Quercus hinckleyi

Simply the species' very small, fragmented current range is a threat to its existence, but The State of Texas has acquired the majority of land containing Hinckley's Oak, decreasing the spatial component of concern. Hybridization with Q. pungens and Q. vaseyana should be noted as a possible future threat, but does not seem to be extensive at this time (U.S. Fish and Wildlife Service 2008, Backs et al. 2016). Certainly genetic threats should be considered for this small population as well (Backs et al. 2015). With the current reproduction method overwhelmingly clonal, continued diversification of genotypes and population of new areas are stunted. Finally, if unique genotypes are not being added to the population, Q. hinckleyi will have limited adaptation capabilities and face an even greater threat from climate change.

This general question propelled Backs et al. (2015) to carry out genetic analysis of all known Q. hinckleyi populations: if this species with a small and fragmented distribution has the common negative symptoms of such a situation (low levels of genetic variability, inbreeding, and limited gene flow)? Microsatellites were used to genotype 204 ramets (individuals), whose leaves were gathered from all three known occurrences. Next, eight loci were analyzed and used to determine levels of genetic variability, population structure, and clonal growth. Results were not entirely as expected, which is good news for Quercus hinckelyi. Genetic diversity was high and no evidence was found of inbreeding. It was determined that there are two distinct subpopulations. The two smallest sites sampled did exhibit extensive cloning, with only seven unique genotypes out of 58 individuals sampled, although the other sites seem to have been reproducing sexually because there is less clonal presence. This cloning does stunt the number of unique individuals, but "allelic diversity and levels of heterozygosity across the metapopulation are comparable to nonthreatened oak species" (Backs et al. 2015). Many believe that Q. hinckleyi's clonal reproduction may actually be an adaptive response to habitat fragmentation and environmental change. This clonality may have ultimately saved the relict species from extinction by helping it preserve a greater number of individual genotypes through the limitation of genetic drift, introgression, and swamping. 

But, cloning likely cannot protect the species indefinitely. Although acorns were found at the larger sites within Big Bend Ranch State Park and there appears to be evidence of recruitment, there is no current evidence of recruitment at the smaller Shafter site. This prevents continued diversification of genotypes, as well as the species' ability to populate new areas by the natural transportation of acorns. Also, Handel observed in 1985 that as clones increase in size, flowers become surrounded with more of the same genetic entity and therefore may produce less viable seed. This is especially true for oaks, since it is generally believed that self-pollination is not successful. As the climate shifts and landscapes change, Q. hinckleyi will have a difficult time adapting without the formation of new genotypes. It is not known why sexual reproduction at the Shafter site is so rare. Backs et al. (2015) theorized that "human-induced habitat degradation, poor regeneration from seed coupled with limited number of genets... wildlife and insect predation... genetic barriers to seed production because of the limited number of genotypes available for crossing... [and] plant and seed predation" all affect this species' ability to recruit new individuals sexually.

In 1992, the U.S. Fish and Wildlife Service published the Hinckley's Oak Recovery Plan. The criterion for removal from the endangered list was to "attain at least 20 viable self-sustaining populations in at least 4 geographically distinct population centres and attain a total of at least 10,000 individual plants. Demonstrate population viability at recovery levels for 10 consecutive years." Within the species' five year review - which did not occur until 2008 - it was found that little new information about Q. hinckleyi had been collected and few recovery actions had been implemented. The strongest outcome at that point was the attainment of the Solitario location by the State of Texas, within Big Bend Ranch State Park, which had prior private control (U.S. Fish and Wildlife Service 2008). But, through their 2015 and 2016 studies, Backs et al. list the fulfilment of three high priority tasks within the recovery plan: "#3212 to assess genetic viability and needs, and #3231 to determine types of reproduction and contribution to population" (Backs et al. 2015), and #3213 to assess incidence of (and potential threat from) hybridization with nearby Quercus species and develop management strategies to address any problems (Backs et al. 2016). It may also be that the 1992 recovery plan needs revisions, in the case of the removal-criterion proving impossible and/or lacking definition.

Moving forward, all of Q. hinckleyi's limited locations should be protected in order to preserve their comparatively extensive genetic diversity. Human impact should be limited, while studies are needed regarding the species' reproductive biology, reaction to climate change, and health following reintroduction of other threatened native species such as the Desert Bighorn Sheep (Ovis canadensis). If more is known about the effects of "self-fertilization, local outcross pollination, and inter-population outcrossing" on Hinckley's Oak, increasingly successful conservation actions can be taken. This may include hand pollination and/or trans-locating some individuals. Finally, it is possible that other isolated populations exist within Texas and adjacent Mexico. Collaborative efforts should be initiated with the aim to locate further potential pockets, placing these areas under protection as well (Backs et al. 2015).

The species is located within three ex situ sites globally, but there are currently no specimens present in the recently-formed Quercus Multi-site Collection, as part of American Public Garden Association's Plant Collections Network (BGCI 2016).