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Plant Focus

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Dwarf cultivars can be ideal for a small garden. Here are three "mini oaks". 

Exploring for Quercus ajoensis and Q. toumeyi

A report by John F. Wiens & Tim Thibault

Objectives

These two species of southwestern U.S. oaks are on the IUCN Red List (Beckman and Jerome 2017, Kenny et al. 2017). Both were assessed for extinction risk. Quercus ajoensis (Ajo oak) is vulnerable, while Q. toumeyi (Toumey oak) is found to have insufficient data. The Huntington, in San Marino, CA, obtained a grant from American Public Gardens Association to study these two species in collaboration with the Arizona-Sonora Desert Museum (ASDM) in Tucson, AZ. The objectives were to scout localities where the two Quercus species had been observed in the past, confirm or deny presence of the species in several mountain ranges which have poorly documented or otherwise dubious records, collect acorns or material for micropropagation, and voucher the species at each location. We took GPS locations of all plants and populations encountered, recorded measurements and field descriptions of trees, and noted habitat and associated species. Vouchers were deposited in herbaria at The Huntington (HNT), Arizona-Sonora Desert Museum (ASDM), and the US National Arboretum (NA), with Morton Arboretum (MOR) slated to receive a set.

Permitting involved the Coronado National Forest, Bureau of Land Management, National Park Service, and US Fish and Wildlife Service.

Estes Canyon
Estes Canyon in the aptly named Organ Pipe Cactus National Monument, home of Quercus ajoensis ©​​​​​​ ​Tim Thibault

Acorns we collected were to be sent to and grown out at The Huntington, ASDM, Boyce Thompson Arboretum (Superior, Arizona), and Starhill Forest Arboretum in Petersburg, Illinois. This was accomplished with Quercus toumeyi, but acorns of Q. ajoensis began germinating in the collection bags. They were sent to ASDM and sown; seedlings have been distributed to the other three institutions.

The field work occurred between April 12 and August 17, 2018. Our base was Tucson, with 1- and 2‑ day trips from there; 23 days in total. At least one of the authors, and often an associate collector or three, were on each trip. The following lists of mountain ranges searched are not necessarily in chronological sequence.

Quercus ajoensis
Anthocyanous new growth on Quercus ajoensis in Alamo Canyon, Ajo Mountains, Organ Pipe Cactus National Monument © Matt Jevnikar

Quercus ajoensis C.H. Muller - Field Log

Ajo Mountains

In early May, we visited the Ajo Mountains in Organ Pipe Cactus National Monument, the type locality for Q. ajoensis (Muller 1954). We went into Arch and Alamo Canyons in this range. These mountains of basaltic flows and tuffs rise dramatically to an elevation of 1,465 meters. The skirt of desert is botanically rich and the canyons even richer. Oaks were found in the north-facing branch of Arch Canyon at 842 to 925 meters, with more in view at higher elevations. Plants here were single to multi-trunked trees up to 7 meters tall by 13 meters wide. Fresh growth was anthocyanous (reddish). Leaves, 1.5 to 3.5 cm long, were blue-green and without hairs on the surfaces, good characteristics of Q. ajoensis. In Alamo Canyon, we also found abundant and similarly large oaks with the same leaf and twig characteristics at elevations from 708 to 750 meters, with more oaks visible higher up.

Quercus ajoensis Alamo Canyon
Quercus ajoensis, a form with smaller leaves, Alamo Canyon © Julie H. Wiens

During routine field work in Alamo Canyon, Peter Holm of OPCNM noticed that Q. ajoensis had already dropped its acorns. He collected approximately 200 acorns from the ground below four trees and sent them to the Desert Museum. Germination from these four mother lineages ranged from 82% to 96%.

Our field work on Q. ajoensis finished in mid-August when we returned to OPCNM to visit Estes Canyon in the Ajo Mountains. There, oak trees up to 6 meters tall by 7 meters wide had good species characteristics. Micropropagation material was collected and voucher specimens taken from six Quercus ajoensis plants at elevations from 790 to 805 meters.

