TRANSPIRATION RATES OF SOME FOREST TREE SPECIES DURING THE DORMANT SEASON

Abstract

Six individuals of each species, each about three years old, were transplanted from clay pots to cylindrical metal buckets of five-quart capacity. In transplanting the seedlings the entire core of soil containing the root system was transferred intact to reduce disturbance of the roots to a minimum. The soil used was a sandy loam with a field capacity of 23.2 per cent. After transplanting, the specimens were placed outdoors for a week prior to beginning experimental work. To prevent catchment of rain water and evaporation from the soil surface the buckets were sealed with two layers of oil cloth which sloped from the stems to the rims of the metal buckets at an angle of approximately 55 degrees. The oil cloth was heavily coated with a sealing compound consisting of paraffin, tallow, beeswax, and rosin. A glass tube, closed by a cork stopper, was inserted through each cover to permit the addition of water. The experiment was performed on a flat roof where there was a minimum of shading by nearby trees and buildings. The specimens were arranged in six randomized blocks with each block having six plants representing each of the six species. The six blocks were located in a bed containing excelsior packing to prevent excessive changes in soil temperature as well as unnatural freezing. The blocks were so arranged that, although the afternoon shade affected the blocks differently, the plants within each block were shaded to the same extent. This arrangement was made to eliminate withinblock variations due to shading differences. The soil in the buckets at the beginning of each experimental period was at the previously determined field capacity, and the equivalent of the transpired water was replaced immediately after each experimental period. Weather data were obtained with a Friez hygrothermograph. Evaporation rates were obtained with standard Livingston atmometers. Total wind velocity for each experimental period was obtained with a cumulative recording anemometer. The gravimetric method of measuring transpiration was employed using a balance with a sensitivity of one gram. Loss in