Biological Services Program FWS/OBS-81 /37 March 1982 THE ECOLOGY OF BOTTOMLAND HARDWOOD SWAMPS OF THE SOUTHEAST: A Community Profile
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~~:137 Fish and Wildlife Service 2 c. U.S. Department of the Interior The Biological Services Program was established within the U.S. Fish and Wildlife Service to supply scientific information and methodologies on key environmental issues that impact fish and wildlife resources and their supporting ecosystems. The mission of the program is as follows: • To strengthen the Fish and Wildlife Service in its role as a primary source of information on national fish and wild life resources, particularly in respect to environmental impact assessment. • To gather, analyze, and present information that will aid decisionmakers in the identification and resolution of problems associated with major changes in land and water use. • To provide better ecological information and evaluation for Department of the Interior development programs, such as those relating to energy development. Information developed by the Biological Services Program is intended for use in the planning and decisionmaking process to prevent or minimize the impact of development on fish and wildlife. Research activities and technical assistance services are based on an analysis of the issues, a determination of the decisionmakers involved and their information needs, and an evaluation of the state of the art to identify information gaps and to determine priorities. This is a strategy that will ensure that the products produced and disseminated are timely and useful. Projects have been initiated in the following areas: coal extraction and conversion; power plants; geothermal, mineral and oil shale develop ment; water resource analysis, including stream alterations and western water allocation; coastal ecosystems and Outer Continental Shelf develop ment; and systems inventory, including National Wetland Inventory, habitat classification and analysis, and information transfer. The Biological Services Program consists of the Office of Biological Services in Washington, D.C., which is responsible for overall planning and management; National Teams, which provide the Program's central scientific and technical expertise and arrange for contracting biological services studies with states, universities, consulting firms, and others; Regional Staffs, who provide a link to problems at the operating level;and staffs at certain Fish and Wildlife Service research facilities, who conduct in-house research studies.
Cover design by Groham Golden FWS/OBS-81/37 March 1982
THE ECOLOGY OF BOTTOMLAND HARDWOOD SWAMPS OF THE SOUTHEAST: A COMMUNITY PROFILE
by Charles H. Wharton Institute of Ecology University of Georgia Athens, Georgia 30602 and Wiley M. Kitchens Edward C. Pendleton U.S. Fish and Wildlife Service National Coastal Ecosystems Team 1010 Gause Boulevard Slidell, Louisiana 70458 Timothy W. Sipe Department of Biology Wabash College Crawfordsville, Indiana 47933
Performed for National Coastal Ecosystems Team Biological Services Program Fish and Wildlife Service U.S. Department of the Interior Washington, D.C. 20240
{esf\ArCh Library DelpBa~tme~t of the Interiot :.,Jo~· 6 ona 1olog1cal Survey ?8g~ern Science Center r f. a.iundome Boulevard ua ayette, Louisiana 70506-315' DISCLAIMER
The findings in this report are not to be construed as an official U.S. Fish and Wildlife Service position unless so designated by other authorized documents.
This report should be cited as follows: Wharton, C.H., W.M. Kitchens, E.C. Pendleton, and T.W. Sipe. 1982. The ecology of bottomland hardwood swamps of the Southeast: a community profile. U.S. Fish and Wildlife Service, Biological Services Program, Washington, D.C. FWS/OBS-81/37. 133 pp. PREFACE
This report is one in a series of The information in this profile will corr.rnunity profiles whose objective is to be useful to environmental ~anagers and synthesize extant literature for specific planners, wetland ecologists, students, wetland habitats into definitive, yet and interested laymen concerned with the handy ecological references. To the fate and the ecological nature and value extent possible, the geographic scope of of these ecosystems. The format, style, this profile is focused on bottomland and level of presentation should make this hardwood swamps occupying the riverine report adaptable to a variety of uses, floodplains of the Southeast whose drain ranging fror.-: preparation of environmental age originates in the Appalachian Moun assessment reports to supplementary or tains/Piedmont or Coastal Plain (see study topical reading material for college wet area Figure 1). References are occasion land ecology courses. The descriptive ally made to studies outside this area, materials detailing the floristics of primarily for comparative purposes or to these swamps have been cross-referenced to .. highlight important points. The sections specific site locations and give the detailing the plant associations and soils report the utility of a field guide hand in the study area are derived from field book for the interested reader. i nves ti gati ons conducted specifically for this project. The senior author wrote the original manuscript and accepts the responsibility In order to explain the complexities for all statements, theories, and figures of the ecological relationships that are not credited otherwise. The co-authors operating in these bottomland hardwood extensively revised, reorganized the for ecosystems, this report details not only mat, and contributed parts of the manu the biology of floodplains but also the script, especially Chapters 3 and 4. geomorphological and hydrological compo nents and processes that are operating on Any questions or comments about or various scales. These factors, in concert requests for this publication should be with the biota, dictate both the ecologi directed to: cal structure and function of the bottom land hardwood ecosystems. We have utilized Information Transfer Specialist the ecol ogi cal zone concept developed by National Coastal Ecosystems Team the National Wetlands Technical Council to U.S. Fish and Wildlife Service organize and explain the structural com NASA/Slidell Computer Complex plexity of the flora and fauna. 1010 Gause Boulevard Slidell, LA 70458
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~ I 1 CONTENTS
PREFACE . . . . iii FIGURES ... . vi TABLES ... . X ACKNOWLEDGMENTS Xii
INTRODUCTION ...... 1 CHAPTER 1. MODERN AND PALEO-GEOMORPHOLOGY OF FLOODPLAINS 4 Introduction ...... 4 Origin and Dynamics of Floodplains 4 Features of Modern Floodplains 8 Paleo-Geomorphology 12 CHAPTER 2. HYDROLOGY. 16 Alluvial Rivers 16 Blackwater Rivers 17 Spring-fed Streams .. 17 Bog and Bog-fed Streams . 20 Flooding Duration and Frequency 20 CHAPTER 3. PHYSICOCHEMICAL ENVIRONMENT 21 Chemical Characteristics of Rivers .•••.... 21 Physicochemical Characteristics of Floodplain Soils 23 CHAPTER 4. FLORA OF BOTTOMLAND HARDWOOD COMMUNITIES 31 Introduction ...... •....•.. 31 The Anaerobic Gradient ..•..•.....•. 31 Plant Responses to Anoxia-related Stresses ... 32 Plant Community Patterns in the Floodplain ...... •.. 37 Disturbance and Succession in Bottomland Hardwood Plant Communities 76 Primary Productivity of Floodplain Forests 80 t CHAPTER 5. FAUNA OF BOTTOMLAND HARDWOOD ZONES 84 ~ Fauna of Zones II and III ..... 84 l Fauna of Zone IV ..•...... 90 Fauna of Zone V ...... • . . . 91 The Use of Bottomland Hardwood Zones by Fish . 92 Trophic Relationships ...... 95 ' Summary of Faunal Utilization .•..... 100 CHAPTER 6. COUPLING WITH OTHER SYSTEMS ...•...... 103 Natural Couplings with Headwater Tributaries and Estuaries 103 Coupling with River Deltas ...... ••••.. 104 Chemical Coupling with the Uplands ...... 104 Modifications of River and Floodplain ...... 105 Chemical Coupling with the Water Table and Atmosphere 107 Coupling Via Faunal Movements ..... 107 Su1T111ary ...... 107 REFERENCES ...... 109 APPENDIX: SOILS OF SOUTHEASTERN FLOODPLAINS 127
V FIGURES
Number 1 Major river floodplains and their associated bottomland hardwood communities within the Carolinas, Georgia, and Florida ..... 2 2 Landsat image of the floodplain of the Oconee River, GA, showing how large alluvial rivers that drain the Piedmont form extensive tracts of bottomland hardwoods below the fall line 5 3 Point bar and meander formation in floodplains 6 4 Diagram of an idealized alluvial floodplain with various depositional environments ...... 9
5 A meander bend and cross section showing levee and ridge and swale topography so common on modern and relict surfaces 10
6 Aerial photomosaic of the lower Roanoke River indicating flood plain features characteristic of rivers approaching the coast. 11 7 Sea level changes between the Sangamon interglacial period and modern times ...... 13
8 Development of present-day relict and modern floodplain surfaces 14
9 Hydrographs of four types of southeastern floodplain rivers and streams ...... 17
10 Hydrographs of an alluvial river showing the possible effects of an increase in floodplain width on water levels, between upstream and downstream ...... 17 11 Two photos showing drydown and inundation of the floodplain in the Congaree Swamp Nati ona 1 Monument ...... 18 12 Relation of flood discharge of Oconee River (GA) to distance downstream ...... 19
13 Diagram of the water budget for Creeping Swamp (NC), July 1974- June 1975 ...... 19 14 Indication of where Tertiary limestones lie at or near the surface, often giving rise to spring-fed rivers and contributing heavily to the Suwannee-Santa Fe system . 19
vi FIGURES (continued)
Number 15 (A) An idealized sequence of NWTC bottomland hardwood zones from a water body to an upland, along a moisture continuum. (B) One-half of a floodplain from mid-alluvial river to bluff, indicating modification of the idealized sequence by the intrusion of a natural levee between Zones II and III. {C) Further modification of the idealized sequence by inclusion of an abandoned river channel ...... 24 16 Diagrammatic scheme of the relationship of bottomland hardwood zones to soil types on a large alluvial river floodplain (Congaree Swamp National Monument, SC) 27
17 Dense surface mat of minute rootlets 28
18 A remarkable example of multiple-trunked stooling of Ogeechee tupelo at Sutton's Lake (Apalachicola River, FL) ..... 34
19 Oak displaying buttressing, common among bottomland hardwoods 35 20 A windthrown diamondleaf oak on a small blackwater creek flood plain illustrates the large diameter of the root crown of bottomland hardwoods ...... 36 21 The correspondence between alluvial floodplain microtopography and forest cover types ...... 38 22 Microtopographic relief on a small blackwater creek floodplain 38 23 A liverwort zone, the upper boundary of which indicates that high water has stayed at that level for at least 16% of the year 49
24 The outermost swale along the Roanoke River (NC) 49 25 Ogeechee tupelos on the Apalachicola River measuring 1 m DBH , (diameter at breast height) ...... 50
26 Scenic Ebenezer Creek is a unique variant of Zone I I ...... 50
27 Drydown in water tupelo on Ebenezer Creek 51
28 The outermost backswamp on an alluvial floodplain 51 29 Tidal forest with characteristic interwoven mat of large roots close to the surface ...... 52
vii
J FIGURES (continued) Number
30 Three shoreline dominants, sweet bay, red cedar, and cabbage palm, characteristic of the tidal zone of an alkaline blackwater river ...... 53
31 A small grove of virgin cypress preserved on Lewis Island 54 32 Large overcup oaks occupy depressions (Zone III) in the dominantly Zone IV floodplain of the Congaree Swamp National Monument 57 33 Sweetgum giants in the Congaree Swamp National Monument .. 61
34 Many Zone IV bottomland hardwoods on Coastal Plain alluvial river floodplains have an understory of Sabal minor ..•. 61 35 The floodplain of the blackwater Canoochee is somewhat anomalous in the co-dominance of the diamondleaf oak with either spruce pine or loblolly pine ...•...... 62
36 Normally an upland species, the loblolly pine also grows in Zone V areas of many floodplains ...... 65 37 An old levee ridge near Cedar Creek supporting Zone V vegetation 66
38 Narrow, long ridges between swales on the lower Roanoke flood plain (NC) of probable late Pleistocene age have an almost diagrammatic zonation of Zone V hardwoods ...... 67 39 An example of understory species taking advantage of the dry environment of a floating log in order to exist in Zone II 75 40 Cross-sectional transects (aspect is looking downstream) of nine southeastern rivers and floodplains, indicating zones (I-V) and major vegetational and natural features . 77 41 A windthrown bitternut hickory on the floodplain of the Murder Creek Special Management Area ...... 79 42 Aerial view of relict rice fields on former bottomland hardwood forests that are presently managed for waterfowl ...... 80
43 The effect of a gradient of flooding on productivity as cor.1pared with a regional level that might be expected in the absence of standing or flooding water ...... 81 44 Organic matter production in ecological zones . 83
viii FIGURES (continued)
Number 45 Comparison of the bottomland hardwoods and characteristic fauna at different reaches of a blackwater river near the coast .. 85 46 Floodplain pools (Zone III) on a Piedmont alluvial floodplain are concentration centers for detrital decow.position and teem with vertebrate life ...... 86 47 Snails of the genera Vivipara are often abundant in shallow aquatic zones (Zones II) above tidal influence ...... 88 48 Six endemic species (and Lampilis splendida) of unionid clams recorded for the Altamaha River, GA ...... 89
49 The crop contents of a wild turkey killed in April in the Arkansas River bottomlands ...... 93
50 Two-way traps with wire mesh wings, set in a small Coastal Plain blackwater creek and in shallow drainways on the floodplain, revealed that 21 fish species, used the floodplain extensively 94 51 Largely terrestrial food chains involving detritus, granivory, frugi vory, and herbi vory . . . . 96 52 Largely aquatic detrital food chains 97
53 Common invertebrates of southeastern rivers 99
ix TABLES
Number
1 Acreages of bottomland hardwoods (oak-gum-cypress and elm ash-cottonwood) and other forest wetland classes in the south Atlantic States ...... 3 2 Comparative sediment losses and land-use practices 7
3 Changes in levee height in upper, middle, and lower reaches of typical southeastern floodplain rivers ..... 10 4 Physicochemical data summarized for Georgia rivers in water year 1977 ••....•...... 22 5 Mean inorganic constituents in selected Georgia coastal plain rivers and in the "world average river" ... 22 6 Physicochemical characteristics of floodplain soils by National Wetland Technical Council Zones 25 7 Comparison of some floodplain soil nutrients to those of Coastal Plain, Piedmont, and mountain soils ...... 29
8 Percentage of organic matter in selected wetland and upland soi 1s ...... 30
9 Trees, shrubs, vines, and herbs characteristic of southeast ern bottomlands and the floodplain zones in \'1hich they most frequently occur...... 39 10 Response of mature bottomland hardwoods, some upland species, and some levee species to varying lengths of time of inundation during growing season. 43
11 Dominance types of Zone II 45 12 Dominance types of Zone III 56
13 Dominance types of Zone IV 58 - 14 Dominance types of Zone V. 63 15 Forest dominance type distributions across the nine floodplain transects illustrated in Figure 40 69 16 Net primary productivity (g dry wt/m 2/yr) for bottomland hardwood communities, compared with other wetland and upland environments ...... 82
X TABLES (continued)
Number
17 Some environmental factors affecting the fauna of the bottom land hardwoods and their relative importance in each bottomland hardwood zone ...... 101 A-1 Soil analysis for floodplain dominance types, Zone I I, alluvial rivers . . 127 A-2 Soil analysis for fl oodp 1a in dominance types, Zone II, black- water rivers . . . . . 128 .. A-3 Soil analysis for floodplain do~inance types, Zone II, tide influenced sections (tidal forests) of spring-fed blackwater and alluvial rivers ...... 129 A-4 Soil analysis for floodplain dominance types, Zone I I I , alluvial rivers ...... 129 A-5 Soil analysis for floodplain dominance types, Zone IV, alluvial rivers ...... 130 A-6 Soil analysis for floodplain dominance types, Zone IV, b1 ack- water rivers ...... 131 A-7 Soil analysis for floodplain dominance types, spring-fed rivers (Zones II and IV) . . . . . 131 A-8 Soil analysis for floodplain dominance types, Zone V, alluvial rivers ...... 132
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ACKNOWLEDGMENTS
The authors reserve their most pro critically read all or portions of the fuse thanks to those individuals (and manuscript: Jay Benforado, Robert Huffman, their organizations) who devoted time to Robert Meade, Helen Leitman, J.M. Lynch, assist in the field: L.L. Gaddy, H. Boyd, Roger T. Saucier, Arville Touchet, and A.E. Radford, J.M. Lynch, L. Peacok, J. Eugene Turner. We acknowledge the very Moore, R. Sharitz, M.M. Brinson, R. special help of Mark Brinson, Steven Sniffen, C. Gresham, J. Pinson, H.M. Leit Forsythe, John Coffin, and Parley Winger. man, A. Redmond, P. Grover, N. Eichholz, R. Kautz, G. Bass, and N. Young. The We extend our sincere appreciation to special logistical support of the Florida Linda C. Lewis, Gladys V. Russell, and Game and Fresh Water Fish Commission Kathy B. Waggoner of the Institute of through Grey Bass, Norman Young, and Neal Ecology, and to Elizabeth Krebs and Daisy Eichholz is particularly acknowledged. Singleton of the U.S. Fish and Wildlife Service, for their dedication to the many We deeply appreciate the efforts of hours of typing provided for the publica those who aided in species identification: tion of this manuscript. We are also S. Gilchrist, W. Heard, R. Guard, T. indebted to Kate Benkert and Hal Rienstra, Wilkins, R. Godfrey, University of Georgia U.S. Fish and ~iildlife Service, for their Herbarium. Those who supplied other as valuable assistance. Finally, profound sistance were R. Jones, C. Coney, J. Cely, thanks are expressed to Gaye Farris, U.S. D. Shure, H.L. Ragsdale , R. Sharitz, J. Fish and Wildlife Service, for her extra Adams, G. Guill, F. Parrish, and A. Benke. ordinary editorial efforts. We are grateful to the following who
xii INTRO DUCT ION
Bottomland hardwoods occupy the broad "seasonally flooded basins or flats" (Shaw floodplains that flank many of the major and Fredine 1956); "mixed bottomland hard rivers of the Southeastern United States woods and tupelo-cypress swamps" (Stubbs as they flow through the Piedmont and 1973); "oak-gum-cypress" and "elm-ash-cot Coastal Plain to the sea. These forests tonwood" (Boyce and Cost 1974); and "deep and their fauna comprise remarkably pro swamps," "narrow stream margins," and ductive riverine communities adapted to a "broad stream margins" (Forest Service Re "fluctuating water level ecosystem" (Odum source Bulletins 1970, 1972, 1974, 1978). 1969) characterized and maintained by a natural hydrologic regime of alternating The extent and distribution of bot annual wet and dry periods. tomland hardwoods in the Southeast are indicated in Figure 1 and Table 1. Diverse The bottomland hardwood communities classification schemes and the inclusion support recognizably distinct assemblages of other categories of forested wetlands of plants and animals that are associated make difficult precise calculation of the with particular landforms, soils, and areal extent of the community; however, hydrologic regimes. The fluctuating hydro acreages appear to be equal in the four logic regime dictating the ecologic func States (North Carolina, South Carolina, tioning of modern floodplains is rela Georgia, and Florida) focused upon in this tively recent, perhaps originating around profile. The latest U.S. Forest Service 18,000 years ago in the late Pleistocene Forest Surveys, standardized in 1930, have period, when changes toward present strong been used in preparing Table 1, which seasonal climates began (Martin 1980). gives combined acreages of the two forest Many floodplain species are traceable to types occurring in each of the Forest Sur Tertiary times, and others originated as vey's physiographic classes. Each forest far back as the Mesozoic. Apparently, type, oak-gum-cypress or elm-ash-cotton rivers and their floodplains have served wood, is dominated singly or in combina as refugia for numerous relict life forms tion by these species (Boyce and Cost which found the dynamic conditions there 1974). suitable. Plants such as tupelo gums, and animals such as alligators, turtles, gar, Table 1 also includes the acreage of bowfin, sturgeon, and amphibians (Siren) forested wetlands other than bottomland survive es sen ti ally unchanged on modern hardwood floodplains. Cypress and wi 11 ow floodplains as relicts from the Age of strands, where water spreads out and moves Dinosaurs. Ironically, in the face of downslope through a wide forest of cy massive land use of surrounding uplands, press, are not included as bottomland floodplains today remain some of the last hardwoods; similarly, bays, pocosins, and refuges not only for floodplain species cypress ponds are excluded from this com but also for upland species. munity profile. Small drains, defined as poorly drained narrow strands lacking a Because the floodplains occupied by well defined stream, include many tiny bottomland hardwoods are transitional in headwater branches and drainways. Although the aquatic continuum between permanent not specifically floodplains, they are water and terrestrial uplands, they are certainly important in filtering drainage elusive to classify. The scheme of Cow from the uplands into the larger systems. ardin et al. (1979) used here classifies Their acreage is large but they are ex bottomland hardwoods as forested wetlands cluded from our calculation of bottomland in palustrine and estuarine ecosystems. floodplain acreage. Large swamps such as Other terms or categories which have been the Okefenokee and Dismal Swamp have been used to classify this community include excluded as well.
1
>l " ...... •••:, ... .• 0 ·,. ,.0 Figure 1. Major river foodplains and their associated bottomland hardwood communities within the Carolinas, Georgia, and Florida. Inset indicates physiographic provinces within the study area. 2 Table 1. Acreages of bottomland hardwoods (oak-gum-cypress and elm-ash cottonwood) and other forest wetland classes in the south Atlantic Statesa (Data courtesy Noel Cost, Southeastern Forest Experiment Station, U.S. Department of Agriculture Forest Service, Asheville, NC.) States Forested wetlands classes FL GA NC SC Total bottomland hardwoods on floodplains 1,149,891 1,435,453 1,618,135 1,110,343 Total other 2,160,906 1,623,052 565,942 717,138 Cypress strands 268,988 9,730 3,037 11,635 Cypress ponds 594,857 200,641 2,581 56,298 Bays &wet pocosins 564,359 186,088 221,307 217,650 Willow heads &strands 39,492 8,405 1,098 Marl flats & forested prairies 2,743 2,745 Sma 11 drains 589,291 1,154,151 328,722 398,629 Other hydric 101,176 64,037 7,550 31,828 alnventory dates: Florida, 1980; North Carolina, 1974; South Carolina, 1978; Georgia, primarily 1972 but includes 1981 survey of southwest Georgia. This community profile has been pre Besides conversion to agriculture, pared in part to provide information for another impact on bottomland hardwoods has management decisions. Like most natural been conversion to tree-farm monoculture. communities, bottomland hardwoods have Numerous examples occur along the flood felt the impact of man. Unfortunately, plains of the Ocmulgee and Oconee Rivers, the absence of uni form treatment of data GA, where the higher elevated bottomland and the screening of it as indicated above hardwood communities are logged,the stumps in publications such as Boyce and Cost bulldozed into windrows, and the terrain (1974}, Langdon et al. (1981), and Turner prepared for pine (or other) monoculture. et al. (1981) make it difficult to use earlier survey figures to calculate this Floodplain rivers have also been impact in terms of loss of bottomland subject to severe impacts, including con Hardwoods on southeastern floodplains over struction of impoundments, diversion time. canals, channelization, dredging, and shortening of channels. These alterations Losses of bottomland hardwoods in change the hydroperiod and may permanently areas outside the specific study region alter the ecology and functioning of the have been severe, none more so than the floodplain. floodplains of the Mississippi River drainage. There conversion of forest to It has not always been recognized agriculture, primarily soybeans, has re that the entire bottomland over which duced by 60% the areal extent of the hard flooding occurs is a functional part of wood community; by 1995, only a projected the wetland system and must be considered 3.9 million acres will remain intact, down as a unit when making resource decisions. from 11.8 million acres in 1937 (MacDonald Because the bottomland hardwoods in the et al. 1979). Although losses of flood study area still retain their ecological plains bottomland hardwoods in the Caro functions and value, environmental manag linas, Georgia, and northern Florida have ers have the opportunity to consider and been much less extensive, few areas in the weigh management alternatives. This pro Southeast have escaped some direct or file provides information to aid them in potential impact of man. this task. 3 CHAPTER 1 MODERN AND PALEO-GEOMORPHOLOGY OF FLOODPLAINS INTRODUCTION and red c 1ays of the Piedmont begins to dissipate at the fall line, where the The complexities of hydroperiod, cli river first encounters the easily erodible mate, soils, and watershed characteristics sedimentary strata of the Coastal Plain. have produced an often bewildering mosaic This dissipation results in deposition of of vegetative zones and associations in alluvium (sands, silts, and clays) which the bottomland hardwood community. To in turn is reworked by riverine processes understand better the complex relationship into meanders. The residual energy of the between hydroperiods and the bottomland flowing water is expended by this lateral hardwood community, one must first con meandering which serves to widen the river sider the geomorphology of the floodplain valley. Rivers adjust their slopes by itself. The biota of the floodplain cannot meandering until they reach a nearly be wisely interpreted or managed, nor can steady-state, with sediment load balanced the impact of man's modifications be cor- · with water velocity and volume. As the rectly evaluated without understanding floodplains widen out, more sediments can watershed-dependent floodplain hydrology drop out from overbank deposition. Remark and geomorphology. The biota alone pro ably broad, flat floodplains are the vide too narrow a viewpoint. result of these processes. Mountain and Piedmont rivers, on the other hand, al The energy of flowing water and the though they form floodplains when topogra sediment load of river flows are ulti phy and soi ls permit, sti 11 retain much mately responsible for the geomorphic potential channel energy. landforms on southeastern floodplains. This chapter discusses processes of water First order variables that determine and sediment distribution on floodplains the behavior of water and sediments in and landforms characteristic of both clude climate, geology, soils, land-use, modern and ancient environments. and vegetation (Morisawa and LaFlure 1979). Variables that describe the chan nel are velocity, slope, flow-depth, ORIGIN AND DYNAMICS OF FLOODPLAINS plan-form (shape from an aerial view point), and width (Gregory 1977). Other The flows and sediments carried by a variables are meander length and meander river are responsible for the origin, belt width (Blench 1972), discharge (vol character, and maintenance of the flood ume of water/unit time), and roughness of plains and their forest cover. The gently river bed (bottom presence of trees, sloping coastal plains of the Southeastern cobbles, dunes, etc.) (Leopold and Wol~an United States provide an ideal environ 1957). These variables are extremely mental setting for floodplain formation. interdependent. Erosional and depositional processes cul minate in a sinuous river channel within a The dominant depositional/erosional broad flat plain bounded by valley walls processes on floodplains are: (1) point or bluffs--the floodplain (Figure 2). bar deposition, (2) overbank deposition, and (3) sheet or gully erosion (scour) and Striking examples (Figure 2) of redeposition on floodplain surfaces in a floodplain formation occur along rivers in sequence of floods (Sigafoos 1964). the study area at the fall 1ine, the abrupt transition between the Piedmont and The point bar is built on convex the Coastal Plain. The excess energy of banks of streams Gr river meanders by lat river flows in passage over the bedrocks eral accretion (Figure 3). Since deposi- 4 Figure 2. Landsat imaae of the floodplain of the Oconee River, GA, showing how large alluvial rivers that drain the Piedmont form extensive tracts of bottomland hardwoods below the fall line, which in this photo runs diagonally from ldwer left to upper right. Milledgeville, GA, is marked M. Photo courtesy Georgia Department of Natural Resources. tion on the convex bank keeps pace with 3.8 cm {1.5 inches) have been documented erosion of the opposite concave bank, the for floods in the Potomac River Basin, VA bulk of the sediment remains stored in the {Sigafoos 1964). Average deposition, how floodplain (Leopold and Wolman 1957). ever, ranges between 0.3 m {1 ft) and 0.6 m (2 ft) in 200 to 400 years (Wolman Though much slower than point bar and Leopo 1d 1957). The bed of the chan formation, vertical accretion by overbank ne 1, as well as the surface of the flood deposition also builds most southeastern plain, accumulates sediment deposits dur floodplain surfaces. Overbank deposition ing floods. Channels are also created and results from high water losing its veloc maintained by these overbank flows and ity and dropping sediments as it traverses accommodate the excess discharge of flood the floodplain, usually by sheetflow or waters. overflow channels. The amount of sediment deposited can vary widely. For example, a On forested floodplains, local ero single flood in the Atchafalaya River sion by overbank flows may produce rapid Basin, LA, caused sediment accumulations recycling and overturn of deposited sedi of up to 46 cm ( 18 inches) over port ions ments. Surface erosion or scour is fo 1- of this vast flood plain. Accumulations 1owed by deposition of comparable magni ranging from 0.3 cm (.125 inches) to tude, and the flootlplain becomes a spatial 5 (1) INITIAL UNIFORM CHANNEL DIRECTION OF FLOW--.