New forest harvest techniques use a mixture of uncut forest strips and narrow cutblock strips to provide wind shelter in the cutblocks, and reduce the windthrow of remnant trees. Several questions are raised by this approach. What is the effect of cutblock width on wind shelter and windthrow? How wide a forest strip is needed to provide adequate shelter? What is the effect of successive cutblocks? In this study we used a simple model to predict the wind flow across different cutblock/forest geometries, with the goal of identifying good designs for reducing windthrow.
A two-dimensional wind model, based on a first-order turbulence closure, was used in this study. This model has been shown to accurately predict the spatial variation of average wind velocity (U) and turbulent kinetic energy (TKE) across a forest edge. Model estimates of U and TKE were used to predict the risk of remnant windthrow for a set of cutblocks near Manning, Alberta. Our previous work showed that U and TKE can be related to tree sway. The cutblock strips ranged in width from 0.4 to 20 canopy heights, with varying amounts of forest border. Our predictions were then compared with field observations of windthrow. The model was able to differentiate areas with high and low windthrow occurrence. We then used the model to evaluate windthrow likelihood in several hypothetical cutblock designs.