56 HARPER: VEGETATION OF THE PINUS TAEDA BELT 
of trees is evidently highest in Virginia, and of shrubs and perhaps 
herbs in North Carolina. 
Without taking up undue space by considering each species 
separately, it may be said that those in the Virginia list are 
mostly species that prefer soils richer.in potash or humus than the 
average of the region.* Those in the North Carolina list are 
largely plants of moist pine-barrens or sandy or peaty bogs, called 
‘‘bog xerophytes’’ by some American ecologists, and ‘‘oxylo- 
phytes’’ by Warming. Some of those in the South Carolina list 
may be restricted in their northward distribution by temperature, 
as suggested in 1907. Others are characteristic of cypress ponds, 
and some apparently prefer more ferruginous or phosphatic soils 
than the average of the region. (This may apply especially to 
the genus Quercus, of which there is one in the first column, none 
in the second, and seven in the third.) Some of the herbs are 
weeds, but just why weeds should be more abundant in South 
Carolina is not apparent. It is probably by such comparisons 
as these, preceded by careful analyses of environmental factors, 
that we can make the most progress in discovering just what is 
the optimum environment for each species. 
Volumetric and dynamic studies. From reports of foresters on 
more or less similar areas (which need not be cited here), the stand 
of timber at the present time may be estimated roughly as 6,000 
board feet of lumber per acre. This is equivalent to 500 cubic 
feet; but to make allowance for slabs, sawdust, tops, saplings, 
bushes, etc., the latter figure should be just about doubled, making 
1,000 cubic feet of wood per acre. : 
The average increment of partly culled forests of Pinus Taeda 
is at least 3 per cent. annually, and as that is the most abundant 
species in the region under consideration we will not be far wrong 
if we take 3 per cent. for the annual increment of the whole 
vegetation, which would make 30 cubic feet of wood per acre per 
year. 
The dry wood of Pinus Taeda weighs 34 pounds per cubic 
foot, according to Sargent, but that of most of the other trees is 
* Several of the same species were found a few years ago to be more abundant 
in the pine-barrens of Mississippi than in those of Georgia; doubtless for similar 
reasons. See Bull. Torrey Club 41: 563. 1914. 
