Relationship between presence of basidiomes, above-ground symptoms and root infection by Collybia fusipes in oaks

Collybia fusipes is a common cause of root rot on oak in the north of Franc e. Collybia fusipes basidiomes can be as frequent on oaks in stands where n o decline of the trees occurs compared with stands where the decline is chr onic. This might be explained by differences in the amount of roots damaged by the parasite. To test that hypothesis, 430 oak trees, Quercus petraea, Quercus robur and Quercus rubra, six forests were selected. Half of them sh owed C. fusipes basidiomes at the trunk base. The association between prese nce of basidiomes and decline of affected trees depended on the forest. The level of infection of each tree by C. fusipes, as well as the crown appear ance, the tree height:diameter at breast height ratio, age and sapwood widt h were determined. The presence of C. fusipes basidiomes was always associa ted with significant root infections. The crowns of the trees deteriorated with increasing level of root infection and the decline was severe only whe n the root damage was heavy. Although the decline of trees that were heavil y damaged by C. fusipes was severe in some of the stands, in others, it was only mild, and so the differences in tree decline between the stands could nor be attributed solely to differences in root infection severity. Trees damaged by C. fusipes seemed not to be subjected to more competition than t heir undamaged neighbour as reflected by a similar tree height:diameter at breast height ratio.