Floodplain Forest and Woodland

Last updated: December 31st, 2024 by Grant Fessler

Overview

As the name indicates, floodplain forests and woodlands are found in the floodplains of streams and rivers. This community type is well-developed in the QC region along the Mississippi River and its numerous tributaries as well as on islands. Floodplain forests typically form on sandy, silty, and clayey alluvium; soil moisture ranges from mesic to wet. Canopies range from open to closed and species composition is largely a result of flooding regime and soil texture. More open canopies in our contemporary floodplain forests are the result of ash (Fraxinus pennsylvanica and F. lanceolata) die-off caused by the emerald ash borer and/or die off related to flooding.

It is no secret that the lock and dam system in conjunction with the large scale industrial agriculture that occurs in the Mississippi River watershed exacerbates and intensifies flooding by artificially raising water levels and sending massive amounts of sediment into the river. Floods used to be a natural disturbance in our bottomland systems, but the magnitude and duration of contemporary flooding is far beyond anything that our natural communities are adapted to. Anthropogenic changes to the landscape have resulted in a dramatic decline in diversity and ecological function of our floodplains. Simply put, few species are well adapted to survive long periods of flooding and siltation. Contemporary flooding has also brought floodwater into portions of the floodplain that, historically, would have rarely flooded, further altering the composition, structure, and function of floodplain communities.

Mesic Floodplain Forest Association

Rich mesic alluvial woodland abloom with *Cryptotaenia canadensis, Galium aparine, Phlox divaricata, Sanicula odorata,* and Trillium recurvatum beneath a canopy of *Juglans nigra* and Ulmus americana in Whiteside County, IL.

This diverse association was likely widespread in our area but has become rare under our contemporary flooding regime. Indeed, few high-quality remnants exist today. Mesic floodplain forest and woodland are typically found on high terraces that flood less frequently relative to lower areas. Sandy soils which allow better drainage are often associated with this type. Mesic upland forest canopy and herbaceous species are characteristic. This community type likely experienced regular fire in pre-settlement times.

Mesic floodplain forests and woodlands are characterized by: Antenoron virginianum, Apios americana, Arisaema dracontium, Asarum canadense var. reflexum, Borodinia dentata, Cardamine bulbosa, Cardamine concatenata, Carex davisii, Carex grisea, Carex jamesii, Carya cordiformis, Carya laciniosa, Carya ovata, Celtis occidentalis, Cercis canadensis, Chaerophyllum procumbens, Cinna arundinacea, Claytonia virginica, Cornus drummondii, Crataegus mollis, Cryptotaenia canadensis, Dicentra cucullaria, Erythronium albidum, Euonymus atropurpureus, Eutrochium purpureum, Fraxinus pennsylvanica, Gymnocladus dioicus, Heracleum maximum, Hydrophyllum appendiculatum, Hydrophyllum virginianum, Juglans nigra, Lactuca floridana, Laportea canadensis, Lilium michiganense, Menispermum canadense, Mertensia virginica, Osmorhiza longistylis, Phlox divaricata, Quercus alba, Quercus macrocarpa, Quercus rubra, Ranunculus septentrionalis, Rudbeckia laciniata, Sanicula odorata, Smilax ecirrhata, Symphyotrichum lateriflorum, Thalictrum dasycarpum, Tilia americana, Trillium recurvatum, Ulmus americana, Verbesina alternifolia, Viola eriocarpa, Viola missouriensis, Viola sororia.

Wet-mesic Floodplain Forest Association

*Chelone obliqua* var. *speciosa* (rose turtlehead) is an emblematic and charismatic species of wet-mesic floodplain forests and woodlands in the Quad Cities. Pictured here in a Mississippi River floodplain in Rock Island County, it associates with *Apios americana, Boehmeria cylindrica, Cinna arundinacea, Elymus virginicus, Lysimachia ciliata, Physostegia speciosa, Solidago gigantea, Stachys hispida,* and Symphyotrichum lanceolatum beneath a canopy of *Acer saccharinum* and *Fraxinus lanceolata*.

