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

A mechanistic model for assessing the risk of wind and snow damage to singl e trees and stands of Scots pine (Pinus sylvestris L.), Norway spruce (Pice a abies (L.) Karst.), and birch (Betula spp.) is presented. The model predi cts the critical turning moment and wind speed at which the trees will be u prooted or break at forest margins. The resistance to uprooting is predicte d using the estimate of the root-soil plate weight to derive a resistive mo ment, while the resistance to stem breakage relies on values for the modulu s 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 design ed to apply (the stand edge). The predictions of the critical turning momen ts needed to uproot and break trees nevertheless give a good agreement on a verage with the Finnish tree-pulling data for Scots pine, Norway spruce, an d birch.