. Canadian forest industries 1892-1893. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. 14 THE CJLUJLDJL LUMBERMAN Decembek, 1893 EFFECTS OF TREES ON CLIMATE. By Prof. B. E. Fernow. A S to humidity of air, we find that the annual evapor- *" ation within the forests is about one-half of that in the open field ; not only is the evaporation within a forest greatest in May and June, but the difference be- tween this and the evaporation in the open field is also then a maximum, which is the saving due to the presence of the woods. The average annual
. Canadian forest industries 1892-1893. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. 14 THE CJLUJLDJL LUMBERMAN Decembek, 1893 EFFECTS OF TREES ON CLIMATE. By Prof. B. E. Fernow. A S to humidity of air, we find that the annual evapor- *" ation within the forests is about one-half of that in the open field ; not only is the evaporation within a forest greatest in May and June, but the difference be- tween this and the evaporation in the open field is also then a maximum, which is the saving due to the presence of the woods. The average annual evaporation within the woods is about forty-four per cent, of that in the field. Fully half of the field evaporation is saved by the presence of the forest. The quantity of moisture thrown into the air by trans- piration from the leaves in the forest is sometimes three times that from a horizontal water surface of the same extent, and at other times it is less than that of the water. The transpiration from leaves in full sunshine is decided- ly greater than from leaves in the diffused daylight or darkness. The absolute amount of annual transpiration observed in forests of mature oaks and beeches in cen- tral Europe is about one-quarter of the total annual pre- cipitation. The percentage of rainfall evaporated at the surface of the ground is about forty per cent, for the whole year in the open field, and about 12 per cent, for the forest, and is greater under deciduous than under evergreen forests. The evaporation from a saturated bare soil in the forest is about the same as that from a water surface in the forest, other conditions being the same. The presence of forest litter like that lying naturally in undisturbed for- ests hinders the evaporation from the soil to a remark- able extent, since it saves seven-eighths of what would otherwise be lost. The total quantity of moisture returned into the at- mosphere from a forest by transpiration and evaporation from the trees and s
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