Chamtel Migration and Vege, ation Patterns in the

Chamtel Migration and Vege,ation Patterns in the Southeastern Coastal Plain DAVID S H A N K M A N Depmment o~ Geogrg,hy University of Alabama Tuscaloosa, AL 35487, U~A. •~ w n c ~ Oamnamigrattonisanm~demmOmmoft~etation ~ in the lower bottomhands o f the southeastern coastal p l a i n o f the United S t a t ~ Lateral ~ m n e l move. merit creates n e w surfa~s by point.bar deposition and the f i l l i n g in o f abandoned channel~ The n e w s u r f a ~ s are rap~ ! y colon~u~ by f l o o ~ . t o ~ m , g opportunis~c s p e c ~ sediment deposi~d during subsequent years" flooding raises y o u n g s u r f a c ~ m a k i n g ~hem less susceptible to inundation a n d m o r e s u i t a b l e f o r the establishment o f less flood-

The continuod premnos o f the y o u n g f o m s t c o m m u n i t ~ s de. ponds p r ~ a ~ v on ~ f o m m U o n o f row s u r f a ~ by c~mnel migration a n d the development o f s h a l l o w swamp~ Shallow swamps are f o r m e d w h e n channel obstructions force water into the adjacent b o t t o m h a n ~ d a ~ forest stands and allowing the ~stablislm~ni o f earty specter Many o f the s t r m m s in tbe ~ W r n coastal p l a i n have been ch~mnelixe~ Stabilized chann~is l i m i t the development o f s h a l ~ swamps and p ~ l u d e ~ f ~ o f p o i n t bars and oxbow ~ Tberefo~ the hargest.scale natural disturbance mechanttm and the most important factor controlling spatial h e ~ t y in the louwr bottomland sit~s has been eliminate~ Channelizatton will likely result in a shift towards a homogeneous floodplain forest c o m p o s ~ o f later suc,cessional mesic ~ that occupied the outer floodplain before channelizatton

latrodaetioa The southeastern U.S. coastal plain is an area of low relief occupied by meandering streams that have crePaper submittod August L 1991; revised manuscript ac~pted April 7, 1992.

176 CzmervmtonBiology Vohtme 7, No. 1, March 1993

Misraci6n de canales y pan'ones de vel~-taci6n en el sudeste de la planicie coetera R e m m u m : La m i s m c t ( m de canales es el prlnctpal determi. nante de los p a m m e s de mgetact6n on has tterras bajas de has phanicies del sudeste costero de Estados Unido~ Los moo. imientos de c4anales iateralos crean hum)as superficies a travds de ha acumuhaci6n de tk~ositos en ha barrem y dei rellono de c a n a l a a h a n d o n a d ~ Las n u e m s ~ son r~t~msonte co~,U~Zas pot ~ o~t~ tole. r a m ~ a i n u n d a c i o n ~ La ~ de sedimentos duranfe i f a o t d a c i o ~ on atk~s ~ elcva has ~ ' . cies j6venes y has hace menos susceptibles a inundaciones y nu~s a p r o ~ _ ~ p a n , el establecimiento de especieS monos tolountes a inundacton~ has ctmles mmUualmente r ~ m . plazan a has que se atablocloron t e m p r m m m e n ~ La pres~g~a continua de J 6 m m s c o m u n ~ u l o s de ~ d~tnmle ~ m r a m o U ~ de ha f o n n a c ~ de n u ~ a s ~ o~gt. _r~_d~s a t r a ~ de ha migracton de c a n a r y del d~arrollo de pantanos ~ j o s Los pantanos bajos ~ f o r m a n cuamio has obsmaztonesonloscana~fuerzanalnguahactalastte. . ~ haja~ ~ O u y ~ d o r o d a ~ de ~ y pe.~rlondo el estableclmlonto de especles~ temprana~ Muchos de los cursos de agua en el s u d m ~ de las phanicie costera han sido canalizado~ Los CAanales ostabiliw~tdos limitan el d ~ a . r r o l i o de los pantanos bajos e impostbilitan ia formaci6n de "point-bars" y la&os curoados de meandros~ Por consi. guientg el raecanismo de ~ natural de mayor escaha y el factor rods tmportante on controhar la hoterogene~ espacial on has ~ bajas ha sido eliminada La canalizact6n resuitard postblontmte on un cambto hacta una phanic~ ~ j a de inundact6n h o m o ~ u w compucsta por t ~ q u ~ de ~ c ~ s m i s ~ a s tard~a~ quo ocupamn has pha. nicies de inundact6n exteriora antes de ha canalizact6n