Quercus ajoensis
New growth on Quercus ajoensis in Arch Canyon, Organ Pipe Cactus National Monument © Matt Jevnikar

Kofa Mountains

The second week of April 2018 brought us to these mountains in the Kofa National Wildlife Refuge. This area is under the jurisdiction of the US Fish and Wildlife Service. The rugged cliffs of lava and tuff rise 1,486 meters above a beautiful but xeric Sonoran desertscrub. Deep canyons harbor an amazing variety of plants, including oaks and California fan palm (Washingtonia filifera). Older herbaria vouchers of oaks from here are variously labeled as Q. ajoensis, Q. turbinella, and hybrids of the two. We hiked into northwest-draining Four Palm Canyon, and soon found oaks, small and shrubby (< 3.5m tall). Leaves were green to blue-green, margins had from 3 to 8 teeth per side and abundant hairs on both surfaces. Based on these leaf characteristics (Tucker and Muller 1956) we suspected the population to be intergrades between Q. ajoensis and Q. turbinella. Plants we collected from came from elevations of 804 to 871 meters, and through binoculars there appeared to be oak trees higher up in the canyon. Palm Canyon, facing west, was much steeper and narrower. There, we found oaks at elevations from 672 to 870 meters elevation. Leaf characteristics were the same as those in Four Palm Canyon, but the plants here were often larger (up to 5 m).

Quercs ajoensis - developing fruit
Developing fruit on Quercus ajoensis Alamo Canyon, Ajo Mountains © Matt Jevnikar

Pinal Mountains

Two herbarium specimens from 1926 and 1955 led us to Devil’s Canyon, in the Pinal Mountains, in mid-May. A rough ride south from Highway 60 brought us through an oak scrubland (1,190 m) with Q. emoryi and shrubby oaks that appeared to have a strong resemblance to Q. turbinella. As we neared the canyon rim, composed of volcanic dacite, those oaks showed some characteristics of Q. ajoensis. The blue-green color and long spines on the marginal teeth hinted at our target species, but much of their appearance pointed towards Q. turbinella. Elevations here were around 1,100 meters. Quercus arizonica and Q. emoryi were found in association.

Quercus ajoensis leaf
One of the larger Quercus ajoensis leaves found in Alamo Canyon © Julie H. Wiens

White Tank Mountains

We headed towards Phoenix to check out a collection site of vouchers variously labeled as Q. ajoensis or Q. turbinella. Most dated from 40-50 years ago from Ford Canyon in the White Tank Mountains at elevations from 616 to 1,219 meters. Rock types here are granites and gneiss. Despite a single recent (2016) voucher from this xeric, Sonoran desertscrub habitat, no oaks were found by our team.

Quercus ajoensis inflorescence
Quercus ajoensis inflorescence, Alamo Canyon © Matt Jevnikar

Sand Tank and Javelina Mountains

In late July, we visited the Javalina Mountains (gneiss substrate) and Bender Springs, in the Sand Tank Mountains (rugged hills of tuff) in the Sonoran Desert National Monument. The latter is on the Barry M. Goldwater Air Force Range. Old collection sites were revisited in this dry, Sonoran desertscrub habitat, but we found no oaks in either range.

Verifying Q. ajoensis
John Wiens and Massimo Boscolo verify identity of Quercus ajoensis © Tim Thibault

Quercus toumeyi Sarg. - Field Log

Mule Mountains

Late July and early August began our intense field work on Q. toumeyi. The Mule Mountains are the type locality for Q. toumeyi (Sargent 1895). The species can be shrubby to a trunked tree. The glossy green, elliptical to lanceolate leaves can be 1.5 cm to 3 cm long with entire to toothed margins. We found a large plant of Q. toumeyi along Highway 80 (on private land) just west of Bisbee (1,579 m). More plants were found on Bureau of Land Management land, for which we did not yet have a permit. Two weeks later, permit in hand, we collected Q. toumeyi acorns there at Juniper Flats, a picturesque pinyon-oak-juniper woodland at 2,081 m. The species was vouchered again at the end of North Juniper Flats Road. There, associated oaks were Q. emoryi, Q. arizonica, and a hybrid between our target species and the latter. The substrate was a conglomeration of sedimentary, volcanic, and metamorphic rock. At 2,149 m elevation, this marked our loftiest collection. Another hike in that range, Zacatecas Canyon, was unproductive, yielding only Q. emoryi and Q. arizonica.

Quercus toumeyi and Q. emoryi in Tex Canyon
Quercus toumeyi and Q. emoryi in Tex Canyon ©​​​​​​ ​Tim Thibault

Atascosa Mountains

We found a potentially new subpopulation of Q. toumeyi on Forest Service road 39, between Sycamore Canyon and Ruby (west of Nogales) in the area of the Atascosa Mountains. These oaks, at 1,725 m elevation, were associated with other Quercus species in a woodland habitat. Soil types there are granite, diorite, and volcanic tuff.

