California Mixed Conifer Forest

These mixed-conifer forests, always with at least two conifer species codominating, occur on all aspects in lower montane zones (600-1800 m elevation in northern California; 1200-2150 m in southern California). This system occurs in a variety of topo-edaphic positions, such as upper slopes at higher elevations, canyon sideslopes, ridgetops, and south- and west-facing slopes which burn relatively frequently. Often, several conifer species co-occur in individual stands. Pseudotsuga menziesii, Pinus ponderosa, and Calocedrus decurrens are the most common conifers. Other conifers that can occasionally be present include Pinus jeffreyi, Pinus attenuata, and Pinus lambertiana (not as common in this as in Mediterranean California Mesic Mixed Conifer Forest and Woodland (CES206.915)). Common subcanopy trees include Quercus chrysolepis and Quercus kelloggii. Arbutus menziesii and Notholithocarpus densiflorus may be common with the oaks in northern areas. Pseudotsuga macrocarpa and Pinus coulteri can be present but are not dominant species in this system in the Transverse Ranges of southern California. Codominant Abies lowiana - Calocedrus decurrens communities in southern California are also included in this system. In the Transverse Ranges, where Great Basin and Mojavean elements are transitioning into the montane zones, Juniperus californica and Pinus monophylla can be mixed with the other conifers. Understories are variable, except in the Sierra Nevada, where in some stands there can be dense understory mats of Chamaebatia foliolosa (and other low, spreading shrubs) which foster relatively high-frequency, low-intensity surface fires. In Oregon, shrubs such as Holodiscus discolor, Toxicodendron rydbergii, Mahonia nervosa, Mahonia aquifolium, and Symphoricarpos mollis are common in addition to graminoids such as Festuca californica, Elymus glaucus, and Danthonia californica. In the north, where Calocedrus decurrens and Pinus ponderosa drop out, this system shifts to North Pacific Dry Douglas-fir-(Madrone) Forest and Woodland (CES204.845).

Pseudotsuga menziesii, Pinus ponderosa, and Calocedrus decurrens are the most common conifers. Other conifers that can occasionally be present include Pinus jeffreyi, Pinus attenuata, and Pinus lambertiana. Common subcanopy trees include Quercus chrysolepis and Quercus kelloggii. Arbutus menziesii and Notholithocarpus densiflorus (= Lithocarpus densiflorus) may be common with the oaks in northern areas. Pseudotsuga macrocarpa and Pinus coulteri can be present but are not dominant species in this system in the Transverse Ranges of southern California. Codominant Abies lowiana - Calocedrus decurrens communities in southern California are also included in this system. In the Transverse Ranges, where Great Basin and Mojavean elements are transitioning into the montane zones, Juniperus californica and Pinus monophylla can be mixed with the other conifers. Understories are variable, except in the Sierra Nevada, where in some stands there can be dense understory mats of Chamaebatia foliolosa (and other low, spreading shrubs) which foster relatively high-frequency, low-intensity surface fires. In Oregon, shrubs such as Holodiscus discolor, Toxicodendron rydbergii, Mahonia nervosa, Mahonia aquifolium, and Symphoricarpos mollis are common in addition to graminoids such as Festuca californica, Elymus glaucus, and Danthonia californica.

In the lower montane of the Sierra Nevada, 33% of the annual precipitation falls as snow and nearly all of it occurs in the fall, winter and spring months. Throughout California, conifers have to contend with summer drought. Winter precipitation is stored as soil moisture, and available water is virtually depleted by the end of September. The dry-mixed conifer system occurs where there is plenty of moisture but not prolonged cold. Shade tolerance, drought tolerance and response to fire of dominant tree species seedlings are important factors governing the composition and successional patterns of this forest system. Ponderosa pine seedlings are intolerant of shade compared to Douglas-fir, white fir, incense-cedar and sugar pine. In fact, abundant evidence indicates that incense-cedar and white fir have increased in ponderosa pine forests since the turn of the twentieth century, with more significant changes seen on xeric locations relative to mesic sites (Barbour et al. 2007). Historically, surface fires occurred every 5-10 years and mixed-severity fires occur about every 50 years. Fire suppression has led to an increase in forest canopy coverage and tree density, but a decrease in trees with >60 cm dbh. In addition, species composition has shifted due to targeted logging of preferred species.

Historically, frequent and low-intensity fires maintained these woodlands. Due to fire suppression, the majority of these forests now have closed canopies, whereas in the past, a moderately high fire frequency (every 20-30 years) formerly maintained an open forest of many conifers.

This system occurs in lower montane zones (600-1800 m elevation in northern California; 1200-2150 m in southern California), including the eastern Klamath-Siskiyou, interior Coast Ranges, Transverse Ranges and Sierra Nevada.