Netherlands loses one-fifth of forest fungi in 15 years after decades of growth

Forest fungi populations in the Netherlands have dropped by a fifth over the past 15 years. The decline follows a period of growth in the 1990s and early 2000s, when many species expanded significantly. Now, some groups have fallen back to levels last seen in the mid-1990s, while others remain above their original numbers despite recent losses.

Between 1994 and 2010, wood-inhabiting fungi—including parasites and saprotrophs—saw a sharp increase of over 25 percent. Litter decomposers, like the common stinkhorn, also grew by around 15 percent during the same period. The most dramatic rise came from nitrogen-sensitive symbiotic fungi, which surged by 136 percent in that time.

Symbiotic species, such as the fly agaric, expanded by roughly 80 percent before 2010. But since then, their numbers have fallen steeply. By 2024, they still sit about 35 percent higher than in 1994, though far below their peak. Nitrogen-tolerant symbiotic fungi, however, have stayed largely stable throughout the changes. The broader decline has been linked to factors like increased nitrogen deposition and dry summers. Wood-inhabiting fungi, after their earlier growth, have now returned to levels similar to those of 1994. Litter decomposers, once thriving, have dropped to just 85 percent of their original distribution.

The overall drop in forest fungi marks a reversal of earlier gains. While some nitrogen-tolerant species have held steady, others—particularly nitrogen-sensitive and symbiotic types—have suffered the most. Current data does not pinpoint specific causes for the decline, nor does it provide comparisons to earlier decades beyond the recorded changes.