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Ask a Master Gardener: Challenges and Strategies for Mature Tree Care

BY: Beau Brodbeck, PhD, Extension Specialist in Community Forestry & Arboriculture, Auburn University www.mobilecountymastergardeners.org


Trees are part of our communities. Every day we drive, park, exercise, or picnic and simply enjoy the beauty trees bring to our communities. The benefits trees provide are countless, ranging from stormwater capture to increasing property values, to reducing cases of ADHD among children. These benefits are NOT tied to smaller species like crape myrtle, palms, or newly planted trees. It is the large, established trees that bring the greatest value to landscapes, neighborhoods, and communities. Yet, these are the very trees we are losing at an alarming rate. A recent study found that Alabama is among the top five states for urban tree canopy loss at a rate of 12,000 acres per year.


Mature trees are lost to new development because it is often cheaper and certainly easier to remove existing trees and simply replant with smaller trees. There is also infill development in older or historic neighborhoods where smaller homes are replaced with larger structures, reducing available space for existing trees. Finally, trees are lost to age. Many Alabama communities were founded well over a century ago and their trees, especially in cities, are reaching the end of their functional life span. Better municipal building codes and ordinances are needed in many municipalities, however, there are some strategies that we can apply in our landscape or neighborhoods now.


When building, remodeling, or landscaping, practice tree preservation strategies. Most tree losses occur due to a poor understanding of tree roots. It’s important to recognize that roots are shallow, growing in the top 20 inches of the soil, extending two to three times a tree’s dripline, and requiring water, organic material, and oxygen to grow. Common construction practices cut roots for foundations, driveways, patios, and even irrigation, which limits the trees’ ability to survive. Soil compaction caused by driving heavy equipment or parking under trees decreases available water and oxygen, as does burying roots by raising the soil grade around trees. Be aware that construction injuries can take years to be evident in trees, often well outside the one-year warranty offered by many builders.


Proper tree preservation is as simple as preserving one foot of radius around tree trunks for every inch in tree diameter (measured 4.5 feet above the ground). A tree measuring 20 inches in diameter will have a tree preservation radius of 20 feet. Erect fences and limit access to this area so tree survival can be enhanced. Plan travel corridors and material storage areas for construction crews. If equipment needs to cross tree preservation zones, lay down 12 inches of wood chips with plywood or steel plates on top to help dissipate compaction (Be sure to remove wood chips at the end of construction.).


Second, hire professionals to care for mature trees. Trees are long-lived organisms with complex physiological processes that require knowledgeable individuals to prescribe treatments to help trees overcome the challenges of growing in urban environments. Poor tree care can dramatically shorten the functional life span of trees. On the Gulf Coast, it is not uncommon to see bad pruning practices, such as topping trees, sold as “hurricane pruning.” Large pruning cuts or excessive pruning can have long-term impacts, including making trees structurally unsafe. When hiring professionals, look for those who have the International Society of Arboriculture Certified Arborist credential. The website Treesaregood.org is a convenient place to search for local Certified Arborists.


Finally, as we move into the peak of hurricane season, be aware that there are increasing conflicts between homeowner insurance providers and trees. The fact that trees can cause damage to homes has not escaped the attention of some providers. It is now common for providers to ask homeowners to remove limbs or trees they consider too close to homes. Sometimes, this is warranted, however, removing large limbs might increase future risk or damage trees. Additionally, removing one tree in a landscape could expose remaining trees to greater wind pressure, increasing their risk of failure. When these cases arise, it is advisable to hire a Certified Arborist who is Tree Risk Assessment Qualified to provide a second opinion.


As hurricane frequency and intensity, along with insurance rates, are projected to increase, so does the potential to impact urban trees. Anecdotally, there is a growing tendency to plant smaller tree species in landscapes from a combination of fear of large trees and increasingly smaller lot and right of way sizes. The magnificent tree arches of historic districts might just become another footnote in history. So, let us protect our aging trees as we may never see their like again.

Mature trees need space both above and below ground to fully develop. This is becoming increasingly difficult in most modern cities. Picture: Magnolia Springs, AL by Beau Brodbeck


Picture and drawing provided by Beau Brodbeck

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