Property characterization3
Ecological Setting and Receptors353
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- Natural Plant Communities and Habitats3531
Ecological Setting and Receptors353The following sections describe the ecological setting of SVDA and potential ecological receptors. Table 3‑2 lists the state and Federal endangered and threatened plants and animals potentially occurring on or in the immediate vicinity of SVDA. Natural Plant Communities and Habitats3531This section summarizes the natural plant communities and habitats of northwestern Illinois that are found at SVDA. Table 3‑3 lists the plant species that have been identified at SVDA. SVDA lies within a major ecotone that extends in an eastward arc from Minnesota to Texas, where a transition occurs from the Eastern Deciduous Forest biome to the Prairie and Plains phytogeographic provinces (Gleason and Cronquist 1964). The ecotone projects eastward of the Mississippi River, encompassing almost a quarter of a million square miles, and then into Illinois, Indiana, Ohio, and Kentucky in what has been characterized as the “prairie peninsula” (Transeau 1935). Gradients in the local soil and hydrological conditions provide the basis for boundary definitions between vegetational/habitat groupings. The excessively well‑drained sands in the higher central region of the installation support very different communities than the poorly drained silty clays along the eastern boundary, or the frequently flooded to temporarily saturated mixed alluvial silt and sand of the bottomlands (Dames & Moore 1994a). Table 3‑2. State and Federal Listing of Endangered and Threatened Plants and Animals Known to Occur or Potentially Occurring On or in the Immediate Vicinity of Savanna Army Depot Activity, Illinois
* Note: SE – State of Illinois endangered ST – State of Illinois threatened FT – Federal threatened E – Federal endangered
INAI Survey Record (1978) as reported by IDC (1994) Bowles and Jones (1991) Table 3‑3. Phylogenetic Listing of Vascular Plant Species Noted During Field Investigations at Savanna Army Depot Activity, Savanna, Illinois
Table 3‑3. Phylogenetic Listing of Vascular Plant Species Noted During Field Investigations at Savanna Army Depot Activity, Savanna, Illinois (Continued)
Table 3‑3. Phylogenetic Listing of Vascular Plant Species Noted During Field Investigations at Savanna Army Depot Activity, Savanna, Illinois (Continued)
Table 3‑3. Phylogenetic Listing of Vascular Plant Species Noted During Field Investigations at Savanna Army Depot Activity, Savanna, Illinois (Continued)
Table 3‑3. Phylogenetic Listing of Vascular Plant Species Noted During Field Investigations at Savanna Army Depot Activity, Savanna, Illinois (Continued)
Source: Illinois Department of Conservation (1992) as reported by Dames & Moore (1994a) Land use practices also have greatly influenced the distribution and composition of SVDA plant communities. The activities of previous owners and installation‑related activities have resulted in physical disturbance to large areas of surface soil. Minor shallow soil and older disturbances have become native serial communities. Areas that have been more profoundly disturbed are highly developed. Areas actively mowed/maintained support low serial‑stage ruderal associations. Cattle grazing is used to keep combustible burnable grass cover low in the munitions igloo areas (Dames & Moore 1994a). Using soil conditions and hydrological regimes, and considering land usage, Dames & Moore (1994a) delineated the installation into the following six simplified vegetational/habitat types, or communities: Bluestem Sand Prairie Association—This community occupies approximately 45 percent of SVDA and is dominant throughout the well‑drained sand prairies and sand savannas at the installation. The grassland/bluestem prairie is a herbaceous community dominated by graminoids (e.g., grasses, sedges, and rushes), but with forbs, which are seasonally dominant in some locations. The majority of SVDA’s grasslands are disturbed from heavy cattle grazing, although several isolated areas of the installation support relatively undisturbed bluestem prairie. The state‑listed endangered beach heather (Hudsonia tomentosa) was noted on the slopes of natural blowouts within the dry sand prairie and sand savanna. Oak‑Ash Savanna Association—This association is present on SVDA in areas where the interaction of geomorphic and hydrologic conditions is suitable for continuous grass cover, but with scattered trees that contribute up to 30 percent cover. Mesic Oak Forest Association—This community grows in several locations of SVDA and is characteristic of an oak‑hickory stand of the Eastern Deciduous Forest biome. Emergent Marshes, Wet Meadows, and Wet Fringe Forests—Emergent marshes typically occur in poorly drained depressional areas and along fringes of ponds, lakes, streams, and rivers. These aquatic communities typically have less than 30 percent vegetative cover. Wet meadows occur in areas saturated less frequently than emergent marshes, and are found in the poorly drained, depressional land forms at SVDA. These early serial, open areas contain moist‑to‑saturated soil, with standing water present for only brief to moderate periods during the growing season. Herbaceous species are dominant, with woody vegetation comprising less than 30 percent of the total areal cover. Wet fringe forest communities of SVDA occur along the floodplains of lower perennial streams, recently disturbed portions of slough, and the Mississippi River waterway. Bottomland Hardwood Forest Association—The Bottomland Hardwood Forest (BLHF) community in this area lies approximately between the elevations of 585 and 600 feet, and is limited at its lower extent by the ordinary Mississippi River pool elevation. Thus, ordinary rising and falling of the water elevation associated with the seasonally controlled river flow level has a major effect on the local high water elevation in the backwater areas of SVDA. The main portion of this vegetational and habitat element at SVDA is within Mississippi River Pool 13, which begins just downstream from L&D No. 12 and continues downstream for approximately 6 miles. Fragments of the BLHF community also occur as strips along the shoreline and scattered islands toward the southeastern end of the installation. The total area encompasses about 4,000 acres, or approximately 30 percent of the installation. The BLHF‑dominated area is a riverine backwater landform composed of braided active and relict channels, oxbow lakes, bars, and islands. Soil consists of river‑deposited silt and sand. The majority of the area meets minimum criteria as Clean Water Act (CWA), Section 404 jurisdictional wetlands. Open Water Systems—Open water systems at SVDA include lakes, ponds, backwater sloughs, and the Mississippi River. Many of these systems include man‑made as well as beaver‑impounded open water systems. Pond systems include all open water of a minimum 0.5 to 20 acres, whereas lakes are greater than 20 acres in area. The communities support both floating and submerged aquatic vegetation. Forest and land management programs have been implemented at SVDA. The forest management program initiated in 1962 for the harvesting of timber is no longer active. As of 1986, approximately 10 million board feet of timber had been harvested at SVDA. The land management program consists of controlling and improving vegetative growth through grazing, mowing, and new plantings (SVDA 1986b). In 1979, the lease included the grazing on 2,491 ha and mowing and weed control services. No chemicals have been used by the lessee. SVDA (1986b) notes that silver maple is the most abundant tree species in the installation’s woodlands, comprising about one‑half the stand. A large elm population has suffered from Dutch Elm disease. Red oaks, birch, ash, and cottonwood (listed in order of abundance) also are prevalent. SVDA (1986b) notes that several small stands of potentially valuable black walnut trees are located on the installation. Download 467.8 Kb. Share with your friends:
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