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 encompasses all of the coastal shrublands found across the coastal ridgelines, rocky shallow slopes, and high wind bluffs of LRU I within MLRA 4B. Elevations typically range from sea level to 150 feet. Slopes vary considerably and aspects are generally south- or west-facing, but will also be found on exposed ridges or shallow slopes on all aspects.

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 low mountains of the Northern Franciscan Redwood Forest, LRU I, lie entirely within the coastal fog zone and are characteristically covered by fog-dependent coast redwoods and Douglas-fir. Historically, unbroken redwood forests occurred and moderated local climate by trapping coastal fog and producing shade. The combination of shade, root competition, young soils with a deep organic debris layer on the soil surface, occasional fire, and silting by floods limits the number of plant species that occur here.

Soil features

Soils vary but are typically mesic and finer-textured with skeletal subsurface horizons. They are well drained with low runoff. A representative soil for this ESG is Tsunami.

Vegetation dynamics

This provisional ecological site concept attempts to describe the coastal scrub areas of this LRU. They exist in a patchy dynamic of dense woody shrub cover and dense, tall herbaceous forbs and perennial grasses mainly along the coastal ridgelines, rocky shallow slopes, and high wind bluffs. As with much of California grasslands, introduced species have gained a significant presence across much of the variety of coastal scrub expressions contained within this ESG. This concept lumps many of the unique scrub expressions into one large concept, due to limited soil mapping that successfully parses out the differences between these types and focuses primarily on the abiotic factors and ecological dynamics that maintain and/or alter these vegetative communities. The extent of this ecological site concept stretches along the coastline portions of LRU I. 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 forests of LRU A and LRU I. This site is generally found below 1000 ft. on the low coastal plains and terraces adjacent to the coastal strand and beaches. The primary factors that prevent these sites from developing into forest are the unstable substrates and high, salty winds that are common along the coastline. Plants in this ESG are highly adapted to the warmer days that dry out the soils, salty air and high winds that are prohibitive of trees and other shrubs commonly found in the adjacent mountains.

Although the soils of this provisional site concept are highly varied, they all share the common variable of higher soil moisture content throughout the year and in most cases the soils within this concept are on harsher and more skeletal soils than those of the coastal scrub sites to the south and inland from the coast.

Primary Disturbances

The primary disturbances to this ecological site are landslides that occur because of a dominance of unstable soils and wet storm events that provide enough water to destabilize the soil/slopes. Native American use along these coastlines would also have likely included burning for various resource management objectives. However, because there are few or no trees in these ecological sites, determination of historic fire frequencies as recorded in tree growth rings is impossible. There is significant debate about appropriate fire intervals in these plant communities and how frequently tribal ignitions (which are known to have been frequent in much of California’s ecosystems) may have impacted these sites.

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley