Humboldt Habitat Types

AerialSCU Kenworthy 512

This aerial photo captures many habitat types, showing agricultural wetlands in the foreground (pastureland in the photo), followed by seasonal freshwater wetlands (not flooded), and a strip of forested riparian corridor in between. In the background a sliver of brackish marsh is visible, which adjoins recently restored salt marsh on its left.

The Freshwater-Saltwater Continuum


When Humboldt Bay was diked in the early 20th century, the area of estuary was reduced by almost 40 percent. Although there is no longer an uninterrupted gradient from rivers and creeks to the ocean water at the bay’s mouth, a complex mosaic of fresh, brackish, and saltwater wetlands occurs in response to tidal influence, freshwater inputs, and the residual salinity of old saltmarsh soils. As a result, there is a rich diversity of habitat types surrounding the bay.

Riparian forest occurs along stream edges in freshwater areas. The canopy layer is dominated by red alder, willows, and Sitka spruce, with an understory of salmonberry, twinberry, California blackberry, and wax myrtle. Lady fern, wood fern, and sword fern create an attractive groundlayer in drier areas, with stands of small-fruited bulrush joined by skunk cabbage in wetter areas. The rich structural diversity of these areas, combined with the many fruit-bearing shrubs, attract a rich bird fauna, especially migrating and nesting songbirds. 

Freshwater marsh was probably limited historically within the Humboldt Bay watershed. It has become quite abundant in areas, such as the refuge, that were converted in the past from saltmarsh to agricultural land but are now managed as shallow seasonal wetlands. Our present day freshwater wetlands range from seasonally to permanently flooded marshes supporting a diversity of plants (cattails, rushes, and pondweeds) and invertebrates that sustain wildlife. Rails, otters, and frogs secret themselves among the dense marsh vegetation. Common waterfowl that use this seasonal habitat include American Green-Winged Teal, Northern Shoveler, American Wigeon, Northern Pintail, Gadwall, and Mallard.

Agricultural wetlands are diked former saltmarshes that support pasture grasses such as ryegrass, velvet grass, and tall fescue, as well as the native wetland species short-awned foxtail and Pacific silverweed. These areas are hayed or grazed to maintain the shortgrass pastures attractive to Aleutian Cackling Geese. They are also used by shorebirds, herons, egrets, and black-tailed deer.

Brackish marsh occurs where salt and fresh water mix or where salts in the soil remain high. These wetlands support native saltgrass, tufted hairgrass, and two species of arrowgrass. The edges of former tidal channels, where water levels are more constant, are lined with seacoast bulrush. These sloughs are used by salmonids and tidewater gobies, all listed species.

Saltmarsh was the most widespread wetland type around Humboldt Bay, but due to diking and draining in the early 1900s only 10 percent of our saltmarshes remain. Of the remaining 900 acres, most have been invaded by the aggressive dense-flowered cordgrass, introduced in the 19th century in the ballast of ships. Cordgrass is currently being removed to restore a diverse community of plants including pickleweed, jaumea, saltgrass, and several rare species.

Intertidal mudflat and eelgrass beds occupy vast areas of the bay. Seemingly barren mudflats teem with life just beneath the surface. Plankton and algae anchor food webs of invertebrates, mollusks, crustaceans, fish, birds, and mammals, including humans. The intertidal flats of South Bay support approximately 2,000 acres of eelgrass, which are critically important to Pacific Brant, other waterbirds, and the bay ecosystem.


From Beach to Forest

ForeduneLanphere Pickart 512   
 Picture: Foredune habitat type at the Lanphere Dunes unit of Humboldt Bay NWR. 
Native foredune grassland is a community restricted to the foredune (the first rise above the beach), and characterized by the native grass Elymus mollis ssp. mollis, which is able to tolerate the intense salt spray and sand deposition that occurs in this habitat. The refuge supports one of the few remaining stands of this community, which is globally endangered. It has been displaced by introduced European beachgrass, which outcompetes native plants, along the entire Pacific Coast. See article: Restoring the Grasslands of Northern California's Coastal Dunes (2.21MB pdf).   


Dune mat is a spectacular community of wildflowers that occurs on semi-stable dune ridges behind the foredune. Beginning in May with beach pea, successive waves of color paint the dunes as different wildflowers come into bloom, including beach buckwheat, seaside daisy, and dune goldenrod. This community is home to two endangered plants, Humboldt Bay wallflower and beach layia. Native solitary bees create burrows in the sand, and are essential pollinators that maintain this community. A variety of invertebrates, including many specially adapted for this environment, occur here. Mammals such as porcupines, gray fox, and striped skunk leave their calling cards in the form of footprints. Dune mat has become extremely rare in the Pacific Northwest, and in many parts of California, due to the spread of European beachgrass, iceplant, and other aggressive non-native species.

Dune swales occur in the depressions between dune ridges and on the deflation plain. These seasonal freshwater wetlands form in winter when loose sand blows away and the water table rises, allowing plants to colonize. First algae and cyanobacteria, and then rushes and sedges occur with many associated herbs such as springbank clover, Pacific silverweed, bird’s-foot trefoil, and willow-herb. Soon, Hooker’s willow and beach pine follow, ultimately creating wooded swales that attract many birds and mammals. Swales provide the seasonal water needed for many amphibian species, including red-legged frogs and Pacific tree frogs.

Moving dunes are the most dramatic of the many landforms found here. Large dunes migrate inland, slowly covering the forest to the east. At the juncture of dune and forest, massive slipfaces slowly engulf trees that become bleached and skeletal as the dunes move forward. Few plants can gain a foothold here, but the constant traffic of mammals moving between forest and foraging areas on the dunes is recorded as an intricate maze of tracks.

Coniferous dune forest occurs east of the moving dunes on older stabilized dunes. The dune forest is an incredibly lush and productive environment, with over 300 species of mushrooms, lichen, and mosses. The forest canopy is dominated by Sitka spruce and beach pine, with lesser grand fir, Douglas-fir, and madrone. The understory varies from dense stands of huckleberry and salal, to more open woodlands with a groundcover of bearberry (ground manzanita), reindeer lichen, and the showy calypso orchid, rein orchid and hooded ladies’ tresses. The largest mammals of the forest are gray fox, but there are many small mammals including the rare white-footed vole.

 ForestedDune Pickart 512   
Picture: Skeleton trees in front of a coniferous dune forest.