Quercus berberidifolia, Q. dumosa


Table of Contents


INTRODUCTORY


California scrub oak in the Santa Monica Mountains National Recreation Area. Photo © 2010 Michael O'Brien.

AUTHORSHIP AND CITATION:
Fryer, Janet L. 2012. Quercus berberidifolia, Q. dumosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
QUESPP2
QUEBER
QUEDUM

COMMON NAMES:
for Quercus berberidifolia:
California scrub oak
barberry-leaved scrub oak

for Quercus dumosa:
coastal sage scrub oak
Nuttall's scrub oak

TAXONOMY:
This review covers the following species:

California scrub oak (Quercus berberidifolia) Liebm.
coastal sage scrub oak (Quercus dumosa) Nutt. (Fagaceae) [52,59,79,94,207]

These species are in the white oak subgenus (Lepidobalanus) [214,217].

In the broadest sense, the Q. dumosa complex includes at least 6 [213]of California's shrubby white oaks, including California scrub oak, coastal sage scrub oak, leather oak (Q. durata), MacDonald oak (Q. macdonaldii), Tucker oak (Q. john-tuckeri), and Sonora scrub oak (Q. turbinella) [171,213]. Hybridization and introgression have led to genetic "blurring" of these species [214,217], and the Q. dumosa complex was realigned several times over the 20th century [214]. As defined by systematists in the early 21st century, the name Q. dumosa refers only to coastal sage scrub oak: a species that lies within a very narrow geographical range in southern California and is primarily restricted to coastal sage scrub communities [52]. Under this narrow taxonomic designation, the name Quercus dumosa is misapplied to many of California's shrubby oaks; most commonly, it has been misapplied to California scrub oak [52,79,207].

This taxonomic dilemma creates confusion as to which taxon is actually being discussed in literature written before the 21st century. Most 20th-century literature that refers to "Q. dumosa" actually applies to California scrub oak [52,79], but entities on the Mojave Desert ecotone that are identified in older literature as "Q. dumosa" may actually be Muller oak (Q. cornelius-mulleri) [171] or Sonora scrub oak [215]. Unlike these strictly southern California species, California scrub oak has a broader geographic distribution that extends into northern California, so except for desert ecotones and other areas of geographic overlap in the southern part of the state, the burden of reassigning species designations to entities discussed in older literature as "Q. dumosa" is somewhat lessened. However, the history of taxonomic confusion means that for oaks in the Q. dumosa complex, species designations used in this review cannot be guaranteed.

To help the reader follow information about the 2 species covered in this review, the following conventions are followed:

1. "California scrub oak" refers to entities that lie within the geographical range of Q. berberidifolia as defined by The Jepson Herbarium [207], with the exception of entities on desert ecotones (where the reports may refer to other species) or in coastal areas where the distributions of California scrub oak and coastal sage scrub oak overlap.

2. "Coastal sage scrub oak" refers to Q. dumosa according to its current classification. Thus, this name coastal sage scrub oak is used only when a) a report clearly identified this species.

3. "Quercus dumosa (sensu lato, sl)" refers to reports in which the distinction between California scrub oak and coastal sage scrub oak was unclear. This includes reports of "Q. dumosa" from older literature in areas where the distributions of California scrub oak and coastal sage scrub oak overlap, since the species described may have been reclassified since the literature was published.

The ecology and reproductive habits of California's shrubby oaks are similar. Although there is confusion over taxonomy, managers may be heartened by the fact that the shrubby oaks have very similar responses to fire [180].

Hybrids: Hybridization, hybrid swarms, and introgression are rampant among the scrubby oaks within the Q. dumosa complex. Additionally, these species may hybridize and intergrade with white oaks that grow primarily as trees. California scrub oak hybridizes with many other white oaks in California [52], including coastal sage scrub oak, leather oak, Tucker oak (Q. john-tuckeri), Sonora scrub oak, Engelmann oak (Q. engelmannii), valley oak (Q. lobata), and Oregon white oak (Q. garryana) [79,214,217]. Putative California scrub oak × Tucker oak hybrids can be found in the South Coast Ranges above Ventura and on the north slope of the Tehachapi Mountains [52]. Named California scrub oak hybrids are:

Quercus × howellii Tucker (Q. berberidifolia × Q. garryana), Howell's oak [216]. These hybrids are noted in Sonoma [6] and Marin [216] counties.
Quercus × macdonaldii Green & Kellogg (Q. berberidifolia × Q. lobata), MacDonald oak [218]; noted in Santa Barbara County and on the Channel Islands [217]

Coastal sage scrub oak rarely comes in contact with other white oaks due to its restricted range. Some high-elevation California scrub oaks near coastal sage scrub oak populations show signs of introgression with coastal sage scrub oak [52]. Named coastal sage scrub oak hybrids are:

Quercus × grandidentata Ewan (Q. dumosa × Q. engelmannii) [89,218], largeleaf oak
Quercus × kinselae (C. .H. Muller) Nixon & C. H. Muller (Q. dumosa × Q. lobata), Kinsel's oak
Quercus × townei Palmer (Q. dumosa × Q. engelmannii), Town's oak [52]. Town's oak is also known by the synonym Quercus dumosa Nuttall var. kinselae C. H. Muller [161].

SYNONYMS:
for Quercus berberidifolia:
Quercus dumosa [155] (misapplied [52])

LIFE FORM:
for Quercus berberidifolia:
Shrub-tree

for Quercus dumosa:
Shrub

DISTRIBUTION AND OCCURRENCE

SPECIES: Quercus berberidifolia, Q. dumosa
GENERAL DISTRIBUTION:
California scrub oak and coastal sage scrub oak occur in the geographical provinces colored below. Note that their distributions overlap only in a narrow portion of the south coast [207].

Distribution of California scrub oak [207]
Distribution of California scrub oak coastal sage scrub oak. Maps courtesy of the Jepson Herbarium [207].

California scrub oak is endemic to California and Baja California Norte [79]. It is the most common shrubby oak in central and southern California; it is especially prevalent at midelevations of the Central and South Coast Ranges [52]. California scrub oak is also common in the Sierra Nevada. A widespread vegetation survey (17,000 plots) in the 1930s found that California scrub oak chaparral occupied 4,070 acres (1,647 ha) in the central Sierra Nevada [208]. California scrub oak occurs on the Channel Islands [160].

United States: CA
Mexico: Baja California Norte [79,218]

Coastal sage scrub oak is a narrow endemic; it is restricted to a portion of the South Coast Ranges of California [52,79]. The Flora of North America [52] restricts coastal sage scrub oak's geographical range to a narrow band that occurs at low elevations and is "almost always within sight of the ocean". The largest population occurs in Torrey Pines State Park, San Diego County [160].

United States: CA [52,79]

SITE CHARACTERISTICS AND PLANT COMMUNITIES:
As of 2012, most published information on these oaks discussed Q. dumosa (sl). Little information was available on the ecology of coastal sage scrub oak. Studies are needed on coastal sage scrub oak's habitat requirements, plant community associations, and general ecology.

Site characteristics: Q. dumosa (sl) generally occupies relatively mesic aspects on dry slopes [52]. California scrub oak tends to dominate the highest elevations of the chaparral belt and grows in a variety of soils. Coastal sage scrub oak is restricted to very dry, coastal locations [52].

Soils: Soils with California scrub oak tend to be shallow on chaparral sites and deeper on oak (Quercus spp. ) woodland sites [9]. They are dry for much of the year [190] and usually nutrient-poor [137,180]. California scrub oak grows on gravelly or rocky slopes throughout most of its distribution [190]. It grows in all soil textures and is common in loams and clay loams [68].

Coastal sage scrub oak grows in sandy soils [52,79] derived from sandstone or granitic parent materials [160].

Parent materials of soils with California scrub oak vary. California scrub oak grows in soils derived from granitic parent materials in the Leibre Mountains of the western Transverse Ranges [31]. In Ventura County, California scrub oak grows in soils derived from sandstone or andesite [163]; it also grows in sandstone-derived soils in the Santa Monica [137,191] and Santa Lucia [195] mountains. In the Central Valley of Santa Cruz Island, California scrub oak pygmy woodlands occur over schist [32].

California scrub oak is rare on serpentine and other mafic soils. In northern California, it does not occur in gray pine woodlands on serpentine soils, but it is a component of gray pine/chaparral and blue oak (Q. douglasii)-gray pine woodlands on nonserpentine soils [81,162]. In the Santa Ana Mountains, California scrub oak was uncommon (2.0% cover) on serpentine soils but common (20.1% cover) on nonserpentine soils [221]. Surveys in Napa, Lake, and Yolo counties found California scrub oak only on nonserpentine, mixed-chaparral plots [189]. However, other surveys in Lake, Napa, and Sonoma counties found California scrub oak on nonserpentine, patchy serpentine, and continuous serpentine soils [74]. In El Dorado County, California shrub oak grew in mafic gabbrodiorite soils that were rocky, dry, and nutrient-poor. It was not a community dominant on these sites; chamise (Adenostoma fasciculatum) generally dominated [229]. California scrub oak is noted on ultramafic soils in leather oak communities of southern California [162], although it is not associated with ultramafic soils in the North Coast Ranges, the Klamath Mountains, and the Siskiyou Mountains [193].

Elevation and topography: California scrub oak grows on dry slopes at elevations from 330 to 5,900 feet (100-1,800 m) [52,79] but is most common below 5,000 feet (2,000 m) [190]. In the Transverse Ranges, California scrub oak is frequent in chaparral below 5,000 feet [15]. Topography on these Transverse Range sites varies from level to steep [222].

Coastal sage scrub oak grows at elevations below 700 feet (200 m) [52,79].

Q. dumosa (sl) chaparral tends to occur on the most mesic sites within the chaparral belt [70,72,222], such as north-facing slopes [70,164,222]. In northern California, Holland [81] found that California scrub oak-dominated communities occurred on relatively mesic sites compared to chaparral communities dominated by other shrub species; California scrub oak communities were mostly at higher elevations (up to 5,000 feet (1,500 m)) of the chaparral belt. In southern California, Hanes [71] found that Q. dumosa (sl) frequency was positively associated with north-facing aspects, steep slopes, high elevations (~ 4,000 feet (1,000 (m)), and relatively long fire-return intervals (P=0.1 for all variables). When Q. dumosa (sl) was found on south-facing slopes, it was usually at the highest elevations (4,000-5,000 feet (1,000-2,000 m)). It occurred on both coastal- and desert-facing slopes [71]. Q. dumosa (sl) is most common on relatively mesic mountain ranges above 3,900 feet (1,200 m) in San Diego County [145]. On Santa Cruz Island, California scrub oak chaparral grows on north-and south-facing slopes [26].

Climate: California scrub oak grows in a mediterranean climate, with hot, dry summers and cool, wet winters. Most precipitation falls as rain, usually from November through April [14,23]. Wet snows may occur in the northern portion of California scrub oak's range [23]. Mean annual precipitation across California scrub oak's distribution in California ranges from 15 to 50 inches (380-1,300 mm) [171]. Q. dumosa (sl) is not a strong desert species; it occurs only on the fringes of the Mojave Desert and is rare in the Sonoran Desert. In the Tehachapi Mountains, which define the northern border of the Mojave Desert and lie in the zone of Q. dumosa (sl)-Sonora scrub oak intergradation [214,215], annual precipitation in the chaparral zone averages around 10 inches (250 mm) [14]. California scrub oak grows primarily on springs and arroyos in the Sonoran Desert of Baja California Norte [150].

Plant communities: California scrub oak occurs in several vegetation formations, while coastal sage scrub occurs in only one. See the Fire Regime Table for a list of plant communities in which California scrub oak and coastal sage scrub oak may occur and information on the fire regimes associated with those communities.

California scrub oak: California scrub oak occurs in chaparral, oak woodland, and conifer woodland communities.

Chaparral:
Northern California—California scrub oak occurs in scrub oak (Quercus spp.), chamise, ceanothus (Ceanothus spp.), and mixed chaparral in northern California. It is an important to dominant component of chaparral on western slopes of the Cascade-Sierra Nevada crest from Tehama County south through the Sierra Nevada [190]. Typical codominant or associated species in the Sierra Nevada include chamise, interior live oak (Quercus wislizeni), manzanita (Arctostaphylos spp.), ceanothus, toyon (Heteromeles arbutifolia), yerba santa (Eriodictyon californicum), and California buckeye (Aesculus californica) [81,110,198].

