Natural Resources
Conservation Service
ecological site group R004BL200CA
Windy coastal perennial grassland terraces and bluffs
Accessed: 09/15/2026
Ecological site group description
Key Characteristics
- Elevated coastal plains
- Dissected coastal plateaus with high acidity – LRU L
- Soils that support upland perennial rangelands
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
This ESG encompasses the varied expressions of perennial grasslands that can be found within LRU L. They are found on the mountains and fluviomarine terraces within the coastal fog influence. Slopes are varied, and aspect does not appear to play a role at this scale.
Climate
The average annual precipitation in this mLRA is 23 to 98 inches (585 to 2,490 millimeters), increasing with elevation inland. Most of the rainfall occurs as low-intensity, Pacific frontal storms. Precipitation is evenly distributed throughout fall, winter, and spring, but summers are dry. Snowfall is rare along the coast, but snow accumulates at the higher elevations directly inland. Fog is a significant variable that defines this MLRA from other similar MLRAs. Summer fog frequency values of greater than 35% are strongly correlated to the extent of coast redwood distribution, which is a primary indicator species in this MLRA. Nightime fog is approximately twice as common as daytime fog and seasonally, it reaches its peak frequency in early August, with the greatest occurrence of fog from June through September (Johnstone and Dawson 2010). The average annual temperature is 49 to 59 degrees F (10 to 15 degrees C). The freeze-free period averages 300 days and ranges from 230 to 365 days, decreasing inland as elevation increases.
The Fort Bragg/Fort Ross Terraces form an elevated coastal plain that has less relief (200-800 feet) than the adjacent low elevation mountains of LRU K. Monthly and annual temperature variations are minimal and summer fog is common.
Soil features
Although the soils of this provisional site concept are highly varied, they all share the common variable of high salt content and almost all are found on Mollisol soils that have thicker, more organically rich horizons than those of the coastal scrub sites to the south and inland from the coast. The cooler, maritime temperatures allow for more soil moisture during the hotter summer days, and the organic matter turnover is greater in these scrub and prairie communities as a result.
The soils found on the mountains and upland landforms are most represented by Abalobadiah, Bruhel and Vizcaino. These are all isomesic, typic fine-loamy or loamy soils that are in the Argiustoll family. These soils all have a water table at greater than 72 inches.
The soils on the fluviomarine terraces and river valley stream terrace landforms are most represented by Boontling, Mallopass, and Windyhollow which are thermic or isomesic, typic fine-loamy, fine or coarse-loamy textures and are in the Argixeroll and Argiustoll families. These soils also have a water table from approximately 21 - 60 inches.
Vegetation dynamics
This provisional ecological site concept attempts to describe the coastal scrub and coastal prairies of 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 many of the unique scrub and prairie expressions into one large concept, due to limited soil mapping that successfully parses out the differences between these types and focuses primarily on the primary abiotic factors and ecological dynamics that maintain and/or alter these vegetative communities. The extent of this ecological site concept stretches along the coastline from approximately Fort Bragg to Bodega Bay. This provisional ecological site concept covers a wide variety of coastal scrub and prairie dynamics and expressions that will need to be further refined to better represent dynamics on a smaller, more ecologically specific scale.
Abiotic Factors
This ecological site is generally found between the coastal strand and redwood and Douglas-fir forests of LRU K. This site is generally found below 800 ft. on the low coastal terraces and bluffs adjacent to the coastal strand and beaches. The primary factors that maintains these sites in either coastal scrub or coastal prairie are the moist, organic-rich soils that also experience heavy, salt-laden winds that are common along this part of the coastline. 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 and trees do not.
Primary Disturbances
The primary disturbances to this ecological site concept are the harsh, heavy salt-laden winds, grazing, and fire. 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. 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.
Major Land Resource Area
MLRA 004B
Coastal Redwood Belt
Stage
Provisional
Contributors
Kendra Moseley
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