Quercus cedrosensis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fagales Fagaceae

Scientific Name: Quercus cedrosensis C.H.Mull.
Common Name(s):
English Cedros Island Oak
Taxonomic Source(s): Jean Louis Helardot. 2012. Oaks of The World. Correze Available at: (Accessed: 11/2016).

Assessment Information [top]

Red List Category & Criteria: Vulnerable B2ab(ii,iii,iv) ver 3.1
Year Published: 2017
Date Assessed: 2016-12-12
Assessor(s): Kenny, L., Wenzell, K. & Beckman, E.
Reviewer(s): Oldfield, S.
Quercus cedrosensis has a fairly large range, along the southernmost part of California and the northernmost part of Baja California (estimated extent of occurrence (EOO) of 80,000 km2), and a small number of isolated subpopulations. Q. cedrosensis has an area of occupancy (AOO) between 200 km2 and 2,000 km2.
Though quantified population information does not exist for this species threats go from desiccation, habitat loss due to fragmentation, unnatural fire regimes, clearing/logging, and land conversions continue to drive declines in AOO, habitat quality, and the number of subpopulations. Based on these factors Quercus cedrosensis is considered Vulnerable.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This Quercus occurs in Baja California (Mexico), where it is concentrated in the northern half, and on Cedros Island located off the west coast of the peninsula. One unverified occurrence is located further south, across the border into Baja California Sur, Mexico. Recent discoveries have also been documented with a small population near the Otay Mountains (California, USA) just north of the border with Mexico. Occurrences in southern California and Baja California include low elevation sites from 75–1,000 m, sometimes up to 1,400 m. Species' occurrences on Cedros Islands however, include higher elevations, beginning at 1,000 m (Muller 1965, le Hardÿ de Beaulieu and Lamant 2010).

The EOO for Cedros Island Oak is approximately 80,000 km2. This species has been well-documented in California, and it occupies about 10 km2 in total (CNDDB 2015). Using a 2 by 2 km grid, the AOO is about 50 km2 in California alone, and 200 km2 total for the whole range. This is likely an underestimation because data is lacking in Mexico where the spatial extent of some subpopulations is not known. Increasing the cell size to 3 by 3 km yields an AOO below 500 km2 (the EN category limit within Criterion B), and a 7 by 7 km grid places the AOO under 2,000 km2 (the VU category limit within Criterion B). It is very unlikely that the true distribution of the species is more extensive than this higher estimation since the species is known to exist in relatively small, isolated subpopulations. For the purpose of this assessment, an AOO of 1,000 km2 will be used as a reasonable estimate.
Countries occurrence:
Mexico (Baja California); United States (California)
Additional data:
Estimated area of occupancy (AOO) - km2:1000Continuing decline in area of occupancy (AOO):Yes
Estimated extent of occurrence (EOO) - km2:78000
Number of Locations:10Continuing decline in number of locations:Yes
Lower elevation limit (metres):75
Upper elevation limit (metres):1400
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Quantified population information does not exist for this species, though a number of subpopulations have been observed. Individuals located on the mainland of Baja California are scattered widely in small subpopulations. Several of these mainland subpopulations are in poor condition, exhibiting die-back from desiccation, elimination by heavy browsing, and other threats. In contrast, the Cedros Island population is vigorous and healthy (Muller 1965). The maritime influence on Cedros Island supports climatic stability, while the mainland's areas of mesic climate continue to deteriorate. The more recent discovery documented near the Otay Mountains occurs within the Las Californias region (southernmost part of California and northernmost part of Baja California) and faces severe threats due to its proximity to the international border (White et al. 2006).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Q. cedrosensis is found exclusively among sclerophyllous vegetation, where shrubs and trees are evergreens with leaves that are thick, leathery, and small. The habitat supporting this vegetation is mostly comprised of open chaparral with rocky soils. In California, Cedros Island Oak is found among patches of Coastal Sage Scrub (CNDDB 2015). This species is adapted to both lowland and mountainous regions, and is usually found as a shrub but can occasionally grow to 5 m tall.
Continuing decline in area, extent and/or quality of habitat:Yes

Threats [top]

Major Threat(s): In southern California, as well as northern parts of Baja California (Las Californias Region), this species is threatened by habitat loss due to land use changes. These changes include road construction and Border Patrol activities as well as urban and rural development (CNPS 2001). Southern California occurrences are 0.5–1.5 m from the Mexican border, making these localities very sensitive to "security" issues. This area is closely surveilled by U.S. authorities for illegal immigration issues and a triple fence was erected, destroying part of the vegetation of this region. Traffic control infrastructure was more recently implemented further implicating the survival of other specimens of this shrub oak. From 2004–2014 in the Las Californias region alone, about 435 km2 area has been attributed to direct habitat loss; half of that lost compromises rare communities. Effects of these losses include habitat fragmentation, unnatural fire regimes, clearing/logging, and habitat type conversions (Stallcup 2015).
On Cedros Island, the high number of introduced mammals, such as goats and dogs, have decreased the native flora and vegetation, although not as severely as on the other large Pacific Islands. This difference could in part be due to evolution in the presence of native herbivores which are absent from the other islands. Credos Island has also experienced deforestation of the southern canyons (Mellink 1993). 
A more alarming threat this species faces, pertaining to its mainland occurrences throughout Baja California into the southern most extent of this species range, is one in which further desiccation could eliminate the mainland subpopulations of Q. cedrosensis, leaving only the insular subpopulation as a relictual endemic. There is an additional concern that mainland populations are facing threats of introgression as leaf morphology begins to shift as well (Muller 1965).

Conservation Actions [top]

Conservation Actions: This species is known to exist in only three ex situ conservation sites around the world (BGCI 2015). Quercus cedrosensis' northernmost range rests within the Las Californias region, where more than 400 rare or endemic species exists. Thus, conservation initiatives are also being prioritized in this region that would require land uses and management to maintain habitat integrity and allow natural ecological processes to continue (Stallcup 2105). The species is also located within three protected areas in Mexico: Parque Nacional Sierra de San Pedro Martir, Area Natural Protegia Valle de Ios Cirios, and Reserva de la Biosfera El Vizcaino. There is no current management or planning for Q. cedrosensis in these locations, and the type of land use allowed within these natural areas is not known. Limited protection is likely provided, but could perhaps be built upon more easily in the future, compared to completely unprotected areas (White et al. 2006).

Citation: Kenny, L., Wenzell, K. & Beckman, E. 2017. Quercus cedrosensis. The IUCN Red List of Threatened Species 2017: e.T30727A2795402. . Downloaded on 21 October 2017.
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