Gary Johnson, UMN Extension Professor, Urban and Community Forestry, Department of Forest Resources
No one willingly lets go of old friends, whether they're human, pets or (ahem) trees. But the reality of life is that there's an aging process that's inevitable and not all problems can be diagnosed and successfully treated. So that old friend that sheltered you from harsh winter winds, shaded you on hot summer afternoons when the heat index was over 100 degrees, greeted you in the spring with a bouquet of flowers...must eventually or prematurely be removed.
Four Questions Before Letting Go
Gardeners of all shapes and degrees tend to be incredibly hopeful. For example, when news comes along that there's a new cure for emerald ash borer (have you heard about the fruit juice and dish soap treatment yet?), the urge is to try it without considering four "critical" questions .
· Is the tree healthy?
· Will the tree remain stable if it stays in the landscape?
· What is the relative value of the tree to you?
· What can your budget reasonably handle?
By the time these four questions are answered, the fate of the tree's future should be obvious.
Is the tree healthy?
Health is a measurement of a tree's ability to photosynthesize normally, store energy for growth and tolerance to stresses, and the eventual release of that energy. If a tree has a species-characteristic crown density, leaf color and size as well as a sufficient live crown ratio, it's generally considered to be healthy. Stand under the tree and look up through the foliage. If it's a Norway maple, you shouldn't be able to see a lot of sky. If it's a honeylocust, you should see blue clearly through the crown. That's an example of characteristic crown density. The same goes for leaf color and size. Don't compare oaks with service berry.
Live crown ratio refers to the vertical mass of foliage. A healthy tree should have at least a 60% live crown ratio, that is, 60% of its height is photosynthetic foliage. If a tree has abnormally small leaves, a thin crown, a deficient live crown ratio, lots of dieback (therefore, less foliage) and defoliates early due to insects or drought...it's unhealthy.
Trees in Minnesota have a relatively short amount of time to create chemical energy (e.g. sugars) and store them up for normal functions (e.g. starches provide energy to grow, leaf out, tolerate defoliations). Full leaf expansion doesn't occur until mid-June (sometimes later) and the photosynthetic season is essentially over by the end of August. Weakened trees have difficulty tolerating or recovering from common stresses. If your tree mirrors the image of an unhealthy tree and it's been that way for awhile, it's not likely that investment s of chemicals and money will turn it around.
Declines in health are most often associated with repeated defoliations (e.g., Japanese beetle or gypsy moth, hail storms, or anthracnose) or chronic drought (several years of seasonal drought). If nothing has been done in the past to intervene and lessen these stresses, trees progress into a decline spiral from which they rarely recover. Healthy trees on the other hand can recover from problems that are shorter termed (termed inciting events) especially with a little care such as watering, mulching, and controlling defoliating insect pests.
Will the tree remain stable?
One of the more difficult decisions to let go happens when a tree is obviously "healthy" but is unstable, too risky for the landscape. What? How can that happen? How can something be that healthy looking be bad for us?
Decay. Decay is the most common reason trees fail in wind storms (well, other than the wind). A healthy tree can have extensive decay in the trunk or buttress roots, which makes it an unacceptable risk in the landscape...too likely to prematurely or suddenly fail and cause property or personal damage. If the decay is extensive and especially if there's an opening to the cavity, don't think twice, find someone with a chainsaw. A good arborist can calculate the strength loss due to decay for you. If it's greater than 33%, the risk isn't worth keeping the tree in the landscape.
Dysfunctional roots. Stem girdling roots, roots of big trees squeezed into tiny spaces (like narrow boulevards or small planting spaces) are often the causes for complete tree failures during wind storms. The bigger the tree, the more severe the root problem, the more likely massive damage will result...not may result, but will result.
