298 CLIMA TIC CHANGES IN THE PRAIRIE REGION. 



The presence of forests shelter the earth's surface, through the agency of theii- 

 dense foliage, from the scorching heat of the sun. It has been conclusively- 

 shown how they act as a source of the perpetual supply of springs. They break 

 the force of the wind in an astonishing degree, and are the direct medium in the 

 retention of moisture over areas within their influence. 



Becquerel states: "That in the valley of the Rhone, a single hedge two 

 metres (a little more than five and a half feet) in height, is sufficient protection 

 for a distance of twenty-two metres (seventy-two feet) in length." 



On the prairies of Texas, Kansas and Nebraska, a narrow belt of Osage 

 orange, or a double row of cottonwood or peach trees, as is well known in the 

 experience of the inhabitants of those localities, is an effectual barrier against 

 the high spring winds of the plains for comparatively extended distances, and 

 the effects of this wind-break are felt at a considerable elevation above the height 

 of the trees or shrubs which compose it. 



These wind-breaks, as they are called on the plains, protect equally from the 

 not infrequent furious storms of winter, and the occasional hot winds of summer. 

 In winter, too, the snow is piled up in great drifts, parallel to the hedge or row of 

 trees, and thus deposited, prevent the frost for some distance from bursting the 

 ground open ; in the spring the snow melts slowly away and soaks the earth 

 thoroughly ; instead of immense creeks, occasioned by the action of the frost, as 

 in exposed situations, swallowing the rains of that season without doing a particle 

 of benefit, the precipitated moisture is evenly distributed, and the earth in a con- 

 dition to retain it. In summer, the air in the immediate region of these timber 

 belts is cool, and the soil in the vicinity retains its moisture for a long time 

 relatively. 



Marsh* says, in regard to the effect of trees as a barrier to the wind : "* * 

 there is no doubt that the effect of cold blasts can be greatly mitigated, and 

 observation shows, that while the tops of the trees are swayed by their violence, 

 the surface will be found calm and warm. * * " 



The constant presence of moisture in forests will be admitted by the most 

 careless observer who has ever lived in a timbered country. This moisture, as a 

 matter of course, must be constantly evaporating, and consequently modifies the 

 heat of the surrounding region. The compact foliage of the forest condenses the 

 moisture from the passing breezes, and refreshing showers on the contiguous 

 country is the result ; were it not for this mass of cooler matter thus presented 

 to the actions of the winds in their transit over the region, there would be no 

 condensation, or at least but little, of their aqueous vapor; in a district, there- 

 fore, destitute of timber, though the currents which sweep over it be fairly 

 freighted with moisture, they part with but little of it, and that portion of a con- 

 tinent would fall under the odium of a "barren waste." This appears to have 

 been the condition of a large portion of the prairie area beyond the ninety-eighth 

 meridian primarily, but which is changing, and rapidly succumbing to the influ- 

 ence of civilization ; every tree, every shrub planted, every acre that is turned 



■'Man and Nature. 



