Prairie vegetation monitoring at Pipestone National Monument: 1998–2017

Leis, Sherry; Morrison, Lloyd

The Heartland Inventory and Monitoring Network has sampled permanent monitoring sites in three vegetation community types (remnant prairie, restored prairie and Sioux quartzite prairie) at Pipestone National Monu-ment 10 times over a 21-year period (1997–2017). Network scientists recorded species identities and estimates of ground cover, ground flora and tree regeneration within these permanent sites. The monument has experienced two brief periods of drought through the monitoring record (2000 and 2012–2014). Fire return intervals varied through time with the longest mean fire-free interval of six years for a prairie community type occurring in 2014. Prescribed fire patterns were associated with ground cover patterns such as increased bare ground after burns or increased litter cover with longer fire return intervals. Mean native species richness peaked in 2001 and 2002 across the prairie types with the Sioux quartzite prairie supporting the most species during that period. The restored prairie supported the fewest number of species. Native species diversity (i.e., Shannon Diversity Index, evenness) followed the same pattern with relatively low levels of within-year variability in the remnant prairie. The woody guild includes trees and shrubs. Trees in particular remained at low levels throughout the study, especially in the Sioux quartzite prairie. The only notable trees observed were a large group of American plum seedlings in one plot in a single year. Species richness and cover of nonnative species—including two invasive grasses, smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis) — remained within the range of variation. Fire was associated with a partial and temporary reduction in the abundance of these two grasses in particular. The abundance of prairie sagewort (Artemisia frigida), a plant of ethnographic importance, was simi-lar from 1999 to 2017, but found infrequently. Lastly, we sought to learn whether environmental factors influenced species composition. We observed only weak relationships between fire and drought levels and species composition. The relationship was weakest for the restored prairie. We concluded that while fire and climate have an influence on species composition, other unevaluated factors are also important. Despite variation in fire regime, drought, and ground cover, prairie plant communities at the monument have been relatively stable through time. Fire appears to have had a beneficial role in reducing woody plant and nonnative plant abundance, at least in some prairie communities within the park. Continued practice of relatively frequent prescribed fire in Pipestone National Monument appears to correspond with high levels of native plant diversity and community stability, even during brief drought events.

Prairie vegetation monitoring at Pipestone National Monument: 1998–2017

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