Natural Resources
Conservation Service
Ecological site F091XY004WI
Terrace
Last updated: 9/27/2023
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.
MLRA notes
Major Land Resource Area (MLRA): 091X–Wisconsin and Minnesota Sandy Outwash
The Wisconsin and Minnesota Sandy Outwash MLRA is the most extensive glacial outwash system in the northern half of Wisconsin. The total land area of the Wisconsin portion is just under 1.4 million acres (2,170 sq miles). The northern half is a former spillway for Glacial Lake Duluth. The flowing meltwater from the draining lake has left behind thick deposits of drift and carved a terraced river valley now occupied by the St. Croix and Bois Brule Rivers.
The northeastern section – the Bayfield hills – is a collapsed outwash plain where drift deposits are thick. Lacustrine materials from Glacial Lake Duluth line the northeastern tip. Moving southwest, the landscape transitions into a large pitted outwash plain. This is an area of extensive kettle holes, and, where the underlying till is less permeable, kettle lakes with some interspersed morainic hills and ridges. The glacial drift deposits are thinner in the southwestern section, although there is still no documented surface bedrock within this MLRA.
The St. Croix and Bois Brule rivers share a channel that lines much of the northwestern border of this MLRA. In some places, the underlying reddish-brown sandy loam till of the Copper Falls Formation is exposed along cut riverbanks, though most of it is covered by a mantle of outwash. Glacial lakes deposited pockets of fine-textured lacustrine materials, most of which were washed away or buried by glacial outwash and meltwater flowing through the channel. East of the channel, some of the silty and clayey lakebed deposits are found near the surface, where they impede drainage and contribute to the formation of extensive wetlands.
Historically, the area supported extensive jack pine (Pinus banksiana), scrub, and oak forests and barrens. The northern portion also supported stands of red pine (Pinus resinosa) and eastern white pine (Pinus strobus) as well. Marsh and sedge meadow, wet prairies, and lowland shrubs dominated the extensive wetland complexes in the southern tip of this MLRA (Finley, R., 1976).
Classification relationships
Relationship to Established Framework and Classification Systems:
Biophysical Settings (Landfire, 2014): This ES is largely mapped as Laurentian-Acadian Northern Hardwoods Forest, Laurentian-Acadian Northern Oak Forest, Laurentian-Acadian Northern Pine Forest, Laurentian Pine Barrens, and Laurentian Oak Barrens,
Habitat Types of N. Wisconsin (Kotar, 2002): The sites of this ES keyed out to three habitat types: Acer saccharum/Vaccinium-Clintonia (AVCl); Pinus strobus-Acer rubrum/Vaccinium-Amphicarpa (PArVAm); Pinus strobus-Quercus/Gaultheria-Ceanothus (PQGCe)
WDNR Natural Communities (WDNR, 2015): This ES is most similar to the Norther Dry-Mesic Forest described by the WDNR
Hierarchical Framework Relationships:
Major Land Resource Area (MLRA): Wisconsin and Minnesota Sandy Outwash (91X)
USFS Subregions: Bayfield Sand Plains (212Ka)
Small sections occur in the Mille Lacs Uplands (212Kb) subregion
Wisconsin DNR Ecological Landscapes: Northwest Sands, Northwest Lowlands
Ecological site concept
The Terrace ecological site is located throughout MLRA 91X on stream terraces and strath terraces primarily along the Saint Croix and Namekagon river valleys. These sites are characterized by shallow to very deep, poorly to excessively drained soils that formed primarily in loamy alluvium or sandy outwash. Some soils formed in lacustrine deposits, or have underlying bedrock, residuum, or till. Sites are subject to occasional ponding or flooding. Few sites with lithic contact remain saturated long enough to meet hydric soil requirements. Soils range from very strongly acid to neutral.
