THE RETURN TO FOREST 



231 



these shade the bushes and gain the mastery. Sometimes the 

 area grows to poplars or birches, and people wonder why the 

 original 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 that are most seedful in that vicinity 

 and which therefore, have sown themselves most profusely. 

 Much depends, also, on the kind of undergrowth that first 

 springs up, for some young trees can endure more or less 

 shade than others. Fig. 398 shows an early stage in the 

 return to forest. 



391. Pasturing and mowing tend to keep an area in grass. 

 This is because the grass will thrive when the 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 grazing or mowing. 

 Consider Figs. 110, 399, 400. The farmer keeps his wild 

 pastures "clean" by turning in sheep: the sheep are fond of 

 browsing. 



392. Some plants 

 associate. They 

 grow together. This 

 is possible largely be- 

 cause they diverge 

 or differ in character 

 (379). Plants associ- 

 ate in two ways: by 

 growing side by side ; 

 by growing above or 

 beneath. In sparsely 

 populated societies 



f . 1? . x 399. Sod and tree societies. About the building the 



(^aS in r Ig. 401) trees find refuge from the mowing machine. 



