PLAN OF REGIONAL DESCRIPTIONS. 25. 



In the regional descriptions all the climatic statistics 

 are not repeated, but only the salient features pointed 

 out. 



Forest types. — The treatment of forest tj^pes is rather 

 brief and superficial, for an exhaustive discussion of this 

 feature would require a great deal more space, and would 

 be of less economic than scientific interest. Abundant 

 details can be found in Mohr's Plant Life of Alabama, 

 previously referred to. 



Fire. — The frequency of fire is noted under the head 

 of forest types, for it varies greatly in different kinds of 

 forests, as well as in different regions. In general the 

 effect of fire in a forest is to keep down underbrush and 

 trees with thin bark or low branches, and thus favor the 

 growth of trees with thick bark and clear trunks, such 

 as most of the pines.* It also returns quickly to the soil 

 the potash and other mineral substances accumulated in 

 fallen leaves, but drives off the organic matter, which 

 would otherwise make the soil more nitrogenous. It 

 may also destroy some insects which would otherwise 

 injure the trees. Most persons who have written about 

 forest fires, especially in the northern states, where 

 such fires are often much more spectacular and awe-in- 

 spiring than they are with us, seem to regard them as 

 an unmitigated evil, or as regrettable accidents, to be 

 prevented by all possible means. In reality, however, 

 fire is a part of Nature's program in this part of the 

 world, and the woods were undoubtedly set on fire by 

 lightning and perhaps other natural causes long before 

 man appeared on the earth. The frequency of forest 

 fires varies greatly in different regions, and in general 

 they are most frequent today in the same regions where 

 they were most frequent in prehistoric times. Fires are 

 and always have been rare in hardwood regions with wet 

 winters and dry summers, like the Tennessee valley and 



by wet winters and dry summers, and its soils are decidedly 

 clayey; but its soil characters are closely con-elated with the geo- 

 logical formation, which is certainly independent of any modern 

 climatic factors. 



*This fact was noted by Sir Charles Lyell in Tuscaloosa 

 County in the spring of 1846. See page 69 of his book cited in 

 the bibliography. 



