September 08, 2022

Historic Trees: The Rare Northern Utah Hybrid Oak

Written by TreeUtah
A close-up of the hybrid oak's leaves A close-up of the hybrid oak's leaves Photo courtesy of the Utah FFSL

In 1954, Rudy Drobnick, a graduate student studying under the famous Utah botanist, Dr. Walter Cottam, was hiking on the west side of the Oquirrh Mountains when he noticed the grove of oaks he was passing through had distinct features, different from others in the area and any he had seen before. Moving forward in his studies with the possibility that he had found a new oak in mind, he shifted the focus of his thesis to this potentially groundbreaking discovery. Through his field research, Drobnick discovered a few additional isolated groups of this distinct oak, including one on the University of Utah grounds nearby what would later become Cottam’s Oak Grove, where Dr. Walter Cottam stationed a tree nursery where he recreated the conditions that would reproduce and confirm Drobnick’s discovery of rare, hybridized oaks.

These hybrids are a product of a historic natural process that took place 5,000 to 7,000 years ago – a time when Utah and the Great Basin region was wetter and hotter. During this time, the habitat zones of the northern quercus gambelii (Gambel or scrub oak) and southern quercus turbinella (sonoran scrub oak or canyon live oak) briefly overlapped. The two species met in the brief intersection of their habitable zones and hybridized, creating the unique gambelii x turbinella hybrid. Cottam recreated this process by pollinating q. gambelli starts with the pollen from q. turbinella on a site similar to locations where the hybrid is found in the wild. This grove of human-produced hybrids is now known as the Cottam Oak Grove and is located in what is now Red Butte Garden & Arboretum. Through this experiment, Cottam was able to effectively prove that hybridization between the two species is possible when conditions are right, confirming their suspected history. This discovery drew biologists from all over the world – they had to see the hybrid oaks.

Now, the hybrid oaks in the wild stand as “living fossils,” providing us with evidence of Utah’s climate past and Cottam’s Oak Grove stands as a relic of Utah’s contributions to the world of science and our community’s ardent engagement with the natural world around us.