Forest Mushrooms Decreased by One Fifth Over the Past 15 Years

Since 2010, the distribution of forest mushrooms has declined, indicating changes in the health of forests in the Netherlands.

17-3-2026 06:30

Since 2010, the distribution of forest mushrooms has decreased. Between the mid-1990s and 2010, there was still an increase. Species that closely cooperate with trees, playing an important role in forest health (such as the fly agaric), saw their distribution area increase by about 80 percent between 1994 and 2010. However, these species have also declined the most over the past fifteen years. This emerges from new calculations by Statistics Netherlands (CBS) based on data from the forest mushroom monitoring network of Mushroom Research Netherlands.

This monitoring network, part of the Ecological Monitoring Network (NEM), counts 119 (of approximately 1,600) species of forest mushrooms in forests on sandy soils. Mushrooms are the fruiting bodies of fungi and grow from fungal threads (mycelium) that develop in soil, among leaves, or in wood. Because mushrooms quickly respond to changing environmental and climate conditions, they are good indicators of the quality of their habitat. How mushrooms fare says a lot about the composition and health of forests.

In the seventies and eighties of the last century, many species of forest mushrooms declined sharply. This was due to emissions of substances (sulfur dioxide, ammonia, nitrogen oxides) that acidify and fertilize the environment (water and soil) [1]. Environmental measures subsequently led to a reduction in emissions of these substances. This resulted in temporary recovery of forest mushrooms from the mid-1990s, mainly of nitrogen-sensitive species.

Uncertainty trend collaborators
(ectomycorrhiza)

Trend litter decomposers
(saprotrophic species forest floor)

Uncertainty trend litter decomposers
(saprotrophic species forest floor)

Trend wood inhabitants
(parasitic and saprotrophic species)

Uncertainty trend wood inhabitants
(parasitic and saprotrophic species)

Three groups of forest mushrooms

Forest mushrooms have three important roles in the forest and are therefore divided into three groups: litter decomposers, wood inhabitants, and collaborators.

The “litter decomposers” (saprotrophic species of the forest floor), such as the large and small stinkhorn, break down dead plant material, such as leaves that have fallen on the forest floor. This group of mushrooms increased by an average of 15 percent between 1994 and 2004, but decreased between 2004 and 2024 to 85 percent of the distribution in 1994.

Wood inhabitants stable after earlier increase

Wood-parasitic fungi, such as the tinder fungus and birch polypore, live at the expense of living but often already weakened or old trees and plants, and can slowly make them sick and cause them to die. Once a tree is dead, there are mushrooms that break down the dead wood, the so-called wood-saprotrophic species. These two groups of “wood-inhabiting” forest mushrooms (the parasites and saprotrophic species) increased by more than 25 percent between 1994 and 2010, but then decreased again to about the 1994 level.

Collaborators of the forest

Collaborating fungi (ectomycorrhiza), such as the fly agaric and chanterelle, grow around the fine roots of trees and exchange nutrients and water for sugars produced by the tree through photosynthesis. These fungi promote tree growth while also benefiting from this symbiotic relationship. After an increase of about 80 percent between 1994 and 2010, this group then declined again. However, the distribution of this group of forest mushrooms in 2024 was still about 35 percent higher than in 1994.

Collaborators most sensitive to environmental changes

The “collaborators” (ectomycorrhiza species) increased from 1994 onwards, partly due to a decrease in nitrogen emissions from agriculture and the largely disappearance of acid rain. Within this group of forest mushrooms, two groups can be distinguished: nitrogen-sensitive (the majority of species) and nitrogen-tolerant species. Nitrogen-sensitive species increased by 136 percent between 1994 and 2010. After that, there was no further decrease in nitrogen deposition, and these forest mushrooms strongly declined again (dry summers played a role). The distribution of nitrogen-tolerant “collaborators” remained almost unchanged during this period.

Uncertainty trend nitrogen-tolerant species

Trend nitrogen-sensitive species

Uncertainty trend nitrogen-sensitive species

(1994=100)

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