- (2) ..... POOL TO POOL - 5 TIMES WIDTH ,,_ x' ~'fi.?Z/W~ POOL B- "- ~ 'CUT BANK - _ -RIFFLE POOL TO POOL - 5 TIMES WIDTH Figure 3. Point bar and meander formation in floodplains. Unstable stream flow in uniform river channels (1) forms pools and riffles (2). A meandering channel (3) develops and eventually exhibits erosion on the concave banks of meanders as well as deposition and point bar formation on the convex banks (4). (After Muller and Ober lander 1978, courtesy of Random House, Inc.) mosaic of erosional and depositional sur nels, whereas silts and clays are carried faces superimposed over material deposited as suspended matter in the water column. earlier by point bar accretion (Sigafoos Silts and clays, the principal components 1964). The features resulting from thesE' of surface floodplain soils, settle out or processes are detailed in the followins form overbank deposits during floods. A se~tions. reduction of particle size downstream may result from the weathering of silt and Sediment clay particles that remain in place for long periods of time between episodes of Sediment source is provided by con downstream transport (Curry 1972). tinual erosion of the landscape throughout geological time. In the Piedmont and Land uses in uplands profoundly af mountains, this source is igneous and fect the quantities of sedi~ent entering a metamorphic rocks (granites, schists, and stream. Before the 1900's, sediment inputs gneisses) which decay or weather under the to southeastern river systems were minimal influence of rainwater. Released compo according to some observers. River pilots nents are sands, silts, and clays, which recalled that as late as 1912 the Tennes are transported by sheet-wash or gully see River was relatively clear even after wash into streams. In the Piedrront this heavy rains (Ellis 1936). fl.ccording to decay produces a soil horizon (vertical one report, the turbid Altamaha River of layer) of saprolite (decomposed rock) up coastal Georgia was once a relatively to 9.2 w. (30 ft) thick. clear stream, and as late as the 1840's it was possible to determine on which tribu The weathered Piedmont saprolite tary (Ocmulgee or Oconee) rains were fall little by little washes downstream. Pied ; ng s i nee much of the Oconee drainage was mont sands are transpofted as bedload in agriculture (Lyell 1849). rolling along the bottom of stream chan- 6 Sediment losses from forested uplands water) and rivers originating in the are usually modest (2.5 cm or 1 inch/ Piedmont 1alluvial) have three terraces 16,000 years; Soil Conservation Service (Pleistocene) above the present floodplain 1977). However, the losses after the that are similar in type of landform, forest is removed can be quite substantial slope, particle size, and composition of (Table 2). When forest cover was reduced sediments to those of the present {Ho lo from 80% to 20% in the Potomac Basin, cene) floodplain (Thom 1967). For example, sediment loading increased eight times the quartz sands of the present point bars (Patrick 1972). The Soil Conservation of the Little Pee Dee River (a blackwater Service (1977) reported losses from crop stream) are similar to those of the higher lands (some of which were once forested terraces. In the Great Pee Dee River (a floodplain) of 38.4 tons/acre/year of top Piedrnnt, or alluvial, strear:), the three soil to the Obion-Forked Deer River (TN). older terraces also have the same composi tion of silts and sands as does the pres It is difficult to distinguish wheth ent floodplain. er sediments are derived from natural or culturally accelerated sources (Strahler Water and sediment supply are not 1956). Several investigators have at continuous but result from discrete cli tempted to estimate losses from the up matic events (Harvey et al. 1S79). The lands by measuring the thickness of sedi largest portion of the total load of many ment layers in coastal floodplains. Soils rivers is carried by high flows on the surveys indicate a loss of 15. 2 cm (6 average of once or twice a year. As inches) of topsoil from the South Carolina flow variability increases and as size of Piedmont in 150 years. Between 1910 and watershed decreases, a lar~er percentage 1934, one Georgia Piedmont watershed lost of sedir.;ents is carried by less frequent 218 tons/km2/year, but by 1974 this rate flows. In many basins 90% of sediment is was reduced by 86% (30 tons/kml/year) moved during floods recurring at least (Meade and Trimble 1974). Happ (1945) once every 5 years (Wolman and Miller concluded an average Piedmont upland soil 1960). Piedmont streams carry 10 times loss of 9.4 cm (3.7 inches) since earliest the sediment of Coastal Plain streams at settlement. the same discharge rate during floods {Meade 19 76). Although agriculture has heavily accelerated the loss of soil from uplands, Slope and Meandering 90% of the sediment from accelerated Pied mont erosion remains on hill slopes and in River systems are remarkably dynamic. stream bottoms (Trimble 1979). In fact, Changes of slope (elevational gradient) the composition of alluvial sedir.ients and which cause rivers to flow can be due to their rate of deposition in some flood (1) crustal uplifting or downwarping plains do not reflect a marked change in responses of the coast to the removal of rate due to agriculture. In South Caro- the Pleistocene ice mass, (2) scour or 1ina, both Coastal Plain rivers (black- erosion which steepens headwaters, or {3) Table 2. Comparative sediment losses and land-use practices (Happ et a 1. 1940). Land use Sediment loss practices (tons lost/acre/year) Oak forest C.05 Bermuda grass 0.19 Cotton (contour plowed) 69.33 Cotton (down slope plowed) 195.10 Barren abandoned field 159.70 •· 7 deposition which flattens downstream formity in the rate of work over the reaches. Deposition by tributaries often various riverbed irregularities than does increases river slope in the region imme the straight channel (Leopold and Langbein diately downstream of their junction with 1966). In addition, the meandering river the main river. This increase in slope and its floodplain apparently present the results from elevation of the river chan most efficient geometry to accommodate the nel bed due to sediment accretion at the mean and extremes of flow variability that juncture of the two streams. have occurred throughout its history. Basic features of swamp rivers and The types of sediment through which streams are their sinuous meanders (Figure meanders pass are important. In a river 3}. Meandering is one way the river accom system, meanders will occur where bank modates slope. Meanders lengthen the path material is comparatively uniform. Mean of the water, adjusting the energy of the ders move slowly if banks are cohesive flow to a uniform rate of energy loss per (silt or clay) and rapidly if banks are unit of stream length (Leopold and Lang easily erodible (sands, silty sands). bein 1966). In other words, the flow rate Depending on the type of sediment load, is stabilized as the slope of the stream meander wavelength can vary ten-fold at a is made more uniform and less steep by given discharge (Schumn' 1969; Thorne and increasing the distance that the water Lewin 1979). traverses in its vertical descent from the Piedmont to the coast. The process can be compared to a skier whose rate of descent FEATURES OF MODERN FLOODPLAINS is slowed by meandering: the consistency and resistance of the snow determine the Although floodplains appear flat and meander path which he follows for his featureless from the air, in reality they particular weight. The path of the water are characterized by diverse topographic bends as uniformly as possible (conforming features as a result of the continual, to a sine-generated curve), minimizing dynamic reworking of their sediments by bank erosion and the expenditure of energy rivers. The low topographic relief of the (Leopold and Langbein 1S66}. After the floodplain landscape is deceptive; a mat water rounds the meander curve, it flows ter of inches in elevation W4Y produce straight until centrifugal and inertial quite distinct ecological zones (see Chap forces are diminished to the point where ter 4). The following sections detail the gravity can turn the water back downs lope origin and the dynamic nature of the major and the process is repeated. The greater geomorphic features of the floodplain l the volume, velocity, or density (water (Figure 4). containing sediment weighs more than water without sediment), the greater the force Channels I and the further the river travels before it is turned back to form the next meander The river channel processes, as dis 1 loop. It follows that meander length and cussed earlier, create and maintain the radius are closely related to the width of floodplain. As a precursor to developing the river. The width of meanders is a meanders, basically unstable flows in the function of water volume, velocity, and stream create a series of pools (scoured density. The development of meanders areas) and riffles (areas of redeposition) occurs at bankful (flood) stages (Thorne through erosion of the stream bank. Ero and Lewin 1979). Meanders occur at fairly sive forces continue to act in meanders. consistent intervals of 7 to 15 times the Scouring occurs on the concave bank of a width of the channel (Dury 1977). meander; conversely, scoured material is deposited on the opposite convex bank River slope adjusts naturally to the (Figure 3). Good basic references on velocity required to transport the load of channel geomorphology are Leopold et al. water and sediment supplied by the drain (1964), Allen (1965) and Schurrrn (1971) as age basin. As slope increases, a stream well as overviews by Thorne (1977) and must cut down (degrade) or develop a sinu Winger (1981). ous course. A meandering reach is stabler than a straight reach (Yang and Song 1979) The stream channel morphology (width, because it more closely approaches uni - depth, slope, and meander characteristics) 8 natural channels and transport sands and silts (Wolman and Leopold 1957). In fact, during overbank flows when the waters M leave the meandering channel, the flood plain surface becomes the high water channel with the current directed straight downslope (valley-axial direction) short ening the pa th of fl ow and increasing the slope of the water surface (Carlston 1965). Only the structure of the intact forest impedes the ravaging flows and pre vents catastrophic scouring of the flood plain surface and valley walls. Under certain conditions, specialized channels are formed. Terned braided and anastomosing channels, they are character ized by the main river channel dividing into numerous interconnected channe 1s. Braiding results from a change in grade or slope so abrupt that coarse sediment, i usually sand, is precipitously deposited. ~ Braiding, however, can occur at any point in a stream where large deposits of coarse sediments occur. For example, large amounts of sand brought down by a channel ized reach of a tributary (Flat Branch) of Figure 4. Diagram of an idealized allu the Alcovy River (GA) have been deposited vial floodplain with various depositional on the main stream floodplain, causing the environments. RC = river channel; M = main flow to braid. Braiding may also direction of meander movement; L = natural occur at river confluences (e.9., Little levee; P = point bar deposits (alternating Pee Dee and Lumber River, SC). Braiding ridge and swale topography); B = back is often a temporary phenomenon. Hhen a swamps; C = channel fill deposits (former river divides and rejoins on a vegetated ox-bow lake); R = ridge (former natural floodplain and the channel configurations levee around adandoned channel); OC = are relatively unchanging, it is better overflow channel; S = swale deposits. termed an anastomosing stream. Both Four Hole Swallip (SC) and parts of the Chipola River (FL) are examples of anastomosing channels. depends on long-term patterns of flow (Blench 1972). High flow regimes are Natural Levees ' principally responsible for the formation of channels, while low flows are responsi During periods of overbank flow, as ble for only minor adjustments in channel waters spread out over the floodplain, morphology (Keller 1977). The process of water currents abruptly slacken, and sus channel formation is greatest at bankful pended sands and silt are deposited as a stage. Therefore, the annual to biennial levee ill1!1ediately adjacent and parallel to flood intervals are more important than the channel. periodic catastrophic flooding (Wolman and Mi 11 er 1968). When flows exceed the Natural levees (Figures 4-6) are best capacity of the river channel, the entire deve 1oped on concave stream banks. They floodplain becomes the channel, and addi also may occur along straight reaches, tional physical factors come into play. although they are usually higher on one side than on the other. Some large rivers Since current velocities are a func may have mile-wide levees; however, the tion of the slope of the water surface, it average river in the Southeast has levees is not surprising that water velocities between 30 m (98 ft) and 100 m (328 ft) over the floodplain during overbank flows wide. Natural levees slope gently to are comparable to the mean velocities of flood basins and back swamps. The height 9 ------" ~·· Table 3. Changes in levee height in upper, middle, and lower reaches of typical southeastern floodplain rivers. Levee height (ft) :_':.'·.1.:·:. RIVER Rivers Upper Middle Lower ...... ' ... , ...... ·.. ·. ·. : : ...... ', Roanoke (NC) 13.0 6.0 0 Great Pee Dee (SC) 6.0 3.0 <2 Apalachicola (FL) S.6 4.5 where elevational relief is liwited to sha 11 ow depression basins and almost imperceptible rises. The term backswamp Figure 5. A meander bend and cross sec also may be applied specifically to peat tion showing levee (L) and ridge (R) and forming environments occupying relict swa 1e ( S) topography so common on modern channels along the outer rim of the flood and relict surfaces. Pioneer and suc plain. cessional plant species anchor the newly formed sandy ridges leading to even more Floodbasin, flat, and backswamp sedi deposition at each high water episode. ments are composed of fine silt and clay Normal helicoidal currents (C) conduct particles. Acid backswamps are environ sediments up the bar slope. ments where deposition is minimal and are constantly wet, having water tables at or near the surface. Most of the floodplain, however, dries out annually. The fine of levees diminishes as rivers approach c 1ays tend to dry and crack in polygonal the coast because the stream's energy to patterns, allowing oxygen to enter. Depos move sand also decreases downstream (Table its in these areas vary with frequency of 3 and Figure 6). Some deeply incised flooding, proximity to the channel, sedi streams with headwaters arising from clay ment load, flow velocity, and substrate rich soils (Tallahala .River, MS) have texture. In many eastern floodplains barely discernible levees. Many black devoid of significant relief, overbank water streams have unimpressive levees, deposits may be coarse and layered. Coarse apparently due to lack of sufficient layers represent the rise to maximum stage gradient in the outer Coastal Plain. A of an individual flood; the alternating breach (or crevasse) in the levee may pro fine 1ayers represent recession of fl ow duce an alluvial fan-shaped feature termed (Allen 1965). a crevasse-splay deposit which spreads out over the floodplain (Allen 1965). Point Bars and Ridge and Swale Topography Floodbasins, Flats and Backswamps Most deposition occurs along the main channel of the swarr.p stream. Materials The term floodbasin specifically are eroded from concave sides of channel applies to vast underfitted floodplains meanders and redeposited on convex bends (floodplains developed under a signifi to form point bars (Figure 3). Small cantly higher flow regime than at present) ridges formed on the point bar by depos i where channel meanders r.iay occupy only a ti on ot bed load material during floods portion, or belt, of the floodplain width. form a temporary natural levee on the con Along southeastern rivers that are not vex side of meanders. The crests of these markedly underfitted, the floodplain ridges r.iay stand higher than natural lev between the natural levees and high valley ees on the concave side. As the river bed wall is generally called ambiguously a moves laterally an~ downstrear.i (Figure 5), 11 backs~1amp 11 or more succinctly a. "flat" a series of ridges for~s with intervening 10 Figure 6. Aerial photomosaic of the lower Roanoke River indicating floodplain features characteristic of rivers approaching the coast. (A) ,Many oak-dominated ridges occur. (B) Levees are high (4 m or 13 ft) and broad (91- 594 m or 300-1950 ft). (C) Large tracts of water tupelo-cypress with logging road networks. (D) Levee heights drop to 2 m (6 ft). (E) Due to mix of late Pleistocene and Holocene influences, floodplain features are very diverse. (F) levees absent, river at base level; floodplain almost pure gum-cypress {logged by barge}. (G) Tributaries now arise de novo from floodplain, indicating tidal influence. (H) Shrub bog with deep peat. (I) Albemarle Sound. (Photoquads: North Carolina Department of Natural Resources and Community Development; data from Lynch and Crawford 1980.) ,.. - ;4 :;; ;4 a a .. depressions or swales. Vegetation quickly basins are microtopographic features· invades and stabilizes each point bar producing only slight elevational and ridge, encouraging further deposition. drainage changes; however, their effect Ridges are composed priwarily of sands. on plant species distribution is often Silts and clays are deposited mainly in marked. swales, forming a sticky clay subsoil (gley), sometimes called "blue mud." Mate Scour channels are small waterways rial eroded from the concave side of one within the floodplain 9enerally formed meander loop is deposited on the convex during high water as flows seek shortcuts: side of the next downstream r.ieander. The for example, cuts or chutes across bends, floodplain is thus "reworked" to the depth or tributary connections to the main of the deepest part of the channel. Sedi channe 1. A high percentage of sand is ments are resuspended by powerful bottom present in the scour channels (and on the flowing crosscurrents (Figure 5). Meanders adjacent floodplain as well) because scour migrate because of the constant erosion channels are areas where sheet flow may (undercutting) and/or slumping of the con carry a substantial bed load of sand cave bank laterally and downslope. Meander across the floodplain flats. migration is slow (<3 m or <10 ft/yr) in small southeastern rivers, particularly Hummocks are small "islands" left those with forested banks. On the other after years of erosion by scour channe 1 hand, meanders in India's huge Kosi River currents. Usually the curved channels in moved 750 m (2,460 ft) in 1 year (Wolman hummock terrains are weblike, weaving and Leopold 1957). around the bases of trees which may be "stooled," often bearing ferns and shrubs Dune Deposits on swollen bases. The top of hummocks ~ay bear trees characteristically found in Aeolian dunes form when strong winds areas of higher elevation, although in blow exposed sand from point bars or other some cases trees such as tupe 1o gums and sources onto the floodplain. Dunes 13.7 rn cypress form hummocks themselves. ( 45 ft) high so met i r.ies a re formed by the deflation (wind removal) of point bar ~iinibasins are shallow depressions sands and other bare areas of the flood that sometimes occur between tree bases. plain (Allen 1965). Several linear series Some may be created by swirling water; of large dunes occurring on the east side others are of ambiguous origin. They are l of the Altamaha River (GA) floodplain are frequently filled with rainwater. Any of probable aeolian origin (Bozeman 1964). detritus trapped in them is rapidly decom So extensive are these dunes that the pro posed by frequent fluctuations between dry pos·ed Big Morter-Snuffbox Project ( Soil and moist conditions. This is in contrast Conservation Service) recommended that to areas around the drier, raised tree l they be artifical ly joined to create a bases where detrital accumulations tend to huge levee to block off part of the flood increase floodplain floor elevations. In 1 plain and divert water from eventually addition, much of the aerobic-anaerobic flowing into certain tidal river distribu nutrient cycling is accomplished in rain taries. Aeolian dunes and those associated filled minibasins (Wharton and Brinson with the relict braided stream channels 1979b) (see Chapter 3). (e.g., little Pee Dee floodplain, SC; Thom 1967) probably were formed by gale-force Pleistocene winds blowing across the PALEO-GEOMORPHOLOGY unvegetated part of the floodplain from the southwest. Dune chains are more likely It is now recognized that Pleistocene to be forw.ed where discharge varies widely ice age climates and hydrology strongly and the floodplain is not heavily vege influenced both terrestrial and aquatic tated (Allen 1965). Discharge is thought landforms. Glacial and interglacial peri l to have varied much more during the Pleis ods during the Pleistocene produced dra tocene when strong seasona 1i ty developed. matic changes in climate, precipitation, and sea level. Increased precipitation 1 Scour Channels, Hunm,ocks and "Mini-Basins" and more intense. frost action during glacial advances caused considerable down Scour channels, hummocks, and mini- s 1ope movement and subsequent transl oca- 12 tion and deposition of surface materials least in part due to a pluvial (rainy) (Whitehead and Barghoorn 1962). The dimin period of much greater rainfall occurring ished relief and aggraded (filled in) 18,000 to 10,000 years ago (Thom 1967; va 11 eys of today's Piedmont are evidence W.G. rt,cintire, Louisiana State University of the tremendous i rrpact of the 1at era 1 Center for Wetland Resources, Baton Rouge; migration of soils during that era (Eargle personal communications). Discharge for 1940). Many common Piedmont soils are many streams subsided about 10,00C years , underlain by organic deposits as much as ago. Runoff decreased to one-seventh of ... 3.7 m (12 ft) thick representing downslope its magnitude 2,000 years earlier (Oury transport and deposition; in one study in 1977). Streams and rivers began to assume South Carolina more than 50% of the sur their underfit characteristics at this face was underlain by these soi ls (Eargle time. 1940). Pollen dating of the soils indi cated they were deposited n~ore than 35,000 Climatic changes, coupled with the years ago, possibly during the waning of more subtle influences of change in grad the first of the two periods of Wisconsin ; ent brought about by 1owered sea 1eve 1s glaciation, the so-called Altonian sub (Figure 7) or tectonic rebound of the stage. 1and, formed another characteristic geo morph i c feature of southeastern flood Some floodplains in the Southeast plains--the floodplain terrace. Increased apparently were affected by the climatic flow volume or, in some cases, an in changes associated with continental gla creased gradient, changed the hydrologic ciation. One striking feature reflecting regime and created a new flo·odplain sur these past climatic regimes is the dramat face, often 1ower than the o1 d one. De ic discrepancy between the size of the creased flow volume or increased sediment floodplain and the size of the present sometimes reversed the sequence, filling day river. Today many streams are too the floodplain back up with new sedi small (in terms of discharge volume and ments. In any event, step 1i ke terraces meander dimensions) to have produced such resulted, many of which are remnants of wide floodplains. Such streams are de prehistoric surfaces. This sequence of scribed as "underfitted" (Oury 1977). This alternating high (degrading) flows and phenomenon is common in alluvial rivers lower (aggrading) flows is diagrammed in and may occur in coastal blackwater Figures 7 and 8. Because precipitation streams (Wharton 1977). A growing body of generally has dee 1i ned into modern ti mes, evidence indicates that the geomorphology of underfitted stream floodplains can be THOUSANDS OF YEARS BEFORE PRESENT explained by the sequence of different 60 40 20 5 hy 13 s ~1 ------00 00 0~ s s F •0 s F • s F 0 Figure 8. Development of present-day relict and modern floodplain surfaces. (1) Sanga mon (S) interglacial stage. (2) Entrenchment (scouring) during waxing Altonian sub stage. (3) Farmdalian (F) interglacial with substage alluviation filling in the former entrenched valley. (4) Entrenchment during waxing Woodfordian substage. Remaining Farmdalian (F) deposits are also known as Deweyville (or Terrace I). (5) Post-Wood fordian alluviation forming modern day Holocene floodplain surface (M) about 4-5,000 years ago. Drawings highly modified from Saucier and Fleetwood (1970). 14 , and rivers have made drastic changes in and Louisiana combines three terraces into their courses, the floodplain has become a "Deweyvi 11 e sequence" lying between the a succession of relict surfaces, each original pre-Wisconsin glacial sediments bounded by terraces older than those deposited in the Sangaw.on interglacial c 1oser to the river. Their i r.iportance period (the Prairie Terrace) and the lies in the hydrologic control they still modern Holocene floodplain (Saucier and exert over the modern floodplain. Fleetwood 1970). At least three terraces can usually Prehistoric floodplain surfaces still be found in southeastern floodplains. The function in the modern hydro logic regime. Holocene terrace is usually the most re Some are inundated by present high water, cent; such terraces are known as "first and relict channels, ridges, and swales bottoms." The next lowest terrace is known bear vegetation associations indistin as the Terrace I, Deweyville, or in South guishable from those on their recent ana Carolina "second bottom," and is distin logues. The Pleistocene has left its guishable en many southern floodplains, imprint in many other ways. The mouths of including the Altamaha (GA), Pee Dee (SC), numerous rivers at the coast (Roanoke, Cape Fear (NC}, the Pearl and Pascagoula Chowan, NC; Escambia, Choctawhatchee, Fl) (MS), and the Sabine, Trinity, and Brazos are narrow, drowned floodplains entrenched (TX) (Gagliano and Thom 1967). Terrace I during the Woodfordian phase of Wisconsin sediments were deposited during a fluvial glaciation. The sediments of Terrace I period 17,000 to 36,000 yea rs ago with may have provided much of the sands for flows that were five to seven times great the barrier islands of the gulf and Atlan er than at present forming giant meander tic coasts (Thom 1967). scars or a braided topography of sandy bars and fossil dunes (Pee Dee River, SC) Other ancient floodplains have been (Thom 1967). In South Carolina, Terrace I variously used by man. Along the Waccamaw lies 1.5 to 3.0 m (5 to 10 ft) higher (SC) the relict ridges support roads and than the modern floodplain and 1.5 to pine plantations while the swales bear bog 6.0 m (5 to 20 ft) below a still higher vegetation. Along the Roanoke (NC) row Pleistocene fluvial or river terrace known crop agriculture occupies most of the as Terrace I I (Gagliano and Thoir 1967). ridges of the higher Pleistocene terraces Another floodplain terrace classification (3 m or 10 ft above MSL). scheme for the Ouachita River of Arkansas • t" 15 -" , CHAPTER 2. HYDROLOGY Water is the driving force of the as 102 cm ( 40 inches) per year from this bottomland hardwood community. As has Cretaceous aquifer. blackwater rivers been shown, water plays a crucial role in become visibly clearer in the fall because forming and maintaining the floodplain by their flow is derived largely from ground transporting and redistributing sediments water base flow. within the system. The rivers and their floodplains are fluctuating water level It is reasonable to assume that ecosystems. Their high flows are brought rivers recharge the shallow aquifers at about by winter-spring rains (peak flow is high water in the flat Pleistocene depos in the surrmer in Florida). Their low flows its, but it is yet to be proven how much correlate with high evapotranspiration rivers contribute to the deeper aquifers. during late su11111:er and dry fall months The net contribution of alluvial rivers to (Wharton and Brinson 1979a). Sources of the principal limestone aquifer is thought water to bottomlands include precipitation to be insignificant (Stringfield and and runoff from mountains and Piedmont LeGrand 1966). Surface streams and swamps (alluvial rivers), groundwater from local may recharge valley aquifers (Wharton convective and storm-front rainfall (lower 1970; Bedinger 1980). Coastal Plain blackwater streams), under ground aquifers (spring-fed alkaline streams), continuous seepage from sand ALLUVIAL RIVERS aquifers (bog and bog-fed streams), and tidal flow. Alluvial rivers in the Southeastern United States originate in the mountains Before development, when intact for and Piedmont and form huge swamps at the ests with thick, organic soil layers cov junction of the Piedmont and Coastal ered the landscape of mountains and Pied Plain. Most of these rivers have periods mont, almost all water to alluvial streams of sustained high flow resulting from the was derived via subsurface (ground water) cumulative effect of many tributaries and flow. Today exposed subsoil horizons in distant rainfall (Figure 9A). Generally, the Piedmont lead to surface runoff which the annual high winter-spring runoff water is now the primary source of water to overflows the floodplain features. Pat t'l'lese streams. On the flat Coastal Plain terns of river discharge vary in different terrain, surface runoff occurs only spo sections of the watershed. For example, radically except when the soils are satu discharge peaks are higher in the Apalach rated (water table at or near the sur icola River (FL) in the comparatively nar face); therefore, rainfall in the Coastal rower upper section with high levees and Plain reaches blackwater streams via steeper gradient, as compared with the ground water (base fl ow) in fall and by flatter s ta9e hydrograph approximately grcund water and surface runoff in winter 48 km ( 30 mi J downstream where the water and spring. Base flo\o,S become the primary spreads out over a much wider ( 5 x) and source to streams during low water or flatter floodplain (Figure 10). Differ drought conditions. ences in wet (flooded) and dry stages can be dramatic (Figure 11). Discharge volumes Surficial aquifers (Hawthorne, Creta may cease to rise and sometimes even fall ceous) may contribute markedly to base as the water flows through the floodplain fl ow. Dur i n9 a fa 11 drought Thompson and toward its mouth (Figure 12). Evapotrans Carter (1955) computed base flow discharge piration after March leafout and surficial from the Tuscaloosa formation to minor aquifer recharge may help account for some Georgia streams ranging from the rainfall of this flow reduction (Mulholland 1979; equivalent of 28 cm (11 inches) to as much Brown et al. 1979). 