Most trees are not well adapted to saturated soil conditions.
With nearly daily rainfall this spring and summer — sometimes in record amounts — the ground became inundated with water. When excess moisture dramatically changes root environment, especially during the growing season, a tree’s entire physiology is altered, which may result in the tree’s death.
Water-saturated soil reduces the supply of oxygen to tree roots, raises the soil’s pH, and changes the decomposition rate of organic material — all of which weaken the tree, making it more susceptible to indirect damage from insects and diseases.
Additionally, with heavy rainfall there is erosion and sediment movement. Exposed roots or roots covered by excess soil add stress to plants. When rain finally stops, the tree’s system often has been so compromised that it can’t perform functions necessary to survival — so it just dies.
When the ground becomes completely saturated, a tree’s metabolic processes change quickly.
Photosynthesis shuts down within five hours; the tree is in starvation mode and lives on stored starches. Water moves into and occupies all available pores that once held oxygen. Any remaining oxygen is used within three hours. Lack of oxygen prevents the normal decomposition of organic matter, which leads to production and accumulation of toxic gases such as carbon dioxide, methane, hydrogen sulfide and nitrogen oxide.
Additionally, there is noticeable root growth loss within seven days. Roots only develop when soil oxygen levels are at 5-15 percent. Soon, pathogens attack decaying roots. Loss of root mass from decay and fungal attack leave the tree prone to drought damage. After two weeks of saturated soil conditions, the root crown area can have so many problems that decline and even death are imminent.
Nutrient uptake is necessary for plants to function. However, in saturated soil, anaerobic organisms — primarily bacteria — replace the aerobic organisms that once existed in the soil. These bacteria convert nitrogen into forms unavailable to plants.
In addition, manganese, iron and sulfur become limited because the soil pH has increased, making the elements unrecognizable. With little to no functioning root system, trees in saturated soils do not have the means to uptake nutrients, even if they were available.
When a tree experiences anaerobic soil conditions, it will exhibit symptoms of leaf loss with minimal to no new leaf formation. This usually appears two to eight weeks after the soil dries out again. Many trees — especially more juvenile and mature trees — will not survive.
Well-established trees may still decline several years later, if they experience additional stresses such as drought or root disturbance from construction.
Little can be done to combat damage caused by soil saturation. However, it is important to enable the tree to conserve its food supply by resisting pruning and to avoid fertilizing until the following growth season.
Mulch removal will aid in the availability of soil oxygen. It is a “wait and see” process. While water is essential to trees’ survival, it can also be a detriment when it is excessive.
Sheila Dunning is a Commercial Horticulture Extension agent at the Okaloosa County Extension office in Crestview.