ated broad alluvial valleys (Fig 1). Vegetation patterns within the alluvial wetlands are highly complex, and it is generally recognized that these patterns are attributable tO differellces ill the flooding regime arid i m n o u n d m e n t of surface water ( B e d ~ e r 1971; Teskey & ~ n c k l e y 19"]7; Robertson et aL 19"]8; McKnight et al. 1981). plain streams flood most years in the winter and

aem~ M / ~ n and Vegee~on

Figure l. Map showing the boundary o f the southeastern U.£ coastal plain and alluvial wetland~ Adopted from Putnam et al (1960). spring. Portions of the floodplain may be submerged for periods ranging from a few days to several weeks, and there is often more than one period o f submergence. Flood frequency and duration are greatest in the lowest bottomland sites adjacent to the channel With increasing distance from the lower floodplain, there is a decrease in flood frequency and a corresponding spatial gradient of plant communities composed of species with progressively lower flood tolerance. Flood frequency and related physical site factors, including soil characteristics, organic matter accumulation, and depth of surface water and the water table, are the basis for most O~ifications of floodplain plant communities (Penfound 1952; H ~ & Forsythe 1981; Wharton et al. 1982). These classifications may identify communities on a broad scale, but vegetation patterns in alluvial floodplains are not entirely dependent on bydrologic gradients. Finer-scale vegetation patterns are attributable to the lateral movement of meandering streams. In the lower bottomlands of the southeastern coastal plain, which include areas within and immediately adjacent to the meander belts, there is a direct relationship between surface age, determined by when a site was last occupied by the active channel, and successional stages of vegetation development (Shelford 1954; Putnam et al. 1960; Klimas 1988; Shankman & Drake 1990). Headwaters of the major coastal plain stream¢ are located in the surrounding physiographic provinces, which are g e n e t ~ y areas of high local relief. Stream gradient and velocity decrease as rivers flow into the relatively fiat coastal plain, where they develop sinuous patterns and broad floodpla/ns. Sediment deposition on the inside of channel bends creates new surfaces, or

177

point bars. Lengthy periods of deposition result in progressively older surfaces with increasing distance from the active channel. Concurrently, the outer concave banks of meanders are eroded. The curvature of the channel bend may increase, eventually coalescing to form a cutoff. 1"he active channel then changes course, leaving an oxbow lake (Leopold & Wolman 1957, 1960). Channel migration has resulted in complex patterns of new surfaces created by point-bar deposition and the filling in of oxbow lakes (Fig,. 2 ). This process results in a mosaic of distinct forest communities whose composition depends largely on surface age and elevatiotL The new surfaces are rapidly colonized by species of high flood tolerance that require flooding for seed dispersal and exposed sites and high light levels for succ~__e~ul_ establishment. Sediment deposited during flooding raises young surfaces, making them less susceptible to later inundation and more suitable for the establishment of less flood-tolerant species that even,,,lly replace the early arrivals. Generally, the early successional species are replaced by the longer-lived, shade-tolerant species that dominate most surfaces within the floodplairL Therefore, the early coloniTJng species are uncommon on older surfaces. Similar relationships between surface age and plant community composition have been noted in the central and western United States (Noble 1979; Everitt 1968; Fonda 1974), Alaska (Bliss & CartOon 1957; Viereck 1970), British Columbia (Hickin & Nanson 1975; Nanson & Beach 1977), Scandinavia (Polunin 1936; Kalliola & Puhakka (1988), and the Amazon River basin (Salo et al. 1986), among other regions. Alluvial valleys occupy a large percentage of the total land surface of the southeastern coastal plain. An under-

Figure 2. Map o f a section o f the lower Mississippi River alluvial valley shoring abandoned charmei~ Adopted from goZb et at (1968).

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Charnel~

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standing of the relationship between channel migration and the presence and successional status of species and plant c o m m u o J t i e s iS ~ t i a l for proper management of bottomland forests in this regiom The purpose of this paper is to describe the linkage between channel migration and vegetation patterns within the southeastern coastal plain and to discuss some implications for the management of bottomland forests and the conservation of plant diversity.

