Technical Services Topic – Trees We Love to Hate

It is reported that the Ailanthus tree is so widespread because its light, abundant seeds were used in the 1800s as a packing material around dishes manufactured in China. Packing materials were disposed along railroad ballast and soon the tree spread throughout the Northeast.

Why would we love to hate trees that can survive extremes of heat, drought, poor soil and pollution, produce abundant seeds, sprout readily, resist diseases and insects, and grow quickly? Trees like this would seem to be ideal for planting in inner cities, high density suburbs and along roadways.
Trees we love to hate have nice names like tree-of-heaven and Norway maple. Let's get to know them.

Tree-of-Heaven

Tree-of-heaven, Ailanthus altissima, is also called stinkweed. Officially, it arrived in North America in 1784 from northern China, where it is native. It has been doing fabulously ever since.

Where does tree-of-heaven grow? The simple answer is anywhere and everywhere. It grows well in garbage dumps, abandoned lots in cities, railroad ballast, roadsides, old fields and in the cracks of parking lots. It spreads so aggressively into yards and landscaping that the laws of Washington, D.C. once forbade planting Ailanthus within the city limits.

Ailanthus normally grows several feet per year from seed, but sprouts can grow six to ten feet the first year after cutting. The wood is soft and decays quickly.

Large pinnately compound leaves, composed of 11 to 40 leaflets, are alternately arranged on stout stems. Each leaflet of an Ailanthus leaf is narrow-oblong and has a small point near the base. When the leaves fall, they leave large horseshoe-shaped scars on the olive-tan stems. The leaves are often confused with those of sumac.

Ailanthus trees are either male or female. The females are acceptable in polite society, while the males account for the common name stinkweed. The flowers of the male tree give off a vile, putrid odor, while the panicles of small greenish-white female flowers, after seed set, produce huge clumps of samaras. Each samara contains a single seed that is easily blown far from the parent tree. This accounts for the quick spread of Ailanthus along rivers, railroads and roadways.

A single Ailanthus can produce 325,000 seeds each year. One study found that a single tree could reliably establish 6,000 to 7,000 seedlings a year. In some urban forests and parks Ailanthus is so common, it is assumed to be a native tree. The tree produces natural toxins that help it compete with native trees and shrubs. On rights-of-way, Ailanthus can quickly drive out native trees and form nearly pure stands. Hand cutting and mowing only encourage it to sprout vigorously from the stump and roots broken by the mower. Herbicides will control the species, if applied properly.

Norway Maple

A common scene in many cities and suburbs, Asplundh crews often encounter Norway maples that have been carelessly planted along streets and under utility lines. Their shallow roots damage sidewalks adn their fast growth/weak wood characteristics make them a prime candidate for our "trees we love to hate" list.

Norway maple, Acer platanoides, is a native of Europe that has become a pest in the United States. The species is present in the urban landscape of almost every city in the U.S. because it is an attractively shaped tree that is tolerant of urban conditions. It has dense green foliage and a broad oval crown.

Norway maple and its cultivars have been favorites of nurseries, landscapers and property owners for over 100 years because they are easy to transplant and grow quickly. They tolerate harsh conditions in a wide variety of urban sites and soils. Now, why do we love to hate Norway maple?

The problem is that Norway maple creates very dense shade which kills turf grass and other sun loving plants. It grows too large for most residential landscapes and its shallow root system damages sidewalks and curbs. This tree will suck the life out of almost any lawn area that it hasn't already shaded out.
A heavy seed producer, Norway maple seedlings become established in gardens, the edges of lawns, fences, woodlots and any other areas of open undisturbed soil. They like full sunlight, but seedlings can persist in the understory for many years where they slowly drive out native plants as they compete for soil nutrients and space.

Perhaps the best way to sum up the Norway maple is a quote from a member of the Massachusetts Department of Environmental Resources, "The darn things will grow anywhere!"
So why do we, as utility arborists, hate them? Both tree-of-heaven and Norway maple have several undesirable characteristics in common-they grow very fast, are invasive, produce weak wood, decay quickly and therefore, can be dangerous to climb. After pruning for line clearance, they quickly grow back into the wires. Every reasonable opportunity should be taken to remove these trees from the utility right-of-way and suggest other species for replacements where appropriate.
There are many other trees we love to hate such as:

- Chinese tallow, Sapium sebiferum
- Melaleuca (cajeput, paper bark tree, punk tree), Melaleuca leucadendra
- Blue gum, Eucalyptus globulus
- Saltcedar, Tamarix ramosissima
- Paulownia (Empress or Princess Tree, Chinese Royale Tree), Paulownia tomentosa
-just to name a few. Look for more about them in a future story.

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