Quercus toumeyi dense
Dense specimen of Quercus toumeyi in Mule Mountains, type locality of the species ©​​​​​​ ​Tim Thibault

Rincon Mountains

A trip into Happy Valley in the Rincon Mountains, just east of Tucson, led us to a population of Q. toumeyi in an oak-grassland habitat. At 1,207 m, this was the lowest elevation at which we found the species. These plants, growing on sedimentary alluvium, yielded a collection of acorns.

Q. toumeyi acorn
Small yet mature acorn of Quercus toumeyi near the ghost town of Ruby, Arizona ©​​​​​​ ​Tim Thibault

Patagonia Mountains

Northeast of Nogales, we surveyed the Patagonia Mountains. In July, a population of Q. toumeyi was found near UX Road (1,733 m) in a pine-oak-juniper woodland. Vegetative buds for micropropagation were collected here. A new subpopulation of that species was found in Aztec Canyon west of Patagonia. Some plants at this site showed evidence of crossing with associated Q. arizonica. This dense chaparral habitat is at 1,322 m. In mid-August we returned and found pure Q. toumeyi in the adjacent Flux Canyon (an oak-grassland habitat at 1,461 m) and acorns were collected. Nearby oaks in Flux Canyon were Q. oblongifolia (and possible hybrids with Q. toumeyi) and Q. emoryi. New locations in this range were later found east of Red Mountain at elevations of 1,390-1,470 m. Again, this was good oak-grassland habitat, with Q. arizonica and Q. emoryi in association. This range is an amalgam of many types of volcanic intrusive and extrusive rock types.

Flux Canyon
Quercus toumeyi, Flux Canyon, Patagonia Mountains ©​​​​​​ ​John F. Wiens

Santa Rita Mountains

The Salero Ranch vicinity lies in the southern Santa Rita Mountains, south of Tucson. In early August, a new population of Q. toumeyi was found here on private land. Just to the north, on public land, more were found at 1,540 m elevation. This is an oak-juniper woodland with Q. arizonica and Q. emoryi in association. Mid-August brought us to Upper Walker Tank, 11 km to the north in the same mountain range. There, we found a healthy population of Q. toumeyi (1,700-1,800 m). Associated oaks in this pinyon-oak-juniper woodland were Q. arizonica, Q. emoryi, and Q. hypoleucoides. The final push in this range was Temporal Gulch, where a vegetative collection of Q. toumeyi was made (1,715 m) in an oak woodland. Associated oaks were Q. arizonica and Q. oblongifolia. Substrate here is similar to that of the Patagonia Mountains.

Q. toumeyi Parker Canyon
Quercus toumeyi at Parker Canyon Lake, south of Canelo Hills, southeastern Arizona © John F. Wiens

Canelo Hills

The field team relocated a population of Q. toumeyi in the Canelo Hills (a chaparral-like oak woodland just west of the Huachuca Mountains) along Highway 83 (1,740 m), south of Sonoita, but no acorns were observed. South of there, at Parker Canyon Lake (1,691 m) plants were again sterile, so we collected vegetative buds. Q. arizonica and Q. emoryi were observed here also. Substrates here are rhyolitic tuff and sedimentary volcanics.

Dragoon Mountains

We collected vegetative buds of Q. toumeyi here in Cochise stronghold, in a pine-oak woodland (1,513 m). Middlemarch Canyon (Forest Service Trail #277), at the southern end of the Dragoons was explored also. There, Q. toumeyi was found in a pinyon-oak woodland near the saddle at 1,793 m elevation. The target species found on this range occurred on sedimentary substrates, as opposed to igneous ones for most of the other sites.

Q. toumeyi immature acorn
Quercus toumeyi leaves and immature acorn on rhyolitic outcrop in Patagonia Mountains © Tim Thibault

Chiricahua Mountains

A visit to Rucker Canyon, a pinyon-oak-juniper woodland in the Chiricahua Mountains, revealed a locally large population of Q. toumeyi (1,791 m). Acorn set was heavy, but they were still green in late July. A return trip in early August gave us ripe acorns. While there, we observed that Q. toumeyi had vigorously re-sprouted after a fire in 2011. Other oak species at that site were Q. arizonica, Q. emoryi, and a possible Q. arizonica × oblongifolia. Substrate is volcanic tuff and sedimentary conglomerates. Southeast of there, on South Fork Trail, an old collection appeared to have been a misidentification of another small-leaved species of oak, as no Q. toumeyi were found.

