Benchmarking the impact of traditional small-scale logging systems used in Mediterranean forestry

The authors conducted a survey of the residual stand damage and soil disturbance caused by harvesting Mediterranean and sub-Mediterranean forests in Central and Southern Italy. Sixty-five stands were inspected, with the double purpose of estimating reference values for logging impacts, and of determining if alternative silvicultural prescriptions result in a different frequency, severity and distribution of stand damage and soil disturbance. Data was collected with simple methods, commonly used in similar studies and suitable for direct application to forest practice. The study indicated that 12-14% of the residual trees are usually damaged during the conventional harvesting of Mediterranean forests. This proportion can grow to 20% when crawler tractors are used. Soil disturbance was detected on 58% of the surface of clear-fell sites, and on 42% of the surface of thinning and partial cut sites. Furthermore, clear-fell sites presented 5 times as many occurrences of disturbance categorized by being greater than 5 cm depth as thinning and partial cut sites. The study also showed an obvious and direct relationship between impact levels and proximity to the main extraction trails. The study indicated that thinnings and partial cuts are not associated to a dramatic increase of stand damage, but they result in a lower incidence of soil disturbance. Extraction by tracked farm tractors causes more stand damage and soil disturbance than extraction by rubber-tired farm tractors or by cable yarders. The introduction of modern technology is likely to determine a dramatic reduction in the use of tracked and rubber-tired farm tractors in forest operations, but it may generate new and different impacts, which should be monitored with much care. Yarding causes the least stand and soil damage, suggesting that silvicultural prescriptions should favor the application of cable logging, if possible.