S Floodplain Forests ince the retreat of the last glaciers from the area we now call Vermont some 13,500 years ago, the flowing water of rivers and streams has been the primary force shaping the land. Over the millennia, the fast moving waters of high gradient streams have eroded soils, thereby lowering the overall surface of the land and creating small and large river valleys. The amount of sediment and the size of sediment particles that a river or stream carries is directly proportional to the gradient of a stream and its volume or discharge. Sediments carried by rivers are deposited when water velocities slow substantially. This soil deposition forms wide deltas if it occurs where the river meets a lake, such as Lake Champlain. Deposition also occurs on the floodplains of rivers, where sediment loads are dropped as slow moving floodwaters spread out over the flat, flooded land. Floodplains are a very active part of our landscape. Streams and rivers are continuously moving back and forth across them, eroding material in some areas and depositing it in others. Within the flood- plain of a typical river valley, several features commonly occur. Levees occur at the top of the banks adjacent to the active channel, and sometimes adjacent to old oxbow channels. The levees are slightly raised above the adjacent floodplain and typically are composed of coarser soil particles that are the first to be deposited by flood waters rising out of the river channel. Oxbows are abandoned channels that have been cut off from the active channel by continual lateral migration of this active channel across the floodplain. Oxbows may retain standing water for many years, but eventually they fill with sediments deposited by floodwaters. Backswamps are low-lying wet areas on the floodplain away from the active channel. Terraces are the remnants of former floodplains that now stand above the active floodplain. Low terraces may occasionally be flooded, while high terraces remain above the flood zone. The floodplain forests that occurred adjacent to the rivers in this region prior to European settlement must have been spectacular. Although we know little about these presettlement forests, we do know that they covered large areas and were likely continuous bands of forest extending unbroken for miles along all of our major rivers. Narrow bands of floodplain forest cover the levee at the mouth of the Missisquoi River. Floodplain Forests / 247
Transcript
Introduction / 247
S
Floodplain Forests
ince the retreat of the last glaciers from the area we now call Vermont some13,500 years ago, the flowing water of rivers and streams has been the primaryforce shaping the land. Over the millennia, the fast moving waters of high
gradient streams have eroded soils, thereby lowering the overall surface of the landand creating small and large river valleys.
The amount of sediment and the size of sediment particles that a river or streamcarries is directly proportional to the gradient of a stream and its volume or discharge.Sediments carried by rivers are deposited when water velocities slow substantially.This soil deposition forms wide deltas if itoccurs where the river meets a lake, such asLake Champlain. Deposition also occurs on thefloodplains of rivers, where sediment loads aredropped as slow moving floodwaters spreadout over the flat, flooded land.
Floodplains are a very active part ofour landscape. Streams and rivers arecontinuously moving back and forth acrossthem, eroding material in some areasand depositing it in others. Within the flood-plain of a typical river valley, several featurescommonly occur. Levees occur at the top ofthe banks adjacent to the active channel, andsometimes adjacent to old oxbow channels.The levees are slightly raised above theadjacent floodplain and typically are composedof coarser soil particles that are the first to bedeposited by flood waters rising out of theriver channel. Oxbows are abandonedchannels that have been cut off from the activechannel by continual lateral migration of thisactive channel across the floodplain. Oxbowsmay retain standing water for many years, buteventually they fill with sediments deposited by floodwaters. Backswamps arelow-lying wet areas on the floodplain away from the active channel. Terraces are theremnants of former floodplains that now stand above the active floodplain. Low terracesmay occasionally be flooded, while high terraces remain above the flood zone.
The floodplain forests that occurred adjacent to the rivers in this region prior toEuropean settlement must have been spectacular. Although we know little about thesepresettlement forests, we do know that they covered large areas and were likelycontinuous bands of forest extending unbroken for miles along all of our major rivers.
Narrow bands of floodplain forest cover thelevee at the mouth of the Missisquoi River.
Floodplain Forests / 247
248 / Wetland, Woodland, Wildland
Forests of towering silver maple and American elm likely covered many of the activefloodplains, with more diverse forests of sugar maple, red oak, and other species onhigher terraces. Native Americans are known to have used floodplains for agriculture,as well, but it is likely that their use was less intense.