16 r BLACKWATER RIVERS Blackwater rivers and tributary streams originate in the Coastal Plain and receive most of their discharge from local precipitation. These streams have nar rower. less well-developed floodplains and reduced sediment loads compared to those of alluvial rivers .. The waters are rela tively clear. but highly colored (coffee colored) due to the presence of organics (humic substances) derived from swamp B. BLACKWATER drainages. A hydrograph of a blackwater stream (Figure ~·B) is characterized by irregular discharge peaks that are due a 1most wholly to fronta 1 or 1oca 1 weather events. Surrrner flooding. as well as more typical winter-spring flooding, may result from local storms. Unlike that of larger alluvial streams (Figure 9A). the hydro C. SPRING FED graph of a smaller blackwater stream may register dry periods during which dis charge may dwindle to near zero. D. BOG STREAM Many blackwater streams are coastal plain tributaries to alluvial rivers. Water levels in some of these streams may be controlled by the discharge levels in the main river creating a "water dam" effect (Wharton and Brinson 1979a). ONOJFMAMJ JAS Ground-water seepage, or base flow, MONTH is a particularly important component of Figure S. Hydrographs of four types of the discharge of bl ackwa ter streams. A southeastern floodplain rivers and study (Winner and Simmons 1977) of a small strearrs. North Carolina Coastal Plain blackwater stream (Creeping Swamp, NC) (Figure 13) resulted in a water budget in which over land runoff accounted for 17.75 cm or 6.99 !50 E inches (17%) and base flow runoff for z 21.69 cm or 8.54 inches (20%) of the total ~ 45 precipitation of 107.29 cm or 42.24 inches. Evapotranspiration accounted for ~40 65.81 cm (25.91 inches) (61%) of the rain z fall. A negligible 2% seeped underground ~ 35 > and was lost to the watershed. .:g30 SPRING-FED STREAMS O NDJ FMAMJ J AS MONTH Spring-fed streams, characterized by Figure 10. Hydrographs (1974-75) of an clear, alkaline flow issuing principally alluvial river (lower Apalachicola River. from underground aquifers are common in FL) showing the possible effects of an northwest Florida and in other areas increase in floodplain width on water underlain by Tertiary limestone aquifers levels. between upstream (solid line. (Figure 14). The discharge hydrograph of River Mile 126) and downstream (dashed a predominantly spring-fed stream (St. line. River Mile 68). (After Leitman Marks River, FL). (Figure 9C) is quite 1978J flat compared to those of alluvial and 17 - ··-·-· ------' t l ... t -"--· Figure 11. Two photos showing drydown (upper) and inundation ,1ower) of the floodplain in the Congaree Swamp. National Monument (SC). Photo courtesy of U.S. National Park Service. 18 2 EV APO- PRECIPITATION TRANSPIRATION 107 cm 161%) 1100%) I OVERLAND I RUNOFF • (17%) BASE RUNOFF~~--..::,.,.__::,~ STREAM 120%) DEEP GROUND WATER OUTFLOW (2%) Figure 13. Diagram of the water budget for Creeping Swamp (NC), July 1S74-June 1975 (after Winner and Simmons 1977). IOL.--~~~~~B~~~-c=------=o DOWNSTREAM ----t~~ Figure 12. Relation of flood discharge of Oconee River (GA) to distance downstream. (A) = Piedmont station (Greensboro); (B) = fall line station (Milledgeville, drainage area 7770 km2 or 3000 mi2) just above the Oconee swamps in the upper Coastal Plain; (C) = downstream station at Dublin; (D) = junction with the Ocmulgee (Mt. Vernon, drainage area, 13,338 km2 or 5150 mi2). (1) = 2-year flood, (2) = 5-year flood, (3) = 10-year flood, (4) = 20-year flood, (5) = SO-year flood, (6) = 100-year flood. (Wharton 1980.) Figure 14. Dotted areas indicate where Tertiary l.imestones lie at or near the surface, often giving rise to spring-fed streams such as Florida 1 s Chipola, Wa kulla, Wacissa, and St. Marks and contri buting heavily to the Suwannee-Santa Fe system. The dashed line is the inner mar gin of the Coastal Plain. (Adapted from Stringfield and LeGrand 1966.) 19 blackwater streams. In Figure 9C, the into the rece1v1ng bog-fed stream. The highest flows are only about twice the streams receive little or no sediment lowest flow. Although most of the base load; therefore, few have floodplains and flow of the stream arises from the uniform most resemble shallow ravines. Their discharge of the spring, hydrographs may hydrographs exhibit extreme fluctuations also indicate local rainfall (Rosenau in response to rainstorms, with little or .et al. 1977). no base flow (Figure 90). Exa111ples are the New and Sopchoppy Rivers in Florida, Spring-fed streams are influenced by which drain giant shrub bogs and bay surface and ground-water fluctuations. swamps in the Bradwell Bay Wilderness Area During flood stages of the Suwannee River (FL). Typically the streams flood rapidly (FL),. the flow from Falmouth Spring is and drain gradua 1ly due to the baffling reversed, and the darker waters of the effect of their dense bay vegetation. Suwannee flow into the spring. At the other extreme, these streams may go dry annually, leaving an exposed bed as does, FLOODING DURATION AND FREQUENCY for example, the Alapaha River {FL); or the entire river channel, bed and all, may Flooding on alluvial floodplains de disappear as the river drops into under pends on the size and slope of the water ground corridors (lower Aucilla River, shed, which, together with soil and slight FL). elevation differences, help explain the variability in forest communities on vari ous floodplains. The duration of flooding BOG AND BOG-FED STREAMS also directly relates to watershed drain age area. Bedinger (1980) concluded that Two additional swamp stream types drainage ar as in the mid-West with less occurring on the Coastal Plain of the than 776 km2 (300 miZ) have fast runoff Southeast are. bog and bog-fed streams. characteristics, with flooding occurring Bog streams ·have 1imited distribution and 5% to 7% of the year. Flooding occurs in generally occupy the linear depressions or drainage areas ranging between i2,950 and swales between adjacent sand ridges and 18,130 kmZ (5,000 and 7,000 mi ). Flood reworked Coastal Plain relict dune depo pl a ins for rivers with watersheds exceed sits. An example is White Water Creek in ; ng severa 1 tens of thousands of square Georgia, located in Cretaceous residual miles are inundated from 18% to 40% of the dune sands. Many bog streams occur within year. Flood peaks are significantly lower I the Florida Panhandle area. Bog streams in basins with lake and wetland areas are characterized by a steady lateral (Carter et al. 1978). seepage from the surrounding sand ridges. Therefore, substrates of these systems are Steep watersheds with dense clay constantly wet and support fire-resistant, soils have "flash" inundations of compara bog-type vegetation. The linear nature of tively short duration. Rivers with intact these streams precludes any significant floodplain swamp forest slow down the rise watershed interception of rainfall beyond and fall of floodwaters (Wharton 1970). that falling directly on the stream. Flood heights diminish markedly as soon as alluvial (Wharton 1980) and blackwater Bog-fed streams, on the other hand, (Benke et al. 1979) rivers top bankful fl ow intermittently due to discharge fron, stage and begin to utilize their flood expansive bog-filled depressions. This plain swamps. i nterr.iittent discharge occurs only after significant runoff from rainfall exceeds Leitman (1978) showed the importance the water storage capacity of the bog. of local rainfall in maintaining saturated The depressions which feed these streams conditions ~t several locations on the are areas of internal perched drainage Apalachicola floodplain where residual underlain by clay aquicludes (impervious water is often perched in backswamps 1 to soil layers that retard the downward wove 2 m (3 to 7 ft) higher tr.an river level. ment of groundwater). These basins are Water levels in these floodplain pools and not incised by streams, water tables gen sloughs rise from local rainfall indepen erally occur at the surface, and excess dently of river st.age. flow from precipitation discharges readily 20 CHAPTER 3. PHYSICOCHEMICAL ENVIRONME~T The physicochemical environment of tions of total organic carbon and low con floodplains (including both aquatic and centrations of dissolved inorganics. soil environments) is a function of the interactions or processes occurring in the Distinctions among blackwater streams water column, in soil, and at the soil can be explained by their different ori water interface. These processes are gins within the Coastal Plain (Wharton and facilitated by the prolonged periods of Brinson 1979a) (Table 4). The waters of flooding (inundation) which saturate the the Satilla River, arising in the lower soi ls and the subsequent periodic inter coastal plain of Georgia, were soft, vals of drydown which de-water the soils. acidic and highly organic, while the chem This cyclic wet/dry regime imparts a istry of the Ogeechee, Canoochee, and unique chemical environment that has pro Ochlockonee Rivers reflect the input found effects on nutrient cycling and the (increased hardness, pH, and nutrients) character and adaptations of the flood from geological formations at their head plain biotic communities. waters. In Florida many rivers clear dur ing low flows, and pH approximates that of subsurface aquifers (pH = 7. 7). During CHEMICAL CHARACTERISTICS OF RIVERS high flows, however, surface leachates add organic acids and lower the pH to 4. 0. The chemical composition of flood The blackwater Santa Fe River typifies a plain rivers and streams reflects water phenomenon especially evident in many sources, headwater origin, and the compo Florida rivers. In its swampy headwaters sition of geological formations through the Santa Fe has a pH of 5.3. In the cen which rivers flow to the coast. Of the tral section, with swamp drainage during three major chemical classes of world high flow and alkaline ground water drain rivers (rock-dominated, precipitation age during low flow, the pH is 6.4; in the dominated, and evaporation-dominated; lower river, fed by artesian springs, the Gibbs 1970), floodplain rivers fall into pH rises to 7. 4. two: rock-dominated and precipitation dominated. Alluvial rivers are rock The distinction between blackwater dominated rivers whose inorganic chemical and alluvial river water chemistry is best load is derived from the products of reflected in the difference in the ratios weathering and leaching of the parent of inorganic to organic constituents. The rocks and soil in the mountains and high concentrations of organic matter in Piedmont. Concentrations of inorganic hlackwater rivers result in a 1:1 ratio of ions are typically higher than total dissolved inorganics to total organics organic carbon (TOC) concentrations whereas the predominance of inorganic com (Table 4). Blackwater rivers arising in ponents in .alluvial rivers leads typically the Coastal Plain, on the other hand, are to a 10:1 ratio (Beck et al. 1974). The precipitation-dominated. Rainfall, which magnitude of the organic load affects the represents most of the water input to concentrations of some of the inorganic these streams, contains relatively low load constituents. For example, only concentrations of dissolved inorganic those inorganic ions such as iron and solids (specific conductance). A compari aluminum, which form complexes with the son of river data in Georgia (Wharton and dissolved organic matter (DOM), are pres I Brinson 1979a) indicated that alluvial ent in greater concentrations in black rivers usually were higher than blackwater water streams (Table 5). Additionally, rivers in nitrogen, phosphorus, calcium, since the bulk of the dissolved organic and magnesium (the latter two constituents constituents are organic acids (humic and increasing water hardness) {Table 4). fulvic), the waters of blackwater·st.r1;ams Blackwater rivers were more acidic (lower are considerably more acidic (low pH) and pH) and characterized by high concentra- highly colored than alluvial streams. 21 Table 4. Physicochemical data summarized for Georgia rivers in water year 1977 (Wharton and Brinson 1979a). Figures in parentheses are numbers of streams for which data were averaged. Hardness Specific Total nitrite Total TDC (Ca, MJ) conductance + nitrate-N phosphorus Rivers (mg/1) pH (mg/1 (µmho/cm) (mg/1) (mg/1) Mountain river 1.8(2) 6.6(2) 3.5 16(2) <0.04(2) <0.02(2) Alluvial river-Piedmont 2.9(6) 6.9(6) 12-18(4) 48-83(6) 0.14 -0.50(3) 0.06(3) Alluvial river-Coastal Plain Ocmulgee-Oconee 4.1(2) 7.2(2) 18-33 68-122 0.09 -0.38 0.08(2) Flint (Newton) 5.5 7.5 30-50 84-144 0.34 -0.63 0.06 Altamaha (Everett City) 7.9 6.6 13-33 60-191 0.02 -C.55 0.07 Blackwater river Ogeechee (Oliver) 8.1 6.9 12-28 47-104 <0.18 0.04 Canoochee (Claxton) 13.2 5.6 6-11 35-57 Table 5. Mean inorganic constituents (ppm) in selected Georgia coastal plain rivers and in the "world average river" (modified from Beck et al. 1974). pH HC0 K Al Mn Rivers 3 Cl so4 Na Mg Ca Si02 Fe Satilla 4. 58 2.6 6.1 0.8 3.70 1. 00 0. 74 1.32 6.6 0.41 I. 05 0.06 Ohoopee 6.25 8.8 5.9 1.0 2. 73 0.86 1. 00 8.69 11. 1 0.04 0. 11 0.01 Ogeechee 6.28 30.2 5.4 1.2 3.42 0.74 1. 01 6.78 12.3 0.03 0.12 0.03 Altamahaa 6.80 29.6 4.0 2.6 3.95 1. 29 0.96 6.25 10.3 0.24 0.08 0.01 World average river 58.4 7.8 11. 2 6.30 2.30 4.10 15.00 13.1 0.67 a Represents conditions in the Georgia coasta 1 plain below the confluence with the Ohoopee River. 22 r In both blackwater and alluvial sys Zone I: river channels, oxbow lakes, tems organic matter represents the link and.per~anently inundated backsloughs between the river and its floodplain. Most of this organic matter is in the dissolved Zones II-V: the active floodplain form termed dissolved organic matter (DO~:) including swales (II and III), flats or dissolved organic carbon (DOC), corr and backswarnps (IV), levees, and posed pri nci pally of humi c substances relict levees and terraces (V) leached from soil, peat, and leaf litter. For example, up to 95% of the total Zone VI: the floodplain-upland tran organic matter in the Altamaha River was sition to terrestrial ecosystems DOfv'. (Reuter and Perdue 1977). Total organic matter averages around 15 mg/1 Examples of floodplain zonation are (Windom et al. 1975), ranging up to 100 depicted in Figure 15. An idealized mg/1 in waters leaching peat deposits floodplain proceeds sequentially frorr: the (Malcolm and Durum 1976). These materials river channel to the surrounding uplands are often chemically and biologically (Zone I-VI) along a sradually increasing inert (i.e., refractory) with concentra elevational gradient (Figure 15A). The tions changing principally in response to presence of natural levees interrupts this discharge additions or dilutions. A small sequence {Figure l5B); depending on eleva proportion of humic substances flocculate tion, the levee may be characteristic of in fresh water and can be seen as "silts" Zones II, III, IV or V. Accordingly, on white sand bars, or are rolled as bed levees are generally excluded from the load particles (J.H. Reuter, Department of N~TC zonal concept. Other geomorphic fea Geophysical Science, Georgia Institute of tures (Figure 15C) contribute further to Technology, Atlanta; personal communica the complexity of zonation patterns on tion). most southeastern floodplains (see Chap ter 4). PHYSICOCHEMICAL CHARACTERISTICS OF FLOOD Flooding produces and regulates the PLAIN SOILS chemical properties of floodplain soils by (1) continually depositing and replenish The alternation of inundation of ing minerals, including essential nutri floodplains during extended high flow per ents on the floodplain (the mineral sub iods of the river with drydown periods sidy); (2) producing anaerobic conditions during low flow conditions produces a spec in the soils; (3) importing particulate trum of soil types across the floodplain. and dissolved organic matter (POM, DOfv'.); These soil types are associated with and (4) removing or exporting accurr:ula elevational gradients which in turn dic tions of organic detritus {principally tate flooding frequency and duration: the degraded leaf litter). The degree to hydroperiod. Differences in elevation and which these processes operate in the six hydroper i ods a re the basis of a sys tern of zones is determined by the hydroperiod classifying the environmental and biotic (Table 6). ' zonation that result from this continuum of fluctuating water levels and soil mois An example of the relationship of ture. A system of six zones, developed by floodplain·soil types to bottomland hard the National Wetlands Technical Council wood zones is illustrated in Figure 16 for (NWTC) (Larson et al. 1981), provides a an alluvial river floodplain, the Congaree convenient framework for portraying the River (SC). The bulk of the floodplain relationship between the bottomland hard floor is Tc:.w Ga\'1 silty clay loam, support wood community and environmental factors ing principally Zone IV forest. However, necessary for effective management consid variations in microrelief or subsurface erations. Throughout the remainder of water table height can 11;ake differences this report these zones wi 11 be referred in surface soils even in s111all quadrats. to as either ecological or bottomland Reynolds and Parrott (1980), found spe hardwood zones. cific soil differences on a 1-ha plot coincidental with different patterns of Briefly, the classification generally tree distribution and postulated (from 28 corresponds to the following broad geomor wells) that water table differences ac phologic floodplain features: counted for the numerous soil differences 23 .. -- .A ... ace sen t:r 12m ...... tr C t SC S O C $ ,. 2@ h f $ ....,. -- • ...... ------A....,.'7~r-t-----+--_J_------IV V VI B ------ IV V VI N ..,::,. C ------ IV V II VI Figure 15. (A) An idealized sequence of NWTC bottomland hardwood zones from a water body to an upland, along a moisture continuum (dotted line represents the depth of the water table). (B) One-half of a floodplain, from mid-alluvial river to bluff, indicates modification of the idealized sequence by the intrusion of a natural levee between Zones II and III. If low enough, the levee may bear Zones II and III; if higher, Zone IV, and higher still, Zone V (C). (C) Further modification of the idealized sequence by inclusion of an abandoned river channel (filled with a clay plug and/or peat). Table 6. Physicochemical characteristics of floodplain soils by National Wetland Technical Council (NWTC) Zones (partially derived from Clark and Benforado 1981). Zone I (permanent water courses) is excluded from this table. Zones Characteristic I I III IV V VI Intermittently exposed; Degree of inundation nearly permanent inun Semipermanently inun Seasonally inundated Temporarily Intermittently and saturation dation and saturation dated or saturated or saturated inundated or inundated or saturated saturated Timing of Year-round except Spring and summer Spring for 1-2 months Periodically During excep flooding during extreme during most of the of the growing season for up to 1 tionally high droughts growing season month of floods or growing extreme wet season periods Probability of 100% 51%-100% 51%-100% 10%-50% 1%-20% annual floodinga Duration 100% of the growing >25% of the growing 12.5%-25% of the 2%-12.5% of <2% of the of flooding season season growing season growing growing season I"\) season !JI Soil texture D9minated by silty Dominated by dense Clays dominate surface; Clay and $ands to clays clays or sands clays some coarser fractions sandy loams (sands) increase with dominate; depth sandy soils frequent Sand:silt: clayb (% composition) Blackwater 69:20:12 74:14:12 Alluvial 29:23:48 34:22:44 34:20:45 71:16:14 Organic matter % b Blackwater 18.0 7.9 Alluvial 4.5 3.4 2.8 3.8 Oxygenation Moving water aerobic; Anaerobic for portions Alternating anaerobic Alternating: Aerobic stagnant water of the year and aerobic conditions mostly year-round anaerobic aerobic, occas i ona 11 y anaerobic (continued) .,. _ Table 6. (Concluded). Zones Characteristic II I I IV V VI Soil color Gray to olive gray Gray with olive gray Dominantly gray on Dominantly Dominantly red, with greenish gray, mottles blackwater floodplains gray or gray brown, reddish bluish gray, and and reddish on ish brown brown, yellow, grayish green mottles alluvial with brown with brown, yellowish red, ish gray and grayish ye 11 owi sh and yellowish brown mottles brown, and brown, with a reddish brown wide range of mottles mottled colors pHa Blackwater 5.0 5.1 Alluvial 5.0 5.3 5.5 5.6 Phosphorus (ppm)b Blackwater 11. 2 9.8 N O'I Alluvial 9.1 6.3 8.1 4.8 Calcium (ppm)b Blackwater 607 .0 346.0 Alluvial 1,079.0 752.0 669.0 186.0 Magnesium (ppm)b Blackwater 98.0 36.0 Alluvial 154.0 140.0 145.0 39.D Sodium (pprn)b Blackwater 46.0 31. 0 Alluvial 94.0 31.0 28.0 23.0 Potassium (ppm)b Blackwater 48 29 Alluvial 51 28 32 20 a Range includes drought years. b See Appendix. VI II V IV V ' ' t D C TC CH C TC C Figure 16. Diagrammatic scheme of the relationship of bottomland hardwood zones to soil types on a large alluvial river floodplain (Congaree Swamp National Monument, SC). Three sources of water are indicated: vertical arrows, rainfall; horizontal solid arrows, normal cyclic flooding from river; and dashed arrows, J:,'eriodic but irregular side flooding by "hill freshets" from a tributary stream. Orders and suborders of recent soil cl ass ifi cat ion are given in parentheses {Soil Conservation Service 1975): D (Zone II), Dorovan muck (Histosol, typic medisaprist); C (Zone V) Congaree silt loam (Entisol, typic udifluvent); TC (Zone III, IV) Taw Caw silty clay loam (Inceptisol, fluvaquentic dystrochrept); CH (Zone II) along distributary, Chastain loam (Inceptisol, typic haplaquept); VI, upland; I, river. within the plot. Hay (1977) noted that by heterotrophic microorganisms in leaf blackwater floodplain soils only 1 m (3 litter in the fall, held for several ft) apart varied in radiocesium levels by months, then mineralized and absorbed by as much as 190%. filamentous algal mats in winter and early spring. It is then released by the dying Mineral Subsidy algae and absorbed by trees and shrubs at leaf-out, with little ol" no net release Both inoroanic sediments and nutri into the water from autumn leaf fall until ents are deposfted on the floodplain dur tree growth in the spring. This tight ing overbank tloocting, although average nutrient recycling offsets potential loss sediment deposits are so thin as to be by flooding or leaching. unnoticeable. The fates of these materials vary. Residence time and biotic utiliza Sediment inputs to alluvial streams tion remain key questions. Some sediments include a high proportion of fine.grained may reside in the floodplain long enough clays and silt from Piedmont runoff (Table to be mineralized by weathering. As flood 6). These are deposited during the rela waters subside, leaves in swamp pools be tively long residence time of wat~r in come coated with silt and clay which may Zone IV backswamps and sloughs. Coinci be trapped by the biotic slime. Other dent with clay deposition is the deposi sediments are redistributed by scour dur tion of various materials adsorbed to the ing flooding. Mineral nutrients may be clay particles, including nutrient ions, transported or trapped adsorbed to sedi metal ions, and pesticides. ment particles (Delaune et al. 1976). Nutrients are incorporated into tissues of Soil Oxygen Conditions the biotic community and into sediments in response to vegetative growth and decay Over the course of a year, floodplain cycles (see Chapter 6). The shallow root soils may vary from being completely systems of many floodplain trees (Figure oxygen-depleted to being as saturated with 17) enable them to take advantage of this oxygen as upland soils. Because gas ex imported mineral subsidy. change is curtailed drastically in water logged soils (Ponnawperuma 1972) and bio Nutrients, notably nitrogen, also are logical res pi ration of the soil microbes conserved and recycled on the floodplain rapidly depletes the available oxygen, (Brinson et al. 1981). Inorganic nitrogen inundated or wet saturated floodplain (N}, especially amrronium, is immobilized soils become anaerobic for extended per- 27 Figure 17. Many bottomland hardwoods have a dense surface mat of minute rootlets which may extract essential minerals from the water following mineralization of bacteria, hyphomycete fungi, algae, or organic detritus and may exchange nutrients with the surfaces of silts, clays and organic matter. iods. The high clay content of floodplain developing efficient methods of transport sediments contributes to the impermeabil ing oxygen to the roots (see Chapter 4). ity of the sediments to water movement and Oxygen diffusion through the roots creates oxygen saturation. Retention of surface an aerobic microlayer in the surrounding water and restriction of oxygenation sediments which facilitates nutrient result in anaerobic conditions usually uptake. Penetration of roots into swamp within 3 days of flooding (Phung and soils is, however, hampered by the imper Knipling 1976). This condition is main meability of soils due to waterlogging and tained until the soils de-water during settling out of fine-grained silts and drydown periods. clays during flooding. As a result, con ditions of nutrient unavailability exist A consequence of floodplain soil over large portions of the swamp flood anoxia is that it severely limits nutrient plain despite soil nutrient concentrations uptake by plant roots. Plant species that are equal to or higher than those in which thrive in zones that a·re flooded Coastal Plain, Piedmont, or mountain soils throughout most of the growing season (Table 7). often have adapted to anoxic conditions by 28 Table 7. Comparison of some floodplain soil nutrients to those of Coastal Plain, Piedmont, and mountain soils. Floodplain values are averages from Zones 11-V (blackwater and alluvial). Samples are from top 6 inches below litter layer. Upland soil samples are from the A horizon. Coastal Plain Piedmont Mountains Overa 11 (Long (Perkins (Perkins floodplain et a 1. 1969) et al. 1962) et al. 1962) Nutrients (ppm) (ppm) (ppm) (ppm) Calcium 606 61.0 70 1. 5 Potassium 35 9.3 56 20.0 Magnesium 102 33.0 21 40.0 Sodium 42 31.0 Phosphorus 8 0.5 8 11. 0 in the upland forest. The floodplain swamp receives large inputs of organic Another consequence of prolonged matter through leaf fall, and some decom anae.robic conditions is pH change. .Under position and incorporation of this matter waterlogged conditions, acid soils in occur. Organic matter decomposition under crease their pH while basic soils decrease anaerobic conditions, however, is slow in pH. The pH of swamp soils in particu (2%-5% per year) in contrast to that of lar tends to rerna in acid throughout the oxygenated waters or aerobic soils (>10%). period of saturation (Kennedy 1970). Flooding and resultant pH changes increase The highest soi 1 organic matter the "mobilization" (or availability to occurs on floodplains draining vast, acid plants) of the macronutri ents phosphorus bogs along rivers such as the Sopchoppy (P), nitrogen (N), magnesium (Mg), and and New (FL), and on floodplains along sulfur (S), and the micro-nutrients iron spring-fed rivers (32%), tidal forests (Fe), manganese (Mn), boron (Bo), copper (40%), and on peat systems (up to 44%}. (Cu), and zinc (Zn) (Teskey and Hinckley Percent organic matter of Zone II soils in 1977). This may offset nutrient limita spring-fed river floodplains and Zone II tion by anoxi a. backswamps with swamp tupelo is also quite high (about 36%). Alluvial river flood Further, pH contro 1s the amount of plains have the lowest organic matter, DOM leaching out of leaves, the amount averaging <5%, a good working figure to precipitated as particles, and the size of separate blackwater and alluvial flood these particles (Kaushik 1975). Acid pH plains (Wharton et al. 1977}. delays precipitation of aggregated parti cles from DOM leachates. Soil Characteristics of NWTC Zones Organic Matter Overall, macronutrient concentrations on floodplains differ markedly from those Organic matter concentrations of of the uplands (Table 7 and Appendix). Ex floodplain soils are intermediate between cept for phosphorus, nutrients (especially those of bogs and po cos ins and those of calcium and magnesium) are generally uplands (Table 8). In situ deposition is higher in floodplain soils than in up the primary fate of-organic detritus in lands. Unusually high concentrations peat-forming and internally draining bogs occur in spring-fed and tidal systems in and pocos ins. Decornpos it ion and remi ner particular. ' a 1i za ti on are the major pathways of litter 29 Table 8. Percentage of organic matter in selected wetland and upland soils. Organic matter Sites (%) References Pocosin 66.8 Woodwell 1958 Swamp 31. 3 Woodwe 11 1958 Floodplain This study Zone II (alluvial) 4.5 Zone II (blackwater) 18.2 Zone II backswa~ps with swamp tupelo 35.3 Zone II springfed rivers 36.0 Zone III {alluvial) 3.4 Zone IV (alluvial) 2.8 Zone IV (blackwater) 7.9 Zone V (alluvial) 2.8 Coastal Plain pines 0.4 Long et al. 1969 Piedmont pines &hardwoods 1.4 Perkins et al. 1962 Mountain hardwoods 1. 5 Perkins et al. 1962 Some zones (see Appendix) are. roughly and exported as particulates or refractory comparable in calcium concentrations humic substances. (660 ppm) to a tulip poplar forest (Shu gart et al. 1976), which is considered Soil micronutrient concentrations eutrophic (Jordan and Herrera 1981). Some tend to be high, especially in acidic floodplain sites (blackwater .Zone IV, sites, although this may depend on the alluvial Zone V) approach oligotrophy amount of inorganic input, or distance (44-75 ppm Ca). In the study area, the from the channel (Appendix). Cobalt stor lowest nutrient levels occur in Zone V. age by swamp tupelo (Eyde 1966) and the high zinc demand of cultivated pecan trees There are marked differences in suggest that some floodplain vegetation organic matter concentrations arrong the may accumulate or need high levels of various zones. Some zones (II and black micronutrients. water IV) have low nutrient availability due to "lock up" of nutrients in organic The precise relationship between matter. This condition occurs particularly soils and vegetational responses in flood in swales and peat-forming soil types. plains is unresolved. It is unknown, for Periodic drydown is very important to example, why the low-nutrient, low-organic nutrient release from organic matter and flats of the Oconee support a magnificent litter. ~/hen drydown is rare or aperiodic wi 11 ow oak stand, or why the old growth (as fo the specific zones above), nutri di amondleaf oak on Turkey Creek has the ents_ tend to be bound in comp 1exes with lowest organic matter of any Zone IV organic matter. On other sites nutrient floodplain. Equally challenging is why concentrations are low as a result of a the mineral-rich Taw Caw silty clay loam lack of inorganic inputs (as in remote of the virgin Congaree Swamp National Mon swales adjacent to the upland). In black ument supports extensive Zone IV wet flats water rivers, nutrients may be complexed with few or no large trees. 