Dutch forest fungi face collapse after decades of recovery and new threats

Forest fungi in the Netherlands have seen dramatic shifts over the past three decades. Between 1994 and 2010, many species thrived as pollution controls took effect. But since 2010, their numbers have fallen sharply, with some groups now at their lowest levels in years.

From 1994 to 2010, symbiotic fungi—species that form close bonds with trees—expanded by around 80 percent. This growth came after cuts in agricultural nitrogen emissions and the near-disappearance of acid rain. Among them, nitrogen-sensitive types like the fly agaric surged by 136 percent in the same period. Meanwhile, nitrogen-tolerant species stayed largely stable.

Wood-inhabiting fungi, including parasites and saprotrophs, grew by over 25 percent in those years. Litter decomposers, such as the common stinkhorn, also spread by about 15 percent between 1994 and 2004. But the trend reversed after 2010.

Since then, symbiotic fungi have dropped steeply, though they remain roughly 35 percent higher than in 1994. The most sensitive species have suffered the worst, collapsing due to rising nitrogen pollution from farming and traffic. Dry summers, particularly from 2018 to 2022, worsened the decline. Soil acidification, clear-cutting, and forest fragmentation have also played a role, according to studies by CBS and Wageningen University.

Litter decomposers have fared no better. By 2024, their distribution had shrunk to just 85 percent of their 1994 levels. Wood-inhabiting fungi, after their earlier gains, have now returned to numbers last seen in the mid-1990s.

Overall, forest fungi populations have fallen by a fifth in the last 15 years. The losses reflect a mix of pollution, climate shifts, and land-use changes. While some species still exceed their 1994 numbers, the downward trend continues to threaten woodland ecosystems.