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 in the dry loamy alluvial soils in the valley basins, fans, and flood plains. Slopes range from 0 to 2% most typically.

Climate

The average annual precipitation in this area is 11 to 53 inches (272 to 1,353 millimeters). Typical averages for this ESG are 16 inches or less. 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 thermic, very deep or deep, somewhat poorly, poorly and well drained drained soils formed in nearly level basins from alluvium from various sources. Soil textures range from clay loams, silt loams to coarse loams. Future work to separate out the drainage classes and finer-textures and coarser textures would be beneficial for management and ecological processes, however much of this site is under cultivation making it more difficult to build ecological site concepts.

Some representative soils include:

Bayshore, a fine-loamy, mixed, superactive, thermic Typic Calciaquolls
Elder, a coarse-loamy, mixed, superactive, thermic Cumulic Haploxerolls
Mocho, a fine-loamy, mixed, superactive, thermic Fluventic Haploxerolls
Pacheco, fine-loamy, mixed, superactive, thermic Fluvaquentic Haploxerolls
Sorrento, a fine-loamy, mixed, superactive, thermic Calcic Haploxerolls

Vegetation dynamics

This ESG covers the areas of the valleys in MLRA 14 that were at one time part of a vast complex of marshes, tidal flats, estuaries, wetlands and wet meadows. The urbanized landscape in the valleys within this MLRA that exists today makes it difficult to imagine the natural landscape prior to human development.

These dry loamy bottoms were likely the mostly fine- loamy-textured depressional and deposition areas and isolated oxbows that were created from the network of freshwater and salt marshes, rivers and streams that ran through these valleys as their seasonal and tidally influenced flood waters stretched across the floodplains and terraces in spring and deposited sediment as they receded during summer. Once the area began to be settled, many of these water dominated ecosystems were drained, leveed, cleared for crops and other agriculture, and urbanized.

As this landscape was de-watered and houses and agriculture took over, the water table for many of these habitats moved deeper and deeper, creating soils that would no longer offer the available soil moisture for many of the plants that had evolved with the hydrologic function of the natural system that no longer existed. These loamy basins may have remained wetter than many of the surrounding soils, due to their prolonged available water capacity and their depressional location on the landscape. The variable range in soil textures will dictate the species composition and production, with the finer soils holding more water that results in more native perennials and forbs and higher annual production overall. The coarser textures will dry out more rapidly through both drainage and evapotranspiration in the summer months making them less hospitable for many of the native perennial grasses and more dominated by annual grasses and forbs. Annual production will still be higher than the other ESGs in bottoms, due to the loamy textures which provide decent available water and slightly slower but still well drained soil conditions.

Historically, this site may have looked similar to the CWHR wet meadow classification, however with the introduction of non-native annual grasses and the impacts from fragmentation, continued de-watering, cultivation, and human alterations such as homes and roads, this site now reflects a lower producing, dry, annual grassland.

Currently, where this site is not under cultivation or urban developments, it is dominated by non-native annual grasses. These include wild oats, soft chess, ripgut brome, red brome, wild barley, and foxtail fescue. Common forbs include broadleaf filaree, redstem filaree, turkey mullein, true clovers, bur clover, popcorn flower, and many others. Perennial grasses, found in moist, lightly grazed, or relic prairie areas, include purple needlegrass and blue wildrye and areas of intermittent ponding will be have sedges and rushes. Species composition is also related to water availability with greater amounts of relic perennial grasses in areas of greater precipitation or soil moisture.

Information from:
John G. Kie
California Wildlife Habitat Relationships System
California Department of Fish and Game
California Interagency Wildlife Task Group

Major Land Resource Area

MLRA 014X
Central California Coastal Valleys

Stage

Provisional