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An Ecological Analysis of the Plant Communities of Piedmont, North Carolina

Henry J. Oosting
The American Midland Naturalist
Vol. 28, No. 1 (Jul., 1942), pp. 1-126
Published by: University of Notre Dame
DOI: 10.2307/2420696
Stable URL: http://www.jstor.org/stable/2420696
Page Count: 126
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An Ecological Analysis of the Plant Communities of Piedmont, North Carolina
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Abstract

1. The Piedmont Plateau is an ancient peneplain lying between the Blue Ridge mountains and the Coastal Plain and extending from Pennsylvania to Alabama. Soils, topography and vegetation are similar from Virginia southward and the North Carolina portion is representative of the whole. 2. An ecological analysis of the naturally occurring plant communities of the North Carolina Piedmont was undertaken to provide basic information for continued research in ecology and silviculture, and in the hope of contributing to the solution of problems of forest management. Since the entire southern Piedmont is a physiographic and biotic unit the results and conclusions derived from this study are of much more than local significance. 3. The study was aimed at a characterization of all the major plant communities on a qualitative and quantitative basis as well as an interpretation of the major successional trends. To this end quadrat sampling was done in stands of every available age class for each major community. Within each stand five layer-communities or strata were distinguished and sampled separately. These were, the dominant or overstory stratum, the subdominant or understory stratum, the transgressives and tall shrubs, the seedlings and low shrubs, and the herbs. Not less than ten list-count quadrats of appropriate size were done for each stratum in each stand. In addition basal area was obtained for trees. This procedure has made it possible to summarize all statistical data in terms of the two important phytosociological concepts: frequency and density. 4. Uplands and lowlands of the region are ecologically distinct because of the perfection of drainage, high summer temperatures and periodic dry spells. They must then be considered separately. The agricultural history of the region has been such that only inaccessible sites or those of inferior quality are free from disturbance or the effects of man. Most of the plant communities are therefore of secondary origin and their consideration must be kept distinct from the relatively restricted primary communities. 5. Almost without exception upland communities have developed on abandoned fields. They are characterized by a few distinct and easily recognized stages of dominance which regularly succeed each other. Fields abandoned for one year are dominated by Leptilon canadense and Digitaria sanguinalis. The second year Aster ericoides with a mixture of Ambrosia artemisiifolia is the important species. By the third year Andropogon (usually A. virginicus) is dominant and it maintains itself until shaded out by pine (P. taeda or P. echinata) whose seedlings may be found among the broom sedge as early as the third year. Pine may overtop the Andropogon by the fifth year and frequently forms closed stands in 10-15 years. Neither of these pines reproduces in its own shade but several hardwoods do. A pine stand is middle-aged by forty years and by then there will have developed a distinct understory of subordinate hardwoods such as red gum, black gum, dogwood and sourwood. In addition several seedling and transgressive oaks and hickories will be present. By 70-80 years the pine is overmature and as it thins out it is replaced by oaks and hickories which have increased steadily in the lesser strata. Eventually (150-200 years) oak-hickory dominance may be attained with scattered pine remaining as relics. 6. Lowland fields may follow a similar pattern if well drained. However, Rubus spp. is an important component of the pre-pine stages and is only gradually eliminated after pine dominance. The understory of the lowland pine stands includes many hardwoods and the species of oak and hickory which appear as the stands mature are typical of lowlands. In addition some beech and hard maple (A. floridanum) are present. Ultimately all but a few pine are eliminated and replaced by these lowland oaks and hickories with beech and hard maple associated. 7. Secondary communities in bottomlands are variable in composition and dominance. When pine does not come into a field, mixed hardwood stands are not uncommon but the same species may also appear in pure stands. Birch dominance occurs occasionally. By 36 years it has an understory and reproduction which indicate its decadence and that elm, red maple and ash will succeed it. Pure stands of sycamore may develop on lowland fields and sycamore too is replaced by maple-elm-ash in some combination. Young mixed stands may include birch, sycamore, red gum, tulip poplar, and other species. Eventual maple-elm-ash dominance is likewise indicated for these mixed stands regardless of the combination of species. The final community is again lowland oak-hickory. 