Technische Universität Berlin

Race Against the Clock

Drought stress is causing countless trees to die. Climate change requires the transformation of German forests into stable mixed woodlands

Birgit Kleinschmit loves the forest – the coolness it provides in summer, the long walks in fall. But now, whenever she walks through the woods, her brow is furrowed with concern. “Countless trees are dying in German forests. The current situation represents an unprecedented disaster,” explains Kleinschmit, forestry researcher at the Chair of Geoinformation in Environmental Planning at TU Berlin. “285,000 hectares have already died, an area three times the size of Berlin.” At the start of 2020, minister for food and agriculture Julia Klöckner appointed Kleinschmit to the federal government’s advisory council for forestry policy. Kleinschmit is one of 15 experts from German universities and institutions advising the federal government on creating the right conditions for a sustainable management of forests and how to adapt them to the climate change.

“We can now clearly see the effects of climate change on German woodlands,” says Kleinschmit. “Storms, drought, an increase in the number of forest fires and huge levels of bark beetle infestation are the prime causes for this disastrous situation.” Precipitation is increasingly shifting from the growing season, which is itself on average becoming longer, to the winter months. Temperatures are rising and during episodes of high rain, water quickly flows off rather than simply trickling away. The soil is increasingly drying out, groundwater levels are sinking and trees no longer receive the water they require. Indeed the drought stress suffered by trees over the past three years has created the perfect conditions for bark beetles and other pests. In many places, it is now having an unexpectedly severe impact, not only on conifers, but also on deciduous trees such as beech and birch, which were previously considered resistant. “An example of this is provided by the Harz Mountains. With its hills and summits covered with dead trees, it offers a sad picture of our native woodlands. Dying trees rob many businesses of their livelihoods and result in large areas being abandoned. Additionally, high costs and the risk to the lives of forestry workers posed by falling deadwood mean that these dead trees cannot be removed from large areas of forest.”

Forests cool the atmosphere, provide drinking water and a place where people can experience nature

The problem is well documented as forests provide important ecosystem services. They store CO2, produced by wood, provide high-quality drinking water and cool the atmosphere. They also provide an environment where people can come to experience nature and relax, play an important role in maintaining biodiversity and provide work for one million people in Germany.

The Federal Ministry of Food and Agriculture is currently developing its “Forest Strategy 2050” report. This already includes a number of wide-ranging proposals from the forestry advisory council about how to adapt forests to climate change. The goal is to create forests that are not only productive, ecologically stable and able to withstand the growing challenges of climate change, but also capable of continuing to fulfill their various functions at current or even higher levels in the future. Particularly important is that the conifer monocultures which so dominate are transformed into mixed woodlands to reflect climate change. The expertise of the members of the advisory council reflects the full range of demands placed on woodland by society. The council is made up of experts from the areas of soil science, hydrology, forest and animal ecology, biodiversity, forest economics, wood science, resource-efficient construction, nature and climate protection, and forest monitoring. Among them is Reinhard Hüttl of the German Research Centre for Geosciences Potsdam.

Vegetation plays a key role in the entire hydrological cycle

The interests of property owners are also reflected in the projects - around half of all woodland in Germany is privately managed. One third belongs to the federal states, 19 percent is owned by local governments and bodies, and four percent is the property of the federal government. “All forest owners are equally confronted with the major challenge of reforesting German woodlands at a time of climate change,” says Kleinschmit in her role as the advisory council’s expert for geoinformation and woodland monitoring. Vegetation is the key interface between the soil and the atmosphere and plays a central role in the entire hydrological cycle. For a number of years, our academic chair at TU Berlin has been working on monitoring the condition of vegetation, and we have set up many projects in this area.”

Satellites, drones and special cameras measure heat and moisture levels

Researchers use modern remote sensing techniques to monitor heat and moisture. Using satellite observations and drones with sensitive thermal and hypersprectral cameras, data are collected on the conditions of both forests and open country as well as on the evaporation of water suffered by leaves, trees and soils. As an example of this, the “Urban Water Interfaces” research training group uses remote sensing data to calculate the water and energy exchange between soil, vegetation and atmosphere in Berlin using machine learning and physical-based modeling. Elsewhere, Kleinschmit’s “Cosmic Sense” research group is exploring the potential of cosmic neutron rays and a variety of remote sensors to calculate soil water content.

Developing an analysis software

The “FIRsT2.0” and “TreeSatAl” projects started this summer at TU Berlin are among the most far-reaching joint research projects on forest damage in Germany. Three million euros have been made available to fund the two projects. Birgit Kleinschmit is speaker of the “TreeSatAl” project. Working with partners from universities and non-university institutions, the project is developing a software to provide forestry and conservation with a precise, continuous analysis of the condition of woodlands and the type of damage they are experiencing. Artificial intelligence (AI) also has a role to play here. Thousands upon thousands of items of data, including data provided by the National Forest Inventory, social media data bases and drone operations are used to train AI algorithms. These will then be able to use satellite data to automatically recognize tree species and the condition of forests, thus providing an extensive and revealing picture. TU Berlin’s AI and remote sensing expert Professor Dr. Begüm Demir is also involved in the TreeSatAI project.

Transforming Berlin’s forests

Drought stress has also plagued forests in Berlin in recent years. Woodland accounts for one fifth of the city’s total area. “Some parks have even had to be closed off due to risk of injury as a result of falling branches,” explains Birgit Kleinschmit. The forests around Berlin are dominated by pine trees and penetrate into the city like the arms of an inverted star, with the most woodland to be found in the boroughs of Reinickendorf, Spandau, Zehlendorf and Köpenick. The Berlin forestry commission (Berliner Forsten) has been working for some time now to transform these pine monocultures into stable mixed woodlands, so as to improve the water supply, further develop the natural management of the forests and help them adapt to the requirements of climate change. The forestry commission calculates that an area of forest the size of Tempelhofer Feld (formerly Tempelhof Airfield) needs to be rejuvenated each year and transformed into mixed woodland if the targets for transformation for 2050 are to be met.

“None of us knows where things are leading. But despite all the problems, this disastrous situation does present us with a chance to quickly transform our forests into multitalent woodlands,” concludes Kleinschmit on an optimistic note. A race against the clock.

Original publication

This text originally appeared in German on 29 November 2020, in the Tagesspiegel newspaper TU Berlin supplement.

Author: Patricia Pätzold