Tallgrass prairie is a fire-dependent ecosystem characterized by tall grasses (up to 10 feet tall), and deep, rich soils. Tallgrass prairie once covered parts of 14 states in the Midwest, including about 80% of Iowa. Today less than 0.1% of the original tallgrass prairie in Iowa remains.
Before the arrival of European settlers in the Midwest, Native Americans set fires in late summer and fall to provide habitat for animals such as bison, elk, and deer, reduce danger of wildfire, ease travel, and increase visibility and safety. Fire and prairie plants are mutually dependent on each other—without fire, the grasses and other fire-adapted prairie plants would be shaded out by trees. Fire stimulates growth of prairie plants by removing dead plant material, allowing sunlight to penetrate to the black earth that follows the burn and reach the new shoots emerging from the ground. Fire promotes the germination of many prairie plant seeds by removing the seed coat. Frequent fires prevent trees from becoming established. Without the flammable grasses of the prairie, the fire would not be able to move across the landscape.
Grazing by large mammals such as bison and elk also helped maintain the plant life in the prairie. The grazing process helps stimulate the growth of many prairie plants, particularly grasses. By selectively grazing on grasses, bison and elk promoted the growth of other plants that were exposed to more sunlight as the grasses were kept short.
Tallgrass prairie plants are deep-rooted, reaching six feet or more below the surface. These roots created the soil that is now valued as crop land. The deep roots hold the soil, preventing erosion where prairie plants have become established.
At Neal Smith NWR, more than 200 species of prairie plants have been seeded into former farm fields. After planting, invasive plants may need to be mowed or sprayed with herbicides to prevent their spread. Prairie plantings are burned to invigorate the growth of fire-adapted species and to control those species that aren’t adapted to fire, and therefore don’t belong in the prairie system. These species include non-native species as well as natives that were historically found in areas that burned less frequently, like river bottoms.
The Refuge also includes about 77 acres of prairie remnants. These areas represent native plant populations that have survived since before the area was settled and plowed. The plants that have survived in these remnants are particularly adapted to the soil types and climate conditions at Neal Smith NWR, so their genetic material is valuable and important to preserve. Seed is collected from these remnants so the locally adapted genes can be passed on and dispersed throughout the Refuge. The history of land use on the remnants prior to the establishment of the Refuge includes fire suppression, intensive grazing, and in some cases plowing or other soil disturbance. Restoring these remnants is a long-term process, and involves removing trees and shrubs, using herbicides to control woody and invasive species, and reintroducing fire to the system. In some cases additional prairie species are re-introduced.
In the absence of fire, many oak savannas have become overgrown with dense stands of fire-intolerant trees. Since fire has not been used in most savannas since settlement times, species such as honey locust, hackberry, and black cherry have grown up. These trees cannot withstand fire when they are young, so did not occur in savannas that were repeatedly burned. Although these species are native, they historically grew in areas such as river bottoms that did not burn easily. Seedlings of these trees are shade-tolerant, meaning they can grow under the canopy of other trees. Oaks seedlings require more light to grow than forest species, so they are not usually found in oak savannas that have become overgrown with dense trees.
Restoring oak savannas often requires removing fire-intolerant trees. This allows light to penetrate to the ground so that herbaceous vegetation including grasses and sedges can grow. Grasses and sedges burn easily, so their growth makes prescribed burning easier to carry out. Oak leaves are also specifically suited to burning, as they curl when they dry, leaving air pockets that facilitate fire. Thinning the trees also allows more air circulation, which makes burning easier. Fire in turn promotes the growth of herbaceous vegetation. Although most oak seedlings will not survive repeated fires, a small number will be able to reach maturity, completing the cycle of life in the oak trees. Oak trees are long-lived, surviving 200 years or more. A healthy savanna will have trees of varying ages so that younger trees will be ready to fill in when old trees die. Even after death, oak trees provide structure that provides habitat for wildlife species including many cavity-nesting birds.
Sedge meadows or wet prairies occur in sunny areas where the soil holds water for extended periods. Like prairies, frequent fire is required to maintain the vegetation, consisting of a wide diversity of sedges, forbs, and other herbaceous plants. Some of the species typical of sedge meadows include blue flag iris (Iris versicolor), prairie milkweed (Asclepias sullivantii), swamp milkweed (Asclepias incarnata), bottle gentian (Gentiana andrewsii), prairie cordgrass (Spartina pectinata), tussock sedge (Carex stricta), Michigan lily (Lilium michiganense), New England aster (Aster novae-angliae), great blue lobelia (Lobelia siphilitica), rattlesnake master (Eryngium yuccifolium), giant St. John’s wort (Hypericum ascyron), and mad dog skullcap (Scutellaria lateriflora). Conditions supporting sedge meadow can be found along streams such as Walnut Creek, as well as drainages, and even on hillsides where seeps emerge. They can consist of small patches or long strips, so the species of plants and animals found in them overlap with the adjacent prairies. Historically, prairie streams were shallow and meandering, bordered by sedge meadows. Some species of sedges form tussocks, creating mounds of higher elevation amidst the moist ground. Sedge meadows are usually dry on the surface for parts of the year, and the soils may dry out during dry spells. At Neal Smith NWR, the lower areas where sedge meadows occurred have been altered by soil erosion depositing silt in low-lying areas. Drain tiles put into farm fields have altered the hydrology so the water runs off more quickly and is not retained in the soil like it once was. Some sedge meadows remnants are found in wet places on the Refuge, primarily seeps that were plowed around because they were so wet. In areas where prairie has been planted into farm fields, prescribed fire is beginning to restore the sedge meadows found within them. Invasive species like reed canarygrass grow in wet places throughout the Refuge and compete with native sedges and other plants. Reed canarygrass can be controlled with methods such as burning, mowing, and spraying, but it is a constant battle. New reed canarygrass seed is brought in when the creek overflows onto the floodplain, which happens during flash flood events. The Refuge is working on reconstructing a sedge meadow in an area that was formerly nothing but reed canarygrass. This area, near the Savanna Trail, contains many of the sedge meadow species listed above.