Quercus dumosa 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fagales Fagaceae

Scientific Name: Quercus dumosa Nutt.
Common Name(s):
English Coastal Sage Scrub Oak, Nuttall's Scrub Oak
Taxonomic Source(s): Trehane, P. 2007-2015. The Oak Names Checklist. Available at: (Accessed: 2 February 2016).

Assessment Information [top]

Red List Category & Criteria: Endangered B2ab(ii,iii,iv,v) ver 3.1
Year Published: 2017
Date Assessed: 2016-11-28
Assessor(s): Beckman, E.
Reviewer(s): Oldfield, S.
Contributor(s): Meyer, E. & McIntyre, P.
The Coastal Sage Scrub Oak (Quercus dumosa) is known to be rare and in decline, facing compounding past and future threats. This scarcity can be seen quantitatively in the recently-reviewed spatial data provided by the California Native Diversity Database, from which the extent of occurrence (EOO) is calculated to be about 12,500 m2, with an area of occupancy (AOO) of  620 m2. Although the number of mature individuals is not known, it can be seen spatially that only three locations remain for Q. dumosa: one cluster in far southern California, another near Laguna Beach, and a final location further north near Santa Barbara. The Laguna Beach location is facing the most stress currently, and may be lost to development. Using Criterion B, the EOO places Coastal Sage Scrub Oak in the Vulnerable category, while the AOO leads to an assessment of the species as Endangered B2ab(ii,iii,iv,v). The AOO, extent of habitat, number of locations, and the number of mature individuals are all projected to continue declining if no changes occur regarding the trajectory of current threats.
Previously published Red List assessments:

Geographic Range [top]

Range Description:

Until the beginning on the 21st century, the title "Quercus dumosa" referred to many species of shrubby white oaks in California. Originally the species name applied to almost all of these shrubs, including Q. berberidifolia, Q. durata, Q. john-tuckeri, Q. cornelius-mulleri, Q. pacifica (all recognized taxa within the complex today)Q. macdonaldii, and Q. turbinellaThe majority of these species inhabit southern California within close geographical proximity to one another, but generally do not occur in mixed stands.

Following further botanic research in the mid to late 20th century, the taxonomy of Coastal Sage Scrub Oak was shifted several times to include various groups of similar southern Californian oaks. Quercus berberidifolia was the last remaining species frequently labeled Q. dumosa, and therefore represents the majority of misidentified herbarium specimens today. The Jepson Manual was the first flora of southern California to publish a delineation aligning with current floras, and finally after about 2012 most references to "Q. dumosa" follow the now-accepted systematics. This newest species description "limits [Q. dumosa] to populations of scraggly shrubs with short petioles, cordate leaf bases, erect curly trichomes on the abaxial leaf surface, and narrow acute acorns that occur at low elevations almost always within sight of the ocean" (Fryer 2012, eFloras 1997, E. Meyer pers. comm. 2015, Ortego et al. 2014, Chester 2004). The species occurs within Orange, Santa Barbara and San Diego Counties of southern California, extending slightly into Baja California, Mexico (NatureServe 2013).

Records contained within the California Natural Diversity Database (CNDDB) have been thoroughly reviewed within the last five years through collaboration with the Jepson Herbarium and the San Diego Natural History museum. They now include only areas where Q. dumosa has been confirmed, although some inland records may still represent hybrids or individuals of Q. berberidifolia (P. McIntyre pers. comm. 2015). Using this vetted spatial data provided by CNDDB, the EOO is about 12,500 m2, with an AOO of approximately 620 m2. These values were calculated using polygonal data representing all areas believed to be occupied by Q. dumosa currently. Fifty five percent of the areas were verified in the field in 2014, while 40% were last confirmed in 2011.