Most vegetation classifications of northern California place California scrub oak in primarily mixed chaparral, with greatest importance on mesic slopes. In Lake County, California scrub oak occurs on the north slopes of mixed chaparral with interior live oak, Eastwood manzanita (A. glandulosa), toyon, and other sprouting shrubs. Chamise tends to dominate south-facing slopes. Mixed-chaparral communities with California scrub oak generally have more gentle slopes and deeper soils (1-2 feet (0.3-0.6 m)) than chamise communities (<12 inches (30 cm) deep) [24]. Jensen [92] described a diverse mixed-chaparral vegetation type in Santa Cruz County that was composed of California scrub oak, Eastwood manzanita, scrub canyon live oak (Quercus chrysolepis), birchleaf mountain-mahogany (Cercocarpus montanus var. glaber), and many other shrub species. The type tends to occur on east-facing slopes, often on chalk soils, with vegetation reaching 4 to 10 feet (1-3 m) tall. These stands may become dense enough to become "almost impenetrable" [92].

California scrub oak and chamise codominated a mixed-chaparral community on the Hopland Field Station in the North Coast Ranges. Bigberry manzanita (A. glauca) and wedgeleaf ceanothus (C. cuneatus) were also common [196].

California scrub oak is a common component of ceanothus chaparral; hoaryleaf ceanothus (C. crassifolius), hairy ceanothus (C. oliganthus), and blueblossom ceanothus (C. thyrsiflorus) are commonly dominant [72].

In the Bureau of Land Management's Central California Region, in Horse Valley and near Willow Creek, California scrub oak occurred in mixed chaparral along with bigberry manzanita, birchleaf mountain-mahogany, and California buckeye. This community occupied north-facing slopes, while coastal sage scrub codominated with black sage (Salvia mellifera) and California buckwheat on south-facing slopes [53].

Southern California—California scrub oak dominates some scrub oak, mixed, and maritime chaparral types in southern California [222]. Chamise, ceanothus, and manzanita are commonly codominant [222]. Except for maritime chaparral, these types are usually on north-facing slopes [70,164]. Mid-1990s inventories of southern California chaparral on National Forest lands revealed that Q. dumosa (sl) occurred in all chaparral types surveyed, including scrub oak, chamise, red shank (Adenostoma sparsifolium), mixed, and coastal sage scrub chaparral. Q. dumosa (sl) scrub oak types tended to occur on north-facing and other mesic slopes, often above chamise or red shank chaparral. When Q. dumosa (sl) was a component of chamise or other very dry chaparral types, it occupied mesic pockets within the type [57].

In coastal southern California, Q. dumosa (sl) dominates a scrub oak series that occurs on mesic sites receiving more than 20 inches (500 mm) annual precipitation. The series occupies mostly north-facing slopes at low and midelevations, but it occurs on all aspects at high elevations. Shrub diversity is usually high, but the herbaceous layer is sparse [168]. In the San Bernardino Mountains, California scrub oak tends to dominate on low-elevation (2,300-3,000 feet (700-900 m)) slopes, while it occurs in mixed stands with interior scrub oak, Eastwood manzanita, and Ceanothus at high elevations (3,900-4,600 feet (1,200-1,400 m)) [146]. California scrub oak maritime chaparral is a rare chaparral type that occurs on the coastal fog belt. Due to urban development, it is one of the rarest chaparral types. Coastal sage scrub oak replaces California scrub oak as the maritime chaparral's dominant species in the fog belt of San Diego County [70].

California scrub oak often codominates mixed chaparral. On the Santa Monica Mountains Reserve, California scrub oak, Eastwood manzanita, chamise, and common deerweed (Lotus scoparius) codominated a chaparral stand on north-facing slopes [68]. California scrub oak is often dominant in some midelevation, cismontane mixed chaparral of southern California [55]. Wedgeleaf ceanothus-California scrub oak is the most common chaparral type in the Tehachapi Mountains, occurring at low elevations (500-3,000 feet (150-900 m)) in discontinuous strips [14]. California scrub oak is widespread in the Leibre Mountains, dominating in the California scrub oak, California scrub oak-chamise, California scrub oak-birchleaf mountain-mahogany, California scrub oak-chaparral whitethorn (Ceanothus leucodermis), and interior live oak-California scrub oak series; these generally occur at higher elevations or on relatively more mesic sites than series in which chamise is the primary dominant [31]. On the eastern slope of the Transverse Ranges, California scrub oak occurs in mixed chaparral with canyon live oak, interior live oak, Eastwood manzanita, chaparral whitethorn, and chamise. Vegetation cover is usually 100% [142].

In San Diego County, California scrub oak codominated in mixed chaparral with Eastwood manzanita, bigberry manzanita, and desert ceanothus. The stand was "very old"; the site had not burned for about 90 years [113]. Mixed chaparral on the San Dimas Experimental Forest, Los Angeles County, was composed of California scrub oak, chamise, hoaryleaf ceanothus, sugar sumac (Rhus ovata), black sage, and Eastwood manzanita. Shrub height ranged from 3 to 13 feet (1-4 m) and canopies were dense. The stands were 42 years old, dating from a wildfire that burned almost 90% of the Experimental Forest [88].

California scrub oak is common in chamise or red shank chaparral (for example, [81,222]). It occurs in mixed red shank-buckbrush-chamise communities on the Los Padres National Forest [41]. In a survey in the Santa Monica Mountains, Q. dumosa (sl) was common in red shank communities but not in chamise communities [17]. On the west slope of the Sierra San Pedro Mártir, Baja California Norte, California scrub oak is a minor species in chamise-desert ceanothus and red shank communities [149], but it is mostly confined to springs and arroyos [150].

California scrub oak occurs in some coastal sage scrub communities. On plots across coastal southern California, California scrub oak had low cover (<4%) in coastal sage scrub communities. California sagebrush had highest cover, followed by chamise, barranca brush, and eastern Mojave buckwheat, respectively [188]. In coastal San Diego County, California scrub oak was an indicator species for mixed chaparral but was negatively associated with coastal sage scrub [206].

California scrub oak dominates some chaparral types of the Channel Islands. On Santa Rosa Island, California scrub oak codominates with chamise on west- and east-facing slopes [38]. Minnich [141] described a California scrub oak/annual grassland vegetation type on Santa Catalina Island and a California scrub oak-toyon/annual grassland vegetation type on Santa Cruz Island. MacDonald oak, a California scrub oak hybrid, occurs as a solitary tree or in hybrid swarms on both islands. California scrub oak also occurs in mixed chaparral on xeric slopes north of the Central Valley on Santa Cruz Island. In these mixed-chaparral sites, it cooccurs with birchleaf mountain-mahogany and island ceanothus (Ceanothus megacarpus var. insularis ) [141]. MacDonald oak, island ceanothus, and chamise codominate in mixed chaparral on low slopes near the Central Valley [16,26,32]. A California scrub oak-lemonade sumac (Rhus integrifolia) community occurs on north-facing slopes. California scrub oak was not regenerating on slopes where feral pigs rooted and browsed [143].

Woodlands: California scrub oak is a component of oak, mixed-riparian, desert, and insular woodland communities.

California scrub oak occurs in the understories and overstories of some oak woodlands of northern California [82]. It is an associated species in blue oak communities of the Coast Ranges and in the Sierra Nevada. In Sequoia National Park, California scrub oak occurs in the understory of blue oaks woodlands along with other sprouting species such as whiteleaf manzanita (A. viscida). Nonnative annuals dominate the herbaceous layer [9]. A California scrub oak-blue oak/annual grass hardwood rangeland type was identified in San Benito and Monterey counties. High numbers of California scrub oak in the sapling class suggested that California scrub oak was gaining basal cover over blue oak. The authors predicted that with further decline of blue oak, this rangeland type may convert to California scrub oak/annual grass woodland [84]. In San Luis Obispo County, California scrub oak codominated with blue oak on xeric sites, while coast live oak (Q. agrifolia) and valley oak codominated on more mesic sites. Gray pine associated with the oaks on all sites. Annual grasses dominated the oak woodlands' ground layers [209]. California scrub oak occurs in the understory of a blue oak community in the Tehachapi Mountains, at around 3,000 feet (900 m) elevation. Gray pine and singleleaf pinyon (P. monophylla) cooccur in the overstory [14]. In Riverside County, California scrub oak chaparral merges into Engelmann oak-coast live oak woodlands, becoming a component of the woodland understory. Since California scrub oak and Engelmann oak hybrid and the stand structure changes gradually on some sites, the chaparral-woodland ecotone is not always distinct [123].

On the Winter Deer Range of Tehama County, oaks, chaparral shrubs, and annual grasses form a woodland-chaparral-grassland mosaic on low foothills. California scrub oak, interior live oak, and wedgeleaf ceanothus codominate at high elevations of the woodlands, while blue oak and wedgeleaf ceanothus dominate at low elevations. Woody species in general are more abundant on north-facing slopes, where they often form dense stands of chaparral. Soils are rocky, very slightly to slightly acidic, and mostly shallow; they are derived from volcanic breccia materials. Soils range from 2.5 to 5.0 feet (0.8-1.5 m) deep on California scrub oak types, averaging 2.5 to 3.3 feet (0.8-1.0 m) deep [23].

California scrub oak is mostly an upland species, but it sometimes grows in riparian communities. It is occasional in Fremont cottonwood-willow (Populus fremontii-Salix spp.) communities in the Central Valley [225]. In the Transverse Ranges, California scrub oak was a component of California sycamore (Platanus racemosa)/chamise riparian vegetation, ranging from 0.7% to 16.3% relative cover [18]. In Baja California Norte, California scrub oak codominated the understories of some riparian willow (Salix spp.) communities. California sycamore and oaks (Quercus spp.) sometimes codominated these overstories; California coffeeberry (Rhamnus californica), chamise, and Baja rose (Rosa minutifolia) were commonly associated with California scrub oak in the understories [186].

Q. dumosa (sl) is noted on desert fringes. It occurs in a Joshua tree (Yucca brevifolia) woodland on the southwestern edge of the Mojave Desert [205].

California scrub oak grows in insular hardwood woodlands of the Channel Islands. Some woodland-chaparral communities of Santa Cruz Island are codominated by California scrub oak and manzanita [26,32]. Density varies; some stands are open enough to be classified as insular woodlands, while chaparral stands are more closed. Island manzanita (Arctostaphylos insularis) typically codominates in California scrub oak woodlands. California scrub oak is a component of fernleaf Catalina ironwood (Lyonothamnus floribundus subsp. aspleniifolius) woodlands of Santa Cruz Island [26]. On Santa Rosa Island, it occurs in coast live oak-island live oak-hollyleaf cherry (Q. tomentella-Prunus ilicifolia subsp. lyonii) woodlands [38].

Conifer- and conifer-oak: California scrub oak grows in cypress (Cupressus spp.), pine (Pinus spp.), pine-oak, and singleleaf pinyon-juniper (P. monophylla-Juniperus spp.) woodlands of southern California. Three vegetation classifications mention California scrub oak (as now classified) growing in association with Tecate cypress (C. forbesii). It occurs in the understory of Tecate cypress stands in San Diego County [233]. On Guatay Mountain in the Peninsular Ranges, California scrub oak is an associated species in high-elevation Tecate cypress groves [7]. It is also an associated species in Tecate cypress communities near Ensanada, Baja California Norte [47]. Sargent cypress (C. sargentii) associates with California scrub oak throughout most of Sargent cypress's range [10].

Several pine woodland or chaparral communities contain California scrub oak. California scrub oak is associated with knobcone pine (P. attenuata) woodlands and chaparral in the San Bernardino [147] and Santa Ana [221] mountains. It is a component of Torrey pine (P. torreyana) woodlands in San Diego County [81,147] and on Santa Rosa Island [38,147]. It also occurs in Bishop pine (P. muricata) woodlands in Santa Rosa Island [38]. California scrub oak occurs on relatively moist slopes of Coulter pine (P. coulteri)/chamise communities of the American Canyon Research Natural Area near San Luis Obispo [29]. It was a minor species in a Jeffrey pine-California black oak forest (Pinus jeffreyi-Quercus kelloggii) in Cuyamaca Ranch State Park [132].

