Plant Communities of Santa Cruz County


  Northern Foredune (21210)



Description 

The northern foredune is dominated by perennial grasses (to 70 cm tall) and low, often succulent, perennial herbs and sub-shrubs (about 10 cm tall). Coverage varies from nearly complete to scattered. The species typically are zoned, with Abronia, Ambrosia, and Cakile usually occurring in the sites most exposed to the wind, and Calystegia and Camissonia in more sheltered sites. Growth and flowering are most active in late spring and early summer, but continue at a reduced rate all year. (Holland 1986) 

History

One can only speculate that these ecosystems are very old and have been in existence in one form or another, as long as the necessary sand and substrate have been present. They have probably fluctuated during the various glacial periods.  As glaciers formed they probably gradually expanded downward toward the sea as sea level fell. Would the flow of sand have been different during glacial periods? As glaciers melted and sea levels rose, these communities may have been inundated by the sea and eventually worked their way back into surrounding plant communities. Sand production was probably greater during the periods of warming and glacial melt. (FMc 7/94) 

Before 1850, dunes were low and parabolic. With the introduction of European beach grass (Ammophilia arenaria), the dunes have become more vertical and immobile. European beach grass was used extensively as a sand stabilizer to prevent the filling of shallow harbors and burial of coastal roads and railroad tracks by windblown sand along the San Mateo-San Francisco coastline. Golden Gate Park in San Francisco was created from sand dunes stabilized by the grass. Very little of original community in its undisturbed or natural cycles remains if we include the effects of introduced species. (FMc 7/94) 

Distribution

The northern foredune strand is located in areas of sand accumulation along the coast, including all locations where active coastal dunes occur and many less extensive areas as far south as Point Conception. (Holland) Commonly found along the north coast from Santa Cruz north to San Francisco, local examples are found at Ano Nuevo and Franklin Point and in the La Selva Beach area from the Pajaro River North to Seascape. (FMc 7/94) 

Site Factors 

The foredune plant series is normally situated on foredunes, as well as on upper beaches. The sites are similar to Active Coastal Dunes, but with less wind and/or a smaller supply of sand and/or more available ground water. The relatively favorable conditions allow the establishment of plants which reduce the amount of blowing sand and partially stabilize the dunes. Drainage is rapid, but the deeper zones may be relatively moist. Plants are subject to desiccating, salt-bearing winds. (Holland 1986) 

Successional Stages

A. Non human-cyclic or catastrophic (fire, floods, landslides, etc.): 

Changes in coastal land forms, and geological movement can increase, or block the movement of sand along the coast and onto the beaches. The changes at Ano Nuevo, from a peninsula to an island within the last 100 years or so, are a good example of this. Changes in stream-flow volume and sediment loads in our coastal streams and rivers can affect the extent of these communities and cause successional changes. (FMc 7/94) 

B. Human caused (logging, agriculture, urbanization, grazing, etc.): 

Off-road vehicles, commercial and housing development, livestock grazing, sand mining, road construction, and effects of introduced species of plants like European beach grass and sea fig and hottentot fig as ground cover have been the principal cause of successional change and destruction of this ecosystem. Reclamation and natural succession are possible in disturbed areas, but it is labor intensive and expensive. Some revegetation projects are underway by Caltrans around Pescadero Creek. (FMc 6/94) 

Associated Communities 

Sometimes it can be overrun by active dunes, or integrated with active coastal dunes toward the coast or with coastal scrub inland. It needs sand for rejuvenation. (Holland 1986) 

Associated Plants

     (Chorizanthe cuspidata cuspidata) San Francisco Bay spineflower 
     (Chorizanthe robusta robusta) robust spineflower 
     (Erysimum ammophilum) coast wallflower 
     (Horkelia marinensis) Point Reyes horkelia 

Associated Animals

     Plover 


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