Natural Resources
Conservation Service
Ecological site R108XC517IA
Wet Loess Upland Flat Savanna
Last updated: 11/04/2024
Accessed: 11/13/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
MLRA notes
Major Land Resource Area (MLRA): 108X–Illinois and Iowa Deep Loess and Drift
The Illinois and Iowa Deep Loess and Drift, West-Central Part (MLRA 108C) encompasses the eastern portion of the Southern Iowa Drift Plain and the Lake Calvin basin of the Mississippi Alluvial Plain landforms (Prior 1991). It lies entirely in one state (Iowa), containing approximately 9,805 square miles (Figure 1). The elevation ranges from approximately 1,110 feet above sea level (ASL) on the highest ridges to about 505 feet ASL in the lowest valleys. Local elevation difference is mainly 10 to 20 feet. However, some valley floors can range from 80 to 200 feet, while some upland flats and valley floors only range between 3 and 6 feet. The MLRA is underlain by Pre-Illinoian glacial till, deposited more than 500,000 years ago and since undergone extensive erosion and dissection. In the northern half of the area the till thickness ranges from 150 to 350 feet and grades to less than 150 feet thick in the southern half. The till is covered by a mantle of Peoria Loess on the hillslopes and Holocene alluvium in the drainageways. Paleozoic bedrock, comprised of limestone, shale, and mudstones, lies beneath the glacial material (USDA-NRCS 2006).
The vegetation in the MLRA has undergone drastic changes over time. Spruce forests dominated the landscape 30,000 to 21,500 years ago. As the last glacial maximum peaked 21,500 to 16,000 years ago, they were replaced with open tundras and parklands. The end of the Pleistocene Epoch saw a warming climate that initially prompted the return of spruce forests, but as the warming continued, spruce trees were replaced by deciduous trees (Baker et al. 1990). Not until approximately 9,000 years ago did the vegetation transition to prairies as climatic conditions continued to warm and subsequently dry. Between 4,000 and 3,000 years ago, oak savannas began intermingling within the prairie landscape, while the more wooded and forested areas maintained a foothold in sheltered areas. This prairie-forest transition ecosystem formed the dominant landscapes until the arrival of European settlers (Baker et al. 1992).
Classification relationships
USFS Subregions: Central Dissected Till Plains (251C) Section, Central Dissected Till and Loess Plain (251Cc), Mississippi River and Illinois Alluvial Plains (51Cf), Southeast Iowa Rolling Loess Hills (251Ch) Subsections (Cleland et al. 2007)
U.S. EPA Level IV Ecoregion: Rolling Loess Prairies (47f), Upper Mississippi Alluvial Plain (72d) (USEPA 2013)
National Vegetation Classification – Ecological Systems: North-Central Interior Dry-Mesic Oak Forest and Woodland (NatureServe 2015)
National Vegetation Classification - Plant Associations: Quercus bicolor – (Quercus macrocarpa, Quercus stellata) Woodland (CEGL005181) (Nature Serve 2015)
Biophysical Settings: North-Central Interior Oak Savanna (BpS 4213940) (LANDFIRE 2009)
Natural Resources Conservation Service – Iowa Plant Community Species List: Woodland, Swamp White Oak (USDA-NRCS 2007)
Iowa Department of Natural Resources: Tallgrass Savanna (INAI 1984)
Ecological site concept
Wet Loess Upland Flat Savannas are located within the blue areas on the map (Figure 1). They occur on upland flats and high stream terraces. The soils are Alfisols that are somewhat poorly to very poorly-drained and deep, formed in loess. Low hydraulic gradients create a shallow depth to an apparent water table during the growing season.
The historic pre-European settlement vegetation on this ecological site was dominated by upland and hydrophytic tallgrass savanna vegetation as the hydric/non-hydric boundary was greatly intermixed. Swamp white oak (Quercus bicolor Willd.) and bur oak (Quercus macrocarpa Michx.) are the dominant trees, and big bluestem (Andropogon gerardii Vitman) and sweet woodreed (Cinna arundinacea L.) are the dominant grasses on Wet Loess Upland Flat Savannas. Other grasses present can include switchgrass (Panicum virgatum L.), prairie cordgrass (Spartina pectinata Bosc ex Link), Canada wildrye (Elymus canadensis L.) and various sedges. The understory likely resembled that of Wet Loess Upland Flat Prairies, potentially including such conservative species as compassplant (Silphium laciniatum L.) and marsh pea (Lathyrus palustris L.) (Drobney et al 2001). Fire is the primary disturbance factor that maintains this site, while herbivory and drought are secondary factors (LANDFIRE 2009).
Associated sites
R108XC504IA |
Loess Upland Savanna Loess parent material that is not shallow to a water table including Downs, Downs variant, Greenbush, Hedrick, Ladoga, and New Vienna soils |
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R108XC515IA |
Ponded Upland Depression Sedge Meadow Loess parent material that is ponded including Sperry soils |
R108XC516IA |
Wet Loess Upland Flat Prairie Loess parent material that is shallow to the water table but classifies as a Mollisol including Garwin, Kalona, Mahaska, Muscatine, and Taintor soils |
Similar sites
R108XC512IA |
Till Backslope Seep Savanna Till Backslope Seep Savannas are lower on the landscape and are a SLOPE: stratigraphic, discharge wetland |
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Table 1. Dominant plant species
Tree |
(1) Quercus bicolor |
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Shrub |
Not specified |
Herbaceous |
(1) Andropogon gerardii |
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