Extent and distribution of prairies in the southeastern United States in the early 19th century

Background/Question/Methods

Before the arrival of Europeans in the Americas, much of the southeastern United States was forested, but a variety of open habitats, such as glades, barrens and prairies, were also present.  The prairies were dominated by a mix of grasses and forbs that included many plant species that were also found in prairies of the Great Plains further west.  To better understand the factors that led to the presence and maintenance of prairies in this region, this study asked two main questions: 1) How much prairie was present in the southeastern U.S.A. in the early 19^th century? 2) On what types of soils and substrates were the prairies located?  To address these questions, historical survey maps were used to document the extent and location of prairies in what are now the states of Alabama, Mississippi, Arkansas and Louisiana.  Created by the U.S. General Land Office from the 1820’s to 1840’s, the survey maps often show landscape features of a single 9.7 by 9.7 km “township”, including rivers, streams, swamps and prairies.  For all four states, we examined every township map for prairies.  Each map with prairie was scanned into the Geographic Information Systems program ArcGIS.  The township maps were georeferenced and prairies were outlined.  The final map of prairies was then compared with contemporary soil maps. 

Results/Conclusions

The historical survey maps show that in the early 19^th century Alabama had about 73,000 ha of prairie, Mississippi had 91,000 ha, Arkansas had 285,000 ha, and Louisiana had about 868,000 ha of prairie.  The prairies were concentrated in three main regions: the Black Belt, which forms an arc from eastern Alabama to northern Mississippi and contained about 145,000 ha of prairies; the Grand Prairie in eastern Arkansas that had about 22,000 ha of prairie, and the coastal prairie of Louisiana that had an area of 795,000 ha.  The soils of these regions differed.  For example, in the coastal prairies of Louisiana, about 60% of the historic prairies sat on clayey and loamy alluvial deposits and an additional 26.4% were on thick loess deposits.  The prairies of the Grand Prairie region of Arkansas also largely sat on alluvial deposits.  In contrast, about 97% of the prairies of the Black Belt region were on chalk outcrops and their derived soils.  This soil difference suggests that the prairies of the southeastern United States have different origins and histories.