Introducing Long Point’s oak trees
The Long Point Basin has 8 species of oaks, distributed widely across many different ecosystems, from oak savannas (displayed in the rightmost photo) to swampy woodlands! These oaks are categorized into two major groups – red oaks (Quercus section Lobatae) and white oaks (Quercus section Quecus), with a few notable differences in the fruit structure and leaf morphology. For species in the white oak group, it takes one year for an acorn to fully mature, while red oak acorns require two years to mature. White oak acorns are sweet, and red oak acorns are bitter. All of Ontario’s species in the red oak group have pointed leaf lobes, whereas species of the white oak group have smooth leaf lobes. Black Oak (Quercus velutina), Northern Red Oak (Quercus rubra), and Northern Pin Oak (Quercus ellipsoidalis) are part of the red oak group, whereas White Oak (Quercus alba), Bur Oak (Quercus macrocarpa), Swamp White Oak (Quercus bicolor), Chinquapin Oak (Quercus muehlenbergii) and Dwarf Chinquapin Oak (Quercus prinoides) are in the white oak group.
Bur Oak description, ecology, and habitat
Bur Oak is a common species in riparian and lowland forests of the Long Point Basin. When it attains maturity, Bur Oak is a large tree, usually around 30 m or more in height. Bur Oak leaves are typically 15-25 cm long, obovate (wider torwards the tip), with 2 or 3 veyr large indentions torwards the base of the leaf. The leaf margins are rounded, with no bristles. In comparison to Chinquapin Oak, the teeth on Swamp White Oak are more blunt and larger. The leaves are deep green above, and pale green or silver on the underside. Autumn foliage of Bur Oak is usually yellow or brown. The mature bark is thick on Bur Oak, contributing the tree’s high fire resistance, with prominent ridges and deep furrows. The acorn is very large, usually 2.5 cm to 5 cm in length, with a distinctive pubescent (hairy) cup covering at least half of the acorn. Bur Oak acorns are readily distinguishable from those of other species.
Bur Oak occurs throughout most of the Great Lakes Region. It is most abundant in southwestern Ontario, especially the Lake Erie Lowland Region, where it is a regular component of lowland forest and riparian vegetation communities. Large populations also occur in Central Ontario southeast of the Canadian Shield. North of it’s main distribution, large numbers of Bur Oak occurs in the Ottawa River Valley. Smaller populations of Bur Oak occur along the St. Mary’s River (separating Lake Superior from Lake Huron), Bruce Peninsula and Manitoulin Island. On Manitoulin, Bur Oak is the main tree species of the Bur Oak savannas – globally rare vegetation community with a vast diversity of rare or threatened species. Across North America, Bur Oak is distributed from the Atlantic coast, through the Mississippi and Ohio River Basins (though it is absent from many areas south and east of the Appalachian Mountains). Bur Oak is also a key component of floodplain forests in the Great Plains, which extends forested ecosystems hundreds of kilometers westward into an otherwise treeless landscape. The westernmost natural populations reach Montana and Wyoming.
In the Long Point Basin, Bur Oak is a common component of floodplain and riparian forests. In riparian forests, it is most commonly found with Black Walnut (Juglans nigra), Hackberry (Celtis occidentalis), Green Ash (Fraxinus pennsylvanica), Blue Ash (Fraxinus quadrangulata), American Elm (Ulmus americana), Slippery Elm (Ulmus rubra), and Basswood (Tilia americana), where it reaches it’s maximum abundance. In forests dominated by shade-tolerant species, such as Black Maple (Acer nigrum), White Ash (Fraxinus americana), and Bitternut Hickory (Carya cordiformis), it is more often observed as a supercanopy species, since Bur Oak cannot regenerate in full shade. On wetter sites, it is sometimes found alongside Silver Maple (Acer saccharinum), and Cottonwood (Populus deltoides). In lowland forest, Burr Oak is often found with White Oak, Red Oak, Red Maple (Acer rubrum), Sassafras (Sassafras albidum), Basswood, and a variety of ashes, elms, and hickories. On the ground-layer, there is a wide variety of shade-tolerant wildflowers underneath the canopy of Bur Oak. Shrubs associating with Bur Oak include Pagoda Dogwood (Cornus alternifolia), Grey Dogwood (Cornus racemosa) Blue-beech (Carpinus caroliniana), Spicebush (Lindera benzoin), American Hazel (Corylus americana), and in riparian forests, American Bladdernut (Staphylea trifolia). On Manitoulin, it grows in mixed woodland alvar savannas with American Elm, Green Ash, White Ash, Basswood, and other hardwoods, with an understory of shrubs (i.e., Dogwoods, Crataegus Hawthorns, and Viburnums) and wildflowers.
Ecological importance of Bur Oak
Like other oak species, Bur Oak acorns are devoured by many wildlife species, especially squirrels (Sciuridae), mice (Muridae), White-tailed Deer (Odocoileus virginianus), Wild Turkeys (Meleagris gallopavo), Woodpeckers (Picidae), Blue Jays (Cyanocitta cristata), and Black Bears (Ursus americanus). Oaks also support highly biodiverse insect community, including 534 species of lepidopterans (butterflies and moths). Bur Oak is associated with the Imperial Moth (Eacles imperialis), Polyphemus Moth (Antheraea polyphemus), Cecropia Moth (Hyalophora cecropia), Buck Moth (Hemileuca maia), Orangestriped Oakworm (Anisota senatoria), as well as other Anisota species and moth species in the Prominent (Notodontidae) family. All of these moths utilize Bur Oak leaves as a larval (caterpillar) food source.
Bur Oak is indicator species in riparian forests, which are among the Long Point Basin’s most species-rich habitats. These floodplain ecosystems, which often occur on highly fertile soils, are a major centre of diversity for canopy trees, understory vegetation. Flora includes over 100 species of wildflowers, and 40 woody plant species! Birds and reptiles are also concentrated here due to the close integration of both terrestrial and aquatic (riverine) habitats – augmenting the total biodiversity of Bur Oak ecosystems.
Fun facts
- Bur Oaks produce the largest acorns of any native North American oak species – reaching 5 cm long!
- These trees are extremely hardy, withstanding temperatures below -40°C in the Manitoba and Saskatchewan. Bur Oaks are North America’s northernmost oak species.
- Bur Oak can reach 500 years old or more under ideal growing conditions – making this species a tree of extreme longevity!
- In the Midwestern United States, Bur Oak was a dominant tree in the savanna regions covering substantial swathes of Missouri, Illinois, Iowa, Wisconsin, and Minnesota. While much of this region has been long converted to mechanized agriculture, remnant savannas remain, particularly around the Driftless Area in Wisconsin. Smaller areas of Bur Oak savanna occur in Ontario, though they too have been impacted by habitat loss.
Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University.
Photos provided by Matthew Palarchio
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To view a directory of all species featured on our website, visit: https://longpointlandtrust.ca/featured-species
