Abstract

A wind tunnel was used to investigate the wind regime in forest clearcuts. The model forest had a uniform height of 15 cm and a density of 500 stems m−2 to simulate an Engelmann spruce stand of height 15 cm and density 500 stems ha−1. It was found that the mean windspeed near the surface at 22 tree heights downwind of the forest edge was about 65% of the potential value obtained when no forest was upwind. From the measured mean windspeed, turbulence intensity and integral scale in the vertical direction, the vertical turbulent diffusivity was calculated. According to the spatial distribution of the vertical diffusivity at one-fifth of the tree height, a quiet zone, a wake zone and a readjustment zone were identified downwind of the forest edge.

Introduction

Despite many environmental concerns, clearcutting still remains the major timber harvesting method in British Columbia, Canada, and in many regions of the world. Forest regeneration in clearcuts is an issue of great public and scientific concern. Tree seedlings in clearcuts often experience temperature extremes, increased water loss due to exposure to the wind, and winter desiccation as a result of snow removal by wind. Blowdown along the edges of clearcuts is also a significant problem in British Columbia and little information is available to assess the effects of clearcut size and shape on wind regime. The purpose of this chapter is to provide information on the wind regime in forest openings. This information is essential to evaluate the effect of clearcut size on seedling microclimate and blowdown potential of clearcut edges.