Recently, it has become increasingly common to find birds and butterflies on clearcuts, species that normally thrive in areas such as hayfields and field margins. Among the species found, several are currently struggling in the agricultural landscape. To delve deeper into the potential of clearcuts as habitats for certain species, LU Land and BECC organised a breakfast seminar on the topic. The text below is a summary of the seminar.

When grasslands disappear and clearings take over

The EU indicator for grassland butterflies, which touches on our Swedish environmental objectives, shows that there has been a sharp decline in butterflies in Sweden and Europe since the 1990s. This is also confirmed in the latest report from The Swedish Butterfly Monitoring Scheme. The decline is mainly due to changes in land use. When cultivated land disappears, fields, meadows and pastures are converted to forest and arable land is used more intensively, this leads to fewer habitats for these animals. At the same time, clearcuts have become more prominent in the landscape, replacing to some extent the dynamic between temporary open fields and the continuous forest that used to exist. Clearcuts might then act as temporary grassland habitats for species that thrive in grasslands. How well this works depends on various factors such as:

• The historical land use at the site of the clearcut.
• The composition of the landscape where the site is located.
• The species present in the surrounding region.
• The availability of food, host plants and habitats in and around the clearcut.
• The size of the clearcut.

Clearcuts as habitats for butterflies 

Many factors come into play when it comes to how well a clearcut functions as a habitat, and the question is whether it is possible to facilitate the species that have begun to utilise the clearcuts as temporary habitats? To better understand this, a Formas project and a doctoral project at Lund University have investigated when, where and why the temporary habitats of clearcuts attract groups of animals that otherwise thrive in the agricultural landscape. Lars Pettersson, Associate Professor and responsible for Swedish Butterfly Monitoring Scheme, was invited to talk about the results of these studies: 

- Generally speaking, for birds the availability of nesting sites is most important, while for butterflies the dynamics between the host plants of the larvae and the plants from which the adult butterflies seek nectar are important.

In her project, Dafne Ram, a former biology PhD student at Lund University, inventoried butterflies on 120 clearings in Skåne and Dalarna. The results showed that there are large amounts of butterflies and a lot of biodiversity on these clearings, including all Swedish indicator species for agricultural land and 75% of the grassland species. What mattered most for the attractiveness of the clearcuts as a habitat was:

• The age of the clearcut - the younger the better before the vegetation starts to grow tall. The greatest number of butterflies are found in the clearcut a few years after felling. 
• The proportion of open habitats in the landscape, such as neighbouring agricultural land and newer clearings. The more open areas - the more species.
• The size of the clearcut had negative effects in the centre of the clearcut but not at the edges. This is partly because the climate in the centre of the clearcut becomes more extreme.

- The conclusions we can draw from this are that newer clearings can be functional habitats for some butterfly species. But since clearcuts are only suitable habitat a few years after they appear, the butterflies must have good dispersal ability to find them soon after they have appeared," says Lars Pettersson.

Clearcuts a complement in a changing landscape

Emma Sandell Festin is a forest manager at the Skånska Landskap Foundation. They manage forests on several properties around Skåne. The preservation and development of biodiversity is one of the goals of their forest management, along with goals for recreation, climate adaptation and production. To achieve these goals, Emma identifies a number of important factors in the practical management of the forest. For example, it is important to favour flowering trees and shrubs, to create woodland edge environments and to fence in the plantation when decidious forest are established to bring up species that are otherwise attractive to grazing.

But what about clearings more specifically - what efforts can be made to favour biodiversity? Emma Sandell Festin gives the example of a 23-hectare forest stand approaching felling in northern Skåne:

• Plan the size and location of the clearing so that it contributes to the creation of a mosaic landscape. That way, the species favoured by a clearing have a future in the landscape and can move to other areas if needed. 
• Divide the clearing into smaller parts, of 1-3 hectares, and wait about 3 - 7 years between each clearing.
• Replant small forest stands with different tree species; mixed forest, plant broad-leafs in fences. It will be a nice forest with good production. 
• Different tree species allow different amounts of light to reach the ground, which affects the ground flora. 
• It is important to promote deciduous trees along roads and watercourses.
• Create woodland edges. However, these require maintenance.

- There is a great variety of what forest owners can do for biodiversity with fairly simple means. And doing these types of measures does not preclude you from still having a production forest. So I would say that  clearcuts can favour certain species - absolutely! But it may require a little more planning than we are used to," says Emma Sandell Festin.