Major Plant Communities 
11 
In the savannah vegetation, we have an example of bog xerophytism 
of a highly specialized type. It is very probable that this formation 
should be included in the same formation as that of the northern bogs. 
I ntil, however, sufficient work is done on both communities to solve 
definitely the relation of their xerophytism to the soil factors, it is 
deemed advisable to treat the savannah situation on a separate basis. 
Sue cession al Relations. There is little doubt that the savannahs in 
former times did not form such conspicuous entities as they now do. 
This was due to the fact that they formerly supported a large number 
of long leaf pine trees together with some loblolly and pocosin pine, 
which tended to hold in check the shade intolerant savannah species. 
The removal of these trees has made it possible for the distinctive 
herbaceous savannah vegetation to thoroughly master the areas it occu¬ 
pies, and if the soil conditions are right, with the aid of fire to also 
invade adjoining areas. In many places, the evidence is incontrovert¬ 
ible that the savannah complex is invading the Ilex-Myrica community. 
As to the ultimate fate of these areas, nothing certain may be said. 
If they are undergoing an invasion of pines, it is extremely slow. 
Annual fires make practically impossible the establishment of pines, 
the only trees that can tolerate the soil conditions. So distinctive and 
permanent are some of the largest of these communties that they may 
be classed as subclimaxes. Or again, since there is no evidence of in¬ 
vasion, they might be regarded as edaphic climaxes. Much more study 
of the savannahs, however, must be made before any definite conclusions 
regarding their successional roles may be reached. 
7. Nyssa-Taxodium (Nyssa aquatica, Taxodium distichum). Swamp 
Forest. 
Distribution. Locally in the Coastal Plain, especially the eastern 
half. 
Habitat. Borders of lakes, ponds, and the smaller rivers. Soil 
high in humus, saturated, sand content variable. 
Physiognomy. Slight xerophytism is evident in the trees of this 
formation; especially prominent is the character of the enlarged or 
buttressed base, a feature associated with the soft yielding substratum 
in which these trees commonly grow. It must he acknowledged that 
the elements of this formation do not differ strikingly from their up¬ 
land relatives, yet occupying the habitat they do, they naturally demand 
a place in a group of their own. 
