SUCCESSION OF ECTOMYCORRHIZAL FUNGI IN ROADSIDE VERGES PLANTED WITH COMMON OAK (QUERCUS-ROBUR L) IN DRENTHE, THE NETHERLANDS

In the period 1986-1988, sporocarps of ectomycorrhizal fungi were counted in 53 plots in roadside verges planted with common oak in Drenthe, The Netherlands, belonging to three vegetation types. Twenty five plots were Hypochaeris radicata-Quercus communities, comprising roadside verges in open landscapes on dry, acid, sandy soils, poor in nutrients. In each plot, the trees were even-aged but varied between 10 and 140 years. The relationship between tree age and numbers of ectomycorrhizal species and sporocarps was studied. The species composition of roadside verges was compared between young trees (10-20 years), medium-old trees (20-50 years) and old trees (50-140 years). The species composition in roadside verges in open landscape with old trees was also compared with the ectomycorrhizal fungi in two further different types of roadside verges with old oak trees, viz the Anthriscus sylvestris-Quercus type, comprising open to half-open plots on soil richer in nutrients, and the Mnium hornum-Quercus type, comprising shady plots surrounded by forest. The data reveal a distinct succession of ectomycorrhizal fungi with increasing tree age. The results are compared with data on succession of ectomycorrhizal fungi in forest stands. It is concluded that the succession cannot be modeled simply as suggested by some authors. Instead, changes in species composition and diversity showed much variation in relation to different environmental conditions. The factors relevant to the course of ectomycorrhizal succession are discussed. The concepts of early- and late-stage fungi are critically considered. It is concluded that this classification is not appropriate for the description of the ectomycorrhizal succession during stand development. A new, provisional classification of ectomycorrhizal fungi on the basis of their appearance during forest succession is proposed.