30 CHAPTER 4. FLORA OF BOTTOMLAND HARDWOOD COMMUNITIES INTRODUCTION organic matter, material adsorbed to sus pended sediments, or solutes in the water Having established in the preceding column (principally dissolved organics). chapters the geological and biochemical The relatively high levels of productivity setting unique to river floodplains, we exhibited by floodplain ecosystems (dis now turn to the component of the ecosystem cussed later) are sustained only through that gives it its name--the bottomland the water and nutrient subsidies provided hardwoods. The plant species that thrive by the watershed and transported by the here are well adapted to the stresses river (Brown et al. 1979; Brinson et al. imposed by the hydroperiod; these trees 1980). The floodplain flora, in partner and their adaptations are a fundamental ship with the macro- and micro-fauna, and i ntegra 1 part of the geo l ogi ca 1 and merely postpones the 1oss of e 1ements to chemical functioning of the ecosystem. the sea. The trapping, assimilation, and partial cycling of nutrients in the flood The plant species and communities plain, essentially a diversion in the that inhabit the floodplain can be use relentless movement of water and sediments fully thought of as buffers that absorb to the ocean, yield an extremely produc and dissipate the physical energies of the tive and unique ecosystem. riverine system. Water movement is slowed and erosion is held in check through the anchoring of sediments by root systems, THE ANAEROBIC GRADIENT the deposition of sediments that are dropped from the slowed water column, and The distribution of flora in the bot the reduction of the water co 1umn by the tomland hardwood ecosystem revolves around spreading out of water (Leopold and Wolman three aspects of anaerobic conditions: 1957). Without the stabilizing forces of the biota to reduce water velocities and (1) the presence and intense selec inhibit subsequent meander movement and tive power of anaerobic condi floodplain scour, these physical altera tions generated by the hydroper tions would be extremely rapid. iod on the floodplain; The buffering role of the plant com (2) the anaerobic gradient, varying munities is also evident in the biogeo in space and time across the chemical cycles of the riverine-palustrine floodplain due to microeleva system. Essential mineral nutrients are tional relief, the soil mosaic, captured from the water-soil complex and and the hydroperiod; and fixed in plant tissues which ultimately support the floodplain's detritus-based (3) the tolerances of plant species trophic network {Wharton and Brinson to this gradient. 1979a). Remineralization by the soil microbiota and rapid uptake by plants Though factors such as 1i ght i nten during favorable (nonflooded) conditions s i ty, soil pH, and nutrient availability partially close the nutrient cycles. But affect plant distributions in other forest the nature of the riverine-palustrine communities. they are secondary to anaero system, in which the variable patterns of biosis in the floodplain community. In flooding and drydown continually interact fact, these other factors are, except for with the floodplain substrate, requires light intensity, functions of saturated active nutrient conservation by the biota soils and thus anaerobic conditions. {Brinson et al. 1980). Floodwaters trans port nutrients not immobilized in organ The anaerobic gradient in the flood isms or bound to soil constituents back to plain and its effects on plant distribu the river, as particulate or dissolved tions have been noted, often as "moisture 31 gradient" or 11 moisture continuum" (Lindsey able for plant uptake and assim et al. 1961; Gemborys and Hodgkins 1971; ilation (Brady 1974; Teskey and Bedinger 1978; Richardson et al. 1978; Hinckley 1977); and Fredrickson 1979; Huffman 1979; Whitlow and Harris 1979; Huffman and Forsythe (5) shifts in nutrient availabil 1981). These terms may be misleading; it ities, partially due to item is not the availability of water, but the (4) (Teskey and Hinckley 1977). inavailability of oxygen due to the pres ence of water. The emphasis on the anae The responses of plants to these and other robic aspect of this gradient generates a flood stresses were reviewed by Teskey and clearer picture of the actual effects of Hinckley (1977), who emphasized that the floodfog and saturated soils on plant sur key to plant survival in flooded condi vival; hence, its use in this report. tions is the adaptability of the root system. PLANT RESPONSES TO ANOXIA-RELATED STRESSES The cessation of uptake and exchange functions through root dormancy or death Stresses Generated by Anaerobic Conditions during flooding affects plant metabolism in several ways. The immediate losses of The effects of periodic or perma these root processes is due to the lack of nent flooding are the crucial selective oxygen. The root system has access to stresses on bottomland hardwood plants and free oxygen, necessary for normal respira are responsible for the sorting of species tion, through only two routes: (1) absorp into broad community types (Huffman and tion from the soil-air-water complex by Forsythe 1981). The plant growing in a the roots themselv~s. or (2) transport saturated substrate must respond to sev from aboveground plant tissues through the eral physical and chemical changes, among vascular system or intercellular spaces to them: the roots. Although a 11 pl ants probably have a shoot-to-root i nterce 11 u1 ar space (1) depletion of available oxygen in network through which oxygen can diffuse soil water, in a period as short to the root system (Salisbury and Ross as 3 days (Nuritdinov and Varta 1978), this system is well developed in petyan 1976; Phung and Knipiing only a few plants (rice, for example). 1976; Teskey and Hinckley 1977); Thus the depletion of soil oxygen by the roots eventually shuts down respiration in (2) shifts in soil pH--variable, root cells. As respiration ceases, water though in general a convergence and ion uptake is inhibited (1) by chang toward neutrality, with acidic ing membrane permeabilities in root cells, soils becoming more alkaline and affecting movement of both water and ions, calcareous soils becoming more and (2) by reduct ng the amount of energy acidic (Grable 1966; Kennedy available for membrane transport, affect 1970; Rahmatullah et al. 1976; ing primarily ion movement. Teskey and Hinckley 1977); The inability of flood-intolerant (3) accumulation of potentially tox species to absorb and use water and nutri ic compounds in the plant, the ents leads to foliar water deficits, sto rhizosphere, and in the larger matal closure, and reduced gas exchange. soil solution; examples are car Consequently, transpiration and photosyn bon dioxide, ethanol, sulfides, thetic rates are slowed, cellular synthe nitrites, aluminum, iron, and sis requiring unavailable nutrients is manganese (Teskey and Hinckley curtailed, and overall plant growth is 1977); impeded (Teskey and Hinckley 1977). The plants literally die of dehydration in ( 4) shifts in the redox states of standing water. chemical species, including es sential nutrients, generally Plant Adaptations to Flood Stresses from more oxidized to more reduced; the reduced forms are Plant adaptations to flood stresses considered generally less desir- may be categorized as p~ysical or meta- 32 bolic. The former includes the prov1s10n root systems (Figure 20) of bottomland of oxygen to the roots or the restoration trees which (1) provide support, (2) of proper root function, or both. Meta increase oxygen use efficiency in satu bolic mechanisms adjust plant biochemistry rated conditions by their pro~imity to to decrease the potentially harmful ef more highly oxygenated surface sediments, fects of anaerobic respiration. The most (3) reduce losses of nutrients from the successful species in saturated conditions system through rapid uptake, and (4) pro are those that possess both physical and tect the floodplain from erosion. metabolic adaptations (Teskey and Hinckley 1977}. The primary metabolic mechanism in flood-tolerant species is a shift in the The abilities of plant species to end-products of glycolysis. Normal glu restore and maintain the stressed root cose metabolism and energy (ATP) prod-uc system lie on a continuum (Teskey and ti on in the cell proceeds via three steps: Hinckley 1977): ( 1) glyco lys is (anaerobic), (2) Kreb' s citric acid cycle (aerobic), and (3) oxi (1) very tolerant--primary root dative phosphorylation (aerobic). In the maintenance, secondary and ad absence of free oxygen, only g lyco lys is is ventitious root growth, completed, and ethanol normally accumu lates as an undesirable end product. (2) moderately tolerant--primary Flood-tolerant species can generate root deterioration, adventitious organic acids instead of ethanol as pro root growth, and ducts of glycolysis (Crawford and Tyler 1969) and thus avoid ethanol toxicity. (3) intolerant--primary root deteri Furthermore, the organic acids may be oration, no adventitious root transported to the stem and leaves growth. (Chirkova and Gutman 1972; Vester 1972) and used in cellular synthesis (Crawford Adventitious and secondary roots pro 1976). duced under flooded conditions are anatom ically different from primary roots in A second metabolic adaptation has ways that enhance root function in satu been described for some tolerant trees by rated soils. They are more porous, facil Hool< et al. ( 1970). The roots of these itating (1) oxygen diffusion from the species oxidize the rhizosphere, prevent aerial shoots (Luxmoore et al. 1973), (2) ing root deterioration and enhancing nu gaseous exchange between root eel ls and trient uptake. soil solution, and (3) perhaps better movement of water and ions into the root Finally, there is some evidence that (Jat et al. 1975). They are also more flood-tolerant species can substitute ni tolerant to elevated carbon dioxide con trate for free oxygen as a terminal elec centrations and exhibit increased anae tron acceptor in cellular reactions robic respiration (Hook and Brown 1973). (Crawford 1976). The reduction of nitrate to ammonium (denitrification) then would Some tree species produce special help maintain cellular energy production root structures other than secondary and and biosynthesis in roots. This benefit adventitious roots. The classic example could occur only if excess nitrate were is the pneumatophores of baldcypress and available in an environment where denitri pond cypress (knees) (Figure 18) and water fication is the prevalent process. tupelo and swamp tupelo (arched roots). Aerial roots may supply additional oxygen Factors Affecting Plant to the root system (Teskey and Hinckley Response to Flooding 1977). Buttress formation (Figure 19) and "stooling" not only provide stabler Of the many factors that influence anchoring in the less firm floodplain plant survival during flooded conditions, soils but al so may help aerate the root the timing, depth, and duration of flood system. waters are the most critical {Teskey and Hinckley 1977; Huffman and Forsythe 1981). Similar functions are provided by the These characteristics are themselves func characteristically wide, shallow, matted ttons of regional precipitation and local 33 Figure 18. A remarkable example of multiple-trunked stooling of Ogeechee tupelo at Sutton's Lake (Apalachicola River, FL). This slough floods to depths of 4.2 m (14 ft}; cypress knees may exceed 3.7 m (12 ft) in height. weather patterns, watershed size and mor aeration (Armstrong 1968; Chirkova 1968) phology, floodplain size and topographic and the release of volatile end-products variation, and drainage rates of flood of anaerobtc respiration, such as ethanol, plain soils. The effects of flooding are ethylene, and acetaldehyde (Chirkova and most critical during the growing season, Gutman 1972). Floodwaters deep enough to particularly during the period of leaf inundate major portions of the stem lenti out. Floods during the dormant season ce ls thus cause reduced oxygen supply to have relatively little effect on the the roots and toxic accumulation of the physiology and survival of bottomland spe anaerobic respiratory products. The second cies (Hall and Smith 1955), other than effect of flood depth is the reduced rate possible damage due to mechanical abrasion of oxygen diffusion through the water or breakage. · column to the roots with increasing flood depth. Finally, seedlings submerged by Flood depth is critical in at least the water column may undergo severe mor three ways. First, stem lenticels (pores) tality through anoxia, mechanical damage, may be blocked. These structures are and siltation. important in some species in both root 34 Figure 19. Oak displaying buttressing, common among bottomland hardwoods. 35 Figure 20. A windthrown diamondleaf oak on a small blackwater creek floodplain (Creep ing Swamp, NC) illustrates the large diameter of the root crown of bottQ,mland hard woods. The thickness ranged from 30 to 46 cm (12 to 18 inches). Such width is probably an adaptation to the high water table, but it also increases contact with the surface water during inundation. Root mats are so wide that few areas of floodplain surface are unprotected from floodplain scour. The importance of flood duration Factors that increase the dissolved should be obvious. With the exception of oxygen concentrations in floodwaters are species of tupelo and cypress, stresses rainfall (Broadfoot 1967), moving water associated with saturated soils and stand (Hook et al. 1970; Harms 1973), and lower ing water cannot be handled by plants water temperatures (Broadfoot and Willis after varying amounts of time that depend ton 1973). In contrast, oxygen concentra on the range of tolerance mechanisms of tions may be reduced through microorgan the individual species. Broadfoot and isma1 respiration, especially in waters Williston (1973) stated that the majority with high concentrations of organic matter bf the bottomland species will not survive or nutrients or both. 2 years of continuous flooding. 36 In addition to the above factors that The National Wetlands Technical directly affect plant survival, the activ Council Zonal Classification ities of soil microbiota are modified by flooded conditions. Decomposition and The zonal classification of flood conversion processes mediated by these plain forest sites proposed by Huffman and organisms, such as mineralization and Forsythe (1981) and implemented by the nitrification, are affected. Wharton and National vJetlands Technical Council (Nv/TC) Brinson (1979a) proposed a nitrogen circu was introduced in Chapter 3. Six zones lation rr:odel for forested wetlands that based on soil moisture and hydrology are summarizes nitrogen flows and the effects defined, ranging from aquatic (Zone I) to of floods. Extended anaerobic conditions upland (Zone VI) ecosystems; Zones II and shutdowns in organic matter decomposi through V represent the floodplain. tion may lead to the immobilization of nitrogen and other nutrients in microor The mosaic distribution of floodplain ganismal tissues. microtopography {Figure 22), soil types, and plant communities makes the use of the term zone somewhat misleading. While many PLANT COMMUNITY PATTERNS IN THE FLOODPLAIN examp~of southeastern bottomlands exist where the plant dominance types are arranged in discrete bands, many others The wide variations in factors that are arranged in a mosaic pattern. influence southeastern bottomland hardwood ecosystem structure and dynamics make a The zonal classification is a practi comprehensive treatment of plant distribu ca 1 sys tern, but like a 11 man-devised tions in these ecosystems a difficult classification, it is flawed. Its use in task, one more detailed than is appropri the analysis of floodplain vegetation is ate for this community profile. Although complicated by several problems, among the selective power of the hydrologically which are (1) the recognition of zones in generated anaerobic gradient is sufficient the field, (2) common species whose adap to separate broad community types based on tations permit them to occur in several dominant woody species (Figure 21), asso zones and (3) the system's exclusion of ciated factors blur the distinctions be natural levees. In spite of these draw tween categories. These factors include backs, the zonal system is a useful frame soil characteristics, detrital decomposi work for the understanding of broad flood tion rates, soil and water pH, nutrient plain community patterns, and hence is availability and turnover rates, flood used here. depth and water velocity, light intensity, and disturbance (natural and man-caused). Woody Species Attributes Differences in community structure and composition among otherwise similar sites A familiarity with the structural and sometimes occur. The mere presence of a functional characteristics of the woody species may not be related to present species of the southeastern floodplains local topography. For example, apparently prepares the reader for a better under dislocated cypress may indicate the exis standing of community distributions. The tence of an old buried waterway (A.L. extant data.support the concept of indivi Radford, University of North Carolina at dual species adaptations to the selective Ch ape 1 Hil l; persona 1 communication). forces of the floodplain environment. The distribution of bottomland tree, shrub, The reasons for such complexity in vine, and herb species over the floodplain floodplain floral distributions are the zones is shown in Table 9. Structural and individual responses of plant species to functional attributes of most of the the highly variable and dynamic floodplain important woody bottomland species may be environment. This section on plant com found in Putnam (1951), Putnam et al. munity distributions emphasizes the domi (1960), and Eyre (1980). nant types of forest cover, and notes associated understory, shrub, and herbace The survival of bottomland hardwood ous components where field observations species under different hydroperiods pro allow. vides a validation of the gradient concept 37 -- Upland forest I White Oak, Blackgum, White Ash, Hickories, Winged Elm, Loblolly Pine) Bald Cypress - Tupelo Sycamore· Sweetgum • American Elm Sweetgum. Willow Oak - Overcup Oak Willow Oak or Water Oak . Upland Forest Water Hickory Diamondleaf Oak - Black Willow A E G H - v-----...,,, ..._ ___ ,!""'_____ .,...... River Channel ------First Bottom (Terrace) Second Bottom (Terrace) Upland Figure 21. The correspondence between alluvial floodplain microtopography and forest c~ver types. (A)= river channel; (B) = natural levee (front); (C) = backswamp or first terrace flat; (D) = low first terrace ridge; (E) = high first terrace ridge; (F) = oxbow; (G) = second terrace flats; (H) = low second terrace ridge; (I) = high second terrace ridge; (J) = upland. The vertical scale is exaggerated. and the zonal classification system (Table 10). Trees in the almost constantly inun dated Zone II may survive with roots partially inundated as much as 90% of the time and die only when inundation is permanent. On the other hand, upland (Zo~e VI) trees not so adapted to maintain themselves during flooding may begin to show signs of stress if constantly inunda ted as little as 2% of the time (dogwood and black cherry) and die as the flooding interval increases to 12% to 17% of the time. Dominance Types and Their Distribution Based upon field observation and studies in the four-state study area, we have classified bottomland hardwoods on floodplains into 75 dominance types organ Figure 22. Microtopographic relief on a ized by zones (Tables 11-14). Although small blackwater creek floodplain (Lower Zones I (open water) and Zone VI (uplands) Three Runs Creek, Barnwell County, SC). are relevant, they are not presented other Areas of similar elevation are similarly than to introduce the nature of Zone I marked. Arrows indicate channels which species. are always filled with water. Quadrat is 100 m on a side. (After Hay 1977.) Each table organizes the dominance types for each zone by topographic setting or uses other features to aid field iden tification. The reader should review 38 Table 9. Trees, shrubs, vines (V), and herbs (H) characteristic of south eastern bottomlands and the floodplain zones in which they most frequently occur (A= abundant, C = common, U = uncommon or localized, R = rare). Species (except some herbs and vines) are in approximate order of their position on the moisture gradient from wettest to driest. Species largely restricted to eco tones (E), levees (L), and peat soils (P) are also distinguished. Nomenclature generally follows Kurz and Godfrey (1962) and Little (1979). Species Ecological zones II III IV V Taxodium distichwn (baldcypress) A X Taxodium ascendens (pond cypress) C X Proserpfoaca sp. (proserpinaca) C X Nyssa aquatica (water tupelo) A X Nyssa biflora (swamp tupelo) A X Nyssa ogeche (Ogeechee tupelo) A X Crinum americanum (strap li1y) A X Leitneria floridana (corkwood) U-R X Tillandsia setacea (needleleaf wild pine) {H) C X Plan.era aquatica (water elm) A X Orontium aquaticum (goldenclub) (H) C X Fraxinus caroliniana (water ash) A X Fraxinus profunda (pumpkin ash) C X Iris virginica (blue flag) (H) C X Chamaecyparis thyoides (Atlantic white cedar) U X Pinus serotina (pond pine) C X Magnolia vfrginiana (sweet bay) C, P X Persea borbonia (red bay) C, P X Sabal palmetto (cabbage palm) C X Ilex myrtifolia (myrtle- leaf holly) C, P X Ilex cassine (dahoon) C, P X Lyonia lucida (fetterbush) A, P X VibuY'num nudum (southern withered) c. P X Leucothoe racemosa (swamp leucothoe) C, P X Clethra alnifolia (sweet pepperbush) C, P X Lyonia ligustrina (male-berry) C, P X Ilex coriacea (large gallberry) C, P X Cyrilla racemosa (titi) A, P X Alnus serrulata (alder) A X Myrica cerifera (wax myrtle) A X Crataegus aestivalis (may haw) U X Forestiera acuminata (swamp privet) C-U X X Hymenocallis crassifolia (spiderlily) (H) C X X (continued) 39 Table 9. (Continued). Species Ecological Zones II III rv-~v liymenocaZlie ocaidentalis (spiderlily) (H) C, P X .lmpatien,'3 ciapensis (j ewe 1weed) ( H) C X X l'riadnwn tubulosum (St. Johns wort) (H) U X X Vernonia g·1:gan tea ( i ron weed) ( H) U X X Seneaio glabellue (butterweed) (H) C X X Woodwardfo areoZata (small chain fern) (H) A X X scrru;ibiZis (H) A Onoc,Zea (bead fern) X X Osmunda ( 1 H) roya fern) ( C X X The palustr>1:s (marsh fern) (H) C X X Smi'. Zaur>:foUa (laurelleaf greenbrier (V) A X X Salix (black willow) A X uc~=~Ul (continued) 40 Table 9. (Continued). Ecological zones Species II I II IV V X X (sycamore) U, L Platanus occidentalis X Rhapidophy llum hystri:.c (needle palm) U X X Populus deltoides (cottonwood) U, L X Crataegus marshalt?:1: (parsley haw) C X Celtis laevigata (sugarberry) U X Rhododendron viscosum ( svrnmp azalea) C X Rhododendron canescens (hoary azalea) C X X Sebastiana lieustrina (Sebastian bush) C X X Smilax 1.ualter1: (coral greenbrier) (V) C X Smilax .smallei (Jackson greenbrier) (V) C X Berchemia seandens (supplejack) (V) A X f./i.sterfa frutei;cens (wisteria) (V) C X X Rhus Pad1'.cans (poison ivy) (V) A X Trachelospermwn difforme (trachelospermum) (V) U X Brunnichfo cirrhosa (ladies eardrops) (V) U X X Bienonia cap1°eolata (cross vine) (V) A X CommeUna vircriniana (spiderwort) (H) C X AmpeZopsis arborea (peppervine) (V) A, L X Tovara vfrginiana (jump seed) ( H) C X ElephantopuB car•ol-Zniana (elephants foot) (H) C X ,IuBticia ovai;a (just i ci a) ( H) C X Carex intumescens (sedge) (H) C X Carex typhina (sedge) (H) C X Carex lurida (sedge) (H) C X Carex fouisfonica (sedge) ( H) C ( CP) X Carex grey-ti (sedge) (H) C X Leer•wia lentfrulaPis (cutgrass) (H) C X Leersia virg1'.nica (cutgrass) (H) C X Oplisemenus BetaPius (H) C X Erianthus si:rictus (plume grass) (H) C X Panicum agrostoides (panic grass) (H) C X Panicwn rigidulwn (panic grass ) (H) U X X Marus rubra (red mulberry) U X X Acer negundo (boxelder) L X Pinus glcibra (spruce pine) C X Arundinaria gigantea (river cane) (H) A X Vaccinium elliottii (Elliott's blueberry) C X Quercus michauxii {swamp chestnut oak) C X Ilex opaca (American holly) A X Quercus nigra (water oak) U-R (continued) 41 Table 9. (Concluded). Species Ecoloqical zones I I II I IV V Carya cordiformis (bitternut hickory) U X Carya glabra (pignut hickory) U X Catalpa bignonioides (catalpa) U, L X Quercus pagoda (cherrybark oak) C X Asimina triloba (paw paw) C X Pinus taeda (loblolly pine) C X Quercus shumardii (Shumard's oak) U-R, L X Quercus virginiana (live oak) U X Serenoa repens (saw palmetto) U X Lindera benzoin (spicebush) U X Fagus grandifolia (beech) C, E X Aristolochia serpentaria (Virginia snakeroot) (H) C X Podophyllwn peltatum (mayapple) (H} U X Chasmanthium laxa (river oats) (H) C X floodplain features (Chapter 1) and refer Plant Communities in Zone I to Figure 40, which illustrates the micro topography of nine selected floodplains. Submerged vascular aquatic plants are Table 15 is cross-referenced to Figure 40, confined to Zone I: rivers, guts, sloughs, thereby providing precise locations of pools, and other permanently inundated many dominance types. areas. The dominant aquatic plant in the Santee River floodplain swamp was an The best ex amp 1es of each dominance introduced species, alligator weed (Alter type have been documented by 1oca l i ty and nanthera philoxeroides) (Dennis 1973). are listed in Tables 11-14. These domi Other species noted in this floodplain nance types are intended to prepare the which are characteristic of the region in reader for the incredible variety of bot general are water weed (Egeria densa), tomland forest communities and associa hornwort (Cera to h llum), water mil foil tions which, as yet, have been little (nYriophyllum, Brazilian elodea, duckweed studied. Occurrence is also indicated in (Lemna perpusilla), Spirodela polyrrhiza, each table as common, ecologically or geo water or mosquito fern (Azolla carolini graphically localized, or rare. ana), Proser}inaca, and frog's-bit (Limno bium spongia. The submerged, thin-leafed Where possible, reference is made to form of spatterdock (Nuphar luteum) is Society of American· Foresters' (SAF) common in many spring-fed rivers. On forest cover types (Eyre 1980); though floodplains with tidal flushing, an inter general and not always applicable in this tidal zone vegetated by quillwort (Isoetes study area, this publication is useful. flaccida), eelgrass (Sagittaria kurzi Huffman and Forsythe (1981) classed a num ana), water milfoil, and Ludwigia may ber of SAF types in their zona 1 descri p occur {Figure 40, St. Marks River). t ions, including Zone VI, and related them to soil moisture regimes for a broad regional spectrum of floodplain types. 42 Table 10. Response of mature bottomland hardwoods, some upland species, and some levee species to varying lengths of time of inundation during growing season. Symbols (•) indicate the limit beyond which species cannot survive inundation of root crown and remain healthy. (Data from Teskey and Hinckley 1977.) % of time inundated during growing season 0 10 20 30 40 50 60 70 80 90 100 Zone II Swamp Tupelo Water Tupelo Zone III Overcup Oak Zone IV Ironwood • Honey Locust Willow Oak Hawthorn • Persimmon • Red Maple • ~ Zone V w Beech Amer. Holly • Water Oak • Pignut Hickory Shagbark Hickory • Swamp Chestnut Oak Zone VI Hornbeam • Dogwood • Black Cherry • Tulip Poplar • B1ackgum • Levee Species River Birch Catalpa • Sycamore Swam tu elo dominance t es 11-16, 18, 19 Fi ure 28. These types occur on The dominance types of Zone II (Table organic black mucks or peats (the latter H) occur in the wettest parts of the if bays are present). The deeper the floodplain: very wet flats, swales, peat, the denser the shrub understory (see s Toughs, and back swamps. Soi ls are satu type 15, vJhich r,ay be characteristic of rated throughout the growing season (100% blackwater river floodplains at elevations the time; Leitman et al. 1981) although approaching sea 1eve1 ). These types on fall drydown of water occurs in a number alluvial f1oodp1ains often occupy the types. Saturation in some types is swa1es and fi1led-in oxbows that flank the by by tidal maintained seepage or fluctua upland. Swamp tupe 1o types dominate stag t . The liverwort (EQ~JlE. pinnag) nant, non-flowing, oxygen~poor sites and growing on trunks of trees in this and can tolerate saturated soils for long other zones in an indicator of flooding periods. depths and duration (Figure 23). Gu!!!.:g~ss domin~nce types .U:_1Ql_ ~-warr--2.!lsl shrub~ dominance lf.i.29J!S 24::11J: Subtle factors determine _!.y~~ 21 . These coriparativeiy rare the relative dominance of ba 1dcypress floodplain environments strongly resemble their up]and wetJand counterparts. Field -~.~.~._,,.., djsttgium), water tupelo (~iss~ swamp tupelo (N. bif1ora), and observations were made at two sites (Tab 1e 11). The shrub bog on deep peat (type 20) tupe 10 (Ji. QgfcheJ in"ttie tupe 1o types, Although water tupe 1o had an unclosed pond pine canopy and occurs on disjunct Piedmont sites, it· is appeared somewhat raised above the flood restricted pl"imari ly to a, luvia J flood- plain surface. The bay swamp (type 21} Ins of the Coastal Plains. Swamp was moist from constant seepage. Jo ts prominent tn floodplains of the ta.I Ptafo. but it is also common in Tidal forest dominance ""types (22=.?1.l.... and ponds and in the brack- 1£.i.9.yres 29-3:rr:-ridal forest types occupy waters fringfng estuaries (Penfound the ffoodplains of al 1 rivers within the ). Water tupelo tolerates deeper and zone of tidal influence, as far as 32 km flooding than does swamp tupelo and (20 mi) inland along larger rivers. Soils riates on sites characterized by this are peats, tight1y bound by interwoven rw11rnn1>r Ogeechee tupe Jo is limited root mats (Figure 29). The water table is ta1 Plain and occurs in two continually high because of lunar or growth formations (see types 4, "wind" tides. Herbaceous layers are on both alluvia 1 and blackwater remarkably diverse and little studied. These flat floodplains include higher 1dcypress is replaced by II on many sites because of its "is 1ands or humrnoc ks whose tops are a 17 r~prodw::tion, slower growth rates, at the same level (about that of storm f icatit stump and root sprout tides} and supporting species that cccur , factors are intensified by on alkaline floodplains (type 26). South d1sturbance, such as periodic ern .red cedar {~erus .?ilicicola) favoring tupelo dominance occupies the banks and hiciher elevations Eyre l S80). Pond of the tidal forest floodplains along ascendens} is the co spring-fed (alkaline) rivers (Figure 30J. some black- It prefers a basic or high-calcium sub ro-9Umson strate. Stands of southern red cedar have been severely reduced in Florida by exten and shrub sub canopies occur in sive logging by pencil companies (Wharton types (2. 3, 4, 9, 10, et al. 1977). The southern red cedar is be extremely dense in an important component of the "hydric ham , W. 21). Subcanopy mock," a seepage wetland vegetated by live types may be 1i mi ted oak (~~ .!'._i rginian~) and cabbage pa Im low light intensities {Sal?.tl £Elmetto;, along Florida's gulf flooding. The herbaceous coast {Wharton et a 1. 1977). Hicant in most types but dense in others (types 4, Atlantic white cedar dominance types ~~- .Atlantic white cedar {~hamaecypa lli th,l'o1s!f_s) is believed to be a distur- 44 ~-.