Czynniki wpływające na zmiany zwięzłości gleb leśnych podczas pozyskiwania surowca drzewnego

The objective of the studies was to determine the penetration resistance (cohesion) of soil compacted at timber harvesting in Scots pine stands subjected to late thinning. The scope of the investigations was limited to two technologies – the mechanized one, using a harvester−forwarder machine set, as well as the motor−manual one, employing petrol chainsaws and a farm tractor for forwarding and dragging of felled trees. The analyses were performed in central Poland, in the Staszów Forest District, for two habitats – fresh mixed coniferous forest and fresh mixed deciduous forest. The measurements of soil cohesion were taken with the use of Eijkelkamp 06.15.SA Penetrologger penetrometer along the five measurement lines situated perpendicularly to the main skidding track. The soil penetration resistance was measured in eight spots for every measurement line: in the middle of the left and right wheel−rut, between the wheel−ruts, on the left and right roadside within a distance of 0.5 and 1 m from the wheel−rut edge, and 10 m from the right wheel−rut; the latter location was treated as the reference. The mechanized timber harvesting caused stronger compaction of soil, particularly in wheel−ruts, where the recorded values of soil cohesion exceeded 3 MPa (fig. 1). For the technology with farm tractor for skidding, the greatest soil compaction was also encountered in wheel−ruts, reaching up to 2.5 MPa. With regard to both logging technologies, the analysis of variability in penetration resistance of the top 10−cm soil horizon revealed a statistically significant increase in soil compaction in wheel−ruts when compared with other measuring points along and nearby the skid track (fig. 2). The employed technology of timber harvesting and the degree of soil cohesion in wheel−ruts were proved to be correlated. In respect of the mechanized variant, the mean value of soil penetration resistance in the top 10−cm layer counted up to 2 MPa and was significantly greater than the one in motor−manual technology, where it did not exceed 1.3 MPa. No significant differences in soil compaction in reference to the investigated forest habitats were revealed, though it was stronger in fresh mixed coniferous forest, with regard to both technological variants. The motor−manual technology caused the increase in soil penetration resistance by 2% on the roadside, nearly 20% in the middle of the skid track and over 70% in wheel−ruts. While the mechanized logging operations resulted in 30% increase in soil cohesion on the roadside, 55% between the wheel−ruts and over 250% inside the wheel−ruts (fig. 3).