INTRODUCTION 19 



the natives of many regions, as in Central Africa, and our own 

 western plains materially reduced the extent of forest lands, by 

 cutting and burning — partly to increase the extent of grass-lands 

 for grazing of cattle or wild game. 



Unfortunately these primitive methods are not unknown in 

 modern lands. The natives of our southern mountains still cut 

 or girdle the trees to clear a corn patch, and in Australia and New 

 Zealand sheep men burn and girdle trees to foster the growth 

 of grass for grazing. 



Of course the destruction of forests for timber or for opening 

 land for cultivation, is necessary; but unfortunately the process 

 has been for the most part both wasteful and injurious to the 

 land. Particularly destructive has been the reckless clearing of 

 mountain slopes, and the resulting washing away of the soil with 

 floods caused by the rapid run-off which the forest cover keeps 

 in check. The land, denuded of its good soil, remains a barren 

 waste, while the fertile soil is carried away by the swollen streams. 



The extraordinary and rapid change in the vegetation of a large 

 area, due to man's activities is especially apparent in the United 

 States, which a century ago was to a great extent untouched by 

 man. The greater part of the country east of the Mississippi was 

 covered with heavy virgin forest, and the great plains were in- 

 habited only by scattered bands of roving Indians. Today in the 

 eastern states the forests have given way to great cities, innumer- 

 able towns and villages, and rich farm lands, where they are not 

 dreary deserts, the results of thriftless lumbering and forest fires. 



Except for the native trees, the predominant vegetation at the 

 present time is largely exotic. None of the staple food crops are 

 indigenous, and the same is true for most of the common fruit-, 

 although some of the latter — like grapes and berries of various 

 kinds, — are of native origin. Even the weeds are mostly foreigners 

 and have driven out the native woodland plants which have 

 retreated before these hardy invaders. 



It is interesting to see, however, that given a chance, the native 

 forest will often come back. All over the older settled regions of 

 New England and the Middle States, the farm lands, deserted 

 when the richer lands of the West were opened up, have already 

 reverted to forest of the same type as that which originally covered 

 them, while the prairies, which fifty years ago were unoccupied 