8. Pine forest does not regenerate on burned and cutover areas. The fast growing subordinate species such as red gum, red maple and many others grow up quickly from sprouts and seed, and pine may be almost completely excluded. Oak and hickory seedlings and transgressives which were present in the old stand likewise profited by the removal of the overstory for they reach tree size and eventual dominance sooner than they would have coming up under the pine. 9. Primary communities are restricted to isolated areas relatively inaccessible to man or valueless for cultivation. The commonest are on small islands and spits formed in streams. On these wet and poorly drained areas the pioneer woody species are willow and alder which frequently form thickets. With stability and drainage the dominants are replaced by birch or sycamore which in turn develop an understory of elm, ash and red maple. The similarity between this and secondary lowland succession is obvious. 10. Bluffs along streams constitute rather mature primary habitats. Because of the variation in exposure, nature of the rock, erosion, etc., there is great diversity in the species present and the degree of development of the plant communities. South facing bluffs have the most xeric habitats in the region and the species are characteristic. Black jack and post oak are common as are several sclerophyllous shrubs, mostly Ericaceae. North facing bluffs are mesic and usually exceptionally favorable habitats. As a consequence they support a great diversity of species among which are a number that are typical of higher and cooler latitudes and altitudes. The rarest species in the region may also be found here. 11. Erosion has played a part in the history of every habitat in the Piedmont. Site quality and ecological development can often be directly correlated with the degree of erosion. Local extremes result in gullying and the exposure of raw subsoils. Revegetation of these areas is almost impossible unless erosion is checked. Then a ground cover of lichens commonly appears with a scattering of legumes and several other typical small herbs. After a period of stability a sequence of herbs comparable to those of old fields appears and pine eventually occupies the site. 12. Bare rock, another primary habitat, is only of local significance. Except for occasional boulders, which are usually of no ecological importance, rock outcrops are common only along stream margins and in bluffs. Mat formation by mosses and lichens precedes the establishment of communities of higher plants. The rates of this development as well as the species involved are highly variable. Several species, rare or uncommon in the region, may be found associated with rock outcrops on both north and south facing bluffs. 13. The climax of the region is oak-hickory as indicated by relic stands and the gradual development of these hardwoods in the understory of pine stands. The commonest upland oaks are white, black, post, northern red, southern red and scarlet. The commonest hickories are white and pignut. Variations in site may result in variation in the composition of the dominant stratum so that, in general, two oak-hickory climax types may be recognized. The best sites are characterized by a preponderance of white oak with black oak an important associate and other oak species present in smaller numbers. On somewhat less favorable sites post oak is most abundant and white oak is relatively much less important. Black oak is absent from this community but black jack oak, absent from the white oak types, is almost always present here. These variations in the overstory species are the major differences in the two types. 14. Because of the agricultural value of lowlands postclimax vegetation is largely confined to narrow strips of rough talus below north facing bluffs. Data obtained from a single extensive old flood plain correlate well with the observations of species found on talus. The dominants are again oak-hickory with the addition of beech and hard maple. Within the moisture range of the type, beech seems to be favored on the best drained areas and maple on the wettest sites. Willow oak is most abundant, swamp red oak is somewhat less so. White oak is always present and overcup and swamp chestnut oak may be anticipated in small numbers. The hickories are likewise characteristic of low lands and include several species of shagbark as well as bitternut. 15. Preclimax is an oak-hickory community associated with dry south facing bluffs or poor soils characterized by an impervious clay hardpan. Stands are usually ragged and irregular with incomplete crown cover and weak development of understory. The character species are post oak and black jack oak with scattered hickories (mockernut, pignut). Such diverse species as white oak, red cedar, black gum, willow oak, ash and dogwood may be found in association. This development is localized and never of great extent. 16. The life forms of the species mentioned in the text were determined according to the system of Raunkiaer. The flora of the Piedmont is hemicryptophytic with a phanerophytic physiognomy. Spectra were also determined for special communities within the region. All climax communities are hemicryptophytic but phanerophytes are nearly double the percentages for the region. Spectra for bluffs serve to emphasize the extremes of the environments. Cryptophytes apparently predominate on north facing bluffs. Spectra for series of successional communities show definite trends in life form changes but also suggest rhythmic fluctuations in these trends.

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