Although trees need water to survive, excess water, like any other plant, can do more harm than good. For a tree to thrive, it must be adequately watered as too little, or excess water can affect its overall health. This leads to the question, can too much water kill a tree?
Too much water can kill a tree because roots get deprived of oxygen when submerged in water for extended periods. Besides the risk of reduced oxygen levels, too much water due to flooding can introduce contaminants and pathogens that trigger rotting, eventually leading to the death of a tree.
These are some of the ways in which too much water affects trees. Read on for a more detailed discussion on rehabilitating your trees after flooding. I’ll also highlight some flood prevention measures you can implement to spare your woodland from adverse effects.
Causes of Flooding
One or a combination of the following conditions can cause flooding around your trees:
- Deforestation
- Excessive rainfall
- Improper farming methods
- Blockage of drainage passageways
- Poor maintenance of drainage systems
- Faulty design of drainage infrastructure
- Constructing settlements on floodplains
How Too Much Water Affects Trees
Too much water affects trees in multiple ways. When roots are entirely covered by water, they struggle to breathe, which leads to gradual withering. The level of submersion plays a massive role in determining the effect of water on a tree.
This water-caused hindrance leads to the accumulation of harmful gases such as nitrogen, hydrogen, and methane around their roots. Consequently, the roots’ ability to nourish the tree gradually deteriorates.
Prolonged flooding leads to the death of more roots, which weakens the tree as a whole. Without early intervention, the root system may get damaged to the extent of no repair, which increases the chances of death due to excess water.
The extent of damage that a tree can suffer from flooding mainly depends on:
- The type of tree
- Its initial condition
- The amount of soil removed from or added
- The duration of the flooding event
- The depth of the water
Compared to conifers like pine, spruce, and fir, broadleaved trees can withstand flooding better. The following table will help you identify and classify trees according to their tolerance or intolerance of too much water.
| Tolerant | Intermediate | Intolerant |
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Physical Damage
Large volumes of fast-moving water, carrying large objects such as snow slabs, rocks, and logs, can cause severe damage to trees by breaking branches and peeling the bark from trunks. This exposes them to disease and decay.
Massive water currents can also knock your trees to an unhealthy leaning position or erode the surrounding soil and expose the roots. Uncovered roots are more prone to disease, freezing, and drying out. Besides, rapid flood waters can even topple or uproot trees!
Physiological Damage
Oxygen Starvation
Without enough oxygen, roots eventually cease growing or working properly and die. However, heavy, woody roots have a higher chance of surviving a flood than non-woody ones.
Furthermore, pathogenic fungi can enter the tree through wounds left by dead roots. A tree that has lost some of its roots because of disease or direct flood damage is more vulnerable to drought the following growing season. Also, it becomes too weak to withstand windstorms during the summer.
Flooding also inhibits the growth of mycorrhizal fungi, which rely on high levels of soil oxygen to thrive. Mycorrhizal fungi are supportive soil organisms that bond with tree roots to boost a tree’s root network and nutrient intake.
Sedimentation
Deposits of silt, sand, or clay 一 ranging between a few inches and several feet can bury the roots deeper into the ground, depriving the tree of enough oxygen over time. To compensate, some tree species may grow new roots in the emergent upper layer of the soil. Unfortunately, other trees will simply wither and die.
Besides oxygen starvation and sedimentation, too much water also causes
- Multiplication of anaerobic bacteria: They reduce the amount of minerals in the soil, such as iron and sulfur, and cause tree roots to decay rapidly.
- Growth of harmful fungi: They decimate the roots by feeding on them.
- Contamination: Floodwaters can poison your trees by spreading toxins or bringing saltwater and salt to your soil, causing the deterioration of your trees’ health.
Symptoms of Flooding
The soil around your trees can get waterlogged without the water rising above the ground. Therefore, it’s advisable to always examine your trees for the following physical symptoms of flooding:
- Yellowing of leaves
- Reduced leaf size and loss of leaves
- Blisters soaked in water on the stems and leaves
- Tiny shoots or water sprouts that emerge from the main stem
- Moss, fungi, or mushrooms at the tree’s base
- Leaf drop
- Crown dieback.
How To Help Trees Recover After Flooding
Post-Flood Inspections of Trees
There isn’t much you can do while the water still covers the ground. As such, it’s best to wait until the water recedes.
As soon as all is clear, have your trees examined for signs of trauma and survivability. Consider the following factors to determine the extent of damage to each tree.
- Discolored leaves
- Trunk and branch damage
- Eroded soil
- Silt deposits at the base of the tree
- Dangerous leaning
Determine Tree Survivability
Start rehabilitating your woodland after flooding damages your trees by enhancing the safety of your property. Trim damaged branches, treat trees for diseases and fungi, and remove dead and dying trees.
Remove any broken branches that can be securely reached from the ground with a clean cut without applying dressing or pruning paint to the cut. Get rid of leaning trees too, because they are a safety risk.
Remove Debris and Mulch
For the time being, remove any mulch that may be present around your trees. Mulch conserves moisture, so getting rid of it can increase oxygen circulation.
Clear debris and excess dirt from around the trees quickly but carefully, leaving only the trees’ native soil. Failure to remove the alien matter will cause the new roots to grow into unsupportive deposits.
Evaluate Damage to the Bark
Examine the entire circumference of each tree to ascertain the damage to the bark. If the damage is not over 10%, your tree will survive, provided it was previously healthy and didn’t suffer root damage during the flood.
But if your tree sustained a 50% or greater bark injury, it’s advisable to get rid of it before disease and decay make it unstable.
Redress the Roots
Due to the profuse erosion and subsequent root exposure, add soil around any trees that remain standing and seem firmly rooted. Do not exceed the original soil level. Usually, there’s a visible texture or color variation at the base of a well-planted tree, which shows the normal soil level.
Check Your Irrigation System
The flooding may have resulted from over-irrigating. If so, tune up your irrigation system. Whether you water by hand or position a lawn sprinkler, reduce the frequency and amount of water.
Watering deeply and infrequently is the ideal irrigation strategy for trees. Therefore, if you’re watering your trees daily, you might be doing them more harm than good.
Apply Nitrogen-rich Fertilizer
Add 1-3 pounds (1/2-1.5 kilograms) of a nitrogen-rich fertilizer per 1,000 square feet (93 square meters), such as a 20-0-0 mixture, to enrich the soil around each tree. The fertilizer will help the tree regain the strength it lost when the water affected its roots.
Enable Long-Term Recovery
Water your trees throughout the dry summer months for the next few years while they sprout new roots after the flood. Their root systems are diminished due to the death of mycorrhizal fungi and their roots.
Spread a level layer of organic mulch 2.5 to 3 inches (6.35-7.62 centimeters) thick around the base of the trees. Wood or bark chips made of cedar, cypress, or other hardwood, as well as shredded hardwood, are the most commonly used organic mulches.
Final Thoughts
It may take your trees two to five years to fully recover from the physical and physiological damage suffered during a flooding event. To enhance their restoration, monitor soil moisture levels continuously and protect them from insects and contamination during recovery.
Inspect your trees frequently for any problems.
Contact an arborist if the tree yellows or loses leaves on a substantial number of its branches so they can decide whether the tree can be saved or has to be removed before it dries completely and falls.
