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Technique and planning  >  Forest technology  >  Soil protection  >  Physical Soil Protection

Article

Physical Soil Protection is not a Luxury

Fig. 1 - The small scale, altering soil characteristics lead to differently distinct tire tracks. Photo: Soil Ecology WSL

Fig. 2 - Forest soil with medium damage Photo: M. Walser (WSL)

Intact soils are a basic condition for the maintenance of an overall sustainability in the forest. For this reason the federal authorities, the Offices for Soil Protection and the Forest Service, as well as the Federal Research Institute WSL intend, with the use of physics, to improve the protection of the forest soil and to elaborate the basic principles and educational concepts.

Intact soils constitute a system with a great potential for self-preservation and extensively assure the performance of all soil functions. Thus, for forest management, it is important to follow the components of physics to protect the soil. Within the Swiss National Forest Programme (Swiss NFP 2004), principles for future forest policies were determined. The preservation of both the soil and drinking water quality became one of the top five priorities.

The requirements concerning soil protection are defined through the sustainable preservation of the soil fertility within the Swiss law for environmental protection. The law states that the soil is defined as fertile when it consists of a site-specific, species-rich biologically active habitat which includes a typical soil structure as well as undisturbed decomposition characteristics of the organic material. In addition, growth and quality of the plants should be unaffected. In respect to the forest, this translates into site conditions where the self-preservation of the site-specific habitat forest, including regeneration, must be guaranteed and sustainable. The root growth of the site-specific tree species may only be restricted by natural limitations and the biological soil activity must enable the uninhibited decomposition of vegetation residues under given local site conditions.

Where does the danger lie?

In large areas of Switzerland’s forests, the use of machines on naturally bedded forest soils causes deep and long lasting soil modifications which affect important soil functions (Fig. 1 and 2). Restricted pore volumes and pore percentages reduced the soil’s transportation capacity for water and air. This capacity however, is an important precondition for intact soil fertility. The first use of the soil by machines not only compacts and deforms the top soil, the heavy weight of the machine and the force dynamic peaks affect the soil through to deeper layers as well.

What can be done?

• An appropriate approach towards a more efficient lumber harvest and the implementation of legal requirements in respect to the preservation of soil fertility should be undertaken.
• Consistent decision tools are to be developed for the careful use of forest soils and for the development of less invasive tracks in forest stands.
• The guidelines and rules for the use of machines are to be developed site- specifically.
• The use of modern technology, cost-benefit considerations and different types of incentive offerings should be examined.
• Precaution strategies for the planning and executing stages should be developed.
• Future elaboration on the recommendations for the advancement of regeneration measures should be developed.

Where are the difficulties?

The interaction between site-specific, machine dependent and procedural factors are difficult to capture as a whole and are therefore difficult to assess. An ecosystem tolerable use of machines, predictions on soil damage, as well as the calculation and justification of threshold values – e.g. of soil water conditions which allow the use of machines – are difficult and challenging to conduct. Ecological findings, economic constraints, technical advancements and social demands to the forest and forestry respectively require basic considerations in regard to future concepts for the protection of the forest soil.

What measures can be taken?

The removal of debris from the storm Lothar has left machine tracks over entire areas effected by the storm. In the future, the policy regarding debris removal should restrict the use of machines to the skidder trails only, including use after calamities.

Track types are to be defined which conform to the guideline and inspection value (VBBo, 1998) and show, in detail, the adverse effects and damage respectively. These values consider the effective bed density of the soil, the rough volume of the pores, the saturated water conductivity, as well as the penetration resistance (BGS, 2004). These values demonstrate that the visible tracks on the upper soil surface always adversely effect the lower soil. These adverse effects are hardly visible to the naked eye but are clearly detectable using the respective data (Fig. 3).

Fig. 3 - Penetration resistance dependent on the soil depth assessed with a PANDA-sensor at an intact reference plot on a track used by a machine once and on another used several times Commentary on figure 3: The reference measurement which was taken on intact soil up to a depth of 100 cm was compared to the results from the track which was used under favorable conditions, i.e. small soil moisture by a full harvester once, and to a track which was used several times under varying soil moisture conditions. It is clearly shown that the values for the penetration resistances only meet values of the reference curve after a depth of 55 cm and 75 cm respectively.

