The Bur Oak (Quercus macrocarpa) is one of the most massive and imposing oaks of the North American prairie-forest border, recognized by its huge acorns that are the largest of any North American oak — up to 5 cm in diameter including their heavily fringed, mossy cups. A tree of the open prairie and savanna, it is exceptionally drought-tolerant, fire-resistant, and long-lived, with specimens known to exceed 400 years.
• Produces the largest acorns of any North American oak — up to 5 cm in diameter with deeply fringed, bur-like cups
• The species epithet "macrocarpa" means "large-fruited," directly referencing the massive acorns
• One of the most drought-tolerant and cold-hardy oaks in North America
• Often called "bur oak" or "mossycup oak" for the heavily fringed, mossy appearance of its acorn cups
• A classic savanna tree of the Midwest, often found standing alone in open pastures and prairies
• The thick, corky bark of young branches provides remarkable fire resistance
• Ranges from New Brunswick and southern Quebec westward through southern Ontario, Manitoba, and Saskatchewan to southeastern Alberta, Montana, Wyoming, and the Dakotas
• Extends southward through the Midwest to Oklahoma, Texas (Edwards Plateau), Tennessee, and the Appalachian foothills
• Most abundant in the Midwest prairie-forest transition zone — Iowa, Illinois, Minnesota, Wisconsin, Nebraska, and the Dakotas
• Occurs at elevations from near sea level to approximately 600 meters
• First described by the German botanist Gotthilf Heinrich Ernst Muhlenberg in 1770
• A dominant tree of the tallgrass prairie-oak savanna that once covered vast areas of the Midwest
• The species occurs in a wide range of habitats, from bottomlands to dry uplands
• In the Great Plains, it is often the only tree species present, forming isolated "oak groves" on prairie hillsides
Size:
• Typically 18 to 25 meters tall, occasionally reaching 30 meters
• Trunk diameter: 0.6 to 1.5 meters, with old-grown specimens exceeding 2 meters
• Crown is very broad, rounded, and massive, often wider than tall in open-grown specimens
• Develops a massive, buttressed trunk base with age
Bark:
• Dark grayish-brown, deeply furrowed into broad, thick ridges
• Thick, corky bark on young branches and twigs — an unusual feature among oaks that provides fire resistance
• Corky wings often develop on young branchlets
Leaves:
• Obovate, 10 to 25 cm long and 8 to 15 cm wide — large and variable in shape
• Deeply lobed with a distinctive large, unlobed terminal lobe (the "cross" shape)
• The central constriction creates a fiddle-shaped or lyrate appearance
• Dark green above, pale and silvery beneath with dense, fine hairs
• Turn yellowish-brown to dull yellow in autumn
Acorns:
• Very large, 2.5 to 5 cm in diameter — the largest of any North American oak
• Cup is very deep, covering one-half to three-quarters of the acorn, with a prominently fringed, mossy margin
• The fringed cup scales give the acorn a "bur-like" appearance (the source of the common name)
• Mature in a single growing season (annual, characteristic of the white oak group)
• Among the sweetest acorns, relished by wildlife
Habitat:
• Occupies an extraordinarily wide range of habitats — from moist bottomlands and floodplains to dry, rocky uplands and limestone ridges
• A hallmark species of the oak savanna and prairie-forest border
• Exceptionally drought-tolerant, surviving on rainfall as low as 380 mm per year in the western Great Plains
• Thick, corky bark provides remarkable resistance to prairie fires
• Tolerates alkaline soils and heavy clay better than most oaks
• Often found as solitary trees in pastures, prairies, and fence rows
Ecosystem role:
• The massive, sweet acorns are among the most valuable wildlife foods — consumed by deer, wild turkeys, squirrels, raccoons, and blue jays
• Large acorns provide more food energy per nut than any other North American oak
• Oak savannas with bur oak are among the most endangered ecosystems in North America — less than 0.1% of the original Midwest oak savanna survives
• Solitary bur oaks in prairies serve as "nurse trees" for other woody species, facilitating forest expansion
• The deep taproot system makes bur oak extremely windfirm and drought-resistant
• Old-growth bur oaks provide critical nesting and den sites in prairie landscapes where trees are scarce
재미있는 사실
Bur oak produces the largest acorns of any oak in North America — and possibly the world — with individual nuts the size of golf balls. A mature bur oak can produce up to 6,000 acorns in a good year, each one containing enough calories to sustain a squirrel for an entire day. The tree's scientific name "macrocarpa" literally means "big fruit," and early settlers called it "mossycup oak" for the thickly fringed, mossy cups that enclose the acorn.
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