FOREST DESTRUCTION. 403 



The forest is then 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 b} r 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- 

 able 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 by 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 

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

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

 the attention has been called to it, the frequency of the little mounds, 

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

 to be veiy great. Positive information is 3 r et lacking b}^ which to 

 judge of the total effect of this curious function of the forest. 



The second effect of temporary 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 finally returns. Take, for 

 example, a recentl} r burned area in the Adirondacks. The surface, if 

 not too rocky in character, 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, rapidl}' 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 may germinate 

 and then pass through their delicate infancy under the protective 

 shadow of trees which will disappear usually before their competition 

 has become seriously 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 tire, and with the disappearance of fire it will gradually but inevi- 

 tably lose its hold. 



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

 cut away. Conspicuous exceptions are the red fir of Washington and 

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



