Klamath Mountains Serpentine Conifer Forest

This system occurs throughout the Klamath-Siskiyou region below 1500 m (4550 feet) elevation on thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils below winter snow accumulations and typically experiences hot and dry summers. Soils are not always rocky; they can be loamy, up to 76 cm (30 inches) in depth, and can be heavy clay. Not all ultramafic outcrops support distinct vegetation; only those with very low Ca:Mg ratios impact biotic composition. These woodlands are highly variable and spotty in distribution. These sites are more productive and can support large-statured (dbh, height) trees, although they tend to be widely spaced. Common species include Pseudotsuga menziesii, Pinus sabiniana, Pinus lambertiana, Pinus jeffreyi, Pinus attenuata, Notholithocarpus densiflorus var. echinoides, Calocedrus decurrens, Arctostaphylos spp., Quercus vacciniifolia, and Xerophyllum tenax. Perennial grasses such as Festuca idahoensis may also be characteristic. Chamaecyparis lawsoniana communities can occur within occurrences of this system in mesic and linear riparian zones. Herbaceous-dominated serpentine fens (and bogs) are treated in Mediterranean California Serpentine Fen (CES206.953).

Common species include Pseudotsuga menziesii, Pinus sabiniana, Pinus lambertiana, Pinus jeffreyi, Pinus attenuata, Notholithocarpus densiflorus var. echinoides (= Lithocarpus densiflorus var. echinoides), Calocedrus decurrens, Arctostaphylos spp., Quercus vacciniifolia, and Xerophyllum tenax. Perennial grasses such as Festuca idahoensis may also be characteristic.

This system occurs throughout the Klamath-Siskiyou region below 1500 m (4550 feet) elevation on thin, rocky, ultramafic (gabbro, peridotite, serpentinite) soils below winter snow accumulations and typically experiences hot and dry summers. Soils are not always rocky; they can be loamy, up to 76 cm (30 inches) in depth, and can be heavy clay. 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 (Kruckeberg 1984, Sanchez-Mata 2007). In some cases, the steepness of the slopes and general sparseness of the vegetation result in continual erosion.

Sites are productive and can support large-statured trees, although they will generally be widely spaced. Trees tend to grow very slowly due to the soil chemistry and textural characteristics which limit available nutrients.

Several important trees in this systems are fire-adapted, but the system as a whole is an edaphically-controlled type. Fire regimes vary depending on the slope position, elevation, fire history, and successional stage. Chamaecyparis lawsoniana-dominated stands have a low frequency of stand-replacing fires with an age class distribution showing >50% of stands are more than 300 years old (Jimerson et al. 1995). Other forest types in this system have more frequent stand-replacing fires. Pseudotsuga menziesii woodlands age class distribution shows >80% of stands were older than 175 years. Pinus jeffreyi occurs on drier sites and has more frequent fires, age classes are evenly distributed from young to old; while Pinus lambertiana has highest age class frequency of stands <175 years. Pinus lambertiana stands burn more frequently due to upper slope positions (Jimerson et al. 1995). Native dwarf mistletoe (Arceuthobium spp.) infest many trees within this system; generally they do not cause mortality but weaken trees sufficiently for bark or engraver beetles or wood borers to successfully attack and kill the tree.

Parker (1990) suggests that species growing on serpentine sites may suffer greater mortality and poorer recruitment after a fire than the same species on adjacent sandstone soils. Landfire (2007a): This type has a very limited distribution and consequently limited information for fire occurrence history. Adjacent mixed conifer forest types have similar characteristics and are detailed below. Surface and mixed-severity fires occur at an average of about 10-15 years (Taylor and Skinner 1998, 2003, Sensenig 2002). Kilgore and Taylor (1979) reported a FRI=19-39 years (N/NE aspects), which may favor mixed fires. Replacement fires with longer (70-110 years) return intervals are possible (Frost and Sweeney 2000). With historic fire regimes, insect outbreaks may have been much reduced compared to current conditions. Snow breakage occurs in the mid-seral closed state about every 5 years. While model is aspatial, most medium- and high-severity fire may actually occur on mid and upper slope positions (Taylor and Skinner 1998, Taylor 2000, Bekker and Taylor 2001).

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 amount of other development (Kruckeberg 1984). Once mature trees have been logged and removed, they are slow to be replaced (Kruckeberg 1984), often >150 years, due to the soils characteristics. Common stressors and threats include logging, fire suppression, and non-native pathogens which are infecting conifers throughout northwestern California and southwestern Oregon. From Jimerson et al. (1995): The Port Orford-cedar root disease (a fungus, Phytophthora lateralis) is fatal to any infected Chamaecyparis lawsoniana, and now infects most stands. Spores are spread by mud on wheels, boots, or other equipment. White pine blister rust (Cronartium ribicola), also a fungus, infests both Pinus monticola and Pinus lambertiana, which can be killed directly by the fungus, or weakened and made susceptible to insects. Regeneration-sized trees are more significantly and rapidly affected than larger trees, which is resulting in shifts in age class distribution and loss of the regeneration layers and hence changes in succession (Jimerson et al. 1995). Fire suppression has lead to increased cover of some shrub species, which will change the characteristics of a fire, including severity and spread (Jimerson et al. 1995). Due to fire exclusion, many of these stands currently exhibit higher density of understory species and young conifer and hardwoods.

In northwestern California, regional climate models project mean annual temperature increases of 1.7-1.9°C (3.06-3.42°F) by 2070 (PRBO Conservation Science 2011). And 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). Potential climate change effects could include: increase fire frequency with warmer temperatures, lower precipitation may result in drier, more flammable fuels, which may exacerbate the fire intensity; and less rainfall and higher temperatures may shift species composition to more drought-tolerant species, such as Lithocarpus densiflorus, and which may also favor non-native species.

In many coastal regions, the interaction between oceanographic and terrestrial air masses may be ecologically important. Intensifying upwelling along the California coast under climate change may intensify fog development and onshore flows in summer months, leading to decreased temperatures and increased moisture flux over land (Snyder et al. 2003, Lebassi et al. 2009, as cited in PRBO Conservation Science 2011). Coastal terrestrial ecosystems could benefit from these changes. However, current trends in fog frequency along the Pacific coast from 1901-2008 have been negative (Johnstone and Dawson 2010, as cited in PRBO Conservation Science 2011), thus the effect of climate change on coastal fog remains uncertain (PRBO Conservation Science 2011).

This system occurs throughout the Klamath-Siskiyou mountains region below 1500 m (4550 feet) elevation.