New Oaks For The Urban Environment:Propagation And Selection Of Hybrid Oaks

Oak trees are one of the most desirable landscape trees in North America because of their wide distribution, great ecological and aesthetic value. Yet, plant propagators have not been able to select oak trees with desirable physiological and ornamental features because vegetative propagation was quite difficult. With new techniques developed at Cornell University, selection within the white oak group has become possible. This study aimed at propagating hybrid oak crosses made between oaks native to New York Stateusing pollen collected all over the world. The primary objective was to test and better understand the layering propagation method combining rejuvenation, etiolation and plant hormone stimulation and then select individuals with both alkaline tolerance to urban soil and good growth vigor for urban landscape use. Approximately 360 hybrid oaks created during 2004 through 2006 were propagated twice in 2009 and 2010. Techniqueswere modified during propagation to better achieve better success. Due to these changes the percentage of new shootslost due to propagation treatment decreased 26%. Different rootabilities were observed among different hybrid types. Comparatively, female parents of stock plants had a stronger effect on the rootability than the male parent. Among the female parents, Quercus xwarei 'Long' REGAL PRINCE and Quercus macrocarpa had the highest rooting percentages, Quercus bicolor and Quercus macrocarpa 'Ashworth Strain' were intermediate and Quercus muehlenbergii was the hardest one to be propagated. There was a significant loss during the first winter of newly propagated oaks after harvested in fall. Those that survived were then used to conduct an alkaline tolerance evaluation in soil pH8.0 with a control treatment of soil pH6.0 in open field and in the greenhouse respectively,during 2010 and 2011. Growth was evaluated and alkaline tolerance rating was measured using a SPAD meter was taken to determine the ability to function in alkaline soil. Some plants grew equally well or even better in alkaline soil, while some other plants showed poor growth and chlorotic symptoms. Consistency can be found throughout the plants propagated in two years. However, due to the physiological features of plants, longer period of observation and further testing is needed to prove that individuals selected from new hybrids have consistent alkaline tolerance and may be very valuable in the urban landscape