------Table 11. Dominance types of Zone II. Topographic Representative Floodplain setting setting Dominance type Occurrence site locations Flats, sloughs, swales, and backswamps. Organic Flats with single (1) Baldcypress-water tupelo, no Common, widespread Roanoke below Williams; soil component low. Flooding regime annual, channels characteristic understory NC; Santee at Hwy 411 with water usually flowing during inundation. bridge, SC Most flats and some sloughs with annual dry down. Principal dominants are baldcypress, (2) Baldcypress-water tupelo, Ecologically or Apalachicola Forbes Is., water tupelo, Ogeechee tupelo, and pumpkin ash water elm-water ash geographi ca 11y FL; Chocktawhatchee above (corresponds most closely with SAF type 102). unders tory localized Hwy 20 bridge, FL (3) Tall, straight Ogeechee Ecologically or Lower Suwannee below tupelo-water tupelo-cypress geographically Manatee Springs, FL pumpkin ash localized (4) Tall, straight Ogeechee Eco 1ogi ca lly or Apalachicola, FL at tupelo-sweet bay-strap geographically River Mile 15.6 {Figure 1 ily localized 25) Flats with (5) Baldcypress-water tupelo Ecologically or Chipola above Hwy 71 anastomosing Ogeechee tupelo-water geographically bridge, FL channels elm-water ash localized (6) Baldcypress-water tupelo Eco 1ogi ca lly or Four Hole Swamp, SC geographically localized Sloughs on (7) Large, stooled Ogeechee Rare Apalachicola at Blounts alluvial river tupelo dominant, with town, FL; Ochlockonee, scattered cypress canopy Porter's Lake, FL Sloughs on black (8) Baldcypress-tall, straight Ecologically or Ogeechee above Hwy 25 water river Ogeechee tupelo-water tupelo geographically bridge, GA localized (continued) Table 11. Floodplain setting Representative Oomi nance type Occurrence site locations (9 Baldcypress with stooled Common Canoochee, Ft. Stewart, Ogeechee tupelo, water GA ash, and water elm Linear backwater (10) Large buttressed cypress swamp Ecologically or Ebenezer Creek below Hwy with stooled water ash geographically 21 bridge, GA (Figures 26, and water elm. Water localized 27); Ogeechee, Dee lake, tupelo stands entirely GA separate (SAF type 103) Swamp tupe1o and swamp tupelo-water tupelo Alluvial flood (11) Swamp tupelo-water tupelo dominated flats, swales, and backswamps. plain flats Ecologically or Choctawhatchee above Hwy ..,. Organic soil component high. Flooding regime swamp palm flats geographically 20 bridge, FL; Yellow at O'\ annual, with water usually standing and anoxic localized Hwy 87 bridge, FL rather than flowing. Complete drydown usually only in drought years. Also included are (12} Wet flats with swamp tupelo Ecologically or Apalachicola below Forbes rare examples of floodplain shrub bogs and bay water tupelo-baldcypress geographically Is., FL swamps. with dense emergents localized (Sagittaria Thalia, Justicia, royal fern'~~- Blackwater flood (13) Swamp tupelo-pond cypress plains Common Satilla at Hwy 252 bridge, GA (14) Swamp tupelo-cypress with Ecol ogi ca lly or little Wambau Natural surface pea ts geographically Area, SC localized (15) Swamp tupelo-pond cypress Common Chowan near Virginia with dense evergreen shrub border, NC understory over deep peat (continued) Table 11 (Continued). Topographic Representative Occurrence site 1oca ti ons Floodplain setting setting Dominance type Swales (16) Swamp tupelo with unique Ecologically or Roanoke, Devil's Gut, NC herb zone (Hypericum geographically tubulosum, Hydrocotyl localized verticillata, royal fern) (17) Dwarfed sweet bay-red bay Eco 1ogi ca lly or Waccamaw, Hwy 9 bridge, pond cypress canopy with geographically SC shrub bog understory over localized deep peat Backswamps adja (18) Swamp tupelo canopy with Common Escambia at Hwy 184 cent to upland Cyril la and Itea as dominant bridge (Figure 28) slope shrubs (19) Swamp tupelo-sweet bay Common Congaree Swamp National Monument, SC; Altamaha near Cox, GA Floodplain (20) Pond pine canopy with dense Rare Upper Three Runs, Aiken, shrub bog (S_AF evergreen shrub bog over SC type 98) deep peat Floodplain bay (21) Sweet bay canopy with dense Rare Chipola above Hwy 71 swamp evergreen shrub understory, bridge, FL royal fern Eco 1ogi ca lly or Altamaha, Lewis Is., Tupelo gum-cypress forests with moderately (22) Baldcypress-water tupelo sweetgum geographically GA (virgin remnant) organic soils. Annual flooding regime present localized (Figure 31) but influenced by lunar or wind tides maintain ing saturated soil conditions. Some fauna (Uca and Sesarma crabs, manatee) of coastal marine affinities (continued) Table 11. (Concluded). Topographic Representative Floodplain setting setting Dominance type Occurrence site locations Tidal forests usually dominated by swamp tupelo (23) Baldcypress-water tupelo Ecologically or Apalachicola at Pinhook, and sweet bay (corresponds most closely with red bay geographically FL (dwarfed alluvial SAF type 104). Trees in lower reaches often localized river forest) dwarfed. Organic soil component high, root mats continuous or interwoven at or near the {24) Cypress-swamp tupelo-sweet Ecologically or Suwannee at East Pass, FL surface. Annual flooding present but regime bay-pumpkin ash geographica 11y (dwarfed blackwater river dominanted by daily tidal fluctuations. An loca 1 ized forest) (Figure 29) intertidal zone with fauna of marine afffnities (fiddler crabs, Neretina snails) usually (25) Swamp tupelo-sweet bay Ecologically or Lafayette Creek at Hwy present. with dense titi-ertcad geograph ica 1 ly 20 bridge, FL understory localized (26) Swamp tupelo-sweet bay Ecol ogica ny or St. Marks, Wakulla, and with cabbage palm and 9eo9raphica1ly Wacissa below Hwy 98 southern red cedar localized bridges, Fl (Figure 30) (27) Swamp tupelo-cypress-sweet Rare Roanoke, Albemarle bay with shrub bog over deep Sound, NC (wind tide peat dominated) Tidal forests dominated by white cedar-sweet Yellow below Hwy 87 bay (28) White cedar-sweet bay and Ecologically or tall shrubs in subcanopy geograph i ca 1 ly bridge, FL ( Il ex cass i ne, l• !!lITll loca 1 ized fo l ia, Cyrilla, Myrica) Nontidal riverine forests, peat-forming with (29) White cedar-pond pine Ecologically or Whitewater at Hwy 137 Atlantic white cedar codominant. Saturation geographically bridge, GA maintained along bay streams by seepage from localized sandhills (Type 29) or in riverine backswamps adjacent to high ground (Type 30). (30) White cedar-swamp tupelo Ecologically or Yellow at Hwy 90 geographically bridge, FL localized Figure 23. The dark area below the pencil is a liverwort (Porella ~innata) zone, the upper boundary of which indicates that high water has stayed at that evel for at least 16% of the year (58 days, not necessarily consecutive). The zone above it is a green moss. The upper boundary of Perella. growth is helpful for quickly determining depth and duration of flooding. Figure 24. The outermost swale (next to the upland) along the lower Roanoke River (NC} supports almost pure stands of either swamp or water tupelo on black. muck soils. Here, in a water tupelo stand, in response to the anaerobic muck, roots form b.locky aerial knees which resemble black rocks. 49 .. Ffgure These Ogeechee tupelos on the Apalachicola River floodplain (River Mile 15.6) are tall, straight, and large, measuring 1 m DBH (diameter at breast height) although along many Coastal Plain rivers they form grotesque, many-trunked stools. In isthe forestcharacteristic pictured, herb. water tupelo is a co.dominant, and strap lily (Crinum americanum) w~if~"l .. a deep Seen1ake-11 1c Ebenezer ke channe Creek 1. Cypress(Effingham buttresses County, GA) bis a unique variant of Zone II, are a normally enlarged. so ·····.····.;g Figure 27. Drydown in water tupelo (Zone II) on Ebenezer Creek (GA). These backwater environments are dominated exclusively by tupelo and cypress. During drydown, nutri ents concentrate, and duckweeds form dense surface layers. Note: (1) the precise height of the high water 1ine (approximately 2 m or 7 ft), (2) relation of buttress swell to high water mark, and (3) counter-clockwise "swirl" of buttresses. Figure 28. The outermost backswamp (Zone II) on many alluvial f1oodp1ains is dominated by a swamp tupelo on acid, highly organic muck soils. Here on the Escambia (Hwy. 184 bridge, FL) the shrub zone {Cyrilla, ltea) is sparse but prominent. There is a clay aqu i c 1ude severa 1 feet be 1ow the surface mucks. Seepage moisture from the adjacent upland, as well as rainfall, may be important to some of these associations. 51 Figure 29. This tidal forest (Zone II) of sweet bay, pumpkin ash, swamp tupelo, and cypress at West Pass (Suwannee River, FL) has a characteristic interwoven mat of large roots close to the surface. This extremely tough layer protects the forest and the shore from the destructive erosion of constant wave action and storm tides. There is no natural levee. High tide comes nearly to the top of the root crowns. Fiddler crabs and olive nerite snails are abundant on the forest floor. Showy herbaceous plants such common.as iris, butterwort (Senecio _g]abellus) and aster (Aster vimineus) are surprisingly 52 Fi~ure 30. Three shoreline dominants, sweet bay (B), red cedar (C), and cabbage palm (PJ, are characteristic of the tidal zone of an alkaline blackwater river (St. Marks, FL). An intertidal zone (T) can be seen between the root zone (H) at the high tide line (partly in shade) and the dark water (W), which has a band of submerged plants (S), here partly exposed. 53 Figure 31. A small grove of virgin cypress is preserved on Lewis Island (Altamaha River, McIntosh County, GA) where they grow in unique association with both sweetgurn and water tupelo. Such giant cypress were characteristic of the upper tidal zone of the great alluvial rivers of the Southeast. Apart from a few shallow sloughs, most of the grove has a moderately dense herb layer including the swamp palm (Sabal minor). Both it and sweetgum are typically found in Zone IV. Cypress here do not have the large swollen base. 54 bance-adapted successional species. Fire Cary2_ aguatica) type (Figure 32) and its is the most common precursor to white variants. These flats are relatively small cedar development, though flooding, wind (about 2 ha or 5 acres) in the Southeast, throws, or logging yield the same effects. and seldom are dominated exclusively by Atlantic white cedar is usually found in these two species. The wet fl a ts of the bog stream swamps on peat overlying sandy Congaree River (SC) are dotted with numer soils that are characteristically poor in ous depressions, so small as to be occup nutrients, in a unique tidal forest type, ied by a single overcup oak. Overcup oak, or in acid backswamps of certain Florida undesirable for lumber, often is left by rivers. 1oggers. A near-virgin stand of overcup oak on the Santee River floodplain (SC) Dominance Types of Zone III contains trees approaching 1.2 m (4 ft) in diameter. Additional sites occupied by Zone III includes the wet flats, this type include small shallow depres bank-edge strips, low levees, and depres sions in Zones IV and V, and narrow bands sions in Zones IV and V. Dominance types bordering deeper depressions that contain (Table 12) in this zone are semi-perma cypress-tupe1o or water elm. Both overcup nently inundated for a major part of the oak and water hickory avoid seedling and growing season, as we 11 as in winter and sprout mortality from inundation by leaf spring. Although the hydroperi od is 1ong ing out late in the spring. Both species (about 6 months), Zone III areas are sub reproduce we 11 ; overcup oak through con ject to annual drydown. Soils are satu s is tent ly good acorn crops, and water rated 40% of the year (Leitman et al. hickory through good mast and prolific 1981). sproutinq (Eyre 1980). Water locust (Gleclitsia aguatica)-water hickory stands Pioneer dominance type (1). The banks ·are rare variants of this type. The ex and point bars of the southeastern rivers tended hydroperiod in the sites occupied often are occupied by the black willow by overcup oak-water hickory and water (Salix nigra) and other species such as locust-water hickory forests inhibits herb silver maple (Acer saccharinum), and some growth, and thus the unders tory is re times cottonwood (Populus deltoides). stricted to sma 11 trees and shrubs ( Eyre These early seral stages are succeeded by 1980). Zone IV types as elevation increases from soil accumulation. The successional se Dominance Types of Zone IV quence is a function of meander movement rates and point bar formation. Rivers Zone IV (Tab 1e 13) forms the bulk of with intact forests on fine cohesive sedi the floodplain on Coastal Plain alluvial ments migrate so slowly that mature forest rivers above tidal influence, chiefly on establishment keeps pace with the river flats or terraces of low relief. Two channel, and pioneer stages never develop. irregularities are common: "washboard" Swift meander movements over unconso l i da terrain caused by parallel scour channels ted sands produce tapered slopes on point (often sandfloored) and "hummocky" terrain bars, and several seral stages may be where trees either stand above the general found. floodplain level on hummocks or have tor tuous scour channels around and through Shrub, small tree, and herb dominance them. Zone IV is seasonally inundated or _!:1pes (2-4). Semi-permanent pools occur saturated for 1 to 2 months of the growing in depressions, old oxbows, and scour season, and more or less continuously channels. They are dominated by several inundated during winter and early spring. species of willows, shrubs (e.g., may haw Soils are saturated about 22% of the year (Crataegus aestivalis)), and small trees (Leitman et al. 1981). Shrub and herb (e.g., water elm (Planera ~aticum)). layers are scanty. Stiff clay soils or subsoils act as aquicludes which pond Overcu oak-water hickor dominance rainwater on alluvial floodplains, while t es 5-10 . The most poorly drained the more porous sands dominating black flats of the floodplain, in which water water floodplains preclude this ponding. stands we 11 into the growing season, are The diamondleaf oak (Quercus laurifolia) characteristically dominated by the over appears to dominate both the alluvial and fUP oak-water hickory (Querc~ lyrata_- blackwater floodplains. It is remarkably 55 Table 12. Dominance types of Zone Ill, Representative Topographic setting Dominance type Occurrence site locations Banks and point bars (l) Black willow-Ward willow-silver maple with occa- Common Altamaha, Wayne Co., GA; sional cottonwood and swamp privet Flint, Dooley Co., GA Pond and depression pools which dry down (2) Water elm ponds Ecologically or Choctawhatchee above (includes some beaver ponds not drying geographically Hwy 20 bridge, Fl down annually) (Closest to SAF type 95) localized (3) May haw ponds Eco 1ogi ca 11y or Canoochee, Fort Stewart, geographi ca 1 ly GA localized (4) Marsh ponds (beaver origin) Common Flint at Hwy 278 bridge, GA Wet flats {SAF type 96) (5) Overcup oak-water hickory Eco 1og i ca lly or Apalachicola at Blounts <.n geographically town, FL; Santee at Hwy 41 O'I localized bridge, SC Shallow depressions in Zones IV and V (6) Overcup oak depressions Conunon Congaree Swamp National Monument, SC (Figure 32) (7) Depression borders (fringing swamp gum ponds) Common Apalachicola, Muscogee Reach, FL River edge associations (8) Water hickory-water locust (bank edge strip) Ecol ogi ca lly or Altamaha, Sansavilla Bluff, geographically GA localized ( 9) Overcup oak-water hickory (strip inside levee) Common Choctawhatchee above Hwy 20 bridge, FL; Suwannee at Fow1er's i31uff, FL (10) Overcup oak-water hickory Common Santee at Hwy 52 bridge, Old levee ridge edges SC; Apalachicola, Chipo1a Cutoff; FL Figure 32. Large overcup oaks occupy depressions (Zone III) in the dominantly Zone IV floodplain of the Congaree Swamp National Monument. Photo by George Taylor. 57 Table 13. Dominance types of Zone IV. Topographic setting Dominance type Representative Occurrence site locations Oak flats-alluvial and blackwater floodplains (1) Oiamondleaf oak (usually with swamp palm unders tory) Common Ogeechee at Hwy 25 bridge, GA; Indiana Field Swamp at Hwy 78 bridge, GA (2) Diamondleaf-willow oak Ecologically or Altamaha at Seaboard geogra phi ca 1 ly Railroad bridge, GA; localized Ogeechee at Hwy 78 bridge, GA (3) Willow oak Ecologically or Oconee at Hwy 280 bridge u, geographically (nearly virgin forest) co localized (Rare) Moderately wet to drier alluvial floodplain (4) Sweetgum diamondleaf oak-green ash flats Rare Savannah, Bear Is., GA (nearly virgin forest) (5) American elm-sugarberry (SAF type 93) Eco 1ogi ca lly or Roanoke, Scotland Neck, geographica 1 ly NC localized Wet flats-alluvial floodplains (6) Diamondleaf oak-green ash Common Congaree Swamp National Monument, SC (7) Red maple-green ash Common Alcovy at Hwy 278 bridge, GA (Piedmont) Wet flats-blackwater floodplains (8) Diamondleaf oak-swamp Eco 1ogi ca 11y or a. with red maple a. Creeping Swamp, Pitt geograpically NC b. with American holly, Styrax americana Co., localized (Rare) b. Waccamaw, Vaughn Pl ace, SC Oak-pine flats-alluvial floodplains (9) Diamondleaf oak-spruce pine Ecologically or Oconee between Hwy 280 geographically and Hwy 46 bridges, GA; localized Choctawhatchee above Hwy (continued) 20 bridge, Fl Table 13. (Concluded). Representative site locations Topographic setting Dominance type Occurrence Ecologically or a. Canoochee, Fort Oak-pine flats-blackwater floodplains (10) Diamondleaf oak-spruce pine a. with Vaccinium elliotii, river cane geographically Stewart, GA (Figure b. 11ith Sabal minor and Sebastiana localized 35) b. Ohoope at Hwy 15 bridge, GA Common a. Chipola above Hwy 17 Islands in Zone II anastomosing floodplain (11) Diamondleaf oak a. with !lex decidua understory bridge, FL b. Aucil1a at Hwy 19/27 b. with Sebastiana understory bridge, FL oak with large, tall Ogeechee Cor:1mon Apalachicola at River Low natural levees (12) Diamond leaf Mile 12, Fl tupelo with JciX of Zone II I, IV, Cor:ir.ion Apalachicola, Muskogee Scour channel toµography (13) Diar:ondleaf oak Reach, and Chipola and V species Cutoff, FL (14) Diamondleaf oak Ecol ogi ca lly or Waccamaw at Hwy 9 Low rid9es of ridge and swale topography geographically bridge, SC localized Ecologically or Altamaha, Fulton Ridge, low Pleistocene dune oak-pine ridges (closest (15) Live oak-diamondleaf oak-willow oak-spruce pine geographically GA to SAF type 89) 1oca 1i zed little Pee Dee, SC (16) Live oak-diamondleaf oak-willow oak Rare Ochlockonee, Porter's (17) Live oak-spruce pine Ecol ogi ca lly or Old levee oak-pine ridge geographically Lake, FL localized Common Yellow, Rockdale Co., GA Successiona1 associations (18) River birch (closest to SAF type 61) (Piedmont floodplains) Rare Roanoke, Seaboard Rail (19) Cottonwood (old diked areas) road bridge, Scotland Neck, NC wet-tolerant, occasionally found as a co Dominance Types of Zone V dominant with swamp tupelo ( type 10), and rarely can be found mixed with a few Zone V comprises the highest eleva cypress. tion floodplain associations occurring on old natural levees, flats, higher ter Floodplain flats dominance types (1- races, and Pleistocene ridges and dunes. lQl. The diamondleaf oak dominates the Inundation averages once yearly {Congaree, Zone IV flats of all the major river SC). See Figure 11 for graphic example. types. Even so, these forests are more Duration of flooding ranges from 2% (5.3 di verse than the wetter overcup oak-water days) to 12. 5% (33 days) of a 265-day hickory types in Zone III. Frequent growing season. Soils are usually sandier associates in this zone are green ash and less fertile than those of lower (Fraxinus pennsylvanica), American elm zones. (Ulnus ameri cana), sweet gum (Li qui 60 . Figure 33. The sweetgum is- a long-lived component of virgin alluvial bottomland forests throughout the Southeast. These giants in the Congaree Swamp National Monument (CSNM) occupy the higher portions of Zone IV floodplain. Lower Zone IV areas may lack the 1arger trees. The CSNM contains a number of nat; ona l and state record trees. Figure 34. Many Zone IV bottomland hardwoods on Coastal Plain alluvial river flood plains {Ocumulgee River, GA) have an understory of Sabal minor, a ?warf palm confi~ed to Zone IV floodplains. The similar but rarer needle pafin(Rhap1dophyllum hystr1x) also occurs here. 61 Figure 35. The floodplain of the blackwater Canoochee (Fort Stewart, GA) is somewhat anomalous in the co-dominance of diamond leaf oak (Zone IV species) with either spruce pine or loblo1ly pine (Zone V species). The herbaceous ground cover is dominated by river cane and grasses such as Panicum rigidulum and Erianthus strictus.. American holly is present. The shallow flooding and permeable soils are probable factors allow ing for a mix of Zone IV and V species. Diamondleaf oaks here grow more slowly than those on the alluvial Oconee floodplain. 62 Table 14. Dominance types of Zone V. Representative Occurrence site locations Topographic setting Dominance type Common Alcovy at Hwy 278 bridge, Low flats (overlapping with Zone IV) (1) Swamp chestnut oak-green ash GA (Piedmont); Congaree Swamp National Monument, SC (2) Swamp chestnut oak-American elm Ecologically or Congaree Swamp National geographically Monument, SC localized Corrmon Oconee at Hwy 280 bridge, High flats (3) Swamp chestnut oak-cherrybark GA; Ocmulgee, Glass oak-spruce pine Tract, Telfair Co., GA (nearly virgin area) O'Iw Rare Flint, Upson Co. , GA (4) Water oak (Piedmont) (5) Cherrybark oak-water oak-loblo11y Common Alcovy at H,1y 278 bridge, (Piedmont) pine-American holly GA {6) Bitternut hickory-pignut hickory with Eco1ogically or Oconee, Wilkinson Co., pa1, paw and swa.:ip pa ln geographica 1 ly GA localized (?) Cherrybark oak-bitternut hickory-pignut hickory Ecol ogi ca l1y or Ogeechee at Hwy 78 geographica J ly bridge, GA (on rises) localized (8) Water oak-loblolly pine Comnon Congree Swamp National Monument, SC (Figure 36); Edisto at Hwy 78 bridge, SC (continued l i Table 14. (Concluded). Representative Topographic setting Dominance type Occurrence site locations Old levee ridges ( 9) Water oak-swamp chestnut oak-spruce pine Common Yellow at Hwy l-10 with river cane-swamp palm understory bridge, FL; Apalachi cola, Chipola Cutoff, FL (10) Beech-American holly Ecologically or Congaree Swamp National geographically Monument, SC (Figure 37); localized Alcovy at Hwy 278 bridge, GA (11) Swamp chestnut oak-southern magnolia-American Ecol ogi ca lly or Apalachicola, Muscogee °'.i::,. holly and river cane geographically Reach, FL localized Floodplain "island" with incipient beech (12) Beech-American holly with Symplocus Ecologically or Upper Three Runs, Aiken, magnolia hammock geographically SC localized (13) Beech-southern magnolia Ecologically or Kiokee, Fowler Tract, geographically Dougherty Co., GA localized Pleistocene ridge (ridge and swale topography, (14) Swamp chestnut oak-cherrybark oak-loblolly pine Ecologically or Roanoke, Devil's Gut, Terrace I) geographically NC (Figure 38) localized Pleistocene Terrace I braided dune (border) (15) Water oak-loblolly pine Ecologically or little Pee Dee below geographically Hwy 378 bridge, SC loca 1ized Scour channels {16) Water oak {mix of Zones III, IV, and V Common Apalachicola, Muscogee species) Reach and Chipola Cutoff, FL Figure 36. Although normally an upland species, the loblolly pine also grows in Zone V areas of many floodplains. These large examples occur on old levee ridges and low ter races in the Congaree Swamp National Monument (SC) only a foot or so in elevation above the lower Zone IV floodplain. Photo by George Taylor. 65 Figure 37. An old levee ridge near Cedar Creek (Congaree Swamp National Monument supporting Zone V vegetation. The large tree to the left of the figure is a cher~ oak. Paw paw and spicebush are common in the understory. On slightly higher par this same ridge, beech occurs. Some upland herbs (may apple, broad beech fern, yam, poison oak) may occur. Photo by George Taylor. 66 Low ridges with certain edaphic con these species (primarily beech) to grow on ditions sometimes support a few white oak "islands" (types 12, 13) and old natural (Quercu~ ~ba) in Zone V associations. levee ridges (types 10,11).. South,~rn mag Although tulip poplar (Liriodendron !_IJJ.J.2.:. nolia (Magnolia .9.randiflora), howPver, is ; fera) is extremely rare in .the study rare on floodplains in the study arPi, area, it can occur in Zone V associations. In areas of ridge and swale topog Dominance t es of other sites 12- raphy (type 14) (Figure 38), Zone V asso 1£1. -Beech Fagus grandifolia or beech ciations occupy the higher elevations, magnolia hammock is frequently the first succeeding the associations of lower ele association encountered at the ecotone of vations. Scour channels, because they floodplain and upland. A beech "fringe" allow rapid drain~ge, frequently contain is characteristic of many Piedmont allu Zone V species mixed with those of Zones vial floodplains. Since beech-southern III and IV (type 16). This is similar to magnolia hammock also exists under seepage the occurrence of 1i ve oak (and saw pa 1- conditions on the uplands (usually adja metto) at the "lip" or edge of banks and cent to the fl oodp 1a ins. Zone VI), the scour channels. high water tables of Zone V often enable Figure 38. Narrow, long ridges between swales on the l~wer Roa~oke floodplain (NC) of probable late Pleistocene age have an almost diagrammatic zonat,on.of Zone V hardw~o~s beginning with diamondleaf oak at the edge of Zone II and progress1ng up through s a P chestnut oak to cherrybark oak. 67 Figure 37. An old levee ridge near Cedar Creek (Congaree Swamp National Monument, SC) supporting Zone V vegetation. The large tree to the left of the figure is a cherrybark oak. Paw paw and spicebush are common in the understory. On slightly higher parts of this same ridge, beech occurs. Some upland herbs (may apple, broad beech fern, wild yam, poison oak) may occur. Photo by George Taylor. 66 Low ridges with certain edaphic con these species (primarily beech) to grow on ditions sometimes support a few white oak "islands" (types 12, 13) and old natural (Quercus alba) in Zone V associations. 1evee ridges ( types 10, 11 ). . Southern mag Although tu 1"",p poplar (Li ri odendron 1.~5.2..:. no 1i a (Magnolia. grandiflora), however, is ifera) is extremely rare in the study rare on floodplains in the study are9 • area, it can occur in Zone V associations. In areas of ridge and swale topog Dominance t es of other sites 12- raphy (type 14) (Figure 38), Zone V asso 1§1. Beech Fagus grandifolia or beech ciations occupy the higher elevations, magnolia hammock is frequently the first succeeding the associations of lower ele association encountered at the ecotone of vations. Scour channels, because they floodplain and upland. A beech "fringe" allow rapid drain~ge, frequently contain is characteristic of many Piedmont allu Zone V species mixed with those of Zones vial floodplains. Since beech-southern III and IV (type 16). This is similar to the occurrence of 1i ve oak (and saw pa 1- magnolia hammock also exists under seepage 11 conditions on the uplands (usually adja metto) at the 1i p" or edge of banks and cent to the floodplains, Zone VI), the scour channels. high water tab 1es of Zone V oft~n enab 1e Figure 38. Narrow, long ridges between swa1es on the lower Roanoke floodplain (NC) of probable late Pleistocene age have an almost diagrammatic zonation of Zone V hardwoods beginning with diamondleaf oak at the edge of Zone II and progressing up through swamp chestnut oak to cherrybark oak. 67 Plant Communities on Natural Levees, 15). The drier river front is dominated Floating Logs, and Stumps by 1i ve oak and saw palmetto (Zone IV); the levee top supports southern red cedar, The zonal classificatfon scheme does cabbage palmetto, and sweetbay (Zones I I not make specific provision for the plant and II I); and the backside contains inner cornnunities that occur on natural levees swamp species such as swamp tupelo in ad and on floating logs and stumps, and thus dition to dahoon (Ilex, cassine) groundsel they will be discussed here. tree (Baccharis glomeruliflora), cabbage palmetto, southern red cedar, sweet bay Natural levees. The height, width, (Magnolia virginiana), and wax myrtle. soil texture, and drainage characteristics of natural levees vary considerably, often There are distinct differences fostering the highest plant species diver between the communities that occupy old sity on the floodplain. Species character levees and the present developing levee, istic of all floodplain zones (II-V) com primarily because of the changing hydro monly occur on levees, not only because of peri od. The trend is for older levees to the differences among levees, but also be become dominated by species characteristic cause of variations on individual levees, of drier sites as the floodplain geomor which are often a mosaic of microenviron phology changes. Good examples are found ments {Radford et al. 1980). in the ridge and swale topography of sections of the Roanoke River (NC). The Recently formed levees on nontidal ridges (old levees) show distinct zonation reaches of alluvial rivers support pioneer from Zone IV species (primarily diamond tree species, particularly on front sides leaf oak) near the swale edge, through ·· (cottonwood, black willow, river birch wet-site Zone V species (swamp chestnut {Betula nigra), silver maple), while oak and cherrybark oak), and finally to mid-seral species (sycamore (Platanus dry-site Zone V loblolly pine. occidentalis), sugarberry, American elm, green ash, and sweetgum) occupy stabilized Floating logs and stumps. In addi- levee ridges and backslopes (see Figure 21 tion to the communities of Zones II-V and and the discussion of Zone IV dominance natural levees, a unique flora sometimes types). Boxe 1der (Acer negundo) and occurs on floating logs (Figure 39) and catalpa (Catalpa bignonioides) are pioneer stump remnants. Dennis (1973) described species that seem to prefer levees to any such communities in the Santee Swamp {SC). other floodplain sites. River birch is Twenty-four species were noted, eleven of often the dominant on sandy Piedmont which did not occur in the larger survey levees as well as on disturbed flood of the swamp. The community samples were plains. homogeneous, dominated by Boehmeri a cylindrica and .t!i'..eericum wa1teria. The Baldcypress (Zone II), and overcup selective forces acting on fallen logs and oak, water hickory, and water locust (Zone stumps are uniform and severe, efficiently III) are found on low stable levees. eliminating species that cannot tolerate Higher, well-drained broad levee ridges, shifting conditions of inundation~ expo such as those on the Roanoke River in sure, and possible substrate instability. North Carolina, may host Zone V species, In addition to Dennis (1973), Conner and including swamp chestnut oak, cherrybark Day (19 76) noted several p1 ants that grew oak, Shumard 1 s oak ( uercus shumardii), on rotting logs and stumps, including paw paw, and spicebush Lindera benzoin) ferns, strap lily (Crinum americanum), (J.M. lynch, Department of Community H menocallis eulae, spiderlily (H. occi Development and Natural Resources, North dentalis , Hyd'"roc'otyle spp., southern wild Carolina Heritage Program, Raleigh; per rice Zizaniopsis miliacea), and Panicum sonal communication). Live oak frequently spp. occupies the high river front edges be cause of the "dry lip" effect discussed Understory Species earlier (Zone V discussion). A structured understory community Tidally influenced forests, like exists beneath the floodplain forest those found on the St. Marks River (FL), canopy that may rival it in species diver show zonation on the present levee (Table sity. Of 110 species found on the Santee 68 Table 15. Forest dominance type distributions across the nine floodplain transects illustrated in Figure 40. The letters in each zone description refer to the site letters in Figure 40. Where applicable, cross-reference is made in parentheses to specific dominance types/variants as they appear in Tables 11-14 in