Rucker Canyon
Quercus toumeyi, Rucker Canyon, Chiracahua Mountains © John F. Wiens

Peloncillo Mountains

A trip along Geronimo Trail in the Peloncillo Mountains was productive. A single Q. toumeyi was found on the Arizona-side of the border with New Mexico (1,502 m) in an open juniper-pinyon woodland. A larger population was found on the New Mexico side, where ripe acorns were collected. Here, Q. toumeyi were mostly shrubs to small multi-trunked trees. This open pine-oak habitat at 1,720 m elevation also hosted Q. arizonica. The rock type here is volcanic tuff.

Geronimo Trail
Quercus toumeyi on the Geronimo Trail, Peloncillo Mountains, New Mexico © John F. Wiens

Other areas searched for Q. toumeyi

The Santa Catalina and Superstition Mountains were scouted early on. Small-leaved forms of other species appear to be confused for Q. toumeyi in these two ranges. While in the Pinal Mountains looking for Q. ajoensis, a single, possibly misidentified herbarium specimen of Q. toumeyi was on our radar. We did a roadside search of the loop from Superior to Globe (Hwy 60), Winkleman (Rte 77), and back up to Superior (Rte 177), a trip ranging from 575 to1,520 m elevation. We saw Q. arizonica, Q. emoryi, and Q. turbinella, but no sign of Q. toumeyi.

Herbarium specimens also led to New Mexico. A side trip to Cookes Range yielded no oaks at the collection coordinates, but elsewhere in the range Q. grisea and hybrids with Q. turbinella were found, but not Q. toumeyi. That species could still be present, although grazing pressure is high in that range. Oaks nearby were Q. grisea, although a greener form than usual. Another New Mexico collection was from Bear Mountain. There, we found a small-leaved form of Q. grisea, but Q. toumeyi was not seen. The Burro and Mangas Mountains were scouted unsuccessfully for Q. toumeyi. In both ranges, small and green-leaved forms of Q. grisea were probably confused for Q. toumeyi, at least in localities of herbarium specimens. An old collection from Mangas Spring is on a private farm and is now inaccessible. Based on other findings, the southern portion of the Burro Mountains could have Q. toumeyi.

Parker Canyon 1
Quercus toumeyi hosting a mistletoe (Phoradendron serotinum subsp. tomentosum),Parker Canyon Lake © John F. Wiens

Conclusion and Future Opportunities

It appears that the U.S. range of pure Q. ajoensis is contracting to just three canyons in the Ajo Mountains. Oaks from other old locations were either not found or were hybrids with Q. turbinella. Fortunately, the remaining U.S. populations are relatively well protected on public lands. However, the recent wildfires and other disasters highlight the vulnerability of being constrained to a small geographic area and underscore the value of collecting and distributing material for ex-situ conservation. Unfortunately, oaks are masting species. With the improved understanding of phenology of the species and collaboration with land managers developed through this grant, our capacity to capture acorns during the next masting event is greatly improved. There is a need for a similar search on the Mexican side of the border. An online search of herbarium records lists five localities on the Baja Peninsula, with only two collections this century.

Parker Canyon 2
Quercus toumeyi acorn, Parker Canyon Lake © John F. Wiens

Our study found Q. toumeyi in ten different mountain ranges throughout Arizona and New Mexico. Populations occur mostly at elevations of 1,500-1,800 m, with lower and upper extremes of 1,207 m and 2,149 m. In addition, the species has populations on protected land in nine of those ranges and these accessions were acquired from each of those ranges. It is frequently locally common where it occurs. Although mostly found on volcanics, it seems not to be specific to a single type of substrate. Although there was some seed predation, one or two species of gall wasps, and a parasitic plant found attacking Q. toumeyi, no significant threat was found to any current population on public land. Of concern for both species are studies (Brusca et al. 2013, Nolan et al. 2018) showing that many plant ranges are already observed to be shifting in response to climate change.

Of the several species mistakenly identified as Q. toumeyi, the most interesting is Q. grisea. In the Red List of US Oaks, the two come out as sister taxa. Their ranges approach each other in southern New Mexico, and may overlap in the Animas, Burro or Cookes ranges.

The recent publication of Q. barrancana (Spellenberg 2014) casts doubt about the extent of the range into Mexico, and surveying for Q. toumeyi in Mexico would be valuable additional work. As for the U.S. side, monitoring of populations to ensure that they are stable would be beneficial.

Quercus toumeyi seems very well adapted to the bimodal rainfall of its native range. Plants in the Rincon Mountains were observed with flowers, early fruit, and mature fruit, both in January and July of 2018. It would be interesting to see if this is a weather anomaly for this particular year, or if the species in fact flowers and fruits twice a year.

