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12 Soils are integral to any functioning ecosystem, providing the nutrients for plants and habitat for many vertebrate animals and insects, and multitudes of microorganisms. They require hundreds of years to develop and are good indicators of the climate, vegetation , and organisms involved in their formation. Therefore, knowledge of them provides suggestions for how best to use landscapes for productive agriculture or for the preservation and/or restoration of more natural conditions. Current soil characteristics indicate that most of Indiana was covered (in “presettlement ” times, shortly before 1800) by beech/maple and oak/hickory forests, with smaller areas of dry prairie, savanna, and wetlands in the northwestern portion of the state. Almost all of this book’s information on soils is presented in this chapter, rather than being distributed among the 8 habitat chapters, as is the case for wildlife. We will first discuss how soils are identified and classified, and describe the national and statelevel databases on soil distribution. We will then survey the soils of Indiana geographically from north to south, using the state’s 10 natural regions, which were defined with some consideration of soil types (Homoya et al. 1985). Soil identification and classification are conducted through the observation of soil horizons and distinctive soil layers in a pedon (the minimum sampling unit of soils, which is generally a 1 m2 soil pit). Soil horizons include the O horizon, or organic layer at the surface; the A horizon, a mixture of organic and mineral matter; the E (eluviation) horizon, a leaching zone; the B horizon, where elements accumulate and clays develop; and the C horizon, the deepest part where the parent rock is being broken down and incorporated into the soil. Characteristic soil layers are also used to identify soil types and are called epipedons if they are at the surface or diagnostic horizons if they are deeper underground . Soil types vary across the landscape with changes in slope, aspect, and moisture retention creating soil catenas. A catena is a change in soil type across a local area where the climate is constant, but changes in topography force changes in drainage and soil aeration. These in turn control the vegetation that will survive, producing distinctive changes across fine spatial scales, such as the transition from a cypress swamp to an oak/hickory stand with just a few feet of elevation change. The U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), and National Cooperative Soil Survey (NCSS) have compiled soil information for all of the United States. The state soil geographic database (STATSGO) was designed for state- and regional-level analysis and management. It is compiled from soil survey data, and land remote-sensing satellite (LANDSAT) images are used to extrapolate this information to the landscape scale (National Cartography and Geospatial Center 1995). The coverage of this database for Indiana is complete, but multiple soil series are aggregated into unique map units. The resultant maps cover the whole state but do not have the finest resolution in soil characteristics, although distinct soil regions are maintained. The mapping scale of STATSGO is 1:250,000 and the minimum mapping unit area is 6.25 km2. Guo et al. (2003) found that the STATSGO database had good spatial coverage across the United States and adequately represented the soil series present throughout, although it excluded rare soil series covering an area smaller than the minimum mapping unit. STATSGO reports all soil units on the map unit level, which aggregates similar soil series into soil associations that describe the general soil characteristics for each region (Map 2.1). Resource descriptions and management uses can be based on these map units. The U.S. Soil Taxonomy (Soil Survey Staff 1999) classification system divides all soils into a nested hierarchy , allowing aggregation at varying spatial scales (Table S-1). Similar soil characteristics are used to aggregate the soil types so that higher-order classes represent similar characteristics of all of the subsequent categories. This is similar to the Linnaean classification system for all living organisms. The soil order is the broadest layer of this classification, with 12 orders representing all of the soils in the world. These are broken down into sub-orders, great soil groups, subgroups , associations, series, and families. Most management and field classification is based on the soil series level, which is analogous to the genus in organism classification. The soil series name, coupled with the textural class, is the soil type, which is analogous to the scientific...

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