California Dry Serpentine Chaparral

This ecological system occurs throughout Mediterranean California (excluding far southern California) on thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils and in areas below winter snow accumulations that typically experience hot and dry summers. Not all ultramafic outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition. This system is highly variable and spotty in distribution. Characteristic plant species include Hesperocyparis macnabiana, Quercus durata, Arctostaphylos viscida, Arctostaphylos pungens, and Arctostaphylos glauca. Common associates include Adenostoma fasciculatum, Ceanothus cuneatus, Fremontodendron californicum, Quercus sadleriana, Quercus vacciniifolia, Garrya spp., Umbellularia californica, Ceanothus pumilus, Frangula californica, and Arctostaphylos nevadensis. California endemics such as Ceanothus jepsonii also occur. Pinus sabiniana can occur at varying cover from trace to more abundant. Many locally endemic and often rare forbs can occur, such as Streptanthus spp., Hesperolinon spp., Eriogonum spp., Madia spp., Mimulus spp., Allium spp., and Asclepias solanoana. This chaparral type tends to have fewer trees than mesic chaparral.

Characteristic plant species include Hesperocyparis macnabiana (= Cupressus macnabiana), Quercus durata, Arctostaphylos viscida, Arctostaphylos pungens, and Arctostaphylos glauca. Common associates include Adenostoma fasciculatum, Ceanothus cuneatus, Fremontodendron californicum, Quercus sadleriana, Quercus vacciniifolia, Garrya spp., Umbellularia californica, Ceanothus pumilus, Frangula californica (= Rhamnus californica), and Arctostaphylos nevadensis. California endemics such as Ceanothus jepsonii also occur. Pinus sabiniana can occur at varying cover from trace to more abundant. Many locally endemic and often rare forbs can occur, such as Streptanthus spp., Hesperolinon spp., Eriogonum spp., Madia spp., Mimulus spp., Allium spp., and Asclepias solanoana. This chaparral type tends to have fewer trees than mesic chaparral.

This system occurs on thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils and in areas below winter snow accumulations that typically experience hot and dry summers. Not all ultramafic outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition. Soils on ultramafics are usually shallow and skeletal, with little profile development. Ultramafic soils impose the following stresses on plants: imbalance of calcium and magnesium, magnesium toxicity, low availability of molybdenum, toxic levels of heavy metals, sometime high alkalinity, low concentrations of some essential nutrients, and low soil water storage capacity (Sanchez-Mata 2007). In some cases, the steepness of the slopes and general sparseness of the vegetation result in continual erosion.

Landfire (2007a) model: Due to the poor soil nutrient levels, biomass accumulation tends to be significantly lower in these serpentine systems than in neighboring patches of sandstone chaparral. As a result, fire frequency and fire severity are reduced. A study at the McLaughlin Reserve (Safford and Harrison 2008) found that time since last fire was nearly four times longer than on non-serpentine sites, and severity was also significantly reduced. The effects of fire on diversity in these systems are less pronounced than in non-serpentine systems, though they may be longer lasting (Safford and Harrison 2004); these authors found that few species on serpentine depended on fire for germination.

Conversion of this type has commonly come from residential and urban development, mining. Many occurrences have been modified by mining, clearing, or other development activities. Ericameria nauseosa colonizes disturbed sites easily, so managers used it in restoration projects. Because shrubs on serpentine are more fire-sensitive and may recruit slowly, they may be especially susceptible to excessively frequent or poorly-timed fires (Parker 1990). Exotic plant species are not a problem in this ecological system because of the nutrient-poor soils.

In the west central coast regions, regional climate models project mean annual temperature increases of 1.6-1.9°C by 2070. The projected impacts will be warmer winter temperatures, earlier warming in spring and increased summer temperatures. Regional models project a decrease in mean annual rainfall of 61-188 mm by 2070. While there is greater uncertainty about the precipitation projections than for temperature, some projections call for a slightly drier future climate relative to current conditions (PRBO Conservation Science 2011). Potential climate change effects could include (PRBO Conservation Science 2011): deep-rooted or phreatophytic species under greater stress and death; drop in groundwater table; more and larger fires; increased fire frequency due to warmer temperatures resulting in drier fuels; increased invasive species due to lack of competition from native species whose vigor is reduced by drought stress, and increased fire intervals favor certain invasive species (Brooks and Minnich 2006); increases in the areal extent of grasslands and concomitant reductions in the extent of chaparral, sage scrub, and oak woodlands; and increased competition for water from all users, and stresses on the already overtaxed water allocation of California agricultural system (PRBO Conservation Science 2011).

This system occurs throughout Mediterranean California (excluding far southern California) into Oregon, on thin, rocky, ultramafic soils.