PRINCIPLES OF GEOGRAPHICAL CLASSIFICATION 



ALABAMA is such a diversified state that it would 

 be impracticable to treat it as a unit in describing 

 its forests. It is desirable therefore to subdivide the 

 area into a number of forest regions, each of which shall 

 be as distinct and nearly homogeneous as possible. As 

 a matter of expediency the subdivisions should not be 

 very numerous, for that would make some of them too 

 small to be shown satisfactorily on a map of convenient 

 size, and require too much repetition in describing them 

 all. In the present report fifteen main divisions are rec- 

 ognized, and some of them subdivided into two or three. 



It is a fact so well known as not to need any demon- 

 stration that differences in type of forests (or other veg- 

 etation), excepting of course differences produced artifi- 

 cially, are nearly always correlated with differences in 

 climate, moisture, soil, or other environmental factors. 

 Hence it is customary in subdividing any area geograph- 

 ically to base the classification of subdivisions on envi- 

 ronmental factors which can be measured or mapped 

 more precisely than can the forest types themselves. But 

 it is not always easy to decide just which factors are 

 most significant in this connection. 



Obviously factors which change somewhat abruptly 

 along definite lines are better adapted for the purposes 

 of geographical classification than are those which vary 

 more gradually and uniformly from place to place; so 

 that the ideal system is one in which the boundary be- 

 tween any two adjoining regions corresponds with a com- 

 paratively sudden change in one or more environmental 

 factors. 



Among the factors influencing tree growth in a state 

 of nature are light, heat, density of the air; amount, 

 composition and fluctuations of water; texture and com- 

 position of soil; frequency of fire; character and amount 

 of subterranean life (bacteria, fungi, worms, insects, 



2G (17) 



