Long tree-free alleys that run through forests are known as aisles. Since the wind blows unchecked through these aisles, they are mainly known to motorists for strong crosswinds. In addition, if they have been artificially created, forest aisles also have an infrastructural benefit or serve as a protective measure and habitat for many animals and plants. However, some aisles are created due to natural processes.
Naturally created forest aisles
If a storm or tornado sweeps through a forest, it is referred to as a storm lane: The trees are knocked down, usually in a straight line. Avalanches can also strike such alleys through the forests. Since, unlike the artificially created ones, they are not cleared, the forests are freed from storm wood and cleaned up after such natural influences.
This is necessary, among other things, to prevent pest infestation by bark beetles. This creates space for new things, and the forest can recover and grow again. New tree species that are more climate-resistant are also being planted, for example in the Bernese Forest.
Artificially created forest aisles
The clearing of alleys through the forests is accepted for the construction of power lines, paths and roads, cable cars, for drawing borders and for the timber industry. Since the awareness for the preservation of valuable habitats and the encroachment that humans have on nature has grown in the meantime, a careful and sustainable approach is insisted on. Aisles must not run through biotopes that are worth protecting, but should bypass them. In addition, the measures are to be limited to the required level. Compensatory and replacement measures such as afforestation can be carried out elsewhere.
Before clearing takes place, extensive planning and environmental impact assessments are made. Protests by the local population and by nature conservationists also call for compromises and proposed solutions. The Thuringian Forest is an example of this.
Since power lines must be free of vegetation, the aisles are regularly maintained and cleared of emerging vegetation. Here, too, more sustainable processes are used; the aisles are no longer mulched to the ground, but bushes are left standing up to a certain height.
In this sense, pipes built higher are more advantageous than lower ones, but lead more often to protests due to the change in the landscape. Often, aisles can even be an enrichment for biodiversity if they are cared for in an environmentally conscious manner. The construction measures are seen as more problematic, as they are initially characterized by noise pollution and the destruction of the vegetation, the soil and the small animals living in it.
Further forest aisles still exist today due to the former course of the inner-German border and further borders with neighboring countries.
The so-called return paths or back alleys also contribute to the formation of forest aisles. They are used for forest operations to transport felled trees to paved roads. While horses were used for this in the past, the logging routes are now necessary for modern machines and vehicles.
Forest aisles for fire protection
Fire protection is an important function of forest aisles. Since the combustible material, ie trees and bushes, is removed over a distance of several meters, the fire in a forest fire cannot spread over this strip or only to a limited extent.
Firebreaks thus form an effective barrier and are mainly used in areas with a high risk of forest fires to protect surrounding forests and settlements. Active fighting of a fire that has already broken out is also possible with this method. Other firebreaks are rivers, mountain ridges and wide roads.
An example of this type of fire prevention is the fire protection corridor around the Ruppiner Heide. The former bombing site is surrounded by other forests and villages. Should a fire break out within the heather, it would be difficult for it to spread across the aisle.
Forest aisles – danger or habitat for flora and fauna?
As already described, the clearing of aisles through the forests is an intervention in the ecosystem, which in the first instance goes hand in hand with the destruction of what already exists. As soon as infrastructural measures are taken, further hazards arise, whether from power lines with which birds collide and from which animals are deterred, or roads whose traffic poses a potential hazard. Aisles also represent barriers for animal species in the dense forest, whose habitat is thus limited.
Since many aisles already exist, it is particularly important to keep them as usable and environmentally friendly as possible through appropriate management. They represent ecological niches for flora that could not prevail in the forest area, and animals that live in low vegetation under warmer and lighter conditions. This includes, for example, the sand lizard.