Gardening in a Global Greenhouse
How will historic gardens survive climate change? Teams of researchers are looking for answers – and using historical records and modern measuring stations to do so.
Dec 18, 2017
Plants in Berlin enjoyed unusually good natural watering this past summer. In average years, though, flowers, bushes, and trees are already feeling the effects of climate change. The climate is warming, and the vegetation is growing thirstier. It needs more water, or it gradually dries out.
The process is affecting home gardens as well as historical parks, including the grounds of palaces and stately homes. But while hobby gardeners can simply replace some plants with others, landscape gardeners are facing serious problems. In historic gardens, the vegetation is part of an elaborately crafted ensemble that needs to be maintained as part of people’s cultural heritage.
How to prepare historic gardens for climate change has been the subject of study since 2014 for an interdisciplinary working group from the Berlin-Brandenburg Academy of Sciences and Humanities that involves numerous universities – including Freie Universität Berlin – and the Prussian Palaces and Gardens Foundation Berlin-Brandenburg. The “Historic Gardens in Climate Change” (Historische Gärten im Klimawandel) project focuses on four historic gardens where the effects of global warming are already apparent: Berlin’s Tiergarten; Babelsberg Park; Branitz Park, in the city of Cottbus; and Wörlitzer Park, in the state of Saxony-Anhalt.
It is a project that is truly dear to the heart of Professor Ulrich Cubasch, director of the Institute of Meteorology at Freie Universität. There are two reasons. First, parks are extremely important to a city’s climate and to those who live there. Second, the diverse perspectives adopted in this interdisciplinary project remind even an experienced scientist like him of just how complex natural habitats are
“If a large old tree suddenly dries out, many scientists also see a direct connection with climate change. On closer inspection, though, other factors also play a role, including soil conditions, watering, parasites, pollutants, and a whole host of others,” Cubasch explains.
He himself was amazed, for example, when soil scientists involved in the project showed him a sample from Babelsberg Park: There were a few centimeters of nutrient-rich humus on the surface, but underneath was nothing but sand. In Berlin’s Tiergarten, the layer of soil was even found to cover rubble from the postwar period. That is not exactly fertile ground even under normal conditions.
If there is climate-related stress on top of it, the vegetation can become sensitive and react negatively. In parks, there is also the added pressure due to use of the space: “Even just playing soccer can tear up the humus layer in a meadow,” Cubasch says. Bicycling is also an issue for parks, since unpaved roads and paths suffer from the traffic.
Paved paths could be a solution in the heavily used Tiergarten, but not at Babelsberg Park. The original, historic condition there is supposed to be reconstructed and maintained in as much accurate detail as possible, Cubasch explains. But what does that entail? During the period when Germany was divided, the border ran through the northern part of the park. Ecologically valuable biotopes such as strips of reeds developed in the border’s shadow.
Should they be removed now because they are not part of the original park design? The project also aims to strike a balance between the concerns of art history and historical preservation on the one hand and protecting biodiversity and urban climates on the other, Cubasch says. Paved paths would namely be more than just an aesthetic change. “Depending on their width, they can have the same effect on a park’s climate as a road.”
Cubasch and his team will spend the next few months developing a climate model for parks at Freie Universität. The route design and plantings can then be simulated on a computer before gardeners actually start to dig. Shade trees, for example, are likely to become increasingly important to city dwellers in the future. “It’s already about three degrees cooler in the Tiergarten now than in heat islands like Alexanderplatz,” Cubasch says. “But if too many trees are planted in the same area, they impede the movement of air, and the park gets warm and muggy.”
Cubasch can draw on an unusual trove of information for modeling purposes. Scientists in Berlin began keeping temperature records back in 1677. And the master gardeners who served prince-electors and kings kept regular notes of how parks and gardens were faring. The climate researchers are now feeding these historical data into the new climate model.
They are also using current measurements taken during campaigns that are being implemented by the Urban Climate and Health working group at Freie Universität under the leadership of Professor Sahar Sodoudi. Once the model is complete, it will be able to simulate the effects of various climate change scenarios and be applicable to other historical gardens and parks.
The scholars and scientists involved in the interdisciplinary working group hope to be able to identify a number of recommended actions as early as 2018, when the project is drawing to a close. Their findings might include things like which park plants will have an especially robust response to changes in climate.
This knowledge will be of limited utility, however, since the size, shape, and color of individual plants play an important role in a park’s overall effect. “Gardens were objects of prestige for royalty,” Cubasch says. “If an exotic tree was specifically imported at the time, you can’t just swap it for something else today.” Climate change, at any rate, was something no one was thinking about back then.
Prof. Dr. Ulrich Cubasch, Institute of Meteorology, Freie Universität Berlin, Email: firstname.lastname@example.org