Forest soils can be disturbed or even damaged by a range of activities, most prominently in the form of soil compaction and soil displacement, frequently resulting in rutting. This may cause massive drawbacks on permanent accessibility to forest stands and a deterioration of future growing potential. Also, tree diseases (such as root rot) could spread faster, with negative impacts on future wood quality and timber revenues. In addition, they affect tree stability making the forest less safe and less attractive to other stakeholders, for instance for recreational users.

Other severe impacts of the degradation of soils are of specific importance for forest contractors: Due to high rutting and wheel slippage, harvesting and the cost of timber extraction is directly negatively influenced by higher fuel consumption and hampered productivity. Recently, TECH4EFFECT partner Georg-August-Universität Göttingen finalized results of their first analyses of trafficability maps resulting in the presentation of their Public Deliverable (D4.1) “Terrain Accessibility for 4 Case Study Areas”.

Four study sites in Europe

To keep disturbances of forest soils to a minimum, it is of utmost importance to gain more knowledge on the sensitivity of certain forest areas when planning and conducting harvesting operations with heavy forest machines. Although some trafficability maps are available already, they are not commonly used due to the lack of information on soil bearing capacity and a high level of specificity. TECH4EFFECT partner, the University of Göttingen, describes the principles of handier trafficability maps and shows evaluations of their application at four case study areas.

The four study areas are located in Finland, Germany, Norway and Poland (Fig. 1) with each area approximately 50 km² large. The selected areas cover flat to hilly-mountainous terrain types and their mean annual precipitation ranges from around 660 to 860 mm. The study sites are primarily stocked with coniferous tree species, despite the site in Germany, covered by beech.

Depth-to-Water-algorithm (DTW) for avoiding soil disturbance

The generated maps rely on the Depth-to-Water algorithm (DTW), which estimates the vertical distance to areas with appearing surface water or water saturated soils (Fig. 2). The main advantage of these mappings is that permanent and perennial stream networks within the forest soils can be detected. This could help forest machine operators identify sensitive areas with regards to trafficability – based on this heavy machinery can be kept out of certain areas with low soil bearing capacity. For direct access of the operators to DTW-maps, all it would take would be an upload of a particular map to the on-board computer of the machine.

One of the principal investigators, Marian Schönauer, says: “To get better knowledge of actual trafficability of skid trails is really important since it has many different, serious affects for forest operations and forest contractors. DTW-maps are a potentially powerful tool for these applications for the future!”

Conclusion

Although these DTW-maps are based on digital terrain models only, they still have the potential to contribute to the reduction of rutting during forest operations, in particular at sensitive sites. Schönauer says: “With the application of the DTW-maps in forest operations, critical areas in terms of low DTW-index, permanent and perennial streams can be identified and avoided by forest machine operators. A sufficient way to facilitate this can be realised by providing the maps on the on-board computers of forwarders and harvesters. Within TECH4EFFECT we are also focusing on a conjunction with other data, for example precipitation data and weather forecasts.” Future work could explore incorporating additional data sources into the algorithm, such as soil moisture and climatic conditions to improve the accuracy and informative value of used maps to predict soil bearing capacity and trafficability of permanent skid trails in particular.

To read the full text please go to the TECH4EFFECT website and download the deliverable as PDF! If you want to test the maps please contact the University of Göttingen directly at foresteng (a) uni-goettingen.

Acknowledgement

When preparing this deliverable, the University of New Brunswick (Canada), especially Professor Paul Arp from the Department of Forestry and Environmental Management (I.U.C. Forestry 311, Fredericton), kindly contributed time and resources to calculate high resolutions DTW maps.

Contact

Georg-August-Universität Göttingen, DI Marian Schönauer (Dirk Jaeger lab)

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