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Moment of Nature - Feb. 26, 2016
Gilland: Wet feet not good for trees
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It doesn’t take a rocket scientist to know we’ve had and continue to have rainy weather. Including the epic weather event last October, we’ve received 36.5 inches rain according to our official rain gauge here at the Public Works Department. While these past months have made for a dreary winter, I’m certainly not going to complain because it’s good for the trees ... kind of. 

Water is necessary not only for human and animal existence but also plants and trees. However, this much continuous rain without periods for the ground to drain and dry is not always a good thing. It’s ironic how, six months after writing about drought and trees, here we are with flooding and trees. 

Flooding in general can affect trees at every stage of their development, from seed germination and flowering to sprouting and vegetative growth. At each life stage, flooding can cause injury, changes in anatomy and form, decline in health and even death. Flood damage to trees develops in four primary ways: 1) soil and tree root physiology changes; 2) flood water physically knocking over trees; 3) saturated soil conditions de-stabilizing tree root-plates; and 4) chronic problems associated with a changed growing environment.

Even though we are not experiencing extreme flood-like conditions such as those which occur along the Mississippi delta, we do have extremely saturated soils. The major impacts of long-term saturated soil conditions on trees are many. First, water-logged soil results in poor aeration. As the soil becomes saturated, water molecules push out oxygen molecules. This causes an immediate constraint in oxygen movement from the atmosphere to the soil and tree. Lack of oxygen leads to the production and accumulation of carbon-dioxide, methane, hydrogen and nitrogen gases. Bottom line: long-term saturated soils can suffocate the root system, which means a decline in tree health or possibly death.

Second, flooding alters soil structure by allowing the soil particles to fall apart from reduced cohesion (glue-holding capacity), the dissolving of metallic and organic coatings and dispersing of clay particles. When this happens, the soil can become somewhat gelatinous in consistency and is less likely to hold the tree root system in place. As a result, a tree is less stable and more likely to fall over because it is no longer being held in place.

Third, flooding causes anaerobic (non-oxygen requiring) organisms to replace aerobic (oxygen requiring) organisms in the soil. These anaerobic organisms cause the loss of nitrogen and a reduction of manganese, iron and sulfur. These components are integral for tree health and growth and a significant reduction in them may adversely affect trees. In addition, anaerobic soil conditions can also foster the growth of some fungal pathogens, which may infect tree roots, leading to potential root rot disease. 

Fourth, flooding increases the pH of our naturally-occurring acid soils. A change in soil pH affects the availability of essential nutrients needed by the tree. If those nutrients are not available in sufficient quantities, tree growth may be temporarily stunted. 

This has been a tough 12 months for our community trees, with months of drought conditions and now months of flood-like conditions. We are bound to see issues, particularly with older trees, regarding poor health and slow growth. These issues may persist for years or may not be evident until the 2017 growing season; only time will tell. Since we can’t stop the rain, what are we to do?

Here are some best management practice activities which can be done now or this spring after the leaves flush out. First, perform a visual assessment of your trees. On a day when it’s not raining, take a 360 degree walk around each of your yard trees. Look up for any broken or cracked branches (a pair of binoculars may be needed) and look down to see if there’s been any soil movement of the root plate, trunk or a sudden lean of the tree. If so, contact me or a tree service company to examine the tree. Second, go to the Clemson Extension office on DeKalb Street to get a soil sample kit. Perform the necessary steps and bring the sample back for testing to determine proper essential element management. Once the soil sample report is sent to you, follow the recommendations provided. Third, do little to no green-wood pruning. This will help the tree conserve food supplies and energy reserves necessary for health and growth. Prune only for safety concerns and ideally only deadwood. Remember not to “top” a tree, not even a crepe myrtle! Fourth, consider aerating your yard this summer. This will help oxygenate the soil for better root growth.

Lastly, be on the look-out this summer for any diseases or insect pests, but do not spray any pesticides without first identifying and knowing what exactly you are treating.

Over the long-run, tree vigor and structural stability may be questionable on many trees around town. However, by paying to attention to basic tree needs (aeration, mulch and fertilizer), we can help our trees overcome their now wet feet.