Berlin is so proud of its trees that it named its most elegant boulevard after them -- Unter den Linden (Under The Lime Trees). But a succession of dry, hot summers followed by cold winters has taken its toll on the indigenous limes and chestnut trees, many of which now have disturbingly brown leaves.
Local politicians and scientists attribute the problem to global warming and have responded with a pilot project to bring new species to the German capital -- species which are normally at home in far hotter climates in southern Europe and Asia.
"We are trying to come up with alternatives to our trees," Matthias Zander from the Faculty of Agriculture and Horticulture at Humboldt University told SPIEGEL ONLINE. The university has planted more than 56 species of trees from various geographic regions in a southern suburb of the city to analyze whether they are better able to weather the German weather.
The trees are far from home and include the Daimyo oak and the Magnolia tree which thrive in Japan and South Korea. The so-called Judas tree lives in Greece and Spain. The species also include the manna ash from the Russian island of Sakhalin and the North American horse apple.
"Extreme situations are becoming more and more common," Zander said. If the trees are weakened by the weather, they can't protect themselves against pests and man-made hazards such as pollution. That in turn affects humans because trees absorb CO2 and release moisture in to the dry city air.
Chestnuts Suffer Most
Among the indigenous German species, the chestnut tree has paid the highest price for climate change, Zander said. But lime trees, which are the most popular among Berlin landscapers, are also suffering.
The newcomers, 800 trees in total, were raised in nurseries all over Europe. The Berliners have 15 trees from each species to experiment with. The resilience of the trees will be tested by giving five of them as much water as they desire, five only the minimum they need to survive; and the remaining five will be watered even less to see how they cope with extreme dryness.
But their ability to withstand the unfamiliar cold of a Berlin winter will be equally important."The crunch point will be whether these trees can also cope with the low winter temperatures," Zander said.
The first results and recommendations will be released when the project under the auspices of the Innovation Network of Climate Change Adaptation Brandenburg Berlin, which was founded one year ago, ends in 2014.
Despite the rising temperatures in Berlin, residents will not have to rename their favorite street to Unter den Palmen (Under the Palm Trees) anytime soon, said Zander. "They aren't winter-resistant enough."