Cedar burn: In a survey conducted 4 years after the 2003 Cedar Wildfire in Cuyamaca Rancho State Park, California scrub oak was considered an indicator species of an early-seral, postfire chaparral community dominated by sprouting shrubs and nonnative annual grasses (P<0.001). Before the fire, this community was codominated by Coulter pine, but Palmer ceanothus (Ceanothus palmeri) and bromes (Bromus spp.) dominated the postfire community. The community occurred at high elevations (up to 5,400 feet (1,650 m)) on east-facing slopes. Prefire basal area of Coulter pine was higher, and fire severity greater, than that in lower-elevation mixed chaparral dominated by wedgeleaf ceanothus. The fire was stand-replacing in both community types [54].

Q. dumosa (sl) is a minor component of some singleleaf pinyon-juniper woodlands. It had 0.3% cover in a California juniper (Juniperus californica)-singleleaf pinyon woodland in the Little San Bernardino Mountains, Joshua Tree National Park [125].

Coastal sage scrub oak: Coastal sage scrub oak occurs almost exclusively in coastal sage scrub communities [52,79] but may finger into chaparral [79]. Although there are many descriptions of other coastal sage scrub communities (for example, [81,188,192]), as of 2012, there were few published descriptions of either coastal sage scrub or chaparral communities where coastal sage scrub oak (as now taxonomically defined) was a component of the vegetation. In coastal sage scrub in San Diego County, coastal sage scrub oak-laurel sumac (Malosma laurina)-lemonade sumac stands occur on north-facing slopes. California sagebrush (Artemisia californica) and black sage dominate south-facing slopes, and chamise stands occupy mesa tops [2]. In San Diego County, coastal sage scrub oak and California scrub oak dominate dense coastal sage scrub oak and scrub oak vegetation types, respectively. Stands are typically 20 feet (6 m) tall, with >75% ground cover [44]. On plots across coastal southern California, coastal sage scrub oak had low cover (<4%) in coastal sage scrub communities. California sagebrush had highest cover, followed by chamise, barranca brush (Ceanothus verrucosus), and eastern Mojave buckwheat (Eriogonum fasciculatum subsp. foliolosum), respectively [188]. In the San Bernardino Mountains, coastal sage scrub oak occurred at 2,400 feet (730 m) on a west-facing alluvial deposit. California sagebrush and California buckwheat (E. fasciculatum subsp. fasciculatum) dominated the community [86]. In chaparral, coastal sage scrub oak occupies relatively mesic sites at high elevations. Sugarbush (R. ovata), hollyleaf cherry (Prunus ilicifolia), and birchleaf mountain-mahogany are often associated or codominant. Stature of these shrubs is short, about 1 to 3 feet (0.3-1 m) tall [169].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Quercus berberidifolia, Q. dumosa
 
Twigs and acorns of a California scrub oak at Pinnacles National Monument. Photo © 2008 Keir Morse. Twig and acorn of coastal sage scrub oak in Placerita Canyon Natural Area. Photo courtesy of ARKive.

GENERAL BOTANICAL CHARACTERISTICS:
Botanical description: California's scrub oaks in the white oak subgenus have highly convergent botanical characteristics; they are distinguished morphologically based on leaf, acorn, and trichome characteristics and by habitat [160]. This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (for example, [52,79,180]).

California scrub oak: California scrub oak is typically a shrub that grows from 4 to 10 feet (1-3 m) tall. It occasionally assumes tree form, sometimes growing up to 30 feet (9 m) tall. DBH ranges from 2.0 to 10.0 inches (5.1-25.4 cm). Plants may be single- to multistemmed. The bark is thin and flaky [180]. Leaves are evergreen [79] and sclerophyllous [70]. Typical growth form is round-topped, with numerous, dense branches that may intertwine [131]. In closed stands, Q. dumosa (sl) may form thickets of short-stemmed individuals [180].

Halsey [70] described California scrub oak as a drought avoider, with deep roots that tap groundwater. Three California scrub oaks that were excavated in the San Gabriel and San Bernardino mountains averaged a maximum root length of 15 feet (5 m), a radial spread of 10 feet (3 m), and 5 feet (1.5 m) in height. Their root systems were extensive, with many branch roots that were 3 inches (7 cm) in diameter. Feeder roots grew in the top 6 inches (1.5 cm) of soil. Among 18 chaparral species, California scrub oak had the deepest root penetration. The roots of one California scrub oak grew 28 feet (8.5 m) below ground through fractured rock. It was the only species where root grafting was observed [78]. Roots of a 7-foot-tall (2 m) plant on a chaparral site penetrated 20 feet (6 m) below the soil surface (Hellmers and others 1955 cited in [99]).

Coastal sage scrub oak: Coastal sage scrub oak is a 3- to 10-foot (1-3 m) shrub. Leaves are subevergreen [52] to evergreen [79] and sclerophyllous. The branches are brittle, often falling off when disturbed [52]. Fruits are solitary or paired [52].

Q. dumosa (sl): The fruits are acorns, a type of nut [52], from 0.5 to 1.5 inches (1.3-3.8 cm) long [131]. With age, the root crown develops into a burl. Burls can become very large and dense after repeated top-kill (see Plant response to fire). In San Diego County, biomass of Q. dumosa (sl) burls ranged from 9.5 to 56.4 pounds (4.3-25.6 kg) [118].

Q. dumosa (sl) is deep-rooted [85,138], with extensive side-branching roots and shallow feeder roots [85]. In San Diego County, Q. dumosa (sl) roots penetrated deeper than the researchers' 1-meter excavations. For roots within 0.3 foot (1 m) of the soil surface, 75% of the total root biomass lay at 8- to 24-inch (20-60 cm) soil depths [118].

Q. dumosa (sl) lives up to about 100 years old [85,180]. Aboveground, most plants are <75 years old due to repeated top-kill from fire [180].

Raunkiaer [183] life form:
Phanerophyte

SEASONAL DEVELOPMENT:
California scrub oak: California scrub oak flowers in spring [52]. The growing season begins early in southern California. In the Tehachapi Mountains, California scrub oak growth and leaf elongation begin in March [14]. California scrub oak may shed leaves in late summer under extreme drought [147]. Acorns mature from early to late fall [181]. Acorns collected from Las Trampas Regional Wilderness in the East Bay area germinated in late October or early November, within a month of being planted. The acorns were planted in common gardens in the Santa Lucia Range and in the northern Sierra Nevada. Development was faster on the Santa Lucia site than in the Sierra Nevada site and faster at low than at high elevations. On the Santa Lucia site, shoot emergence and elongation started in mid-November at low elevations (46 feet (23 m)), in mid-January and February at middle elevations (1,840 feet (560 m)), and in late April at high elevations (4,462 feet (1,360 m)). On the Sierra Nevada site, shoot emergence and elongation started in January at low elevations (320 feet (98 m)), in mid-February and March at middle elevations (2,380 feet (725 m)), and in early May at high elevations (4,130 feet (1,260 m)) [133,134]. In a common garden in Carmel Valley, California scrub oak seedlings broke bud and began leafing out in late March, and leaves were fully expanded by late May. This development was significantly later than that of deciduous coast live oak or blue oak (P<0.05) [135].

Coastal sage scrub oak: Coastal sage scrub oak also flowers in spring [52].

Q. dumosa (sl): Acorns disperse in fall, and fall rains stimulate germination [102]. Q. dumosa (sl) acorns ripen in November and December in the San Gabriel and San Bernardino mountains [85]. The leaves are shed in spring, when new evergreen leaves displace them [118,137,180].

Phenology of Q. dumosa (sl) was monitored in the Santa Monica Mountains. The site was in mixed chaparral at 600 feet (180 m) elevation. Stems began growing in mid-March and stopped on 15 May, attaining 0.8 to 1 inch (2-3 cm) in new growth. Leaf expansion occurred from 16 April until early summer [226].

REGENERATION PROCESSES:

Q. dumosa (sl) reproduces from acorns and from sprouts. Sprouting is more common.

Pollination and breeding system: California scrub oak and coastal sage scrub oak are monoecious [39]. Self-pollination is rare in California scrub oak [119].

Seed production: California scrub oak [1,137,180,217] and coastal sage scrub oak [1,79] acorns mature in 1 year.

Acorn production of Q. dumosa (sl) is typically "erratic" [97], although California scrub oak acorn production was noted as "continuous to next fire" in Tecate cypress stands in southern San Diego County. California scrub oaks were producing acorns in all seral stages, including closed Tecate cypress stands [233].

Seed dispersal: Q. dumosa (sl) acorns are dispersed by granivorous animals [102,106,181] or fall near the parent plant. There is potential for long-distance dispersal by birds; however, predation of animal-cached acorns may be high [97]. In a study near Lake Arrowhead, squirrels consumed 100% of the acorns of several scrub oak species present on study plots [181].

Seed banking: California scrub oak has a transient seed bank. Its acorns are viable for less than 1 year [70,102,106]. Animals, including scrub jays [67,122] and rodents [233], may cache acorns of Q. dumosa (sl) and other California oaks in the soil, and unretrieved acorns have a greater likelihood of establishing than unburied acorns [67,122].

Germination: Q. dumosa (sl) acorns do not require stratification [13,184] and may germinate soon after falling off the tree [13,133,134]. In southern California, Q. dumosa (sl) acorns remained viable for at least 2 months after collection [179]. In the laboratory, Q. dumosa (sl) germination ranged from 80% to 90% [28].

Seedling establishment and plant growth: Germinant development and seedling emergence are likely slow in the field. In the laboratory, California scrub oak acorns required about 2 months to complete germination. Seedling growth of the seed lot was "irregular". Growth rates varied among individuals and seemed independent of the various day/night temperature regimes under which they were grown [78].

Best Q. dumosa (sl) germination apparently occurs beneath moist litter or soil, and fire does not enhance germination rates. In the laboratory, Q. dumosa (sl) germination was significantly better at room temperature (70 °F (21 °C)) than at higher temperatures (P<000.1) [100]. Sustained high temperatures were lethal to acorns, although acorns tolerated short bursts of high heat (250-300 °F (120-150 °C)) [100,102]. Germination rates were higher in soil than on filter paper (P<0.05) [100], suggesting that buried acorns may have better emergence rates than acorns on the soil surface. Light and charate—features of early postfire sites—had no significant effect on Q. dumosa (sl) germination [100].

Seedling establishment of Q. dumosa (sl) is most common in late succession [166]. For good recruitment, Q. dumosa (sl) appears to require a year of plentiful rains—especially during fall and winter seedling emergence—on chaparral landscapes that have not burned for half a century or more [102,106]. In southern California , a Q. dumosa (sl) stand that was >100 years old showed high levels of seedling recruitment, averaging 2,500 five-year-old seedlings/ha, 700 ten-year-old seedlings/ha, and 100 twenty-year-old saplings/ha. Across age classes, there were about 100 plants/ha for 20- to 120-year-old stands [99]. In the Santa Ana Mountains, Q. dumosa seedlings established under the canopies of chaparral stands that were 55 to 155 years old and had deep litter layers, but seedlings were rare in younger stands. The ratio of seedlings:live adults was nearly 2:5 in a stand that had not burned in over 60 years [96].

Density and cover of Q. dumosa (sl) in a mature chaparral stand in the Santa Ana Mountains [96]
Age class
Density
Basal area
plants/ha stems/ha m²/ha
Dead, mature shrubs 700 1,600 1.5
Live, mature shrubs 3,420 7,480 31.1
Seedlings 1,300 had not produced sprouts yet <0.1

Surveys in the San Gabriel and San Bernardino mountains found that Q. dumosa (sl) seedlings were generally rare [85]. However, high numbers of Q. dumosa (sl) seedlings have been noted on old burns (see Postfire seedling establishment).

Q. dumosa (sl) may establish more readily and in larger numbers than associated woody species that also have a transient seed bank [166]. In a planting study in Carmel Valley, California scrub oak showed good establishment relative to other oak species. The site was a common garden within a blue oak savanna. Survival of California scrub oak seedlings was 100% in their 1st year and 81% their 2nd and 3rd years [65].

