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Winter 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

March 6, 2012

Red Maple: Chancing an early spring

Warming temperatures have sprung open the flower buds of red maple, one of the first trees to bloom as winter fades. Each bud unfolds about half a dozen tiny, dark-red blossoms, each shaped like a wee tulip. Although most red maples bear either exclusively male or female flowers, some trees produce both, the proportion of which can be highly variable from year to year.

Red maples yield a sap as sweet and flavorful as that of a sugar maple. However, the window for making red maple syrup has passed: Once the tree "breaks bud," the sap's chemistry changes, imparting an unpleasant taste to the syrup.

By the time leaves begin to unfurl later this month, fertilized female flowers will have elongated into long, drooping stalks bearing small pink samaras, winged seeds that will ripen, drop and whirl to the ground in April.

Those seeds can quickly germinate in a wide range of soils and conditions, helping red maple become one of the most abundant trees in eastern North America. The tree is capable of adapting its root structure to grow in anything from swamps to rocky hillsides. It is, however, susceptible to numerous diseases and is highly vulnerable to damage from fire and sapsuckers, woodpeckers that trigger damage when they tap sap.

One leaf disease might be thwarted by climate change. A Duke University study revealed that infections of a certain fungus were less common and less severe in red maples exposed to higher-than-normal concentrations of atmospheric carbon dioxide. Those conditions made leaf chemistry less palatable to the fungus and caused leaf pores to reduce the size of their openings, making it harder for the fungus to enter the leaves.

But global warming may not be a total boon for the tree. An unusually warm February — such as this year's — can encourage fruits to develop too rapidly and fall victim to the freezing temperatures that might still be part of the March mix.

A longer growing season could also imperil red maples in the fall if the trees are still green when the first killing frost hits. That would prevent the maples from retrieving critical nutrients stored in the leaves.

SOURCES: Ohio State University Extension, Oak Ridge National Laboratory, Arnoldia, Global Change Biology, Duke University, U.S. Forest Service

Red Maple flowers, male and female; Acer rubrum