Sydney Chatfield

Western Utah is home to two distinct species of oak, Gambel oak (Quercus gambelii) and Dixie live oak (Quercus turbinella), which can hybridize to form an intermediate species that has been named Quercus x undulata. In spite of previous research on these shrubs, we are still unsure of how the hybrid has survived in small isolated locations well outside of the range of one parent species (Q. turbinella, which is restricted in Utah to Washington, Kane, and San Juan Counties). We performed a microhabitat niche modeling study at the Three Peaks Recreation Area (Iron County, Utah) to characterize the abiotic and biotic factors most predictive of Q. x undulata, and to contrast the niche of Q. x undulata with Q. gambelii, which also occurs locally at Three Peaks. We collected plot-level data to determine abiotic and biotic niche factors correlating with the presence/absence of Q. x undulata, including slope, aspect, soil type, soil chemistry, vegetation cover, and other associated woody plant species. We found that, while both oaks prefer shallow-soiled areas at Three Peaks with exposed granitic bedrock, Q. x undulata was significantly more likely to occur in south-facing exposures, while Q. gambelii showed less evidence of preference in aspect. We hypothesize that this microhabitat preference of Q. x undulata reflects the adaptation to hotter conditions of its Q. turbinella parent, and that growth in hotter, drier microhabitats may explain the persistence of similar hybrid patches throughout western Utah, including more northerly sites even further removed from the current distribution of Q. turbinella. Our surveys also revealed the presence of a few Q. turbinella individuals at Three Peaks, representing a first report of this hot-desert species in Iron County. These results will provide the basis for further studies of the evolutionary history and ecological requirements of these fascinating native Utah plants.