The German forest of today is facing extinction
Climate Change, Monocultures and Mold Fungus: The Forests in Germany are in Trouble. For decades, deciduous and coniferous trees in this region have been suffering from the effects of extreme weather and provide a good feeding ground for pests. Forestry must and is changing, warn experts.
Gnarled oaks, light beech groves and deep, dark forests of spruce: The forests, which people now like to hike through during their vacation weeks, will not be around much longer, according to forestry experts. "People like to imagine the forest as it was in their childhood, but the forests are changing now," says Henrik Hartmann, head of the Forest Protection Institute at the Julius Kuhn Institute in Quedlinburg.
The trees are struggling with the effects of climate change. Heat waves, long dry periods, and storms weaken them. While the forest suffered under the extreme weather conditions of the past years, many pests such as insects and fungi profited from the rising temperatures. They drive the forest transformation forward, says Ralf Petercord, forest construction expert at the Forest Ministry in North Rhine-Westphalia.
Spruces: Larvae of the Pine Bark Beetle eat the bark layer
This is most noticeable in spruces. For centuries, forestry has relied on fast-growing trees, and monocultures have emerged - which in some regions, such as the Harz, have been a good food source for the pine bark beetle larvae since 2018. In some areas, there are hardly any old spruce forests left. Spruces have the highest mortality rate of all tree species.
"At least the high altitude areas of the German Middle Mountains were still considered safe, but even there, where it used to be cool and moist enough for spruces, the pine bark beetle is attacking stressed needle trees in large numbers," says Markus Kautz from the Forest Experiment and Research Institute Baden-Wuertemberg. Pure spruce forests could perhaps only survive in the rough high altitude areas of the Alps in the end.
Oaks: Two-pointed Oak Prachtbeetle
Almost half of the examined oaks showed a clear crown thinning in the latest forest condition survey. Such weakened trees are sought after by the Two-pointed Oak Prachtbeetle, whose larvae live under the bark like those of the pine bark beetle. In some regions, the beetle has already caused damaging stands of beech and oak.
"If oak forests are weakened, for example, by the oak bark beetle community, by flooding or something else, then the beetle can become a problem," says Dominik Wonsack, also from the Experiment and Research Institute Baden-Wuertemberg. "Then the trees can no longer defend themselves against the beetle." Then entire oak stands could die.
Beeches: Complex disease causes problems
Without human influence, forests in Germany would still be dominated by beeches. Currently, beech species account for 16 percent - but they often don't do well either. "At the end of the century, beeches will no longer be able to grow 30 to 40 meters high, the forests will become lighter and lower," predicts Hartmann.
In addition, the so-called beech complex disease causes problems that often occur after a heat or drought event. "It starts with cracks in the trunk and a mucus flow." Then the bark comes off, the wood rots, and various fungi and wood-boring beetles like the beech bark beetle appear. "We don't know one hundred percent what's going on", says Hartmann. It might be related to a bacterial infection.
Maples and oaks are affected by fungi
With maples, however, the enemy is known: the fungus Cryptostroma corticale. If it infects a tree, the bark peels off in a flat manner, and beneath it, a sooty black powder appears: Spores of the fungus. The so-called sooty bark disease was not even a topic among foresters ten years ago, says Hartmann, but now entire stands are affected. "That usually goes fatal for the tree."
Domestic maple stands have been severely decimated by the Ash Dieback. The cause is once again a fungus: False White Stagshorn (Hymenoscyphus pseudoalbidus). If it infects trees, shoots and branches die off, leaves wilt and dry out, the stem turns brown - eventually the ash tree dies. Recently, however, researchers at the Leibniz Centre for Agricultural Landscape Research (ZALF) have described a new idea in a study: They found a bacterium on healthy ash trees that can inhibit the growth of the fungus. Whether this works in practice is to be investigated. Equilibrium no longer functions
"Basically, trees defend themselves against insect and fungal infestation, and they do so very effectively", says forestry expert Petercord from North Rhine-Westphalia. "But the equilibrium between trees and other organisms often no longer functions." If it's too dry, for example, decay organisms can enter through the roots, or the tree doesn't have enough strength to produce defensive substances against chewing insects.
Petercord has given up on the ash tree, and he looks at beech and beech trees very critically. The development with the oak is also not good. "The main tree species are all going to lose ground", he is sure. Instead, other species have the chance to grow much more frequently in Germany: the hornbeam, for example, the quaking aspen, or also the elm.
Monocultures have no future
Experts know: Monocultures have no future. Pine forests have been converted to mixed forests for more than 30 years, as the Forest Stewardship Council explains. And elsewhere? Which trees should foresters plant now? "We need a variety of seedlings, because we don't know how it will climate-wise", says institute leader Hartmann.
All experts speak of a permanent mixed forest, in which young trees grow next to as many old trees as possible. Which species should be in it is to be tested, says Hartmann. "We can keep native tree species, but not everything that was native until the end of the century will still be native", says the scientist. That's why species from other regions are also in the spotlight. "These species should be viewed differently, not as foreign species, but perhaps as future native species."
A new European study involving the Thuenen Institute for Forest Ecosystems also comes to the conclusion that forests should be supplemented with trees from other regions in the future. In the report, there is talk of a "supported migration," where tree species are selected from remote regions because they are best adapted to the future climate. Trees planted today must eventually adapt to the climate in 100 years.
The impact of Climate Change on forest ecosystems is leading to an increase in pests, such as the Pine Bark Beetle, which are thriving in the warmer temperatures and weaker trees. This is particularly evident in spruce forests, which have seen high mortality rates due to these pests. (Climate Change, pests, spruces)
Education about the changing climate and the impact on forest ecosystems is essential to promote sustainable forestry practices. This includes understanding the role of monocultures in exacerbating the problem and the need for a diverse range of tree species to create more resilient forests. (Climate Change, Education, monocultures, diversity)
