Water Loss from the Floor of a Subarctic Forest

Abstract

Evapotranspiration was measured from a subarctic forest near Churchill, Manitoba, during July and August 1992. Total stand evapotranspiration was measured via standard micrometeorological techniques; evaporation and transpiration from several components of the forest floor were measured with lysimeters, plant physiological, and micrometeorological techniques. Total evapotranspiration from the forest floor accounted for 65% of the daytime stand water loss, ranging from 45 to 87%. The relative contributions of the forest floor surfaces to total evaporation were dependent upon their areal percentage cover and their evaporation rate. On average, the vascular shrub layer and the nonvascular (lichen and moss) surface covers contributed 42 and 49% of the forest floor evaporation, respectively. Standing water, which covered the smallest area of the floor, contributed about 9%. Analysis of the absolute evaporation rates from different surfaces showed that water and mosses evaporated about 1.3 to 1.4 mm d¹, and the drier surfaces (hummocks and lichen) evaporated about 0.9 mm d⁻¹. Immediately following rain events all surfaces evaporated at about the same rate. These results suggest that although the water loss from floor of a subarctic forest can be the largest component of stand evapotranspiration, it is the distribution and quantity of surface types, and of vascular and nonvascular plants which determine the overall role of the forest floor in stand water loss.