Magazine article American Forests

The Sagacious Bur Oak

Magazine article American Forests

The Sagacious Bur Oak

Article excerpt

Maybe when the bur oak is in full leaf, you can call it just a very large tree. In the winter though--when its structure and the almost knurled twisting of its branches are more evident--the bur oak is a show-stopper. This tree has character. It seems to say, "I've been around the block a few times and I have some wisdom for the rest of you, if you would just listen."

The rugged bur oak (Quercus macrocarpa) is forgiving as well. It tolerates poor soils; wide soil pH ranges; and, with its extensive root system, serious drought conditions. It cannot, however, tolerate repeated flooding.

Able to live 200 to 400 years and named for its bristly husks, or caps, bur oak goes by the names prairie oak, blue oak, scrub oak, or mossycup oak. It resides in the wild in deep rich bottomlands, where it attains a large size, and on dry ridges and western slopes, where it grows small and gnarled.

The tree grows across the eastern United States as far west as Montana and western Texas, with its native range extending to the foothills of the Rockies, where it is typically reduced to a shrub.

Bur oak has a history of adapting to take advantage of its space. Its relatively thick, fire-resistant bark and natural resistance to drought allowed it to compete successfully with prairie grasses. In pioneer days, many an unfortunate traveler in need of a new wagon tongue, wheel hub, or spoke sought out the bur oak, groves of which were also viewed favorably as home sites for early settlers in Iowa and other prairie regions. Today bur oak is the state tree of both Illinois and Iowa.

DESCRIPTION

When you plant a bur oak, leave it plenty of room. These shady beauties can grow 50 to 80 feet tall with an impressive canopy spread of 40 to 100 feet. The thick bark is dark gray and deeply furrowed, breaking into distinct ridges.

The leaves are 10 to 12 inches long and half that wide, large with rounded lobes. They grow alternately along the stems to some, the shape suggests a bass fiddle. The leaves are dark shiny-green above and lighter green to gray below. Fall color is yellow-green to brown.

Bur oak flowers may appear on old or new wood, often just as the leaves unfold. Buds of up to 1/4 inch appear in fall, covered with fine, pale gray hairs.

One of the tree's most spectacular features must be its acorns, which at 3/4 to 1 1/2 inches long are the largest of all native oak acorns. Almost round, they have a bur or mosslike fringed cap that covers at least half the nut--sort of an acorn with a bad hair day. It usually takes 7 to 10 years for a bur oak to produce its first acorns but the nuts mature in a single growing season and sprout soon after they drop in autumn. They can send a taproot 4 feet deep in the first year.

A mature bur oak might produce 5,000 acorns in a year with this heavy production every three to five years. After birds get their share, squirrels and other acorn lovers hoard what they need, and insects such as weevils finish up the feast, only 25 to 50 might actually sprout, and fewer than half make it to maturity.

The wood is hard, heavy, and strong with an interior color that varies from off-white to light brown. Because it is flexible and waterproof, the wood is appropriate for barrels and boat-building, and its high density makes it an excellent firewood.

USE IN THE LANDSCAPE

A bur oak can be magnificent on new home sites with plenty of growing room. Unfortunately, homeowners often unwittingly harm the bur oaks by removing moisture-retaining natural leaf mulch and replacing it with thirsty lawn grass, causing permanent dehydration.

Remember that virtually all the bur oak's feeding roots lie within the top 4 to 6 inches of soil--exactly the same area occupied by turfgrass roots. A tree living in turf can't compete for food and may live only half its life expectancy. Instead, surround the trunk with non-competitive groundcovers. …

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