Composition of an Upland, Streamside Forest in Piatt County, Illinois

Abstract

Oaks and hickories comprised 48% of the 224 trees per acre and 83% of the average stand basal area of 102 ft2 per acre in a 34-acre portion of the Robert Allerton Park, located on rolling uplands along the Sangamon River. Such sites were among the first to be invaded by woody species following glaciation. The well-developed GrayBrown Podzolic soils of the area reflect a longer period of forest occupancy than in the Groves which were characteristic of the Illinois Prairie Region. White oak (Quercus alba L.) and black oak (Q. velutina Lam.) were the leading dominants, followed in order of importance by red elm (Ulmus rubra Muhl.), pignut hickory (Carya glabra (Mill.) Sweet.), red oak (Quercus rubra L.), American elm (Ulmus americana L.), mockernut hickory (Carya tomentosa Nutt.), sugar maple (Acer saccharum Marsh.), white ash (Fraxinus americana L.), and shagbark hickory (Carya ovata (Mill.) K. Koch). INTRODUCTION East-central Illinois is located in the Grand Prairie division (Vestal, 1931) and the Prairie Peninsula section of the Oak-Hickory Forest region described by Braun (1950). The upland forests of eastcentral Illinois are considered to be of two general types: those occurring along the major streams and rivers, and those isolated from the main bodies of timber in Groves. Recent papers (Boggess and Bailey, 1964; Boggess, 1964; Boggess and Geis, 1966) have considered in detail the composition of the Grove forests. River systems were believed to have been the major migratory pathways of woody species into the Illinois prairie following glaciation (Gleason, 1923). Upland sites bordering these migration routes have therefore been occupied by forest vegetation for a longer period of time than the Groves. The greater degree of soil development on such sites in part substantiates a longer period of forest occupancy. This paper, fourth in a series describing the woody vegetation of natural areas owned by the University of Illinois, concerns the composition of an upland, streamside forest in Piatt Co., Illinois. DESCRIPTION OF THE AREA The 1,500-acre Robert Allerton Park is located along the Sangamon River 4 mi SW of Monticello in Piatt Co., Illinois, and has been owned by the University since 1946. About 50l% of the park is accessible to the public, while the remainder is maintained as a plant and animal reserve. The protected portion includes 437 acres of upland timber, predominantly oak-hickory in composition. In 1963 a natural area of 34 acres, located in the SE'4, Sec. 29, T18N, R5E, 3 PM (Long 88039'W; Lat 39059'N), was permanently established. The forest within this natural area is essentially in virgin condition. 89 This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:19:23 UTC All use subject to http://about.jstor.org/terms 90 THE AMERICAN MIDLAND NATURALIST 78(1) The experimental areia lies on the Cerro Gordo moraine overlooking the river to the northwest. The topography is that of a rolling upland, decreasing in elevation to the south. At the southern end of the area, the surface levels into a bottom formed by the Willow Branch, a tributary of the Sangamon River. Total relief within the area is about 40 ft (12 mi). SOILS The soils within the experimental area are developed in 1 to 5 ft of loess overlaying glacial till of Wisconsin age. A soil survey conducted by the Soil Conservation Service, and recent investigations by Bailey et al. (1964) and Soerianegara (1965) indicate that the major portion of the soils are well-developed Gray-Brown Podzolic soils. Loess depths range from a minimum of less than 15 inches in Miami silt loam, through Xenia and Russell silt loams with 15 to, 36 inches, to a maximum of 36 to 60 inches in Birkbeck and Manlove silt loams. Internal soil drainage reaches, a maximum in the well-drained profiles of Miami, Russell, and Manlove silt loams. Birkbeck and Xenia silt loams are moderately well drained. These soils are characterized by very dark brown (1OYR 2/2) to dark gray (tOYR 3.5/1) silt loam Al horizons, dark brown (tOYR 4/3) to dark yellowish brown (tOYR 4/4) A2 horizons, and welldeveloped silty clay loam B horizons. A detailed profile description of Russell silt loam, developed in 38 inches of loess over loam till, has been given by Bailey et al. (1964). Some of the important characteristics o'f this profile are given in Table 1. METHODS OF STUDY In 1963 the 34-acre (13.75 hectare) natural area was permanently divided into 50-meter square sample blocks (0.61776 acre). Partial blocks were also established to include as much of the uniform mateTABLE 1.-Selected properties of Russell Silt Loam (GrayBrown Podzolic, Typic Normudalf)