This is Part 2 of a series. Part 1 can be found here.
Many urban trees only live about 20% of their life due to issues like pests and disease but mostly can be linked back to improper care and installation. A tree should live more than 50 years and up to 100 years depending on their species. A recent USDA study analyzing tree life expectancy in urban areas finds the typical street tree living between 19-28 years. However the ideal life span of a white oak is 600 years, and the average life span of a red maple can be between 75 to 150 years in the Illinois wilds.
Some basic knowledge of tree care can help your urban tree live longer.
1) The best thing for a tree in an urban environment is pruning. The worst thing you can do is improper pruning. Topped trees and stubbed branches weaken new growth and create an avenue for insect and disease. Proper pruning allows strong structural growth, protection from wind, and reduces the risk of tree failure.
The reason urban trees need to be pruned vs. forest trees is that they grow massive side branches, which are usually shaded out in a forest environment. Start corrective pruning the second season of your tree’s life.
2) In the industry, we say “mulch like a bagel, not like a muffin.” Never allow mulch to contact the trunk of the tree. Use hardwood or cypress mulch; avoid rock and artificial mulches. Mulch two to four inches deep as wide as you are willing to go. Properly mulched trees will require less irrigation, less competition with grass roots, and keep trees safe from lawn mower damage.
3) Strangling roots (commonly called girdling roots) circle the base of the tree rather than spreading out, providing a weak anchor and and cutting off the sap flow to the stems and leaves. These trees will decline and die within five to twenty years. Girdling roots are caused by improper planting, mulch muffins (aka mulch volcanos), obstructions like sidewalks and curbs, and poor soils.
Signs of girdling roots include: absence of a trunk flare at ground level, leaning trunks, bark cracks, branch dieback, and leaf issues. Data collected at University of Minnesota concluded that a third to half of the trees that fall after a storm can be attributed to girdling roots. It is much easier to prevent girdling roots rather than fix them when tree starts showing signs of decline. At planting, cut off circling roots, follow good planting practices and monitor tree to avoid girdling roots in the future. Some tree species are naturally prone to girdling roots like maple, ash, crabapple, linden, pine, and oak—all common in central Illinois.
4) Do not stake your tree unless you have to, and remove them after one season. Only use staking materials if wind is an issue at the site, or to protect from vandalism. Staked trees do not grow strong, develop poor root systems, and suffer from rubbing against their support system.
Learning basic tree care, you are increasing the life of your trees and ensuring that it will outlive you, a gift to the next generation.