Date of Award
Master of Science
William R. Graves
The genus Carya is largely composed of taxa endemic to eastern North America. This entire group of long-lived, durable, and aesthetically pleasing trees has been ignored by horticulturists because of issues related to their production as well as performance in the nursery and landscape. Hickories develop large, dominant taproots and supposedly produce few lateral roots, which are often associated with increased transplant success. Hickory seedlings are also considered to exhibit a lag phase in shoot growth, an additional disadvantage that hinders their production. The main objectives of the research presented in this document were to explore potential production methods that may alter the root morphology of hickories that offer characteristics advantageous for horticultural use, and to examine the physiological responses of hickories endemic to bottomland environments to root-zone water content. The first root pruning experiment was performed to study the morphological responses of seedlings of Carya aquatica, Carya cordiformis, Carya laciniosa, Carya ovata, and Carya tomentosa to root pruning and root pruning plus auxin shortly after germination. The results of the study suggest that not all hickory taxa develop similarly. Additionally, root pruning and root pruning plus auxin do not hinder shoot growth, may enhance fibrous-first order lateral root formation, and can also promote taproot branching. The second root-pruning experiment was designed to investigate the effects of severity and timing of root pruning of one-year-old Carya cordiformis on root and shoot development. We found that one-year-old Carya cordiformis are tolerant of moderate and severe root pruning when dormant, and that severe taproot pruning may decrease root and shoot growth if performed once buds begin to swell. The moisture-stress experiment was performed to determine the tolerance of Carya aquatica and Carya laciniosa to various root-zone soil moisture levels, which may infer the capacity of these taxa to perform in extreme soil conditions typical of urban landscapes. Photosynthesis, stem water potential, root and shoot biomass, as well as leaf surface area of plants of Carya aquatica and Carya laciniosa exposed to drought and flood conditions were measured. These two species responded similarly to both drought and flooding. We conclude that the hickories as a group should not be dismissed from horticultural application because each taxon develops differently. Root pruning offers a viable technique for the modification of root morphology. Furthermore, both Carya aquatica and Carya laciniosa should be considered as resilient landscape selections and rootstocks. Each of the species of Carya included in this thesis deserves further study to facilitate their production for horticultural application.
Brandon Michael Miller
Miller, Brandon Michael, "The horticultural potential of six species of North American hickories" (2017). Graduate Theses and Dissertations. 15376.