Are your trees drowning? Many parts of the country have experienced a wetter-than-normal fall, which has left many trees sitting in soil saturated with water. Too much water sitting at the base of a tree can cause myriad problems. A traditional life preserver might not be the answer for these leafy giants, but a little knowledge – and knowing where to seek assistance – can help trees survive excessive moisture.
Too much water can be as bad for trees as too little water. While some trees are suited to survive occasional floods, most are not. In addition, as a tree becomes older, its ability to adapt to abrupt environmental changes decreases.
“Trees must maintain a proper water balance,” says Tchukki Andersen, BCMA, CTSP* and staff arborist with the Tree Care Industry Association. “Although most trees can withstand moisture conditions from very dry to very wet for short periods of time, continued extremes can cause serious problems, depending on the tree species,” Andersen explains. Some species (such as some oaks, pines and junipers) have adapted to survive drier conditions. Trees that grow along rivers (such as willows, poplars, cottonwoods and sycamores) and trees that grow in or around swamps and ponds (such as red maples, gums and pond cypress) can also grow in wet conditions.
Flood injury occurs when soil becomes saturated with water. There doesn’t need to be an actual flood to cause flood injury.
Has flooding damaged my trees?
Flood injury is usually expressed through changes in the foliage. One symptom in particular, chlorosis, is commonly caused by flood injuries. Chlorosis is the yellowing of leaves caused by a decrease in the amount of chlorophyll (green pigment) in the leaves.
This symptom can look like a symptom of a disease but is often caused by non-disease problems, such as excessive water. A professional arborist can determine if chlorosis is caused by a pest, which might be possible to manage, or by water damage.
When flood conditions are prolonged, root dieback occurs. During root dieback, soil is so saturated that there is not enough oxygen available to the tree roots. Without the proper balance of oxygen and carbon dioxide, roots can’t survive. Eventually the tree is not able to absorb adequate moisture, despite the flood condition.
The tree will exhibit symptoms similar to leaf scorch, where a tree’s leaves turn brown and die due to a lack of moisture in the leaves.
Symptoms of flood injury, in the order that they develop on the foliage, are:
- slight wilting or drooping of the foliage
- yellowing (chlorosis) and browning (necrosis) of leaf edges
- browning in the center of the leaf
The symptoms usually start at the top of the tree or on the ends of branches, and spread throughout the entire crown. The symptoms are often more severe on the side of the tree facing the prevailing winds.
What to do
The best prevention for this problem is to avoid planting flood-intolerant trees in areas that are frequently flooded. That’s easy to say after the fact, but in planning a future landscape, this would be the best recourse to avoiding plant damage. There are a variety of wetland trees and shrubs that can tolerate flooding better than other trees.
For those trees in an existing landscape, there are not many practical short-term solutions other than improving drainage. Whenever changes in drainage are made, the impact to all the affected landscape plants needs to be considered. Avoid creating problems for flood-tolerant plants by providing drainage for intolerant plants.
What else can you do?
If you are unsure about your tree’s health, consult a professional arborist who will treat the causes of tree health problems. Use TCIA’s search tool to hire a professional arborist or tree care company.