Articles

How Long Should I Expect My Tree to Last?

The life expectancy of a tree is influenced by a number of factors.

Updated:

August 30, 2022

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Photo credit: Brian Wolyniak, Penn State Extension

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I was asked the other day how long we should expect our landscape tree to remain viable? My answer was, "it depends." Many things go into deciding how long we may have a particular tree to serve in a space. We might think of this as its service life. Trees growing singly in a 2-foot sidewalk pit in a commercial area may survive 10 years or less. The same trees planted in landscape systems of five or more, resembling a grove, may survive 50 years and longer.

Our other facilities, such as our roof or our air conditioner have a finite service life. They are inanimate, and never get better nor perform more strongly than the first day they were installed. We don't expect them to last forever. Trees, and tree landscapes, on the other hand are alive, and they improve in providing benefits for a time as they thrive, grow larger, and function well.

The term "service life" implies providing satisfactory performance throughout the period. The more the growing conditions resemble the natural forest the plants grow in, the longer and better they can serve. What determines how long a tree in the landscape can be expected to perform well? In this article, we consider:

Defects
Growing space
Species

Defects make trees more likely to fail

When trees break or become too diseased to function satisfactorily, we might say they "fail to perform". Trees fail when forces act on them to overcome their structural or reserve strength. This often occurs during storm events, and every year countless storms rage through the United States. Research in Minnesota in the early 2000's found that, by far, most of the trees that failed had structural defects. Defective trees are more likely to fail in a given situation than one without defects. In 2012, the US Forest Service prepared an excellent resource to show seven types of hazardous defects to look for in trees.

Consider that wounding from any cause may likely result in a defect forming. We cause many such wounds by pruning to meet site constraints, or through poor cultural practices. Engineering and infrastructure changes often cause wounds or space constraints that create defects if the trees are not removed immediately. Trees need space to grow.

Trees with sufficient rooting space survive longer

After assessing more than 150 trees in Puerto Rico exposed to Hurricane Georges in 1998, Drs. Duryea and Kamp at the University of Florida found that trees with more rooting space showed greater survival in high winds. To provide anchorage, roots need to spread beyond the canopy edge (the dripline) and grow deep into the soil. Sidewalks, curbs, buildings, parking lots, driveways, and other structures restrict root development. They found that a strong supporting root system with adequate rooting space is the most critical factor to the ability of trees to withstand high winds in urban landscapes.

The street side tree on the left has a growing space likely to limit its service life considerably compared to the tree on the right. Photo credit: Scott Sjolander, Penn State Extension.

Give trees enough rooting space providing sufficient water, oxygen, and suitable chemical properties based on their mature size. We recommend that no trees be planted in tree lawns less than 2 feet wide, or in tree planting pits less than 4 feet long by 4 feet wide by 2 feet deep or providing 32 square feet of fertile soil. Large trees need space of at least 5 feet by 10 feet by 4 feet deep, providing 200 cubic feet of fertile soil. These spaces provide the very minimum soil water storage needed to survive typical moderate drought conditions.

Place no trees within 50 feet of a busy intersection or within 20 feet of driveways, fire hydrants, or utility poles. This removes the tree from areas needing access or visibility for human living. Further, it makes trees less likely to be damaged or less likely to hit humans or properties if they do fail. This is a minimal recommendation, and many needs often compete for it. Other experts call for even more space, and colleagues have created structural systems such as engineered soil blends and suspended sidewalks to borrow needed space from competing activities that high priority gray infrastructure is built to serve.

Some species just naturally live longer

This fact is largely driven by genetic disposition. Fast growing species like willows are likely to have shorter functional service lives than longer lived species like oaks that tolerate a given site condition as well. Site conditions such as poor oxygen conditions or lack of sufficient water reserves can cut to survival short. Other factors are important, such as how the plant was grown, how it was cultured, and how it was cared for after installation. An excellent Pennsylvania research-based resource available to consider species and horticultural variety characteristics is Landscape Tree Factsheets.

Consider life span when managing systems like urban forests for longevity. Over-mature trees that may cause injury or harm should be removed to reduce risk when needed. Remove trees that are likely to fail before other causes break them. Consider removing tree species that have demonstrated poor survival in storms, especially if they are structurally weak or functionally likely to fail and endanger lives or property. Have a Certified Arborist inspect your trees for signs of disease and decay in trees.

This ash tree is likely to fail within the next couple years and damage the house it grows next to. Photo credit: Scott Sjolander, Penn State Extension.

How long should a landscape be expected to last? We should look at the landscape in its context. Some surrounding uses and conditions seem stable for years, while others are dynamic. The public street environment is a good example. Storefronts and spaces surrounding a landscape in the commercial district change every few years, and trees are routinely sacrificed to make way for higher priority excavation and construction. Other landscapes, such as 12-foot tree lawns in some residential neighborhoods may seem unchanging for 50 or 75 years.