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Victims of summer heat: All the spruce trees in Bonn city forest are nearly dead

Victims of summer heat : All the spruce trees in Bonn city forest are nearly dead

The condition of the trees in Bonn's city forest seems to be more dramatic than previously thought: According to a status report given to the city council by the administration, it will take years to cut down all the dead trees.

Attentive walkers, joggers or cyclists will hardly recognize the Bonn city forest in the near future: Even here in Bonn, advanced climate change with increasingly extreme weather conditions has left a damaging mark. So many trees are already dead or dying that the forestry department will only be able to secure the forest areas near paths, roads and neighboring properties in the coming months. It will take several years to cut down all the dead trees, the city administration relayed in a status report to the city council.

Within three years, the administration's assessment has reversed itself dramatically. In 2018, city forester Sebastian Korintenberg used restrain in an interview with GA. Speaking about the condition of Bonn's forest, he said at the time, "Fortunately, we don't have to worry hugely about that." There will be the one or other tree dying from the dry conditions, he said. "But in general, our forest is very well adjusted to our regional climate and can survive a longer dry phase as well as a longer period of freezing weather.”

600 pines and about 200 beech trees were cut down

The reality seems to be different in the spring of 2021. Those who appreciate the forest as a source of peace and recreation are often disturbed by the noise of chainsaws in these weeks. As can be seen in the city administration's document, the equivalent of more than 600 pine trees and about 200 beech trees have fallen victim to the climate crisis. This corresponds to about 1,000 and 750 solid meters of wood, respectively. Douglas firs, larches or birches are also affected, adding another 750 solid cubic meters. While the beech trees mainly suffer from the drought, the pine trees are also affected by Diplodia fungus, which the declining trees cannot fight off. According to the forestry department, the spruce population from the post-war period, which accounted for five percent of all trees, is now completely dead. The trees have been unable to reach water-bearing layers in the soil with their shallow roots during the past extremely dry years. The bark beetle did the rest. The figures are all the more drastic because the city forest, with 610 hectares, accounts for only 15 percent of the forest area in the city.

According to estimates by the administration, the situation will continue to worsen in the coming months. "The pine is dying rapidly at the moment on partly sandy soils. In addition, drought damage is increasingly occurring in beech trees and birch trees," it says. Douglas firs, hemlocks or larches are also shedding huge amounts of needles in some cases. It is uncertain whether or not such bare trees can recover permanently.

Foresters try to limit damage

The city foresters really have no choice but to limit the damage. In these weeks, they are out and about on the numerous roads stretching through the forests, marking diseased or dead trees for felling. Time is pressing, because dying beech, sycamore or birch trees could drop dry branches at any moment and hit passers-by. It will take several years to remove all the dead trees in the 35-meter corridor on both sides of the paths, parking lots and buildings. For the city, this also means an economic loss. "Timber marketing is not possible here for the most part, as much of the wood cannot be sold right now due to fungal decay and low-quality assortments," warns the forestry administration. Add to that, right now there is an oversupply of wood from other forests in Germany. In 2020, however, 885 solid cubic meters of pine wood and 106 solid cubic meters of deciduous tree wood were sold as firewood. Over 800 cubic meters of unsaleable residual wood remained in the forest as deadwood. Among other things, it serves as a breeding ground for insects and, in the future, as fertilizer.

The city administration said it had already adapted its subsequent plantings in 2017 in coordination with the Naturland Association for Organic Farming. It aimed to plant species adapted to the location and to a significantly changing climate. In 2018, city forester Korintenberg told the GA that massive reforestation would not be necessary, with a reference to sustainable forest management. The forest should be able to rejuvenate itself, he said. The extent of the damage in the following years forced a rethink. By the end of March, 23,000 new trees had been planted in the damaged areas. How many of these will survive will only become clear in a few years. Even in normal years, only 80 percent of the seedlings survive on average. They are particularly sensitive to heat stress.

Orig. text: Martin Wein

Translation: ck