Intact floodplain forests are now an uncommon natural community in Vermont.They are uncommon, not because of restricted environmental conditions under whichthis community occurs, but because the vast majority of the floodplain landscape inVermont and the region has been converted to agricultural use. Much of the forestclearing in Vermont occurred in the latter half of the 1700s and the beginning of the1800s, with up to 75 percent of the land area cleared by 1850. Floodplains wereundoubtedly prized as agricultural lands for two reasons: their high fertility associatedwith annual flooding and deposition and the absence of stones and rocks characteristicof most of Vermont’s glacially derived soils. Floodplains are still prized for agriculturetoday. Consequently, although approximately 75 percent of Vermont is now reforested,only fragments of floodplain forest remain and very few areas have been allowed torevert to natural forest.
A particular threat to remaining floodplain forests is the establishment of non-nativeor exotic plant species. Invasive exotic plants are non-native species that have beenintroduced into a region and that aggressively colonize natural communities and oftenout-compete some native plant species. Typically, invasive exotics colonize areas ofdisturbed soils and then may spread into less disturbed areas. In this respect, floodplainforests are an ideal site for colonization by this group of plants. Exposed soils are acharacteristic and natural condition of floodplains because of the annual erosion anddeposition of the alluvial soils. In addition, many floodplain forests have an opencanopy or occur as narrow strips, both conditions that allow additional sunlight to reachthe forest floor and contribute to the establishment of invasive exotics. In a recentstatewide study of floodplain forests, 37 species of non-native and invasive exotic plantswere identified. The following list includes those species that are a particular threat tonative flora and community structure in floodplain forests.
Dams have been constructed on many of Vermont’s rivers for purposes of floodcontrol and hydro-electric power generation. These dams pose a significant threat toriverine floodplain forests. The operation of most dams results in an alteration of thenatural flooding regime upstream and downstream of the dam. This may lead todecreased scouring and erosion of the floodplain, processes that are integral to thedynamic nature of these communities. Altered flooding regimes can also alter thecomposition of vegetation in the floodplain forests. Impoundments above the damsinundate and eliminate natural riverside communities, including all types of floodplainforests, Riverside Grasslands, River Cobble Shores, and in some areas, CalcareousRiverside Seeps. Impoundments also act as large settling basins, trapping sedimentsin the impoundment that would naturally be deposited as alluvium in downstreamfloodplains. Lakeside Floodplain Forests are similarly threatened by significant alterationof water levels in Lake Champlain by changing flows into the Richelieu River.
Lakeside Floodplain Forests are flooded each spring by a rise in water levels of theadjacent lake. They are typically flooded for longer periods than Riverine FloodplainForests. Lakeside Floodplain Forests also have well developed soil horizons, as theyreceive little annual deposition of alluvium.
Floodplain Forest Natural CommunitiesRead the short descriptions that follow and choose the community that fits best.
Then go to the page indicated and read the full community profile to confirm yourdecision.
Silver Maple-Ostrich Fern Riverine Floodplain Forest: This forest is found in thefloodplains of moderate-gradient rivers. Silver maple and ostrich ferns are the dominantspecies and the soils are typically well drained sandy alluvium. Boxelder may beabundant in young forests. Go to page 250.
Silver Maple-Sensitive Fern Riverine Floodplain Forest: These forests occur inthe floodplains of large, low-gradient rivers. Silver maple is the dominant tree, butgreen ash and swamp white oak may be present. Sensitive fern and false nettle arecharacteristic. Soils are moist, typically mottled, silty alluvium. Go to page 254.
Sugar Maple-Ostrich Fern Riverine Floodplain Forest: This uncommonfloodplain forest type occurs along small to moderate sized, high-gradient rivers inareas of calcium-rich bedrock. Sugar maple, white ash, basswood, boxelder, and ostrichfern are common. There can be a diverse herbaceous layer. Soils are well-drained,sandy alluvium. Many examples of this community type are uplands. Go to page 257.
Lakeside Floodplain Forest: These forests occur primarily within the flooding zoneof Lake Champlain. Silver maple and green ash are the dominant trees. Herbs includesensitive fern, false nettle, marsh fern, white grass, and Tuckerman’s sedge. Surfaceorganic layers are present in the moist silty soils and there are mottles near the surface.Go to page 260.