This association floods more frequently than mesic floodplain forests but less frequently and for shorter durations compared to wet floodplain forests. Flood-intolerant species largely drop out of the association, but these communities can still be relatively diverse, especially compared to communities with high flood frequency.

Wet-mesic floodplain forests are typically include: Acer saccharinum, Apios americana, Anemone canadensis, Betula nigra, Boehmeria cylindrica, Carex frankii, Carex grayi, Carex grisea, Carex lupulina, Carex muskingumensis, Carex tribuloides, Carex typhina, Carya illinoensis, Carya laciniosa, Celtis occidentalis, Chelone obliqua speciosa, Cinna arundinacea, Cornus drummondii, Cornus obliqua, Elymus virginicus, Fraxinus lanceolata, Fraxinus pennsylvanica, Gymnocladus dioicus, Leersia virginica, Lobelia siphilitica, Lycopus virginicus, Lysimachia ciliata, Persicaria punctata, Physostegia speciosa, Platanus occidentalis, Populus deltoides, Quercus bicolor, Quercus palustris, Quercus macrocarpa, Rudbeckia laciniata, Ruellia strepens, Sambucus canadensis, Smilax hispida, Solidago gigantea, Stachys hispida, Stachys tenuifolia, Symphyotrichum lanceolatum, Symphyotrichum lateriflorum, Symphyotrichum ontarionis, Thalictrum dasycarpum, Toxicodendron radicans, Ulmus americana, Viola missouriensis, Vitis riparia.

Wet Floodplain Forest Association

A typical wet floodplain forest with a near-monotypic carpet of *Laportea canadensis* beneath a canopy of *Acer saccharum* in the floodplain of Rock River near its confluence with the Mississippi in Rock Island County, IL.

Wet floodplain forests typically experience flooding on an annual basis. The soils are saturated or flooded for a significant portion of the year but usually drain by mid to late summer. Silt loams and silty clay loams are common soil types associated with these communities. The canopies are typically composed of Acer saccharinum, Fraxinus lanceolata, Fraxinus pennsylvanica, Populus deltoides, Salix nigra, and Ulmus americana. In contemporary wet floodplain forests, Acer saccharinum often dominates in nearly monotypic stands. Fraxinus lanceolata and Fraxinus pennsylvanica were historically co-dominant species in floodplain forests, but their populations have been severely impacted by the invasive emerald ash borer. Accordingly, these species are now more frequently encountered as saplings in the shrub layer and understory. Large canopy gaps are now common in wet floodplain forests due to Fraxinus die-off. Vines are significant components of wet floodplain forest structure. Smilax hispida, Toxicodendron radicans, and Vitis riparia are often the only species present. Herbaceous diversity is often low, and, in many instances, the ground layer is dominated by large swathes of Laportea canadensis.

This association is typified by: Acer negundo, Acer saccharinum, Bidens frondosa, Boehmeria cylindrica, Carex lupulina, Elymus virginicus, Fraxinus lanceolata, Laportea canadensis, Leersia virginica, Leersia oryzoides, Persicaria punctata, Pilea pumila, Populus deltoides, Salix nigra, Sicyos angulatus, Smilax hispida, Symphyotrichum lanceolatum, Toxicodendron radicans, Ulmus americana, Vitis riparia.

This community grades into floodplain marsh and mudflats in lower areas and wet-mesic floodplain forest on slightly higher ground.

References

Guldner, Ludwig F. 1960. Vascular Plants of Scott and Muscatine Counties. Davenport Public Museum, Davenport, IA.

Houser, J.N., ed., 2022, Ecological status and trends of the Upper Mississippi and Illinois Rivers (ver. 1.1, July 2022): U.S. Geological Survey Open-File Report 2022–1039, 199 p., https://doi.org/10.3133/ofr20221039.

Illinois Department of Natural Resources. 2023. Illinois Natural Areas Inventory Standards and Guidelines (revised edition). Springfield, Illinois. 105 pp.