Nitrous oxide emission and methane consumption following compaction of forest soils

Fluxes of the greenhouse gases, N2O and CH4, were measured across a skid trail at three beech (Fagus sylvatica L.) forest sites with soils of different texture. At each site three skid trails were established by applying two passes with a forwarder. Soil compaction in the middle of the wheel track caused a considerable increase of N2O emissions with values elevated by up to 40 times the uncompacted ones. Compaction reduced the CH4 consumption at all sites by up to 90%, and at the silty clay loam site its effect was such that CH4 was even released. These changes in N2O and CH4 fluxes were caused by a reduction in macropore volume and an increase of the water-filled pore space (WFPS). Additionally, the slipping of the forwarder's wheels led to a mixing of the humus layer with the mineral soil, which resulted in a new layer. This layer reduced gas exchange between the soil and the atmosphere. Trace gas fluxes were altered in the trafficked soil and in the adjacent areas. Despite the significant changes in the trace gas fluxes on the skid trails, the cumulative effect of the two gases on the atmosphere was small with respect to total emissions. However, if soil trafficking is not restricted to the established skid trail system the area of compaction and consequently the atmospheric load by greenhouse gases may increase with every harvesting operation.