HOW TO IDENTIFY�
250 / Wetland, Woodland, Wildland
ECOLOGY AND PHYSICAL SETTINGThis is the classic floodplain forest found on the moder-
ate gradient portions of most of Vermont’s major rivers.These forests occur on the active floodplain and generallyreceive annual overbank flooding, although water tablesmay be well below the ground surface for most of thegrowing season. Levees and old channel meander scars arecommon micro-topographic features, reflecting the verydynamic nature of floodplains associated with steep tomoderate gradient rivers. The alluvial soils of these flood-plain forests are primarily sandy loams that are generallywell to moderately well drained, without mottles in theupper portion. Due to annual soil deposition, there isgenerally no surface organic layer, although there may bethin buried lenses of decomposing organic material mixedwith the alluvial soil. This floodplain forest type is almostalways considered a wetland.
DISTRIBUTION/ABUNDANCESilver Maple-Ostrich Fern
Riverine Floodplain Forestsoccur throughout New England,New York, Pennsylvania,Maryland, Québec, andOntario, with similar forestsalso present in the Midwest.
Fern Floodplain Forest can be awe-inspiring. Towering silver maples withpillar-like trunks and arching crowns up to100 feet high create the impression of acathedral interior. The near lack of shrubsadds an open, airy quality, but this cathe-dral is full of life. The rich, alluvial soilsproduce a luxuriant growth of ostrich fernand other herbaceous species that mayreach shoulder or head height.
Although silver maple dominates thecanopy of these forests, cottonwood maybe an important component at some sites.Large cottonwood trees may reach heightsof 100 feet and have diameters at breastheight of five feet or more. The fact thatthese immense trees are typically less than90 years old indicates the quality ofgrowing conditions in floodplain forests.Other tree species may include Americanelm, slippery elm, hackberry, and boxelder.Silver maple and boxelder seedling andsapling regeneration is common wherethere are canopy openings. Shrubs are verysparse or lacking, but large riverbank grapevines frequently reach into the lowercanopy. Ostrich fern forms a nearlycomplete ground cover in many of theseforests and wood nettle may be abundantin patches. Although seldom abundant,Wiegand’s wild rye, Canada brome, andwild cucumber are highly characteristic ofthis floodplain forest type and occur rarelyoutside the floodplain habitat.
Invasive exotic plants are a particularthreat to this community. The annualdeposits of rich, alluvial soils provide anideal substrate for many invasive exotics,enabling them to become established,thrive, and often exclude less competitivenative species.
ANIMALSRiverine floodplain forests may be
important breeding habitat for severalspecies of migratory birds, including veery,yellow warbler, eastern wood pewee,northern rough-winged swallow, greatcrested flycatcher, blue-gray gnatcatcher,warbling vireo, yellow-throated vireo, and
northern oriole. The cerulean warbler is anextremely rare breeding bird in Vermont andits numbers have been declining across itsrange. This small bird is strongly associatedwith large areas of mature floodplain forest.Riverine floodplain forests provide importanthabitat for river otter, mink, muskrat, andbeaver. Backswamps and old river meanderscars that hold water after regular springflooding may provide important breedingareas for several species of amphibians,including American toad, wood frog, springpeeper, spotted salamander, and blue-spotted salamander. Although little is knownabout the invertebrates of these forests, thecommon twelve-spotted tiger beetle may befound in this and other Riverine FloodplainForest communities. Also, the ostrich fernborer is a moth that is closely associatedwith the dominant fern in this community.
VARIANTSNorthern Conifer Floodplain Forest:
This floodplain forest type occurs primarilyin the northeastern portion of Vermont.This seasonally flooded forest type alonghigh gradient streams is typically dominatedby balsam fir, red spruce, balsam poplar,and red maple, which form an opencanopy. Speckled alder may be abundant.This community is poorly understood andadditional inventory work is needed.
