116 TRANSACTIONS OF THE 4 
EVAPORATION AND SOIL MOISTURE IN 
RELATION TO FOREST PLANTING. 
BY CLARENCE F. KORSTIAN.* 
With the great diversity of sites which are available 
throughout the Intermountain Region for forest planting, 
it has been difficult to select those upon which success is 
assured, especially toward the lower limits of tree growth 
in the chaparral or oak-brush zone, without a knowledge 
of the relation of climate to plant growth. Heat and mois- 
ture have long been recognized by plant geographers as 
fundamentally important in determining the character 
and distribution of plant associations. Only within the 
last decade, however, have plant ecologists made material 
advancement in the quantitative measurement of the 
water relations of plants. The importance of serious 
quantitative research to determine the relation of climate 
to the growth and development of vegetation can scarcely 
be over-emphasized. When the adverse climaticfactorsare 
known failures may be largely averted by the judicious 
selection of sites and of those species especially adapted 
to withstand the limiting factors. With uniformity of the 
soil the amount of moisture in the soil available for plant 
growth, the evaporating power of the air or the combined 
effect of the two factors is very frequently the determin- 
ing criterion of a plant association. It has been repeatedly 
shown that the evaporating power of the air affords a 
rather concise and satisfactory summation of the com- 
bined effects of temperature, humidity and air movement 
insofar as these factors influence transpiration A detailed 
study, therefore, of the evaporating power of the air and 
of the available soil moisture for a given site not only af- 
fords an expression of the water relations of the plants of 
that site but also considers the other factors mentioned. 
This problem is being studied intensively on the 
Ephraim Canyon watershed of the Manti National Forest 
in Sanpete County, Utah. During the last two growing 
*U. S. Forest Service, Ogden, Utah. 