Heavy browsing can slow or stop growth of Q. dumosa (sl). In the Tehachapi Mountains, heavy cattle browsing in the early 1900s apparently arrested oak (Quercus spp.) regeneration for decades [14]. On a new burn in northern San Diego County, heavy browsing pressure from mule deer, small mammals, and moths—combined with an outbreak of powdery mildew—resulted in high mortality of Q. dumosa (sl) sprouts compared to mortality of chamise and desert ceanothus sprouts, which were less heavily browsed [139]. See Importance to Wildlife and Livestock for further information on this study.

Q. dumosa (sl) seedlings and saplings are reported as slow-growing [85]. Saplings may persist in the understory for decades. Sapling root crowns gradually develop into burls, especially with repeated top-kill by fire or under heavy browsing pressure [110].

In the Santa Ana Mountains, Q. dumosa (sl) showed a positive correlation of stem diameter to plant age (r²=0.78). Keeley and others [96] present a model to predict stem age based on stem diameter.

Vegetative regeneration: Q. dumosa (sl) sprouts from the root crown or burl after fire (for example, [96,103]) or other top-killing events, including browsing [33,139], herbicide application [83,90,174,176,177], and cutting [129]. On chaparral sites across California, Keeley [103] noted a few Q. dumosa (sl) sprouts that had originated from roots. Heavily browsed California scrub oaks on Santa Cruz Island sprouted from the base after feral domestic sheep were removed in the late 1950s [32,33]. California scrub oak sprouts were noted on clearcut fuelbreaks in San Diego County [224].

However, California scrub oak and coastal sage scrub oak do not require top-kill to sprout, and adult plants may produce sprouts in all stages of succession [96]. Fites-Kaufman and others [51] classify Q. dumosa (sl) as a "fire-neutral" species that sprouts continuously, with sprout recruitment after fire similar to sprout recruitment without fire. On old burns (>54 years) in the Santa Ana Mountains, Q. dumosa (sl) replaced old stems with new sprouts continually, so stems dating back to the last fire were relatively rare [96].

Although Q. dumosa (sl) seedlings and saplings usually grow slowly, sprouts may grow quickly, especially if they arise from well-developed burls [165]. Sapling sprouts usually show rapid growth after top-kill by fire [110]. On the Laguna-Morena Demonstration Area, Cleveland National Forest, Q. dumosa (sl) sprouts that were produced after either burning or clipping had higher rates of photosynthesis and growth than mature plants [75].

SUCCESSIONAL STATUS:
Q. dumosa (sl) is shade intolerant [180]. However, it occurs in all stages of succession in chaparral, coastal sage scrub, and open woodlands [96,159]. It may regenerate from sprouts in all successional stages, but typically establishes from acorns only in mature (>50 years) stands [96]. Zedler [235] suggested that long-lived, sprouting species, such as California scrub oak and coastal sage scrub oak, can survive from early postfire successional stages through senescence without risk of successional replacement [235]. In Tecate cypress stands in southern San Diego County, California scrub oak occurred in all seral stages of postfire development, including closed stands [233].

Since Q. dumosa (sl) occurs primarily in chaparral or coastal sage scrub, its successional development in these fire-adapted ecosystems is primarily set back by fire. On burned mixed-chaparral sites across northern California, Biswell and others [24] found that soils were typically bare in the 1st postfire winter, but California scrub oak sprouts were common by postfire year 5 [24].

Although it is adapted to frequent chaparral fires [99], frequent fire is apparently not required to maintain Q. dumosa (sl) stands on many sites. Keeley [99] reported that Q. dumosa (sl) was the "clear dominant" on a 100-year-old burn in southern California. Q. dumosa (sl) regeneration was stable due to basal sprouting of old plants. Keeley reported that Q. dumosa (sl) plants were "not dying out and in fact appear to represent a relatively stable community". On a site that burned in a 1919 wildfire on the San Dimas Experimental Forest, Angeles National Forest, crown cover of Q. dumosa (sl) had not changed from surveys conducted in postfire year 14 (1933) and postfire year 34 (1950) [117]. In the San Gabriel Mountains, comparisons of 40- and 63-year-old chaparral burns in adjacent canyons showed little difference in Q. dumosa (sl) density relative to burn age. However, density of chamise and hoaryleaf ceanothus was less on the older burn than on the younger burn. Prefire measurements were not available [170].

Plant response to fire provides more examples of Q. dumosa's (sl) role in postfire succession.


FIRE EFFECTS AND MANAGEMENT

SPECIES: Quercus berberidifolia, Q. dumosa
Species names: The names "California scrub oak" and "coastal sage scrub oak" are used for reports that clearly refer to these species as they are currently defined. "Quercus dumosa (sl)" is used for reports in which is distinction between the 2 species is unclear. See Taxonomy for more information.

FIRE EFFECTS:

Immediate fire effect on plant: Q. dumosa (sl) has thin bark that is easily charred [178], and Q. dumosa (sl) is usually top-killed by chaparral fires [148,178,191] in summer or fall. Even though Q. dumosa (sl) is relatively unflammable, its close association with more flammable vegetation in mixed chaparral usually ensures that aboveground parts are consumed [178]. However, spring fires, or fires in communities with low fuel loads, may only scorch Q. dumosa (sl) [45] (see the Cleveland National Forest study in Fuels, below).

Postfire regeneration strategies (adapted from [202]):
for California scrub oak:
Tree with a sprouting root crown, burl, and/or root sprouts

for both California scrub oak and coastal sage scrub oak:
Tall shrub with a sprouting root crown, burl, and/or root sprouts
Ground residual colonizer (on site, initial community)
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)

for Q. dumosa (sl):
Geophyte, growing points deep in soil

Fire adaptations and plant response to fire:

Fire adaptations: California scrub oak ([4,25,71,168], review by [56]) and coastal sage scrub oak [168] have adapted to fire by sprouting from the root crown or burl. Many have classified California scrub oak as a postfire obligate sprouter (for example, [56,70,71,105]).

Burls generally take time and multiple fires to develop from seedling or sapling root crowns. On old burns across California, Keeley [103] noted Q. dumosa (sl) seedlings and saplings had developed burls only at a 76-year-old burn in San Ignatio, San Diego County. In chaparral ecosystems of southern California, Hanes [71] noted that Q. dumosa (sl) root crowns that had burned repeatedly developed into "rather massive structures" that were 3 to 6 feet (1-2 m) across at the ground surface. He noted the "overriding dominance" of Q. dumosa (sl) in the 2nd postfire decade. By then, Q. dumosa (sl) had grown taller than chamise and associated shrubs, and it had begun to shade them out [71].

Although Q. dumosa (sl) bark is typically thin, the bark of old trees may be thick enough to endure fire. For old trees with relatively thick bark, the outer, dead bark layer may char and slough off, while the living, inner cambium layer remains undamaged. According to a model developed in southern California, a 5-inch (13 cm) DBH Q. dumosa (sl) has bark approximately 0.25 inch (0.63 cm) thick, while a 15-inch (38 cm) DBH individual has bark approximately 0.9 inch (2.3 cm) thick. The authors noted that except for large trees, Q. dumosa (sl) is "almost always topkilled during a fire" [180].

Plumb and Gomez [180] stated that although Q. dumosa (sl) hybridizes freely with other scrub oaks in California, "precise identification of shrub-sized oaks is probably unnecessary from a practical management basis, because small trees—those with stems less than 3 to 6 inches (7.6-15.2 cm)—will almost always be killed to the ground", and all of California shrubby oaks sprout after top-kill [180].

Plant response to fire: Q. dumosa (sl) may sprout in all stages of postfire succession. It generally establishes from acorns late in postfire succession.

Postfire sprouting: Q. dumosa (sl) sprouts from the root crown or burl after top-kill by fire ([4,66,70,71,78,105], Franklin and others 2004 personal observation [55]). Plumb and Gomez [180] noted that if Q. dumosa (sl) fails to sprout in weeks just after fire, it usually sprouts by the next postfire growing season. Surveys of burns in the San Gabriel and San Bernardino mountains found that Q. dumosa (sl) shrubs were sprouting "vigorously" from their root crowns [85]. Holland [81] noted that California scrub oak communities of northern California recovered from fire more quickly than other chaparral communities. In southern California, analyses of sprouting responses of chaparral species 1 and 2 years after wildfires in 2003 determined that California scrub oak's sprouting ability was not related to fire severity (P<0.32) [115]. In mature shrubs, Q. dumosa's (sl) massive underground burl [118] likely protects it from even severe fires.

Keeley [99] reported that Q. dumosa (sl) is "quite resilient" to frequent fires. On five 9- to 88-year-old burns in Los Angeles County, aboveground portions of all Q. dumosa (sl) shrubs examined dated back to the last fire, with stems sprouting from the root crowns [105]. Q. dumosa (sl) shrubs that have been repeatedly top-killed by fire may develop large, dense burls. In San Diego County, mean biomass of Q. dumosa (sl) burls was about twice that of its stems, leaves, and excavated roots combined [118].

In late postfire succession, California scrub oak recruitment often remains in the sapling stage in the chaparral understory until fire top-kills the overstory. Top-killed California scrub oak saplings typically grow quickly after fire. Keeley and Davis [110] suggest that because of this, California scrub oak may be indirectly fire-dependent for completion of the sapling-to-mature shrub stage of its life cycle.

On the San Dimas Experimental Forest, some Q. dumosa (sl) shrubs sprouted as soon as 10 days after a July wildfire. The site had not burned for at least 40 years; the plant community was chamise-Q. dumosa (sl) chaparral. Forty-nine percent of Q. dumosa (sl) stumps were sprouting the November following the wildfire, and 70% were sprouting by December [174]. Slope position and soil moisture apparently affected ability of burned Q. dumosa (sl) stumps to sprout [174,175]. The author observed that Q. dumosa's (sl) best sprouting response occurred near the base of slopes, where soils were deep and relatively moist, while few Q. dumosas (sl) sprouted on shallow, rocky soils. Sprouting response did not seem related to elevation [174].

Q. dumosa (sl) sprouting response 4.5 months after a July wildfire on the San Dimas Experimental Forest [174]
Variable Response
Percent of sprouting stumps by elevation 78% at 2,100 feet (n=118 stumps, 92 sprouted)
68% at 3,100 feet (n=25 stumps, 17 sprouted)
64% at 4,100 feet (n=118 stumps, 76 sprouted)
For sprouters, number of sprouts/stump 44% had <6 sprouts
32% had 6-12 sprouts
24% had >12 sprouts
Height range of sprouts/sprouting stump 15% were <6 inches
10% were 6-12 inches
66% were >12 inches

Part of the burn had been sprayed with a 2, 4-D and 2, 4, 5-T mixture five months prior to the fire; a smaller portion of the sprayed-and-burned area had also been sprayed the previous year. Spraying had been conducted to clear fuelbreaks. About 90% of once-sprayed Q. dumosas (sl) sprouted after the fire. Q. dumosas (sl) sprayed in consecutive years had fewer and smaller sprouts than those sprayed only once [174].

Q. dumosa (sl) sprouting response after 1 or 2 herbicide applications and a wildfire. Surveys were conducted 5 months after the fire [174].
Variable 1 application, n=33 stumps 2 applications, n=34 stumps
Percent of sprouting stumps 91% 88%
Number of sprouts/stump 17% had <6 sprouts 33% had <6 sprouts
10% had 6-12 sprouts 17% had 6-12 sprouts
73% had >12 sprouts 50% had >12 sprouts
Height range of sprouts/sprouting stump none was <6 inches 1 was <6 inches
1 was 6-12 inches 8 were 6-12 inches
29 were >12 inches 21 were >12 inches

Postfire growth of California scrub oak and coastal sage scrub oak sprouts is usually rapid. Pase [168] reports that in chaparral communities, these oaks and their associated shrubs usually attain 50% to 60% of prefire crown cover by postfire year 10 and 80% to 100% crown cover by postfire year 50. Coastal sage scrub oak and other shrubs in coastal sage scrub oak communities may reach prefire crown cover by postfire year 10 due to the relatively shorter stature of shrubs in coastal sage scrub vs. chaparral communities [169]. After widespread, Santa Ana-driven wildfires occurred across southern California in the fall of 1993, Keeley [107] monitored recovery of chaparral species on 90 burned sites. These sites varied in prefire stand age, species composition, and severity of the 1993 fires (based on skeletal remains of the shrubs). On sites with California scrub oak, 98% of burned, skeletal California scrub oaks were sprouting from the base the next spring [107,108,112]; this was the highest level of sprouting success for the 12 sprouting species that were monitored. Although for many species, sprouting ability declined significantly with plant age (as determined by root crown diameter, P<0.001), sprouting ability of California scrub oak was not significantly associated with root crown diameter [108]. California scrub oak had a similar response after the 2002 McNally Wildfire on Sequoia National Forest. This fire burned "ancient", 150-year-old mixed-chaparral stands as well as mature stands (50-60 years old). For California scrub oak, rates of postfire sprouting were lower in the ancient stands (81.7%) than in the mature stands (97.1%), but were still higher than those of all associated sprouting species except hollyleaf redberry (Rhamnus ilicifolia) [115].

