Illinois Natural History Survey - University of Illinois

Botany of the Savanna Army Depot

In 1917, at the height of World War I, the United States Army was searching for remote, sparsely populated sites to test and store munitions. A huge expanse of sand near the Mississippi River in northwestern Illinois (Carroll and Jo Daviess counties) fit the bill and the Savanna Army Depot was established. Now, 80 years later, the depot is being decommissioned. The Illinois Department of Natural Resources (DNR), together with various federal agencies, is gathering data to help plan the depot's future. Our team of botanists from the Illinois Natural History Survey's (INHS) Center for Biodiversity is responsible for surveying the plants.

The Army probably did not recognize the tremendous biological significance of the depot when it was established, but its extensive sands are very unusual in Illinois. Previous DNR-sponsored surveys of the depot had located 11 threatened or endangered plant species. With increased access to the base, we discovered one additional state endangered species and many previously unknown populations of the others. We also found at least one plant previously unknown from Illinois that should be a candidate for threatened or endangered status.

Many of the depot's rare plants are western species that reach their eastern limits on sandy habitats in western Illinois. Two of these, hairy umbrella wort (Mirabilis hirsuta) and fragile prickly pear (Opuntia fragilis), are known in Illinois only in Jo Daviess County, and the latter is known only from the Savanna Army Depot. Others, like James's clammyweed (Polanisia jamesii) and shaved sedge (Carex tonsa) have their largest Illinois populations on the depot. Some of the depot's animals show a similar pattern. For example, the only population of white-tailed jackrabbits (Lepus townsendii) east of the Mississippi River was at the depot. Unfortunately, the jackrabbits disappeared in recent years, probably due to habitat changes and increased numbers of coyotes.

INHS Center for Biodiversity Researchers (l-r) Mike Moore, Geoff Levin, Rick Phillippe, and Kate Kramer at Savanna Army Depot.

Perhaps even more significant than the individual plant species are the depot's natural communities. Most noteworthy are its extensive prairies and savannas. The savanna habitat, which consists of trees, typically oaks, scattered through a grassland, has almost disappeared from North America. Only about 6,400 acres of tallgrass savanna remain in the United States, about 0.02% of the presettlement total. Prairies have seen similar losses. The depot, with about 3,500 acres of savanna and prairie, preserves the most extensive remaining stands of these communities in the state.

The natural communities of the depot are not pristine, however. For obvious reasons, the Army has vigorously suppressed fires, which are vital for preserving both prairie and savanna from encroaching forests. Cattle have been used to reduce grassy vegetation and thereby reduce fire intensity. Though the cattle probably have slowed forest encroachment, they have also modified the grassland and forest vegetation. We have been uniquely able to document changes in the depot's vegetation because not long before the Army acquired the land, noted ecologist Henry Allan Gleason, then at INHS, published a paper describing the vegetation of the major sand deposits in Illinois, including the region that became the depot. Overall, we observed that forest cover of the depot has increased, particularly in areas that formerly were savanna. In addition, the abundance of some shrubs and grasses has increased, whereas other grasses and forbs that are probably dependent on periodic fires have decreased in abundance.

Still, much of the Savanna Army Depot remains in vegetation that with proper management could significantly recover. Nowhere else in Illinois can one look across a landscape so extensively covered with prairie and savanna. As decisions are being made for the depot's future, our research provides the information needed to find ways to use the land that help preserve this remarkable remnant of our state's natural heritage.

Geoffrey A. Levin, Kenneth R. Robertson, Kathryn A. Kramer, and Loy R. Phillippe, Center for Biodiversity

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