Early Forest Devdotnnent Polar b r s The creation of point bars by lateral accretion is the dominant process for the development of new floodplain surfaces. The slower water velocity on the inside of channel bends allows sediment deposition. Vertical accretion will raise surfaces that are eventually exposed during low water levels. The progressive lateral development of point bars and simultaneous erosion of the outer banks will cause streams to shift their position across the valley bottoms while maintaining a nearly COt~gant eh=nncJ w i d t h (Wolman & Leopold 1957). Young point bar surfaces typically are dominated by black willow ( Salix nigra ), cottonwood (Populus del¢oides ), and silver maple (Acer saccharinum ) (Shelford 1954; Hosner & Mincider 1963; Klimas 1988). The eariiest colonizers produce many seeds that are disseminated by wind and water, and they are usually the first terrestrial species to ~ . ~ e established on new surfaces exposed by receding water during the late spring

and stlmqler. The alluvial streams of the coastal plain flood most years, submerstn8 new point-bar surfaces and young seedlings that established there. Seedlinss of the early colopizit~ SpeCies carl tolerate lol~ periods of partial inundation (Hosner 1958). However, black willow is the only one of the early colonizers that can survive long periods of complete submersion, and therefore it is the dominant species on the most frequently flooded surfaces (Hoaner 1958; Homer & Minckler 1963). Dominance on youn8 point bars is also strongly related to differentialratesof growth and mortality. Black willow seedlinss grow faster than those of cottonwood or silver maple. Therefore, they are less likely to be completely submerged during the following years' flooding and quickly grow taller than cottonwood or shyer maple seedlings that became established concurrently. Black willow is short-lived, however, and stands begin to decline within 20-30 years of initial colonization (Shelford 1954; Hosner & Minclder 1963). Cottonwood and silver maple will dominate on surfaces that are a few decades older and farther from the channel, because they grow to a greater height and live longer than black willow (Fig. 3). The early colonizers form dense, even-aged stands. Silver maple is moderately shade tolerant and will successfuliy establish beneath a broken forest canopy. Conversely, black willow and cottonwood are shade intolerant, and their reproductive success is limited primarily to newly created, bare surfaces. Dominance of early point-bar colonizers decreases with distance from the channel and, except for silver maple, few are present

green ash - sugod0erry - wote¢ hickory - woter locust

silver mopie - cottonwooa |

I

b l o c k w~low - # N e t m o ~ e i

I 0

i

I 40

I 80

I 120

I 160

S u r f a c e A g e (Years)

Figure .~ Profile o f a point.bar forest stand showing sequential tree dominance on progressively older surfaces next to the Hatchie River in western Tennessee

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Skm/m~

Chanae/~

on surfaces more than 100 years old. They are eventually replaced by slower-growing shade-toleram spedes that may have become established with thi: black willow, cottonwood, and silver maple seedlings but that were slower growing and initially suppressed in the understory (Hosner & Minckler 1963). The rate of channel misration can be highly variable from one river or river segment to the next. Streams with fine cohesive alluvium migrate more slowly than those with unconsolidated, coarse sediments. Also, along gende bends, bank erosion and sedimentation are slow. As the curvature of the bends increases, the current is forced toward the outside of the bend, increasing erosion there and accelerating point-bar development on the opposite bank (Hickin 1974). Distinct seral stages ate observable where there is rapid point-bar deposition (Fig. 3). Conversely, where channel migration is slow, late successional plant commoJlities, which ind u d e few of the earliest colonizers, will be very near the channel Forest community composition on a point bar is u.~mny a better indication of surface age than distance from the channeL ~domxl

Cl~m~Js

Abandoned meanders, or oxbow lakes, created by channel cutoffs, are common features in alluvial valleys of the coastal plain. Young oxbows typically hold water during most of the year, limiting colo~iTation to floodtolerant species, primarily black willow, water tupelo ( N y s ~ aquat/ca), and bald cypress (Taxodium distt. ~ m ) . The ~ colonizers initially establish at the lake margins, where seasonal water-level fluctuations expose surfaces necessary for gem~mtion. Establishment of terrestrial vegetation at the center of the abandoned chartnet occurs only afterdeposition of sediment and organic debris creates new surfaces that are exposed during low water levels (Shanknmn & Drake 199o). Oxbow lakes along the largest streams in the coastal plain, such as the Mississippi River, can continuously hold water for centuries. Along smaller streams, and particularly those with a high sediment load, the o x b o w lakes fillin within a few decades. Most oxbow lakes have little flow for most of the year. However, flood scour of some former channel beds slows sediment accumula~orL Black willow is fast growing and typically dominates the youngest surfaces of abandoned channels (McJ.e(xl & McPherson 1973). Because it is short-lived, however, it is replaced by water tupelo and/or bald cypress within a few decades (Fig. 4). Like the other early colonizers, water tupelo and haiti cypress seeds arc spread by floodwater. Survival of seedlings depends on growth to suftident height so that in later years they will not be completely submerged for long periods of time (Demaree 1932). Shelford (1954) suggested that this only occurs if successive drought years followed establishment;

