Lincoln Boyhood Historic Resource Study

SOILS

Figure 4: 1935 Map Showing Percent of Sheet Erosion and Gullying by County (Sieber and Munson, 1994: 86) (click on image for an enlargement in a new window)

In the northern two-thirds of Indiana, soils are generally deep, silty, light-brown loams that are the result of glaciation. The unglaciated southern portion of Indiana has thinner, less fertile soil that consists of heavy clays, brown silt loams, or yellowish silty to sandy deposits. Their fertility was greatly depleted by pioneer farming practices that relied on a succession of corn crops without any crop rotation. Over the course of the nineteenth century, deforestation further contributed to problems with erosion and also led to increased instances of flooding and drought. During the 1930s, 100,000 acres in southern Indiana were assessed to be in serious stages of erosion (Figure 4). [7]

Soils in Spencer County are formed in the Ohio River floodplain and terraces, from sands derived from Pleistocene glacial outwash and related lacustrine deposits, from fine-grained windblown (loess) deposits, and from weathered sandstone and shale bedrock. The Silvan-Alford-Hosmer Association consists of silts and loess derived from windblown deposits on the eastern edge of the Wabash River Valley. These soils are found on gently rolling hills and ridges, and are generally well-drained. The Zanesville-Gilpin-Montevallo Association soils form in dissected sandstone and shale uplands in the northern half of Spencer County. These soils are moderately to poorly drained. The rugged character of this area of the county historically has not lent itself to profitable agricultural pursuits. [8]

The alluvial terrace soils along the Ohio River, primarily of the Wheeling series, are developed in silty and sandy alluvium. The well-drained Wheeling soils provide a rich basis for agricultural endeavors, an asset important to Paleoindian cultures, successive Indian tribes, and Euroamerican settlers. In comparison, related alluvial terrace soils such as Sciotoville soils are moderately well drained, Weinbach soils are somewhat poorly drained, and the Giant soils are poorly drained. The Bloomfield-Princeton Association formed in the sand dune belt along the eastern edge of the Wabash Valley. The Bloomfield and Chelsea soils are well drained fine sandy loams that also were conducive to crop cultivation, while the Ayrshire and Lyles soils are somewhat poorly drained loamy fine sands. [9]

CLIMATE

Pollen studies conducted in areas adjacent to southern Indiana indicate several climatic shifts occurred in Indiana during the Holocene Period. As the glacial ice sheets retreated across North America, spruce-dominated boreal forests occupied areas adjacent to the ice margins, including northern Indiana. Open subarctic grasslands were also present, probably in a complex mosaic on the landscape defined by local conditions. [10] Gradual warming occurred after 10,000 B.C. and spruce forests were replaced by northern oak and pines. [11]

A dryer, warmer climatic interval occurred from 5000 to 2000 BC. This resulted in a significant retreat of grasslands from northern Indiana, Illinois, Iowa, and Minnesota. [12] The effects of this warming are unknown for the oak and pine forests of southcentral Indiana but, presumably, there was some shift of localized prairie areas. Subsequent to 2000 BC, a climate much like the present prevailed, with occasional cooler and wetter episodes, and a modern deciduous forest.

As the southernmost portion of Indiana, Spencer County presently has a continental climate with cold winters and warm, humid summers. The average temperature is 37 degrees F. in winter, and 78 degrees F. in summer. During the summer, however, temperatures above 90 degrees F. are not unusual. The total annual precipitation is around 45 inches, of which 23 inches fall from April through September. Average seasonal snowfall is 10 inches. Brief droughts are not uncommon during summer, and can negatively affect agricultural yields. The prevailing wind is from the south/southwest. Tornadoes and severe thunderstorms occur occasionally in spring and summer. As such, severe climactic conditions presently are an exception, rather than the norm for Spencer County. The relatively warm temperatures, combined with the extensive bottomlands and adequate rainfall, contributed to the establishment of varied and extensive flora and fauna in the county. [13]

FLORA AND FAUNA

The Federal government's General Land Office initially surveyed Indiana between about 1799 and 1834, providing some documentation of the climax forests. [14] Bearing trees were recorded during the survey, providing information on the vegetation as it existed prior to Euroamerican settlement. Upwards of seven-eighths of the state's land area was forested during this period, with walnut, ash, poplar, elm, hickory, maple, and oak constituting the predominant species.

A wide variety of animal resources were available to the aboriginal and early Euroamerican inhabitants of Spencer County. In the Indiana of 1816, it is estimated that as many as 66 species of mammals existed, including bison, elk, black bear, mountain lion, gray and red wolf, porcupine, eastern spotted skunk, wolverine, river otter, and lynx, as well as current inhabitants, such as white-tail deer, red and gray fox, eastern cottontail rabbit, striped skunk, opossum, beaver, raccoon, and groundhog. [15] Federal surveys also recorded over 300 edible plants in Indiana, including nuts, fruits, berries, roots, and tubers, that would have provided a significant source of food for prehistoric inhabitants. In southern Indiana, the marshes and swamps created by the Ohio River and its tributaries provided a habitat for aquatic birds, while the waterways themselves were sources of turtles, freshwater fish, and mussels. [16] Archaeological investigations undertaken in Spencer County in the early to mid-twentieth century discovered several Archaic-period shell middens that attested to the reliance of some prehistoric peoples on rivers as a source of food. [17]

The ready availability of a variety of food sources and the relatively temperate climate combined to make southwestern Indiana an area of intensive occupation during the prehistoric period. As previously noted, deforestation throughout Indiana, and particularly in southern Indiana, had a profound effect on the natural environment by promoting soil erosion and altering drainage patterns. With approximately 100,000 acres of land in southern Indiana experiencing severe erosion by the 1930s, remedial reforestation programs were initiated to counter this environmental degradation. [18]