ss tanleaelia 
HARPER: THE ‘“‘PocosIN” oF PIKE County, ALA. 217 
sand, making more humus all the time, and crowding out the 
intolerant sand-hill plants, as in normal succession the world over; 
and it is probably still spreading slowly but surely. The pocosin 
vegetation is simply the climax for that type of soil, while the sand- 
hill vegetation is the pioneer. 
In explaining this succession there is one environmental factor 
that must not be lost sight of. Most of the plants in the pocosin, 
Fic. 4. Typical pocosin vegetation. Magnolia grandiflora (the largest trunk), 
Osmanthus, Batodendron, Prunus caroliniana, etc. Ground covered with undecayed 
leaves 
as in other hammocks, are very sensitive to fire. Fire often 
sweeps through the upland pine-oak-hickory woods that are 
common on the better soils of the same region, but the sand-hill 
vegetation is ordinarily too sparse and open to carry a ground 
fire any distance, so that it protects the pocosin vegetation on 
three sides from any fires which may originate in the surrounding 
country. Protection on the remaining side is afforded by the 
swamps and bottoms of Walnut Creek, or the broken topography. 
The hammocks of the Altamaha Grit region of Georgia are similarly 
protected from fire by the creek swamp on one side of them and 
the sand-hills on the other, and this protection has been an essential 
factor in determining their present vegetation.* 
__ Finally this Alabama pocosin throws: valuable light» on the 
. See E Bull. Torrey Club 38: 524-525. I91I. 
