ROTATION OF FORESTS 



223 



bushes and gain tbe mastery. Sometimes the area grows 

 to poplars or birclies, and people wonder why the origi- 

 nal forest trees do not return; but these forest trees may 

 be growing unobserved here and there in the tangle, and in 

 the slow processes 

 of time the poplars 

 perish — for they are 

 short - lived — and 

 the original forest 

 may be replaced. 

 Whether one kind 

 of forest or another 

 returns will depend 

 largely on the kinds 

 which are most 

 seedful in that 

 vicinity and which, 

 therefore, have 

 sown themselves 

 most profusely. 

 Much depends, 

 also, on the kind 

 of undergrowth 

 which first springs 

 up, for some young 



trees can endure ^"''- '""' '"""'■ "'^"^^ ^^""^ °^ '''' roadside. 



more or less shade than others. Figs. 373 and 374 show 

 two stages in the return to forest. 



364. Pasturing and mowing tend to keep an area in 

 grass. This is because the grass will thrive when tlie tops 

 are repeatedly taken off, whereas trees will not. Note 

 that the wild herbs and bushes and trees persist along the 

 fences and about old buildings, where animals and mowing 

 machines do not take them off. A sod society means graz- 

 ing or moiving. Consider Figs. 96, 875, 37G. The farmer 