Successional Floodplain Forest:Floodplain forests are commonly found inearly- to mid-successional stages due to thevery dynamic nature of active floodplains.These young forests are typically dominatedby boxelder but may also be dominated byblack willow or cottonwood. Butternut isan occasional dominant in abandonedagricultural land. In southern portions ofVermont, sycamore is an important treespecies in early-successional floodplainforests, being one of the few tree speciesthat successfully colonizes river cobble andgravel shores. Sycamore may persist inthese forests for a long time. Ostrich fernand several species of invasive exotic plantsare common.
RELATED COMMUNITIESSilver Maple-Sensitive Fern-False
Nettle Riverine Floodplain Forest: Thisfloodplain forest is distinguished from thesilver maple-ostrich fern type by theabundance of sensitive fern, false nettle, andgreen ash, the longer duration of annualflooding, and the finer-textured soils.
Sugar Maple-Ostrich Fern RiverineFloodplain Forest: This forest occurs onhigher floodplain terraces and adjacent tohigher gradient portions of rivers. Manyspecies common to upland hardwoodforests and rich woods are present andthe soils are better drained than in otherfloodplain forest types.
Alluvial Shrub Swamp: These flood-plain communities are typically dominatedby speckled alder although black willowmay be common. Frequent flooding may beresponsible for maintaining the dominanceof shrubs. In some cases this communitymay be successional to a floodplain forest.
MANAGEMENT CONSIDERATIONSThere are very few undisturbed
examples of this or other riverine floodplainforest types in Vermont, as most have longago been converted to productive agricul-tural uses. Protected forests on privateand public lands are generally the onlyfragments of the floodplain forests thatoriginally occurred in Vermont. Invasiveexotic plants pose a particular threat tothis and other riverine floodplain forests.
Wood nettle – Laportea canadensis
Profile / 253
CHARACTERISTIC PLANTS
TREESAbundant SpeciesSilver maple – Acer saccharinumOccasional to Locally Abundant SpeciesCottonwood – Populus deltoidesAmerican elm – Ulmus americanaSlippery elm – Ulmus rubraHackberry – Celtis occidentalisBoxelder – Acer negundoBlack willow – Salix nigraButternut – Juglans cinereaSycamore – Platanus occidentalis
Department of Fish and Wildlife (VDFW)Hartland Rivershore Natural Area, Hartland,
The Nature ConservancyLamoille River Delta, Milton and Colchester,
Sand Bar Wildlife Management Area,VDFW
Otter Creek at Cornwall Swamp, Cornwalland Salisbury, VDFW
White River Wildlife Management Area,Sharon, VDFW
Richmond Corridor, Richmond, RichmondLand Trust
South Bay Wildlife Management Area,Coventry, VDFW
SELECTED REFERENCES AND FURTHER
READING
Sorenson, E., M. Lapin, B. Engstrom, andR. Popp, 1998. Floodplain forests ofVermont: some sites of ecologicalsignificance. Vermont Nongame andNatural Heritage Program.
Floodplain Forests / 253
254 / Wetland, Woodland, Wildland
ECOLOGY AND PHYSICAL SETTINGThis is Vermont’s wetter riverine
floodplain forest type. It occurs onfloodplains adjacent to the lower gradientportions of our larger rivers, includingdeltas, and also in wetter depressionsof floodplains associated with moremoderate gradient rivers. These forestsreceive annual overbank flooding fromthe river, in some cases in both the springand fall. The soils are alluvial withgenerally a silt loam texture, althoughclay loam and very fine sandy loam soilsare also encountered. Most soils havemottling within the upper four inchesof the soil surface. There is generallyno surface organic layer as the leaf litterdecomposes quickly and mixes with newalluvium. This floodplain forest type isalways considered a wetland.
VEGETATIONIn mature forests, large silver maple
trees have towering trunks with high,arching branches that form a densecanopy. Green ash is largely a speciesof the Champlain Valley and is abundantat some sites. American elm is also acommon canopy associate, althoughmany large individuals of this species arenow dead or dying. Swamp white oak isless common. In mature forests, such asthose that occur on the deltas of theLamoille and Missisquoi Rivers, the large,arching silver maples reach diameters ofnearly four feet, heights of over 100 feet,and ages up to 130 years.
