Resumen
Aim of study: The primary objective of this paper was to compare the effects of different types of forestry machine chassis on the compaction of the top layers of soil and to define the soil moisture content level, at which machine traffic results in maximum compaction.Area of study: Measurements were conducted in eight forest stands located in Slovakia and the Czech Republic. The soil types in the stands subjected to the study were luvisols, stagnosols, cambisols, and rendzinas.Material and Methods: The measurements were focused on tracked and wheeled (equipped with low pressure tyres) cut-to-length machines, and skidders equipped with wide and standard tyres. The bulk density of soil was determined from soil samples extracted from the ruts, the centre of the skid trail, and the undisturbed stand. To determine soil moisture content, at which the soil is the most susceptible to compaction, the Proctor standard test was employed.Main results: The moisture content for maximal compaction fluctuated from 12% to 34.06%. Wheeled machines compacted the soil to 1.24 ? 1.36 g.cm-3 (30.3 ? 35.4 % compaction) in dried state. Bulk density of soil in stands where tracked machine operated was lower, ranging from 1.02 to 1.06 g.cm-3 (25.3 % compaction).Research highlights: All wheeled machines caused the same amount of soil compaction in the ruts, despite differences in tyres, machine weight, etc. Maximum compaction caused by forestry machines occurred at minimal moisture contents, easily achievable in European climatic conditions. Keywords: soil compaction; bulk density; soil moisture content limits; cut-to-length machines; skidders.