Effects of slash reinforcement of strip roads on rutting and soil compaction on a moist fine-grained soil

Machines used for final felling operations are heavy and the risk for rutting and soil compaction can be considerable under unfavourable soil conditions. It is known that slash reinforcements of strip roads reduces rutting and soil compaction, but few studies are after traffic with large forwarders on moist fine-grained soils. An increased interest to utilise logging debris for energy production has made it important to know if and where slash is needed for strip road reinforcement. The aim of the study was to evaluate if slash reinforcement of strip roads influences rutting and soil compaction on a moist fine-grained soil, and to quantify these effects. The study was designed as a factorial experiment with factors slash depth in the strip road and number of machine passages. The effects of 0, 10 and 20 cm slash, and one, two and five passages were studied. The first passage was made with a 20.5 Mg harvester and subsequent passages by a 37 Mg laden large forwarder. Rut depths increased with number of machine passages but were not influenced by slash depth. Slash reinforcement of strip roads significantly reduced changes in soil dry density and soil porosity in the upper 20 cm of the soil. An increased number of machine passages increased soil dry density in the upper 20 cm and reduced air filled pore volume in the upper 30 cm of the soil. In the uppermost 20 cm of the soil, observed soil dry density increase after one machine passage on strip roads without slash was higher than after five machine passages where strip roads were covered with 20 cm of slash.