Pine (Pinus sylvestris L.) trunk irregularity due to exposure to wind

Abstract

Trees in a stand have different positions and those in the outer stand ring are most exposed to the wind. Around the crowns of border trees the wind causes turbulence which affects trees in the centre of the stand. All the trees in the stand resist the wind, which loses its strength; the deeper in the forest, the weaker the force of the wind. Those trees exposed to the wind for a long time may have eccentric trunks, while deeper in the forest there are fewer trees with eccentric trunks. The research was carried out in 9 pine stands of the 5th age class in North-West Poland. Each stand had an open space facing to the west. In each stand, sample plots were selected and marked in three different zones: A) heavy wind force (zone close to the border with open side), B) medium wind force, C) small wind force (zone furthest from the open space). Eccentricity was calculated as the ratio between the smallest and the biggest DBH. The results showed that deeper in the forest the tree trunks were less eccentric. The differences were statistically proven. In zone A, the longest diameters of approx. 89% of the trees were oriented east-west. This can be explained by the predominantly western (or close to western) winds. In zones B and C, eccentric trees with their longest diameters directed east-west amounted to 82 and 79% respectively. The trees deeper in the forest more frequently had a regular (not eccentric but round) trunk shape.