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// SPECIES PROFILE · TREE · NATIVE · FOUNDATIONAL

Bur Oak

Quercus macrocarpa

The cornerstone tree of the prairie–forest ecotone — a massive, extremely long-lived white oak with corky-winged twigs, deeply lobed leaves, and the largest acorns of any North American oak, cradled in fringed bur-tipped cups that give the species its name. Bur oak is the classic open-grown savanna tree of the central US and southern Plains: a single trunk that branches low and wide, with thick fire-resistant bark that shrugs off the prairie burns most other oaks cannot survive. In NE Oklahoma it anchors the bottomlands and prairie groves of Tulsa, Pawhuska, Bartlesville, and the Verdigris–Caney river corridors, where individual trees standing today predate Oklahoma statehood by a century or more.

// QUICK FACTS
Family
Fagaceae (beech family)
Group
White oak (section Quercus)
Native range
SE Manitoba → Texas; common in OK Cross Timbers, prairie groves & bottomlands
USDA hardiness
Zones 3–8 (Tulsa = 7a/7b)
Mature size
60–80 ft × 60–80 ft typical · to 100+ ft on best alluvial sites
Lifespan
200–400 yrs typical · documented to 400+ in OK
Acorn
Largest of any NA oak — up to 2 in long; cup half-covered, fringed
Mast
Heavy crop every 2–5 yrs; first acorns at age 30–35
Sun
Full sun (shade-intolerant after the seedling stage)
Soil
Tolerates everything — alkaline limestone, dense clay, sand, seasonal flooding
Water
Deeply taprooted; extremely drought-tolerant once established
Wildlife
Hosts >500 lepidoptera spp.; mast for turkey, deer, squirrel, wood duck
Ecological role
Savanna keystone · fire-adapted oak · mast tree
Bur Oak (Quercus macrocarpa) — open-grown savanna form with broad spreading crown
Quercus macrocarpa — open-grown savanna form, broad spreading crown over a wide-spaced bole. Photo via Wikipedia / Wikimedia Commons.

Identification

[ field key — bark · corky twigs · lobed leaves · fringed acorn ]

Habit & bark

Open-grown bur oaks are broad-crowned and almost as wide as tall, with a short, massive bole and heavy horizontal limbs — the classic "savanna tree" silhouette. Forest-grown trees are taller and narrower. Bark is thick, deeply furrowed, grey-brown to dark grey, breaking into rugged plates — one of the thickest barks of any North American hardwood and the source of the species' exceptional fire tolerance. Old trunks may exceed 4 ft in diameter.

Twigs — the corky giveaway

The most reliable single field mark: young twigs and small branches develop conspicuous corky wings or ridges, especially on vigorously growing trees and in the lower crown. No other common Oklahoma oak develops corky-winged twigs — if you see them on a deeply lobed-leaved white oak, you have Q. macrocarpa. Buds are small, chestnut-brown, blunt-tipped, with light pubescence at the tip.

Leaves & acorns

Leaves are large (4–10 in long), obovate, deeply lobed with a single deep central pair of sinuses that nearly reach the midrib, dividing the leaf into a wide upper "fan" and a narrower lower portion — a uniquely "fiddle-shaped" outline. Dark green above, paler and slightly fuzzy below; yellow or yellow-brown fall color.

The acorn is the second giveaway: up to 2 in long (the largest of any North American oak), oval, and seated in a deep cup covered with a fringe of soft mossy bristles around the rim — the source of both the common name "bur oak" and the alternate "mossycup oak." Ripens in a single season (white-oak group).

Confusables

Often confused with white oak (Quercus alba, eastern Ozarks) — white oak's leaves are smaller with shallower, evenly spaced lobes and the acorn cup is shallow and warty without a fringe. Confused with post oak (Q. stellata, Cross Timbers) — post oak has the cross-shaped, leathery leaf and a small acorn in a shallow cup. Bur oak's fiddle-shaped leaf, fringed bur-cup acorn, and corky twigs together distinguish it from every other Oklahoma oak. It hybridizes with white oak (×Q. bebbiana) and rarely with Gambel oak in overlap zones.

Habitat & Range in NE Oklahoma

Quercus macrocarpa has the largest north–south range of any American oak, from southern Manitoba and the Red River of the North to the Texas Hill Country. It reaches its climatic optimum in the tallgrass-prairie / oak-savanna ecotone of the central US, and NE Oklahoma sits squarely in that band. Locally you find it as the dominant overstory tree of bottomland prairie groves on alluvial soils along the Arkansas, Verdigris, Caney, and Bird Creek watersheds; on upland Cross Timbers savanna in mixed company with post oak, blackjack oak and black hickory; and on the limestone breaks of Osage and northern Tulsa Counties at the western edge of the Ozark uplift. It is largely absent from the sandstone ridges that favor post oak monoculture and from the wettest swamp interiors that favor overcup oak and water oak.

