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

The ESG is found on marine terraces and fluviomarine terraces close to the ocean on mostly gentle slopes (<15%) at elevations below 1,000 feet. It is mainly found between the ocean and the first main north-south ridge, where frequent heavy summer fog and sea spray are intercepted by a tree canopy, adding a significant amount of moisture to the soil.

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

Eolian sand deposits and depth to water table provide the growing conditions more suitable for Bishop pine and a less stunted pygmy cypress and shrubs to dominate. Representative soils are Cleone and Tregoning, both coarse-loamy soils that have an effective rooting depth that is limited by saturation for brief or long periods following episodes of heavy rain from December through April. The saturated zone starts between the depths of 30 and 48 inches and extends to a depth of more than 60 inches. These soils are nutrient poor and extremely acidic (<4.5 pH), contributing greatly to the stunted and twisted growth forms of the vegetation.

Vegetation dynamics

This provisional ecological site concept attempts to describe the basic understanding of the very acidic terraces of LRU L. This concept is primarily supported through literature and available information from the Mendocino County Survey. This provisional ecological site concept covers the specific marine terraces that are very acidic and have a water table between 20-40 inches and are generally somewhat poorly drained. They are within close proximity to the coast and at the lower elevations that spend longer periods within the summer coastal fog. This site is similar to F004BL100CA, however the greater depth to water table and slightly less extreme acidity are both significant enough to impact vegetation composition and increase vegetation production. It is also commonly associated with F004BL100CA and F004BL102CA. 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.

This ecological site is a unique area within LRU L found on wave cut marine terraces that have restrictive horizons which perch water and are very low in pH. Hesperocyparis pygmaea (pygmy cypress) and Pinus muricata (Bishop pine) dominate the shallow and acidic soils within these wave cut terraces.

Soils have water available for plant growth most or all of the year, and average soil temperatures at a depth of 20 inches vary by less than 5 degrees C between summer and winter.

Primary Disturbances

The primary disturbance to this ecological site is urbanization and human developments that either de-water the site or completely obliterate it. Fire plays a prominent role in the life history and reproductive patterns of bishop pine, which is a prominent species in this ESG. Bishop pine is a serotinous, closed cone species, meaning some or all of its cones are locked shut until high heat loosens the resin coating the cones, unlocking seed chambers and allowing seed to be dispersed in large quantities following fire. Similar to other closed cone species, fires in bishop pine forests are often high intensity and stand replacing, though serotiny tends to be less pronounced in the northern portion of this species’ range (Cope, 1993). This fire relationship is suggestive of historic fire occurrence in this ESG, but the frequency of fire among the bishop pine in this area is unclear and not well studied. Historically, fires caused by a mix of lightning, tribal burning and early ranching were common in coastal mountains of northern California.

Citations

Cope, Amy B. 1993. Pinus muricata. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/tree/pinmur/all.html [2025, March 6].

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley