be ELEMENTARY FORESTRY. 
and this factor, being under the control of human agency more 
than any other possible modifier of climate, must therefore be 
of greatest interest to us. It is clear, from what has been stated 
so far, that the influences of the forest, if any, will be due mainly 
to its action as a cover protecting the soil and air against insola- 
tion and against winds. That the nature of a cover, its density, 
thickness, and its proper position has everything to do with the 
amount of protection it affords, everybody will admit. A mos- 
quito net is a cover, so is a linen sheet or a woolen blanket, yet 
the protection they afford is different in degree and may become 
practically none. It will also be conceded that it makes a great 
difference whether the cover be placed before or behind the 
wind. Just so with the influence of the forest; it makes all the 
difference whether we have to do with a deciduous or conifer- 
ous, a dense or an open, a young low or an old high growth, 
and what position it occupies with reference to other climatic 
elements, especially to prevailing winds and water surfaces. In 
the following discussions, when the word forest is used, unless 
differently stated, a dense growth of timber is meant. 
“The question of forest influences on water supplies can be 
considered under three heads, namely—influence upon precipi- 
tation or distribution of atmospheric water; influences upon 
conservation of available water supplies; influence upon the dis- 
tribution or ‘run-off’ of these supplies. 
INFLUENCE UPON PRECIPITATION. 
“Whether forest areas are, or are not, capable of appreciably 
increasing precipitation within their limits or on neighboring 
eround is still a matter of dispute, and the complexity of the 
elements which must enter into the discussion has so far baf- 
fled solution based upon definite and strictly scientific observa- 
tion. Yet new evidence is accumulating all the time which 
apparently shows that under certain conditions forest areas 
obtain larger precipitations than open grounds, that is, they 
may inerease at least the amount of precipitation over their own 
immediate and near lying areas. 
{In Minnesota popular opinion inclines to the belief that 
there is a close connection between the existence of forests and 
the rainfall of this section, and that with the disappearance of 