Q. dumosa (sl) may continue sprouting through late postfire succession. Keeley [103] noted Q. dumosa (sl) shrubs sprouting from the roots across sites in California, "often a meter or more from the main trunk". It had been 60 to 120 years since the last fire on these sites [103].

Examples of recovery in various plant communities: As of 2012, most published fire studies did not distinguish between California scrub oak and coastal sage scrub oak, and nearly all reported results were from locations where the distributions of the 2 species overlap. Nearly all of these studies were conducted in mixed, Q. dumosa (sl), or other types of chaparral vegetation; examples of postfire succession in communities clearly identified as coastal sage scrub oak were not found in literature (as of 2012). The following studies provide examples of Q. dumosa's (sl) postfire recovery in the 1st or 2nd decade after fire.

In a mixed-chaparral riparian community on the Los Padres National Forest, a crowning, early June wildfire reduced Q. dumosa (sl) importance for at least 3 years after fire. Based on the presence of dead, burned stems measured in postfire year 1, Q. dumosa (sl) had 12.6% relative frequency, 15.2% relative density, and 3.3% relative basal area just prior to the 2002 Wolf Wildfire. Q. dumosa (sl) stems were "common, but small". Top-kill resulted in significant reduction in relative mean density of Q. dumosa (sl) in postfire year 1. Postfire sprouting rate was high for Q. dumosa (sl), with more than 80% of root crowns sprouting in postfire year 3. Most of these sprouts were between 0 and 13 inches (33 cm) tall; maximum sprout height was 5.9 inches (15 cm) [19].

Q. dumosa (sl) sprouts were present in small numbers in surveys of burned sites in Waterman, Barrabca, Fern, and San Antonio canyons, southern California; however, these sprouts grew quickly. Chamise and Eastwood manzanita dominated most burns, which ranged from 1 to 25 years old. Across sites, mean Q. dumosa's (sl) mean sprout height ranged from 3.5 feet (1.1 m) on 3-year-old burns to 4.9 feet (1.5 m) on 10-year-old burns and 12.5 feet (3.8 m) on 25-year-old burns. No Q. dumosa (sl) seedlings were detected [85].

Although Q. dumosa (sl) sprouts generally grow rapidly, disease or browsing may hinder postfire recovery. On the Cleveland National Forest, Q. dumosa (sl) sprouts averaged 2.5 times the maximum photosynthetic rate of 34-year-old stems, as measured in June. Sprouting occurred after prescribed fire or handclearing. However, in August and September, photosynthetic rates of plants sprouting after fire were less than those of mature, unburned plants. The authors did not attribute this directly to drought; instead, they suspected that an outbreak of powdery mildew (Cystotheca lanestris), which resulted in dieback of new shoots, was responsible [75,76]. On six 6-month to 1.5-year-old burns in the San Gabriel Mountains, Q. dumosa (sl) and chaparral yucca (Hesperoyucca whipplei) were the 2 most common codominants after chamise. Mule deer browsed all 3 species heavily on some sites, but browsing did not affect the relative abundance of these shrubs. Browsing pressure on Q. dumosa (sl) was mostly moderate (46% use), but 4% of Q. dumosa (sl) plants were completely consumed. Q. dumosa (sl) tended to dominate north-facing slopes. Q. dumosa's (sl) postfire mortality averaged 7.0%; its postfire density averaged 79 live plants/acre vs. 6 dead plants/acre; and frequency of live plants averaged 37.5%. [116].

As the San Gabriel Mountain study [116] suggests, early postfire abundance of Q. dumosa (sl) is often greater on north- than on south-facing slopes, and this trend likely continues throughout postfire succession on most sites (see Elevation and topography). A November survey, completed after an August wildfire on Otay Mountain, San Diego County, found Q. dumosa (sl) sprouts were most frequent on northwest-facing slopes, while chamise was most frequent on southeast-facing slopes. Overall densities of sprouting shrubs were similar on all aspects, ranging from around 5,000 to 9,000 shrubs/ha [58]. On the Santa Monica Mountains Reserve, California scrub oak dominated north-facing slopes prior to a wildfire. In postfire year 2, it codominated with common deerweed on north-facing slopes. By postfire year 3, however, laurel sumac and sugar sumac assumed dominance on north-facing slopes. In general, species diversity and turnover rates were higher on north-facing than south-facing slopes in these early postfire years (P<0.05) [68].

Q. dumosa (sl) growth may be slow on some burned desert sites. After a wildfire in Joshua tree scrub in Joshua Tree National Park, California scrub oak regeneration was mostly root crown sprouts. In postfire year 4, its growth rate had slowed to about half of that in the previous 3 postfire years. California scrub oak height was less on burned than on unburned sites in postfire year 4. On south-facing slopes, California scrub oak height ranged from 0.8 to 1.2 feet (0.2-0.4 m) on burned sites and 3.8 to 4.1 feet (1.1-1.2 m) on unburned sites. On north-facing slopes, it averaged 1.7 to 2.0 feet (0.5-0.6 m) on burned sites and 3.3 to 3.7 feet (1.0-1.1 m) on unburned sites. Sprouts were not yet flowering in postfire year 4, and a single California scrub oak seedling was located in a burned area. In postfire year 5, California scrub oak density was 40% less on burned compared to unburned areas [4]. In a Joshua tree woodland on the southwestern edge of the Mojave Desert, California scrub oak averaged 0.2% frequency on unburned plots and 0.6% frequency on burned plots. Six burned and adjacent unburned sites were evaluated; the sites were burned in wildfires approximately 3 to 13 years prior to the study [205].

In a desert chaparral community in the San Ysidro Mountains, however, California scrub oak had some of the highest importance values of all shrubs occupying canyons and ridges in early postfire succession. In July 1975, a wildfire burned the desert chaparral, which was dominated by hairy yerba santa (Eriodictyon trichocalyx), sugar sumac, and California scrub oak. Plots were inventoried from postfire month 2 (that summer, in September) to postfire month 10 or 11 (the next spring, in May or June). California scrub oak commenced sprouting that summer and was more productive in canyons than on ridges. Among sprouting species, California scrub oak contributed 19% of total postfire reproduction [211,212].

Response and utilization of California scrub oak on 2 sites, 2 to 10 months after a July wildfire in desert chaparral [212]. Values are means.
Variable Canyon Ridge
Importance value 33% 54%
Spouts/plant

summer, 7*

not present
fall, 58 59
winter, 26 36
spring, 86 62
Biomass (g/plant, dry weight) summer, 2 0
fall, 231 29
winter, 120 16
spring, 340 255
Browsed (%) summer, 0 summer, not present
fall, 26.37 43.09
winter, 29.16 33.49
spring, 0.83 1.31
Total seasonal productivity browsed (%) summer, 0 summer, not present
fall, 13.02 fall, 40.34
winter, 9.36 winter, 36.41
spring, 0.31 spring, 0.38
Length of unbrowsed sprouts (cm (SD)) summer 4.3, (0.5) summer, not present
fall, 30.9 (1.1) fall, 17.8 (not available)
winter, 28.4, 1.8 winter, 17.8 (not available)
spring, 44.4 (1.3) spring, 33.0 (0.9)
*Summer data were collected in Sept.; fall data in Nov.; winter data in Feb.; and spring data from May-June.

In Cuyamaca Rancho State Park, California scrub oak was not abundant after a forest fire but was important after a chaparral fire. California scrub oak was absent from burned plots 2 years after a prescribed winter fire in a mixed-conifer stand, although it was present on unburned control plots. Jeffrey pine and California black oak dominated the stand; California scrub oak was an important component of the prefire community. See Fire Management Considerations and the Research Project Summary of Martin's [132] study for further details on this study. In a 2007 study, conducted 4 years following the Cedar Wildfire in Cuyamaca Rancho State Park, California scrub oak was considered an indicator species of early-seral, postfire chaparral vegetation [54] (see the Cedar burn section of Plant communities).

A survey conducted 6 years and 9 months after a 1970 wildfire in Malibu found Q. dumosa (sl) occurred at 16% frequency. The associated species were species typical of mixed chaparral (mostly chamise, with sugar sumac, deer weed, and other sprouting shrubs) [191].

Postfire seedling establishment: Most Q. dumosa (sl) seedlings do not establish until at least 40 years after fire. A few California scrub oak seedlings may establish in early postfire years [4], but root crown sprouting is the primary means of early postfire regeneration. Many [35,95,167,234] report that scrub oak sprouts but "does not establish seedlings" [35] in early postfire succession. A laboratory study found Q. dumosa (sl) did not respond to conditions induced by fire (high temperatures and charate) that enhance germination in some "fire-following" species [100]. See Seedling establishment and plant growth for more information on this study.

Q. dumosa (sl) seedlings were noted in the San Gabriel Mountains on chaparral sites that had not burned for 40 years [170]. More frequent fires may eliminate seedlings, and very short fire-return intervals may result in Q. dumosa (sl) decline. In southern California, Keeley ([103,104], 1991 unpublished data cited in [101]) found thousands of Q. dumosa (sl) seedlings on chaparral sites that had not burned for 100 years or more. He stated that "it is apparent that long fire-free conditions are required for seedling establishment by...fire-persister shrub species" such as Quercus dumosa [101]. On 60- to 120-year-old burns across California, mean density of Q. dumosa (sl) seedlings and saplings ranged from 0 to 8,890 plants/ha. Keeley rarely found seedlings on burns <50 years old [103]. He concluded that Q. dumosa (sl) requires "long fire-free periods for successful reproduction and potential population expansion" [104]. Surveys of 6- to 61-year-old burns in the Peninsular Mountains of San Diego County and Baja California Norte found no Q. dumosa (sl) seedlings. Greatest cover of mature Q. dumosa (sl) plants was on 12-year-old burns in San Diego County (11%) and on 49-year-old burns in Baja California Norte (9%) [148]. In Tecate cypress stands in southern San Diego County, California scrub oak seedlings were rare in early postfire succession. Greatest seedling establishment was observed in a 90-year-old stand that had patches of deep litter. California scrub oak seedlings occurred in clumps, suggesting establishment from rodent or other animal caches [233].

It is unclear how important a role acorn-caching birds and rodents play in promoting establishment of Q. dumosa (sl) seedlings in postfire or other succession. Studies are needed in this area.

FUELS AND FIRE REGIMES:

Fuels: Q. dumosa (sl) communities are highly flammable during summer and fall, but they may be relatively less flammable than other chaparral types. Fuels in California scrub oak and coastal sage scrub oak communities may be more sparse, and moister, than fuels in chaparral without those oaks, especially on north-facing slopes [63]. Laboratory and field studies found the branches and foliage of Parry manzanita (A. parryana), California scrub oak, hoaryleaf ceanothus, and chamise ranked least to most flammable, respectively. These live fuels were collected near Riverside from October to December and burned either outside in open containers or indoors on raised fuelbeds [204,237]. Moisture content of California scrub oak fuels averaged 60% for fuels <6.3 mm in diameter [204]. In a laboratory experiment, oven-dried Q. dumosa (sl) leaves produced a moderate-intensity flame compared to 7 associated chaparral shrubs, so Q. dumosa's (sl) overall flammability rating was moderate. Leaves were collected at the Rancho Santa Ana Botanic Gardens in Claremont [153]. In another laboratory experiment, fresh California scrub oak leaves ignited at a lower mean temperature (628 °F (311 °C)) than leaves of chamise or hoaryleaf ceanothus, but California scrub oak leaves had the widest range of ignition temperatures among the 3 species. Average time to ignition ranged from 1 to 4 seconds for all 3 species [49]. Bond (unpublished data cited in [111]) suggested that species that can regenerate independently of fire, such as Q. dumosa (sl), tend to be less flammable than those that require fire for regeneration, such as chamise.

