Forwarder traffic impacted over at least four years soil air composition of two forest soils in northeast France

Soil atmosphere composition results from a balance between biological activity and gas transfer, both likely to be affected by soil compaction following heavy traffic. We monitored soil atmosphere composition, temperature and moisture once a month for three years in the trafficked (by a wood-loaded forwarder) and undisturbed plots of two sites in the NE part of France. Our aim was to assess the impact of compaction on soil air composition and to test if soil restoration resulted in undisturbed levels of gas production/consumption and transfer. Soil air oxygen, O2 and carbon dioxide, CO2 contents were the two soil gasses most sensitive to compaction and climatic variations. During at least the first year following compaction at 30 cm depth, heavy traffic resulted in an increase in soil atmosphere CO2 concentration ([CO2]) whatever the air-filled pore space. Following the first soil drought experienced at both sites, this initial impact disappeared toward an effect alternating between an increase in [CO2] when water filled pore space and a decrease when the soil was dry. The same interchanging impact was observed for soil air O2 content but with opposite trends. We assumed that soil cracks formed in the trafficked treatment due to lower resistance to stresses when the soil dried out drastically during summer droughts, resulting in an increase in soil gas diffusion while considering same soil temperature and air-filled porosity. However, three to four years following heavy traffic, soil air-filled porosity was still significantly decreased and gas production/consumption seemed to be still affected by compaction.