Wisconsin Nature

How Trees Strengthen Our Forests

Trees are beautiful to observe in all seasons, often with lush greenery in the spring and summer, and glorious, colorful foliage in the fall. They also provide necessary ecological services to the habitats in which they grow. Numerous types of wildlife thrive because of trees, mak­ing the forest a lively place to visit.

Schlitz Audubon is comprised of land cleared for farming during European settlement and is home to sev­eral forest habitats. Forests here include remnant old growth, classified as sugar maple-beech forests, which also include well-known species such as oak, basswood, and cherry. The Center also has mid-successional for­ests, containing fast-growing trees like paper birch and Aspens. Our hardwood swamp habitat hosts trees that favor wetlands.

Three tree species living in these habitats that are of­ten overlooked are the shagbark hickory, ironwood, and hackberry. Each of these plays an important part in the proper functioning of the ecosystem. Good conserva­tion practice is to plant diversity in a forest, which helps when invasives like the Emerald Ash Borer attack a par­ticular species. All three of these species are native to the region and will grow well with our soils and hydrol­ogy. They are distinctive in their anatomy, offering a refreshing sight to visitors who encounter them. Drew Shuster, Director of Conservation, likes to think of each tree species as a color on a palette used to make a painting.

Shagbark Hickory

Hike out near the pavil­ion and see a well dis­tinguished species, the shagbark hickory, Carya ovata. This species is part of the hickory family and is identified almost ex­clusively by its impressive bark. The bark offers an aesthetically pleasing ap­pearance, with asymmet­rically descending, curving strips that cover the surface of the trunk, making it look shaggy.

It is a large, deciduous canopy tree that can grow as tall as 100 feet witha spread of up to 60 feet. The foliage has five, and occasionally seven, pinnately compound leaflets with the largest one at the end of its stalk. The yel­lowish-green leaves turn yellow to orange in the fall. The tree is nourished through taproots, likes dry or moderate soils, and can live in either full sun or partially shaded areas.

Uses of Shagbark Hickory

These hickory trees have many human uses, and were a food source for Native Americans, who harvested the nuts. The wood is hard, which histor­ically made it excellent for making wagon wheels, and currently is used for tool handles. The shagbark hickory is plentiful at the Center – our conservation team plants it every spring, mostly in the Woodland Loop. Its range includes the eastern US.

Shagbark hickory is very important as a habitat for wild­life. It is a home to about 100 insect species, which feed on its bark, foliage, and plant juices. As a host plant for the caterpillars of two species of butterfly and many kinds of moths, including three for whom it is their sole food source, this species is indispensable. This in­sect-friendly tree creates a food source for birds, who feast on the many insect species that live on it. Birds at­tracted to this tree include warblers, tanagers, flycatch­ers, gnatcatchers, and vireos. Other animals find shelter in the shagbark hickory, including bats and small mam­mals, who nest in it.

The hickory nut that grows on the shagbark hickory rip­ens in the fall and is a nutrient rich food, though it takes the tree 40 years to grow them. They are eaten by Blue Jays and Red-bellied Woodpeckers, as well as birds found north of the Center, including bobwhites and pheasants. Mammals that eat their nuts are squirrels, raccoons, rab­bits, and foxes.


The ironwood tree, also known as American hop horn­beam, Ostrya virginiana, is a member of the birch family. See one located close to the Visitor Center near the bike rack, as well as some near the Pavilion and near the North Ravine. One of the tree’s primary features is its fruit, which is a nutlet that looks charm­ingly like hops. The bark is smooth and gray as a young tree but becomes plated with strips as it matures. This reveals a difference from the tree’s look-a-like cousin, the American hornbeam, also called musclewood, whose bark remains smooth as it ages. This species prefers sunlight to dappled shade and acidic, well-drained soils, though it is very adaptable and can tolerate dry soils.

Ironwood’s serrated leaves are like those of the paper birch. The ironwood grows to about 75 feet tall, making it a sub-can­opy tree. While not the tall­est tree, it is important to the structure of the for­est, as some birds prefer to nest lower than near the top of the canopy. In the fall the light green leaves turn yellow, or­ange, and red.

Uses of the Ironwood Tree

The ironwood tree has many human applications. Historically, people used the hard wood to make sleigh runners and tools, and still make fenceposts and tool handles from it. Native Americans used the inner wood to treat numerous ailments. Though it can be slow-growing, ironwood makes a great street tree. The conservation team planted ironwood as part of the Storm Water Wetland & Ravine Restoration Proj­ect, as it fit the habitat where restoration was taking place.

This tree species is widespread, found almost everywhere in the US east of the Mississippi and in some midwestern states east of the Rockies, growing in the same habitat as the shagbark hickory. It is a slow-growing tree that begins to mature in about 50 years and provides food and cover for squirrels and birds such as woodpeckers and nuthatches, who eat the nut­lets. In the north, the tree provides food and shelter for pheas­ants, bobwhite, and Ruffed Grouse. At the Center, Wild Tur­keys eat the tree’s buds in winter. The gnarled branches and jagged bark provide shelter for invertebrates, and it is occa­sionally a host tree for the caterpillars of red-spotted purple and Eastern tiger swallowtail butterflies, as well as several moth species. The abundance of insects makes the ironwood a great food source for insect-eating songbirds.


Look for hackberry trees, Celtis occidentalis, along the Terrace Loop and on the bluff near the Milner Deck. They are large deciduous canopy trees relat­ed to the elm tree, growing to about 100 feet tall or more, but size can vary depending on the region. Its range includes parts of southern Canada, and the eastern US east of the Mississippi and west to Nebraska. Visitors will distinguish this tree by its light brown to silvery gray bark, which has a corky, wart-like texture. It likes wet soils, but is adaptable, and lives in open areas in early successional forests south of the Wiscon­sin Tension Zone. The yellow-green asymmetrical, ovate leaves are arranged in an alternate pattern on the slender branch and turn yellow in the fall.

Uses of the Hackberry

This species makes an especially good street tree, too. Native Americans sought hackberry as a food source, subsisting on the berries. The tree’s hardwood is used to make furniture and floor­ing. Our conservation team is planting this tree in the Hardwood Swamp as part of its restoration.

The hackberry is insect-friendly and is host to the tawny emper­or and hackberry emperor butterflies. It attracts numerous but­terflies and insects, making it a great tree for spring birds, such as migrat­ing warblers and Gold­en-crowned Kinglets. The tree’s valuable berries are rich in calories, and are high in fats, carbohydrates, and proteins. They ripen on the tree in September providing fall and winter food for birds, espe­cially fall migrants. Cedar Wax­wing, American Robins, Northern Flicker, and Yellow-bellied Sapsuckers all feast on the berries. Resident species such as Wild Turkeys and Northern Cardinals also turn to hackberries in winter, when food is scarce. The hackberry provides cover for white-tailed deer and small mammals.

Visitors to the Center can view these species all year, with shag­bark hickory and ironwood occurring near the main building. If you enjoy a good fall hike, look for the hackberry near the Terrace Loop. These trees are appealing for their fall colors and are beautiful all year round.

Written with contributions from Drew Shuster and Jacob Kempinski.