Drought threatens fungi and forest ecosystems in Bavaria

Prolonged drought has left many forests with hardly any mushrooms, and recent rainfall has done little to change the situation, BR reports. The shortage is frustrating for mushroom foragers but could have far-reaching consequences for forests.

At Ammersee, the forest floor remains extremely dry. Christoph Hahn, a mycologist and chairman of the Bavarian Mycological Society, said it was therefore unsurprising that few mushrooms could be found. At this time of year, he would normally expect to see several typical species.

“I would expect the first brittlegills to be here,” Hahn said. Common summer mushrooms such as the broad-leaved funnel cap would also normally be found on dead wood. “And here there is absolutely nothing. Zero. That means the prolonged drought is clearly leaving its mark.”

Although it has recently rained, the moisture has probably not reached deeper layers of soil, Hahn said. “The ground is still completely dusty and hard. For now, it is just a drop in the ocean.”

Fungi face a double water problem

The effects are not limited to visible mushroom fruiting bodies. Underground, mycelia form extensive fungal networks that are an important part of the ecosystem. Many fungi live in symbiosis with trees. Through their connections with roots, they help plants absorb water and minerals and receive nutrients from the trees in return.

Fungi themselves also need sufficient moisture, particularly to produce fruiting bodies. “The fungi then have problems getting water from somewhere to form fruiting bodies,” Hahn explained.

On the forest floor, the mycologist found only a dried-out puffball from the previous year. The mycelium could still be present in the tree stump, he said, but it apparently currently lacks the energy to produce new fruiting bodies.

The absence of mushrooms does not necessarily mean that they have disappeared. The fungal network may still survive in soil or wood. Whether it can withstand the drought and later produce fruiting bodies again depends on how long and how severely the water shortage continues.

Uncertainty over the mushroom season

It is difficult to predict whether mushroom foragers will still find what they are looking for this year, or in which regions. The decisive factor is how severely the drought has damaged the mycelia.

“A mosaic is to be expected,” Hahn said. Mushrooms could still grow in soils that retained water and were less severely affected. In other areas, they could fail to appear altogether.

Recent rainfall could improve conditions, but a brief shower is not necessarily enough after a long drought. Many fungi can resume their development only when sufficient water reaches the soil and remains available there for a longer period. The situation could then change partly within just a few days.

Climate change could accelerate species loss

Hahn is even more concerned about the long-term consequences. In his observation, Mediterranean mushroom species are already moving into the region. They could fill gaps left by the disappearance of native species.

The main problem, he said, was the speed of climate change. “The number of these dry events per decade is increasing massively.” If the trend continues, nature may be unable to adapt quickly enough, potentially leading to increased species loss.

The issue involves more than individual mushroom species. Fungi are an important part of the forest ecosystem: they decompose dead wood, return nutrients to the cycle and maintain close connections with trees. Changes in fungal communities could therefore affect the entire interaction within the forest.

Mycologist rejects non-native tree species

Hahn said forests needed to be transformed quickly, preferably using native tree species that were better able to cope with changing conditions.

He opposes the idea of planting large areas with non-native species that are considered particularly drought-resistant. This could disrupt the entire interaction between fungi, bacteria, microorganisms and trees in the soil, he said.