Tuesday, October 5, 2004

Plant for the Day: Indian Blanket, Gaillardia pulchella

Indian blanket ranges across the grasslands of North America, and even extends into the Southeast on sandy soils along roadsides and on dunes. Although not as common in most prairie locales as the dominant grasses, it provides a burst of color where it occurs. Indian blanket is a member of the largest plant family in the world—the aster or composite family. Other common members of this family include dandelion, goldenrod, asters, and sunflowers. The name composite refers to the fact that the blossom, which looks like a singer flower, is actually a collection of many flowers—each ray, which looks like a petal, is a complete flower. Indian blanket is an annual plant, and flowers in early to mid summer.

As we moved into western Kansas, then into Nebraska, pockets of mixed grass prairie became more common. Like the short grass prairie to the west, the vegetation is dominated by members of the grass family—nonwoody plants with small, inconspicuous flowers. In this region, the little rainfall that does occur is concentrated in the summer, during the growing season. The dense root systems of the grasses are concentrated in the shallow zone of the soil that holds moisture briefly after summer storms, before it evaporates.

A gradient exists across the Plains from short grasses in the west to much taller grasses and other herbaceous plants in the east. The moister conditions of the eastern Plains are more favorable for plant growth, and net primary productivity—the rate at which plants accumulate biomass—increases accordingly. From west to east across Nebraska alone, annual rainfall increases from just over 10” to nearly 25”. The higher rainfall also favors plant species that require more moisture. In the mixed grass prairie of western Kansas and Nebraska, the grasses range from 2-4’ in height. The Dust Bowl of the 1930s affected this area more severely than the tall grass prairie to the east, because rainfall in the western part of the Plains is typically more unpredictable than farther east. Settlers who tried to farm this area experienced many years when crops failed, thanks to the prolonged drought. Many abandoned their farms, pulled up stakes, and sought more productive land in California. John Steinbeck’s classic, The Grapes of Wrath, tells a typical story of Plains farmers affected by prolonged drought during the Dust Bowl.

The vegetation gradient across the prairies is linked to a soil gradient as well. Here in western Kansas and Nebraska, the soils are medium to dark brown on the surface. Farther east they are almost black, thanks to the greater plant productivity, hence the greater abundance of organic matter incorporated into the soil when the plants die. West to east variation in precipitation also causes variation in the movement of calcium in the soil. Farther east, higher rainfall causes calcium to be translocated to a greater depth in the soil, forming a hardpan in the subsoil. As rainfall diminishes, to the west, the layer of calcium accumulation becomes shallower and shallower. In some areas in western Kansas and Nebraska, it is only several inches below the surface. It forms a hard layer that resembles light rock, called "caliche"; and it influences moisture availability for plants.

This is also the section of the Plains where center-pivot irrigation is most common. One-fifth of the irrigated land in the U.S. is in the High Plains, a region extending from eastern Colorado through Nebraska, and southward to Texas. Cultivation in this area is supported with “fossil” underground water supplies—aquifers that contain water that accumulated in permeable rock layers near the end of the Ice Age when climatic conditions in the area were wetter. There is not adequate rainfall in the modern era in many places within this region to restock water once it is withdrawn from the aquifer. As a consequence, the depth to the water table has increased dramatically in the last century; in some parts of this region, the height of the water table is 70’ lower than it was in the 1940s before widespread use of irrigation for cultivation.

Just south of McCook, Nebraska, we encountered the Republican River floodplain, which we rode along for many miles to the east. The development of irrigation for farming in the High Plains has contributed to a reduction in the discharge (the amount of water moving through the channel per unit time) of the Republican River in the last 50 years. With even less water available for increasing demands on water resources, conflicts over water use in the drainage basin have become more intense. In an area where rainfall is low and the vegetation is sparse, the Republican River provides important habitat for many species. The riparian corridor includes woodlands of cottonwoods, willow, and box elders; cattail marshes; grassland; and shrublands on the drier sites.

