VEGETATION TYPES. 
147 
sand a foot or two in diameter, made by the “salamander,” (a ro¬ 
dent, Geomys Tuza Floridanus *) are rather conspicuous. Ant¬ 
hills, and diminutive mounds made by some unidentified animal 
with a burrow about three-eighths of an inch in diameter, are fre¬ 
quent, and burrows of the “gopher” (a turtle, Testudo or Gopherus 
Polyphemus) and pits of the “doodle-bug” or ant-lion are occasional. 
These animals together must move almost every particle of the up¬ 
permost foot or two' of the soil every few years, and counteract to 
a very large extent the leaching effect of the summer rain, which is 
probably what has made the relatively lifeless soil of the scrub and 
damp flatwoods so poor. 
An equally important factor in the development of high pine 
land vegetation is fire. Every tree in this type has its bark blackened 
at the base, and every stump and prostrate log is charred, from the 
fires which probably recur at any one point about once in two years, 
on the average. These fires, quite different from the forest fires of 
the far north, run through the grass and only occasionally get up 
into the tree-tops, and then only in isolated cases, not spreading 
from tree to tree as they do in the scrub and the dense northern 
coniferous forests. In pre-historic times lightning must have been 
the principal agency for starting fire. Although lightning is usually 
accompanied by rain, a pine tree set on fire by it (as often happens) 
might continue to burn until after the sun came out and the grass 
dried off, and then fall over and set the grass on fire. And al¬ 
though fire might not be started in this way on any one square mile 
more than once in several decades, a fire in an unbroken pine forest 
could easily spread over many square miles, so that every acre of 
such forest would be likely to be burned over every few years. The 
fires are most frequent in early spring. 
The Indians, imitating Nature, fired the woods at more or less 
regular intervals to keep down the underbrush and facilitate hunt¬ 
ing, it is said, and civilized man keeps up the practice for various 
reasons, such as to improve grazing and to prevent injury to tur¬ 
pentined trees by having too much inflammable material burn at 
once, as might happen if several years elapsed between fires. Many 
fires are also set accidentally or carelessly; but now there are so 
many roads, railroads, clearings, and other barriers that any one 
*For notes on the distribution and habitats of this animal in Florida and 
adjoining states see Science II. 35:115-119. Jan. 19, 1912. 