If certain conventions are followed and timely precautions against increased site-specific risks are taken, a minimization of soil damage is possible. In addition to a knowledge of soil characteristics and their sensitivity, precaution must also include the knowledge of processes in order to understand and apply the correlation between adverse effects and an optimal use of the technique. Soil protection begins with the selection of an appropriate machine (weight, number of wheels) and the respective equipment (tires, Boogie-bands, etc.). The careful use of machines requires an accurately designed operation system for transport tracks.

Depending on weather conditions, the site-specific soil water content is one of the basic factors to be measured in order to decide machine use. The more humid the soil is, the higher the sensitivity to pressure through weight; therefore, if possible, machines should be used on alternative, less sensitive soils.

Up-to-date site maps for the Cantons (with soil maps based on soil profiles) are an important basis, particularly for planning. For the forest, complete soil maps that show, per mapping unit and list in a table, parameters such as grain size, skeleton fraction, degree of water logging, fraction of humus, type of humus as well as soil type are rare. The information system ProFor+ (TU Munich, Chair for Forest Work Science and Applied Computer Science), a powerful tool, allows assessments to be made at the soil/machine interface on the above outlined data base. For each mapping unit, the system provides a threshold for soil water content which allows assessment for whether machines should drive over the soil or not. This allows a site-related risk- and sensitivity-analysis of the soil. The various tools are tested in selected test areas for their suitability in regards to our questions.

For the specific, site-related preconditions and the subdivided structure of ownership in Switzerland, discrete concepts are needed which are based on existing concepts. Among others, peculiarities often consist of patchy, heterogeneous site mosaics as well as changes in forest management and forest organization.

Fig. 4 - Visual typing of the tracks (overview) Photos: M. Walser (WSL)

Regeneration

Soils damaged by driving often need a very long time to recover. Some of them are also irreversibly damaged. On strongly affected soils, appropriate restoration measures may speed up the revitalization process in small areas. They should support the natural regeneration processes. Various actions are tested to increase rooting, pore volume and the biological activity of the affected soils

Overview for all of Switzerland

Within the frame of the Swiss National Forest Inventory (NFI), changes of forest soils due to mechanical impacts are registered. A pilot study conducted in the Canton Fribourg describe the first results which show that such impacts occur on close to 10% of all samples.

Outlook

With the project "Using Physics to Protect the Forest Soil" the Federal Office for the Environment (FOEN), together with the Swiss Federal Research Institute WSL, want to develop a basis and teaching concepts to improve the use of physics to protect forest soil. The experts assume that long-term affective actions can primarily be reached by specific training in education and through further education. An accompanying group consisting of representatives from the forest service, the soil protection, the association of the forest entrepreneurs, the centre of learning for forest and the team for certification should support the acceptance and realization of soil protection actions on all levels.

Further information

• BGS Dokument 9, 1999: Physikalischer Bodenschutz. Juris Druck und Verlag, Dietikon.
• BGS Dokument 13, 2004: Definition und Erfassung von Bodenschadverdichtungen. Positionspapier der BGS-Plattform Bodenschutz. Landwirtschaftliche Lehrmittelzentrale, Zollikofen.
• BUWAL, 2004: Umwelt 2/2004, Bodenschatz Bodenschutz.
  
• ProFor+, Version 1.0.1, 2004 : Lehrstuhl für Forstl. Arbeitswissenschaften und Angewandte Informatik, TU München.
• WAP, 2004: Waldprogramm Schweiz, Schlussbericht: Schwerpunkt Waldschutz, Schriftenreihe Umwelt Nr. 363, BUWAL.
• VBBo, 1998: Verordnung vom 1. Juli 1998 über Belastungen des Bodens. SR 814.0. EDMZ, Bern.

• 
  Translation: Dawn Meister, Stallikon

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• Original article in German (PDF, 1.0 MB)

Internal links

• Forest soil as a carbon store
• Heavy metals in Swiss forest soils
• Soil stability: When porcini, chanterelle and co. make common cause with plants