Missoula's Aging Urban Forest and Its Norway Maples

Why does Missoula have so many Norway maples?

Because settlers planted what they knew. The City's plan records that the Missoula valley's first imported trees arrived in 1874, fruit trees and Norway maples planted around a home, and that from 1909 into the 1930s dozens of neighborhood improvement districts laid out curbs, sidewalks, boulevards and street trees. The predominant tree chosen was the Norway maple, which the plan says remains the predominant canopy species in the rights of way of Missoula's historic districts.

The plan names the neighborhoods where it is most concentrated: the majority of right-of-way trees in the Northside, Westside, University and Rose Park neighborhoods are Norway maples.

How much of the urban forest is Norway maple?

About three in ten public trees. The plan's 2014 inventory put Norway maple at 30.5 percent of roughly 24,400 street trees, and maples of all kinds at 39.4 percent. A Montana DNRC fact sheet built on the same inventory work, analyzed in 2016, reports 22,537 street trees of 117 species and puts Norway maple at 31 percent, stating that Norway maples are overrepresented.

Earlier estimates were higher still. The plan notes that a 2003 census suggested the species made up about 60 percent of the public tree resource, and that its share has fallen through annexation, new development, a wider census area and removals as old trees decline.

The benchmark the plan uses is that no single species should exceed 10 percent of an urban forest, no genus 20 percent and no family 30 percent. Missoula's street trees, it says, do not meet that recommendation.

How old are these trees, and what shape are they in?

Old for a street tree, and declining. The plan describes Missoula's Norway maples as very near the end of their lifespan. Although the species was about 30 percent of the trees, it accounted for 41.5 percent of the trees rated poor and 43.1 percent of those rated very poor.

Across all species, the plan's inventory rated 21.5 percent of public trees poor, 8.4 percent very poor and 1.3 percent dead. The DNRC fact sheet reports 31.3 percent in good condition. The plan projected that about 31 percent of the urban forest would be removed within ten years, and a similar share in the decade after.

These figures are now about ten years old. They describe the trend rather than today's exact count, and the City's Urban Forestry Division holds the current inventory.

Why does it matter that they were planted so close together?

Spacing is one of the defects the City identified. The plan says the maples in the five older neighborhoods were planted 20 to 25 feet apart, while the optimal spacing for a tree of that size class is 30 to 35 feet. Crowded trees compete for water and light and grow into one another.

The plan also lists what people have done to the trees since. Topping was the most common cultural defect in the inventory and improper pruning the third. The plan is blunt that topping produces a high-risk tree with splayed regrowth, not a safer one. Our guide to why topping fails and what to do instead covers the alternatives.

What is the City doing about it?

The first of the plan's 16 goals is to create and maintain a diverse urban forest. Among its recommendations are a City-funded replacement program planting 400 trees a year in the five neighborhoods with aging Norway maples, which the plan calculated would replace about 8,800 maples over roughly 22 years, and staggered planting so that the next generation is not all one age. Those are the plan's recommendations as written in 2015. We have not found a City report on progress against them, so ask Urban Forestry for the current picture.

On the ground, the City says its Urban Forestry Division prunes boulevard trees block by block on a cyclical basis, assesses publicly owned trees each year and removes approximately 100 to 150 annually once a tree poses more liability than public benefit. It also runs an annual spring planting, and lists sites where public trees have been removed among its priorities.

Who looks after the maple in front of my house?

Both you and the City, in different ways. The City states that its Forestry Division oversees all activity in the right of way, that homeowners are responsible for maintaining the land and caring for the trees there, and that any pruning, planting or removal of a boulevard tree must be done by a licensed and insured ISA Certified Arborist and approved by the Urban Forestry Division before the work. Residents can call the Division to learn when their block is scheduled for pruning or to request an inspection.

This is general information, not legal advice. For anything specific, contact Urban Forestry at the City. Our guide to Missoula tree permits and the right of way explains the permit steps, and we take on permitted boulevard work as part of our tree services.

What can a homeowner do to keep an old maple going?

Water it. The plan identifies drought stress as a common problem for Missoula street trees, in a semi-arid valley that it says averages about 14 inches of precipitation a year. The City's watering guidance says mature trees need a minimum of two inches of water a week from May to October, applied deeply across the area under the branches, not as a light sprinkle that only feeds the grass. It suggests setting out cans to measure and checking that a screwdriver pushes six to eight inches into the soil.

The City also recommends two to four inches of wood mulch pulled back from the trunk, a deep watering after leaf drop and another before leaf-out. Our guide to watering trees through a Montana drought goes further. On timing, the 2024 edition of the City's street tree list notes that trees that bleed sap, such as maple and birch, should be pruned in late summer or fall.

When is it time to let a maple go?

When the defects can no longer be pruned out. The plan's condition ratings are a useful yardstick: a tree in poor condition has dieback through 30 to 50 percent of the crown or has been topped, and pruning will not improve it. A tree in very poor condition has major dieback or multiple hazards.

Large dead limbs over a sidewalk, a parked car or a roof are the practical trigger. Our guide to the signs a tree is about to fail lists what to look for, and for a boulevard tree the City asks residents to report hazardous trees or hanging limbs to Urban Forestry.

What should replace it?

Something else. The City's 2026 approved street tree list, as we read it, does not include the straight Norway maple, though it offers other maples along with oaks, honeylocust, ginkgo, resistant elms and many more. Boulevard planting needs a City permit and a species from that list.

For a tree in your own yard the choice is yours, and our list of the best trees to plant in western Montana is a starting point. You will find guides to other valley trees in the Montana Tree Guide.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a tree assessment and an ISA Certified Arborist will look at the tree with you.

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