This document will help you understand types of tree damage caused by floods, and what you can do after floods.

• Water covering the soil reduces the supply of oxygen to the tree's roots. Roots must have oxygen to survive and grow.
• Flooding changes the pH of soils; acidic soils become less acidic while alkaline soils become less alkaline.
• Roots contend with high concentration of toxic compounds, like alcohol and hydrogen sulfide, from waterlogged soils.
• Sediments carried by the water and deposited over the roots reduce the supply of oxygen to the roots (as little as three inches can be harmful).
• Ice flows and debris carried by rushing waters can remove bark and damage tissues.
• Erosion exposes the roots to drying and susceptibility to wind throw.
• Flood waters can smother foliage on lower branches.
• Flood waters may contain harmful runoff from urban development or agricultural fields. The roots may absorb the runoff.

• Prune off broken branches and remove debris.
• Rake off sediment left by the flood. To locate the extent of the roots, look up. Roots usually extend at least as far out as the canopy.
• Don't allow the tree to become further stressed during summer and autumn months. Water appropriately and fertilize if necessary.
• Put it into perspective. Flooding during the growing season typically is more harmful to trees than flooding during dormant periods. Short periods (<2 weeks) of floods in the growing season can be tolerated by most trees.
• Salvage and replant. Salvage the timber and firewood of killed trees before fungi or other pathogens rot and destroy it. Take advantage of scoured floodplains and freshly-eroded stream banks to reseed and transplant. Replant with tolerant species, such as red maple, tamarack, willow and black ash.

For more information consult the Iowa State publication "Understanding the effects of flooding on trees," or contact the University of Minnesota Department of Forest Resources Extension and Outreach office at 612-624-3020.

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