the discussions of each zone. For example, (II-1) refers to Zone II (Table 11), baldcypress-tupelo dominance type 1. Table 12 has Zone III dominance types; Table 13, Zone IV; Table 14, Zone V. River, river class, Zones and location I I III 1V V Other sites & remarks Congaree, SC, D) Baldcypress- E) Depression pools B) Flats C) Tributary levee A) Present river levee alluvial water tupelo (I I I-6) ( I V-6) with some (Zones III-IV-V) (II-1) beech (V-10) G) Swamp tupelo-sweet F} Old levee ridge H) Upland slope 0) bay backswamp with loblolly \0 adjacent to upland pine (V-8) (II-19) Ochlockonee, FL, J) Pond, with D) Overcup oak flat F) Old G) Present natural A) River channels quasi-alluvial, stooled water (III-5) levee, levee, with water at Porter's lake ash and water with 1ive oak, Vaccinium elm (II-7) oak, spruce elliotii (V-8) pine, and swamp palm (IV-17) H) Shoreline I) Overcup oak cypress with water hickory water elm flat (II-I5) (II-2) E) Slough with water ash (II-9) (continued) Table 15. (Continued). River, river class, Zones and location II II I IV V Other sites & remarks Ochlockonee, FL C) Slough, with (continued) Ogeechee tupelo (II-7} B} Acid bog with swamp blackgum- sweet bay- sphagnum dominance B Swamp tupelo- a sweet bay- " sphagnum backswamp adjacent to upland (II-19) Apalachicola, FL, C) In hummock ter- A) River channel large alluvial, rain ( I I-2) near mouth at B) Present low 1evees Forbe's Island E) Slough, with Ogeechee tupelo (not stooled) Note: Hummocks are 4 ft (I I-2) above mean water level; also support a mix of D) Wet flats, with Zone IV and Zone IV baldcypress-water species (Ogeechee tupelo canopy, tupelo, water tupelo- water elm-water red maple-green ash- ash subcanopy sweet bay) (II-2) (continued) Table 15. (Continued). Zones River, river class Other sites & remarks and location n rn IV V Broad levee A) River channel Alcovy, GA, E) Old oxbow with F) Low wet B) Piedmond alluvial water tupelo flats, with with swamp (at Hwy 278 (II-1) red maple chestnut oak bridge) green ash (V-2) (IV-7) C) High levee ridge (dotted line), with beech (V-10) D) Scour channel topography, -...J diverse plant ..... composition, often white oak and pignut hickory (V-16) G) High flats, with swamp chestnut oak and green ash (V-1) H) Old flat levee, with cherrybark oak-lobolly pine American holly (V-5) (continued) Table 15. (Continued}. River, river class, Zones and location lI III IV V Other site & remarks Canoochee B) Slough; bald- C) Pond with may- E} Flats, D) Scour channel A) River channel blackwater at cypress with haw {III-3) with dia edge. with live Fort Stewart, stooled Ogee- mondleaf oak or water oak GA chee tupelo- oak-spruce and saw palmetto water ash-water pine canopy (VI-16) elm (II-9) and American holly, river cane, and Vaccinium elliotti (IV-8) Roanoke Northern C) Wet flat, with E) Middle and upper A) River channel alluvia 1 river water tupelo position of at Devils Gut, NC baldcypress; ridges: transi B) Natural levee formerly domi tion from swamp nated by bald chestnut oak to G) Second terrace, now cypress ( II-1) cherrybarl< oak mostly cultivated to loblolly pine pine (V-14) Note: Zonation from Zone IV to Zone Von D) Swales, with ridges (E) in ridge water tupelo and swale topography; baldcypress ecotone between Zone (II-1) II swales and ridges with diamondleaf oak F) Terminal swale, (IV-2) with swamp tupelo on deep muck (II-6) (continued) Table 15. (Continued). Zones River, river class, IV V Other sites & remarks and location II III A) Anastomosing river Wet flats; 0) Island, with Chipola, C) diamondleaf spring-fed, baldcypress-water B) Shallower channel on tupelo canopy, oak, swamp alkaline, dogwood, and slough anastomosing and water elm- water ash sub- possum haw at Hwy 71 (IV-11) H) Upland bridge, FL canopy (II-5) E) Peat depression adjacent to up- land; bay swamp ...... on peat with w ericad subcanopy (II-21) D) Flat 11 islands, 11 A) River channel Suwannee C) Floodplain sur- with cabbage tidal forest face (approxi- palmetto-southern B) Exposed root mat of on alkaline mately high tide red cedar-swamp riverbank trees blackwater level), with palm-wax myrtle river at pumpkin ash-swamp Note: The islands in Suwannee, FL tupelo-sweet bay- (D) bear levee and dwarfed bald- hydric hammock species. cypress (II-24) Until further study, they are placed in Zone IV. (continued) Table 15. (Concluded). River, river class, Zones and location I I I II IV V Other sites & remarks St. Marks, H) Inner swamp; A) River level at low tidal forest blackgum-sweet tide; dense sub- of spring-fed bay-cabbage merged bed alkaline river palm-southern (Sag it tari a at St. Marks, red cedar-wax kurzianaJ FL myrtle (II-26) B) River level at high tide C) Intertidal zone, with (D) quillwort (Isoetes flaccida) mats and (E) Ludwigia repens F) Exposed root mat of tree G) Natural levee 1. Front side: live oak-saw palmetto 2. Top: southern red cedar cabbage palmetto sweet bay 3. Backside: groundsel tree and dahoon, in addition to Zone II inner swamp species Figure 39. An example of understory species taking advantage of the dry environment of a floating log in order to exist in Zone II. Photo by Gordon Fritz. 75 River, SC floodplain, for instance, 25 The diversity of the bottomland hard were canopy trees, while 28 species were wood canopy increases with the complexity shrubs or subcanopy trees, 15 woody vines, of floodplain topography. Figure 40 and 2 woody grasses, and 40 herbaceous species Table 15 describe exa11;ples of the varia (Dennis 1973). The importance of the tions encountered on floodplain transects. herbaceous ground cover on a floodplain is Alluvial rivers, such as the Congaree, a function of light and areal extent of Ochlockonee, and Alcovy (Figure 40) often zones of higher elevation (Zones IV and V) exhibit the greatest topographic and plant where these species are most often found community diversity. In contrast, the (Knight 1973). In Zone IV floodplains, floodplains of many Coastal Plain black "sedge glades" are someti1J1es found. In water and spring-fed rivers (Figure 40) the Congaree Swamp (SC), dominant sedges generally are more uniform topographi are Carex 1urida and .f_ • .9.!:2.l'.i, while .f... cally, and the plant community diversity intumescens, C. atlantica, and Leersia is lower. virginica are common. Other common ground cover plants are crossvine (Aniso stichus Regular tidal flooding caused by capreolata), southern vein orchid (Haban lunar or wind energy imparts a distinct eria flava), violet (Viola affinis), character to plant communities under its poison oaic(Rhus toxicodenclron) and swamp influence. These forests are the least milkweed {Asdepias incarnata}. The major studied of a 11 river swamps (Beaven and composite is the butterwort (Seneci o Oosting 1939). They occupy the 1ower 16 glabellus). Common shrubs and vines on to 32 km (10 to 20 mi) of many unaltered North Carolina floodplains are spicebush floodplains, primarily in Florida and (Lindera benzoin), buckeye (Aesculus Georgia (Figure 40). High tides raise the sylvatica), Viburnum spp., Japanese honey- water levels in the floodplain (or "tide suckle (lonicera jaronica), greenbrier plain") to the most elevated portions of (Smilax rotundifolia , poison ivy (Rhus_ the relief with fair regularity. Tidal radicans), grapes (Vitis spp. ), and black swamp fores ts usually extend upstream berry (Rubus spp.) (Knight 1973). Herba until levees appear. The floodplains of ceous ground cover is less extensive in these forests are dominated by Zone II more frequently inundated parts of the species, except for higher islands con floodplain. A characteristic and wide taining Zone IV species such as diamond spread herb in Zone II of many floodplains leaf oak, swamp palm, southern red cedar, {in the Coastal Plains) is goldenclub and cabbage palm. These floodplains are (Orontium aguaticum). Useful species distinctive in harboring animal species lists for floodplain understory and ground characteristic of more brackish downstream cover plants are found in Oosting (1942), waters, such as fiddler crabs (Uca) and Houck (1956), Beard (1958), and Wells square-backed crabs (Ses~). Another (1970). interesting aspect of the tidal forest is the presence of an intertidal zone, either Floodplain Transects of Selected South mud or sand, which is often vegetated by eastern Rivers extensive mats or beds of submerged or aquatic vegetation (such as Isoetes, To provide a sharper focus on the Ludwigia repens, Cabomba cardiniana, complexity of floodplain ecosystems, Elodea spp., or Nuphar ~teum). Figure 40 portrays nine southeastern allu vial, blackwater, spring-fed, and tidally influenced floodplains via horizontal DISTURBANCE AND SUCCESSION IN BOTTOMLAND transects. The spatial relationships HARDWOOD PLANT COMMUNITIES between ecological zones and forest domi nance types are diagrammed and accompanied Several examples of di strubance and by Table 15, which depicts these relation success i ona 1 trends have been referenced ships. . The rivers profiled here are the in the preceding sections of this chapter. same referenced in Tables 11 through 14, They will be summarized here along with where specific site locations were given others that have not yet been mentioned. for dominance types and variants observed in the field. 76 CONGAREE R!VER, SC ROANOKE At VER, NC B E E B D C 8 A C ED EDE FG NA~~~~tFT~~~UARN~ --A B ZONE ~11 V IV Ill IV Ill IV II I V IV OCH LOCKONEE RIVER, Fl ZONE_,, V II V II V II B C D E F GHA A J CHIPOLA RIVER, FL C C E H Ill II IV VII I Ill IV II II APALACHICOLA RIVER, FL II D E A B C SUWANNEE RIVER, Fl C D C D C B A II-IV II IV IV II ALCOVY RIVEH, GA A D E F V V IV IV-V V CANOOCHEE RIVEB, GA A B E C E D E Ill IV-V figure 40. Cross-sectional transects (aspect is looking downstream) of nine southeast ern rivers and floodplains, indicating zones (I-V) and major vegetational and natural features (A-J). This figure is cross-referenced to Table 15, which provides an expla nation for each vegetational or natural feature category (A-J) of each floodplain. See Table 15 also for cross references to dominance types (Tables 11-14) found on these transects. Flooding inhibits point bar succession (see Chapter 1), slows natural levee development and The most common natural disturbances community establishment on levees, and can in bottomland ecosystems are associated forestall the filling in of scour chan with floods. The biota are to a variable nels, swales, and depressions between hum degree adapted to flood forces. Annual mocks. Moderate flooding enhances mature inundations adapt the bottomland hardwoods community development through less damag for the larger and more catastrophic flood ing effects on plant survival and growth events that occur with low frequencies and through reduced erosion and net depo (100- to 1000-year floods). The wide, sition of floodwater sediments. shallow root crowns and trunk buttresses, which are adaptations to the moist, anae Fire robic conditions, serve to counter exces sive scour and toppling by flood or wind. Fire is not important as a natural Deleterious effects may occur, however, disturbance in bottomlands because of the depending on flood timing, frequency, prevalence of water and the lack of a sub depth, and velocity. The categories of stantial litter layer. This is especially flood disturbances include (1) anaerobic true of the wetter portions of alluvial conditions, (2) mechanical abrasion and floodplains. However, Putnam (1951) states breakage of plant tissues, (3) siltation, that a serious fire season occurs on an (4) propagule and seedling washout, and average of about every 5 to 8 years in bottomland hardwood forests (in the Mis (5) erosion. sissippi Valley). It is conjectured that Flooding may retard or speed succes the Indians maintained canebrakes in Zone sional trends. Severe erosive flooding V understory by deliberate fall burning, 77 perpetuating and increasing large cane probability of propagule recruitment. stands, which are now relict. Though Understor~ shading may limit the develop crown fires are rare, ground and surface ment of diverse, well-stocked seedling and fires may occur. These fires move rapidly sap 1i ng 1ayers, retarding success ion across the floodplain floor, damaging or (Gaddy et al. 1975). destroying all trees less than 10 years old, as well as shrubs and herbaceous Biotic Disturbances growth. In addition, ground fires open wounds in larger trees, increasing sus At least three categories of biotic ceptibility to disease and insect attack. disturbances exist in the floodplain: (1) propagule predation and seedling and sap Fire is a major determinant of com ling herbivory by browsing animals, (2) munity composition in selected vegetation disease, and (3) insect outbreaks. The types. Infrequent but regular fires favor quantitative effects of these variables on Atlantic white cedar while inhibiting pl ant community structure and composition have received little attention. Cattle southern red cedar (Eyre 1980). and deer browsing can kill seedlings H.S. Larsen, writing in Eyre (1980) particularly if floodwaters concentrat~ indicates that fire may sweep into the browsing on higher ground in the flood dense shrub zone of sweet bay-swamp plain. Baldcypress seedlings are even tupelo-red bay sites alor:g the narrow bot eaten, and water tupelo will survive only tom of perennial streams during drought one cropping by deer (F. Vande Linde forest~r, Bruns\'lick Pulp Land Company'. years. It is possible that the narrow Brunswick, GA; personal communication). peaty swamps along small streams with At lantic white cedar or pond pine canopies (type 29) may burn in drought years. The Conner and Day (1976) discussed the only recent instance of a widespread fire effects of grazing by the forest tent on a floodplain in the study area occurred caterpillar on both baldcypress-water prior to 1976 on the Oklawaha River (FL). tupelo and bottomland hardwood forests in Louisiana. Water tupelo is most severely Gaddy et al. (1975) described the affected, suffering extensive defoliation. successional sequence in the Congaree These authors suggested that the increas Swamp (SC) that begins with either fire or ing frequency of outbreaks over wide areas clearcutting, and proceeds from even-aged is due to a corresponding increase in the sweetgum-intolerant hardwood stands to areal extent of tupelo-dominated sites. more mature communities dominated by dia These sites, in turn, occur as a result of mondleaf oak and more tolerant hardwoods. the selective logging of baldcypress (see below). Conner and Day (1976) also specu late that the susceptibility of water Windthrow tupelo to defoliation may be one factor Windthrow is the primary disturbance that formerly favored the maintenance of to plant succession on floodplains in the nearly pure stands of baldcypress. study area. Gaps in the canopy resulting from fallen canopy trees (Figure 41) are Lumbering common in the floodplain. Topplings due to old age, disease, soft sediments and Selective cutting and clearcutting insecurely anchored root systems, root generate some of the most noticeable scour, lightning strike, or fire cause changes in floodplain fores ts. The heavy openings in the canopy that temporarily exploitation of baldcypress is the classic stimulate understory woody and herbaceous example. Such logging has shifted the growth. The factors that influence suc forest composition on countless sites. cessi ona l response to such gaps include Cypress stumps endure for many years, and gap size, existing composition of seed their presence may indicate what the orig lings and saplings and their relative ; na 1 forest on a given site was 1i ke and shade tolerances, possible inhibition due something of the hydrology. Many areas to shading by extensive understory tree which now support water tupelo (e.g., the (paw paw, holly (Ilex opaca), ironwood Altamaha River, GA), green ash (e.g., the (Carpinus carolin-faria)) or canebrake Great Pee Dee River, SC), or water tupelo development, site characteristics, and g.reen ash (e.g.'! the Oklawaha River, FL} 78 Figure 41. This windthrown bitternut hickory on the floodplain of the Murder Creek Special Management Area (Oconee National Forest, GA) illustrates the large opening created by this natural event. In mature forests such openings are common enough to provide vegetation in all states of succession. The virgin forest thus has its own system of uneven-aged management. formerly bore fores ts of very 1a rge creeks, providing a reservoir to supply cypress. Klawitter (1962) discussed the water to the rice fields, even on coastal three periods of baldcypress logging on islands (e.g., Hobcaw Barony, SC). This the Santee River (SC). system persisted until 1885 (Klawitter 1962). When the tidal flooding method was Clearcutting of hardwoods other than developed in South Carolina in 1750, baldcypress may also lead to entirely new large-scale rice plantations became feasi forest overstories. Sweetgum and shade ble, and entire floodplain forests of intolerant hardwoods pioneer after clear cypress were burned or buried by slave cutting in the Congaree Swamp (Gaddy labor (e.g., Santee River, SC). The fields et al. 1975), and mid-seral sugarberry with their remnant levees from these American elm-green ash stands fol low plantations are used today as waterfowl extensive logging of Zone IV (Nuttall oak refuges (Figure 42). willow oak) forests in the Mississippi Va l1ey. Unsuccessful attempts at cotton and other agriculture have taken place on many Agriculture southern floodplains, especially in the great fa 11 1i ne swamps of the Flint and The growing of rice has completely Oconee Rivers in Georgi a (Wharton 1977). altered many floodplains. Rice culture These abandoned areas support a variety of was introduced around 1700 in Zone II forest cover. One area on the Roanoke swamps on smaller streams that emptied River (NC) bears an almost pure stand of into large navigable rivers (e.g., Wambau large cottonwoods. Boxelder flats can be Creek and Santee River, SC). Reserve found in such disturbed areas along the dams were constructed across sma 11 feeder Chattahoochee and Alcovy Rivers (GA). 79 Figure 42. Aerial view of relict rice fields on former bottomland hardwood forests that are presently managed for waterfowl. Photo courtesy of the Georgi a Department of Natural Resources. PRIMARY PRODUCTIVITY OF FLOODPLAIN FORESTS detrital decomposition rates, except in systems with permanently ponded water; {3) High productivities of the floodplain periodic "flushing" of accumulated refrac forest (Conner and Day 1976) are made tory organic detritus and metabolic by possible by several subsidies offered to products; and (4) the operation of several the floodplain by the watershed and river, mi crobi a 1 conversion processes character including particulate and dissolved or istic of widely varying conditions, such ganic matter, water, soil (especially clay as nitrification, denitrification, ammoni and silt), and nutrients (inorganic, fication, methanogenesis, sulfate reduc sediment-adsorbed, and organically com tion, and general nutrient mineralization plexed). These inputs support what is (Wharton and Brinson 1979a). essentially an increased rate of ecosystem community metabolism, reflected in (1) In addition to these physical and annual litterfall and nutrient turnover chemical subsidies, the river contributes rates as high or higher than most temper macro- and microfauna during flood periods at! dectduous forests; (2) relatively higH that both speed detrital decomposition and 80 participate in the floodplain 1 s food chains, nutrient cycles, and import-export pathways. The major factor contributing to the t high productivity of the floodplain forest :: is the pulsing of the wet-dry cycle. > Conner and Day (1976) made an analogy 0 -::J between these floodplain forests and the "t, tidal marshes in terms of the positive e effects of fluctuating water levels: a. "This periodic flooding acts somewhat in the same manner as tidal flooding in saline marshes, in that fluctuat Stagnant Seasonal flooding ing water levels are energy subsidies Slowly Abrasive which control variations in hydric flow Ing flooding conditions, temperature, nutrient Stress Subsidy-Stress levels, and available oxygen (Hester 1973; Butler 1975)." Figure 43. The effect of a gradient of flooding on productivity as compared with Bottomland hardwood communities that a regional level that might be expected in either are permanently flooded with slow the absence of standing or flooding water. moving to stagnant water, or are regularly The graphic model takes the form of a damaged by unusually high and irregular stress-subsidy curve. For southern swamps destructive floods are not as productive Conner and Day (1976) estimated annual net as communities that undergo periodic mod production for stagnant, slowly flowing erate floods. This has been illustrated and seasonal flooding conditions as of the clearly (Figure 43) by Odum (1978), who order of 0. 2, 0. 7, and I. 2 kg dry matter graphically compared the productivity of per square meter, respectively (Odum stagnant, seasonally flooded, and abra 1978). sively flooded systems with a regional average of all wetland and upland forest types. "Forest production appears to peak at Communities in permanently ponded the once-per-year flood frequency if conditions, or on sites where poor drain flooding is during the winter because age leads to continuously high water this regime furnishes the optimum tables and the accumulation of acidic peat environment for plant growth in terms soils, have lower productivities primarily of nutrient input by flood waters, because of 1ow nutrient turnover, due to summer soil moisture, and possibly anoxia, nitrogen limitation, and low pH. aerobic conditions during the summer Brown et al. (1979) and Conner and Day leading to inorganic nutrient release (1976) presented data that demonstrate the from organic debris." reduced productivities of still water systems. Primary productivity data in the lit erature are much more common for the tree Productivity values gleaned from the canopy and woody subcanopy (sma 11 trees literature for 19 upland and bottomland and shrubs) components of floodplain com forest types are presented in Table 16 and munities than for the herbaceous, aquatic generally support the concept of a flood vascular, and nonvascular components. subsidy depicted in Figure 43. A second Aquatic plant productivity in river chan verification of this concept is shown in nels and drainage tributaries, permanent Figure 44, where productivity data from ponds, and temporary s 1oughs and swa l es sites in several zones are plotted (from has received the least attention. Brinson Gosselink et al. 1981). Gosselink et al. and Wharton (1979a) suggested that the (1981) stated: productivity of alluvial stream communi- 81 Table 16. Net primary productivity {g dry wt/m2/yr) for bottomland hardwood communities (primarily Zone II), com pared with other wetland and upland environments. New primary productivity Community type (g dry wt/m2/yr) References Dwarfed cypress strand (FL) 367 Carter et al. 1973 Okefenokee cypress forest (GA) 595 Schlesinger 1978 Oak-hickory upland (MO) 600 Rochow 1974 Cypress-water tupelo (IL) 678 Mitsch et al. 1~77 Drained cypress strand (FL) 681 Burns 1978 Cypress-tupelo (Green Swamp, FL) 760 Mitsch and Ewel 1979 Oak-pine uplands (NY) 796 Whittaker and Marks 1975 Slash pine flatwoods (FL) 830 Golkin 1981 Northern hardwood upland (NH) 898 Whittaker and Marks 1975 Cypress-hardwood (Green Swamp, FL) 950 Mitsch and Ewel 1979 Mature cypress dome (FL) 956 Brown 1981 Elm-ash-sweetgum (Zone IV) (IL) 967 S. Brown (pers. comm.)a Spruce-fir upland (Great Smokies) 980 Whittaker and Marks 1975 Upland cove forest (TN) 1050 Whittaker and Marks 1975 Cypress strand (FL) 1111 Burns 1978 Riverine cypress-water tupelo (LA) 1140 Conner and Day 1976 Mixed bottomland hardwoodsb (LA) 1174 Conner and Day 1976 Cypress-water ash creek forestc (FL) 1607 Brown 1981 Tulip poplar upland forest (TN) 2400 Whittaker and Marks 1975 aSandra Brown, Department of Forestry, University of Illinois, Urbana. bRed maple-water tupelo-box elder-cottonwood-cypress-swamp dogwood-willow (mix of Zones II and IV with pioneer species). cAlso contains diamondleaf, oak, sweetgum, red maple (mix of Zones II and IV). Flow partially regulated by low dam. ties is probably low because of heavy silt philoxeroides, Myriophyllum spp., Lemna loads. Productivity of the Satilla River spp., ~irodela spp., Egeria densa, and Okefenokee Swamp does not seem to be Ceratophyllum spp., Limnobium spp., and limited by low nutrient availability and Azolla spp. {Dennis 1973). acidic conditions. Brinson observed ex tensive production of filamentous algae in The prominence of the herbaceous floodplain ponds during the winter dormant ground cover varies dramatically among the season and suggested that this component forest cover types, as discussed in the may provide a temporary sink for inorganic previous section on dominance types. In nutrients during winter and early spring. genera 1, the highest herb densities and productivities are found on the driest Aquatic vascular productivity can be floodplain sites (heavy growths of various high in localized areas, depending on composites follow drydown in Zone IV). light intensity and water velocities. This is a function of hydroperiod and Species that may contribute heavily to light intensities. One species that can community productivity are Alternanthera produce tremendous amounts of biomass in 82 a: >- 2000 "' •14 -..E C) z 0 1600 •13 i= u :::, 0 19 0 er: 24 0.. 1200 20 23 er:>- 22 <( 2 18 a: 0.. 800 21 ...I 17 <( 16 :::, z z 15 <( 400 0 10 100 FLOODING FREQUENCY - YRS FLOOD Figure 44. Organic matter production in ecological zones (adapted from Gosselink et al. 1981). Numbers represent specific floodplain sites. short periods is river cane. Wharton (SC), including Smilax spp., Vitis spp., {1977) reported that this plant may pro cross vine (Ani sostichus careolata}, duce 4506 kg of edible leaves per hectare supplejack (Berchemia scandens , poison (4000 lb per acre) per year, and 11 to 16 ivy (Rhus radicans), climbing hydranger tonnes of organic material per hectare (5 (Decumeria barbara), Virginia creeper to 7 tons per acre) within the first 3 (Parthenocissus uin uefolia), and trumpet years of growth. vine (Campsis radicans . The contribution of this component to community productivi A striking feature of many floodplain ties may be large locally, particularly in plant communities is the prominence of canopy gaps created by windthrow and along woody vines. Dennis (1973) recorded 15 river banks. species in study plots in the Santee Swamp 83 CHAPTER 5. FAUNA OF ES Bottom land hardwood fores ts supp~rt. a coastal forest compris diverse fauna that matc~es the_ flor_-1st1c tupelo, pumpkin ash, swe:t and hydrologic complexity wh~c~ is so . -~a 1 ' . and cypre~s which characteristic of these commun1t1~s. The tr car; to an association of moisture gradient and hy~ropenod~ of c;eechee tupelo, water tupelo, floodplains provide a habitat contrn~um . , and cypress. The fauna] for a wide range of aquatic to.terrestrial 1ons cn~~ge _abruptly from a brack- to aerial species. The fauna 1s here also ish . s~a1 ,-fiddler crab community treated within the zonal concept. Because ·-----··-1... _n___ - ; to a freshwater snai]. of the large numbers of taxa, only abun . comr,unity (Vivipara-Cambarus) at dant or dominant animals or groups can be the point upstream where natural levees mentioned. {For further information, see f i rs t occur. Wharton et al. 1981.) Some overlap among zones occurs, especially between Zones IV ~:auoi nvertebrates dominate Zone II and V, which share many species. The and the wetter depressions and pools of mobility of many species and their over Zone I I I. Parsons and Wharton (1978) doc lapping distribution in response to vary unented a eye l i c sequence of dominant ing environmental regimes make combining r.acroinvertebrates in isolated pools (Fig discussions of faunal assemblages in Zones ure 46) (Zone III) in Piedmont flood II and III useful. It should be recog /J la ins: initially s tonef lies dominated, nized that placing an animal in one or tallowed uentially by the isopod even two zones does not necessarily As~llus sp. and amphipod .t!Yalella azteca, restrict it to these areas. Floodp1ain sr:a 11 o l icochaete v1orrrs and midge fly lar inhabitants are opportunists, and many vae, and ~finally an association of sphae· move freely into irregularly flooded or riid clans (Sphaeriur.: and Musculium). dry areas over the year. Sklar and ner {1979) found an almost eaual distribution of arr:phipods, oligo d;aetes, gastropods, and turbell?ria~s FAUNA OF ZONES II AND III (densities of 10,700/m2) on vegetat1on1n a tupelo s:urn-cypres s association. Beck Invertebrates (1977) found that detrital substrates, such as Zone II soils, were ex.tremelpro· . Given the diversity of vegetationa1 duct i ve, a vera o i ng 2885 organi sms/m rn. a domrnance types in Zone II, it is not s ur large alluvial~ systerr (Atchafalaya Bas1,n, pri sing to find that faunal components LA.). The dominant r:iacroinvertebrates we'.e also vary. In terms of fauna, the environ a tubificid annelid . (Pelosc?lex. ment of .a tupelo gum-cypress forest viith ~ hydrop~r1ods approaching a year is mark setosus), an isopod C!::rc~us lrneatu~a'flY e~ly different from a similar forest in a ar:1phipod (Gammarus ~1gr1nusT, (~haob~rus (Caen)l), ~hantom ~ndge !arv(~h t~dal area with daily water level fluctua ~ 1·toiiomusJ. tion or a forested site with permanently 12.!Jnct 1 pennis J, a ch 1 ronom1 d - finger· a· pu l rronate _s n~ i .1 ( Phys a(1 ~ ) found saturate~ s~ils. An example of this phe a)• 9 8 nomenon is 1llustrated in Figure 45 for a nail clam (£.1~1d1um). Ziser nisms per an average density of 1296 horg\ths in a c?astal section of the blackwater Suwannee o of duckweed and water yaci e the ;,ver (FL). The tree associations within - d · ants wer one II of the Suwannee change with dis Louisiana sv,amp. The omin . (Ph sa, ta~ce fr~m the coast in response to less- naidid worm (De.r:Q), three sna~ls orWafid en, ng t1 da l influences (i.e. to the Ferrissi~_ and Promenetus), a sel flies extent of ct ·1 · . ' mite \.tli:s!I'2zetes T, two d:~k swil1llller ties) Th a1 Y ,~undat1on and sa1ini- 1 s_s:_hnura), ~ a and biting . . . e vegetative changes are changes s trio 11;,and midge 1n species morphology as wen as species 84 = Figure 45. Comparison of the bottomland hardwoods and characteristic fauna at dif ferent reaches of a blackwater river near the coast (Suwannee, FL}. (H) is high tide; (L) low tide. Upper figure: River Mile 4, intertidal zone, largely exposed roots; tidal forest of dwarfed swamp tupelo, pumpkin ash, sweet bay and cypress with: (A) fiddler crab (Uca minax) and (B) olive nerite snail (Neretina reclivata). Lower figure: River ITTe ~ntertidal zone wide, with: (G) spatterdock (Nuphar luteurn), fanwort (Cabomba carol ina) and Elodea sp.; forest is tall Ogeechee tupelo-water tupelo pumpkin ash-cypress with: {C) crayfish (Procambarus seminolae), (D) snail (Vivipara ~eorgianus), (E) dwarf salamander (Eurycea guadridigitata), (F) southern leopard frog Rana utricularia). 