Ecological site group description

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 is found on smooth, gently sloping, 0 to 10%, alluvial fans and flood plains subject to occasional overflow from local streams. They frequently occur in small or narrow valleys as long stringers.

Climate

The average annual precipitation in this area is 11 to 53 inches (272 to 1,353 millimeters). This ESG is influenced by coastal fog and averages over 30 inches a year in precipitation. The higher amounts of precipitation occur at the higher elevations in the area north of San Francisco. Most of the rainfall occurs as low- or moderate-intensity, Pacific frontal storms during winter. This area is very dry from midspring to midautumn. Snowfall is rare. The average annual temperature is 54 to 61 degrees F (12 to 16 degrees C). The freeze-free period averages 315 days and ranges from 265 to 365 days. It is longest near the coast, and it becomes shorter with elevation.

Soil features

The soils of this ESG are very deep, well drained and formed in alluvial materials derived from granitic rocks.

Representative soil is Farallone, a coarse-loamy, mixed, superactive, isomesic Cumulic Haplustoll.

Vegetation dynamics

This ESG attempts to describe the coastal scrub and coastal prairies near the coast of MLRA 14. 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 limited remaining soils that are not cultivated, grazed, or urban land. Future work will need to be done to better understand the soil and site characteristics that drive the vegetation expression more specifically.

This ESG is generally found in the valley bottoms near the coast intermixed with redwood and Douglas-fir mountains in MLRA 4B. This site is generally found below 1000 ft in small or narrow valleys on alluvial plains or in valley bottoms as long stringers with slopes less than 10%. The primary factors that maintain these sites in either coastal scrub or coastal prairie are the occasional overflows from local streams, they are well drained but have occasional seeps following the strata seams in the parent materials. Coastal scrub and herbaceous species are more readily able to colonize and stabilize and adapt to these conditions, which explains why they dominate these narrow valley soils.

The primary disturbances to this ecological site concept are hydrologic alterations (climate changes--decreasing fog influence, decreased yearly rains, extended droughts, etc.), fire, and grazing. Historically, lightning-ignited fires are thought to have occurred in the adjacent and associated 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. 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.

Major Land Resource Area

MLRA 014X
Central California Coastal Valleys

Stage

Provisional