aM Vege~/on

179

(a) C

C

Co) C

C

Figure 4. Profiles of abandoned channel forest stands in western Tennessee showing (a) an oxbow lake with bald cypress occurring only at the channel banks, and (b) a meander scar with large bald cypress near the former channel banks with smaller individuals in She interim. Species are:. c, bald cypress; m, sugar maple; S, sugafOetyy; p, swamp priveg w, black willow;, e, water elnt Source Shankman (1991). thus, tupelo-cypress regeneration may be highly episodic. Bald cypress and water tupelo are at least moderately shade-intolerant, and their regeneration is discontinuous after the development of a forest canopy. Bald cypress longevity exceeds that of the other bottomland spedes within its range (Stahie et aL 1985, 1988), and it will likely dominate the abandoned channels for several centuries. Within 500 years of initial colonization, however, bald cypress stands rapidly decline; they are only occasionally found on older surfaces (Shankman & Drake 1990). Channel Olmmu~ons and Shallow Swamps Along meandering streams, large trees regularly fall into the channel because of bank failure or blowdown. Often small channels become dogged with downed trees, which increases sediment dqx~ition because of slower water velocity (Keller & Swanson 1979; Phillips & Holder 1991). Sediment accumulation behind logjams reduces the channel cross-sectional area and can force water to flow across the adjacent floodplain and sometimes through former channels. Beaver dams, which are common throughout much of the coastal plain, have a similar effect (Naiman et al. 1986; Butler 1991). Because the bottomhnds are areas of low relief, a small

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increase in the water level can submerge large areas that may have previously flooded for only short periods each year. Most bottomland tree species are unable to survive more than one or two years of continuous inundation (Broadfoot & Williston 1973). Therefore, almost all trees are killed after the development of a shallow swamp caused by channel obstaxtctio~ Bald cypress is the only terrestrial species that can occasionally regenerate on permanently flooded sites. It establishes on downed logs and on floating vegetation mats that are composed of fine sediment and partially decayed organic matter interwoven with the dense root systems of aquatic plants (Hunt 1943; Dennis & Batson 1974; Huffman & Lonard 1983). Most inundated sites eventually are exposed, however, because of blockage breakup, beaver dam failure, or prolonged drought (Wells 1942). The occasional drying of these sites allows the establishment of terrestrial species, mostly bald cypress and---to a lesser extent---water tupelo, which occur in even-aged stands. Few bottomland tree species succeSsf~dlly establLcJ1 i n t h e cypress-tupelo understoty if frequent or long-term flooding continues.

•

vegetationDynamics Most of the areas within the lower bottomlands are periodically occupied by the active channel. The lower floodplain surfaces are formed, eroded, and reformed, resulting in complex patterns of old point bars and meander scars. These surfaces support plant communities at early stages of successional development. Slowgrowing, shade-tolerant species establL~h beneath the early colonizers. The reproductive success of laterarriving species depends on a high tolerance to flooding and on sediment deposition, which buries the base of the tree (Sigafoos 1964; Hupp & Morris 1990). Among the most common of these on sites that may be submerged for long periods are water hickory (Carya aquat/ca), overcup oak ( Q u o ~ lyrata), sugarberry (Celtis laevigata), and water locust (Gledttsia aquat/ca). Drier sites that flood annually but that rapidly dry after the water recedes support a larger number of species, including silver maple, sweetgum (L/qu/dambar styraciflua), green ash (Fraxinus pennsylvanica ), and hackbegry (Celtis occidentalis) (Fig. 5). Because of their potential size and longevity, they will eventually replace the earlier colonizers. Coastal plain streams generaliy ¢:arry large amounts of suspended sediment. Successive floods deposit sediment~ creating new higher surfaces that eventually obliterate meander features, such as natural levees and former channel bank.¢ occurring alOng recently abandoned channels, or ridge and swale topography on modern point bars. Sedimentation rates are highly variable, depending on stream discharge, watershed and channel