Because California scrub oak and coastal sage scrub oak are typically shrubs, they have proportionately more fine fuels than oaks that grow as trees. About one-third to one-half of their aboveground biomass is composed of leaves and small twigs. Green [61] reported that the high surface area:volume ratio and air spacing of Q. dumosa (sl) shrubs encourages fire spread and tends to increase fire severity compared to oaks growing as trees. However, compared to associated chaparral shrubs, the surface area:volume ratio of Q. dumosa (sl) leaves and twigs (126.0 cm²:cm³) is about average [187].

Live fuel moisture of Q. dumosa (sl), which is deep-rooted, is generally higher than that of more shallow-rooted species such as chamise. A review reported that under weather conditions suitable for prescribed burning, fires that spread readily through chamise chaparral often go out when reaching patches of California scrub oak. A laboratory study, using plants collected in October [152] in the San Gabriel Mountains, found the moisture content of Q. dumosa (sl) terminal twigs was lower than that of 5 associated chaparral shrubs. For samples collected in October (simulating fire-season conditions), moisture content of Q. dumosa (sl) twigs averaged 31.6%. Moisture content of saturated twigs (simulating winter conditions) averaged 40.3% [151]. In general, thick leaves, including those of Q. dumosa (sl), were less flammable than the leaves of thinner-leaved species such as tree tobacco [152].

When summer prescribed fires were conducted on the Cleveland National Forest, mixed California scrub oak-desert ceanothus-chamise chaparral had the lowest dead fuel load, making it less flammable than other chaparral types. Several trial runs were needed to develop a successful prescription for this mixed chaparral. When a prescribed fire was conducted in a similar community in April, California scrub oak and chamise were dormant and desert ceanothus was in bud burst. Live fuel moistures were at their lowest points of the year. Fire carried into some California scrub oaks, but it burned in the canopy for <10 seconds. The fire pruned the lower canopy of California scrub oak and temporarily reduced California scrub oak's litter layer; however, when scorched California scrub oak leaves dropped, they left a "large input" of new litter. See Dougherty and Riggan [45] for the fire prescriptions used and descriptions of the sites burned.

Under extended drought, moisture of Q. dumosa (sl) may drop to levels conducive to rapid fire spread. Under severe fire weather conditions, Q. dumosa (sl) fuels may generate higher fire intensities than those of chamise or red shank [111]. The dry, often dense in chaparral communities with Q. dumosa (sl) may provide ideal conditions for fire ignition and spread in some years. Chaparral that has gone decades without fire is most at risk for extremely severe fires [71]. A FARSITE [50] simulation of fire behavior in chaparral-annual grassland mosaics of San Diego County predicted that the slowest rate of fire spread would be in foothill annual grasslands, with spread rates increasing in coastal sage scrub oak, then California scrub oak, with valley annual grasslands showing the fastest rate of fire spread [44].

Q. dumosa (sl) usually accumulates a deep litter layer [85]. In northern California, Holland [81] noted that California scrub oak communities accumulated more litter between fires than other chaparral communities. On the San Dimas Experimental Forest, Q. dumosa (sl) litter and woody debris averaged 17.7 tons/acre (dry weight) on the floors of 31-year-old chamise, hoaryleaf ceanothus, and black sage stands; this was significantly more biomass than the litter and woody debris of associated species in those stands (P=0.1). Mean depth of Q. dumosa's (sl) litter and woody debris was 1.4 inches (3.6 cm) [117]. In southern California, mixed chaparral codominated by California scrub oak usually had the deepest litter, sometimes more than 8 inches (20 cm) thick. Mixed chaparral with Q. dumosa (sl) tended to occur on north-facing slopes; stands were typically 10 to 18 feet (3-5 m) tall. Nearly pure California scrub oak chaparral also occurred mostly on north-facing slopes, but its litter was only moderately deep (<7 inches (18 cm)). California scrub oak stands were 4 to 12 feet (1-4 m) tall. Litter was not described for maritime chaparral types, but in maritime California scrub oak chaparral, stands were usually <6 feet (2 m) tall. Coastal sage scrub oak replaced California scrub oak as the dominant in maritime chaparral of San Diego County. Stand structure was similar to that of maritime California scrub oak chaparral, but vegetation in coastal sage scrub oak maritime chaparral was less dense [70].

Q. dumosa's (sl) sclerophyllous leaves may decay slowly on some sites. In a California scrub oak-chamise-desert ceanothus community in San Diego County, California scrub oak litter was the slowest to decay among the 3 dominant species. Bagged California scrub oak litter decayed most rapidly when buried, decayed slowly on the ground surface, and showed almost no decay when hung in the shrub canopy. Litter bags were positioned in fall and left for 6 months to 2 years before collection. After 2 years, there was approximately a 15% loss of biomass for California scrub oak leaves on the soil surface and an approximate 22% loss for buried bags [232]. On a mixed-chaparral site in San Diego County, however, decay rate of Q. dumosa (sl) leaves was about average among associated shrub species. Q. dumosa (sl) foliage showed a decay rate of 21% in 18 months (Yielding 1987 cited in [48]).

Fuel loads in chaparral may reach 30 to 40 tons/acre (Philpot 1963 cited in [71]). Green [63] found that 5 to 10 years after fire in Q. dumosa (sl)-mixed chaparral, stands generally contained ≤10% dead fuels, which were mostly burned stems left from the fire. Stands with 10% to 20% dead fuel were "quite resistant" to prescribed fire, but stands might burn with dead fuel loads of 25% to 35%. On south-facing slopes, this might occur 20 to 25 years after fire. Q. dumosa (sl)-mixed chaparral stands that were 40 to 80 years old might have 40% to 50% dead fuels. Coastal sage scrub communities typically had thicker litter layers and proportionally higher dead fuel loads, so they usually burned at a younger age and had wildfires more frequently than mixed chaparral with Q. dumosa (sl) [63].

Wakimoto [223] provides models to estimate total and species' fuel loads, including that of California scrub oak, in mixed-chaparral communities of southern California. Weise and others [227] provide a model to help predict spread of ignited California scrub oak, Parry manzanita, hoaryleaf ceanothus, and chamise fuels based on fuelbed studies in the laboratory. Variables examined included fuelbed depth, windspeed, and slope [227].

Fire regimes:
Chaparral: California's chaparral communities have stand-replacement fires. Most vegetation is highly flammable during the late summer-early fall fire season, so fires are intense [12]. Biswell [22] noted that in summer, fire hazard is "extremely high and wildfires are common". In southern California, the Santa Ana Winds, which drive dry air from the Great Basin to the Pacific coast, bring high temperatures and <10% humidity; they may reach 62 miles (100 km)/hr [109,111]. They are most common in autumn, usually lasting about 3 days but sometimes blowing for 2 weeks. Duration of Santa Ana Winds is critical in determining fire size (review by [111]). A report by National Weather Service personnel stated that Santa Ana Winds "create the worse fire weather conditions in the country because several days or weeks of these winds occur every autumn, at the time natural fuels are at their driest" [194].

Coastal sage scrub has active crown fires that occur mostly in summer or fall. Human ignitions have likely increased fire frequency from historical frequencies. For the most part, fire sizes may be less than they were historically, although some fires might have burned thousands of hectares [109]. Fires usually burned up to 80% of the landscape, but fire intensity was variable. Different-sized fires produced a landscape mosaic of different age classes (review by [111]). Historical fire-return intervals averaged about 10 years in coastal sage scrub communities [98]; however, fire-return intervals of several decades were also common (review by [111]).

Aspect, marine influence, and species composition influence fire-return intervals in chaparral [12]. Chamise, for example, is highly flammable, and chamise-dominated communities may burn relatively frequently [12]. Q. dumosa (sl) is less flammable than chamise (see Fuels). Fire-return intervals of mixed chaparral are variable, depending on local site conditions, past fire use, and elevation [198]. They typically range from 20 to 50 years but fires may be as short as 10 years ([70], review by [198]) to 25 [12,24] or as long as 100 years (review by [198]). Minnich [146] estimated a mean fire-return interval of 70 years for chaparral in San Diego County. He surmised that this was similar to the historical mean [146]. Presently, most of the area burned is due to a small number of large fires. This is especially so in southern California, where fires are mostly human-ignited and occur in fall [12].

Models developed by Franklin and others [56] suggest that as an obligate postfire sprouter, California scrub oak is best adapted to stand-replacement fires at frequent to moderate intervals (35-70 years). On burned sites in coastal southern California, Q. dumosa (sl) had greatest cover in the 9- to 21-year-old age class (18.6%). Cover was similar in the 2- to 8-year-old (10.3%), 22- to 40-year-old (12.5%), and 41- to 96-year-old (12.5%) age classes [71]. This suggests that Q. dumosa (sl) is adapted to variable fire-return intervals in southern California's coastal chaparral. On the San Dimas Experimental Forest, crown cover of Q. dumosa (sl) had changed very little in 1933 and 1950 surveys, taken in postfire years 14 and 34, respectively. In mixed chaparral, Q. dumosa (sl) crown cover was 0.7% in postfire year 14 and 0.8% in postfire year 34 [117].

Chaparral types in general are stable despite differences in fire-return intervals. Halsey [70] writes that under a natural fire regime, "chaparral replaces chaparral". He reports that a 5-year-old chaparral community has accumulated enough fuels to support another fire (Halsey 2005 unpublished data cited in [70]). Hanes [72] reported that "generally, the impact of man on chaparral has not been extensive". Despite considerable effort and expense to replace or modify chaparral, the shrubs reestablish [72]. Except in early postfire years, when chaparral is less likely to burn, the age of a chaparral stand has little relationship to its chances of burning [154].

Many authors confirm that Q. dumosa (sl) chaparral is stable over time. Biswell's [22] studies in the 1940s and 1950s showed little change in total acreage of California chaparral, but the shrub component had increased in oak woodlands with a shrubby understory. A large vegetation survey (17,000 plots) in the 1930s found that California scrub oak chaparral occupied 4,070 acres (1,647 ha) in the central Sierra Nevada; 467 acres (189 ha) of this had burned. Vegetation maps of scrub oak (Quercus spp.) chaparral types in the 2000s showed a gain of 27,278 acres (11,039 ha) over the 1930s area. The map survey did not separate California scrub oak from other scrub oak types or burned from unburned areas [208]. In San Diego County, comparisons of vegetation-type maps from the 1930s and 2001 showed a slight increase in California scrub oak cover but not in frequency. Mean California scrub oak cover and frequency were 14% and 31%, respectively, in the 1930s compared to 17% and 33% in 2001. The area burned frequently: out of 649 plots, 41% had 1 fire and 40% had 2 or more fires, with the number of fires recorded ranging from 0 to 8/plot. Cover of California scrub oak and other "obligate resprouters" was positively correlated with elevation (maximum=5,118 feet (1,560 m), P<0.01) and northeast aspects (P<0.001), while slope, stand age, and fire frequency had no significant relationship with presence of California scrub oak and other sprouting species [55]. In studying 56- to 120-year old chaparral sites across California, Keeley [103] found all sites were dominated by sprouting shrub species, and invasion of tree seedlings was minimal. For Q. dumosa (sl), basal cover ranged from 2.4m²/ha to 38.2 m²/ha; sprout numbers from 0 to 16.5 ramets/genet; and density of seedlings and saplings from 30 to 8,890 plants/ha. Sprout density was greatest at the northernmost site. Q. dumosa (sl) was overtopping Ceanothus on some sites. These stands had high loads of dead Ceanothus and chamise; this "contrasted markedly" with the general lack of mortality in Q. dumosa (sl) [103]. Surveys on private chaparral communities in California showed no net change in California scrub oak cover from 1984 to 1994; it remained at 50% in scrub oak and mixed-montane chaparral [144]. Minnich [146] stated that as a vegetation type, chaparral appears stable.

