Effect of Previous Flood Exposure on Flood Tolerance and Growth of Three Landscape Shrub Taxa Subjected to Repeated Short-term Flooding

Abstract

Ilex glabra ‘Shamrock’ (‘Shamrock’ inkberry holly), Itea virginica ‘Henry's Garnet’ (‘Henry's Garnet’ sweetspire), and Viburnum nudum ‘Winterthur’ (‘Winterthur’ possumhaw) were flooded for 0 (non-flooded), 3, or 6 d, first in a greenhouse and then outdoors. Flooding treatments were in a factorial combination of greenhouse flooding treatment × outdoor flooding treatment. Following each flooding period, plants were allowed to drain for 6 d and received no irrigation. Plants in the 3 and 6 d flood treatments experienced a total of 7 and 5 flood cycles, respectively both in the greenhouse and outdoors. All taxa maintained 100% survival during greenhouse and outdoor flooding. Following greenhouse flooding, final size index (SI) of I. virginica ‘Henry's Garnet’ and I. glabra ‘Shamrock’ decreased with increasing flood length; V. nudum ‘Winterthur’ had no differences in SI among treatments. Following outdoor flooding, there were no differences in flooding treatment for relative size index (RSI) of I. glabra ‘Shamrock’, no clear effect of flooding treatment on RSI for V. nudum ‘Winterthur’, and RSI of I. virginica ‘Henry's Garnet’ was lowest in plants that were not flooded in the greenhouse. RDW and SDW of I. virginica ‘Henry's Garnet’ and I. glabra ‘Shamrock’ tended to be lowest in plants that were initially flooded in the greenhouse for 6 d, while there was no clear effect of either greenhouse or outdoor flooding on RDW and SDW of V. nudum ‘Winterthur’. When exposed to flooding in the greenhouse I. virginica ‘Henry's Garnet’ seemed to better tolerate outdoor flooding, while the other two taxa did not appear to gain any benefit from previous flood exposure. All three taxa sustained growth throughout all phases of the experiment and maintained good visual quality indicating that all three would be tolerant of repeated, short-term flooding.