Vegetation monitoring in goat prairies at Effigy Mounds National Monument

Leis, Sherry

Effigy Mounds National Monument has diverse vegetation because of its proximity to the Mississippi River, geologic formations, and cultural history. One of the unique plant communities within this landscape is goat prairie. Also called oak openings, juniper glades, or hill prairies, goat prairies are typically located on southwest facing aspects on the edges of bluffs. They typically have shallow soil with rocky limestone or sandstone substrates and a scattered overstory of oak and juniper trees. Goat prairie vegetation is diverse and includes species characteristically found in prairies, savannas, or woodlands. Historically, fire was an important ecological disturbance maintaining these plant communities. The Heartland Inventory and Monitoring Network established vegetation monitoring sites in the goat prairies because of their unique plant species composition. Vegetation has been monitored at eight goat prairie sites three times since 2001. Monitoring of canopy closure, midstory and overstory composition, ground cover, and ground flora composition and abundance occurred in 2001, 2005, and 2017. We also developed a 23-year record of the Palmer Drought Severity Index and a spatial fire occurrence record to complement the monitoring data. Although invasive species treatments have occurred, a quantitative assessment of those efforts is presented elsewhere (Bell and Young 2017). Ecological disturbances were limited in the goat prairie sites. During the monitoring period, the mean Palmer Drought Severity Index indicated that most years had adequate or wetter than normal conditions. Some high wind events occurring in or near the park also had the potential to affect the monitoring sites, but documentation of how these events impacted the sites was not available. Furthermore, very little prescribed fire occurred within the goat prairie sites. Tree reduction occurred in the vicinity of one goat prairie (Site 14), and crews noted herbicide damage at one site (Site 4) in 2017. Overall, a limited suite of management actions have occurred in the eight sites. The tree layers indicate that succession may be occurring. Canopy closure is progressing, consistent with a longterm remote sensing study. Midstory and overstory trees have increased in basal area, but tree density has not increased. Tree species characteristic of these xeric communities continue to be present, including white oak (Quercus alba), bur oak (Q. macrocarpa), and chinkapin oak (Q. muehlenbergii). Regeneration of all size classes has been variable through the monitoring period, although large saplings appear to have declined. Ground flora species richness and diversity exhibited a complex pattern. While gamma diversity (park-wide diversity) increased, site species richness declined. Beta diversity (diversity across sites) also increased, signaling sites may be differentiating into more unique communities. An analysis of six species characteristic of either prairie or forest communities showed that there is a great deal of variability in species abundances across the eight sites. No clear trend was determined among this suite of species. Guild abundances demonstrated decline in most guilds in 2005. No clear source for this decline was apparent. A few non-native species were present in low abundance in the goat prairie sites. The goat prairie sites continued to have characteristic overstory and ground flora species, but some metrics indicate that management actions could benefit these sites, such as methods that reduce the overstory within and possibly adjacent to the sites. Given that plant communities in the uplands at the park are on a continuum of soil depth and substrate with more shallow soils occurring near the bluff edges, resetting the successional trajectory using fire or thinning treatments throughout the continuum could be beneficial.

Vegetation monitoring in goat prairies at Effigy Mounds National Monument

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