A fire history of San Diego County's wildlands was constructed using fire records from 1900 to 1997. Both California scrub oak and coastal sage scrub oak occurred in the chaparral vegetation [228], and both may have also been present in the coastal sage scrub vegetation. The study found that fires were more frequent in chaparral and coastal sage scrub vegetation than in herbaceous, forest, and desert vegetation types. Over time, fire frequency was stable in chaparral and increasing in coastal sage scrub. Chaparral was the largest vegetation type, covering about 884,805 acres (358,068 ha). Coastal sage scrub ranked 3rd in size (233,947 acres (94,675 ha)); desert vegetation ranked 2nd. Seventy-seven percent of chaparral's total area, and 72% of coastal sage scrub's, burned during the study period. Most chaparral vegetation was 30 to 50 years old; most coastal sage scrub was 0 (newly burned) to 30 years old. Compared to other vegetation types, more of the chaparral and coastal sage scrub vegetation had reburned (30% and 39% of their total areas, respectively). Chaparral had reburned an average of 7 times; coastal sage scrub had reburned an average of 6 times. The number of ignitions and area burned decreased with elevation [228].

Some argue that fire exclusion does not work in California's chaparral. Hanes [71] faults the failure of the fire exclusion policy to deal with time, writing that "Eventually any stand of chaparral will catch fire and burn". He sees chaparral wildfires as both natural and inevitable [71], finding no good evidence that chaparral wildfire can be prevented (Pillsbury 1963 as cited in [71]). Fire-return intervals in southern California chaparral have ranged from 40 to 60 years in the 1900s. Minnich [146] contends that this does not differ substantially from presuppression-era fire-return intervals, although fire size may have increased in the 20th century. Humans have replaced lightning as the most common source of ignitions in chaparral of southern California. Keeley and others [111] concluded that because "fire prevention has been ineffective at eliminating human fires, presently and for the foreseeable future, fire suppression is required just to maintain some semblance of the natural fire regime".

The effects of climate change on the fire regimes of chaparral and coastal sage scrub ecosystems are difficult to predict. Keeley and others [111] postulate that increases in carbon dioxide may increase plant growth and consequently, fuel loads and continuity. However, increased leaf areas and plant productivity—coupled with increased summer temperatures—may reduce available soil water in these droughty ecosystems, reducing or negating the effects of increased carbon dioxide on fuel loads. They concluded that human land uses of these ecosystems will probably be a stronger factor in determining future fire regimes of these shrublands than other global changes, including climate change [111].

Oak woodlands: California's oak/grass woodlands historically experienced surface fires every 5 to 25 years [200]. These frequent fires burned at low severities, which tended to kill shrub seedlings and keep the shrub layer short [69,219]. Native perennial grasses likely fueled these mostly fast-moving fires [69]. Occasional mixed-severity fires also occurred [172]. Because these communities form a mosaic with or lie between chaparral and low-elevation ponderosa pine woodlands, chaparral shrubs or conifers formed pockets where fire crowned, resulting in more lethal effects to vegetation, especially nonsprouting species [219]. This regime of frequent surface fires and occasional mixed fires likely maintained California scrub oak as an understory shrub.

After nonnative annual grasses replaced native perennial herbs in the groundlayer vegetation [3], the annual grasses became the primary fuel in oak woodlands. With fire exclusion, chaparral shrubs have invaded the understories of many oak woodlands, increasing fuel loads, fuel continuity, and flammability of the oak woodlands [25].

California Indians set fires in oak woodlands and forests regularly [57]. Q. dumosa (sl), a component of many of these communities, likely benefitted from this practice. California scrub oak grows in ponderosa pine-California black oak woodlands of Yosemite Valley. Ethnographic records indicate that Miwoks burned the valley often [18], in part to promote seed production in oaks and pines (see Other Uses). California Indians also burned the woodlands and forests in the Tehachapi Mountains regularly (Jepson 1910 cited in [14]). During the early 1900s, the ranch hands who were the last to drive cattle down from the foothills routinely ignited the rangelands to keep shrubby vegetation low [14].

See the Fire Regime Table for further information on fire regimes of vegetation communities in which California scrub oak and coastal sage scrub oak may occur.

FIRE MANAGEMENT CONSIDERATIONS:
Q. dumosa (sl) has adapted to stand-replacement, chaparral fires at intervals varying from <5 to 90+ years. It may gain dominance after several fires in "rather close succession" [34]. In chaparral, its ability to sprout with or without fire [51,96] likely makes it less vulnerable to relatively long fire-free intervals than associated species such as chamise, which become senescent on landscapes that have not burned for nearly a hundred years [71,77]. Because California scrub oak is not shade tolerant [180], long fire-free intervals in oak or oak-pine woodlands probably results in its successional replacement by less shade-sensitive species.

Fire for resource benefit: Chaparral is often close to residential and other urban areas, so prescribed fires may be considered too risky in most locations. However, prescribed fire is not needed to return fire to chaparral landscapes. Keeley and others [111] stated that there "may be little justification for using fire for resource benefit, since vast portions of shrubland landscape currently experience a higher than normal fire frequency". "Lack of fire does not appear to pose a risk because postfire studies demonstrate that both chaparral and coastal sage shrub regeneration are highly resilient to even the most extreme fire events occurring after a long hiatus of burning" [107,111,114].

Escaped fires are hazardous in crown-fire ecosystems such as chaparral, especially in the wildland-urban interface. There are strict limitations on acceptable wind speeds, air temperatures, relative humidities, and fuel moisture levels (see [111] for details). The window for acceptable fire weather is so narrow that chaparral fuels may be too wet too burn under prescribed conditions [61], especially for stands <20 years old [111]. At Camp Pendleton, for example, an attempted late-summer prescribed fire failed to burn a Q. dumosa (sl) community when relative humidity was 65% and windspeed was 8 miles (13 km)/hour [36].

There may be benefits in using prescribed fire on some sites with California scrub oak, however. Prescribed fire in 3- to 5-year intervals may be used to reduce California scrub oak height and density, making browse more accessible to ungulates [130]. On the Hopland Research and Extension Center, several treatments were applied to mixed chaparral to reduce shrub density and height, which was >6 feet (2 m), and to increase herbaceous forage. Cattle and domestic sheep were stocked on the rangeland. All plots were crushed to encourage fuel continuity and fire spread, then burned under prescription and seeded with herbs. Some plots had no treatments other than fire. On other plots, treatments used in combination with fire included grazing; herbicide spraying; and grazing and spraying. Treatment sequence was [156].

1. Mechanically crush shrubs (summer 1956); burn all plots (fall 1956)
2. Seed all plots with pasture grasses and forbs; exclose rodents, mule deer, and livestock from a portion of the area and allow grazing on the rest (fall 1957)
3. For herbicide plots, spray with a mix of 2,4-D and 2,4,5-T (June 1958); respray sprouts (summers of 1959, 1963)
4. For grazed plots, reburn to reduce sprouts (falls of 1959, 1963)
5. Reburn fire-only plots (falls of 1967, 1970); grazed plots did not need this treatment because grazing had controlled sprouts by this time

By 1972, the herbicide treatment had proven most effective in reducing shrub height and density, followed by grazing and reburning, reburning alone, and grazing without reburning, respectively. No visual differences in shrub height or density were apparent on grazed vs. ungrazed plots. For burn-only plots, follow-up prescribed fires were set every 3 to 4 years to keep shrub stands short and open. The authors concluded that when fire is "used in conjunction with grazing, its effectiveness is greatly improved—in this study about 60% less brush grew when the burned area was grazed" [156]. Grazing treatments were not described in the study.

Green [62,63] provides information on developing fire prescriptions in chaparral. On the North Mountain Experimental area near Banning, he conducted a mid-May prescribed fire in chamise chaparral to reduce fuels. Q. dumosa (sl) tended to grow in thickets; in those areas, Q. dumosa (sl) height (12 feet (4 m)) and fuel volume were about double those of chamise. See Green [60] for information on moisture contents of Q. dumosa (sl) and other shrubs, the fire prescription and behavior, and fuel load contributions of individual shrub species. Fuel loads of Q. dumosa (sl), and total fuel loads of all shrub species, are shown below [60]:

Mean shrub fuel weights (tons/acre) before prescribed fire and in postfire year 1. Data were collected in chamise chaparral in North Mountain Experimental Area, California [60].
  Prefire Postfire Prefire Postfire
Fuel consumed (%)
 
Q. dumosa (sl)
Total, all shrubs
Q. dumosa (sl)
Total, all shrubs
Standing live 5.0 3.0 27.5 8.0 40 70
Dead 0.5 0 7.5 0.3 100 95

Reducing fuel loads manually or mechanically is an option in chaparral-urban interfaces or other areas where prescribed fire is considered too risky. In Rancho Santa Fe, San Diego County, the California Division of Forestry initiated a fuels-reduction program in a neighborhood with designated open space. However, the "open space" was a dense stand of 60-year-old mixed chaparral dominated by California scrub oak, chamise, and nonnative river redgum (Eucalyptus camaldulensis) and purple pampas grass (Cortaderia jubata). The stand was decadent: 50% to 80% of standing plants were dead, with many dead branches on live plants and much woody debris on the ground. The area was designated a "very high fire hazard zone". In the treatment, only dead material was harvested from California scrub oak and other native shrubs, but since most standing plants were dead or contained high amounts of dead material, this greatly reduced stand density. Additionally, river redgum and purple pampas grass, both of which are highly flammable, were treated with herbicide, and woody debris was removed. All woody material was chipped and spread on equestrian trails to reduce potential for trail erosion. Besides successfully reducing fuel loads, these treatments increased recreational use of the area. The authors reported that the "open space" was impenetrable prior to fuel reduction, but the community used it regularly afterwards [43].

Prescribed fire is generally less risky in oak woodland and oak-pine communities of California, and it has been successfully used to reduce abundance of Q. dumosa (sl) and other shrubs in the understories of those communities. In the Oakzanita section of Cuyamaca Rancho State Park, a prescribed fire was ignited on 3 December in a ponderosa pine-California black oak forest. This community had a dense chaparral understory dominated by pointleaf manzanita; California scrub oak was the 3rd most common understory shrub. California scrub oak density on study quadrats was 55 plants/ha before the fire; 6 months after the fire; its density was reduced to 0 plants/ha. Overall, shrub density was significantly reduced by the fire (P<0.01). The authors concluded that if applied at frequent intervals, prescribed fires can help keep the chaparral understory under control [123]. See the Research Project Summary of this study for information on the fire weather, prescription, behavior, and the effects of this fire on other shrub, tree, and herbaceous species. In addition to the Oakzanita site, the Research Project Summary provides information on 2 other prescribed fire studies conducted in ponderosa pine-California black oak forest sites in Cuyamaca Rancho State Park.

Other fire management considerations: Studies on a burned area of the Ventura River Watershed suggest that California scrub oak postfire growth is not affected by rehabilitation treatments using seedings of nonnative annual grasses. Italian ryegrass (Lolium multiflorum) was seeded the winter after a July wildfire. California scrub oak was dominant on the site before and after the fire. After fire, it was more important on seeded areas (83% total shrub basal area) than on unseeded areas (74% of total). However, associated chamise, Eastwood manzanita, and many native herbaceous species were more important on unseeded than on seeded areas [157]. California scrub oak was sprouting "vigorously" the next spring, and "appeared unaffected by the ryegrass seeding" [163].

Limited data suggest that the effects of burned Q. dumosa (sl) litter on associated plant species may vary. These effects are not well studied or well understood. One study suggests that the burned, once-thick litter layers of Q. dumosa (sl) may enhance growth of groundlayer species. The year after summer wildfires in chaparral on the San Dimas Experimental Range and in a ponderosa pine forest on Donner Ridge, cover of herbaceous vegetation was significantly greater on Q. dumosa (sl)-dominated sites compared to sites dominated by chamise, Eastern Mojave buckwheat, or ponderosa pine (P=0.1). The authors attributed this enhanced growth to higher nutrient levels under Q. dumosa (sl) than under the other community dominants. The ash layer in Q. dumosa (sl) was the deepest among the 4 community types [185]. However, a laboratory experiment suggests that water-repellent soil layers that may form beneath burned Q. dumosa (sl) may impede the ability of some plant species to obtain soil water. In a burn chamber, old, undecomposed California scrub oak litter distributed heat 0.4 to 1.2 inches (1-3 cm) into a sand substrate when the litter was burned. This created a water-repellent layer at that depth. This water-repellent layer was deeper and wider than those created under old, undecomposed litter of annual grasses or chamise, but it was not as deep as that created under Coulter pine litter [42].

