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 mostly confined to the protected ravines, footslopes, and high stream terraces of LRU M where the coastal fog remains for the longest duration of time during the year and throughout the hot summers. Slopes range from 30-75% at elevations from 50 to 1700 ft.

Climate

The mean annual precipitation is about 30-50 inches, with average annual temperatures between 50 and 57 degrees F. Frost-free days are between 275 and 360 days.

The Point Reyes/Farallon Islands LRU 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 of this ESG are variable, but where this ecological site can be correlated to soils that have been mapped, the soils are isomesic, udic, loamy-skeletal alfisols on residuum weathered from sandstone. The cooler, maritime temperatures and protected aspects allow for higher retention of soil moisture during the hotter summer days, and the fog influence provides key moisture to the redwood foliage and soil moisture content as well.

A representative soil for this ESG would be Dipsea and Cronkhite soils. They are deep, well drained or moderately well drained soils with a loam or gravelly loam surface and clay loam subsoil. Both soils are underlain by weathered sandstones and shales.

Vegetation dynamics

This provisional ecological site concept attempts to describe the small remaining areas of coastal redwoods of this small LRU. This concept historically would have covered many other areas within this LRU, however land use and increases in overall temperature over the past 100 years have made it difficult for coast redwood to re-establish into much of its previous habitat, confining it down to areas that are not conducive to urban sprawl and maintain protection from late afternoon heat in the summers.

Abiotic Factors

This ecological site is generally found directly adjacent to the mountains of MLRA 15. It site is generally found below 1000 ft. and the primary factors that maintain these sites in coast redwood are the fog influence, protected slopes and northerly aspects that maintain higher soil moisture during the warm periods of the summer.

Primary Disturbances

Historically, the primary disturbance to this provisional ecological site concept was lightning-ignited fires, timber harvesting for settlement in San Francisco, and Native American burning. Lightning-ignited fires occur in coastal California and habitats of LRU M and MLRA 15 would have burned repeatedly over time across many soil types and landforms. Between soil and landform differences and frequencies and intensities of burning that would interact with interannual weather patterns, cultural burning and lightning storm events, this would have created a patchwork of areas with varying stages of vegetation structure and composition.

Timber harvesting during the gold mining era in California removed a lot of the old growth redwoods in the mountains that surround San Francisco. It’s strong, straight wood and height made it a prime species for harvest. Historically, the reference state for this ecological site would likely have been much more extensive before the harvesting of trees that were as easily accessible as they are in near proximity to San Francisco. As the fires became less and less frequent and harvesting slowed, redwood has re-established dominance in areas that were not as heavily impacted by the coastal winds and winter storms.

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley