California Moist Serpentine Woodland and Chaparral

This ecological system occurs in Mediterranean California in the north and south Coast Ranges and the northern Sierra Nevada, on cool northerly and concave slopes and toeslopes with thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils. Not all ultramafic outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition. These systems are highly variable and spotty in distribution, and the composition of individual stands can be very diverse, especially the shrubs (often individual species have low cover). Hesperocyparis sargentii, Pinus sabiniana, Garrya congdonii, Quercus durata, Umbellularia californica, and Frangula californica ssp. tomentella are characteristic. Common associates include Heteromeles arbutifolia, Adenostoma fasciculatum, and the California endemics Arctostaphylos viscida ssp. pulchella and Ceanothus jepsonii. In some settings Arctostaphylos glauca, Styrax redivivus, or Cercocarpus montanus var. glaber can be common. Occasionally, Chamaecyparis lawsoniana may be present. Common grasses and forbs can include Melica torreyana, Festuca idahoensis, Iris spp., and locally endemic serpentine forbs (Senecio spp. and others). Structurally, this system is sometimes woodland in character, but it can also be an arborescent chaparral, depending on fire history. Herbaceous-dominated serpentine fens (and bogs) are treated in Mediterranean California Serpentine Fen (CES206.953).

These systems are highly variable and spotty in distribution, and the composition of individual stands can be very diverse, especially the shrubs (often individual species have low cover). Hesperocyparis sargentii (= Cupressus sargentii), Pinus sabiniana, Garrya congdonii, Quercus durata, Umbellularia californica, and Frangula californica ssp. tomentella (= Rhamnus tomentella ssp. tomentella) are characteristic. Common associates include Heteromeles arbutifolia, Adenostoma fasciculatum, and the California endemics Arctostaphylos viscida ssp. pulchella and Ceanothus jepsonii. In some settings Arctostaphylos glauca, Styrax redivivus (= Styrax officinalis), or Cercocarpus montanus var. glaber (= Cercocarpus betuloides) can be common. Occasionally, Chamaecyparis lawsoniana may be present. Common grasses and forbs can include Melica torreyana, Festuca idahoensis, Iris spp., and locally endemic serpentine forbs (Senecio spp. and others). Structurally, this system is sometimes woodland in character, but it can also be an arborescent chaparral, depending on fire history.

This ecological system occurs in Mediterranean California in the northern and southern Coast Ranges and the northern Sierra Nevada, on cool northerly and concave slopes and toeslopes with thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils. 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 (Kruckeberg 1984). 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 (Kruckeberg 1984, Sanchez-Mata 2007). In some cases, the steepness of the slopes and general sparseness of the vegetation result in continual erosion.

Structurally, this system is sometimes woodland in character, but it can also be an arborescent chaparral, depending on fire history. Landfire (2007a): Stand-replacing fires occur mostly in the shrub-dominated stages. In the conifer-dominated late-seral closed stage, surface fire is also important. Mean FRI is generally greater than that of the surrounding forested landscape (including the lower elevation California Mesic Chaparral (CES206.926) - perhaps double (Nagel and Taylor 2005) - due to the lack of flammability of many young shrub fields without a long history of fuel accumulation.

Within this system, Hesperocyparis sargentii dominates some occurrences as woodlands or as dense shrubby thickets (Griffin and Critchfield 1976). This tree begins bearing cones by 3-7 years of age, and abundant cone crops are produced that require 2 years to mature. The serotinous cones remain closed on the tree until opened by the heat of a fire or from desiccation due to age. Seeds establish best on bare mineral soil. Seedling mortality is high on shaded sites with abundant litter because of damping-off fungi (Esser 1994b, Barbour 2007). Hesperocyparis sargentii has serotinous cones. Burned trees usually release large quantities of seed after fire, and seedlings establish as dense thickets. No information was available on fire-return intervals. To maintain a stand, fire-return intervals of greater than 7 years will allow new cone crops to develop (Esser 1994b).

The mesic chaparral stage of this system generally burns in high-intensity, stand-replacing crown fires that may burn thousands of acres in a single event (Landfire 2007a). However, there is a considerable range in the flammability of shrub species (e.g., Adenostoma fasciculatum is "flashier" than Arctostaphylos spp.). Large, stand-replacement events can interact with seed availability and, hence, influence post-fire successional pathways differently than for smaller, less severe fires. Mean fire-return intervals are highly variable across the range of this system depending on species composition and other factors. Sediment cores taken from the Santa Barbara Channel in central California dating from the 16th and 17th centuries indicate that large fires burned the Santa Ynez and Santa Lucia mountains every 40-60 years. Season of burning plays a large part in species composition. Occasionally, frost affects mortality and increases fuel buildup.

Quercus durata is an important shrub in this system. Plants sprout from swollen root crowns and root suckers after damage to their trunks; they sprout rapidly following fire (Sawyer et al. 2009). Small mammals and jays cache acorns, which other wildlife also eat.

Conversion of this type has commonly come from mining, geothermal power development, logging for various purposes (fenceposts, homes, small amount of commercial timbering, firewood) which has removed the trees, and minor amounts of other development (Kruckeberg 1984, Barbour 2007). Conversion to agriculture is not a factor as the soil types are not conducive to agricultural use. Invasive plant species that are often threats to other California ecosystems may be less of a threat in serpentine ecosystems; however, some invasives are finding their way into serpentine soils (Batten et al. 2006). In the last century the high frequency of human ignitions has reduced the mean fire-return interval to 30-35 years in southern California (Landfire 2007a).

In the west central coast regions of California, 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 except in the Klamath Mountains and possibly into Oregon.