In a declining oak forest, a thinning treatment was performed in August 2004, targeting trees belonging to two decline classes. The whole ectomycorrhizal (EM) community was dominated by the fungal symbionts Clavulina cinerea, Tomentella sublilacina and Russula spp. The potential activities of eight secreted enzymes, involved in mobilizing nutrients (N, P) from soil organic matter, were measured on these three EM types in winter and spring 2006 using multiwell microplate photometric and fluorogenic methods. The enzymatic activities recorded in winter were generally significantly higher than in spring. Most of the enzyme activities studied, and particularly phosphatase and b-glucosidase, changed according to both decline class and sylvicultural treatment. In spring, each anatomotype displayed different enzymatic profile according to the decline class. These results suggest that the potential enzymatic activity of ectomycorrhizae adapts to the changes resulting from the sylvicultural treatment and reacts to the anthropic disturbance by adjusting to the new resource structure. 2007 Elsevier Ltd. All rights reserved.