Home » Plants » Quercus macrocarpa

Bur Oak (Quercus macrocarpa)

Also known as mossycup oak, mossycup white oak.

Page contents

Summary

A rugged oak native to North America, with a wide distribution, ranging farther west and north than most oaks that also occur in the east.

Range - Expand

This map is based on the FHWA's ERA. This data overestimates native ranges, especially around the edges, as this post explains. We have not yet reviewed this map.

USDA Plants Profile for Quercus macrocarpa

Illinois Wildflowers Page for Quercus macrocarpa

Fire Effects Information System (FEIS) Article for Quercus macrocarpa

Description

Highly variable in size and other characteristics. Grows to 160ft (50m) in height in moist woodlands, but as a smaller shrub on dry, rocky cliffs.

Mature trees have thick, deeply-grooved bark and a small number of large, thick branches. Especially when growing on open sites, the tree forms large horizontal branches lower on the tree, and ascending branches higher up. In forests, often grows with a more elm-like vase-shape, with large branches curving and ascending. On the harshest sites, the branches take on a gnarled shape.

The leaf shape is highly variable. Most leaves exposed to full sunlight are deeply lobed, often with deep cuts close to the leaf base and shallow cuts close to the leaf tip, leading to a spade-shape at the front of the leaf. Leaves in shade are broad, full, and lack deep lobes, looking similar to those of the closely-related swamp white oak. Leaves grow up to 12 inches (30 cm) long, and have a tough texture, typically a shiny dark green above and covered in silvery hairs beneath.

The acorn cup is very large and encloses more of the acorn than is typical for white oaks, covering at least 1/3rd, often more, and occasionally enclosing the entire acorn. In an opposite trend to many species, acorns tend to be smaller at the southern end of its range.

The root system involves both a deep taproot and wide, spreading roots.

Similar Plants

White Oak (Quercus alba)
View - Compare

Habitat

This species has a complex relationship to habitat that is hard to describe concisely, and often poorly understood. It is found in a range of different habitats, but more common in the midwest than the east. Found in savannahs and prairies as well as bottomland forests. Adaptable to a wide range of conditions and soil types, but often found on harsher sites where other large trees cannot thrive.

Among the most cold-tolerant of North American oaks, and ranges the farthest north; can grow in areas with a growing season as short as 100 days. Very tolerant of drought, and slightly tolerant of temporary flooding, but intolerant of prolonged flooding during the growing season.

Seems largely indifferent to soil types, tolerant of well-drained as well as poorly-drained soils.

Relationship to fire is complex: mature trees are highly resistant to fire, and on many sites, especially where it is the dominant tree, it persists indefinitely only due to frequent burning, and can be displaced by other trees if fire is suppressed. However, fire suppression can allow it to colonize prairies as one of the first large tree species. On other sites, it can be found in areas that do not burn naturally, as a more minor forest component.

Life Cycle

Unlike most white oaks which germinate immediately and become established before winter, the acorns of Bur Oak require cold stratification in the northern part of its range, and germinate in spring. However, in the rest of its range, the seeds germinates soon after falling an before winter. Acorns can die if they dry out too much, and do not persist in the seed bank.

The acorns germinate well in exposed mineral soil, with some studies showing that leaf litter actually decreases germination rates, although others showing they increase seedling establishment and survival.

Upon germination, the tree quickly establishes a taproot, but shoots and leaves do not typically emerge until after the winter, or after establishment of an extensive root system for seeds germinating in the spring.

Survival of seedlings, moisture preference, and shade tolerance is governed by many factors and can be wildly variable in different habitats and different parts of its range. In many places, its establishment is aided by drought, as it is highly drought-tolerant and the dry condition reduce competition from other vegetation. In other regions however, it more easily becomes established in mesic conditions. When invading drier prairies, it is most likely to get established on wetter, more shaded sites. Young trees can be damaged by browsing by deer and livestock.

Growth rate can be wildly variable on different sites, depending on light levels, moisture, and soil fertility.

Established trees are long-lived, often living 300-400 years or even longer. Seed production typically starts around 35 years of age, peaks between 75 and 150 years, but continues as the tree ages. Large seed crops are typically produced every other year. A late frost following a prolonged warm period can hinder seed production by damaging flower buds.

Unlike most oaks, bur oak occasionally produces multi-seeded acorns, usually with 2 seeds but occasionally as many as five. Although a majority of acorns only hold one seed, as many as one-in-five can have two or more seeds, although this characteristic varies by individual tree.

The large, heavy acorns are mostly animal-dispersed, mostly by small mammals and occasionally by blue jays.

Mature trees are highly resistant to fire, due to heavily insulated bark. Younger trees are more vulnerable to being top-killed, although they are more likely to resprout after a fire. Trees begin developing fire resistance when they reach about 3 feet in height. Bur oak leaf litter is slow to decompose and highly flammable; the leaf shape tends to curl and dry out, sitting loosely on the ground, even after a snowy winter. The leaves themselves form a fuel for fire, as well as a mechanism for spreading fire. Woody debris falling from trees is also slow to decay and has a high heat content, also providing fuel for fire.

Uses

Planted as a large shade tree and landscaping plant; well-adapted to urban conditions and exposed sites.

The wood is desirable, and has similar properties to other white oaks. It is highly rot resistant, and easy to glue, stain, and finish

This species has also been used for remediation of coal mining sites, where it has sometimes been able to survive conditions with high soil acidity (as low as 4) and low phosphorus content.

The acorns are considered among the most palatable of oak species, and were historically consumed by Native Americans, and to a lesser degree by early European settlers.

Notes

One of the common names, "mossycup oak", references the moss-like appearance of the acorn cup.

Photo gallery