Many wildlife species use California scrub oak's postfire sprouts as food and California scrub oak burns as habitat (for example, [116,139,212,230]). In desert chaparral in the San Ysidro Mountains, bighorn sheep averaged 43% consumption of postfire California scrub oak sprouts, with some California scrub oaks consumed "to near ground level". Behind sugar sumac, California scrub oak sprouts were the 2nd most utilized browse [212] (see discussion of the San Ysidro Mountains study for more details). A study in the San Gabriel Mountains showed desert bighorn sheep ewes prefer new California scrub oak burns as winter and spring rangelands [80]. Populations of insectivorous rodent and lizard species may increase after fire [126,127]. See Importance to Wildlife and Livestock for details on these population studies.


MANAGEMENT CONSIDERATIONS

SPECIES: Quercus berberidifolia, Q. dumosa

FEDERAL LEGAL STATUS:
None

OTHER STATUS:
As of 2012, NatureServe [158] ranked coastal sage scrub oak as a G1-G2 species: Imperiled to Critically Imperiled due to extreme rarity and a very restricted range. Coastal sage scrub oak was probably never very common. It is considered one of California's rarest and most endangered species, at high risk for further decline [52]. The narrow strip of coastline that constitutes its habitat is among the most desirable and expensive real estate in California [160,171]. Real estate development is considered its greatest threat. California scrub oak is ranked Globally Secure [158].

IMPORTANCE TO WILDLIFE AND LIVESTOCK:
California scrub oak is an important browse species for ungulates. Its typically low growth form makes branches easily accessible [131]. Surveys in the San Gabriel and San Bernardino mountains found that mule deer browsed Q. dumosa (sl) heavily [85]. In a Lake County study, mule deer browsed California scrub oak at about 53% mean frequency from February through April. They consumed California scrub oak browse most heavily in May, when frequency of use averaged 79%. California scrub oak was among 5 of the most-used species in the mixed-chaparral community. On unburned sites with dense shrub cover, California scrub oak acorns comprised 60% use, by volume, of the mule deer diet in February. Acorns were little used for the rest of the study period and were not consumed on open, unburned stands or on an 18-month-old burn [21]. On the Tehama Winter Deer Range, mule deer browsed California scrub oak nearly year-round except for March and November green-up periods. Use was heaviest in winter, peaking in January at 80% frequency and 31% of the total volume of their diet [124]. On the Hopland Field Station, California scrub oak comprised 51% to 59% of the diet of domestic goats. The community was codominated by California scrub oak and chamise; the domestic goats browsed both species about as much as expected based on those species' relative dominance [196].

Ungulates and other browsing animal species generally favor Q. dumosa (sl) sprouts over older Q. dumosa (sl) browse. In northern San Diego County, a 6.2-acre (2.5 ha) plot in a chamise-desert ceanothus community was burned under prescription on 9 December 1981. The summer after the fire, nearly 100% of all sprouting species, including Q. dumosa (sl), survived and were sprouting. Mule deer browsed Q. dumosa (sl) sprouts in June and July (postfire months 7-8); Q. dumosa (sl) was the only shrub they selected. Small mammals browsed other shrubs but preferred Q. dumosa (sl); they browsed 20% of sprouting Q. dumosa (sl) plants the 1st summer after the fire and 45% in the 2nd summer. California oak moths browsed Q. dumosa (sl) leaves in August and September (postfire months 9-10), causing an 11% loss of leaf tissue [139].

Herbivorous rodents consume Q. dumosa (sl) browse. Based on food cache contents, Q. dumosa (sl) leaves were a preferred food of San Diego woodrats on the San Dimas Experimental Forest. California scrub oak acorns were also stored but were not a major food source [87]. In Mendocino County, dusky-footed woodrats were positively associated with California scrub oak density (Cavarallo1978 cited in [159]). In a cafeteria study using plant species collected from a coastal sage scrub community near Irvine, western harvest mice, California mice, cactus mice, deer mice, and little pocket mice browsed California scrub oak as much as expected based on availability (7% California scrub oak cover; 6%-25% consumption), and Pacific kangaroo rats browsed it more than expected (25%-50% consumption) [136]. See Wirtz [230] for information on rodents using burned and unburned chamise-ceanothus-manzanita-Q. dumosa (sl) chaparral stands.

Many mammal and bird species consume California scrub oak acorns. When a 5-year drought on Santa Cruz Island was broken by spring and summer rains, California scrub oak produced acorns that fall, while coast live oak required another year to produce acorns. The California scrub oak mast was the primary food of feral pigs the first fall following the drought [173]. American black bears [203], mule deer, cattle [21], and various small mammals and birds also consume Q. dumosa (sl) acorns. A statewide analysis found Q. dumosa (sl) comprised 5.8% of the band-tailed pigeon's November diet [199].

Plant communities with Q. dumosa (sl) are important habitat for mule deer and bighorn sheep. Mule deer may use chaparral and oak woodlands with California scrub oak frequently. In California scrub oak chaparral, mule deer generally prefer early-seral burns, where sprouts are accessible for browsing. The Tehama Winter Deer Range, where California scrub oak is a dominant species, is valuable habitat for mule deer [124]. Ungulate use of California scrub oak habitats may vary with site and season, however. On the Mendocino National Forest, female mule deer used mixed chaparral with California scrub oak less than expected based on its availability, preferring montane Oregon white oak-California black oak forests [128]. A model predicts that 15-year-old ceanothus-chamise-California scrub oak burns provide optimal habitat for bighorn sheep in the San Gabriel Mountains [27]. A study there found desert bighorn sheep used mixed chaparral as winter and spring rangelands; California scrub oak dominated north-facing slopes of the chaparral mix. Ewes used new burns within the mixed chaparral matrix more than expected based on the availability of new burns (P<0.001). Based on hunting harvest data, mule deer also preferred these burns as habitat [80].

Many bird species use Q. dumosa (sl) habitats. See Stanton [201] for a list and discussion of birds using burned coastal sage scrub vegetation in Los Angeles County. Q. dumosa (sl) was a dominant species on north-facing slopes in this study [201]. Wirtz [231] provides a list and discussion of birds using mixed chaparral with Q. dumosa (sl) as habitat.

Newly burned chaparral communities provide important habitat for rodents and reptiles that prefer open, early-seral shrublands. Agile kangaroo rats were observed on burned areas soon after an August wildfire in chamise-Q. dumosa (sl)-hoaryleaf ceanothus in Riverside County, and their population increased over 5 postfire years. Deer mice inhabited the burn by postfire year 3 [182]. In the San Gabriel Mountains, western fence lizards, common side-blotched lizards, western whiptails, and California whipsnakes were observed 1 to 3 years after a wildfire in a chamise-Q. dumosa (sl)-manzanita-ceanothus chaparral stand. These reptiles are known to prefer open habitats [197].

In the Laguna Mountains, San Diego County, San Joaquin fence lizards used California scrub oak branches as perches. Overall, the lizards apparently preferred basking on charred California scrub oak branches on wildfire-burned sites over other types of perches on other sites, although they also perched on live California scrub oak branches, rocks, and boulders. Generally, dark-colored San Joaquin fence lizards were observed most often on charred California scrub oak branches, while light-colored San Joaquin fence lizards were usually seen on light-colored substrates. The authors speculated that the wildfire increased the carrying capacity of the chaparral site for San Joaquin fence lizards due by creating substrates favorable for thermoregulation [127] and by increasing the supply of insects. Flowering peaked in early postfire years on the burn. Both reptiles and rodents hunted insect pollinators that were attracted to the burn by the mass of flowers [126].

Q. dumosa (sl) is a host of gall-forming Cyinpine wasps [40].

Palatability and nutritional value: Palatability of Q. dumosa (sl) browse is rated good for mule deer [46,190] and domestic goats [46,64,131] and poor for domestic sheep, cattle, and horses [46,190]. On Santa Cruz Island, feral domestic sheep preferred chamise to California scrub oak browse. California scrub oak height tended to increase with increasing browsing pressure in the California scrub oak-chamise woodlands [33]. On a new burn in desert chaparral, bighorn sheep consumption of California scrub oak dropped from postfire month 2 to postfire month 11, as leaves became increasingly leathery [211]. See the discussion of this San Ysidro Mountains study for details.

Q. dumosa (sl) provides a steady supply of moderate-quality protein year-round [20]. On sites across southern California, nitrogen content of the leaves was approximately proportional to concentrations of nitrogen in the soil [48]. Young sprouts are preferred over older browse [190], and the nutritional value of sprouts drops over time. In Lake County, protein content of California scrub oak browse decreased with time since burning [28].

See these sources for information on the nutritional value of Q. dumosa (sl) browse: [20,46,190] and this source for the nutritional value of its acorns: [8]. Sampson and Jesperson [190] provide nutritional analyses of California scrub oak in Tehama County, and Yeilding [232] provides information on nutritional content of California scrub oak litter in San Diego County.

Cover value: California scrub oak provides thermal, hiding, and escape cover for many birds and mammals, including mule deer and black-tailed jackrabbits [11,190]. California scrub oak provides shade for domestic livestock [190] and perching and nesting sites for many birds [220]. Dense oak chaparral, which is sometimes dominated by California scrub oak, provides thermal cover for small predators such as gray foxes and bobcats.  Fallen oaks provide cover for deer mice, skunks, and squirrels.  Northern raccoons frequently use hollow oaks as dens [11].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Q. dumosa (sl) is recommended for erosion control [85,190] and provides watershed protection [137,180]. See these sources for information on propagating and planting California scrub oak and coastal sage scrub oak: [28,85,181].

OTHER USES:
Q. dumosa (sl)is generally too small to provide high-quality firewood [137,180] or lumber.

Acorns of Q. dumosa (sl) and other oaks were a food staple of California Indians [5], although its acorns were apparently not preferred [210]. Chesnut [37] reports that Q. dumosa (sl) acorns are extremely bitter, so California Indians rarely used them. In the Interior Peninsular Ranges, the Cahuilla used meal from California scrub oak acorns as filler, mixed with the more palatable meal of California black oak acorns [15].

OTHER MANAGEMENT CONSIDERATIONS:
Mixed-chaparral communities with a California scrub oak component were rated moderately invasible, based on presence of nonnative, invasive woody species and soil water content during the dry season. Coastal sage shrub communities were rated highly invasible, and Mojave Desert scrub was rated low in invasibility. Mixed chaparral was susceptible to invasion by shrubs from mediterranean regions elsewhere on the globe, including Acacia spp., brooms (Cytisus spp., Spartium spp.), and tree tobacco (Nicotiana glauca) [91].

California scrub oak seems fairly resistant to herbicides. At least 3 applications may be required to control sprouts [176]. In the San Gabriel Mountains, California scrub oaks were sprayed with a mix of 2,4-D and 2,4-5-T in May 1950. California scrub oak density was 49 plants/100 feet² during the postspray growing season of 1950. Density dropped to 35 plants/100 feet² after a 2nd treatment in October 1951 and to 7 plants/100 feet² after a 3rd treatment in June 1953. Pretreatment density was not reported [93].


APPENDIX: FIRE REGIME TABLE

SPECIES: Quercus berberidifolia, Q. dumosa
The following table provides fire regime information that may be relevant to California sage scrub and coastal sage scrub oak habitats. Follow the links in the table to documents that provide more detailed information on these fire regimes.

Fire regime information on vegetation communities in which California sage scrub and coastal sage scrub oak may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [121], which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
California Grassland
California grassland Replacement 100% 2 1 3
California Shrubland
Chaparral** Replacement 100% 50 30 125
Coastal sage scrub** Replacement 100% 50 20 150
Coastal sage scrub-coastal prairie** Replacement 8% 40 8 900
Mixed 31% 10 1 900
Surface or low 62% 5 1 6
Montane chaparral Replacement 34% 95    
Mixed 66% 50    
California Woodland
California oak woodlands Replacement 8% 120    
Mixed 2% 500    
Surface or low 91% 10    
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
California Forested
California mixed evergreen Replacement 10% 140 65 700
Mixed 58% 25 10 33
Surface or low 32% 45 7  
Coast redwood Replacement 2% ≥1,000    
Surface or low 98% 20    
Mixed evergreen-bigcone Douglas-fir (southern coastal) Replacement 29% 250    
Mixed 71% 100    
*Fire Severities—
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [73,120].
**Either California scrub oak or coastal sage scrub may occur in communities marked with a double asterisk; information from other communities in this table applies only to California scrub oak.

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