This paper analyses earthworm communities distribution in relation to humus structure and vegetation dynamics in the sylvigenetic cycle of a subnatural mountain spruce forest. Observations come from the Extern North Alps. The earthworms reaction to vegetation changes was studied using two scales of investigation-the eco-unit scale and the tree scale. The sylvigenetic cycle was represented by a 200-m- long transect including the four main developmental phases of the forest (innovation phase, aggradation phase, biostatic phase and degradation phase). Fifteen plots were investigated on the transect. In each plot, a humus profile was described. Earthworms were collected by spraying formaldehyde on each plot. The opération was reapeated three times . The results showed, on one hand, a strong heterogeneity of earthworms distribution within the developmental phases of the forest (eco-unit scale). On the other hand, on the plots, it is observable that earthworms distribution and the age of trees are connected (tree scale). Therefore, earthworms reaction to vegetation dynamics appears strongly at the scale of the trees, whereas worms distribution seems to be more dependant of the abiotic conditions at the eco-unit scale.