Foliage changes color too early: drought is the death sentence for some beeches

Tree leaves typically turn brown, red, and yellow in the fall before falling.

Foliage changes color too early: drought is the death sentence for some beeches

Tree leaves typically turn brown, red, and yellow in the fall before falling. In recent years, beeches in particular have already lost their leaves in summer. What does this mean for the trees?

The leaves of many beech trees have changed color too early this year and have fallen from the trees. For some of the trees, this is a death sentence, experts say. The reasons for the early loss of green color are therefore heat and drought. It's not the first year this has happened. "We have been observing this damage since 2018, primarily in central Germany," said Gitta Langer from the Northwest German Forest Research Institute in Göttingen.

It is a so-called beech vitality weakness, which the research institute is currently researching. Among other things, southern Lower Saxony and northern Hesse as well as some regions in southern Hesse, Saxony-Anhalt and Thuringia are affected. In addition to the foliage, the trees also lose branches in the treetops and bark.

The heat and drought of the following years would have increased the severity and spread of the damage, Langer said. The occurrence of the damage depends "very much on the location and the water storage capacity of the soil," explained Christian Ammer, Professor in the Department of Silviculture and Forest Ecology in the Temperate Zones at the University of Göttingen.

As a result of the disease, increasing infestation by beetles and fungi such as the coin-shaped bark ball fungus has been observed in beeches since 2019, as reported by the Lower Saxony State Forests, among others. Both young and old trees are affected. The fungus causes a soft rot, which ultimately means that the affected beeches are no longer stable and unbreakable, said Langer.

The scientists were not able to provide concrete figures on the extent of the beech vitality weakness in Germany. One indication are recently presented figures from the Swiss Federal Research Institute for Forest, Snow and Landscape (WSL). According to this, up to 10 percent of the beech trees that discolored and shed their leaves in July 2018 died within three years.

The WSL observed 830 trees that had shed their leaves too early and 139 that kept their leaves until autumn. Trees in low-precipitation regions and on dry soil were particularly affected.

According to the WSL, the loss of leaves and branches in beech trees continued to increase after 2018, even though they received little water in the years that followed. Ultimately, many of them died. Accordingly, beeches on wetter soils recovered in the following years. "The shedding of the leaves is therefore not to be interpreted as a protective mechanism for the tree to better survive the dry season, but as a sign of weakness," explained one project employee.

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