California Serpentine Grassland

These grasslands are of very limited distribution in California within the Coast Ranges, Sierra Nevada, and Transverse Ranges on deep soils with serpentine-rich parent material. Not all serpentinite outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition. In this system, native bunchgrass dominates, though typically in less dense cover than other perennial bunchgrass types. Characteristic species include Calamagrostis ophitidis, Eschscholzia californica, Vulpia microstachys var. ciliata (= Festuca grayi), Poa secunda (= Poa scabrella), Hemizonia congesta ssp. luzulifolia (= Hemizonia luzulifolia), Nassella cernua, and Nassella pulchra. Historic fire regimes in this system are not well known.

This ecosystem occurs on deep soils with serpentine-rich parent material. Not all serpentinite outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition.

Serpentine soils are relatively infertile soils and mycorrhizal relationships are considered important to plant survival (Jimerson et al. 1995). Hopkins 1986 (as cited in Jimerson et al. 1995) found that 98% of the herbaceous plants in the serpentine grassland communities of the Santa Cruz Mountains were mycorrhizal. Ectomycorrhizae are often associated with members of the Ericaceae family, a well-represented family in the serpentine flora (Jimerson et al. 1995).

Conversion of this type has commonly come from mining and geothermal power development, agricultural and timber development. Common stressors and threats include mining and geothermal power development, agricultural and timber development, shrub-removal land management practices and application of fertilizer, seeding of palatable grasses, and severe erosion following intensive land use (Kruckberg 1984). Nitrogen deposition in serpentine areas adjacent to urban zones like the south Bay Area where N fallout has contributed to the increase of non-native grasses such as Lolium perenne which is out competing some of the native species essentially through fertilizing the soil (Weiss 1999).

The projected impacts of climate change on thermal conditions in northwestern California (where most but not all serpentine grasslands are located, but serves as a good representation of the type of projected change for much of California) mean annual temperature increases of 1.7-1.9°C by 2070. For the same time period mean diurnal temperature range will be warmer winter temperatures, earlier warming in the spring, and increased summer temperatures. Regional climate models project a decrease in mean annual rainfall of 101 to 387 mm by 2070. Currently, there is greater uncertainty about the precipitation projections than for temperature in northwestern California, but with some evidence for a slightly drier future climate relative to current conditions (PRBO Conservation Science 2011). Decreased precipitation and higher summer temperature may result in lower biomass production and loss of plant vigor over all of the grassland ecosystem.

This system is found in the Coast Ranges, Sierra Nevada, and Transverse Ranges of California on deep soils with serpentine-rich parent material. It may also occur on serpentine in the Klamath Mountains of southern Oregon.