Deposits of airborne nitrogen and sulphur have decreased in recent years. Yet, wild mushrooms have become increasingly rare in Dutch forests since 2000. Nitrogen-sensitive species in particular have been reduced in number. Wild mushroom species insensitive to high atmospheric concentrations of nitrogen or species responding positively to high amounts of nitrogen have not been reduced at such a fast rate.
Many mushroom species on the brink of extinction
There are about 3,500 mushroom species in the Netherlands. Approximately 500 species are under (serious) threat and figure on the so-called Red list. Nearly 200 species have already become extinct.
Mushrooms are quite useful. They break down organic matter and produce nutrients for trees. If certain mushroom species become extinct, the chances of survival for other plants and animals are also diminishing.
High pollution levels
Eutrophication and acidification are the main causes for the declining mushroom population. Since 1981, the level of pollution has dropped dramatically, but the mushroom population has not thrived in the period 2000–2006. The current level of pollution appears to be still high for mushrooms in comparison to their natural habitat. Moreover, the pollution levels have hardly dropped in recent years.
The quality of soil life in forests is still not back at its prior level. As a result, mushrooms and plants cannot benefit fully from the reduction in deposits of eutrophying and acidifying substances.
Increase and decrease of mushrooms
Soil disturbance and accelerated vegetation growth also cause deterioration. Since 1999, major disturbances were detected in 25 percent of measuring points in the Counting grid. The soil is frequently disturbed by digging, driving with heavy equipment, dumping of mud and manure and scattering of wood chips. Most disturbances permanently or temporary lead to higher concentrations of nitrogen in the soil.
Lodewijk van Duuren (CBS) and Mirjam Veerkamp (Nederlandse Mycologische Vereniging)