Mechanical stability of Scots pine, Norway spruce and birch: an analysis of tree-pulling experiments in Finland

2000

S. 143-153

1 Abb., 5 Tab., 39 Lit.

Unselbständiges Werk

200068302

Tree pulling experiments were conducted in Eastern Finland (1995-1996) involving 51 Scots pines (Pinus sylvestris L.), 33 Norway spruces (Pinus abies (L.) Karst.) and 11 birches (Betula spp.) under unfrozen soil conditions and 20 Scots pine when the (podzol) soil was frozen. The trees were pulled over with a winch attached at a stem height of 6 m and the force required to uproot or brak the tree was recorded, together with detailed measurements of the physical characteristics of the tree. Analysis of the data showed that the maximum resistive bending moment was most significantly and positively correlated with diameter at breast height (DBH) and tree heigt (H). Tree height multiplied by the second power of DBH provided the best prediction of the maximum resistive bending moment required for uprooting, allowing the species to be ranked in the following decreasing order of resistance: Scots pine>birch>Norway spruce. Correspondingly, the third power of breast height diameter served best to explain the maximum resistive bending moment for stem breakage, with the following decreasing order of resistance: birch>Scots pine>Norway spruce. Highly tapering trees were more liable to stem breakage than uprooting, and vice versa. All the Scots pine broke under frozen soil conditions, and higher bending moments were needed for stem breakage than under unfrozen soil conditions. The modulus of rupture of the broken stems, as derived from the maximum resistive bending moments for stem breakage, showed the following decreasing order of resistance: birch>Scots pine>Norway spruce.