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Flood-Tolerant Trees

  • Larry Hodgson

    • Given the global climate disruption of the current era, floods are more common than ever … and happen at seasons when they never occurred in the past. While I would hope your home is built on high ground, far from any raging, flood-engorged river or overflowing lake, part of your property might not be. 

    How trees adapt to flooding varies from species to species. Photo: James Brooks, Wikimedia Commons

    The nearby lake or river is likely bordered by trees, as they’re often used to help prevent erosion and, besides, it’s not always possible to do any kind of intensive gardening on a sloping riverside. Plus, trees simply look good near any body of water. 

    So, how does flooding affect them?

    Not Good for Roots

    Being underwater for extended periods is not good for tree roots. They need oxygen which they usually get from air stored in tiny spaces between soil particles, but when the soil is flooded, these air spaces fill with water and out goes the oxygen. Roots then are placed in an anaerobic condition: they can’t get the oxygen they need for respiration. Roots soaking constantly in water can lead to numerous problems, like a buildup of toxic compounds within the tree, reduced nutrient uptake, but especially root death. And too many dead rootlets can kill the tree.

    Mother Nature has provided some trees with adaptations to flooding. Many can tolerate a week or so of flooding, especially when it occurs early in the spring while they’re dormant. Others, like cottonwoods (Populus deltoides and related species and hybrids), naturally grow on floodplains and can take months of flooding, often standing tall and perfectly green well into summer when spring floodwaters are slow to drain away.

    Flood Tolerant Trees

    The silver maple (Acer saccharinum) is an example of a highly flood-tolerant tree. Photo: tennesseewholesalenursery.com

    Here are some examples of trees naturally adapted to flooding … and that you might want to consider planting in areas subject to water overflow. All are able to survive flooding or saturated soils for 30 to 120 consecutive days during the growing season.

    Intermediate Flood-Tolerant Species

    Bur oak (Quercus macrophylla) is one of several oak species that tolerates some flooding. Photo: USDA

    These trees will tolerate flooding for up to 30 days during the active growing season. Only plant them near a body of water if any flooding is likely to be of short duration.

    Flood-Intolerant Trees

    Ginkgos (Ginkgo biloba) can tolerate almost anything … but not flooding. Photo: Ginkgotree, Wikimedia Commons

    The following trees, largely ones normally found in upland situations in the wild, can be damaged by only a few days of constant soaking during the growing season. Even while dormant, much more than a week of saturation can kill them outright. 

    Avoid planting the following trees in areas where flooding is even a possibility. 

    What to Do After Flooding?

    There’s not much you can do after a flooding incident but wait. If healthy new growth appears, all is probably fine. If new growth is weak or chlorotic and the tree doesn’t recover within a year, it would be worthwhile having it assessed by a professional arborist. 

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