Natural Resources Conservation Service Ecological site R018XI103CA Thermic Ultramafic Foothills Moderately High Magnesium Content (Ca:Mg Ratio 0.5 To 2) Accessed: 09/24/2021 General information Approved. An approved ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model, enough information to identify the ecological site, and full documentation for all ecosystem states contained in the state and transition model. Figure 1. Mapped extent Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated. 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 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 18 to 40 inches in most of the area (precipitation generally increases with elevation and from south to north). 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. Due to extreme latitudinal differences in MLRA 18, Land Resource Units (LRUs) were designated to group the MLRA into similar land units. LRU Description: This LRU (designated XI) is located on moderate to steep mountains and hills in the Sierra Nevada Foothills. It also includes mesa formations from volcanic flows, where vernal pool habitats occur. Various geologies occur in this region: metavolcanics, granodiorite, slate, marble, argillite, and quartzite, as well as ultramafic bands to a limited and localized extent. Soil temperature regime is thermic and soil moisture regime is xeric. Elevation ranges between 300 and 2000 ft above sea level. Precipitation ranges from 18 to 42 inches annually. Most precipitation falls between the months of November and March in the form of rain. Dominant vegetation includes annual grasslands, blue oak (Quercus douglasii), interior live oak (Quercus wislizeni), chamise (Adenostoma fasciculatum), buckbrush (Ceanothus cuneatus), and California foothill pine (Pinus sabiniana). 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), 261Ca, the Western Foothills 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 6b, Northern Sierran Foothills. Nature Conservancy Biophysical Setting is the California Xeric Serpentine Chaparral (NaturServ, 2015). Ecological site concept Ultramafic bedrock is characterized by its low Ca:Mg ratios and high heavy metal accumulations and is thus toxic to many plants; it is usually associated with stunted growth or reduced productivity. The Ca:Mg ratio for this ecological site ranges from 0.5 to 2 in the subsurface horizons . The influence of soil chemistry is readily apparent by virtue of its influence on vegetation composition, production, and species distribution. The plant communities in this ecological site are strikingly different than the adjacent non-serpentinite derived soils, (shifting from blue oak woodland to chamise chaparral on serpentinite; see McGahan et al., 2009 and Kruckenburg, 1984). The parent material is easily identifiable as having minerals associated with serpentine vegetation (i.e. olivine, pyroxene, lizardite, peridotite, serpentinite). This ecological site is constrained by parent material that is slightly less toxic to plant life than other ultramafic ecological sites within the Sierra Nevada Foothills, which have lower Ca:Mg ratios (less than 0.5). The shrub component is the dominant functional group in most of the community phases. In this ecological site, chamise (Adenostoma fasciculatum) form dense near monocultures, while buckbrush (Ceanothus cuneatus), California yerba santa (Eriodictyon californicum), buckthorn (Rhamnus spp.), and manzanita (Arctostaphylos spp.) are present in lower quantities. Forbs and grasses are usually sparse, except in the post-fire community phase. The production RV is about 615 lbs per acre and ranges between 436 and 1280 lbs per acre. Associated sites R018XI102CA Thermic Ultramafic Foothills Extremely High Magnesium Content (Ca:Mg Ratio Less Than 0.5) This site occurs on hill slopes with lower Ca:Mg ratios (0.05 to 0.5), and have therefore more toxic effects to plant life (lower annual production and different species compositions). Buckbrush (Ceanothus cuneatus) and California foothill pine (Pinus sabiniana) are the most common species. R018XI104CA Thermic Ultramafic North-Facing Steep Slopes This site occurs on adjacent, steep (60-90%) north-facing hill slopes. Ca:Mg ratios are variable in this site. A diverse array of shrubs are present (toyon (Heteromeles arbutifolia), manzanita (Arctostaphylos spp.), buckbrush (Ceanothus cuneatus), and buckthorn (Rhamnus spp.)) often in the understory of dense California foothill pine. Table 1. Dominant plant species Tree Not specified Shrub (1) Adenostoma fasciculatum (2) Eriodictyon californicum Herbaceous Not specified Physiographic features This ecological site likely occurs in ultramafic bands extending among throughout the entire Sierra Nevada Foothill region. However, the ecological dynamics are specific to ultramafic bands in the northern foothills LRU and is most recognizable from Tuolumne to Placer Counties, CA. The ecological site occurs on loamy to loamy-skeletal soils on footslopes and backslopes of all aspects and slope gradient ranges between 3 and 60% (central tendency is between 15 and 35 % slope). Soils occur on elevations between 300 and 1,730 feet above sea level (central tendency is between 800 to 1150 feet). Table 2. Representative physiographic features Landforms (1) Hill Elevation 91–527 m Slope 3–60% Climatic features This ecological site is a found in a broad Mediterranean climatic region, with hot, dry summers and cool, wet winters. Mean annual precipitation is around 27.5 inches and ranges between 22 to 33 inches per year, mostly occurring between November and April in the form of rain. Mean annual air temperature ranges between 48 and 74 degrees F. The frost free period is 213 to 223 days and the freeze-free period is approximately 217 to 235 days. Maximum and minimum monthly climate data for this ESD were generated by the Climate Summarizer (http://www.nm.nrcs.usda.gov/technical/handbooks/nrph/Climate_Summarizer.xls) using data from the following climate stations (equally weighted): 41428 Camp Pardee (Period of record = 1959 to 2014) 46172 New Melones Dam (Period of record = 1992 to 2014) 48713 Sutter Hill CDF (Period of record = 1999 to 2014) The data from multiple weather stations were combined to most accurately reflect the climatic conditions of this ecological site. The New Melones Dam weather station is in a nearby area, but is at slightly higher elevation, and precipitation was considerably higher. The selection of Camp Pardee and Sutter Hill CDF had lower precipitation but are located further north, where the central tendency of the site occurs. Table 3. Representative climatic features Frost-free period (average) 218 days Freeze-free period (average) 226 days Precipitation total (average) 711 mm Influencing water features Soil features The soils in this ecological site are formed from the colluvium and residuum of serpentinite and other ultramafic rock. Soils are shallow (17% of mapped area) to moderately deep (83 % of mapped area), and have loamy-skeletal textures. The bedrock is a restrictive layer found between 10 and 39 inches of depth. Gravels (< 3 inch diameter) range between 0 to 10 % cover, while larger fragments (>= 3 inch diameter) are 0 to 18 % cover. Subsurface gravels range between 2 to 22 % and larger fragments occupy 7 to 26 % by volume. The soils in this ecological site are well-drained to excessively well-drained and the permeability class ranges from slow to very slow. The most commonly occurring soil component in the map units outlined below is Crimeahouse (loamy-skeletal, smectitic, thermic Mollic Haploxeralfs). This ecological site is also associated with major component of Hennekenot (loamy-skeletal, mixed, superactive, thermic Lithic Argixerolls) and Henneke (clayey-skeletal, magnesic, thermic Lithic Argixerolls. The primary difference between the Crimeahouse of soils and Hennekenot/Henneke suite of soils is the depth class (moderately deep and shallow, respectively) and the thickness of the mollic epipedon (the Hennekenot/Henneke soils having a thicker and possibly more organic input than the Crimeahouse soils). Henneke soils differ from Hennekenot by the magnesic mineralogy class and soils of a higher clay content. The common characteristic shared by all soils in this ecological site is the high level of magnesium relative to calcium. The Ca:Mg ratio of subsurface