Bur oak is the most fire-tolerant of the eastern oaks. Its corky-thick bark insulates the cambium from low-intensity surface fires that top-kill virtually every other tree species, including its close relatives white oak and post oak. This is the trait that allowed bur oak to anchor the historical oak savanna — the fire-maintained mosaic of widely spaced large trees over tallgrass prairie that once dominated the region from north Texas to Wisconsin. With fire suppression since the early 20th century, bur oak savanna has converted to closed-canopy woodland (with suppressed bur oak regeneration and increasing maple, elm, and hackberry) almost everywhere it has not been actively burned. Restoration burns at the Tallgrass Prairie Preserve (Osage County), Oxley Nature Center, and Tulsa-region county parks aim to recover this structure.

On disturbed urban sites bur oak is one of the toughest large native trees available: it tolerates compacted construction-site clay, alkaline parking-lot runoff, mowing damage, and the periodic Oklahoma droughts of 2011–2014 and beyond. The deep taproot makes transplanting harder than for most landscape trees but is exactly why mature bur oaks survive when shallower species die.

Ecology & Wildlife Value

[ acorn mast · lepidoptera · cavity nesting · oak wilt ]

Mast & mammals

Bur oak acorns are one of the most important wildlife foods of the region. Wild turkey, white-tailed deer, fox squirrel, gray squirrel, raccoon, and wood duck all feed heavily on the large sweet white-oak-group nuts, which lack the bitter tannins of red-oak acorns and so are eaten in the same fall they ripen rather than cached long term. Mast cycles run on a 2–5 year heavy/light pattern; in bumper years a single mature open-grown tree can drop several hundred pounds of acorns.

Lepidoptera & insect food web

Like all native oaks, bur oak supports an extraordinary insect food web — oaks rank #1 among North American genera for documented lepidoptera host associations, with more than 500 butterfly and moth species using oaks as larval hosts in the eastern US. Doug Tallamy's research at the University of Delaware has made this oak-as-food-web-keystone the central argument for planting oaks in residential landscapes. Galls produced by oak gall wasps (Cynipidae) are conspicuous on bur-oak twigs and leaves and are almost entirely cosmetic.

Cavities & structure

The heavy lateral limbs and long lifespan of bur oak make it a premier cavity tree for screech owls, fox squirrels, raccoons, pileated woodpeckers, and (historically) Carolina parakeets. Open-grown savanna bur oaks with broad horizontal limbs are also disproportionately important as raptor perches and red-tailed hawk nest trees across the prairie–forest ecotone.

Mycorrhizae & soils

Bur oak forms ectomycorrhizal associations with hundreds of fungal partners, including many of the choicest edible fungi (Boletus, Cantharellus, Russula). The deep-rooted oak/grass system of an intact savanna is one of the most effective belowground carbon sinks in the central US, building the deep mollisol soils that originally made the region the world's most productive farmland.

Oak wilt — never prune in spring/summer: Bur oak is susceptible to Bretziella fagacearum (oak wilt), a fatal fungal vascular disease spread by sap-feeding nitidulid beetles attracted to fresh wounds. Oak wilt is established in the eastern half of OK and across the Ozarks. Do all pruning between Nov 1 and Feb 15 while the beetle vectors are inactive; never prune, transplant or wound oaks April–July. If a wound is unavoidable in the growing season, paint it immediately with a tree-wound dressing (the only context in which wound paint is recommended for oaks). Watch for symptoms: rapid leaf bronzing/wilting from the crown down, midsummer leaf drop, mature trees dead within 1–2 seasons. Report suspected cases to OSU Extension or the Oklahoma Forestry Services.
Plant for centuries: A bur oak planted today as a one-gallon whip will outlive every fence, building, and human on the property by a wide margin. Choose its site with that timeline in mind — clear of foundations, septic systems, and overhead utilities. The mature canopy will be 60–80 ft across.

Horticulture & Care

[ planting · siting · cultivars · pruning · pests ]

When to plant intentionally

Bur oak is the right choice when you want a permanent, large-scale, very low-input shade tree for a Tulsa-region property — the kind of planting that defines the next century of a place. Use it as a specimen lawn tree, the canopy of a recovering savanna or silvopasture, the upwind anchor of a windbreak, or as the long-life backbone of a residential pollinator and wildlife planting. Avoid small urban courtyards, shallow soils over bedrock with no run-on, and sites within striking distance of building foundations.

