’ 
218 Harper: THE ‘‘PocosIN” OF PIKE CouNTY, ALA. 
relation of evergreens to soil and succession. Although a great 
deal has been written about the phenomena of succession in 
various parts of the world, no one yet seems to have published 
any satisfactory short definition of pioneer and climax vegetation 
by which they may be recognized wherever found, without knowing 
the species; and consequently every ecologist has his own views 
on these points, and perhaps no two of them agree exactly. It 
is probably pretty generally agreed that normal succession (biotic 
succession of Cowles*) involves enrichment of the soil in some 
way; and as evergreens, in temperate climates at least, are well 
known to be most abundant in the poorer soils,t I supposed until 
about two years ago that no typical climax forest could contain 
any evergreens; and that view has found expression in my writings. 
Closely connected with that belief was one which seems to be still 
very generally held, namely, that for every (climatic) region 
there is one climax type of vegetation toward which all others are 
tending. I am now pretty well satisfied, however, that almost 
every type of soil has its own characteristic pioneer and climax 
vegetation, more or less distinct from those of other types. 
The proportion of evergreens in a given habitat or region seems 
to be correlated with the amount of available potash (and perhaps 
other minerals) in the soil,t and therefore should not be affected 
much by the sort of succession whose essential feature is the 
accumulation of humus, or the progress of nitrification. Although 
an admixture of humus is indeed believed to increase the availa- 
bility of the mineral plant foods in soil, a soil totally Jacking in 
potash or lime would gain none of these ingredients from humus 
formed in place. It is even possible that in soils deficient in 
soluble minerals—as is the case with most sandy and peaty soils— 
and protected from fire like our pocosin, a considerable proportion 
of the potash within reach of the roots of trees is locked up for 
several years at a time in the dead leaves which lie on the ground 
undecayed, and thus the proportion of evergreens may actually 
increase with succession, as it does in the present case, where the 
ravines have the most evergreens and the sand-hills the fewest. 
* Bot. Gaz. 51: 171-180. 1911; Ann. Assoc. Am. Geogrs. 1: 12-I9. 1912. 
t See Rep. Mich. Acad. Sci. 15: 197. 1914. 
¢See Geol. Surv. Ala. Monog. 8: 28-29; Torreya 13: 140, 141, 143; Bull. 
Torrey Club 40: 398. 1913. 
