Wood-destroying fungi find the best conditions after wet summers – old giant trees in the botanical garden are felled
Trees in the city are under stress due to their unfavorable locations. Fungal attack also inhibits their vitality. In Styria, too, the rainy, humid summers of recent years have contributed to better conditions for wood-destroying fungi. Even the trees in the Botanical Garden of the University of Graz are not spared these consequences, as its director, Christian Berg, told the APA.
It is around 100 years old, has a mighty trunk around 15 meters high and an imposing treetop – but the last hours of the American hackberry tree – one of the oldest trees in the Botanical Garden of the University of Graz and now popular street tree in cities – are numbered. For years it has been attacked by the ash tree sponge, a dangerous tree pest. The parasite has now decomposed a large proportion of wood inside and formed several fruit bodies.
“When you see the mushroom body, it is already too late, removing it is of no use, because the mushroom is inside,” explained the Graz botanist. “I was hoping that I would not experience it, but the care measures can no longer prevent the felling, as the stability of the tree is no longer guaranteed,” said the head of the botanical garden with concern. It doesn’t help that the colleagues in other European botanical gardens are doing the same and report about climate-related failures of their giant trees.
“In the last few decades, tree deaths have increased, especially in urban areas,” reported Berg. According to the Graz experts, longer periods of drought and temperature rises are a problem for the plants, but the wetter summers of recent years, as in previous years, also offer the fungi the best growing conditions. Fungi then have an easy job with very old or already heavily stressed trees.
Peter Bohn, head of the tree protection department of the city of Graz, referred to the multitude of harmful influences that weaken trees: “Winter road salt, smoke gas emissions, compacted soils. The more the trees are affected, the easier it is for the fungi to close the trees settle.” Fungal infestation also occurs again and again in the street trees in Graz, but no clear tendency towards an increasing fungal infestation has been determined so far.
In view of the multitude of stress factors in the city of Graz, when it comes to new plantings, the path of diversity is in any case: “The more feet you stand on, the better you stand,” says Bohn. With many native tree species, however, you are no longer on the safe side in urban areas. “Unfortunately, it is the case that they can hardly meet today’s road requirements. Sycamore maple, for example, is sensitive to salt,” added Bohn. When it comes to replanting, for example, pagoda trees, gleditschia, a new breed of elms that are resistant to the pathogen causing Dutch elm disease – or the hackberry tree, which is considered to be climatically resistant.
In the Botanical Garden, the old hackberry tree has also been provided for offspring: the gardeners have already continued to cultivate seedlings in advance and replacement plantings are being carried out at a suitable location. The remains of the old tree will be used for research: In particular, the large number of lichens and mosses that colonized the tree will be recorded.
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