Dutch forest fungi boom and bust leaves scientists puzzled

Dutch forest fungi have seen sharp changes over the past three decades. While some species expanded rapidly in the 1990s and early 2000s, their numbers have since dropped back to earlier levels—or worse. New data reveals a mixed picture of growth followed by decline across different types of fungi.

Between 1994 and 2010, wood-inhabiting fungi—including parasites and saprotrophs—spread by more than 25 percent. However, their distribution has since shrunk to roughly the same levels recorded in 1994. Symbiotic species, such as the fly agaric, saw an even bigger rise of around 80 percent in the same period. Yet their numbers have also fallen since then.

Nitrogen-sensitive symbiotic fungi experienced the most dramatic shift. Their distribution surged by 136 percent up to 2010, only to collapse in the years that followed. Litter decomposers, like the common stinkhorn, expanded by about 15 percent between 1994 and 2004. But by 2024, their presence had dropped to just 85 percent of their original 1994 range. Overall, forest fungi populations have declined by a fifth over the last 15 years. Current research does not pinpoint specific causes for the drop in symbiotic species within Dutch forests. While drought stress has been linked to declines in mycorrhizal fungi in agricultural settings, no direct evidence ties this to forest ecosystems in the Netherlands.

The latest figures show a clear reversal in forest fungi trends. After years of expansion, many species have returned to—or fallen below—their 1994 distribution levels. The reasons behind these shifts remain unclear, leaving researchers with unanswered questions about the future of Dutch forest ecosystems.