The Urban Pantheist

Tar spot fungus Rhytisma acerinum grows on a Norway maple Acer platanoides leaf.

Forgive me for not presenting a picture of Norway maple in full. Any wide angle photo of my yard is likely to feature them, and you can click the Norway maple link to see dozens of photos of this common naturalized alien. Norway maple is an attractive shade tree well suited to the city and suburbs. It is also a pernicious invasive species, threatening to invade our forests and transform them into barren monocultures. I have cut down all the Norways small enough to yield to hand tools, but several large specimens still dominate the property. The small ones cut down in spring have sprouted fully viable shoots of leaves, and if I didn't continually strip them they would come right back to be giant trees.

Another risk presented by Norway maples is its susceptibility to tar spot, a parasitic fungus that affects only maple trees. It causes no great harm, but can ruin the appearance of foliage (a major part of the New England tourist industry) and potentially weaken vulnerable trees. Norways are so common and so frequently infected, that they must be spreading this fungus to native trees; no alarm has been called, to my knowledge, but we shall see what the next few years brings us.

Dawn redwood at Arnold Arboretum. Jamaica Plain neighborhood in background.

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Photos by urbpan. Location: Harvard Street, Brookline.

Urban species #297: Norway maple Acer platanoides

The first people to plant Norway maple trees in North American cities must have found the project very satisfying. They grow quickly, and grow very straight, and have pleasing symmetrical crowns of shade-producing foliage. They handily endure the various hardships of urban life, and can be planted in the smallest square of soil in a sidewalk. Unfortunately, they have become invasive pests that threaten the forests surrounding the city. Many mixed hardwood forests in southern New England are becoming dominated by Norway maples, which grow much more closely to one another than native trees. They compete for soil area and sunlight, displacing forest herbs and wildflowers.

They are one of the few species of tree in the city that will plant themselves. Often they are found along fences and other hard-to-mow areas, squeezing into whatever space is available. Cutting them down often only encourages them to resprout (as is also the case with another troublesome city tree, Ailanthus altissima. I have found, managing some areas of a wildlife sanctuary, that repeated cutting eventually stresses the tree to death, whereupon it often sprouts turkey tail mushrooms. In past years I would feed the cut saplings to my captive deer, but this fall the Norway maples developed tar spot and anthracnose fungus, and their leaves were dry and unpalatable.

Norway maple looks similar to sugar maple, but can be told by its very smooth bark, very straight growth, and relatively larger leaves. The leaf stems of Norway maple ooze white latex sap when broken, which other maples do not. Norway maples stay green longer than native maples (unless they have succumbed to fungus) and in late fall turn yellow rather than red or orange. The wings most of our native maple samaras (fruits) are at an angle to one another, forming a U (see boxelder, for example), while Norway maple samara wings are flatter, forming a shallow V.


There are various cultivars of Norway maple, including strains with leaves that are purplish.

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Photos by cottonmanifesto. The maple foliage in a playground in Coolidge Corner, Brookline, seems to be bursting into flame.

Urban species #292: Sugar maple Acer saccharum

Sugar maples are the glory of the northeastern deciduous forest. With autumnal colors of vivid orange, blood red, and flames of yellow they glow amidst the ochre ashes and birches, and deep greens of the pines. Unfortunately, they do not survive the rigors of city life very well. Traffic compresses the soil around their roots, depriving them of water, soot clogs the pores of their leaves, and opportunistic wood decay fungi move in to claim weakened limbs. Most of the sugar maples in walking distance from my house are showing visible signs of decline. But their popularity shows no signs of flagging, and they continue to be chosen for city parks and streets, beginning to die almost as soon as they are dropped into their root holes. Sugar maples are sensitive to heat, as well, and cities are warmer year-round than the surrounding countryside. The man-made increase in temperature may drive the range of sugar maples north, out of the United States. The sugar maple's leaf on the flag of Canada will gain new meaning.

Ironically, there are more sugar maples in North America today than there were before European colonization. When Europeans learned that these beautiful trees could be induced to bleed sweet syrup in wintertime (actually, its sap must be evaporated to about one fortieth of its original volume to become syrup), they planted thousands in the forests of New England. The majority of sugar maples alive today are the offspring of trees planted by humans. In parts of the city where the sugar maple has enough soil for its roots, they provide shade in summer, a welcome burst of color in autumn, and austere beauty in winter.



A young sugar maple photographed in September, in Olmsted Park, beginning to change.

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Urban species #124: Silver maple Acer saccharinum

Silver maple is easily distinguished by its shaggy bark and its jagged and deeply indented leaves, whose whitish undersides give the tree its name. Silver maple was commonly chosen for urban plantings in the past, but is being used less often in recent years. On the one hand, the tree grows fast, matures to a great height, and is tolerant of urban conditions. On the other hand, its wood is brittle, and large limbs frequently break off in storms. Fear of lawsuits is a primary cause of this tree's decline in cities, according to The Urban Tree Book.

Silver maple is native to eastern North America, naturally occurring in areas with moist soils. Many animals are drawn to it for food and shelter, including squirrels, muskrats (who eat flowers and fruit that fall into the water), and birds. The fruit it produces is the familiar paired winged seeds unique to maples, and the silver maple's fruit is the largest of the genus.

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