Btotogy Volume 7, No. 1, March 1993

cr~mrm~

Point Bars

2. i~,~t~em Illinois

Figure 5. Transition of Wee-speciesdominance on young surfaces created by the filling of abandoned channas and point.bar deposition $ourc~ (1) $hanknum 1991; (2) Hosner ~, Minchler 1963; (3) Shelford 1954; (4) Klimas 1988 disturbances such as deforestation and channeli~tion, composition of eroded material, and flooding frequency. Sedimentation rates on frequently flooded sites along streams with high sediment loads can exceed one cm per year. Along channelized streams, vertical accretion has exceeded 5 cm per year (Hupp 1987). The higher surfaces have lower flood frequencies, which allow the establishment of species that only occasionally occur on younc~r, wetter surfaces. These in-

dude American beech (Fagus grandifolia ), American elm ( Ulmus americana), cherrybark oak (~uercus fal. cata

vat'.

p a ~ g o d a e f o l / a ) , s w a m p chu~-~tlut o a k ( ~ u o r c l ~ ¢

michauxii), water oak ( Q ~ nigra), and willow oak (Quercus phellos), among many others (Teskey & Hinckley 1977; McKnight et aL 1981). These older surfaces encompass the largest area of many active floodplains, extending f r o m near the meander belt to the outer floodplain margins. Beyond the lower bottomland sites, the distribution of plant communities conforms fairly well to the classification schemes developed for the active floodplains in the southeastern United States ( HuJEman & Forsythe 1981; Wharton et aL 1982). The active floodplains of many alluvial streams in the southeastern coastal plain are b o u n d e d by latePleistocene terraces (Duty 1977; Alford & Holmes 1985; Saucier 1987). These surfaces are renmants of

andent floodplains formed during interglacialperioda, when average discharge, channel width, and meander wavelength were much greater than at present. Pleistocene river terraces encompass large parts of alluvial river valleys. They rarely flood, however, and they support many upland species that are uncommon in modern floodplains. Large portions of the active floodplain

~mne/M/trY/on and V ~ n have been undisturbed by lateral channel movement throughout the Holocene. But all surfaces within the alluvial floodplain, includin~ Pleistocene terraces, are susceptible to channel erosion~

Omanelization and Decline of Plant Diversity Biotic patterns across many landscapes are largely a consequence of natural disturbance (White 1979; Pickett 1980). Major disturbance (including fire, windstorms, av=,l.-tnches, insect infestation, channel migration) often destroys stands covering areas ranging from less than a hectare to hundreds of square kilometers. Plant communities at different stages of recovery from disturbance create discrete vegetation patches and large-scale spatial heterogeneity (see, among others, Marks 1974; Sprugel 1976; Bormann & Likens 1979; Romme 1982; Veblen 1985). Early successional specie: *-bose that rapidly colonize new surfaces or sites on which the previous stand has been destroyed---are eventually replaced. Therefore, periodic disturbance is necessary for the regeneration of opportunistic species and the continuation of landscape diversity in many habitats. Channd migration is a major determinant of landscape and biotic diversity in the lower alluvial-habitats of the southeastern coastal plain. The early colonizing species have the reproductive and ecological characteristics necessary for succes_~ful establi~ment on new alluvial surfaces: regular seed production, wind- or waterdispersed seeds, fast growth rates, and high flood tolerance (White 1979). Environmental conditions no longer favor the establishment of these species, as overbank deposition raises surfaces and reduces foodinp. and after a continuous forest canopy develops. Therefore, the initiation and continual presence of the young forest commnnities depend largdy on the development of new surfaces and on floodin& which disperses seecL Under natural hydro-geomorphic conditions~ the rate of channel migration and creation of new surfaces by point-bar deposition and the filling-in of oxbow lakes maintain early colonizing species in the lower floodplain However, these communities are threatened in some areas by river channelization, a common flood control measure in the southeastern coastal plain. Chamlelizafion ustl~lly includes wideninE and deepening the channel and shortening its length by artificially cutting off meanders. Channelized streams must be dredged periodically to maintain a straightened alignment (Brookes 1988). Cleared and stabilized channels will limit the development of shallow swamps in the adjacent bottomlands and preclude the formation of point bars and oxbows, the primary regeneration sites for many species. Therefore, the largest-scale natural disturbance mechanisms and the most important factors controlling spatial heterogeneity in the lower bottom-