Shrubs are generally sparse, althoughwinterberry holly may be abundant inpatches. Saplings and seedlings of silvermaple, green ash, and swamp white oakare often present but are seldom abun-dant. Sensitive fern is the dominant herb,often forming a nearly complete groundcover with other herbs interspersed inlow abundance. Wood nettle is abundantin patches at some sites and absent fromothers, whereas false nettle is seldomdominant but is characteristic of thisfloodplain forest type. Other herbaceousplants include marsh fern and whitegrass.
Silver Maple-Sensitive Fern RiverineFloodplain Forestsoccur throughoutNew England, New York,Pennsylvania, Québec,and Ontario. InVermont, they occuron the lower gradientportions of our largerrivers, including deltas.There are few largeexamples of thiscommunity remainingthroughout its range.
Profile / 255
ANIMALSRiverine floodplain forests may be
important breeding habitat for severalspecies of migratory birds, including veery,yellow warbler, eastern wood pewee,northern rough-winged swallow, greatcrested flycatcher,blue-gray gnatcatcher,warbling vireo,yellow-throated vireo,and northern oriole.Riverine floodplainforests provideimportant habitat andcover for river otter,mink, muskrat, andbeaver. Backswampsand old river meanderscars that hold waterafter regular springflooding may provideimportant breedingareas for severalspecies of amphibians,including Americantoad, wood frog, springpeeper, spottedsalamander, and blue-spotted salamander.
VARIANTSSuccessional
Floodplain Forest:Floodplain forests are commonly found inan early- to mid-successional stages due tothe very dynamic nature of active flood-plains. Black willow is common as anearly-successional tree species in floodplainforests of this type.
RELATED COMMUNITIESSilver Maple-Ostrich Fern Riverine
Floodplain Forest: This floodplain forestis distinguished from the silver maple-sensitive fern type by the abundance ofostrich fern, the shorter duration annualflooding, and the better-drained, coarser-textured soils.
Lakeside Floodplain Forest: LakesideFloodplain Forests are very similar invegetation to Silver Maple-Sensitive FernRiverine Floodplain Forests. They oftenhave low abundance of herbaceousspecies. They differ in having soils that
receive little alluviumduring annual floodingand consequently havewell-developed surfaceorganic layer. Theyalso differ in having alonger flooding regimeand in being adjacentto Lake Champlain.
CONSERVATION
STATUS AND
MANAGEMENT
CONSIDERATIONSAs with other types
of riverine floodplainforests, the SilverMaple-SensitiveFern type has beenlargely converted toagricultural use.However, some highquality examplesremain, especially onthe deltas where ourlarger rivers flow into
Lake Champlain. Invasive exotic plants area threat to this community type.
PLACES TO VISITMissisquoi River Delta, Swanton and
Highgate, Missisquoi National WildlifeRefuge
Halfmoon Cove, Colchester, VermontDepartment of Fish and Wildlife (VDFW)
Derway Island, Burlington, Winooski ValleyPark District
Lamoille River Delta, Milton and Colchester,Sand Bar Wildlife Management Area,VDFW
Rock River Floodplain, Highgate, VDFWLaPlatte River Marsh, Shelburne, The Nature
Conservancy
River otters are active throughout the yearalong river corridors.
TREESAbundant SpeciesSilver maple – Acer saccharinumGreen ash – Fraxinus pennsylvanicaOccasional to Locally Abundant SpeciesAmerican elm – Ulmus americanaSwamp white oak – Quercus bicolor
SHRUBS AND VINESOccasional to Locally Abundant SpeciesWinterberry holly – Ilex verticillataPoison ivy – Toxicodendron radicansRiverbank grape – Vitis riparia
Sorenson, E., M. Lapin, B. Engstrom, andR. Popp, 1998. Floodplain forests ofVermont: some sites of ecologicalsignificance. Vermont Nongame andNatural Heritage Program.
