The German forest is doing badly: Among other things, dry phases and pollutants put a strain on the trees. In addition, more and more forest is being cleared for agriculture, transport and industry, says Ute Eggers, consultant for bird protection at the Nature Conservation Union (Nabu). On top of that, soils would be compacted. In the meantime, another factor has come into play: forests are becoming more important as a location for wind energy.
Wind turbines have been established on agricultural land since the 1990s. Other suitable locations at a sufficient distance from settlements are rare. Nevertheless, the installed capacity of onshore wind turbines should double in the coming years, according to a central goal of the federal government. The Wind-on-Land Act, which came into force on February 1, stipulates that at least two percent of the area in each federal state will be available for wind turbines by 2032.
The range in the non-city states is currently between around two percent in Schleswig-Holstein and 0.2 percent in Baden-Württemberg. Forest-rich federal states in particular should now increasingly rely on wind turbines in the forest. According to the Wind Energy Agency, there were almost 2,300 wind turbines in wooded areas at the end of 2021, accounting for a total of eleven percent of the capacity installed on land.
Modern wind turbines could also be erected in low mountain ranges and foothills, says the managing director of the German Wind Energy Association (BWE), Wolfram Axthelm. Southern Germany in particular offers a lot of potential for this.
But conservationists warn that regulations for species protection would be undermined for expansion in the forest. Can climate protection and species protection in the forest be reconciled at all? Nationwide, forest takes up a third of the area, says Marie-Luise Plappert from the Federal Environment Agency (UBA). This large area should not be ruled out for wind energy because "it gives you leeway".
On average, half a hectare of forest is cleared for each wind turbine. Nevertheless, the construction is worthwhile in terms of climate protection: even in the first year after construction, such a system saves many times over in CO₂ equivalents. In addition, for the wind energy no higher quality forests with centuries-old deciduous trees would be used, but rather low-quality stocks, says Plappert. In some cases, forest areas damaged by storms or beetle infestation are also used.
The decisive factor for plant operators is the so-called wind potential - the average wind volume - at a location, explains BWE Managing Director Axthelm. A species protection check is also part of the approval process. "Landscape protection areas can be included in the search for areas for wind energy expansion," the federal government expressly states on the Wind-on-Land Act.
According to Axthelm, it is often stipulated in the approval process that trees must be planted elsewhere to compensate for a deforested area. The authorities made sure that not only conifers were planted, but that there was an appreciation of monocultures.
However, at least initially, new plantings cannot fully fulfill the ecological functions that make the forest so important, counters Nabu expert Eggers. She refers to forests as habitats that are important for the climate, water balance, oxygen production and air filtration.
Every system changes a forest, emphasizes Eggers: the soil is compacted, many species are disturbed and driven away by the noise of the construction work, among other things. Bats, owls and woodpeckers could lose their roosts during deforestation. A finished system can act as a barrier, reduce habitats through avoidance behavior and deteriorate their quality over long periods of time.
And: Again and again, birds and bats collide with rotor blades. For bird species, the risk of this depends, among other things, on physique, position of the eyes and behavior, explains Eggers. A red kite, for example, looks intently at the ground when looking for food and often does not recognize the systems in time. Rare species are also affected by collisions - such as large, long-lived birds that have relatively few offspring a year. Deaths are more difficult to cope with in such species than in species with frequent and numerous offspring.
BWE Managing Director Axthelm points out that wind turbines are becoming increasingly large, especially in regions in southern Germany with less wind and also in forest regions, with hub heights of up to 220 meters. This reduces the risk of collision, especially with low-flying species. Nabu expert Eggers disagrees that it cannot be said in general that higher wind turbines are generally associated with a lower risk of bird strikes. Birds of prey, cranes and pigeons, for example, mostly fly at altitudes of more than 50 metres.
Some bats also live primarily in forests. For example, noctule bats (Nyctalus noctula) often fly close to wind turbines when they are near their daytime roosts, as Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research explains. These quarters are central habitats and the bats are particularly active there.
According to the law, the systems are currently operated with strict shutdown requirements in the first two years of operation in order to minimize the risk of bats being struck. For example, during the high summer months, operations are stopped at night due to certain environmental factors, such as special temperatures and wind speeds. Bats only become more active above a temperature of ten degrees Celsius. In contrast, their flight activity decreases significantly at higher wind speeds of around five meters per second (equivalent to 18 kilometers per hour).
In the first two years, according to Voigt, the operator can record the activity of bats in the vicinity of a wind turbine using ultrasonic detectors in the nacelle - i.e. the machine house at the height of the hub. Improved switch-off criteria can then be derived from this for the following years, which should better protect the bats with optimal use of wind energy production. “Depending on the location and the type of system, the energy loss due to switch-off devices is generally 1 to 4 percent of the annual energy yield,” says Voigt.
In many federal states, there are no criteria as to how far away systems have to be from bat roosts. In his opinion, a minimum distance of 500 meters would make sense. This not only reduces the risk for the animals, but also for the temporary shutdowns, which reduce the energy yield and thus the profitability of the systems.
The so-called "Helgoländer Paper" gives recommendations for distances for birds. According to the paper published by the state working group of bird sanctuaries (LAG VSW), systems should maintain a minimum distance of ten times their height from bird sanctuaries. They should therefore be at least 3000 meters away from white-tailed eagle eyries and 1000 meters from seagull breeding grounds.
The expansion of wind energy is necessary in order to make progress with the climate goals, emphasizes Nabu expert Eggers. However, it must be done in an environmentally friendly way and cause as little damage as possible. Because at the same time as the climate crisis there is also a crisis in biodiversity - i.e. a great loss of animal and plant species.
Bat researcher Voigt advocates for compensation areas: A study on noctule bats has shown that the animals avoid places with wind turbines beyond their day roosts. So they lose living space – which has to be recreated elsewhere. According to Voigt, a corresponding proportion of the forest should be removed from human use and left to nature conservation.
"Aha! Ten minutes of everyday knowledge" is WELT's knowledge podcast. Every Tuesday and Thursday we answer everyday questions from the field of science. Subscribe to the podcast on Spotify, Apple Podcasts, Deezer, Amazon Music, among others, or directly via RSS feed.