181

land sites have been eliminatecL In the absence of channel migration, the point-bar communities of black willow, cottonwood, and silver maple would largely d i ~ p ~ t r in less than 100 years. Meander scar stands dominated by bald cypress would begin to decline within 400-500 years. Both communities would eventually be replaced by forest vegetation now occurring on older, higher floodplain surfaces. Early successional species will occasionally become establi~ed on other sites, such as along small tributaries and the banks of channelized streams; they have the potential to colonize other disturbed areas, including those deared of forest vegetation such as abandoned agricultural fields. The earliest colonizers are dispersed predominantly by water and therefore are limited to the portion of the alluvial valley subject to flooding Channelization is not successful at significantly reducing flooding in all cases (Hill 1976; Brookes 1988; Shankman & Samson 1991). However, along stream segments where a reduction in flood frequency and depth occurs, the potential distribution of early successional species is restricted to a narrower portion of the floodplain. Further, drier bottomland sites may be invaded by floodintolerant species that previously could not regenerate in the alluvial wetlands. Therefore, chal~qeliT-~_tionwill likely result in a shift toward a homogeneous floodplain forest composed of later successional mcsic species that occupied the outer floodplain before channelization A detailed understanding of terrestrial vegetation patterns in the alluvial wetlands of the southeastern coastal plain depends on recoEn~i~iug the relationship between physical processes, both hydrologic and geomorphic, and life history characteristics of floodplain species. Channelization causes dramatic alteration in floodplain hydro-geomorphic processes. The effects of channelizalion on terrestrial vegetation have been frequently addressecL However, most predictions of the impact of ch_2nnelization on vegetation have focused on the direct effects of channd excavation, changes in hydrology, and land-use changes that occur afterwards. Little attention has been given to the effects of channeliT~tion on bottomland plant commuRitics by precluding the creation of new surfaces. Management of alluvial wetlands for the conservation of terrestrial vegetation diversity must ind u d e unobstructed channel migration and the setting aside of large enough areas of the lower bottoml~rlds tO include surfaces with vegetation at all stages of development. Otherwise, species occurring only in early succession or within a narrow range of surface ages will greatly diminish in importance. Caed Alford,J. J., and J. C. Holmes, 1985. Meander scars as evidence of major climatic ch~nSe in southwest Louisiam.Annals of the Association of American Geographers 75:395-403.

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Ve~t~o~

Bedinger, M. S. 1971. Forest species and indicators of floodin8 in the lower White River Valley, Arkansas. US. Geological Survey Professional Paper 750-C, Washington, D.C. Bliss, L C., and J.E. Cantlov_ 1957. Succession on river alluvium in northern Alaska. American Midland Naturalist 58:452469. Bormann, E E., and G. E. Likens. 1979. Pattern and process in a forested ecosystem. Springer-Verlag New York New York. Broadfoot, W. M., and H. L WiilistotL 1973. Flooding effects on southern foists. Journal of Fottstry 71:584-587. Brookes, A. 1988. Chatmelized rivers: perspectives for environmental nmnagement. John Wiley & Sons, New York, New York Butler, D. P,. 1991. The reintroduction of the beaver into the south. Southeastern Geographer 31:39-43. Demaree, D. 1932. Submerging experiments with Taxodiunt Ecology 13:258-262. Denni£~ W., alld W. BalK)ft. 1974. The floating 1o8 and stump

communities in the Santee Swamp of South Carolin~_ Castanea 39:166-170.