ECOLOGY AND PHYSICAL SETTINGThis natural community is characteristic of the flood-
plains associated with our higher energy, higher gradientrivers, primarily in areas of calcareous bedrock or surficialgeology. It is also found on terraces (former floodplains)above some of our lower gradient rivers, although we havelimited information about this forest type because they havebeen nearly completely converted to agricultural use. Thesefloodplains are less frequently flooded or flooded for shorterduration than other types and have well-drained to moder-ately well-drained soils. The soil texture is typically a finesandy loam over a sandy subsoil, and mottling is oftenabsent. There is generally no surface organic horizon orsignificant profile development in these alluvial soils. Theseare generally upland soils, but small hydric soil inclusionsmay be present in old meander swales. Only someexamples of this community type may qualify as wetlands;the majority are uplands.
VEGETATIONUnlike our other floodplain forests, silver maple is absent
from this community. Sugar maple is the dominant tree inthe relatively closed canopy, but white ash is abundant atsome sites. Basswood usually occurs in low abundancerelative to sugar maple and white ash but is characteristicof these forests. On well-drained sites, red oak may beabundant, and on younger sites in the southern part of thestate there may be large sycamores mixed in the canopy.Black cherry is another canopy associate.
These forests typically have more structural diversity thanthe silver maple floodplain forest types, with sugar mapleand white ash common in the subcanopy. The small tree,musclewood, is also characteristic of the subcanopy and tall
Floodplain Forests are knownto occur throughout NewEngland, New York, and NewJersey, and likely occur inOntario and Québec. InVermont, this communityis associated with most ofour rivers that flow throughareas of calcareous bedrock.Very few examples of thiscommunity remainthroughout its range.
Floodplain Forests / 257
258 / Wetland, Woodland, Wildland
shrub layers of these forests, although itsoverall cover is low. Other than regenera-tion of tree species, especially sugar maple,there are few low shrubs, although thevines poison ivy and Virginia creeper areoften present. Ostrich fern dominates thediverse herbaceous layer. Other speciesthat are commonly present include whitesnakeroot, zigzag goldenrod, bottlebrushgrass, lady fern, and graceful sedge.
Rich woods species such as wild ginger,bloodroot, Sprengel’ssedge, and hairy-leavedsedge are also associatedwith these floodplainforests. Vernal flora,especially wild leeks, maybe present in abundance.The Winooski River isnamed after the NativeAmerican word for“onion,” supposedly dueto the abundance of wildleeks in the forests alongits banks. The uncommonplant Wiegand’s wild-ryeis occasional in this typeof floodplain forest. Lessfrequent are the uncom-mon Goldie’s wood fernand the rare shrubsAmerican hazelnut andhairy honeysuckle.
ANIMALSRiverine floodplain
forests may be important breeding habitatfor several species of migratory birds,including veery, yellow warbler, easternwood pewee, northern rough-wingedswallow, blue-gray gnatcatcher, warblingvireo, yellow-throated vireo, and northernoriole. This community also providesimportant habitat and cover for river otter,mink, muskrat, and beaver. Backswampsand old river meander scars that hold waterafter regular spring flooding may provideimportant breeding areas for several speciesof amphibians, including American toad,wood frog, spring peeper, spotted sala-mander, and blue-spotted salamander.
VARIANTSSuccessional Floodplain Forest:
Floodplain forests are commonly found inearly- to mid-successional stages due to thevery dynamic nature of active floodplains.These young forests are typically dominatedby boxelder but may also be dominated byblack willow or cottonwood. Butternut isan occasional dominant in abandonedagricultural land. In southern portions ofVermont, sycamore is an important tree
species in early-succes-sional floodplain forests,being one of few treespecies that successfullycolonizes river cobbleand gravel shores.Sycamore may persist inthese forests for a longtime. Ostrich fern andseveral species ofinvasive exotic plantsare common.
RELATED COMMUNITIESSilver Maple-Ostrich
Fern Riverine Flood-plain Forest: Thisfloodplain forest isdistinguished from theSugar Maple-Ostrich Ferntype by the dominance ofsilver maple and the lackof understory develop-ment and absence ofherbaceous species that
are typical of rich woods and uplands.Rich Northern Hardwoods: Rich
northern hardwood forests have well-developed soil profiles that were notformed by recent alluvium. They also arenot dominated by ostrich fern and typicallydo not occur in river floodplains.
