BIOTIC FACTORS 



279 



Fire is particularly destructive upon very thin, sterile soils and 

 especially in the transitional region between forest and prairie, where 

 both types of vegetation are struggling for control. Wherever natural 

 reforestation today is accomplished with difficulty, it is exceedingly 

 difficult to reconstruct the original, natural appearance of the forest or 

 to delimit exactly the forest and grassland climaxes (Fig. 144). 



In humid regions, which present no special hindrances to regenera- 

 tion, fire is a periodically repeated phenomenon, even a form of cultiva- 

 tion. True cultivation with the aid of fire is still employed on a large 



Fig. 144. — Example of the systematic destruction of the Quercus ilex climax 

 forest in the Mediterranean region by charcoal burners; Majorca. [Photo by Hoffmann- 

 Grobety.) 



scale in Finland and in the Atlantic regions of Europe. Elsewhere 

 fires are employed in the destruction of noxious shrubbery, for the 

 improvement of pastures, for increased blossoming (bee pasture), 

 for cattle or game feed, and probably also for the mere pleasure of 

 burning and, finally, out of sheer carelessness. 



Effect of Fire upon Succession. — Fires are always followed, whether 

 the original vegetation is destroyed partially or entirely, by a secondary 

 succession, which tends anew toward the climax. Careful examination 

 of changes in the vegetation after fires has been made in England, 

 Finland, southern France, North America, and probably elsewhere. 