Severed root systems. Street widening projects, new or repaired buried utilities, roots cut during house construction activities cause instability issues. Most trees (if they're healthy...ironically) recover from construction activities or anything that cuts the normal root spread...only to topple during the next wind storm or the next one or the next one. It's not worth it. If roots are cut within a few feet of a large tree on two or more sides, it's unstable. If it's near a house, utility wires, roads, etc, it's an unacceptable risk.
What's its relative value?
You could hire a certified arborist to calculate the monetary value of the tree, but that's not what I'm referring to. Is there an emotional or sentimental value to the tree? Did Grandpa plant it with you on Arbor Day when you were a kid? Did Mom love the apples it grew and made the best pie from them? Oooh, tough call if it's removal time.
Relative values for everything are as unique as the individuals that own them. Some people collect objects, take pride in weed-free lawns or drive pick-up trucks with carpeting in them. Others purge, are willing to clean bathrooms every day if it means avoiding lawn work or buy trucks for work, not show and wouldn't pay an extra nickel for carpeting.
Trees that are special (unusual species, extra large size), well -placed for shade or blocking a nasty view, showy in the spring or autumn or host a tire swing or tree house are trees that are hard to let go. You may never see another tree like that again, so the cost of care may not be an issue. Whatever it takes to save it will be done...as long as it's relatively healthy and stable.
Individual windbreak trees, individual trees that are part of a woodland or trees that are so far from your house or normal activities area have less value. Their absence will not be as noticeable as the sentimental trees or the tree that your always rely on for shading the patio in the afternoon. Younger or smaller trees tend to tug at the heartstrings less, too. If the tree has only been in the landscape for a few years, there's usually less of an emotional attachment and it probably isn't shading the landscape that much.
What's your budget?
It often comes down to this: groceries or the ginkgo. Tree care doesn't come cheap, especially if it's a large tree and the care is long term. Trees are an investment, part of the infrastructure of your landscape, just like fences, garages and patios. Deferred maintenance has never worked for building longevity and quality and it doesn't work for trees either.
If a tree is regularly straining your budget by demanding life support maintenance, you'll probably be in favor of removing it. Why on earth would someone on a limited budget invest money year after year controlling apple scab on a crabapple when there are crabapples that are disease resistant? Get rid of the money pit and plant a new, lower maintenance crabapple...they're just as pretty.
If, however, the tree is well-placed, provides a valuable service, is healthy and stable, the investment to keep it healthy and stable is probably money well-spent. Inject that American elm with fungicides that will prevent Dutch elm disease. Treat those bur oaks with oak wilt...they can be saved. Don't let gypsy moth or Japanese beetle repeatedly defoliate that linden...there are both chemical and biological controls for those problems.
A reality check is needed for comparing control options to giving up and removing the trees. The expenses related to keeping trees free of oak wilt or emerald ash borer may seem onerous, sometimes $100-300 every 2-3 years. However, removing large trees near homes doesn't come free, either. A large tree within dropping distance of a home can cost $1,000 to $6,000 or more to remove...and then you're left with nothing but fire wood. No shade, no fragrance, no privacy. All of a sudden, maintenance money seems a bit cheaper.
The final decision.
That well-placed, healthy, mature tree needs some significant pruning and cabling work on it, as well as some other health management treatments...is it worth it? Most likely. Keep in mind that it could be an ash. There are very effective treatments for preventing or treating ash trees for emerald ash borer. Don't give up if the tree is worthy of saving just because it's an ash.
That tree has been repeatedly topped under the power lines for years and looks like a mop on a tree trunk. Get rid of it! It's most likely filled with decay and there are many better alternatives such as smaller trees or trees not planted under the lines.
Construction activities have cut the roots within 4-5 feet of your mature silver maple on three sides...it's too risky for it's own good and it's time to replace it. Don't take a chance.
The apples on that Yellow Transparent are unbelievably delicious and you can't buy them in stores anymore! Control the apple maggots and apple scab.
Your male ginkgo has a little surprise for you...it's a female and the odor gets a bit stronger each year if you don't clean up the mess in the autumn! What to do? It's your call on this one.