Assessing Tree Damage Resulting from Flooding

Well, are youready to try growing trees in flood-prone areas again? We've alllearned some difficult lessons in 1993 as flood waters coveredparks, golf courses, marinas, and low-lying residential areas.However, it is still too soon for any conclusions to be drawn aboutlong-term damage to trees and shrubs. We may not know the fullimpact flooding had on our landscape plants until next year.Severe cold arriving unseasonably early (November), or anexceptionally hard winter may push some plants, already stressed bythe effects of flooding (oxygen-deficient soils), over the edge.Several tree species are already displaying symptoms associatedwith flood injury. Defoliation of linden (Tilia spp.) and blackwalnut (Juglans nigra) have been reported. Early-seasondefoliation is always alarming, but does not automatically indicateimminent plant death. Pruning of defoliated branches or decisionsabout removal should be delayed until trees can be thoroughlyassessed next spring. And what about conifers such as spruce(Picea spp.) and pine (Pinus spp.) that experienced temporaryflooding? Experience tells us that these trees will probablesurvive if the soils don't remain water-logged. However, the lowerbranches that were covered with flood waters in many cases havesustained some injury. Again, make sure branches are dead beforeremoving them.

When the time comes for planting or replanting in flood-proneareas, it is imperative that appropriate species be chosen. A fewof the more common flood-tolerant tree species are listed below.

Acer rubrumRed Maple
Acer saccharinumSilver Maple
Fraxinus pennsylvanicaGreen Ash
Gleditsia triacanthosHoneylocust
Liquidambar styracifluaSweetgum
Platanus acerifoliaLondon Planetree
Populus deltoidesEastern Cottonwood
Quercus bicolorSwamp White Oak
Quercus macrocarpaBur Oak
Quercus palustrisPin Oak
Salix spp.Willow
Taxodium distichumBaldcypress
The species listed withstood at least 180 days of water coveringtheir root systems.

(The data on the flood tolerance of tree species was contained inthe article Flood Tolerance in Plants: A State-of-the-Art Review byT.H. Whitlow and R.W. Harris in the Vicksburg, Mississippi:U.S.Army Engineer Waterways Exp. Sta. Tech. Report E-92.)

This article originally appeared in the August 25, 1993 issue, p. 141.


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