MANAGEMENT CONSIDERATIONSIntact examples of this community are
rare in Vermont. Due to the rich, productivesoils, most examples were cleared foragricultural use long ago. Alterations inflooding regime, scouring, and sedimentdeposition associated with dams pose asignificant threat to this and other rivershoreand aquatic communities. There are only afew, small protected floodplains in the statethat include this natural community type.
PLACES TO VISITRandolph Village Floodplain, Randolph,
Village of RandolphWhite River Wildlife Management Area,
Sharon, Vermont Department of Fishand Wildlife
Townshend Dam Floodplain, Townshend,U.S. Army Corps of Engineers
SELECTED REFERENCES AND
FURTHER READINGSorenson, E., M. Lapin, B. Engstrom,
and R. Popp, 1998. Floodplain forestsof Vermont: some sites of ecologicalsignificance. Vermont Nongame andNatural Heritage Program.
CHARACTERISTIC PLANTS
TREESAbundant SpeciesSugar maple – Acer saccharumWhite ash – Fraxinus americanaOccasional to Locally Abundant SpeciesBasswood – Tilia americanaMusclewood – Carpinus carolinianaAmerican elm – Ulmus americanaRed oak – Quercus rubraSycamore – Platanus occidentalisBlack cherry – Prunus serotinaCottonwood – Populus deltoidesButternut – Juglans cinereaRed maple – Acer rubrumBlack ash – Fraxinus nigraHophornbeam – Ostrya virginianaBoxelder – Acer negundo
SHRUBS AND VINESOccasional to Locally Abundant SpeciesChokecherry – Prunus virginianaAlternate-leaved dogwood – Cornusalternifolia
ECOLOGY AND PHYSICAL SETTINGLakeside Floodplain Forests have been identified
primarily along the shores of Lake Champlain, with smallexamples along the shores of Lake Memphremagog. Theytypically occur in former lake coves and at the mouths ofrivers and streams as a complex of wetland forest types andmarsh. When occurring in old lake coves, there is often anarrow beach ridge along the lake with a marsh or Button-bush Swamp filling the deepest portion of the former cove.Red or Silver Maple-Green Ash Swamp may be present onorganic soil on the landward side of the former cove. Theclassic Lakeside Floodplain Forests often occur as a bandbetween these organic soil wetlands and the uplands;however, there are many variations on this pattern.
The soils of Lakeside Floodplain Forests are typicallysilts or clay loams. Although the soils usually do not showevidence of substantial recent alluvial deposition, they wereformed by deposition in former glacial lakes. Annual lakeflooding undoubtedly deposits some very fine soils andcontributes to the rich growing conditions in these forests.Surface organic layers may be several inches thick andmottling is usually present to the surface. Although lakelevels drop by summer, the soils in Lakeside FloodplainForests typically remain moist because they are fine texturedand hold water.
Lake Champlain reaches its highest water levels duringthe months of April, May, and June, when the averagemaximum level is over 100 feet. These extended high-waterperiods mean that Lakeside Floodplain Forests must toleratelonger periods of inundation than the riverine floodplainforests. It is common to see dead saplings and young treesin the lowest portions of Lakeside Floodplain Forestsbecause unusually high lake levels may persist into thegrowing season.
DISTRIBUTION/ABUNDANCELittle is known about
the regional distribution ofthis community. In Vermont,Lakeside Floodplain Forestshave been identified fromthe shores of LakeChamplain, with smallexamples on the shoresof Lake Memphremagog.
LAKESIDE FLOODPLAIN FOREST
Profile / 261
LAKESIDE FLOODPLAIN FOREST
Very slight changes in elevation inLakeside Floodplain Forests appear tohave substantial impact on the herb, shrub,and sapling layers. The lowest parts of thelakeside floodplain have low coverage ofherbs and may have dense thickets of silvermaple seedlings. Slightly higher on thefloodplain, marsh fern is common, andin areas elevated several inches more,winterberry holly and sensitive ferndominate the herb and shrub layers.
VEGETATIONThe narrow lakeside beach ridges in the
part of the floodplain closest to the lake areformed by wave action and deposition ofsandy soils. Silver maple, green ash,cottonwood, and American elm are thedominants of the canopy here. There arefew shrubs, and the herbaceous layer issparse, including sensitive fern, whitegrass,and wild mint.
