FOREST DESTRUCTION. 403 



Tho forest is tlien the great moderator of geological action by trans- 

 portation and here it renders one of its greatest services to man. 

 Another service, indicated hut not yet fully explained by observations 

 already made, is the preparation, on land suitable for agriculture, of 

 fertile soil for human use. The introduction of decaying vegetable 

 matter, with the resulting liberation of carbonic-acid gas at consider- 

 abl(> depths in the mineral soil when roots die, is one of the means. 

 Another, far more frequent, geologically speaking, than is apt at first 

 glance to appear, is the plowing of forest soil })y the wind. This 

 takes place when trees are overturned and their roots carry with them 

 to the surface considerable quantities of mineral soil as yet little 

 mixed with vegetable matter. Into the hollow from which this soil 

 came the leaves are washed and blown. Small quantities of humus 

 tind their way in from the edges and a deposit of fertility is made a 

 foot or two oi' three below the general level of the surface. When once 

 the attention has been called to it, the frequenc}^ of the little mounds, 

 which remain long after the tree itself has entirely rotted away, is seen 

 to be very great. Positive information is yet lacking b\^ which to 

 judge of the total eti'ect of this curious function of the forest. 



The second effect of temporar}' forest destruction is to produce what 

 may be called the preliminary vegetation and afterwards to modify the 

 character of the forest itself when the latter tinall}^ returns. Take, for 

 example, a recently burned area in the Adirondacks. The surface, if 

 not too rocky in chai'acter. is densely occupied, within a year or two, 

 with tire cherry, raspberries, and similar short-lived vegetation. In 

 the shadow of these forerunners young trees start, but they are of 

 comparatively worthless kinds. Fire cherry and poplar are usually 

 the most common species. Short-lived, rapidly growing trees of little 

 value in themselves, their principal use is to prepare a seed bed in 

 which the seeds of spruce and pine, maple and birch ma}' germinate 

 and then pass through their delicate infancy under the protective 

 shadow of trees which will disappear usually ))efore their competition 

 .has })ecome seriousl}' dangerous, and sustained by the rich humus they 

 have prepared. These are the wise nurses of the new forest, which 

 retire when their charges are old and strong enough to shift for them- 

 selves. In the Rocky Mountains the lodgepole pine and the quaking 

 aspen-the latter one of the trees called poplar or popple in the North- 

 east — are the principal nurses of more valuable kinds. Both form 

 pure stands of their own and both attain subordinate commercial value. 

 The lodgepole is spreading over enormous areas through the agency 

 of fire, and with the disappearance of tire it will graduallv but inevi- 

 tably lose its hold. 



Not all trees reipiire nurses when their elders have been burned or 

 cut awa}. Conspicuous exceptions are the red fir of Washington and 

 Oregon, the redwood of California, and over large stretches from 



