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

LRU 18XC is located on moderate to steep mountains and hills in the Sierra Nevada Foothills east of Fresno, CA. The major differences between the southern and northern foothills are the dryer climate (12 to 37 inches of annual precipitation), greater summer/winter temperature variation, and steeper topography of the southern foothills. The geology of this region is predominately granitoid. The elevation ranges between 300 and 4100 feet above sea level. Warmer temperatures and lower precipitation (than at higher latititudes) allow for blue oak grasslands to exist at higher elevations. The soil temperature regime is primarily thermic, however some mesic soils are found at higher elevations of 18XC. At these upper elevations, the break in soil temperature regime (between thermic and mesic) is highly aspect dependent. Southern and western aspects at the steep, high elevations promote chamise-yucca plant assemblages. Buckeye is common in the concave positions. Riparian trees that are generally absent from the northern LRU’s include California Sycamore (Plantanus racemosa) and lemon scented gum (Eucalyptus citriodora).

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), M261Fc, the Lower Granitic Foothills and M261Fd, Southern Granitic Foothills Subsections.

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 6c, Southern Sierran Foothills.

Ecological site concept

This site is characterized by moderately deep to very deep soils occurring on all hillslope positions except toeslopes on foothills and mountains formed from granitic parent material. Slopes typically range from 6 to 60%. Annual precipitation typically ranges from 23 to 27 inches per year. Elevation typically ranges from 1000 to 4350 feet.

The high available water capacity associated with these moderately deep to very deep soils leads to productive woodlands. However, soils derived from granitic materials tend to be subject to erosion because of their coarse-textured surface horizons. This becomes more apparent in chaparral dominated states, where intense fires are more common. The most representative soil components include Ahwahnee and Sierra. Production can be expected to be lower on the Ahwahnee soils due to the coarse-loamy and relatively shallow soil when compared to Sierra, however both soils would likely respond similarly to disturbance and management, particularly after erosion. Sierra soils may favor slightly larger trees, especially in the undisturbed state and in the lower sloping positions. Ahwahnee soils are moderately deep and are classified as coarse-loamy, mixed, active, thermic Mollic Haploxeralfs. Sierra soils are very deep and are classified as fine-loamy, mixed, active, thermic Ultic Haploxeralfs.

Vegetation includes open oak woodland with scattered California foothill pines (Pinus sabiniana) and buckbrush (Ceanothus cuneatus). Blue oak (Quercus douglasii) tends to be dominant in the overstory component. Scattered interior live oak (Quercus wislizeni) also occurs. Herbaceous annuals such as soft chess (Bromus hordeaceus), ripgut brome (Bromus diandrus), wild oat (Avena fatua), and fillaree (Erodium spp.) tend to dominate in the understory and collectively range from 2000 to 3500 lbs per acre.

Associated sites

Similar sites

Table 1. Dominant plant species