Dry river bluff (S3)
Dry river bluff communities consist of sloughing, dry, sandy riverbanks. They occur along the outside meander bends on major or minor rivers that flow through thick outwash and old glacial lakebed deposits on sand plain settings. Some examples are several hundred feet high. Bluffs occur where a river cuts into a terrace to form steep slopes, often to the angle of repose. These slopes are highly unstable. As the river erodes sand at the base, the areas higher on the slope slide downward, continually exposing fresh sand. The sand is interspersed with tree trunks and chunks of turf eroded from the terrace directly above. Portions of otherwise dry sand bluffs are mesic or slightly enriched from laterally surfacing groundwater. Bluffs range from sparsely vegetated, open sandy areas to a woodland structure, depending on past disturbance.
Vegetation takes root sporadically as various areas stabilize. Islands of intact vegetation sometimes detach from the top of the bluff and either perch partway down the slope or slide into the river. Seeps may occur at portions of otherwise dry sand bluffs are mesic or slightly enriched from laterally surfacing groundwater.
Along the upper
Along the Merrimack and Soucook Rivers, the nutrient-poor, sandy soils on some south and west-facing slopes and bluff edges support populations of the rare species wild lupine (Lupinus perennis) and golden heather (Hudsonia ericoides). These plants are able to persist on these slopes despite the destabilizing effects of riverbank erosion and groundwater seepage. Some stretches of bluff at these sites are too unstable to support wild lupine or golden heather; other areas are stable enough to support trees and other vegetation that shade out the two rare plants. Rivers are dynamic systems, however, and the long-term perpetuation of this community depends on the preservation of large areas of riparian corridor to allow for the migration of the community as the river’s channel meanders.
Characteristic vegetation: Plants typical of dry, sandy, disturbed sites characterize this community, including little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), poverty oatgrass (Danthonia spicata), awnless brome grass (Bromus inermis), quack grass (Elymus repens), redtop (Agrostis gigantea), shorter sedge (Carex cf. brevior) and other sedge species in section Ovales, shaved sedge (Carex tonsa), sand sedge (Carex rugosperma), round headed bush-clover (Lespedeza capitata), jointweed (Polygonella articulata), intermediate pinweed (Lechea intermedia), bristly sarsaparilla (Aralia hispida), white snakeroot (Eupatorium rugosum), arrow-leaved violet (Viola sagittata), biennial evening primrose (Oenothera biennis), fireweed (Erechtites hieraciifolia), common speedwell (Veronica officinalis), wild lupine (Lupinus perennis), golden heather (Hudsonia ericoides), sweet fern (Comptonia peregrina), gray birch (Betula populifolia), paper birch (Betula papyrifera), and mosses.
Good examples of this community can be found along the Merrimack River in Canterbury and Concord.
Dry river bluffs sometimes occur adjacent to Appalachian oak - pine forest systems and pitch pine sand plain systems.
Dry river bluff community at Muchyedo Meander on the Merrimack River (photo by Dan Sperduto)
Strip of dry river bluff community above the CT River (photo by Ben Kimball)
Dry river bluff above the Merrimack River in Concord (photo by Ben Kimball)