SNOW ABLATION IN SMALL FOREST OPENINGS IN SOUTHWEST ALBERTA

Snow ablation in circular forest openings 0, 1, 3, and 5 H in diameter (where H is the average height of adjacent uncut trees (21 m)) was measured in early to mid-April, using snow pans with perforated false bottoms to allow measurement of melt and evaporation. Snowmelt accounted for 70 to 90% of total ablation. Evaporation was small, primarily because meteorological conditions were not favourable. Ablation rates were lower in the 1 H opening than in the 0, 3, and 5 H openings. The 1 H openings were colder because net radiation in the uncut forest and larger openings was 3 to 4 times greater. Wind speeds in the larger openings were 7 times greater than in the 0 and 1 H openings. Daily snowmelt rates in 0 and 1 H openings varied from 0 to 5 mm/day compared with 7 to 20 mm/day in 3 and 5 H openings. Meteorological data indicated that snow ablation was affected by advective energy transfer within openings and between the openings and surrounding forest. Ambient weather suggested that conditions favourable for advection occurred 24 to 53% of the daylight hours during the study period, and that advection was more important in the larger openings.