Like all habitat systems, upland forests and woodlands result from a variety of factors such as soil type, underlying rock types, aspect, hydrology (water flow patterns), and climate. A variety of plants and animals prefer or require upland forests and woodlands.
Healthy forests and woodlands lead to healthy soils and streams. They stabilize soils, slow runoff, and encourage water to seep into the ground. Fish and other aquatic species require healthy forests and woodlands to survive.
Wooded areas also offer us hiking and canoeing adventures, hunting and fishing, mushroom foraging, wildlife watching and nature photography, beautiful wildflowers, spectacular fall color, and a place to cultivate serenity.
Distinguishing Forests from Woodlands
We all know that wooded areas are places where trees predominate, but land managers are careful to distinguish between true forests and true woodlands. There are some big differences between the two.
Technically speaking, forests have a closed canopy permitting very little light to penetrate to the ground below. There are often several overlapping layers of trees, with a midstory of shade-tolerant shrubs and small trees and a ground flora comprising a sparse layer of soft-stemmed plants. Canopy trees tend to be relatively closely spaced, and their crowns rather narrow.
Woodlands have a more open canopy (30 to 100 percent cover), and their sparse woody midstory allows more sunlight to reach the ground. This light permits the growth of a dense ground cover constituting a variety of grasses, sedges, and wildflowers. Canopy trees in true woodlands are relatively widely spaced, with rather spreading crowns.
Fire plays a large role in maintaining true woodland habitats, which would otherwise eventually turn into forest. Many decades of fire suppression have diminished Missouri’s amount of true woodland habitat. Land managers today are working to restore Missouri’s woodlands, often with controlled burns targeting woody undergrowth.
There is a gradient between forests and woodlands, and between woodlands and savannas, which are even more open and grassy than woodlands.
Types of Upland Forests and Woodlands
Over the years, ecologists and land managers have devised several systems for describing our upland forests and woodlands, often using amount of soil moisture, underlying rock types, and/or dominant tree types as labels. Below, we divide them into broad categories by the amount of soil moisture.
Upland Wooded Habitats Vary by Soil Moisture
A convenient way to describe Missouri’s various types of upland forests and woodlands is by the amount of moisture the soil holds. This one characteristic of the land has a great influence on the plants and animals that live there.
Soil moisture is determined by precipitation, slope, drainage, and the amount of sand or organic materials in the soil. Three basic terms are used to describe the amount of moisture available in the soil: dry, mesic, and wet.
The meanings of “dry” and “wet” are obvious, though they do have technical definitions. “Mesic” (MEE-zik), a less familiar term, means that a “moderate” amount of moisture is available. Mesic soils are moderately well drained, though the water is removed somewhat slowly, so the ground is somewhat moist for a significant amount of time.
As you might expect, soil moisture often corresponds to elevation: hilltops, glades, and bluff tops tend to have our driest soils, while bottomlands and other low, flood-prone areas are wet. Mesic soils often lie in between.
Our upland forests and woodlands fall into three main categories: dry, dry-mesic, and mesic. (Our wet and wet-mesic forests are bottomland forests, treated on a separate Habitats Field Guide page.)
1. Dry Woodlands
In Missouri, dry woodlands typically occur on south- and west-facing slopes with shallow, rocky soils, and in upland areas generally: hilltops, glades, and bluff tops, often on rocky, sandy, or thin soils. Although we have some dry-mesic forests, Missouri has no true forests that are classified as dry.
In our dry woodlands, the dominant trees, having little moisture, are typically fairly short, 30 to 60 feet, and the understory is relatively open, with scattered shrubs. The groundcover (herbaceous) layer is dominated by sedges, grasses, and wildflowers.
Typical Plants in Dry Woodlands
The main canopy trees in dry woodlands include post oak, blackjack oak, chinquapin oak, black oak, white oak, bur oak, black hickory, white ash, shortleaf pine, sugar maple, and winged elm. In the Bootheel’s rare dry sand woodlands, southern red oak is a dominant canopy tree.
