Fig. 5. Effects of number of skidding cycles on medium-textured boreal forest soils by wide-tired skidders and forwarders (Table 1) on air-filled porosity of wet soil. Air-filled porosity was measured in the field using an air pycnometer after the soil was trafficked. Only air-filled porosity data (Table 2) for the sites and depths that had a soil water potential of -15 kPa or higher (Table 1), were combined to produce the means and standard errors.