats, and Lake Cerknica is the only area in Slovenia where this bird regularly nests. Uncut areas provide refuge for hares, grasshoppers, butterflies, birds, and many other animals. These zones offer shelter during mowing and in the colder part of the year when mown meadows no longer provide enough cover.
Uncut vegetation at Lake Cerknica is also important for successful fish spawning and amphibian breeding, as they hide their eggs and spawn in it. The riparian reed beds offer protection from predators and shade the water surface to prevent overheating.
The Importance of Proper Mowing Planning – The Value of a Mowing Mosaic
Not all meadows are the same. Many different species, including endangered ones, require different management approaches. It is important that mowing is carried out only once, or at most twice a year, and without fertilization. In some dense reed stands, mowing should be completely abandoned.
One of the key measures is late mowing, after August 1st, which allows the corncrake and other species to successfully raise their young. However, this timing negatively affects the dusky large blue butterfly, which lays its eggs on the flowers of the marsh gentian at that time. For this species, early mowing in June is more suitable—but that, in turn, is not appropriate for the corncrake.
There are many such conflicting situations, which is why it is important to apply different management approaches and a well-thought-out plan to create a mosaic of life that will preserve the rich natural heritage of Lake Cerknica with pride.
*“Kravina” is a local term for communities of tall sedges, which are the dominant plants at the lake and can easily be mistaken for meadows by the untrained eye.
The note was prepared by Rudi Kraševec, biologist at Notranjska Park.
