The increasing timber demand and the spreading mechanization of forest operations in France have led to call into question the sustainability of forest soil management. Indeed soil compaction following heavy traffic often causes lasting physical degradations that strongly influence other soil properties related to the ability of a site to sustain forest productivity. Two experimental sites were designed in the North-East of France to study the changes of soils after mechanized forest harvesting, on the short and the long-term. These sites are representative of highly sensitive soils to compaction. They present the same general functioning (Neo-Luvisol), but they differ on some physical (strength, bulk density, clay content and mineralogy) and chemical (pH, chemical saturation) properties. As soil deformation under intense stresses at the soil surface induces changes of voids volume, size and connection, it may impact heat, water and gas transfer and biological activity. All of these perturbations are supposed to alter soil atmosphere composition whose variations after heavy traffic may be a good diagnostic tool of soil compaction’s state. To confirm or invalidate this hypothesis the soil atmosphere composition is studied on the two sites, in control and compacted plots. The forwarder traffic led to an increase in bulk density of 17% to 26% compared to the initial values in the first 10cm and to an increase in soil CO2 concentration, especially during wet periods, in the two sites. These changes of soil atmosphere composition, the increase in mechanical resistance to penetration and the decrease in water infiltration will probably impact root growth, gas emissions, microbial and faunal activity and probably have a negative feedback on soil recovery dynamic.