Forest Vegetation of the Lower Alabama Piedmont

Abstract

Forest community types were distinguished for the lower Alabama Piedmont using a combination of two agglomerative clustering algorithms with a similarity sorting technique. All stands classified in 8 of the resulting 10 community types has within—type similarity values of at least 45%. Ordination by reciprocal averaging using the tree basal areas indicated that community types can be segregated into three topographically defined groups: streambottom communities (Sweetgum—Water Oak—Red Maple and Small Steambottoms), mesic upland communities (White Oak, Chestnut Oak, Pine—Hardwoods, Mixed Oak—Hickory, and Loblolly Pine), and xeric upland communities (Oak—Pine, Blackjack Oak—Pine, and Longleaf Pine). A reciprocal averaging ordination using understory plants successfully separated most of the same community types. The combined clustering—similarity sorting procedure identified "core " stands that provide a clearer representation of definable forest community types than would have resulted from inclusion of atypical or transitional stands. The combination of classification for description of vegetation and ordination for definition of vegetation—site relationships proved complementary and useful. The highest tree species diversities were in mesic upland hardwood and pine—hardwood communities; the lowest were in pine communities. Diameter size class distributions revealed general underrepresentation in the seedling/sapling size classes for all important canopy species, even the climax Quercus and Carya. Underrepresentation was most severe in wet—to—mesic stands. Natural succession from pine toward hardwood dominance is more rapid on bottomlands, stream terraces, and other moist sites than on drier, more fire—prone uplands. Forest cutting practices of many nonindustrial owners accelerate the trend toward dominance of hardwoods, even on uplands.