General information

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.

MLRA notes

Major Land Resource Area (MLRA): 018X–Sierra Nevada Foothills

Major Land Resource Area (MLRA) 18, Sierra Nevada Foothills is located entirely in California and runs north to south adjacent to and down-slope of the west side of the Sierra Nevada Mountains (MLRA 22A). MLRA 18 includes rolling to steep dissected hills and low mountains, with several very steep river valleys. Climate is distinctively Mediterranean (xeric soil moisture regime) with hot, dry summers, and relatively cool, wet winters. Most of the precipitation comes as rain; average annual precipitation ranges from 15 to 55 inches in most of the area (precipitation generally increases with elevation and from south to north). Soil temperature regime is thermic; mean annual air temperature generally ranges between 52 and 64 degrees F. Geology is rather complex in this region; there were several volcanic flow and ashfall events, as well as tectonic uplift, during the past 25 million years that contributed to the current landscape.
 

LRU notes

The Tuscan Flows LRU is the northernmost Land Resource Unit in MLRA 18. It occurs down slope of and is geologically related to the southern Cascades; however, its inclusion in MLRA 18 stems from the ecosystem’s close resemblance to other Sierra Nevada Foothill systems. This LRU is situated on a low elevation volcanic plateau at the northeast end of the Sacramento Valley. The geology includes, but not limited to late Pliocene and Quartenary basalt, andesite and andesitic lahars (mudflows). Several cinder cones dot the landscape and active fluvial processes are occurring in the larger canyons. Elevation generally ranges between 250 and 2000 feet above sea level, but can range as high as 3000 feet on the highest hills. Precipitation is among the highest in MLRA 18, ranging from 30 to 55 inches annually. Mean annual air temperature ranges between 56 and 62 F. Frost free days (generally exhibiting an inverse relationship with elevation) range from 184 to 282 days.

Classification relationships

CLASSIFICATION RELATIONSHIPS
This site is located within M261F, the Sierra Nevada Foothills Section, (McNab et al., 2007) of the National Hierarchical Framework of Ecological Units (Cleland et al., 1997), M261Fa, the Tuscan Flows Subsection.

Level III and Level IV ecoregions systems (Omernik, 1987, and EPA, 2011) are: Level III, Central California Foothills and Coastal Mountains and Level IV, Ecoregion 6a, Tuscan Flows.
 

Ecological site concept

This site is characterized by shallow soils derived from mudflow breccia and other volcanic rocks. It occurs on undulating to hilly volcanic ridges and sideslopes of hills. The soil temperature regime is thermic. Slope gradient typically ranges from 5 to 40%. Mean annual precipitation typically ranges from 31 to 44 inches, and elevation ranges from 460 to 2050 feet.

The overriding abiotic factors on this site controlling vegetation expression are shallow, sometimes rocky soils with very low available water capacity (< 3 inches). These conditions prevent the establishment of woody vegetation and the vegetation community is dominated by annual herbaceous plants. Common soil components for this ecological site include the Inks and Toomes series. Inks soils (Loamy-skeletal, mixed, superactive, thermic, shallow Ultic Argixerolls) are shallow soils formed in material weathered from consolidated or cemented sediments from volcanic rocks. Toomes (Loamy, mixed, superactive thermic Lithic Haploxerepts) are very shallow and shallow soils formed in material weathered from tuff breccia, basalt, and andesite.

This vegetation community consists of annual grasses and forbs with very few trees or shrubs. Occasional blue oak (Quercus douglasii) occur, but they are most common in deeper soils. Dominant plants for this site include soft brome (Bromus hordeaceus), wild oat (Avena fatua), and Italian ryegrass (Lolium perenne spp. multiflorum). Annual production data is lacking for this site, but seems to be heavily skewed towards greatest production of herbaceous annual plants (especially annual grasses).

Associated sites

Similar sites

Table 1. Dominant plant species