Quercus ajoensis (Ajo oak) and Q. toumeyi (Toumey oak) are native to the southwestern U.S. and both are included on the IUCN Red List; Q. ajoensis is vulnerable, while data about Q. toumeyi are insufficient. For this project, which took place in April 2018, both were assessed for extinction risk. The Huntington Library, Art Collections, and Botanical Gardens (HTN) in San Marino, California, obtained a grant from American Public Gardens Association (APGA) to study these two species in collaboration with the Arizona-Sonora Desert Museum (ASDM) in Tucson, Arizona. The objectives were to scout localities where these species had been observed in the past, confirm or deny their presence in several mountain ranges which are poorly documented, collect acorns or material for micropropagation, and voucher the species at each location. GPS locations of all plants and populations encountered were recorded, measurements and field descriptions of trees were taken, and habitat and associated species were noted. Vouchers were deposited in herbaria at HNT, ASDM, and the U.S. National Arboretum (NA), with Morton Arboretum (MOR) slated to receive a set. Permitting involved the Coronado National Forest (CNF), Bureau of Land Management (BLM), National Park Service (NPS), and US Fish and Wildlife Service (USFWS).
Quercus ajoensis, a form with smaller leaves, Alamo Canyon © Julie H. Wiens
Acorns from both species were collected and sent for propagation to HNT, ASDM, Boyce Thompson Arboretum (Superior, Arizona), and Starhill Forest Arboretum in Petersburg, Illinois. The Q. ajoensis acorns, however, began germinating in the collection bags. These were sent to ASDM and sown; seedlings have been distributed to the other three institutions.
It appears that the U.S. range of pure Q. ajoensis is contracting to just three canyons in the Ajo Mountains in Organ Pipe Cactus National Monument. Oaks from other known locations were either not found or proved to be hybrids with Q. turbinella. Fortunately, the remaining U.S. populations are relatively well protected on public lands. However, 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 improved understanding of the phenology of the species and collaborations 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 similar projects 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.
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, respectively. In addition, populations of the species exist on protected land in nine of those ranges and these accessions were acquired from each of those ranges. Frequently, it is locally common where it occurs. Although mostly found on volcanics, it seems to not be specific to a single type of substrate. Despite 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 have already been 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 U.S. 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.
Matt Jevnikar and Tim Thibault with Quercus toumeyi at Upper Walker Tank in the Santa Rita Mountains © John F. Wiens
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. As for the U.S. side, monitoring of populations to ensure that they are stable would be beneficial.
Q. 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 yearly. 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, email@example.com
Tim Thibault (Organizer and Senior Collector), Curator, Woody Plant Materials, Huntington Library, Art Collections, and Botanical Gardens, San Marino, CA, 91108, firstname.lastname@example.org
The original version of this report appeared in the February 8, 2019 edition of the journal Dendrology.
Edited by Sandy Masuo, AZH editor