A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine, Norway spruce, and birch

Abstract

A mechanistic model for assessing the risk of wind and snow damage to single trees and stands of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula spp.) is presented. The model predicts the critical turning moment and wind speed at which the trees will be uprooted or break at forest margins. The resistance to uprooting is predicted using the estimate of the root-soil plate weight to derive a resistive moment, while the resistance to stem breakage relies on values for the modulus of rupture determined for different species of timber. A tree is assumed to be uprooted if the total turning moment exceeds the support provided by the root-soil plate anchorage. Similarly, a tree is assumed to break if the breaking stress acting on the stem exceeds a critical value of the modulus of rupture. The model is in general quite sensitive to parameter changes, which partly results from the location in the forest to which it was designed to apply (the stand edge). The predictions of the critical turning moments needed to uproot and break trees nevertheless give a good agreement on average with the Finnish tree-pulling data for Scots pine, Norway spruce, and birch.

Influence of clear-cutting on the risk of wind damage at forest edges

“…In principle, the susceptibility of a stand to wind damage is controlled by tree and stand characteristics such as tree species, tree height, tree diameter, crown area, rooting depth and width, and stand density, which are in turn determined by forest management (Coutts, 1986;Gardiner, 1995;Gardiner et al, 1997;Lee and Black, 1993;Kerzenmacher and Gardiner, 1998;Peltola et al, 1999aPeltola et al, , 2000Dunham and Cameron, 2000;Zhu et al, 2000). Furthermore, large differences in the risk of wind damage can be observed between regions and locations that differ in their topography and/or climate (Copeland et al, 1996;Peltola et al, 1999b;Quine, 2000;Proe et al, 2001).…”

“…The highest risk of wind damage is most likely to be found where there are sudden changes in wind loading to which the trees are not acclimated, as in stands adjacent to recently clear-felled areas or in stands that have recently been thinned intensively (Neustein, 1965;Kolstock and Lockow, 1981;Laiho, 1987;Lohmander and Helles, 1987;Peltola, 1996a,b;Gardiner et al, 1997Peltola et al, 1999a). Therefore, the most basic questions in the planning of forest management are how new clear-cuttings and/or thinnings may affect the speed and direction of local airflow and how the wind hits the downwind forest (Peltola, 1996b;Peltola et al, 1999a;Talkkari et al, 2000).…”

“…Therefore, the most basic questions in the planning of forest management are how new clear-cuttings and/or thinnings may affect the speed and direction of local airflow and how the wind hits the downwind forest (Peltola, 1996b;Peltola et al, 1999a;Talkkari et al, 2000). Neustein (1965), for example, has suggested that small clearings can reduce the sweep of wind within them.…”

“…Mechanistic models (Peltola et al, 1999a; have correspondingly been developed for predicting the critical wind speed and/or probability of a given tree in a stand being uprooted or broken under a range of silvicultural and wind conditions.…”

“…Talkkari et al (2000), for example, integrated the mechanistic wind damage model HWIND (Peltola et al, 1999a) with the airflow model MS-Micro/3 (Walmsey et al, 1993) under Finnish conditions, andBlennow andSallnäs (2000) integrated HWIND with the WAsP airflow model (Mortensen et al, 2000) under Swedish conditions to test the ability to identify actually damaged stands at current forest edges. In both cases the integration of these component models seemed to have great potential for identifying the stands likely to suffer actual damage under given wind conditions.…”