Flood-tolerant trees

With the start of spring comes the melting of snow and arrival of standing water or floods. Here’s a look at what trees are tolerant and intolerant of flooding.

Flooding is a fairly common occurrence in Michigan, especially in the spring when snow melt is accompanied by rain, and later in the year following heavy thunderstorms. After a flood, we frequently receive phone calls from homeowners wondering how long their trees can survive being underwater. As with most things, the answer is “It depends.”

For the most part, short-term flooding (two or three days) should not cause too many issues with trees. Trees that are flooded when they are still dormant will be less effected by flooding than if the inundation occurred during the middle of the growing season. The type of tree also makes a huge difference in its ability to survive flooding. Many tree species can survive months under water while others may be killed by just a few days of inundation.

In general, a species’ native habitat can give us a pretty good clue as to how well it can recover from flooding. Upland species, such as hickory and many oaks, usually do not survive flooding while bottomland species, like red maple or sweetgum, are more tolerant of flooding. Most evergreen conifers are relatively intolerant of flooding. Exceptions are white spruce and arborvitae, which can tolerate some flooding. Also, deciduous conifers (larch, baldcypress and dawn redwood) are usually very tolerant of flooding. Flood tolerance ratings of trees can sometimes be confusing, and species listed as tolerant on one list may be listed as intolerant on another.

The table presented below is excerpted from one of the most comprehensive reviews of flood tolerance in trees and provides a good reference. As you’ll note in the table, green and white ash were among the most flood tolerant of our common landscape trees. Understanding the relative flood tolerance of trees will be increasingly important as we think about replacement species for ash.

Relative tolerance of trees and shrubs to flooding during the growing season (Source: Whitlow and Harris 1979)

Species Common
Name
Very
Tolerant¹
Tolerant ² Somewhat
Tolerant³
Intolerant4
Acer negundo Boxelder X X
Acer rubrum Red maple X
Betula nigra River birch X
Carya ovata Shagbark hickory X
Celtis occidentalis Hackberry X
Cephalanthus occidentalis Buttonbush X
Cereis canadensis Redbud X
Cornus florida Flowering dogwood X
Crataegus mollis Downey hawthorn X
Fraxinus americana White ash X
Fraxinus pennsylvanica green ash X X
Gleditsia triacanthos Honeylocust X
Gymnocladus dioicus Kentucky coffeetree X
Juglans nigra Black walnut X
Liquidambar styraeiflua Sweetgum X
Nyssa sylvatica Blackgum X
Platanus occidentalis Sycamore X X
Populus deltoides Eastern cottonwood X
Prunus serotina Black cherry X
Quercus alba White oak X
Quercus bicolor Swamp white oak X
Quercus imbricaria Shingle oak X
Qucrcus macrocarpa Bur oak X
Quercus palustris Pin oak X
Quercus rubra Red oak X
Salix nigra Black willow X
Sassafras albidum Sassafras X
Taxodium distichum Baldcypress X
Ulmus americana American elm X
Ulmus rubra Red elm X

1 Very Tolerant: Able to survive deep, prolonged flooding for more than 1 year.
2 Tolerant: Able to survive deep flooding for one growing season, with significant mortality occurring if flooding is repeated the following year.
3 Somewhat Tolerant: Able to survive flooding or saturated soils for 30 consecutive days during the growing season.
4 Intolerant: Unable to survive more than a few days of flooding during the growing season without significant mortality.