Description & Significance

Alexander Oak Savanna falls within the Western Prairie ecological landscape and supports dry prairie/very open oak savanna on south to southwest-facing slopes, which grade to mesic and even isolated wet prairie/savanna in scattered areas at the toe of the hillslopes. There is a high-quality remnant open oak woodland (not open oak savanna) on the hilltop immediately north of the easterly prairie / open savanna remnant, which grades into more degraded oak woodland and undifferentiated forest northward, eastward, and westward. Additional historical open oak savanna is generally degraded and occupies mostly south, west, and southeast slope positions. An old railroad right of way runs from northwest to southeast in the western part of the property and supports some remnant populations of native plants. A quarry in the northern part of the property also supports some populations of native plants. A field in the southern part of the property has been planted to prairie, and an intermittent stream corridor runs just south of that field and west of the old railroad right of way. See Attachment A, Map 3for plant community areas.

Attachment C shows the intermittent stream, topographic contours, and hillshade from LIDAR. Elevation ranges from below 960 feet along the intermittent stream in the far northwest corner of the property to above 1060 feet on the hilltop in the central part of the property. The hillshade map shows that much of the western part of the hilltop was removed and is now surrounded by a rim of piled material, and the area just to the east was disturbed by quarry activity. The old railroad right of way in the western part of the property and former cultivated field in the southern part of the property are also clearly visible. Wisconsin Geological and Natural History Survey mapping (Attachment D) indicates that Alexander oak savanna is underlain by quaternary deposits consisting of River Falls formation (sandy till with some meltwater stream sediment) and Middle Ordovician bedrock of the Ancell Group (St. Peter and Glenwood formations). The United States Department of Agriculture Web Soil Survey maps prairie / open savanna areas to Dorerton, very stony-Boone-Whalan complex soils, and the hilltops Whalan silt loams. These indicate Sinnippee Group bedrock underlying the hill that is not mapped in Attachment D. Two similar hill features with similar elevation directly to the north are mapped to Sinnippee Group bedrock and were likewise quarried for shale (Decorah Formation). Elsewhere soils are fine sandy loam and silt loam (Attachment E).

CONSERVATION SIGNIFICANCE
Dry prairie and savanna at Alexander Oak Savanna support ground plum (Astragalus crassicarpus, WI Endangered), kittentails (Besseya bullii, WI Threatened), prairie turnip (Pediomelum esculentum, WI Special Concern), prairie ragwort (Packera plattensis, WI Special Concern), and rock stitchwort (Minuartia dawsoniensis, WI Special Concern). Prairie bushclover (Lespedeza leptostachya, WI Endangered, Federally Threatened) and Carolina anemone (Anemone carolina) are historical to the site but have not been observed since before 2000. Many other prairie species are present, including hoary puccoon (Lithospermum canescens), porcupine grass (Hesperostipa spartea), and silky aster (Symphyotrichum sericeum). In the oak woodland, an old-growth sod containing veiny pea (Lathyrus venosus), northern bedstraw (Galium boreale), grove sandwort (Moehringia lateriflora), and Pennsylvania sedge (Carex pensylvanica) remains. Oak woodland / closed savanna old-growth sods are exceptionally rare, because most have been destroyed by grazing, shading, or the build-up of oak litter in the absence of fire. Here wind export of litter from the convex landform has likely allowed this sod to persist on the hilltop through a period of fire exclusion. The property also supports rusty patched bumble bee (Bombus affinis, WI Special Concern, Federally Endangered) and falls within a United States Fish and Wildlife Service-mapped high potential zone, which means there has been a recent observation of the species in the immediate vicinity. See Attachment F for a rare species table, biotic inventories (vascular plants, butterflies and moths), and list of species used in the prairie planting. See Attachment G for recent site photographs.

Usage Policies

Not Allowed:

• Collecting Plants, Seeds, Rocks or Animals without permission from The Prairie Enthusiasts

Ownership History

Dick and Joan Alexander purchased the property in 1965, and used it for decades as a resource for family activities, hunting and firewood gathering. 

The WI chapter of The Nature Conservancy recognized the conservation significance of the site and secured first right of refusal in 1985, which was transferred to The Prairie Enthusiasts in 2003. The Saint Croix Valley Chapter of The Prairie Enthusiasts worked on the site since the 1990s in cooperation with the former owners, Dick and Joan Alexander. This work has included brush and tree removal, invasive species control, addition of local genotype seed (including a prairie planting in the formerly cultivated field) and prescribed burns. 

In 2018, the Alexanders generously accepted an offer from TPE for the purchase of the property, ensuring its continued resource recovery through TPE management.

Management

Our goals for the site are to:

• Restore and maintain historical prairie, oak savanna, and oak woodland on the site.
• Maintain and improve habitat for rusty patched bumble bee and other invertebrates.
• Restore and maintain habitat for savanna bird species.

Prior to 2000, the site was managed by The Nature Conservancy through their volunteer site steward program.  Since assuming management responsibility in 2000, TPE’s efforts have focused on the removal of such invasive species as buckthorn, Siberian elm, and red cedar. Regular prescribed burns are conducted in late winter or early spring. TPE has also re-introduced appropriate species native to this area by overseeding portions of the site with locally collected seed.

The restoration work has been done mainly by TPE volunteers, but the chapter has also received land management grants from the U.S. Fish and Wildlife Service and the Wisconsin Department of Natural Resources to hire contractors to assist with this work.  We have also been fortunate to have the assistance of many University of Wisconsin River Falls students who have participated in a variety of site management activities.  Throughout TPE’s management history of the site.

All work days are listed on our chapter page under Events.  Reminders are sent to everyone on the St Croix Valley eNews list.