Basis for calculation
The calculations take into consideration the wind load affecting the surface of the tree crown, the material properties of green wood, and the stem's geometry.
The wind load assumptions that are used in the calculations are those stated in the current European standard EN 1991-4-1/NA:2012-12. The material properties of green wood originate both from what is known as the Stuttgarter Festigkeitskatalog (Wessolly, L. 1989) and from comprehensive studies carried out in England by Gwendolyne Lavers (The strength properties of timber. Building Research Establishment Report, HMSO,London. Lavers, G. M., 1983). It is also possible to estimate the influence that cavities, notches or openings in the stem might have with regard to public safety.
The calculation will result in the display of a safety factor for the tree under inspection. If crown reduction is necessary and feasible, a crescent-shaped cutting contour will also be displayed with specific reduction parameters (in m and %). If this measure is likely to reduce the overall stability of the tree and thus shorten its lifespan, it may be advisable to remove the tree completely. This recommendation should, however, be carefully appraised.