Before Europeans settled North America, bison were common through the midsection of the continent. They ranged east all the way to the Appalachians; in fact, bison inhabiting the Southeast during presettlement times visited a salt lick just east of Athens, GA. The arrival of European settlers to the Plains brought several changes affecting the native inhabitants of this area. Interestingly, the native peoples living in the Plains at this time relied more heavily on farming than on hunting bison. When Europeans introduced horses in the mid-1500s, however, their way of life became much more dependent on bison. Horses enabled them to follow large herds moving across the Plains, making it easier to hunt them. But other changes quickly followed for both bison and native peoples of this area. European settlers also introduced cattle, which competed with bison for forage, and tended to crop the plants to a shorter height than bison do in their grazing. Fences restricted the bison's broad-ranging movements. Construction of the trans-continental railroad in the mid-1800s provided a way to transport slaughtered bison to markets in the east. Although we don’t know the exact numbers of bison inhabiting the Plains when Europeans arrived, historians estimate that the number of bison in the prairies fell from 30-70 million to a mere 1000 by the late 1800s! With conservation efforts, populations have now expanded to 65,000; most of the remaining bison live in national parks and other preserves.

West of Hastings, Kansas, we passed a marker commemorating the Oregon Trail. The Oregon Trail stretches from Independence, Missouri to Oregon City, Oregon—a 2170-mile long trip that took 5 months to complete by wagon train in the 1800s. The Louisiana Purchase in 1803 extended the western frontier of America to the western Rocky Mountains, but the region known as “Oregon Country” (Oregon, Washington and part of Idaho) still belonged to the British, which made many Americans eager to settle the region and claim it for the U.S. Lewis and Clark's expedition in 1803 was intended to open Oregon Country to settlement, but the route was not feasible for families traveling by wagon. It took 40 years for the first successful wagon train to reach Oregon along a new route, but that opened the gates to westward migration, and by the late 1800s, about 300,000 had pushed westward along the Oregon Trail. The British soon realized that with so many Americans settled in the region, the Oregon Country was, in practice, no longer theirs; and they ceded Oregon Country to the United States in 1861. At many sites along the Oregon Trail, one can still see remnants of the great westward migration, from broken, abandoned wagon wheels to deeply rutted soil, still compacted over a century later from the weight of thousands of wagons.

To reach Iowa, we had to cross the Missouri River, which forms the border between Nebraska and Iowa. In this part of its drainage basin, the Missouri River shows some of the classical traits of a stream that meanders across its broad floodplain. As streams leave their headwaters, where they originate, their gradients eventually become flatter, and their energy is directed more towards lateral migration of the stream channel across the floodplain, rather than channel downcutting. The floodplain is a broad, relatively flat corridor along the channel, with a veneer of water-transported sediment deposited during floods, when water overflows its channel. As water moves down the curving stream channel, it cuts into the outside of curves, where the water moves fastest, and deposits sediment on the inside of curves. This causes the channel to meander, or to migrate gradually across the floodplain in an increasingly sinuous manner. Eventually these ever-larger loops will bend back on themselves and be short-circuited, as water takes the most direct route downstream and cuts through the large loops. These cut-off meanders are called “oxbow lakes”, and several of them are evident along the Missouri River right upstream from Omaha and Council Bluffs.

Carter Lake, an oxbow lake just north of our route across the floodplain, formed unusually quickly during the winter of 1877. When an ice mass dammed the Missouri River channel at a horseshoe-shaped meander known as the Saratoga Bend, the stream began to form a new, shorter channel that would bypass the meander and its ice dam. High stream discharge with the spring thaw enabled the stream to finish the cut-off very quickly; and by mid-summer, the meander was completely cut off, forming Carter Lake. The channel’s new route saved steamboats traversing this stretch of river a half day’s travel, thanks to the much shorter distance. It also stranded the city of Carter Lake, Iowa, west of the Missouri River, surrounded by the state of Nebraska on three sides! Such political problems frequently arise where rivers form state boundaries, because their channels shift positions over time.