Finally, Q. toumeyi deserves further horticultural evaluation. It may prove a valuable foundation plant or informal hedge for dry climates.

Authors’ Contact Information

John F. Wiens (Organizer and Senior Collector), Nursery Horticulturist – Botany Department, Arizona-Sonora Desert Museum, Tucson, AZ, 85743 - jwiens@desertmuseum.org

John F. Wiens
John F. Wiens in a grove of Ajo Oaks, Alamo Canyon, Ajo Mountain, Organ Pipe Cactus National Monument © Julie H. Wiens

Tim Thibault (Organizer and Senior Collector), Curator, Woody Plant Materials - The Huntington, San Marino, CA, 91108 - tthibault@huntington.org

Santa Rita Mountains
Matt Jevnikar and Tim Thibault with Quercus toumeyi at Upper Walker Tank in the Santa Rita Mountains © John F. Wiens

Other Participants

The Huntington:

Raquel Folgado (Primary Contact and Lab Technician) Cryopreservation Research Botanist
Alicia Baugh (Nursery Technician and Associate Collector) Propagator
Taylor La Val (Lab Technician) Plant Conservation Technician
Josette Tin (Lab Technician) Plant Conservation Technician
Sean Lahmeyer (Associate Collector) Plant Conservation Specialist

Arizona-Sonora Desert Museum:

Mark Fleming (Organizer and Associate Collector) Curator of Botany
Erik Rakestraw (Associate Collector) Assistant Nursery Horticulturist
Massimo Boscolo (Associate Collector) Horticulturist
Matt Jevnikar (Associate Collector) Horticulturist
Julie H. Wiens (Associate Collector) Horticulturist/Plant Records Technician
Jason Wiley (Associate Collector) Horticulturist

Collaborators and Contributions

Cathy Babcock, Boyce Thompson Arboretum, serving as ex-situ site
J. Travis Columbus, Rancho Santa Ana Botanical Garden, advice on sites within Cookes Range
George Ferguson, University of Arizona Herbarium, phenology advice for these species
Wendy Hodgson, Desert Botanical Garden, advice on sites within Kofa Mountains
Peter Holm, Organ Pipe Cactus National Monument, collected acorns and provided locality data for oaks within the national monument and the Sand Tank Mountains
Guy Sternberg, Starhill Forest Arboretum, serving as ex-situ site

References

Beckman, E. and D. Jerome, 2017. Quercus toumeyi. The IUCN Red List of Threatened Species 2017: e.T34683A2854238. https://www.iucnredlist.org/species/34683/2854238 \

Brusca, R.C, J.F. Wiens, W.M. Meyer, J. Eble, K. Franklin, J.T. Overpeck, and W. Moore. 2013. Dramatic response to climate change in the Southwest: Robert Whittaker’s 1963 Arizona Mountain plant transect revisited. Ecology and Evolution 3 (10): 3307-3319, 3636.

Kenny, L., K. Wenzell, and D. Jerome. 2017. Quercus ajoensis. The IUCN Red List of Threatened Species 2017: e.T194050A2295211. http://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T194050A2295211.en

Muller, C.H. 1954, A New Species of Quercus in Arizona, Madroño 12 (5): 140-145.

Nolan, C., J. Overpeck, J. Allen, P. Anderson, J. Betancourt, H. Binney, S. Brewer, M. Bush, B. Chase, R. Cheddadi, M. Djamali, J. Dodson, M. Edwards, W. Gosling, S. Haberle, S. Hotchkiss, B. Huntley, S. Ivory, A. Kershaw, S. Kim, C. Latorre, M. Leydet, A. Momohara, P. Moreno, S. Muller, B. Otto-Bliesner, C. Shen, J. Stevenson, H. Takahara, P. Tarasov, J. Tipton, A. Vincens, C. Weng, Q. Xu, Z. Zheng, and S. Jackson. 2018. Past and future global transformation of terrestrial ecosystems under climate change. Science 361 (2): 920-923.

Tucker, J.M. and C.H. Muller. 1956. The Geographic History of Quercus ajoensis, Evolution 10 (2): 157-175.

Spellenberg, R. 2014. Quercus barrancana (sect. Quercus, white oaks), A new species from northwestern Mexico. Phytoneuron 2014-105: 1–12. http://phytoneuron.net/2014Phytoneuron/105PhytoN-Quercusbarrancana.pdf.

Sargent, C.S. 1895. Notes on North American Oaks. Garden and Forest 8: 92, f. 13, 14. https://www.biodiversitylibrary.org/item/107527#page/105/mode/1up