The paper concerns an analysis of differences in extent and characteristics of disturbances in outer soil layers, having occurred due to timber harvesting during the growing as well as winter seasons. The research areas were located in four upland mature stands – two beech and two fir ones. Felling works, conducted there in the above-mentioned seasons, were performed in the long timber system with skidding by means of a tractor of a skidder type. Performing works in winter, at thick snow cover, reduced the area of disturbed soil by 55% in fir stands and 30% in beech ones. Statistically significant differences were also recorded in respect of the depth of damages; in summer season they were more than twice as deep. Having analysed the quality of soil disturbances, it was established that the ones that emerged in winter were less harmful, being of rather minor and superficial nature. Compaction of soil was exclusively observed over surfaces where felling works were performed in the growing season. The conducted research confirmed that timber harvesting in winter is much less harmful to soil than it is in summer.

Keywords: timber harvesting, damage to soil, summer and winter season, ground disturbance, soil compaction