The flood-plain behind thebeach ridgeand marsh istypically a silvermaple domi-nated forest.This forest hasvery few shrubsand a verysparse groundcover thatincludes whitegrass, beggar’sticks, and closerto the marsh,water-willow.Silver mapleseedlings maynearly cover the ground in some areas,but few survive the flooding of thefollowing spring.
This low diversity forest grades into aslightly higher elevation silver maple forestclosest to the uplands. Green ash is animportant component of the canopy in thisforest, with swamp white oak occurringoccasionally. Green ash is especially
tolerant of flooding. In mature forests, thetall, stately silver maples and green ash mayreach heights of 100 feet and diameters ofthree feet. Silver maple and green ashregeneration are abundant as both seed-lings and saplings, and there are scatteredpatches of winterberry holly. Sensitive fernis the dominant herb and may cover muchof the forest floor. Although seldomabundant, false nettle is characteristic ofthis forest type. Other herbaceous speciesinclude whitegrass, marsh fern, beggar’sticks, and Tuckerman’s sedge. The uncom-mon cattail sedge, yellow water-crowfoot,and Gray’s sedge are all closely associatedwith Lakeside Floodplain Forests.
ANIMALSLike Riverine Floodplain Forests,
Lakeside Floodplain Forests provide habitatfor several bird species that use deciduous
forests nearopen water for breeding:veery, yellowwarbler,easternwood pewee,blue-graygnatcatcher,warblingvireo, yellow-throated vireo,and northernoriole. Thedead trees thatfrequentlyoccur at thelakeward sideof theseforested
wetlands provide nesting cavities for woodducks and pileated woodpeckers. Greatblue herons establish nesting rookeries inthe tall silver maples, and green herons usethese trees as perches. Mink and raccoonare common in this community, and theirtracks are frequently seen in the baremuddy soils. Northern leopard frogs maybe abundant in these forests.
These water-stained and buttressed green ash and silvermaple trunks are signs of extended high water periods.
Floodplain Forests / 261
262 / Wetland, Woodland, Wildland
CHARACTERISTIC PLANTSVARIANTSNone recognized at this time.
RELATED COMMUNITIESSilver Maple-Sensitive Fern Riverine
Floodplain Forest: This riverine flood-plain forest is very similar in vegetation tothe Lakeside Floodplain Forest. It differsin that it occurs adjacent to rivers, has soilsformed from annual alluvial deposition,and typically has a flooding regime ofshorter duration than the Lakeside Flood-plain Forest.
CONSERVATION STATUS AND
MANAGEMENT CONSIDERATIONSDue to their lengthy spring flooding,
Lakeside Floodplain Forests have not beenas extensively cleared for agricultural usesas Riverine Floodplain Forests. LakesideFloodplain Forests would be threatenedby any significant alteration of water levelsin Lake Champlain by changing flows intothe Richelieu River. There are high qualityexamples of this community on privateland and several protected examples onpublic and conservation lands.
PLACES TO VISITLittle Otter Creek Wildlife Management
Area, Ferrisburgh, Vermont Departmentof Fish and Wildlife (VDFW)
Sand Bar Wildlife Management Area,Milton, VDFW
North Hero State Park, North Hero,Vermont Department of Forests, Parks,and Recreation
Drowned Lands, West Haven, Helen W.Buckner Memorial Preserve at BaldMountain, The Nature Conservancy(TNC)
LaPlatte River Marsh, Shelburne, TNC
SELECTED REFERENCES AND FURTHER
READINGSorenson, E., M. Lapin, B. Engstrom, and
R. Popp, 1998. Floodplain forests ofVermont: some sites of ecologicalsignificance. Vermont Nongame andNatural Heritage Program.
TREESAbundant SpeciesSilver maple – Acer saccharinumGreen ash – Fraxinus pennsylvanicaOccasional to Locally Abundant SpeciesSwamp white oak – Quercus bicolorAmerican elm – Ulmus americanaCottonwood – Populus deltoidesBlack willow – Salix nigra
SHRUBS AND VINESOccasional to Locally Abundant SpeciesWinterberry holly – Ilex verticillataButtonbush – Cephalanthus occidentalisRiverbank grape – Vitis riparia
