What to Consider When Replanting Trees After Storms
Following the loss of trees in Nashville from two severe weather events — the March tornado and the May derecho — many people have had questions and concerns about replacing trees. Here, we’ll go over some of the key factors to consider: what kind of tree to choose, where to plant it and how to maintain it to mature growth.
What to Consider When Replanting Trees After Storms
A Tree’s Vulnerability
Many of the trees ripped up by storms are older and have defects, according to Michael Davie, NTCC board member and master arborist with Bartlett Tree Care. While some healthy trees can be affected by winds, trees have generally evolved to withstand strong winds and storms. Even in the aftermath of especially strong storms, the trunks and branches of most healthy trees remain.
The best way to keep trees healthy and durable is with regular maintenance and care; having an arborist trim branches is important, but homeowners themselves can fulfill some responsibilities. This includes keeping trees watered weekly when the soil is dry, and keeping the roots intact by not digging nearby.
Urban trees require routine maintenance for a variety of reasons, Davie points out. Trees planted in urban environments still grow the way they have for hundreds of millions of years in the forest, but that might not be the way we want them to grow next to a house. A tree might be structurally unsound, for example, because it has extended its branches, reaching for as much light as it can get, even at the expense of losing a branch later on. When a tree branch grows over a roof, the residents may be uneasy knowing a massive branch is hanging over their bedroom during a storm.
Trees may grow lopsided due to losing a large branch on one side or getting a utility trim. A storm may have broken a tree trunk down the center decades ago and while the tree managed to hold itself together with scar tissue, it is unsafe if close to a home. A tree may be suffering from any number of diseases, some of them terminal to the tree’s long-term health, such as the Emerald Ash Borer or Dutch Elm Disease. These health and structural deficiencies are virtually harmless to human life when they occur in the forest, but they need correcting when they occur in an urban context.
Risk Factors of Trees
When deciding to plant a tree, there are several characteristics to be aware of that affect its durability and fitness for the urban landscape:
Size, Shape and Placement – The size of a tree is often the first thing people think of when they judge a tree’s safety during a storm. Some trees pose virtually no risk to life or property, such as small understory trees like Redbuds, Dogwoods, Cherry Trees or Japanese Maples. But these small trees also have limited benefits in comparison to large canopy trees that provide shade for houses and neighborhoods, reduce cooling costs and absorb storm water runoff. Not all large trees are imminent risks; some, like the Tulip Poplar, which grows with a single hardwood column, stands against most any gust of wind. Black Walnut is also a notably strong wood type that has a good growth form. Placement of a tree can also limit risk. Consider the size of a tree at maturity when deciding how far to plant it from a home.
Wood Strength – There are two general types of wood strength: softwood and hardwood. Softwood trees tend to be lower in strength and more brittle, which makes them more susceptible to storm damage. Softwoods include the Hackberry, Silver Maple, Bradford Pear and White Pine. Hardwood trees are higher in strength and flexibility, and therefore less likely to fall or break in a storm. Hardwood species include the Tulip Poplar, Ginkgo, Oak and Eastern Red Cedar.
Branch Structure – Some trees grow more horizontally and some more vertically. Some have branch growth patterns that are not structurally sound. One notoriously problematic tree is the once-popular Bradford Pear, which often splits or topples during storms due to its poor branch structure. Trees often need gentle guidance from an arborist to ensure the branch structure is strong. Silver Maples, for example, tend to branch in weak, near-vertical V patterns as they grow.
Root Growth Patterns – Roots are the anchors of trees, and a compromised root growth pattern makes a generally weaker anchor. Trees like the White Pine have compact root growth patterns while achieving disproportionate height -- putting the tree at higher risk of falling once it becomes large. Other trees, such as the Ginkgo, have very deep-growing roots that provide more stability.
Wind Resistance – Tree leaves, structures, surrounding trees, prevailing winds and tree density can determine how likely a tree is to fall and where it may fall. Tree leaves that are light and airy, such as those on the Bald Cypress, are more aerodynamic than those of the Maple, for example. Where structures are built next to trees, the chance of a tree falling may increase or decrease depending on whether the structure(s) block winds or channel them. Removal of large trees from our neighborhoods due to infill development also increases the chance of tree failure. As trees that grew up together become large and mature, they collectively shield each other from straight-line winds by forming a sort of collective buffer. As development occurs in our neighborhoods, it puts holes in the defenses that trees once had, making them more susceptible to strong winds.
The Process of Replanting
The exact spot where a tree has been torn up or knocked down in a storm isn’t a good place to plant a new tree. It’s best to pick a spot nearby, where the soil is undisturbed and doesn’t have broken pieces of roots and wood chips in the ground. It’s also important that the planting site is appropriate for the tree, in terms of light, soil acidity and drainage. The right tree will be the one that fits the requirements of the location. Once a type is chosen, the tree’s shape will determine how it should be pruned and maintained over its lifetime to prevent contact with surrounding utility lines or buildings. Checking with an arborist or the Tree Corps can help you make the decision that’s best for your location.
To maintain your urban trees so that they are strong and durable, an inspection by an arborist is recommended at least every 2 to 3 years. An arborist can recommend trimming needs while also inspecting trees for pests or diseases. Most tree problems are avoidable with good preventive care.