Historically this Ecological Site was occupied by forest communities dominated by various mixtures of pine and oak species. Specific mixtures were largely dependent on frequency and severity of disturbances, particularly fire and subsequent seed-bed conditions and availability of seed sources. White pine (Pinus strobus) has been the most persistent species in forest communities due to its biological and ecological characteristics of great longevity, resistance of old trees to fire damage and moderate tolerance to shade by seedlings and saplings. Red oak was often present as an associate species. Virtually all stands on this Ecological Site were harvested during the late 19th and early 20th centuries and post-logging fires were almost universal. Today’s forests are dominated by any mixture of aspen (Populus tremuloides and P grandidentata) and several species of oak, e.g.: red (Quercus rubra), bur (Q. macrocarpa) and swamp white (Q. bicolor). White pine is not yet well represented in most communities, but where seed source is present, it often occurs in the seedling and sapling layers. Red maple is well represented on some sites, and is absent on others. It appears that once established, it is capable of remaining a permanent component of communities in absence of fire. Also, on less well drained sites there often is a significant presence of paper birch, balsam fir or white spruce.
The Terrace ecological site differs from others by occurring only on stream and strath terraces—landforms found along river valleys that used to flood frequently when the water levels were higher during and after Wisconsin’s most recent glacial advance. The Floodplains ecological site is most similar but occurs on lower landscape positions closer to the river on active floodplains. Vegetation sensitive to frequent and prolonged flooding can be supported by Terraces.
Associated sites
F091XY003WI |
Floodplain These sites occur in depressions and flats on floodplains. They form in sandy to silty alluvium and are somewhat poorly to very poorly drained. They are subject to flooding. They are found adjacent to Terraces on lower, more frequently flooded landscape positions that are closer to the river. |
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Similar sites
F091XY010WI |
Acidic Sandy Upland These soils formed primarily sandy outwash, but some sites formed in loamy alluvium over sandy outwash, and other sites are sandy outwash underlain by lacustrine deposits. Soils are very deep and are moderately well to somewhat excessively drained. These soils are characterized by the presence of a spodic horizon. Their vegetative communities are dry to dry-mesic with poor to medium nutrient requirements, similar to those found on Terraces. |
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F091XY011WI |
Sandy Upland These soils formed primarily in sandy outwash or sandy eolian deposits, but some sites formed in sandy lacustrine or loamy alluvium underlain by sandy outwash. Soils are very deep and are moderately well or somewhat excessively drained. They are neutral to extremely acid. They can be differentiated from Acidic Sandy Uplands by their lack of a spodic horizon. Their vegetative communities are dry to dry-mesic, similar to those found on Terraces, but they may be slightly more tolerant to lower nutrient status. |
F091XY014WI |
Acidic Dry Upland These soils formed in sandy and gravelly outwash. Soils are very deep and are excessively drained. They are characterized by the presence of a spodic horizon. Their vegetative communities are dry to dry-mesic with poor to medium nutrient requirements, similar to those found on Terraces. |
Table 1. Dominant plant species
Tree |
(1) Pinus strobus |
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Shrub |
(1) Corylus |
Herbaceous |
(1) Pteridium aquilinum |
Click on box and path labels to scroll to the respective text.
Ecosystem states
T1A | - | Stand replacing disturbance e.g., blow-down and fire, or clear-cutting followed by fire. Regeneration by natural seeding or planting. |
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R2A | - | Fire control, time, natural succession. |
T2A | - | Grazing by livestock. Disruption of tree regeneration and ground vegetation. |
T2B | - | Removal of natural vegetation, plowing, fertilizing, irrigating, planting agricultural crops. |
R3A | - | Removal of livestock from stands. |
T3A | - | Removal of natural vegetation, plowing, fertilizing, irrigating, planting agricultural crops. |
State 1 submodel, plant communities
1.1A | - | Light to moderate intensity fires, reducing or eliminating advance tree regeneration. |
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1.2A | - | White pine and red oak regeneration re-establishes. |
State 2 submodel, plant communities
Communities 1, 5 and 2 (additional pathways)
2.1B | - | Removal of White Pine |
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2.1A | - | White pine regeneration in mixed stand of white, red, and sometimes Jack pine. |
2.2A | - | White pine seeding in from natural seed source or under-planted. |
2.2B | - | White pine seeding in from natural seed source or under-planted. |
2.3A | - | White pine seeding in from natural seed source or under-planted. |
2.4A | - | White pine seeding in from natural seed source or under-planted. |
2.5B | - | Time without disturbance, natural succession |
2.5C | - | This pathway occurs with fire when Jack pine seed sources is available or when planted. |
2.5A | - | Repetitive clearcutting and burning of earlier stands |