Understory plants, shrubs, and vines in dry woodlands include New Jersey tea, fragrant sumac, Carolina buckthorn, catbriar, dwarf hackberry, serviceberry, and lowbush blueberry. In the Bootheel, deciduous holly and American hazelnut are notable understory species.
Groundcover (herbaceous) plants in dry woodlands include little bluestem, Indian grass, sedges, tick clovers, yellow pimpernel, woodland brome, rock muhly, sideoats grama, bristly sunflower, poverty grass, dittany, asters and goldenrods, pussytoes, Indian physic, and yellow crownbeard. In the Bootheel’s dry sand woodlands, there are rough buttonweed, rushfoil, sweet goldenrod, variegated milkweed, wood rush, eastern prickly pear, tick trefoils, and prairie bush clover.
2. Dry-Mesic Forests and Woodlands
Dry-mesic sites have more moderate amounts of soil moisture, so the canopy trees grow taller — 60 to 90 feet — and straighter than in drier sites.
Dry-mesic forests and woodlands occur mainly on ridges and east-and west-facing slopes. Soils average 3 feet in depth and are mainly silt loams.
Dry-mesic forests have a moderately developed, shade-tolerant understory. Because the canopy and understory shade the floor of these forests, the ground flora’s heyday is in the spring; by midsummer it is patchy.
Dry-mesic woodlands typically share many of the same species as the nearby dry-mesic forests, but being woodlands, they have a more open canopy and a patchy to absent understory, permitting a well-developed, prominent groundcover.
Before European settlement, much of today’s Ozark forested landscapes were dry-mesic woodlands or savanna. Managed burns seek to restore these historic habitats.
Also, before widespread lumbering, shortleaf pine dominated vast tracts of the Ozarks; most of these pine forests and woodlands grew back as oak-hickory forest. Land managers have been working to restore our pine and oak-pine forests and woodlands.
Typical Plants in Dry-Mesic Forests and Woodlands
Dominant or canopy trees include white, black, and several other oaks; shagbark, mockernut, and pignut hickories; and shortleaf pine. Other characteristic trees include maples and ashes.
Understory trees, shrubs, and woody vines include flowering dogwood, American hazelnut, fragrant sumac, eastern hop hornbeam, lowbush blueberry, serviceberry, Virginia creeper, summer grape, and Carolina buckthorn.
Herbaceous or ground flora plants abound, though in true forests, most are dormant except in spring before the trees leaf out; in woodlands, grasses, sedges, and wildflowers are prominent all season long. Typical ground plants include sedges and grasses, tick trefoil, trillium, Christmas fern, black cohosh, spring beauty, toothwort, and false Solomon’s seal.
3. Mesic Forests and Woodlands
Our mesic forests and woodlands lie in areas between wetter lowlands and drier heights. Their soils are deep and loamy, and they typically occur on steep north- and east-facing slopes and ravines. The canopy is tall (often more than 90 feet).
As with dry-mesic forests, mesic forests typically have a well-developed understory of small trees and shrubs that restricts the ground layer to a profusion of spring wildflowers, before the forest floor is shaded.
Also like their dry-mesic counterparts, mesic woodlands have a more open canopy and a sparse understory, allowing a lush ground flora throughout the growing season.
Typical Plants in Mesic Forests and Woodlands
Typical canopy trees in mesic forests and woodlands are northern red oak, white oak, sugar maple, basswood, black walnut, white ash, bitternut hickory, and, in southeastern Missouri, beech.
Understory plants include spicebush, maples, pawpaw, and grape vines.
The ground layer is lush in spring with many wildflowers, including bloodroot, Dutchman’s breeches, wild ginger, bellwort, hepatica, and trillium. There is also a variety of ferns, including broad beech fern, maidenhair fern, fragile fern, and narrow-leaved spleenwort.