Riverine Mud Flat/Beach

Overview: Distribution, Abundance, adapted to quickly colonize unvegetated substrates under Environmental Setting, Ecological Processes conditions of maximum light availability and minimal com- As water levels drop in summer or fall, patches of bare sand, petition from pre-existing vegetation. mud, gravel, or cobbles are exposed along the banks or within channels of rivers and streams. The Riverine Mud Flat/Beach Community Composition: Composition and community is best developed within the floodplains of the Structure state’s larger, low gradient rivers, especially in southwestern Plants that become established on these newly exposed, and central Wisconsin. Soil development on the flats and bars somewhat ephemeral habitats include sedges, grasses, rushes, is minimal owing to the frequent flood disturbance. During and seedlings of woody species such as sandbar willow (Salix the growing season, these areas are colonized by an assem- exigua) or eastern cottonwood (Populus deltoides). Initially, blage of herbs and sometimes shrubs and saplings. Plant graminoids of short stature may be prevalent, among them cover on the newly exposed mud flats and beaches is highly several of the “flat sedges” such as flat sedge (Cyperus odo- variable, progressing from an essentially unvegetated condi- ratus) and bearded flat sedge (C. squarrosus), spike-rushes tion following floods associated with snowmelt and spring such as needle spike-rush (Eleocharis acicularis), blunt spike- rains, to sparse cover as the waters recede, to denser stands of rush (E. obtuse), common spike-rush (E. palustris), creep- graminoids and various forbs by late summer and early fall. ing love grass (Eragrostis hypnoides), tufted love grass (E. Floods typically affect the Riverine Mud Flat/Beach veg- pectinacea), autumn sedge (Fimbristylis autumnalis), small- etation annually, and these may be accompanied by erosive flowered hemicarpha Lipocarpha( micrantha), and several scouring, sediment deposition, and local shifts in the loca- rushes (Juncus spp.). Other native herbs associated with this tion and extent of the sandbars, mud flats, and channels. The assemblage in such habitats are water star-grass (Zosterella colonizing plants tend to be annuals, short-lived perennials, dubia), marsh purslane (Ludwigia palustris), and moist bank or perennials with light, wind, or water dispersed propagules pimpernel (Lindernia dubia). In common with other high energy and frequently dis- turbed environments such as Great Lakes beaches and dunes, opportunistic weedy plants are also characteristic of river- ine mud flats and beaches. However, as the slate is erased annually and succession is set back, these are apparently not serious problems except in cases where the flood regime has been altered in some way that favors the weeds and the devel- opment of a more or less permanent weed-dominated com- munity. Examples of the nonnative weeds occurring in these

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Locations of Riverine Mud Flat in Wisconsin. The deeper hues shad- ing the ecological landscape polygons indicate geographic areas of greatest abundance. An absence of color indicates that the commu- Meanders of the Black River have created unvegetated steep cut- nity has not (yet) been documented in that ecological landscape. The banks and extensive flats of exposed sand and silt. Such areas receive dots indicate locations where a significant occurrence of this com- heavy use by waterbirds, turtles, and invertebrates. Jackson County, munity is present, has been documented, and the data incorporated Western Coulees and Ridges Ecological Landscape. Photo by Eric into the Natural Heritage Inventory database. Epstein, Wisconsin DNR. environments are green carpetweed (Mollugo verticillata), the hairy-necked tiger beetle (Cicindela hirticollis) and sandy black mustard (Brassica nigra), winged pigweed (Cycloloma stream tiger beetle (C. macra). atriplicifolia), and Russian thistle (Salsola tragus). Rare plants associated with this type include smooth rose Conservation and Management Considerations mallow (Hibiscus laevis) and the apparently extirpated yerba- Management considerations are predicated on maintaining de-tajo (Eclipta prostrata). natural disturbance dynamics characterized by the periodic The mud flats and sandbars are used as foraging and rest- floods that will maintain and rejuvenate this community and ing places by shorebirds, wading birds, and raptors, e.g. the its assemblage of habitat specialists in their entireties some- Bald Eagle (Haliaeetus leucocephalus), and by mammals where within the floodplains of our river systems over time. such as American mink (Neovison vison), North American Given the uncertainties and dynamics inherent in predicting river otter (Lontra canadensis), and raccoon (Procyon lotor). flood disturbance frequency and magnitude at any given loca- Turtles strongly associated with large rivers, including the tion along a major river, this will be a challenging problem. northern map turtle (Graptemys geographica), Ouachita These communities have gotten little attention from plant map turtle (G. ouachitsensis ouachitensis), false map turtle ecologists and at this time are perhaps better known and (G. pseudogeographica pseudogeographica), smooth softshell understood by invertebrate enthusiasts, birders, and rogue turtle (Apalone mutica), and eastern spiny softshell turtle sun worshipers. (Apalone spinifera) make heavy use of these habitats as nest- ing and basking areas. Additional Information In recent decades, a comprehensive statewide survey of Information on similar or related natural communities may be grasshoppers (Kirk and Bomar 2005) has documented the found in the natural community descriptions of Coastal Plain use of this and related communities as important habitats for Marsh, Inland Beach, and Interdunal Wetland. Also, in the both common and rare grasshopper species. Among the lat- “Selected Habitats” section of this chapter, see the descriptions ter are the Gladston’s spur-throat grasshopper (Melanoplus for Dredge Spoil Island and Lacustrine Mud Flat. The U.S. gladstoni) and the spotted-winged grasshopper (Orphulella National Vegetation Classification type most closely matching pelidna). Sandbars associated with several of the large rivers in Riverine Mud Flat/Beach is CEGL002049 Riverine Sand Flats southwestern Wisconsin support rare tiger beetles, including – Bars Sparse Vegetation (Faber-Langendoen 2001).

FROM: Epstein, E.E.. Natural communities, aquatic features, and selected habitats of Wisconsin. Chapter 7 in The ecological land- scapes of Wisconsin: An assessment of ecological resources and a guide to planning sustainable management. Wisconsin Department of Natural Resources, PUB-SS-1131H 2017, Madison.

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