Countries occurrence:
Mexico (Baja California); United States (California)
Additional data:
Estimated area of occupancy (AOO) - km2:620Continuing decline in area of occupancy (AOO):Yes
Estimated extent of occurrence (EOO) - km2:12500
Continuing decline in extent of occurrence (EOO):No
Number of Locations:3Continuing decline in number of locations:Yes
Upper elevation limit (metres):200
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Because the species concept underwent so much upheaval until very recently, it is very difficult to create a comparison in population size and distribution through time. It is known that the habitat of Q. dumosa has decreased due to human development, but some believe that the species' range was fairly limited even before anthropogenic influence. The conclusion can also be made that at least some of the remaining habitat will continue to undergo conversion near the highly sought after southern California coast. It is possible that this rare shrub is close to falling into the Critically Endangered category of Criterion A (population size reduction), but there is not enough data currently to calculate a percent reduction.
Current Population Trend:Decreasing
Additional data:
Continuing decline of mature individuals:Yes
Population severely fragmented:No
Continuing decline in subpopulations:Yes

Habitat and Ecology [top]

Habitat and Ecology:Quercus dumosa inhabits almost exclusively chaparral communities in which it dominates or codominates, found on coastal bluffs, hillsides, canyons, and mesas, including the fog belt of San Diego County. Where the soil is sandy (derived from sandstone or granite) this evergreen shrub thrives, establishing an extensive root network. Coastal Sage Scrub Oak can grow from 1 to 3 m tall, and is reported to produce fruit that germinates easily but only successfully establishes during moist years. Fire events are not generally a concern for this species, and the absence of fire seems to leave Q. dumosa unaffected. Vigorous sprouts emerge from the stump after fire passes through, forming a large canopy within a few years (Fryer 2012, Backs 2014, CNPS). This species is confirmed to be part of at least one of California's Floristic Provinces (South Coast), and is also generally believed to exist within the Peninsular Ranges and a small section of the San Jacinto Mountains (Fryer 2012, Rosatti and Tucker 2016).
Continuing decline in area, extent and/or quality of habitat:Yes

Threats [top]

Major Threat(s): The most pervasive threat to Coastal Sage Scrub Oak is also likely the most obvious; human development along the coast has left very little intact habitat (E. Meyer pers. comm. 2015). This desirable real estate is continuing to undergo conversion from chaparral to housing (Backs 2014). 
Past misclassification of other Quercus species as ‘dumosa’ likely hindered possible conservation initiatives during times of extreme human development since the rarity of this species had not yet been discovered (Backs 2014).
Altered fire regimes, due to both human influence and climate change impacts, are believed to be a source of some threat. Rigorous resprouting after fire protects Q. dumosa from complete wildfire destruction, but the species seldom recruits seedlings for 10 to 20 years following the fire event. This means that long fire-free periods are necessary for substantial reproduction and the potential for population decline reversal (Keeley 1992).
The low elevation and dry habitat occupied by Q. dumosa generally protects it from hybridization with other similar white oak species, but some putative hybrids are known with Q. engelmannii and Q. lobata. Some introgression is also seen where Q. berberidifolia borders populations of Q. dumosa (eFloras 1997).

As of 2013, NatureServe has ranked Coastal Sage Scrub Oak as Imperiled (second highest threat category), naming it one of California's "rarest high risk for further decline." Threats listed include development, ORV use, and fire. Fryer adds hybrid swarms, introgression, and a brittle, easily-disturbed frame as further threats (2012).

Conservation Actions [top]

Conservation Actions: In 2012, Fryer states that "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."

Rancho Santa Ana Botanic Garden in Claremont, California, has propelled conservation efforts through seedling propagation in their nursery, including more than 30 plants (GBIF 2015). Seedlings have been sold to the public through their Grow Native Nursery, but they do not currently offer Q. dumosa (GNN 2016).
Established in 1996 by the U.S. Fish and Wildlife Service, the San Diego National Wildlife Refuge covers approximately 45 km2, with 75% of the land representing Coastal Sage Scrub Oak habitat. This is part of the Multiple Species Conservation Program (MSCP), "a landscape-wide habitat conservation plan to preserve habitat and species while allowing appropriate development...[where] restoration strategies are guided by ongoing biological surveys and species monitoring programs."
The California Native Plants Society notes Q. dumosa as "commonly available" in nurseries, including El Nativo Growers, Inc., Moosa Creek Nursery, Rancho Santa Ana Botanic Garden, RECON Native Plants, Santa Barbara Natives, Tree of Life Nursery, Yerba Buena Nursery.

Botanic Gardens Conservation International (BGCI) reports 17 ex situ collections cultivating this species globally (2016).

Citation: Beckman, E. 2017. Quercus dumosa. The IUCN Red List of Threatened Species 2017: e.T34662A2853964. . Downloaded on 20 September 2017.
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