Planting & establishment

Pruning

Prune only between Nov 1 and Feb 15 to avoid oak-wilt vectors (see warning above). Young bur oaks benefit from light structural pruning to establish a single dominant leader and a balanced scaffold of widely spaced lateral limbs — do not over-prune, and never remove more than 25% of the live canopy in one year. Mature open-grown trees rarely need any pruning beyond removing dead wood.

Pests & diseases

Notable cultivars & selections

Bur oak is rarely cultivar-bred — the species is so variable and so often grown from local seed that named selections are uncommon and largely confined to the upper Midwest. The most reliable strategy in NE Oklahoma is to grow from locally collected acorns from a healthy parent tree on a comparable site — you get the regional genetic adaptation built in. Notable named selections include:

Cultivar / selection Origin / habit Distinguishing feature Notes for Tulsa
'Cobblestone' Earl Cully selection · uniform upright Strong central leader, more upright crown than typical bur oak Reasonable urban street-tree form; available from larger nurseries.
'Boomer' / 'Streetspire' Modern narrow-form selections Narrower crown for tighter spacing Useful in residential lots that can't accommodate a 70-ft spread.
Q. macrocarpa var. oliviformis Northern variety · smaller acorns Smaller leaves, smaller acorns, often less corky twigs Range edge; the typical southern variety is what's normally seen here.
×Quercus bebbiana (bur × white) Natural hybrid Intermediate leaf shape, intermediate acorn cup Encountered occasionally where bur oak and white oak overlap in the eastern Ozarks.
'Heritage' (× Q. robur) Bur × English oak hybrid Faster growth, narrower upright crown, mildew-resistant A nursery-grown urban shade tree; accept that it is not the pure native.
Local seed-source seedlings Acorns from regional parent trees Full genetic diversity, locally adapted The recommended choice for permanent NE Oklahoma plantings.

Cultural & Material Uses

Bur oak's combination of long life, exceptional wood quality, and edible acorns has made it one of the most useful trees of the central US to both Indigenous and settler cultures.

Sources & Further Reading

  • USDA NRCS PLANTS Database — Quercus macrocarpa: plants.usda.gov/plant-profile/QUMA2
  • USDA Forest Service Silvics of North America, Vol. 2 (Hardwoods) — Johnson, P.S. (1990), Quercus macrocarpa: srs.fs.usda.gov/pubs/misc/ag_654 — quercus/macrocarpa
  • USDA Forest Service Fire Effects Information System (FEIS) — Quercus macrocarpa: fs.usda.gov/database/feis/plants/tree/quemac
  • Oklahoma State University Extension — Oak Wilt: Identification and Management (EPP-7615) and the OSU Forestry & Natural Resources series on prairie–woodland restoration.
  • Oklahoma Forestry Services — oak wilt, bur oak blight, and storm-damage pruning recommendations for Oklahoma landowners.
  • Tallamy, D.W. (2007), Bringing Nature Home, Timber Press — on the keystone role of Quercus in the lepidoptera-driven food web of eastern North American gardens.
  • The Nature Conservancy / Tallgrass Prairie Preserve — bur oak savanna restoration program, Osage County, OK.
  • Lady Bird Johnson Wildflower Center — Native Plant Database, Quercus macrocarpa: wildflower.org — QUMA2
  • Missouri Botanical Garden Plant Finder — Quercus macrocarpa cultivar profiles.
  • Wikipedia — Quercus macrocarpa: en.wikipedia.org/wiki/Quercus_macrocarpa (CC BY-SA 4.0; portions of the description, range, and ecology summarize Wikipedia content).
  • Harlow, B. & Marshall, S.L. (Eds.), The Council Oak — history of the Lochapoka Muscogee Council Tree, Tulsa, OK.
  • Anderson, R.C. & Brown, L.E. (1986), "Stability and instability in plant communities following fire", on oak savanna fire ecology.

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Companion Planting

[ guild · polyculture · cross-layer pairings ]

In a Cross Timbers oak-hickory savanna, bur oak pairs naturally with: chickasaw plum (Prunus angustifolia), cardinal flower (Lobelia cardinalis), eastern gamagrass (Tripsacum dactyloides), shumard oak (Quercus shumardii), fragrant sumac (Rhus aromatica), and joe-pye weed (Eutrochium purpureum).

bur oak works best as a canopy or sub-canopy partner above the herbaceous and shrub layers.