UTAH ACADEMY OF SCIENCES 195 
able precipitation, rather than as a result of their influence 
in attracting precipitation. 
The great unbroken forest covers of the Sierras, and 
the Pacific northwest, are a result of the heavy winter 
rains and snows; and the beautiful forest blanket over 
the Yellowstone region is due to the ample moisture in 
both winter and summer. Indeed, there are ‘limited 
regions where the canyon air movement prevents the 
seeding of trees, though moisture be abundant. 
In the process of transpiration the loss of moisture 
in conifers amounts to from 100 to 200 times the weight 
of dry matter produced, according to an investigator. 
This amount is comparatively small, as will be noted in 
examining the weight of water actually escaping in this 
manner. Even in this western region where precipita- 
tion is light, and much needed, the transpiration losses 
do not seem greatly important. 
A greater loss results from interception, in which 
process rain water is suspended on the foilage and sub- 
sequently evaporated. The conifers catch much greater 
amounts of water in this manner than do the broad- 
leaved trees. The amount may, according to a study by 
Robert E. Horton, reported in the Monthly ‘Weather 
Review recently, amount to from 0.02 to 0.07 inch per 
shower, though manifestly the amount per acre will 
vary with the density of the forest cover, and the height 
of the trees. 
The loss is estimated, from studies made by Mr. 
Horton, to range from 25% to 100% of the total rainfall, 
depending on the rate, duration, and amount of the rain- 
fall. The average is given somewhere around 25% to 
40%. This loss thus becomes rather important at times, 
since the rain interception comes in summer chiefly, 
when rain is most needed. 
There is a modifying influence of the forest on the 
amount of general evaporation of the moisture that is com- 
paratively important, due to the diminished wind move- 
ment, the lower temperatures, and diminished insola- 
tion. Evaporation losses in Utah from a free water sur- 
face may reach five feet in a summer. Raphael Zon, in 
a paper on forests and water conservation, uses the 
statement that the evaporation loss from an area covered 
