Ecological site group R004BM201CA(15489)
Windy coastal beaches and dunelands
Last updated: 03/07/2025
Accessed: 03/15/2025
Ecological site group description
Key Characteristics
- West of the San Andreas fault line on the Pacific Plate – LRU M
- Soils that support upland rangeland vegetation
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
Physiography
Gently sloping to steep (2-50%) dunelands with elevations that range from sea level to 500 ft.
Climate
The average annual precipitation is 25-35 inches with annual average temperatures between 53-56 degrees F, and frost-free days from 300-365 days.
The Point Reyes/Farallon Islands LRU M includes the Point Reyes Peninsula, Bodega Head and the sand spit at the north end of Bodega Bay, and the offshore Farallon Islands. The maritime climate is temperate and humid, and fog often occurs. Heavy coastal winds are an influential factor in vegetation expression in this LRU that occur primarily in the summer months, explaining the large extent of coastal prairies and coastal scrub species along much of the coastline. Where trees are present along or near the coastline and within the reach of these heavy winds, the tree canopies form unidirectional windswept crowns.
Soil features
The soils in this group are dominantly near the coast. The dune lands are very deep, with very low available water capacity and formed dominantly by wind-blown deposits and range from loose dunes to somewhat stabilized dunelands, which are found on the Sirdrak soils. The Sirdrak soils are very deep, somewhat excessively drained with a surface horizon that is very dark grayish brown sand. Of minor extent it will also include beaches, Hydraquents, Kehoe, Sirdrak Variant, and Tomales soils.
Vegetation dynamics
This provisional ecological site concept attempts to describe the coastal scrub and coastal prairies of dunelands within this small LRU. They exist in a continuum of herbaceous to dense woody shrub cover wherever the cooling influence of the Pacific Ocean moderates the summer drought (high evapotranspiration rates). This concept lumps the unique scrub and prairie expressions into one large concept, due to no soils mapping within much of this LRU. The extent of this ecological site concept stretches along the coastline from approximately Bodega Bay sand spit south to the coastal bluffs near Bolinas. This provisional ecological site concept covers a narrower range of coastal scrub and prairie dynamics, however since there is no soils information for most of this LRU, future work will need to be done to better understand the soil and site characteristics that drive the vegetation expression for this provisional ecological site concept.
Abiotic Factors
This ecological site is generally found between the coastal strand and Douglas-fir-redwood and bishop pine forests of LRU M and LRU K. This site is generally found below 1000 ft. on the coastal strand, coastal dunes, and coastal plains and terraces. The primary factors that maintain these sites in either coastal scrub or coastal prairie are the unstable substrates and high, salty winds that are common along the coastline and their adaptability to the warmer days that dry out the soils too much for trees and other shrubs commonly found in the adjacent mountains. Coastal scrub and herbaceous species are more readily able to colonize and stabilize and adapt to these heavy winds and salty conditions, which explains why they dominate these open plains along the coastline.
Primary Disturbances
The primary natural disturbances to this ESG are fire and wildlife grazing and unstable soils. Historically, lightning-ignited fires are thought to have occurred in the surrounding forested habitats every 30-135 years and with the winds, would have burned significant acres across many soil types and landforms. Between soil and landform differences and frequencies and intensities of burning that would be interacting with yearly weather patterns that shifted between wet years to drier years, this would have created a patchwork of areas that returned over time to forest while others remained in coastal scrub and grassland. It is also believed that native grazers were common in these lower gradient coastal plains and may have contributed to the open nature and complex patchwork of coastal scrub and prairies. In combination with the fires and periodic droughts, grazers may have assisted in maintaining areas with good soils in more herbaceous vegetation and the less ideal soils in a more coastal scrub and grass patchwork expression. Native American use along these coastlines would also have included burning to maintain as much of the coastal prairies as possible, often times quite frequently to improve hunting and grass and forb production for plant harvesting.
Grazing has had a much more significant influence on this ESG in the more recent history within LRU M, as there are several historic ranching operations and small dairies sharing this areas forage and covering most of the coastal prairie and coastal scrub shrublands in this LRU. This has assisted in maintaining some of the more diverse coastal prairie native perennial grasslands left in the state since burning is no longer occurring, due to the yearly removal of biomass by the native and livestock grazers that allow the perennials to be more competitive with the invasive species pressures that are a common threat to this ecological site. Livestock grazing was grandfathered into the land uses of the Point Reyes National Seashore and continues today, however some of the historic ranches no longer operate cattle and those areas have become more heavily dominated by coastal scrub species over time. However, the tule elk herd and invasive albino deer that can be found in this area have helped maintain large areas of the coastal prairie where cattle no longer graze.
