Microclimate of clear-cut, forest interior, and small openings in trembling aspen forest

Abstract

Solar radiation and air temperature near the soil surface and soil temperatures were measured from 15 June to 6 September 1993 in a 100m × 150m clear-cut, an 18m × 150m east-west strip, a 9m × 150m east-west strip, a circle of 18m diameter, a circle of 9m diameter, and a closed canopy trembling aspen forest near Chapleau, Ontario. Seasonal solar radiation totals were highest in the clear-cut and decreased by 32% in the 18m strip, 43% in the 9m strip, 45% in the 18m circle, 74% in the 9m circle, and 82% in the forest. The seasonal decline of daily radiation totals was greatest in the 18m strip, 9m strip and 18m circle as the radiation regime shifted from one dominated by direct radiation at midsummer to one dominated by diffuse radiation in late summer. The seasonal average air temperature at seedling height varied by only 0.7°C among treatments, but greater temperature extremes occurred in larger canopy openings. Average maximum-minimum temperature differences were 17.1°C in the clear-cut, but these decreased to 10.1°C in the forest. Average daytime-night-time seedling height air temperature differences were twice as large in the clear-cut as they were in the forest. Differences in daytime air temperature among openings were related to differences in shortwave irradiance. Both seasonal average soil temperatures and soil temperature extremes became higher as canopy opening size increased. Differences in soil temperatures among openings were greatest early in the season, and diminished as regeneration of shrubs, herbs, and grasses developed. Consideration of the autecology of white spruce and trembling aspen suggests that the circle of 18m diameter and strip of 9m width are best suited for white spruce establishment.