S/maoa~ Hunt, K. 1943. Floating mats on a southeastern coastal plain reservoir. Bulletin of the Torrey Botanical Club 70:481-488. Hupp, C.P,. 1987. Determination of bank wiO~ning and accretion rates and vegetation recovery along modified West Tennessee streams~ Pages 224-233 in Proceedings of the International Symposium on Ecological Aspects of Tree.Ring Analysis. Palisades, New York Hupp, C. R., and E. E. Morris. 1990. A ~ o r p h i c approach to measurement "offsedimentation in a forested wetland, Black Swamp, Arkansas. Wetlands 10:107-124. Kalfiola, IL, and M. pub,kt-~ 1988. River dynamics and vegetation mosaicism: a case study of the River Kalllgjohk~ northemmost Finland. Journal of Biogeography 15:703--719. Keller, E.A., and F.J. SwansorL 1979. Effects off large organic debds on chaonel form and fluvial ~ Earth Surfaces Process 4:361-380. Klimas, C.V. 1988. Forest vegetation off the leveed floodplain of the Lower Mississippi River. Lower Mississippi River Envirotunental Program Report 11. U& Army Corps off Engineers, Mississippi River Commission, Vickstm~ M t ~ L

Drury, G.H. 1977. Undedit streams: retrospect, perspecr, and prospect. Pages 281--293 in ICJ. Gregory, editor. River channel change~ John Wiley & Sons, New York New York

Kom, C. R., W. B. Stein~ede, Jr., F. k K r i n i r - ~ , P,. T. Saucier, P. g. Mabrey, F. k Smlth, and A. ~ Fleetwood. 1968. Geological investigations of the Yazoo Basin, Lower Mississippi Valley. Te~n~cal Report 3-480. U.S. Army Eosineer Waterways Experiment Station, Vicksburg, Mississippi

Everitt, B. L 1968. Use of cottonwood in an investigation of the recent history offa flood plain. American Journal offScience 266:417-439.

Leopold, L B., and M.G. Wolmark 1957. River channel patterns.- b . i d ~ m e a n d e r ~ and ~ t u.s. G e o ~ l Survey ~ o n a l Paper 282-B, Wa~hin~on, D.C

Fond& R.W. 1974. Forest succession in relation to river terrace development in Olympic National Park, Washington, Ecology 55027-942.

Leopold, L B., and M. G. WolmatL 1960. River meanders. Geological Society off America Bulletin 71:769-794.

Hickin, F.J. 1974. The development of meanders in natural river--channels. American Journal of Science 274:414-472.

Marks, P. L 1974. The role ofpin cherry (Prunus Pensy/van/ca L ) in the maintenance of stability in northern hardwood ecosystems. Ecological Monographs 44:73-88.

I~ckln. E.J., and G. C. Nansotx 1975. The chm-acter of channel migration on the Beatton River, Northeast British Columbia, Capatl~ Geological Society of America Bulletin 86:487-494. Hill, & 1~ 1976. The environmental impacts of agricultural land drainage_ Journal of Environmental Management 4:251274. Homer, J.F. 1958. The effects of complete inundation upon seedlings of six bottomland tree species. Ecology 39:371-373. Homer, J. F., and L S. Minckler. 1963. Bottomland hardwood forests of southern Iilinois---regeneration and succession. Ecology 44:29--41.

McKnight, S.J., D.D. Hook, O.G. Langdon, and P,. L Johnson 1981. Flood tolerance and related characteristics off trees of the bottomland forests of the southern United States. Pages 2 9 - 6 9 in J. IZ Clark and J. Benforado, editors. Wetlands of bottomland hardwood forests. Elsevier, Amsterdam, The Netherlands. McLeod, IC W., andJ. K. McPherson. 1973. Factors limiting the distrilmtion of Salix ntgra Bulletin of the Torrey Botanical Club 100:102-110. Na!man, R.J., J. M. M e " o , and J. E. Hobble. 1986. Ecosystem alteration of boreal forest streams by beaver (Castor canadens/s). Ecology 67:1254-1269.

Hufftnan, ll T., and S.W. Forsythe. 1981. Bottomland hardwood forest communities arid their re~tion to anaerobic soil conditions. Pages 187-196 in J. R. Clark and J. Benforado, editors. Wetlands off bottomland hardwood forests. ELsevier, Amsterdam, The Netherlands.

Nanson, G.C., and H.F. Beach. 1977. Forest succession and sedimentation on a meandering-river floodplaln~ northeast British Columbia, Canada. Journal off ~ 4:229251.

Htd~man, R. T., and lh I. Lonard. 1983. Successional patterns on floating vegetation mats in a southwestern Arkansas bald cypress swamp. Castanea 48:73-78.

Noble, M. G. 1979. The origin offPopulus deltoides and Sal/x interior zones on point bags along the Minnesota River. American Midland Naturalist 102:59-67.

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