186 MINNESOTA STATE HORTICULTURAL SOCIETY. 
ture and humidity will be small, and an exchange of the conditions of the 
two air columns, the one outside and the other under the cover, will take 
place rapidly, and the effect will be inappreciable. 
Hence it would be foolish to expect climatic changes from the small 
plantings, which the single farmer is apt to make on his homestead. It 
would be like expecting to heat a large room with a single gas flame. 
Wind-breaking effects, to be sure, he will realize, in the nearest neigh- 
borhood to the grove, but no perceptible modification of his climatic con- 
ditions. 
Yet many small gas flames, properly distributed, will be quite effective 
in the heating of a room, and similarly many smaller plantations, each 
being sufficiently large and dense so as not to permit a too rapid exchange 
of conditions with the outside, will effect climatic changes. 
The ameliorating capacity is simply a question of volume or mass of 
two air strata of different conditions, to be placed in counterpoise like the 
balancing of scales. And as here we know that a longer lever will allow 
a smaller weight to exert more force, so one manner of placing our timber 
belts will be more effective than another. 
Let it be wel! understood that there is nothing small about the forces 
that produce climatic conditions, that, hence,to exert any influence upon 
it, the means must be proportionate to the antagonizing forces. 
Hence forest areas, to serve as climatic factors, must be large, and they 
must be dense. Success in forest planting is best attained in a dense 
stand, anyhow not less than 8,000 to 10,000 seedlings to the acre, most of 
them not to develop into trees of size, but to serve as cover to the soil to 
prevent evaporation, and to be of any inferior kind that keeps a dense 
foliage, for in’ climatic effects success is attained if proportion to the 
success of shading the ground. 
If then it is proposed to ameliorate the climate of prairies and plains by 
forest planting, I want to impress you with the fact that such can be done 
only by planting in masses, properly disposed; that it is not the tree which 
influences the climate, but masses of dense foliage, withdrawing large 
areas of soil from the rays of the sun. Forest planting of this kind is ex- 
pensive in the start, especially since returns cannot be expected soon. 
Good results in the shortest time, then, can be expected only from a sys- 
tematic, well-directed and associated effort, and here your association can 
find as fruitful a field for action as in any direction, in devising plans for 
co-operation in ‘“‘Foresting the Great Plains.” 
The elements of such a plan would seem to be as follows: divide that 
part of your state which needs it, into re-foresting districts, according 
to configuration or other natural conditions, or else proceed by counties; 
ascertain in each district, by correspondence and otherwise, where 
the poorest lands, that can be most advantageously devoted to tree 
growth, are situated, especially on the higher portions; ascertain also 
the situation and extent of existing groves and their condition; then 
determine upon the desirable location of an interrupted series of timber 
belts running in their greatest breadth north and south, or nearly so; 
each 5 to 6 miles in length and 1 to2 miles in width, and so disposed as to 
cover from 20 to 30 per cent. of the area. 
To secure the planting and to have it done in proper manner, organize 
a co-operative forest credit bank, somewhat in the manner of the build- 
