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How Flooding Affects Trees

Originally posted on Men's Journal | By Emily Fazio | Last updated Aug 7, 2024 2:00 PM ET

Flooding has become an increasingly common issue, and over time, it has significantly impacted our landscapes. While homes and infrastructure often take center stage in discussions about flood damage, trees are also profoundly affected.

"When flood water comes in, it saturates the soil, compacting it, and driving out air," shares Blake Watkins, Certified Master Arborist and Operations Partner at Monster Tree Service. The effects have much to do with the history of flooding in your region. Just as some trees can withstand cold temperatures or high elevations, trees in other areas are better equipped to navigate storm surges and heavy rains. "Trees like Crepe Myrtles, Red Maples, and Magnolias are common species that grow naturally in floodplains. They are naturally adapted for low oxygen soils that are found in floodplains and in the poor, compacted soils of the urban and suburban environment. Native Oaks and Pines, on the other hand, aren't as flood tolerant and will be more susceptible to the aftereffects of flooding."

Understanding how flooding impacts the trees on your property can guide recovery efforts and prevent long-term damage.

The Immediate Impact of Flooding on Trees

Root Suffocation and Oxygen Deprivation: Waterlogged soil limits the amount of oxygen available to tree roots. When these roots are submerged for extended periods, they begin to suffocate, leading to symptoms like yellowing leaves, wilting, branch dieback, and stunted growth.
Soil Erosion and Stability Issues: Floodwaters can cause significant soil erosion, which undermines the stability of trees. As soil is washed away in areas with poorly draining soil, roots may become exposed or weakened. This makes trees more susceptible to toppling. Check the base of trees for soil erosion, including exposed roots and uneven ground.

Long-term Effects of Flooding on Tree Health

Nutrient Deficiencies: Flooding not only washes away topsoil but also essential nutrients within it. Trees deprived of these nutrients can exhibit symptoms such as discolored leaves, poor growth, and reduced vitality. Over time, nutrient deficiencies weaken trees, making them more vulnerable to environmental stressors.
Increased Susceptibility to Pests and Diseases: Weakened trees are more prone to pest infestations and diseases. Flood-damaged roots and trunks can become entry points for pathogens. Common issues include fungal infections, root rot, and increased attacks from pests like borers and beetles. Watch for unusual spots, mold, or pests on your trees.

Assessing and Mitigating Flood Damage to Trees

Perform an initial assessment. Check for visibly damaged trees — broken branches, exposed roots, and leaning trunks. Note any signs of stress like leaf discoloration or premature leaf drop. "Trees that have leaned over or shifted in the flood may be seriously unstable," cautions Watkins. "If the tree is large enough to cause harm or damage if it falls, have an arborist out to inspect it and to consider removal. Young trees that have shifted may be replanted. Keep the root ball covered and moist until it can be replanted and restaked."
Clean flood debris and sediment that settled over tree roots. "Any deposited sediment after a flood should be removed at least to outside the dripline of valuable trees," shares Watkins. "If soil and mulch has washed away from the base of a tree, it needs to be replaced to cover any exposed roots while leaving the root-trunk interface, also known as the root crown, free from soil and mulch."
Monitor your trees over time for delayed symptoms. Maintain a consistent watering schedule, avoiding overwatering to prevent further stress. "Consider fertilizer or soil conditioning treatments after a flood. Contact an arborist to inspect your tree after a flood and for the subsequent years, as changes to the soil can have long lasting effects that don’t present themselves until years later," advises Watkins. Trees can display a wide range of symptoms. Pay attention to the whole tree, from leaf loss at the tree crown to the curling of leaves and root injury.

Preventive Measures to Protect Trees from Future Flooding

Improve Soil Drainage: Tree experts recommend enhancing the soil drainage around trees to significantly reduce the impact of future flooding. Techniques include creating swales or berms to redirect water flow, using gravel or sand to improve soil structure, and installing drainage systems. Proper mulching can also improve soil aeration and water absorption, saving entire trees from the effects of poorly drained soils.
Choosing Flood-Resistant Tree Species: Planting flood-resistant tree species is a proactive way to minimize future flood impacts. Species like Bald Cypress, Swamp White Oak, and River Birch are naturally more resilient to waterlogged conditions. When planting, consider the elevation and natural water flow of your landscape.

How can I tell if my tree is suffering from root suffocation after a flood?

Signs that a tree is suffering from a reduced supply of oxygen include yellowing leaves (or a premature fall color), wilting or downward curling, stunted growth, and overall decline in tree health. Inspect for soil saturation and check the roots for signs of decay. It's a long recovery period, so be sure to monitor for plant stress over time (including during the dormant season).

What are some flood-resistant tree species I can plant?

Examples include Bald Cypress, Swamp White Oak, and River Birch. These species are more adapted to wet conditions and can withstand prolonged flooding better than others. You might even see them thriving alongside fast-moving water, capable of withstanding flood events and more saturated soil conditions.

Can I save a tree that has been severely affected by flooding?

It depends on the extent of the damage, whether it's a flood-sensitive tree, and whether there are additional stresses. Early intervention and consistent care can help, but an arborist at a tree services company is best able to provide specific guidance tailored to your tree’s condition.

This article first appeared on Men's Journal and was syndicated with permission.

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