Bur Oak

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Bur Oak (Quercus macrocarpa) in the white family of Oaks
Maybe when the Bur Oak is in full leaf, it is just a very large tree, but in the winter, when the structure and the almost knurled twisting of the branches of the tree are much more evident, the Bur Oak is a show stopper. It has character. It has a statement – “I’ve been around the block a few times and I have some wisdom for the rest of you, if you would just listen”, or something like that.

Bur Oak tolerates poor soils, wide soil pH ranges, and--because of its extensive root system-- serious drought conditions. However, it will not tolerate repeated flooding. Known to live for 200 to 400 years, bur Oak is also called "prairie Oak", "blue Oak," scrub Oak", or "mossycup Oak". It is found in the wild in deep rich bottomlands where it attains a large size and on dry ridges and western slopes where it is small and gnarled. It is called "bur" Oak because its acorns have bristly husks, or caps.

Bur Oak is native to the upper Midwest but it grows in many different sites. The most western of the eastern Oaks, its native range extends all the way to the foothills of the Rockies where it is typically reduced to a shrub. It is found widely over the eastern United States as far west as Montana and western Texas. Often it is the only tree on hillsides in the western part of Iowa. There you can find whole stands of nothing but bur Oak, while in the eastern part of the state and most of the rest of its range, it is found with a variety of other species including other Oaks, hickories, white ash, white elm, basswood and aspen. In these settings the bur Oak is referred to as a "wolf" tree because as other adjoining trees die, it broadens its branches to fill up the newly voided space.

Bur Oak is regarded as a prairie tree species because it was often associated with the prairie-forest border in the days before prairies where turned into farmland. It’s kind of like the bur Oak was the first tree to jump into that all grass ecosystem and found a way to adapt. Because of its relatively thick, fire-resistant bark and natural resistance to drought, it historically competed successfully with prairie grasses. It survived the heat of the flash grassfires that swept over large areas during dry periods.

Bur Oaks are large trees that need room to spread. They will grow to 50 to 80 feet tall, developing an impressive leaf canopy diameter of 40 to 100 feet. The National Champion Bur Oak measures 96 feet by 103 feet located in Paris, Kentucky. Bur Oaks typically have wide spreading, coarse-textured branches. They usually grow straight up eight or nine feet before sprouting their first branch. Their bark is dark gray, thick and so deeply furrowed that it breaks into distinct ridges. On small branches and twigs it is brownish, roughened and corky. Some references indicate that bur Oak, like other Oaks, are slow growing trees. This description is not universally accepted by the experts. Some research done by the folks at the Arnold Arboretum in Boston showed that their Oaks grew more quickly than did their hickories, elms, and maples when all were planted at the same time.

Ten to twelve inches long and half as wide, bur Oak leaves are large with rounded lobes. They grow alternately along the stems. They form deep sinuses on their lower half, while their upper half has very shallow lobes. The top portion of the leaf is more wavy than lobed. To some, the leaf shape suggests a bass fiddle. Dark shiny green above, leaves are lighter green to gray below. Fall color is yellow-green to brown, not terribly exciting.

Bur Oak flowers occur as spikes of many florets.correct? They may appear on old or new wood, often just as the leaves unfold.

Largest of all the native Oak acorns, the bur Oak acorn is ¾ to 1½ inches long. It is almost round with a bur or moss-like, fringed cup covering half or more of the acorn--sort of an acorn with a bad hair day. It usually takes 7 to 10 years before a bur Oak produces its first acorns. Unlike many other Oaks, the acorns mature in a single growing season and sprout soon after they fall in the autumn. They can send down a taproot four feet deep just in the first year. In nature a mature bur Oak might produce 5000 acorns in a single year, this heavy production occurring about every 3 to 5 years. But after the birds get their share, the squirrels and other acorn lovers hoard what they need, and the insects such as weevils finish up the feast, maybe only 25 to 50 might actually sprout and fewer than half of those will make it to maturity. In the meantime, a whole bunch of critters have had dinner.

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