Trees of Dickinson County: Oak

Iowa's state tree is the oak, although the State Legislature never designated a specific species of oak.

The state has 12 species of native oak trees:

• Pin oak
• Red oak
• Shingle oak
• Northern pin oak
• Black oak
• Blackjack oak
• White oak
• Bur oak
• Swamp white oak
• Chinkapin
• Post oak
• Dwarf chinkapin oak

Of those, two or three are native to northwest Iowa. The most common tree would be the bur oak, distributed statewide, and the red oak is also native to northwest counties. The northern pin oak is considered native to northern Iowa according to some sources and specifically to northeast Iowa according to other sources.

We'll discuss all three species that are most likely native to Dickinson County:

Bur oak (Quercus macrocarpa)

Bur oak trees are distributed throughout Iowa and are common in both oak savanna habitats as well as deciduous forests. They can live as long as 300 years.

(Learn about native oak savanna habitats here)

Size

Bur oaks are stately trees, growing slowly. They live hundreds of years but are an average of 50-100 feet tall.

Habitat

Oak savannas are a common home of the bur oak, where the canopy is made of large oaks and the savanna floor is a healthy mix of native prairie grasses and flowers.

Bur oaks grow well in prairie settings with dry-mesic to wet-mesic soil, and they also grow well in denser forest settings, although in forests they tend to grow taller and straighter amidst competition.

In overgrown forests, bur oaks can get choked out by other, more shade tolerant species, because bur oaks love full sun.

Leaves

Bur oak leaves are quite easy to decipher, with their deep, curved lobes. Fine hairs make the underside look lighter in color.

Seeds

Like other oaks, bur oaks produce acorns. They have a hairy cup that extends far around the seed.

Wildlife love bur oak acorns and have been recorded to enjoy them more than red oaks because of lower tannins, making them more mild-tasting.

Red oak (Quercus borealis)

The bur oak is a slow-growing species, but red oaks tend to grow faster with enough sunlight.

Size

Red oaks grow up to 80 feet tall but are quite stout, with a trunk of up to 3 feet.

Habitat

These oaks are also distributed statewide and also love full sun, although they can tolerate part shade.

Their native tendency was to grow on moist, loamy soils on north-facing slopes, although they are used in urban landscaping and can deal with dry and acidic soils.

Leaves

Red oak leaves may be what you think of when you think of an oak leaf. It has 7-11 lobes that are much sharper than the lobes of the bur oak leaf, and the leaves have bristled tips.

Seeds

Red oak trees also produce acorns that are eaten by a variety of wildlife.

Northern pin oak (Quercus ellipsoidalis)

Also called the Hill's oak, this one has a discrepancy about where it's actually natively located in Iowa. It could or couldn't be native to northwest Iowa specifically, or it could just be a northeastern Iowa species.

Size

The northern pin oak is a little smaller tree, growing up to 75 feet with a diameter of 2 feet.

Habitat

The northern pin oak isn't all that popular for landscaping since its lowest branches tend to grow down, but it is a great species for oak savanna restorations as it withstands controlled burns very well.

This species of oak also likes full sun but will tolerate partial shade.

Leaves

Pin oak leaves are similar to red oak leaves with sharper tips on the lobes. However, the sinuses are deeper, reaching almost three-quarters of the way to the midvein.

Seeds

This oak also produces acorns in a finely hairy cup that covers only one-third to one-half of the acorn. These seeds are eaten by a variety of wildlife.