Soil watermap usage in planning of thinnings

Abstract: Off-road driving with heavy machinery (harvesters and forwarders) in logging operations nowadays is essential. It is the main reason why efficiency of harvesting has increased so significantly. Unfortunately it also has its downsides – one of which is increased soil damage in strip roads. Soil damages may have impact on tree growth in the stand, on future regeneration success or in nutrient loss. There is also a risk of increased mercury leaching from soil. There are several ways to decrease damage to soil during logging operations, like logging in winter time when soil is frozen, using light weight machinery, etc., but most of them are not appealing to industry since they either increase cost or decrease efficiency or both. In efforts to further decrease impact to environment and increase efficiency new ways to improve logging operations have to be found. One of these ways is using soil watermaps that are based on depth-to-water index (DTW). This GIS–based index is based on precise LiDAR scans of terrain, field inventory and sophisticated GIS processing. End result – soil watermap shows potential wet areas in stand that could be more susceptible to rutting. By using these maps, theoretically, it is possible to reduce damage to soil. Aim of this study was to test accuracy of soil watermaps in Norway spruce (Picea abies) thinnings. After selecting stands, locations of strip roads and soil damages were registered. Data analysis revealed that overall stand wetness according to soil watermaps didn’t show any correlation with amount of soil damage. Damaged parts of strip roads were significantly more often located on wet areas. Soil watermap value distribution analysis showed that most important difference between undamaged and damaged parts of strip roads where for areas with values 0 – 0.6 (the most susceptible to rutting). Comparison of stand re-planning using soil watermaps proved that it is possible to decrease trafficking on wet areas that are projected by soil watermaps.