85 00 O'I Figure 46. Floodplain pools (Zone III) on this Piedmont alluvial floodplain (Alcovy River, GA) are concentration centers for detri ta l decomposition and teem with invertebrate life. Mayfly nymphs reach densities of I000/m2, crus tacea average 1750/m2, stoneflies average 828/m~ and fingernail clams reach a maxima of 1500/m2. High productivity in small pools is due to silt enrichment, abundant detritus (biomass 1.24 kg/m2 dry wt), and absence of predators (Parsons and Wharton 1978). Arthropods, crustaceans, and mollusks (Amphiuma means), which seek refuge in dominate the macroinvertebrates of the root holes and crayfish holes during dry Congaree, Swamp (SC). Three dragonflies down. The amphibious salamanders include (Epiaeschna heros, Tetragoneuria _f,Ynasura, the southern dusky (Desmognathus fuscus Gomphus ~xilisr-are abundant and assumed auriculatus), the many-1 ined (Sterochi lus associated with Zone II. Crayfish such as marginatus)°, and the dwarf (Eurycia quad..: the red Procambarus clarkii (west of the ridigitata). The mud salamander TPseudo Mobile sysfeiTi}andf. 7roglodytes (east of triton montanus) and the two- lined sala A1tamaha system) are along with crayfish mander {E. bis l i neata) occur around the from Zones IV) an important food for a edge of Zones II and III. host of vertebrates such as the eel, cat fish, warmouth, amphiuma, glossy water Frogs are less specific to Zone I I snake, ibis, otter, and raccoon. Densi but include the cricket frog, river frog ties ranging from 21 to 46/m2 have been (Rana heckscheri), and southern leopard reported (Koni koff 1977; V. Lambou, Envi frog, and at breeding times several other ronmenta 1 Protection Agency, Las Vegas, species such as the bird-voiced tree frog NV; personal communication). Crayfish, in (!!.YlE. avivoca). Some depression pools fact, form one-third of the faunal biomass (Zone III) may support annual breeding of the Suwannee River floodplain (Wharton aggregations of spotted and marbled sala 1977). Large fishing spiders (Dolomedes_ manders, as we 11 as temporary water-breed spp.) and Pirata maculatus, which are ing frogs and toads from Zones IV and V. found under the liverwort Porell a £.}aty .Q!i~idea, are characteristic of Zone II. Only a few reptiles are locally abun Several snails (Vivipara, Ca~loma, dant in Zone II areas. The dominants Pomacea, and !:ioptax) live in and around appear to be the eastern mud turtle (Kino Zones I I and I I I Figure 47). Fingernail sternon subrubrum), glossy water snake clams of the genera Sphaerium, Euper~, (Natrix rigida), perhaps the mud snake Musculium, and Pisidium often dominate the (Farancia abacura), and certainly the red benthic biomass~-:r-zones II and III. These bellied water snake (Natrix erythrogaster) tiny ( Figure 48. The six endemic species (and Lampsilis splendida) of unionid clams recorded (Johnson 1970} for the Altamaha River, GA. First column: Lampsilis dolabraeformis, Elliptic shepardiana; second column: Lampsilis splendida, Alasmidonta arcula, _!:lliptio spinosus (the unique spiny clam, a relict species); third column: Anodonta gibbos~, Elliptio hopetonensis. Specimens and assistance courtesy Georgia Power Company Environmental Laboratory, Atlanta. the seeds are eaten by squirrels. l embo 1 a) were by far the dorni nant litter organisms, accounting for about 92% to 95% Although the rice rat occasionally o~ the organisms during any season. The appears in Zone II, small mammals are usu mites comprised 48.1% and 77.4% of the ally absent in most of it. Mink, raccoon, total population count in the summer and beaver ·and otter may use tupelo gur., fall, respectively; the springtails, 47.6% cypress forests (Zones II and III) in par and 13.1%. Both groups are detrital ticular. "shredders" important to the decomposition processes in the upper 1itter and humus 1ayers. FAUNA OF ZONE IV Earthworms, important food sources Invertebrates for salamanders and shrews, are also an abundant and important component of the The invertebrate fauna of Zone IV can litter fauna. Parsons and Wharton ( 1978) be subdivided according to their dominant found three genera of earthworms (Eisenia, use of this floodplain zone: Allolobophora, and Spargano[Jhilus) in the floodplain of the Alchovy River (GA). {1) inundatfon fauna inverte Harper ( 1938) noted that earthworms brates occupying the substrate (principally the genera Diplocardia and and water colun1n during periods Helodrilus) preferred dense, packed flood of flooding plain soils with water tables below 23 cm (9 inches). (2) litter fauna -- invertebrates occupying the 1eaf 1 i tter 1ayer Other invertebrate fauna us·i ng Zone during dry periods IV throughout the year and throughout their entire life cycles are principally (3) persistent fauna inverte- crayfish and insects. Some 23 chimney brates occupying the floodplain bui 1ding floodplain crayfish species occur habitats in various life history east of the Mississippi River and 19 east stages throughout most of the of the Escambia River (FL) (Wharton et al. 1981). Severa 1, such as Procambarus year. pubischelae and f_. serninolae, seem to Sniffen (1980) characterized the favor blackwater floodplains; others on almost all floodplains are Cambarus inundation fauna of the Creeping Swamp di ogene~ and Procambarus acutus. Many {NC) floodplain (Zone IV} as a large and insect species whose larvae inhabited diverse component of this small blackwater sloughs and pools within Zones II and III fioodplain. The most conspicuous inverte may be found in Zone IV as flying adults brates were six species of "red" lumbricu during drydown. Mobile species, such as lid worms and four species of "white" dragonflies and butterflies, span many enchytraeid worms, three tubellarian flat zones. Some, like the abundant snout worm species, and severa 1 roundworm spe butterfly (Li bytheana bachmani i) and the cies. Oligochaete worms and copepods were hackberry butterfly (Asterocampa celtis), numerically the most abundant i nverte can be categorized by their larval prefer bra tes (16,470/m2). Isopods, although ence for sugarberry, a Zone IV tree. fewer in number than the worms, were the nant biomass component (1114 mg dry Vertebrates ) . Os tr a cods were numerous (.829 /rr, 2), as were nematodes ( 4348/m 2). tr,1dge fly Amphibians, especially salamanders, larvae, amphipods, water mites and co1l em are abundant in Zone IV. The marbled sal a were also abundant. amander (Ambys toma opacum) is generally restricted to this zone; others such as There are relatively few definitive the mud sa 1amander (Pseudotriton montanus) s ies of the 1 itter fauna of floodplain seldom occur elsewhere. The dominant cormunities in Zone IV. Grey (1973) con plethodontid salamanders include the two ducted the most thorough faunal survey of and three-lined salamanders (Eurycia). is particular habitat. His_ study of _the The four-toed salamander (Hemidacty1um) Santee River (SC) floodplain determined occurs here and in Zone II. The green and that tes {Acari) and springtails (Col- 90 leopard frogs (Rana) and cricket frogs Two of the few vertebrates that are {Acris) are dominant anurans; the upland confined almost exclusively to Zones IV chorus frog (Pseudacris niqrita) and grey (and V) are the semiaquatic swamp and tree frog (Hyla versicolor) are common marsh rabbits (Syvilagus aguaticus and~ locally. The bird-voiced tree frog (~~ pa l us tri s). Swamp rabbi ts are found more avivoca) occurs here and in other zones, often in Piedmont floodplains while marsh especially at breeding time. rabbits are confined mainly within the Coastal Plain. The swamp rabbit is adapted Reptiles in Zone IV are represented with large feet and slightly splayed, by the abundant bo.x turtle (Terrepene strong-nailed toes for swimming and tra carolina); the giant gulf coast form (I_. versing unconsolidated terrain (Lowe £· major) also occurs on floodplains. 1958). Herbivorous swamp rabbits reached There are few snakes in Zone IV other than a density of 5.6 individuals per 100 acres the rat snake ((laphj~ obsoleta) and sub in the Lowe study on the Oconee River, GA. species. Boyd 1976 encountered copper heads and rattlesnakes in Zone IV study areas, but these snakes (more characteris FAUNA OF ZONE V tic of Zone V) may have come from a nearby hillside. Tinkle (1959) reported the black Invertebrates racer {Coluber constrictor), kingsnake (Lampropeltis getulus), and ribbon snake Many invertebrate species are common (Thamnophis sauritus) on a narrow levee both to Zones IV and V as well as to ridge, assumed to be Zone IV from the site levees (Wharton et al. 1981). The detri description (or in succession to Zone V), tivore community of the predominantly Zone although these snakes are not frequently V Alcovy River (GA) floodplain is charac encountered in Zone IV. terized by abundant millipedes (Cherokia georgiana, Narceus americana) and camel Many bird species are found in Zone crickets (Ceuthophilus racili es). Also IV. In a study in the Congaree Swamp, abundant are a scarab Onthopha us) and numbers of species were similar among three carabid beetle genera 0Carabus, floodplain Zones II, IV and V; however, Abacidus, and Chlaenius}. The grazer com population densities were almost always munity includes two katydids (Ptero h lla highest in Zone IV (Hamel 1979; Hamel and camellifolia, Scudderia rhombifolium. Brunswig 1980). Characteristic birds in Other grazers.common to Zones IV and V and the Congaree Swamp are the barred owl, abundant in the Congaree Swamp are the downy and red-be 11 i ed woodpeckers, and zebra swa 11 owta i1 (Graphium marce llus) cardinal (Hamel 1979). The wild turkey is (whose larvae feed on the paw paw), the known to nest and feed in Zone IV (Kennedy Carolina satyr (Euptychia hermes sosybia), 1977). In fact, bottomland hardwoods sup the red spotted purple (Limenitis archip port the highest population densities (1 ~ astanax) and the pearl crescent per 10 acres vs 1 per 25 acres of upland) (ftlysoides tharos) butterflies. of eastern wild turkey (Florida Game and Fresh Water Fish Commission 1978). Of the spiders shared by Zone.s IV and V, the most abundant ground d~tellers on a Dominant Zone IV floodplain mammals Piedmont floodplain are the wolf spiders are the deer mouse in the Piedmont, the (Schizocosa ocreata, Lycosa helluo), and cotton mouse in the Coastal Plain, and the in the Congaree, Schizocosa crassipes. In golden mouse in creek swamps and areas of the Congaree the dominant aerial spiders dense shrub and vine growth. Short-tailed are the orb weaver (Neoscona arabesca}, and southeastern shrews are abundant in the spinyback (Micrathena graci1is), and this zone but may retreat to higher zones Frontinela spp. during innundation. Most of the larger marmials in Zone IV are also common to Zone Most of the 11 species of snails V. The woodrat (Neotoma floridana), which recorded from Congaree probably inhabit nests in the ecotone adjacent to the up Zone V. The dominant ones are the great lands, forages in Zones IV and V. It nests zonite (Mesomphix vul~atus), the white- in Zone IV along spring-fed rivers. 1ipped forest snail Mesodon thyroidus) 91 and the cannibal snail (Haplotrema con Zones IV and V are the principc. l cavum). environments of the rare and endangered ivory-billed woodpecker, Bachman's warbler Vertebrates and probably the couqar (Wharton et a 1. 1981). Black bears (on Bear Island) ccn Zone V shares vertebrate species com gregate on the higher, unlogged, acorn mon to uplands as well as Zone IV. The rich Zone IV and V bottomlands. Upland large, spotted salamander floodplain (Germany) fish yield was 14.6 adult crayfish (Procambarus acutus and kg/ha (13 1 b/acre) wi_th a 20-day inunda Fa 11 icambarus uhleri), both floodplain tion, increasing to 49.2 kg/ha (44 lb/ varieties. acre) with a 198-day inundation, with the delayed effects recognizable a year later Fish trapped on the Creeping Swamp (Stankovic and Jankovic 1971). floodplain feed on floodplain inverte brates, principally copepods, ostracods, The use of the floodplain by fishes amphipods, isopods and midge fly larvae in a blackwater creek {Creeping Swamp, (Chironomidae) (Robert Sniffen, Institute Pitt County, NC) was studied by Walker of Marine and Coastal Research, East Caro (1980) by use of two-way weir traps in lina University, Greenville, NC; personal shallow drainways on the floodplain (Zone communication). Delicate forms such as II) (Figure 50). With the exception of oligochaete worms and flatworms (Planaria) the redfin pickerel, fish moved on the disintegrate rapidly and leave few or no floodplain only at night. Most fish were i dent i fi ab 1e fragments; hence their con caught in January through March, the time tribution to fish diet may be underesti of maximum inundation, although large mated. Both Woodall et al. (1975) and fluctuations occurred at other times in Arner et al. (1976) on the Luxapali1a these small streams (watershed approxi River (MS, AL) found a preponderance of mate 1y 80 km2 or 31 mi 2). Common species "terrestrial" invertebrates in stomachs of (in order of abundance on the floodplain) fish collected on the floodplain. were pirate perch, redfin pickerel, flier, mud sunfish, eastern mud minnow, American Holder et al. (1970) compared the eel, banded sunfish, creek chubsucker, fish populations of inundated floodplains blue-spotted sunfish, redear sunfish {Zone II) and sloughs of the Suwannee (shel lcracker), bowfin, shiner, brown River. While the standing crop over the bullhead, pumpkinseed, bluegill, golden floodplain averaged much less (11-17 kg/ha shiner, warmouth, redbreast sunfish, swamp or 10-15 lb/acre during the 3- to 10- darter, and green sunfish. Included in month inundation period) compared to that the catch of the floodplain weirs were 928 of the sloughs (262 kg/ha or 234 lb/acre), 93 Figure 50. Two-way traps with wire mesh wings, set in this smal 1 Coastal Plain black water creek {Creeping Swamp, NC) and in shallow drainways on the floodplain, revealed that 21 fish species used the floodplain extensively. With the exception of four species, more individuals were taken on the floodplain than in the channel. Although most fish utilized the floodplain from January through March, flooding occurred fre quently at other times in this small watershed (80 km2 or 31 mi2) (Walker 1980). 94 the surface area of the floodplain was TROPHIC RELATIONSHIPS much larger. Sloughs were sampled after the water had ceased flowing off the Energy flow in riverine systems floodplain, and fish were concentrated by involves both detritus and grazing path falling water levels. Holder et al. ways. Although rivers appear to shift (1970) stated that "high water over the from autotrophy (predominantly grazing floodplain provided space, food, and pathway) in mid-sections to heterotrophy increased habitat for the reproduction and (predominantly detritus pathway) in lower growth of fish." sections (Vannote et al. 1980), many lower river "detrital" food chains may still Movement of fish on floodplains often involve zooplankton "grazing" on phyto is keyed to temperature. Ho 1 der et al. plankton. For example, Wallace et al. {1970) found ripe males and females of (1977) found over 300,000 diatoms/liter in several species trying to cross the sill the lower Altamaha River (GA). The graz between the Okefenokee Swamp and the ing pathway is important even in Coastal Suwannee River coincident with high water Plain blackwater streams; Patrick (1972) at the following time and water ternpera characterized these streams as being domi tures: fliers, bowfin (February, March, nated by the di atom genera Eunoti a and 11 °-13°( or 52°-56°F); yellow and brown Actinel la. For clarity, trophic pathways bullheads (March, ll°C or 52°F); warmouth on the floodplain have been divided into (March-April, 16°-l9°C or 60°-67°F); chain two systems (dry system pathways and wet pickerel (March-April); lake chubsucker system pathways). These two "systems" are (April, 21°-24°C or 70°-76°F). not always clear cut. For example, mal lards prefer to feed on acorns when they Floodplains are important spawning float during inundation. The dry system areas for several species of herring (Figure 51) is functional during drydown {CluJeidae). Hickory shad (Alosa_ medio when the floodplain is not inundated. cris spawn in oxbow lakes, sloughs, and While the system is largely detrital, the tributary streams of the Altamaha River grazing pathway of the terrestrial faunal (GA) (between River Mile 20 and 137). assemblage is also pronounced, with appre Blueback herring (~losa ae.§..!_i_yalis) spawn ciable consumption of the products (nuts, in the same areas of the cottomland hard berries, leaves, bark) of the bottomland woods; they have remarkably adhesive eggs hardwoods and other primary producers. which adhere to twigs and objects on the floodplain floor and resist being swept Trophic pathways in the litter layer away by sheet fl ow. Ripe bl uebacks were of the dry system are similar to those in taken in an over 161-km (100-mi) long sec the uplands. Gist and Crossley (1975) in tion of the Altamaha in backwater lakes trophic studies of upland forest found and flooded low areas ttthat are accessible that millipedes consume up to 120 g/m2/yr to these fish only during spring flood of deciduous 1 i tter detritus. Fungal stages 11 (Adams and Street 1969). hyphae were the principal food of snails and collembolans. The predatory mites Studies of larval fish on the flood consumed primarily collembolans. plain or in sloughs and waterways deep within the floodplain suggest that the The second trophic system, (Figure immature stages of roughly one half of the 52) is a wet system functioning in pools fishes of the lower Mississippi River used and during inundation. Primarily detri the floodplain as a nursery (Gallagher tal, it involves the bulk export of detri 1979). Analysis of the temporal, spatial, tus into sloughs, oxbows and rivers, thus and size distribution of larval fishes feeding a largely aquatic fauna. Aerial supported this contention; spa1~ning of 7 swarms of midge flies, mosquitoes, and out of 10 of the most corr:mon taxa took mayflies emerge periodically, however, to pl ace in backwater habitats (Atcha.fa 1aya regale legions of swifts, tree frogs, Basin, LA) (Hall 1979). Temporal and bats, and dragonflies. spatial delineation of niches of larval fish on the floodplain have been sumr.:ar Si nee much of the energy of the wet ized further by Larson et al. (1981) and system is exported, the process needs to Wharton et al. (1981). be summarized in more detail. Detritus 95 PRIMARY \ ·. ~~ DETRITIVORES AND A FEW SCRAPERS, GRAZERS Figure 51. Largely terrestrial food chains involving detritus, granivory, frugivory, and herbivory. The detrital chains begin with the most abundant invertebrates, probably oribatid mites and three groups of collembolans, followed by earthworms, rove beetles, camel crickets, millipedes and crayfish. Their predators include mesostigmatid mites, wolf spiders, carabid beetles, salamanders, and various frogs and shrews. Top predators include the barred owl (which also takes crayfish), rat snake, and swallow-tailed kite. Other important food chains are based on grazing of the plant products. Acorns are eaten by bluejays, grackles, woodpeckers, ducks, wild turkey, raccoons, various mice, squirrels, deer, and bear. Other nuts (hickory, pecan, beech, etc.) also are important. Rodents and box turtles graze fungi. Beaver and swamp and marsh rabb1ts are direct grazers on herbs and barks. Berries (haw, holly, possumhaw, grapes, supp 1ejack, sugarberry and water, swamp and Ogeechee tupe 1os) feed wintering birds like robins, as we 11 as omnivores such as raccoons and bears. -~G'WiY COLLECTORS DETRITIVORES GRAZERS Figure 52. Large1y aquatic food chains based upon detritus processed by enormous numbers of detritivores: various annelids (Tubifex, Nais), collembo lans, crustaceans (isopod ~. amphipod Hyalella, copepods, crayfish); nematode worms and larval insects (midge and biting midge, mayfly). Coarse and fine particulate organic matter is filtered .from the water by a host of organisms, including cladocerans, larval insects (caddisfly, blackfly) and clams. Other animals, such as mosquito larvae, tadpoles and snails are scrapers and grazers. Aerial swarms of midge flies and mosquitoes are preyed upon by dragonflies, chimney swifts, bats, and tree frogs. Aquatic predators include water mites, diving beetles, larvae of stoneflies and dragonflies, some cranefly larvae and many fish, leeches, turtles and amphiumid salamanders. Top predators include softshell turtle, pickerel, water snake, alliga tor, otter and the wading birds {limpldn, egret, yellow-crowned night heron, white ibis). (leaves, twigs} is in the form of coarse caddisf1ies and other organisms are algal particulate organic matter (CPOM, particle grazers~ and blackfly larvae (Simuliuw) size >1 mm), fine particulate organic can even trap bacteria, it is theFPOM matter (FPO~i·, particle size BEETLE LARVA - ~ • •MmG OLIGOCHAETE Figure 53. Common invertebrates of southeastern rivers: (A) snag fauna of a Coastal Plain blackwater river, (B) blackwater river drift fauna, (C) Coastal Plain alluvial river drift fauna, (D) bottom sand fauna of a Coastal Plain blackwater river. Black water river data from Satilla River, GA (Benke et al. 1979); alluvial river data from Altamaha River, GA (Gardner et al. 1975). (Modified from Wharton et al. 1981.) 1975), especially where some follow nor~al Stomach analyses of various verte metabolic mineral pathways in organisms brates (Figure 49) have yielded data on (90Sr as Ca, 13 7 Cs as K). Radioactive ele food preferences. The use of the huge ments adsorb on algae and particulate acorn crop and other foods has been matter, but their assimilation by aquatic reviewed (Wharton et al. 1981). Tight fauna is strongly reduced (from 90% to coupling of dietary needs and floodplain 10%) by adsorption to inorganic clays hydrology is suggested by Fredrickson ingested with the food. (1979) and Drobney {1977). They found that a high protein intake essential to Unlike the bioaccumulation of pesti wood duck egg production is gained from cides, studies suggest that highest con aquatic and terrestrial macroinvertebrates centrations of radionucl ides typically at the edge of high water as it advances occur at lower trophic levels; algae may or recedes through Zones III, IV, and V. concentrate 137Cs 25,000 times while fish may do so only 1000 times {Nelson et al. Unsupported opinions about the value 1972). On the other hand, large hatches of an animal species in food webs can be of emerging insects such as chi ronomi ds highly misleading in floodplains. For carry only small quantities of radionu example, the largely cryptozoic and cl ides from the system {Nelson et al. fossorial salamanders appear to be an 1972) while deer, who graze herbs, shrubs, insignificant component of possible food and mushrooms, may acquire considerable webs, yet they are very efficient convert amounts of radionuclides. ers of energy into biomass and are prob- 99 ably the floodplain's most abundant verte floodplain zones, support the greatest brate in either numbers or biomass. In a faunal diversity (Wharton et al. 1981). northern hardwood forest just one species With Zone IV, Zone V provides larger of salamander (Plethodon cinereus) made amounts of forage foods than more inun five times more new tissue than the entire dated zones which 1ack either nut-bearing bird community, and the biomass of all hardwoods or a subcanopy and ground cover salamander species was larger than the bearing fruits, berries, and seeds. Zones biomass of breeding birds (Burton and II and III, important for detrital produc Likens 1975). Net annual production of tion and transport, are the primary sites new tissue by the salamander population of aquatic secondary production on the was about equal to that of mice and shrews floodplain. Coupling between zones not withstanding (see Chapter 6), it appears (Potter 1974). in summary that the faunal regimes of the floodplain can be divided into (1) a SUMMARY OF FAUNAL UTILIZATION detritus-dominated aquatic regime centered Faunal resources and diversity among in Zone .II (and to a lesser extent in the floodplain zones are summarized in Zones III-V) and (2) a grazing-foraging Table 17. The near upland areas of Zone food web in Zones IV and V that is more V, although the least extensive of the terrestrial than aquatic. 100 Table 17. Some environmental factors affecting the fauna of the bottom land hardwoods (and the ecosystem in general), and their relative importance in each bottomland hardwood zone. (Zone Ila is tupelo gum cypress; Zone Ilb is swamp black gum-cypress backswamp). Importance: O negligible or none, 1 low, 2 moderate, 3 high. (Wharton et al. 1981J Zone Factors Ila Ilb III IV V Retardation of "side flooding" from tributary streams (damming effect) 1 2 1 2 3 Organic matter production 1 2 2 3 2 Detritus source for feeding downstream life by annual inundation (includes coastal estuary) 3 3 3 2 1 Detritus source for feeding downstream life on 5-7 year pulse cycle (includes coastal estuary) 1 2 2 2 3 Diversity of oak species (acorns for food) (excluding Quercus palustris, bicolor, macrocarpa, imbricaria) 0 0 1 3 3 A mix of white oaks (bear each year) and red oaks (bear every second year) 0 0 2 2 Availability of non-coniferous nut- bearing trees other than oaks (hickories, pecan, beech) 0 0 1 2 3 Diversity of berries and soft fruits in high canopy (sugarberry, tupelo, black gum, 1 1 0 2 3 persimmon, etc.) Availability of berries and soft fruits in subcanopy and shrub zone (deciduous holly, haws (Crataegus), mulberry, paw paw, Elliott's blueberry, American holly, swamp palm, tall gallberry, etc.) 1 2 1 3 3 Availability of berries and soft fruits of vines (Jrapes, poison ivy, supplejack [Berchemia, etc.) 1 1 1 3 3 Availability of herbs as browse for birds and mammals (cane, greenbrier, jewelweed, sedges, etc.) 1 1 1 2 3 Availability of small terrestrial fauna (insects, snails, earthworms, etc.) 0 0 0 2 3 (continued) 101 Table 17. (Concluded). Zone Factors Ila IIb I II IV V Availability of aquatic macro- invertebrates 3 3 3 3 0 Availability of chimney-building floodplain crayfish 2 2 2 3 1 Forage for adult fish (when flooded) 3 3 3 3 2 Refuge for young fish (when flooded) 2 3 2 3 3 Diversity of forest strata (for bird guilds, etc.) 1 3 1 2 3 Availability of ground-level hiberna- tion sites (stump-holes, logs, leaf base of swamp palr.i, crayfish burrows) 0 0 0 3 3 Availability of aboreal hibernacula (tree cavity sites in old growth forest) 3 3 3 3 3 Presence of rare and endangered species (e.g., Swainson's and Bachman's warblers, ivorybilled and red-cockaded woodpecker) 0 0 0 2 2 Diversity of fish species 3 2 1 0 0 Diversity of ar.iphibians and reptiles 1 1 1 2 3 Dive rs i ty of sma 11 mamma 1s 0 1 1 2 3 Breeding bird diversity and density of individuals 1 1 2 3 3 Refuge for "terrestrial" fauna from high water 0 0 0 0 3 Refuge for fish during low water 3 3 2 a 0 Forage and cover for species on adjacent uplands (skink, toad, pine vole, mole, least shrew, fox, etc.) 0 0 1 2 3 Totals: 32 39 35 59 64 102 CHAPTER 6. COUPLING WITH OTHER SYSTEMS NATURAL COUPLINGS WITH HEADWATER TRIBU Apalachicola Bay is not the only TARIES AND ESTUARIES ex amp 1e of an estuary dependent on water pulses and intact forests. Day et al. Bottomland hardwoods are coupled to (1977) found that a Louisiana river swamp other upstream and downstream systems (Bayou des Allemands) fed pulses of car principally by river flows. Tributaries bon, nitrogen, and phosphorus to Barataria and terrestrial inputs via valley walls Bay (which produces 45% of the State's serve as linkages to upland ecosystems commercial fish catch) precisely when that flank the floodplains laterally, but migrant species were entering the estuary upstream-downstream linkages are function for feeding and spawning. Similar phenom ally more important. For example, Apala ena have been noted in Chesapeake Bay chicola River flows are coupled both to (Copeland 1966). In fact, estuaries in the the mountains of northern Georgi a and to Southeast generally are more productive in coastal estuaries by significant metero areas near the mouths of rivers (Copeland logical and biological phenomena. The 1966). Apalachicola River is a driving force and regulating mechanism mediating the chem The importance of freshwater delivery istry and biology of Apalachicola Bay. from the Piedmont and Coastal Plain via The salinity regime of the bay is largely floodplain rivers cannot be overestimated. a function of river flow fluctuations and Deliveries to estuaries include large patterns of local rainfall. River flow in amounts of organic matter and vitamins turn is controlled by plant cover and such as B12 from blackwater rivers (Burk floodplain and upland watershed drainage holder and Burkholder 1956). Both micro (Livingston et al. 1976). organisms and plankton are capable of rapidly and efficiently absorbing leached Livingston et al. (1975, 1976) showed DOC in coastal environments (Crow and that the cyclic productivity of Apalachi MacDonald 1978) and may be able to use cola Bay not only depends on annual pulses riverine DOC. Thomas (1966) speculated of organic detritus and silt from bottom- that the Altamaha flushed the rich phos 1and hardwoods, but a 1so on the large phates of the estuaries seaward as far as sca le import of detritus during a major 5- 24 km (15 mi). 11indom et al. (1975) to 7-year pulse originating in the moun showed that the nutrient load in riverine tains of north Georgia. These longer discharge in the South Atlantic Bight is pulses are linked with peaks in commercial equivalent to 100% of the annual inorganic fish catches (Livingston et al. 1976; phosphorus requirement and 20% of the Meeter et al. 1979) through the trophic nitrogen requirement of salt marshes in dynamics of the detrital food web. Second the region. Annua 1 freshwater discharge ary production may be keyed to these link onto shelf areas is equal to 39% of the ages to the point that each kind of tree total water volume out to the 20-rn con leaf may have its own special estuarine tour, perhaps contributing significant food web (Sheridan and Livingston 1979; amounts of trace minerals, silicates, White et al. 1979). An important point is organic nutrients, and humic acids (Haines that this 5- to 7-year pulse very strongly 1975). Under the influence of wind and involves the bottomland hardwood Zone V high water, the Suwannee River (FL) peri from which accumulated organic matter is odically turns the Continental Shelf exported. The importance of periodic waters black and pushes water hyacinth flooding thus extends we 11 beyond the 1- rafts as far as the Cedar Keys area, 11 to 2-year flood cycle. nautical miles from its mouth. 