Impact of mechanized logging on compaction status of sandy forest soils

Impact of skidding traffic on bulk density and penetration resistance of two sandy forest soils was examined in Putte (the Netherlands). Different levels of compaction were applied by varying the number of skidding cycles: one pass harvester (H), one pass harvester and forwarder (H + F), and multiple passes of both machines (Max). Bulk density and penetration resistance were measured on the undisturbed surface (UD), between the wheel tracks (BT) and within the tracks (WT). For WT, treatment H induced a clear increase of both soil properties in the upper 30 cm of the soil profile compared to the UD. The continuation of the passes to Max only resulted in a limited rise in bulk density. However, penetration resistance was significantly higher in Max in comparison with H. BT values were situated between UD and WT. Here, on site 1 both properties decreased with increasing number of passes, while on site 2, we observed the opposite, which was probably associated with the soil water status at time of harvesting. Measurements taken within tracks where logging residues were piled up to 40 cm revealed that a brash mat could reduce the compaction level to a considerable extent. The relationship between bulk density and penetration resistance appeared to be non-linear, with bulk density becoming insensitive to penetration resistance changes at higher penetration resistance values. On these sandy soils, we recorded significant increases of bulk density and penetration resistance, but rarely exceeding growth limits for optimal root elongation. However, as amongst other things, sandy soils are expected to recover very slowly and certain soil processes may already be influenced at lower compaction levels, designated skid trails should also on this soil type be used to minimize the influence on the ecosystem.