The changing macromycete flora in the Netherlands

Changes in this century in the composition of the macromycete flora in the Netherlands were studied by a comparison of excursion reports, mapping of selected species, and repeated mycocoenological studies in permanent plots in forests. The three approaches show similar trends. Among saprotrophic macromycetes of forest litter only a few species show a significant increase or decrease, but most saprotrophic species of grass- and heath-lands are markedly decreasing, due to modern agricultural practice, notably the use of artificial fertilizers.

Lignicolous macromycetes are in general increasing, in particular parasitic species, an increase mainly ascribed to the ageing of forests. Among the ectomycorrhizal macromycetes not a single species showed a significant increase, but at least 55 out of 126 species showed a significant decrease. This decline is strongest among species exclusively, or mainly, associated with coniferous trees. At least 15 ectomycorrhizal species seem to have disappeared completely from the Netherlands. Natural forest development, changes in forestry and agriculture and collecting of carpophores are excluded as important factors effecting these changes. The decrease of ectomycorrhizal fungi is mainly attributed to acid precipitation and its effects on soil chemistry and the vitality of trees. However, the exact process is still unknown. Two hypotheses that may explain this phenomenon are discussed.