Tree death in German forests continues

Tree death in German forests continues

Beeches with crown thinning and drought damage. © Petra Dühnelt/ Thünen Institute

The German forest is still doing badly: According to the current forest condition report, only 20 percent of all forest trees are healthy, the treetops of all others have thinned to a greater or lesser extent. Although 2021 was less hot and dry than previous years, forests and soils have not recovered sufficiently. All the main tree species in the forest are affected, but the spruce continues to have particularly high mortality rates, as the report shows.

How is the German forest doing? Since the mid-1980s, this question has been regularly examined with the help of forest condition surveys. For this purpose, specially trained experts examine the condition of the crowns of the forest trees every year from mid-July to mid-August in sample areas systematically distributed over the entire forest area in Germany. An important indicator for assessing the condition of the tree is crown thinning, which indicates the deviation from a healthy tree with full needles or full leaves. From 25 percent one speaks of a clear crown thinning. The Thünen Institute for Forest Ecosystems examines the raw data provided and uses it to calculate the nationwide results. These are compiled in the annual forest condition report.

Highest level of damage since the surveys began

The Forest Condition Report 2022 has now been published – and it does not bring good news. Because the condition of the German forests has not improved. “Although there was no significant deterioration in the proportion of damage levels across all tree species compared to the previous year, the level of damage is still at the highest level since recording began in the 1980s,” said Federal Minister of Agriculture Cem Özdemir, summarizing the results.

According to the forest condition report, the positive effects of the somewhat rainier weather in 2021 were not sufficient to sustainably improve the condition of the forest after the three years of drought from 2018 to 2020. Despite the favorable weather in some regions of Germany, the soil’s water reservoir could not be completely refilled after the dry period, as the Thünen Institute for Forest Ecosystems explains. In addition, the year 2022 was again too dry and warm and there were three winter storms in quick succession in spring 2022. They knocked down many weakened trees and caused large areas of damage and more deadwood in the forest. This in turn increases the risk of pest infestation of the trees.

Older trees and spruces are particularly affected

Specifically, the survey showed that around 35 percent of all forest trees in Germany have a significantly thinned crown of 25.9 percent on average. Only every fifth tree is without a warning level and can therefore be considered healthy. Older trees over 60 years old are particularly affected: 42 percent of them show significant damage. Of the trees younger than 60 years, only around 15 percent have significant damage, but according to the forest condition report, their condition has also shown a negative trend over the past few years. According to the forest condition report, the poor condition affects all four main tree species: spruce, pine, beech and oak.

With 29.6 percent, the mean crown thinning of the spruces is at a similarly high level as in the previous year. At the same time, however, the mortality rate for this common forest tree rose to a new record of 4.4 percent in 2022. The spruce is dying off extensively at lower altitudes below 700 m, as reported by the Thünen Institute. The main causes are the drought of recent years and the bark beetle infestation. Damage to the second conifer among the main tree species, the pine, has also increased significantly. A sad record was set in 2022 with an average crown defoliation of 23.8 percent. Since the start of the forest condition survey, there have never been so few pine trees without visible damage as this year. In the case of beech and oak, little has changed compared to the previous year. Their average crown defoliation is 27.5 and 26.9 percent.

Cause is multifactorial

But what can be done to save the forest? The cause of the forest dieback in the 1980s was relatively simple: the acid rain caused by air pollutants caused the soil to acidify and damaged the trees. When the guidelines for keeping the air clean and exhaust gas values ​​were tightened, air filters and “first-aid measures” such as forest liming brought about a significant improvement. However, the current forest dieback has more complex causes. On the one hand, the trees suffer from climate change and the associated extremes of heat and drought. On the other hand, nitrogen inputs from traffic, industry and agriculture also affect them.

This means that today it is much more difficult and time-consuming to help the forest. On the one hand, it is important to limit the further progression of climate change through climate protection and at the same time to convert the forests so that they are more resilient. To achieve this, more tree species must be grown or planted that can withstand longer periods of drought and heat waves. However, this is complex and takes decades. On the other hand, it is necessary to reduce nitrogen inputs, for example by reducing excessive fertilization and by stricter limitation of nitrogen oxide emissions from traffic and industry.

Source: Johann Heinrich von Thünen Institute, Federal Research Institute for Rural Areas, Forests and Fisheries; Forest condition report 2022

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