Forest and Shade Trees of Iowa

Part 5: Good Places to See Trees in Iowa

404 i o wa’s f o r e s t s Forest communities, then, change over both time and space, which complicates our efforts to describe and name them. The following paragraphs describe five basic types. There are variations on each of these, and where the environment changes gradually with distance, two adjacent communities may blend. The oak-hickory community occurs on dry uplands and on south- and west-facing slopes. The dominant trees are usually one or more of the following : white oak, bur oak, black oak, Hill’s oak, chinkapin oak, and shagbark hickory. Other common trees include white ash, black cherry, quaking and bigtooth aspens, red oak, American basswood, and, in southeastern Iowa, shingle oak and mockernut hickory. Ironwood, chokecherry, and various shrubs grow in the shade of the taller trees. The oak-maple-basswood community occurs in moist but well-drained uplands, especially on north- and east-facing slopes and terraces in the larger stream valleys. Red oak, sugar or black maple, and American basswood usually dominate, with maple decreasing and the others increasing in relative abunUpland woods are dominated by oaks and hickories in most parts of Iowa. i o wa’s f o r e s t s 405 dance westward. Maple drops out of the community in western Iowa and red oak in the extreme northwest. Other large trees often found in this community are white oak, shagbark and bitternut hickories, black walnut, white and black ashes, and formerly American elm. Small trees that are common locally include ironwood, American hornbeam, serviceberries, and Ohio buckeye. The bottomland hardwoods community occurs on primary floodplains and low-lying terraces along rivers and streams. The dominant species are usually one or more of the following: silver maple, green ash, hackberry, black walnut, cottonwood, and, in some places in eastern Iowa, river birch. American elm was once a conspicuous member of this community, but large trees of this species are now scarce because of Dutch elm disease. Other tall trees that are characteristic of the bottomland hardwoods are sycamore, honey locust, Kentucky coffee tree, black and peachleaf willows, bitternut and shellbark hickories , pin oak, shingle oak, swamp white oak, butternut, and black ash. The riparian community forms a narrow belt along lakeshores, stream banks, mudflats, and sandbars. Dominant trees include cottonwood, silver maple, boxelder, and various willows. Several other species from the adjacent bottomland hardwoods community may occur to a greater or lesser extent. The northern conifer-hardwoods community occurs on steep, moist, usually north-facing slopes in northeastern Iowa. This community is centered in the northern Great Lakes states, and many of its most characteristic species drop out as they approach Iowa. The trees and shrubs that do range into Iowa are often found as minor constituents of other communities instead of a community by themselves. They include white pine, balsam fir, Canada yew, paper and yellow birches, mountain maple, quaking and bigtooth aspens, and black ash. Stewardship of Iowa’s Forests Forests grow and persist without human intervention, so it is sometimes assumed that the best thing we can do is to leave them alone. To be good stewards , however, we need to monitor and actively manage our woodlands, even if our main goal is preserving biodiversity. Why is this so? Since Iowa was settled, people have extensively altered the landscape. Some natural forces no longer operate, and species occur here that never existed before. As a consequence, our forests are changing in ways that are not always desirable. Northern trees such as these white pines and balsam firs grow on steep, north-facing slopes in northeastern Iowa. i o wa’s f o r e s t s 407 One unfortunate change is the invasion of alien species. Common buckthorn , honeysuckles, and garlic mustard take over the woodland understory, crowding out native species and making it difficult for some trees to reproduce . The emerald ash borer, spreading west from Michigan, may eventually kill most ash trees in Iowa, while the gypsy moth is a serious threat to oaks and other trees. Grazing by livestock is also harmful to the forest. The soil becomes compacted and erodes, runoff increases, the canopy trees lose vigor and decline, the saplings needed to regenerate the forest are destroyed, and biodiversity decreases . Even deer, a native animal, can damage a forest if present in too great a number. Exclusion of fire is another change that has...