Investigating the impact of ground-based logging systems on soil characteristics applying emerging methods.

Reducing the soil impact of forest operations is a priority for improving sustainable forest management. Logging activities may alter soil in terms of both compaction and rutting. The overall aim of this thesis was to use an emerging methods approach to summarize how ground-based logging systems affect the soil in different working conditions. The thesis is based on four studies: the first applied a meta-analytic approach to machinery-induced soil compaction and its effect on the growth of forest plants; two studies tested new methods of rutting estimation after the trafficking of forest machinery; the last study addressed soil damage caused by skidding and forwarding under specific work conditions. The studies investigated the effects of ground-based extraction systems, including physical soil parameters for assessing compaction (i.e., bulk density and soil penetration resistance) and emerging methods for rutting measurements (i.e., 3D soil models obtained by portable laser scanning and Structure from Motion derived from photogrammetry, with images collected from a ground-based stand or higher altitudes by drones). The results of the meta-analysis showed the effects of soil compaction caused by machine trafficking on both morphological and physiological plant characteristics, especially in fine-textured soil. The most notable results of the other studies highlighted the irrelevant role of driving direction on soil damage during forwarding on a 25% slope. On the contrary, to reduce soil compaction, downhill skidding is preferable to uphill skidding. The results showed that low tyre pressure may mitigate the effects of forwarding on soil compared with higher tyre inflation pressure (i.e., 150 kPa vs. 350 kPa). The pressure on the ground caused by logging vehicles affects the wheel tracks, but to some extent, also the soil between the tracks. In general, the area affected by soil impacts was larger in skidding than forwarding due to the effect of dragged logs. Rutting estimation with photogrammetry and portable laser scanners showed promising results in terms of high-resolution data. It also reduced the time necessary for field surveys and obtaining accuracy compared to manual measurements. Nevertheless, the presence of free water in ruts or brush mats can affect the accuracy of results.