Historically, this ecological site would likely have been much more extensively covered by the coastal prairies due to the repeated burnings by many of the coastal tribes and the scrub species would have likely been more confined to the rocky bluffs, steep slopes, and exposed ridges. As the fires became less and less frequent, the coastal scrub species was able to encroach back into the prairies and dominate much of the coastline. Areas where grazing still occurs either by livestock or native grazers, tend to maintain the open prairies, however they have become a mix of native perennials and forbs and annual grasses and forbs since the introduction of the non-native seed sources and heavy pressures from grazing. Fire to this ecological site is less likely now, due to the urban development and cultivation of much of these areas along the coast.
The sandy beaches and dunes have been lumped into this site concept. They are a narrow portion of this LRU and since there are no soils to correlate to, the groupings are coarse and it was determined that for now, there would only be one site for this area of LRU M. The beaches and dunes do support a unique assemblage of species. The dunes rise above the reach of the highest tides and are exposed to the strong summer winds. To keep from being completely buried by sand, beach strawberry and beach morning glory can grow up new shoots from horizontal underground stems. The sand has few nutrients available for plants, so dune lupine allows special bacteria into its roots that converts nitrogen in the soil into a form plants can use. Much of the grass that is currently found in these dunes is European beachgrass, a highly invasive. Iceplant, native to South Africa, has likewise colonized a large portion of these dunes, thanks to its fleshy leaves that prevent water loss and help it outcompete native vegetation (Point Reyes National Seashore website, accessed 4/20/18).
Barbour, M. G. 1978. Salt Spray as a Microenvironmental Factor in the Distribution of Beach Plants at Point Reyes, California. Oecologia 32:213–224.
Barbour, M. G., T. Keeler-Wolf, and A. A. Schoenherr (Eds.). 2007. Terrestrial Vegetation of California. University of California Press.
Buell, A. C., A. J. Pickart, and J. D. Stuart. 1995. Introduction History and Invasion Patterns of Ammophila arenaria on the North Coast of California. Conservation Biology 9:1587–1593.
Carboni, M., R. Santoro, and A. T. R. Acosta. 2010. Are some communities of the coastal dune zonation more susceptible to alien plant invasion? Journal of Plant Ecology 3:139–147.
D’Antonio, C. M., and B. E. Mahall. 1991. Root Profiles and Competition between the Invasive, Exotic Perennial, Carpobrotus edulis, and Two Native Shrub Species in California Coastal Scrub. American Journal of Botany 78:885–894.
Hardy, M. A., and M. A. Colwell. 2012. Factors Influencing Snowy Plover Nest Survival on Ocean-Fronting Beaches in Coastal Northern California. Waterbirds 35:503–656.
National Park Service Staff. 2015. Coastal Dune Restoration Environmental Assessment. Point Reyes National Seashore, USDI-National Park Service, Washington, DC.
Pardini E.A. et al. 2015. Early Successional Microhabitats Allow the Persistence of Endangered Plants in Coastal Sand Dunes. PLoS ONE 10(4): e0119567. doi:10.1371/journal.pone.0119567.
Soil Survey Staff. 1985. Soil Survey of Marin County Area, California. USDA-Natural Resources Conservation Service, Washington, DC.
Web Soil Survey. USDA-Natural Resources Conservation Service, https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx, Accessed October 24, 2019.
Major Land Resource Area
MLRA 004B
Coastal Redwood Belt
Stage
Provisional
Contributors
Kendra Moseley
) icon wherever it occurs. Drag and drop items to reorder. Cookies are used to store briefcase items between browsing sessions. Because of this, the number of items that can be added to your briefcase is limited, and briefcase items added on one device and browser cannot be accessed from another device or browser. Users who do not wish to place cookies on their devices should not use the briefcase tool. Briefcase cookies serve no other purpose than described here and are deleted whenever browsing history is cleared.Click on box and path labels to scroll to the respective text.
