. Animal Ecology. Animal ecology. 21 22 °C FIG. 9-2 Gradient of air temperatures medium height at night (after Waterhou and 1955). 23 24 25 )ve (a) tall grass and (b) short grass on 26 TALL GRASS SHORT 10 GRASS perature; beneath the litter in the central Ohio area temperatures do not usually go below freezing (Christy 1952). A covering of snow gives added pro- tection against freezing of the leaf litter. Another study (Wolfe et al. 1949) revealed differences be- tween temperatures above and below a snow covering 2 to 10 cm deep during a period of two months aver- aged °C, and on one occasio
. Animal Ecology. Animal ecology. 21 22 °C FIG. 9-2 Gradient of air temperatures medium height at night (after Waterhou and 1955). 23 24 25 )ve (a) tall grass and (b) short grass on 26 TALL GRASS SHORT 10 GRASS perature; beneath the litter in the central Ohio area temperatures do not usually go below freezing (Christy 1952). A covering of snow gives added pro- tection against freezing of the leaf litter. Another study (Wolfe et al. 1949) revealed differences be- tween temperatures above and below a snow covering 2 to 10 cm deep during a period of two months aver- aged °C, and on one occasion reached °C. Relative humidity decreases from the ground stratum upwards. In a young elm-maple forest in Tennessee, the relative humidity from mid-February to mid-August averaged per cent at the surface of the leaf litter, per cent in the herb stratum meter above the ground, per cent in the shrub stratum at meter above ground, and per cent in the trees at meters above ground (Adams 1941). In this same forest, the rate of evaporation between May and November in the four strata respectively averaged , , , and cc per week. In a spruce-fir forest in Wyoming, the average weekly evaporation at meter was cc, at 1 meter cc, and at 3 meters cc (Fichter 1939). In the Tennessee elm-maple forest mentioned a nd (c) 2 13 in grass of moment ago (Adams 1941), the average daily mid- summer light intensities measured with a MacBeth illuminometer for ground, herb, shrub, and tree (be- neath the canopy) levels were respectively , , to foot-candles; in early May, before the foliage was fully developed, intensities of , , , foot-candles were measured. Under the leaf litter and in the soil, the light intensity was, of course, zero. Above the trees it was doubtless several thousands of foot-candles. light intensities from the sun occasionally reach 15,000 foot-candles. There are,
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