Quercus graciliformis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fagales Fagaceae

Scientific Name: Quercus graciliformis C.H.Mull.
Common Name(s):
English Chisos Oak, Graceful Oak, Slender Oak
Quercus canbyi Cory & Parks
Quercus graciliformis var. parvilobata C.H.Mull.
Taxonomic Source(s): Nixon, K.C. 1997. Fagaceae. In Flora of North America North of Mexico. Vol. 3. Oxford University Press, New York and Oxford.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered C2a(ii) ver 3.1
Year Published: 2017
Date Assessed: 2016-11-18
Assessor(s): Beckman, E.
Reviewer(s): Oldfield, S.
Contributor(s): McNeil-Marshall, A.
The Slender Oak, also known as Chisos Oak (Quercus graciliformis) is a unique and isolated oak, with a small, specialized habitat. Only one population (Blue Creek Canyon, Brewster County, Texas) has been verified and well-documented, with one other nearby area recorded but needing further research (Juniper Springs). All reported locations of Slender Oak within Mexico cannot be considered accepted at this time due to taxonomic confusion. More than one misidentification has been discovered in the last few decades, as older herbarium specimens are studied again, which has raised overall doubts as to the accuracy of past identifications within Mexico (Poole et al. 2007).

Using only the Chisos Mountains of Texas localities, the area of occupancy (AOO) is calculated to be 24 km2. The total number of known mature individuals rests around 100 or more, but this needs field confirmation. Continuing decline in population size, extent of occurrence (EOO) and AOO are not currently evident, but it has been observed that recruitment rates will lead to a population decline in the future if no changes occur.
Under Criterion B2, Q. graciliformis falls within the Endangered category, with an AOO of greater than 10 but less than 500 km2, number of locations less than 5, and continuing decline projected in the number of mature individuals. But, because there are less than 250 mature individuals total, continuing decline projected, 90–100% of verified mature individuals in one subpopulation, this species is Critically Endangered under Criterion C2. Therefore Quercus graciliformis is assessed as Critically Endangered C2a(ii).
Previously published Red List assessments:

Geographic Range [top]

Range Description:Quercus graciliformis is found above 1,650 m only in the Chisos Mountains, west Texas. Its range is extremely limited, covering less than 65 km2 total. Some reports of the species have been documented in Coahuila, Mexico, but consensus has not yet been reached by the botanic community (Poole et al. 2007). There is also chance of Chisos Oak in Chihuahua, Mexico, since suitable habitat is possible and no extensive searches have been completed (NatureServe). Jean Louis Helardot (2012) states that Q. graciliformis is even distributed into Nuevo Leon and Tamaulipas, Mexico, further east of Coahuila, but these reports have not been verified. Only using verified localities (points from the Chisos Mountains in Brewster County, Texas), the AOO for Q. graciliformis is 24 km2.
There has been taxonomic confusion in the past with Q. canbyi and Q. gravesii. Most botanists now agree on Slender Oak's status as a true species, but Mexican taxonomist Romero-Rangel (2006) does still categorize Q. graciliformis as a synonym to Q. canbyi. More research is necessary, though for this report Graceful Oak will be treated as a unique species due to important morphological differences and general agreement on its taxonomic status.
Countries occurrence:
United States (Texas)
Additional data:
Estimated area of occupancy (AOO) - km2:24
Number of Locations:1
Lower elevation limit (metres):1650
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:There are two small pockets of Q. graciliformis known currently in Big Bend National Park, which is potentially the full extent of the species' range. The first subpopulation, inhabiting Blue Creek Canyon, represents the largest, most morphologically consistent location currently known. The group is possibly comprised of 100 or more individuals, covering approximately 13 km2Some evidence of successful recruitment has been recently observed, with no signs of population decline at this time. But, it is likely that current recruitment levels will not be substantial to maintain the population in the future if no changes are made. Juniper Springs supports the second known putative subpopulation of Slender Oak, where some doubt stands regarding which species these trees represent. Morphologically, there is not enough similarity to the Blue Creek Canyon subpopulation to be sure of their taxonomic categorization (A. McNeil-Marshall pers. comm. 2016). More research is needed to confirm this second locality, which was published under the label Q. gracilifomis by Powell, in his 1998 book entitled Trees and Shrubs of the Trans-Pecos and Adjacent Areas.
Current Population Trend:Stable
Additional data:
Number of mature individuals:100-200Continuing decline of mature individuals:Yes

Habitat and Ecology [top]

Habitat and Ecology:Quercus graciliformis is a small, semievergreen tree, growing to 8 m tall, and named for its skinny, arching branches. It grows within dry, oak woodlands lining the canyon floors of the Chisos Mountains, and is especially known to be present in areas with a high water table (NatureServe). There is widespread difficulty in distinguishing Q. graciliformis from Q. canbyi, but the former produces fruit which matures in two years, while the latter only requires one year for fruit maturation (Powell 1998). Known plant associates include Fallugia paradoza, Acacia greggii, Rhus virens, Chilopis linearis, Gymnosperma glutinosum, Dalea formosa, Diospyros texana, Ungnadia speciosa, Fraxinus greggiee, and Morus microphylla (Poole et al. 2007).

Threats [top]

Major Threat(s): There are no pressing threats to Slender Oak currently, but some smaller threats do persist. Since the population is entirely or almost entirely held within Big Bend National Park, the only direct anthropomorphic threat is recreational activities (NatureServe). This is not likely to deeply damage the population, but the Blue Creek Canyon Trail does cut within the majority of the most vibrant and known subpopulation's extent. There is also possible threat of water withdrawals lowering the high water table supporting this species, although this has not yet been recorded on the ground. The main concern is believed to be wildfire, with Q. graciliformis' key subpopulation inhabiting one relatively narrow canyon, where one event could do extensive damage. It is thought that this species will resprout after fire like most oak species, but an intense burn would certainly be a severe threat to at least one generation (A. McNeil-Marshall pers. comm. 2016). Reports have also been made regarding the species' hybridization with Q. emoyri, but this does not seem to yet be an extensive threat (FNA 1993).

Conservation Actions [top]

Conservation Actions: Big Bend National Park protects all, or the majority of, Q. graciliformis' population to a certain extent. There also exist 11 ex situ collections globally which propagate this species (BGCI 2016).

Citation: Beckman, E. 2017. Quercus graciliformis. The IUCN Red List of Threatened Species 2017: e.T30954A63729730. . Downloaded on 22 September 2018.
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