103 The deli very of up 1and sediments by upstream. Dredging the Savannah's channel the rivers is especially important to in the estuarine sector has allowed salt estuarine systems. Rivers directly or water intrusion much farther upstream indirectly provide sands for the construc (Joseph Birch, University of Georgia, tion of coastal features. The Piedmont is Institute of Ecology, Athens; personal one of the major sources of sediments that communication). Dredging in the Savannah are deposited in estuaries or picked up by severely reduced larval mayflies, stone l ongshore currents and carried southward. flies, true flies, and beetles, important The Santee River (SC) is (or was) the aquatic foods for fish (Patrick et al. possib1e source of hornblende-rich sands 1967). of Georgia's continental shelf (Carver 1971). During extreme floods, silts from In addition to couplings with head upstream may be deposited on downstream waters and lower estuaries, floodplains salt marshes. Lunz (1938) described the are coupled laterally with the uplands on effects of a Santee River flood which either side via tributaries as well as deposited a layer of silt 25 mm (1 inch) sheet flow and colluvial soil deposition thick in marshes in the Cape Romain area. directly from the adjoining bluffs. Intact tributaries are extremely important to periodic movements of fish and other fauna COUPLING WITH RIVER DELTAS (Hall 1971; Gasaway 1973). In North Caro lina, tributaries functioned as corridors How alluvial rivers are coupled to for mass movements of large fish moving their deltas was exemplified by the down upstream and large movements of smaller stream effect of the diversion of 88% of fish moving downstream, as well as for the Santee River's flow into the tidally significant moverr:ents of frogs, crayfish, dominated Cooper River to gain 1.5% of and turtles in both directions (Hall South Carolina's electric generating power 1971). These movements are season a 1, a (Kjerfve 1976). The Cooper River subse fact making it imperative not to judge the quently eroded so severely that the U.S. importance of tributaries from limited Army Corps of Engineers annually dredged temporal sampling of the fauna. 7600 x 103 m3 of sediments from the Charleston estuary. Saltwater intrusion drastically changed the vegetation in the CHEMICAL COUPLING WITH THE UPLANDS delta of the Santee fro111 fresh to brack ish. Santee rice plantation managers had Although tributaries and non-point to convert wetlands (former rice fields) source runoff add pesticides, nutrients, which were being managed as freshwater toxic metals, coliform bacteria, and other impoundments for waterfowl habitat to substances to river systems, water quality brackish water management units. A hard may improve significantly as water flows clam (Mercenaria mercenaria) industry through the floodplain. The floodplain evolved within the expanded estuarine with its vast bac kswamp functions as an zones of the mouth of the river. Upstream important filter and sink for agricultural the growth rate of water tupelo was appar excesses of nutrients and biocides. One ently reduced following diversion (R.A. of the first studies of filtering capacity Klawitter, retired forester, Northern (Kitchens et al. 1975) indicated that the Forest Fire Laboratory, Missoula, MT; per Santee River floodplain significantly sonal communication}. reduced bacterial counts and nutrient con centrations from the pol luted Wateree As a result of the nature of the tributary. Nutrient reduct ion, part i cu- integral coupling, any rr,anipulation in the 1arly phosphorus, was attributed to assim upstream reaches of a river can have pro ilation by aquatic vegetation, mat algae, nounced effects at all levels on the sys and trees as water passed through the tem below. Dredging and especially short swamp. Yarbro (1979) found agricultural ening the river by cutting across meander inputs dominated the phosphorus budget of loops have increased bank erosion by a small North Carolina blackwater creek increasing water velocity. Conversely, swamp, tota 11 i ng 300 mg P/m2 /yr as com downstream alterations may affect sys terns pared to 70 mg P/m2/yr from rainfall and 104 28 mg P/m2/yr from additional surface run lower than those in the lake into which off. The swamp effectively removed 30% to they eventually emptied (Brown et al. 57% of these additions. 1974). For further reviews of swamp filtering action, see Wharton {1970, 1977, The floodplain's capacity for improv 1980), Wharton and Brinson (1979a), and ing water quality operates on two scales. Kibby (1979). The first is the small, unleveed creek swamps along tributary branches of the The movement and immobilization of major rivers. For example, Lowrance (1981) pesticides and metals by humic substances found comparable swamps along the Little (humic and fulvic acids) is a particularly River of Georqia reduced nitrate, sulfate, important aspect of the swamp's filtering calcium, and - magnesium concentrations in process. Humic substances react with met passage to the river. Reductions were als by exchange, adsorption and chelation. dramatic: runoff from a hogpen within 50 m This is particularly important in black (164 ft) of the creek was not detectable water rivers (DOM> 10 mg/1) since signif downstream. Lowrance (1981) concluded that icant quantities are complexed (Reuter and conversion of even a sma 11 part of the Perdue 1977). Excess humic acids tend to floodplain riparian ecosystem to fields immobilize mercury (Miller et al. 1975) would increase stream loadings of most and other heavy metals (Giesy and Briese nutrients except phosphorus, with the 1978). The fate of these substances after largest effect on nitrate movements. Ni complexation is important. Humic acids, trogen and carbon compounds, taken up by being insoluble, tend to be immobilized as anaerobic bacteria, are converted to gas bottom sediments. Soluble lighter fulvic eous forms by processes such as denitrifi acids, constituting the bulk of DOC in cation and respiration during their pas southeastern rivers, sometimes complex sage through the riparian zone (Henderick with water contaminant metals; largely son 1981). On a second and larger scale, unavailable as microbial foods, they do a complex network of distributaries in not enter the downstream food chain some floodplains slowly partitions the ( Reuter and Perdue 1977). Some of these flow out over large areas of the flood flocculate with electrolytes at the inter plain, accomplishing nutrient reduction face of fresh- and saltwater. of the same magnitude as tributaries (Kitchens et al. 1975). Another important consideratfon is the residence time required for processes The magnitude of the problem of point involved in water quality improvements. source pollution is in many cases severe. Residence time is the time that water Industrial releases of lignins and wood remains over the floodplain floor and in sugars affect the col or and odor of the the sloughs and depressions. Examples of Altamaha River for at least 40 km (25 mi) processes are conversion of DOM to POM by downriver, contributing to the growth of microbes (Slater 1954; Brinson et al. the white filamentous bacterium Sphaero 1980) or by freezing (Giesy and Briese tilus, which clogs fishermen's nets in the 1978), the complexing of metals with ti da 1 zone. Concentrations of PCB' s ex organic matter, the adsorption of ions by ceeding FDA maximum levels (5 ppm) have clay particles, and the establishment of been found in many fish species in south reducing conditions essential to operate eastern rivers (Veith et al. 1979). the metabo 1i c pathways of su 1fate reduc tion, deni trification and methanogenesis. The fi 1teri ng capacity of the swamp Obviously, any human activities which could be useful in treating manmade efflu decrease residence time, such as channeli ents. Tributaries from the Savannah River zation, interfere with or eliminate these Plant (SC) have trapped and held radioac vital floodplain functions. tive l3 7Ce, preventing major contamination of commercial and sport fish species in the Savannah River (Wharton 1977). A MODIFICATIONS OF RIVER AND FLOODPLAIN cypress swamp above a peat substrate has effectively treated the sewage of Wild Construction or other modifications wood, FL, for 20 years. Bacterial levels on fl oodp 1a ins may cause profound changes measured in the effluent were actually in their ecology. Man's direct or indirect 105 moved back and forth seasonally in the manipulation of the hydrologic regime may estuary, and floods flushed out accumu result in a complete transformation of lated sediments with a periodicity of 3 to river and floodplain morphology (Schumm 5 years (Meade 1976). This flushing action 1969). C1ear1y, anything that man does to no longer occurs, and sediments accumulate the natural, orderly river channel will in the estuary and must be removed by induce changes as the river attempts to costly dredging. regain its original efficient configura tion. Sediment inputs resulting from Another ex amp 1e of direct downstream cl earcutting, or sediment starvation from effects is fl ow regulation by huge reser reservoir construction, dredging, shorten voirs on the Roanoke River (NC). The ing and even snagging and dragging are Roanoke River (NC) has a "dead zone" 6- among potential impacts. 12 m (20-40 ft) wide from near the levee top down to the river devoid of all bot The construction of reservoirs can tom land hardwoods except a few willows at have both direct and indirect effects, the the upper edge. This zone, with numerous result of coupltng the natural energy of fallen dead trees, resulted from water moving water with man's complex of activi levels held artificially high by upstream ties on the uplands. While the dissolved discharges, well into leafout time. In solute chemistry of the water is not mark swales along the Roanoke the lack of edly changed, the sediment load settles former flushing action may have caused and is reduced as a result of the stilling several feet of silt to accumulate (Pat effect of the reservoir. Release of water White, Williams Lumber Company, Mackeys, from the reservoir results in scour and NC; personal communication). resuspension of sediments that move stead i1y downstream as the upper segment of the Indirectly, flow regulation is having river lowers its bed (Schumm 1971). In an even more pronounced effect on bottom- the Red River below Denison Reservoir 1and hardwood communities. Damming may (OK), scour widened the channel from 1.5 severely modify or eliminate the seasonal to 3.0 m (5 to 10 ft) per year but the hydroperiod, allowing upland row-crop river did not regain its pre-reservoir agriculture and forestry on the flood sediment load for 322 km (200 mi) (Ein plain. On the Savannah River (GA) flood stein 1972). The large dams above Augusta, plain, below a series of large reservoirs GA, virtually have stopped sediment move in the Piedmont, hundreds of acres of Zone ment from the Piedmont (Meade 1976). Res IV bottom1and hardwoods are being sheared ervoirs on the Santee and Savannah trap off, and the floodplain is being planted from 85% to over 90% of incoming sediment. in soybeans. Even without flow regula Since as much sediment still is carried in tion, the floodplains of many southern the lower reaches as in pre-dam days, rivers are being cleared of bottomland Meade concluded that the immediate source hardwoods and prepared for conversion to must be the river bed, banks, and flood pine plantations, although, ironically, p1ain. Other factors may include extensive hardwoods often outgrow pines on these shortening and dredging of the Savannah by sites. Planted loblo11y stands on the the Corps of Engineers with corresponding Altamaha, Oconee, and Ocmulgee Rivers in gradient increase and much abnormal bank Georgia have developed a thick understory destruction. Meade stated that since 1910 of wax myrtle and sweetgum, typical Zone reservoirs on the Savannah River have re IV species, which may indicate the land is duced the sediment load delivered to the still most suitable to the natural commun ocean by 50%, thus depriving the Continen ity. Such systeffi-wide changes threaten or tal Shelf of its former river influx of eliminate the life support functions of inorganic nutrients. floodplain zones. Flood peaks higher than the 1- to 2- The most serious impacts of reser year inundations are also impaired by dam voirs on bottoml and hardwoods downstream ming. Much riverborne sediment deposits in arise from regulating the normal annual estuaries are in the "sediment-trap" at rise and fall of the river to which the the freshwater-saltwater interface. In who 1e sys tern is keyed. The effects of pre-dam days the locus of these deposits 106 reservoirs can be summarized: (1) reduc anadromous, catadromous and other marine tion of silt and associated nutrient species. Blue crabs occur to RM (river inputs for some distances be l 0\-1 dams, ( 2) mile) 50 in the Altamaha. The southern excessive bed and bank scour below dams flounder (Paralichthys lethostigma) and with accompanying modification or exter striped mullet (Mugil cephalus) migrate r.iination of benthic and epibenthic fauna, and feed as far as 193 km (120 mi) up the (3) loss of bank-stabilizing vegetation by Altamaha, while two common coastal fishes, frequent flow changes, (4) disruption of the hogchoker (Trinectes maculatus) and normal fish breeding and feeding on the the needlefish (Strongylura marina), actu floodplain, (5) elimination of sufficient ally spawn in the mid-reaches of the river high water for the annual flushing of (John Adams, Georgia Power Co., Environ detritus from the floodplain, and (6) mental Laboratory, Atlanta; personal com encouragement of clearcutting, site con munication). Various shad species parti version to tree plantations and row crop tion the river into spawning and nursery agriculture on formerly saturated flood sections (Adams and Street 1969; Adams plains. 1970). Awerican shad (Alosa sapidissima) spawn in the Altamaha itself between RM 60 and 120, with primary nursery centers at CHEMICAL COUPLING WITH THE WATER TABLE AND RM 21-30 and RM 100-110. Hickory shad (A. ATMOSPHERE mediocris) spawn in floodplain oxbows, sloughs, and tributaries between RM 20 and It is seldom acknowledged that Pied 137. Blueback herring (A. aestivalis) mont alluvial rivers crossing the Coastal spawn on the floodplain floor between RM 5 Plain may have numerous blackwater tribu and 137, with primary nurseries between RM taries, the DOM of which is subsequently 10 and 30. Examples of catadromous spe camouflaged by suspended inorganics. The cies are American eel and mountain mullet lower sections of alluvial rivers are, in (Agonostomus monticola), the latter in effect, chemically mixed rivers, in pro gulf coast rivers. portion to the respective discharges that each type stream contributes. Likewise, Striped bass formerly traveled up the there is lateral coupling with the under Savannah as far as Tallulah Gorge and ground aquifer in limesink zones. At times stil 1 ascend many Coastal Plain streams. of high water, acid blackwater r:1ay enter Two species of sturgeon (Atlantic and and corrode underground corridors; con shortnosed) ascend rivers entering the versely, aquifer flow at times raises the Atlantic slope. Other animals such as pH and the nitrate level of the river mana~ees use the Altamaha at least to the (Kaufman and Dysart 1978). 1i mit of tidal range and go up the Suwan nee to Manatee Springs. The glochidian Wetlands, includinq bottomland hard larvae of many cl ams can travel up- and woods, modify temperature and moisture downstream attached to fishes, often content of the lower atmosphere. They providing a mechanism for repopulating ameliorate freeze conditions and provide depleted areas. a more equitherma l refuge for many anima 1s which could not otherwise exist at that Terrestrial fauna may be coupled to latitude. Wetlands modify lake and sea the uplands, as when deer who base their breezes, the urban boundary layer, and home range on floodplains graze in up even the behavior of tropical cyclones. lands. Conversely, upland forms such as In Florida, relatively minor changes in the black racer and pine vole may use the land-water coverage and soil moisture floodplain at drydown. The narrow green result in surprisingly large changes in belts of bottomland hardwoods also provide sea breezes, cumulus cloud formations, and routes for migration and restocking. precipitation (Gannon et al. 1978). SUMMARY COUPLING VIA FAUNAL MOVEMENTS In summary, bottomland hardwood Rivers and their floodplains are swamps are i ntegra 11y coupled to the sur also coupled with marine systems through rounding uplands, downstream estuarine 107 of an apparent resilience to specific systems, and the atmosphere. By virtue of disturbance, the ecological values of the these couplings, the swamps provide inval bottomland hardwoods can be impaired by uable services and resources to the envi development or alterations which do not ronment. 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Developments in Agricultural and [Editor's note: published under same Managed-forest Ecology, vol. 11. title in 1978 by the Geologic and Elsevier Scientific Publishing Co., Water Resources Division and the New York. Resource Planning Section, Office of Planning and Research of the Georgia Whighom, D.F., and S.E. Bayley. 1978. Department of Natural Resources, Nutrient dynamics in fresh water Atlanta, Ga.] wetlands. Pages 468-478 in P.E. Greeson, J.R. Clark and J.E. Clark, Wharton, C.H. 1980. Values and functions eds. Wetlands functions and values: of bottoml and hardwoods. Pages 341- the state of our understanding. Am. 353 in Transactions 45th North Ameri Water Resour. Assoc., Minneapolis, can -W1ldlife and Natural Resources Minn. Conference. Wildlife Management Institute, Washington, D.C. White, D.C., R.J. Livingston, R.J. Bobbie, and J.S. Nickels. 1979. Effects of Wharton, C.H., and M.M. Brinson. 1979a. surface composition, water column Characteristics of southeastern river chemistry and time of exposure on the systems. Pages 32-40 j_I)_ R.R. Johnson composition of the microflora and and J.F. McCormick, tech. coords. associated macrofauna in Apalachicola Strategies for protection and manage Bay, Florida. Pages 83-116 .f.!!_ R.J. ment of floodplain wetlands and other Livingston, ed. Ecological processes riparian ecosystems. Publ. GTR-W0-12, in coastal and marine systems. Plenum U.S. For. Serv., Washington, D.C. Press, New York. 125 Whitehead, D.R., and E.S. Barghoorn. 1962. their formation. Pages 87-109 in Pollen analytical investigations of U.S. Geol. Surv. Prof. Pap. 282-C::- Pleistocene deposits from western North Carolina and South Carolina. Wolman, M.G., and J.P. Miller. 1960. Mag Ecol. Monogr. 32: 347-369. nitude and frequency of forces in geomorphic processes. J. Geol. 68(1): Whitlow, T.H., and R.W. Harris. 1979. 54-74. Flood tolerance in plants: a state of-the-art review. U.S. Army Engi Hoodall, W.R., J.G. Adams, and J. Heise. neers Waterways Experiment Stn. Tech. 1975. Invertebrates eaten by Altamaha rep. E-79-2. Vicksburg, Miss. 161 pp. River fish. Presentation; 39th Meet. Ga. Entomol. Soc., St. Simons Island, Whittaker, R.H., and P.L. Marks. 1975. March 19-21. Methods of assessing terrestrial pro ductivity. Pages 55-118 in H. Lieth Woodwell, G.M. 1958. Factors controlling and R.H. Whittaker, eds. Primary pro growth of pond pine seedlings in ductivity of the biosphere. Springer organic soils of the Carolinas. Ecol. Verlag, New York. Monogr. 38: 219-236. Windom, H.L., W.M. Dunstan, and W.S. Gard Yang, C.T., and C.C.S. Song. 1979. ner. 1975. River input of inorganic Dynamic adjustments of alluvial phosphorus and nitrogen to the south channels. Pages 55-67 in D.O. Rhodes eastern salt-marsh estuarine environ and G.P. Williams, eds:-- Adjustments ment. Pages 309-312 in_ F.G. Howell, of the fluvial system. Kendall-Hunt J.B. Gentry, and M.lf." Smith, eds. Publ. Co., Dubuque, Iowa. 372 pp. Mineral cycling in southeastern eco systems. U.S. Energy Res. and Devel. Yarbro, L.A. 1979. Phosphorus cycling in Adm., Tech. Inf. Center. Available the Creeping Swamp floodplain ecosys from: NTIS, Springfield, Va. tem and exports from the Creeping Swamp watershed. Ph.D. Dissertation. Winger, P.V. 1981. Physical and chemical Univ. of N.C. at Chapel Hill. 231 pp. characteristics of warmwater strea~s: a review. Pages 32-44 in Warmwater Young, S.A., W.P. Kovalek, and K.A. Del Streams Symposium. Am.-·-Fish. Soc. Signore. 1978. Distances travelled by autumn-shed leaves introduced into Winner, M.D., Jr., and C.E. Simmons. 1977. a woodland stream. Am. Midl. Nat. Hydrology of the Creeping Swamp 100(1): 217-222. watershed, North Carolina with refer ence to potential effects of stream Ziser, S.W. 1978. Seasonal variations in channelization. U.S. Geol. Surv. water chemistry and diversity of the Water Resour. Invest. 77-26. 54 pp. phytophilic macroinvertebrates of three swamp communities in southeast Wolman, M.G., and L. Leopold. 1957. River ern Louisiana. Southwest. Nat. 23 floodplains: some observations on ( 4) : 545-562. 126 APPENDIX SOILS OF SOUTHEASTERN FLOODPLAINS Tables A-1 through A-8 describe soil or ashed at 500°C for 4 hours prior to characteristics in sampled dominance types analysis. and river floodplain classes within the study area. Organic matter was determined by the Walkley-Black method. Depending on the Soil samples were co 11 ected non amounts of si 1t and clay present, organic randomly from a depth of 8 to 30 cm (3 to matter may be overestimated. The error of 12 inches) below surface litter zones, in overestimation due to water driven off the center of the most mature group of from clay and silt was computed on the trees. No samples were taken from a typi basis of 8% error with 5% clay-si'lt and ca 1 microtopographic relief features at 30% error with 85% clay-silt (Broadbent the site, nor were samples taken where 1953; Klawitter 1962); corrected percent there was evidence of logging, vehicle organic matter appears in parentheses in passage, scour channels, or upland erosion Tables A-1 through A-8. sources. Macronutrient concentrations were Mechanical analysis of percent clay, determined by plasma emission spec silt, and sand was by the Bouyoucos trometry, fol lowing extraction by the method. Samples with very high organic double-acid method. matter were subjected to hydrogen peroxide 127 Table A-1. Soil analysis for floodplain dominance types, Zone II, alluvial rivers. C=clay. SI=silt, S=sand, O.M.=organic matter. Soil com onents % Macronutrients m River floodplain description pH % O.M. C s s ca K Mg Na p Escambia: swamp tupelo-cypress 4.8 48a 1804 160 484 174 14.0 Roanoke: swamp tupelo swale 5.3 50(39.5)b 20 24 50 2728 49 268 47 9.2 Choctawha tchee: water tupelo-cypress 5.4 32a 1412 105 448 244 14.0 Escambia: swamp tupelo backswamp 4. 7 31a 299 94 119 66.. 11. 0 Tar: water tupelo-cypress 5.0 27a Roanoke: water tupelo swale 5.1 34a 1981 105 400 155 12.4 ..... Great Pee Dee: water tupelo-cypress 5.2 4.6 53 22 24 708 71 248 56 9.2 N co Apalachicola: mixed gum-cypress 5.5 6.0 38 40 22 1920 64 119 39 6.8 Santee: water tupelo-cypress slough 4.9 5.1 71 12 17 884 58 233 40 12.8 Apalachicola: water tupelo-cypress 5.0 5.3 48 27 25 Apalachicola: gum-cypress wet flat 5.4 5.9 61 23 16 1108 40 113 51 9.6 Escambia: water tupelo backswamp 5.3 4.2 28 27 35 Choctawhatchee: cypress wet flat 5.2 5.2 43 22 35 960 30 102 24 9.2 Ogeechee: mixed gum-cypress slough 7.3 3.9 49 17 34 1140 44 145 38 7.6 Ogeechee: mixed gum-cypress flats 5.6 5.2 39 19 42 831 52 115 31 6. 7 abData uncorrected. Values in parentheses are corrected for error of overestimation. See Appendix introduction. Table A-2. Soil analysis for floodplain dominance types, Zone II, blackwater rivers. C=clay, SI=silt, S=sand, O.M.=organic matter. Soil COmQonents r%) Macronutrients rQQm~ River floodplain description pH % O.M. C SI s Ca K Mg Na p Little Wambau: swamp tupelo on peat 4.7 51(43.9)b 11 9 80 682 59 108 62 10. 0 Litt 1e Pee Dee: swamp tupelo-cypress 5.3 29(26.l)b 3 7 90 Yell ow: swamp tupelo-water tupelo-bay 5.3 21(16.8l 17 37 46 684 60 150 44 9.6 Waccamaw: swamp tupelo swale (Terrace I) 5.0 11(8.l)b 17 28 59 456 26 35 32 14.0 I-' N \.0 Waccamaw: swamp tupelo-laurel oak 5.2 9(7.6)b 11 14 75 Waccamaw: swamp tupelo-cypress flat 4.9 5.9 13 24 63 Big Wambau: mixed tupelo gum-cypress slougha 6.2 6.0 42 21 37 Big Wambau: mixed Zone II-IVa 5.8 5.9 25 31 44 2404 40 187 38 8.4 Suwannee: swamp tupelo-cypress-pumpkin ash 6.2 27(21. 9)b 23 18 60 6648 86 454 91 42 Suwannee: mixed tupelo gum-cypress-pumkpin ash 6.5 36(27.8)b 27 27 46 5176 109 455 78 142 ~Old rice cultivation areas. Values in parentheses are corrected for error of overestimation. See Appendix introduction. Table A-3. Soil analysis for floodplain dominance types. Zone II, tide-influenced sections (tidal forests) of spring-fed blackwater and alluvial rivers. C=clay, SI=silt, S=sand, O.M.=organic matter. Soil components (%) Macronutrients (ppm) River floodplain description pH %O.M. C SI S Ca K Mg Na P Yellow: sweet bay-white cedar 5.2 53d 1404 144 588 196 14.4 Sopchoppy: sweetbay-swamp tupelo-wax myrtle 5.7 rf 1324 36 628 183 29.0 St. Marks: swamp tupelo-sweet bay-wax myrtle 6.2 54(45.4l 6 21 73 2462 97 556 145 41. 2 Aucilla: (Zones II-III-IV mix) 6.3 23(19.3)b 14 13 73 2852 35 400 80 12.0 Suwannee: swamp tupelo-cypress-pumpkin ash 6.0 49(39. 7)b 17 23 60 5784 323 870 1011 55 Suwannee: swamp tupelo-cypress-pumpkin ash 6.4 52(40.6l 20 30 50 5488 78 499 65 46 Apalachicola: mixed tupelo gum-cypress-Thalia 5.3 22(15.4)b 46 36 18 1676 92 180 53 8.0 Escambia: sweet bay-cypress-white cedar 5.4 19(15. l)b 28 17 55 776 116 456 224 15. 2 Choctawhatchee: swamp tupelo-bay 5.5 3"6a 1213 164 616 664 18. 0 ..... w 0 a bData uncorrected. Values in parentheses are corrected for error of overestimation. See Appendix introduction. Table A-4. Soil analysis for floodplain dominance types, Zone III, alluvial rivers. C=clay, SI=silt, S=sand, 0.M.=organic matter. Soil components (%) Macronutrients ~ River floodplain description pH % O.M. C SI S ra K Mg Na P Ochlockonee: overcup oak-water hickory 4.7 4.6 2 25 73 188 26 40 19 16.0 Santee: overcup oak-water hickory flat 5.2 3.1 70 13 17 568 28 205 30 8.0 Apalachicola: near levee 5.4 2.2 56 23 21 980 19 106 28 56 Apalachicola: behind levee 5.3 4.8 44 24 32 Apalachicola: overcup oak-water hickory 5.5 2.1 60 24 16 Ogeechee: overcup oak-ash-elm flat 6.0 3.3 31 21 43 708 37 82 34 5.3 Table A-5. Soil analysis for floodplain dominance types, Zone IV, alluvial rivers. C=clay, SI =s i lt, S=sand, O.M.=organic matter. Soil com~onents (%} Macronutrients r~~mJ River floodplain description pH % O.M. C SI s Ca K Mg Na p Santee: mixed Zone IV-V 5.2 3.8 47 20 33 472 37 168 33 8.0 Santee: old growth laurel oak 5.1 3.6 49 14 37 436 46 133 20 7.6 Apalachicola: l au re 1 oak 6.0 3.2 60 11 29 1196 26 128 28 6.4 Great Pee Dee: green ash stand 6. 7 2.6 38 31 31 794 34 220 38 12.7 Oconee: wi 11 ow oak flats 5.2 2.1 25 22 47 448 19 74 20 6.0 ...... Oconee: subsoil of wet flats 5.3 2.0 49 22 29 w..... Ogeechee: laurel oak 8.2 2.3 24 14 62 1408 15 9 32 2.8 Ogeechee: laurel oak-swamp palm 6.7 2.5 22 11 67 460 32 36 29 3.6 Ogeechee: laurel oak near river 5.4 4.9 44 21 35 932 39 156 42 5.9 Ogeechee: sandy surface soil 5.9 1. 3 14 6 80 220 18 34 23 3.4 Ogeechee: c 1ay subsoil 8.3 0.8 33 10 57 778 14 91 64 2.9 Ogeechee: laurel oak away from river 7.4 2.7 33 25 42 484 28 68 33 3.8 Apalachicola: scour channels 5.7 0.9 12 10 78 378 15 37 17 4.0 Table A-6. Soil analysis for floodplain dominance types, Zone IV, blackwater rivers. C=clay. SI=si1t, S=sand. O.M.=organic matter. Soil corneonents {%} Macronutrients {[![!ffi} River floodplain description pH % O.M. C SI S Ca K Mg Na p Waccamaw: laurel oak-willow oak swale 4.3 18(14.6)a 15 23 62 84 27 32 34 8.4 Black: laurel oak-wi 1low oak 4.7 11( 9.4)a 9 12 79 102 30 16 39 11. 0 Indian Field: laurel oak flat 5.1 11( 9. l)a 15 17 68 1144 40 66 33 13.0 Little Pee Dee: laurel oak-red maple 5.4 10( 8,5)a 12 12 76 Little Pee Dee: laurel oak 5.7 5.7 13 12 75 160 24 35 31 10. 0 Canoochee: laurel oak-spruce pine 5.5 5.5 11 14 75 88 34 47 23 11. 6 Turkey Creek: old growth laurel oak 5.2 2.4 10 9 82 496 19 22 23 5.2 ..... w N aValues in parentheses are corrected for error of overestimation. See Appendix introduction. Table A-7. Soil analysis for floodplain dominance types, spring-fed rivers (Zones II and IV). C=clay, SI=silt, S=sand, O.M.=organic matter. Soil comeonents (%2 Macronutrients r1212m2 River floodplain description pH % O.M. C SI S Ca K Mg Na p Wacissa braids: pumpkin ash-red maple 6.3 52(40. l)a 19 34 48 l>/aci ssa: 1au rel oak-sweet bay-cabbage palm 6.5 17(15.3)a 5 5 90 3056 18 234 26 9.2 f'iacissa: subsoil at site above 6.6 1.1 18 18 65 Chipo1a: 1aure1 oak-American holly-sabal pa 1m 5.8 1. 8 8 5 87 320 13 25 20 6.4 aValues in parentheses are corrected for error of overestimation. See Appendix introduction. Table A-8. Soil analysis for floodplain dominance types, Zone V, alluvial rivers. C=c lay, SI=s ilt, S=sand, O.M.=organic matter. Soil com~onents (%) Macronutrients (1212m} River floodplain description pH % 0.M. C I S Ca K Mg Na p Och1ockonee: water oak-spruce pine 6.4 6.6 8 12 80 Apalachicola: water oak-swamp chestnut ...... w oak-spruce pine 5.5 3.6 24 22 54 540 30 46 24 5.6 w Yellow: swamp chestnut oak-spruce pine 5. 1 1.4 9 13 78 136 13 16 17 4.0 Ogeechee: cherrybark oak-hickory 7.1 2.7 25 16 57 226 27 56 25 4.0 Ogeechee: cherrybark oak 6.7 0.8 25 21 54 146 12 22 21 2.8 50272 ·101 REPORT DOCUMENTATION l·l,_REPORT NO. 3. Recipient's Accession No. PAGE FWS/OBS-81/37 4. Title and Subtitle 5. Report Date The Ecology of Bottomland Hardwood Swamps of the Southeast: March 1982 A Corrmunity Profile 6. 7.Author(s) Charles H. Wharton (U. of Georgia), Wi1ey M. Kitch~- ·a:·PerformingOrganizationRept.No. (USFWS}, Edward C. Pendleton (USFWS), Timothy ~--=e.....:('-'-'W-=ab::...::a::..::-s..:..:.h.....:C:....::o.....:l.~e::...,,gL;Ce_,___)~--~-~~------t 9. Performing Organization Name and Address 10. Project/Task/Work Unit No. Institute of Ecology University of Georgia 11. Contract(C) or Grant(G) No. Athens, Georgia 30602 (C) (G) 12. Sponsoring Organization Name and Address 13. Type of Report & Period Covered U.S. Fish and Wildlife Service Biological Services Program -----~,------i Department of the Interior 14. Washington, DC 20240 ------'"------·-·---··------; 15, Supplementary Notes 1------·---- -· ····------! - 16. Abstract (Limit: 200 words) This report synthesizes extant literature detailing the ecology of bottomland hardwood swamps in the Southeast. The geographic scope focuses the report to the hardwoods occupying the floodplains of the rivers whose drainages originate in the Appalachian Mountains/Piedmont and Coastal Plain (NC, SC, GA, and FL). The origin and dynamics of the floodplains are described and related to hydrology and physiographic.provinces. Further, the biogeochemistry and interactions between the riverine and floodplain environments are discussed in conjunction with floodplain biology. Plant and animal community structure and ecological processes (productivity) are detailed and organized by ecological zones. The final chapter discusses the ecological value of.the floodplain ecosystems and the nature of their relationships to adjacent uplands, downstream coastal estuaries _and the atmosphere. !------··------··------l 17. Document Analysis a. Descriptors swamps, floodplains, soils, vegetation, water quality b. ldentifierS/()pen-Ended Te,ms bottomland hardwoods, alluvial rivers, blackwater rivers\ coastal plain streams, fauna, ecological zones, couplings, anaerobic gradient, nutrient cycles, flood stress e. COSATI field/Group 19. Security Class (This Report) 21. No. of Pages 18. Availability Statement I Unclassified i 133 + xii Unlimited 1------j~---._.__._,.~- -- 20. Security Class (This Pagel ; 22. Price Unclassified 1 See Jnstructrons on Reverse OPTIONAL FORM 272 (4-77) (See ANSI-Z39.18) (Fo,merly NTIS-35) Oepartment of Commerce <; U.S. GOVERNMENT PRINTING OFFICE: 1982..... 570-800