Prairie Plant Community Monitoring in Three Heartland Network Parks

Reconstructed prairie at Homestead National Historical Park (top left), reconstructed prairie at Herbert Hoover National Historic Site (top right), Sioux Quartzite prairie at Pipestone National Monument (bottom left) and reconstructed prairie at Pipestone National Monument (bottom right).

NPS

Park Prairies

Herbert Hoover National Historic Site (NHS) in Iowa, Homestead National Historical Park (NP) in Nebraska, and Pipestone National Monument (NM) in Minnesota all protect tallgrass prairie communities. In the past, natural fire, grazing, and drought preserved these imperiled ecosystems. Now, park managers use techniques like prescribed fire and mowing to maintain the tallgrass prairie. These three parks contain reconstructed prairies (a type of prairie restoration), and Pipestone NM also has remnant tallgrass prairie (original, native prairie) and a unique prairie type called Sioux Quartzite prairie that is located among the areas with Sioux Quartzite outcrops and surface rock.

Prairie reconstructions began at Homestead NHP in 1939—one of the oldest prairie reconstructions in the US—and at Herbert Hoover NHS in 1971. The Pipestone NM prairie restoration history is less clear. The western 80 acres, previously under cultivation, were left fallow in 1956 and some reseeding occurred in 1986. The removal of grazing and other treatments at the park also served to protect the remnant and Sioux Quartzite communities at Pipestone NM.

The Heartland Inventory and Monitoring Network monitors prairie plant communities in these parks to help park managers protect these special habitats.

Map of Homestead National Historical Park (HOME), Nebraska, Pipestone National Monument (PIPE), Minnesota, and Herbert Hoover National Historic Site (HEHO), Iowa. Also shown is Effigy Mounds National Monument (EFMO), another park in the Heartland Network.

NPS

Prairie Monitoring

Monitoring began at Homestead NHP and Pipestone NM in 1997 and at Herbert Hoover NHS in 2004. We collect information on climate; fire history, how many plant species are present, how much of the ground is covered by each plant species (a measure called plant cover that is an estimate of abundance), and how much of the ground is bare, covered by rocks, grass litter, or other materials. We also count the tree seedlings and saplings growing in the prairie. Long-term monitoring of plants in prairies helps us understand how prairies may be changing over time and provides information for evaluating the effectiveness of prairie management techniques.

Mary Short monitoring prairie plants at Homestead National Historical Park in 2022.

NPS

What We Found

Climate

Herbert Hoover NHS and Homestead NHP have similar air temperature patterns, but Homestead NHP has less rainfall. Pipestone NM is drier and cooler than the other two parks. Changes in climate could influence the prairies and how they are maintained. In the future, parks may have to take actions like flood management, wildfire protection, and seeding with species that are adapted to new climates to maintain prairies under changing conditions.

Climate Averages

Climate averages for Herbert Hoover National Historic Site, Homestead National Historical Park, and Pipestone National Monument. Climate data are based on 30-year averages (1981–2010)

Climate Parameter	Herbert Hoover NHS	Homestead NHP	Pipestone NM
Annual Precipitation	954.79 mm (37.59 in)	791.46 mm (31.16 in)	718.31 mm (28.28 in)
Average Annual Temperature	10.7°C (51.3°F)	10.7°C (51.3°F)	7.2°C (45.0°F)
Average Annual Maximum Temperature	16.7°C (62.1°F)	17.2°C (63.0°F)	13.2°C (55.8°F)
Average Annual Minimum Temperature	4.8°C (40.6°F)	4.2°C (39.6°F)	1.1°C (34.0°F)

Prairie Plants

Plant diversity in prairie reconstructions often declines over time, but only Pipestone NM experienced a decline (19% decrease). Herbert Hoover NHS had a 49% increase in native plants, and Homestead NHP had no change in native plants since monitoring began. When these prairies were first reconstructed very few species were planted, but more have been seeded over time. Some of the patterns we are seeing in native plants may be a result of how long it has been since the prairie reconstruction was started. In other words, we may be seeing these prairies at different stages of maturation.

Pipestone NM prairies have less forb (wildflowers) and grass cover than the other two parks, probably because of the park’s unique geology with more exposed rock on the ground. Grasses tend to be declining on all three parks. Tree encroachment into the grasslands at Herbert Hoover NHS and Homestead NHP is a concern. When woody plants move into prairies, the prairie can start transitioning to shrubland, savannah, or woodland communities. An important part of maintaining prairies is keeping woody shrubs and trees out. Although Pipestone NM qualified as a shrubland community type in 1988 based on woody cover (mean = 13.3%), current levels at Pipestone NM fit the definition of tallgrass prairie. Herbert Hoover NHS and Homestead NHP prairies are very close to qualifying as shrublands based on the amount of woody plants present.

Nonnative plants were more abundant at Pipestone NM, but Herbert Hoover NHS experienced an increase in nonnative species over time (Figure 1). Homestead NHP consistently had few nonnative plants over the years monitored (Figure 1). Smooth brome may require additional management actions to reduce abundance at Herbert Hoover NHS and Pipestone NM. Kentucky bluegrass may also be on the rise at Herbert Hoover NHS.

Figure 1. Mean nonnative species cover (%) in Herbert Hoover National Historic Site (HEHO), Homestead National Historical Park (HOME), and Pipestone National Monument (PIPE) from 1998 through 2022. Plant cover is a measurement that tells us how abundant plants are.

NPS

---

Prairie at Homestead National Historic Park after a prescribed burn.

NPS

Did You Know?

Assessing and comparing tallgrass prairie information from three parks at once can help managers understand how similar management actions at other parks are affecting prairie maintenance. Each park has used prescribed burning, but Herbert Hoover NHS has not been burned since 2011 because of administrative challenges. Periodic brush hogging (mowing) also occurs on the parks to treat problematic plants or as a replacement for prescribed fire, but the timing, location, and frequency of treatments vary between parks.

A focused study of the fire histories of these parks may demonstrate how the role of fire and access to treatments affects tallgrass prairie reconstructions in general. Previous studies have indicated that increases in woody plants at Herbert Hoover NHS were related to fewer fire treatments, but fire had a lesser role in shaping the plant community at Pipestone NM.

Even though factors like climate and land use history may differ between these parks, they have some similar challenges with respect to maintaining the integrity of prairie communities. Analyzing data across all three parks helps managers make informed-decisions about prairie management actions in their individual parks.

For More Information

View the Full Report. Visit the Heartland Inventory & Monitoring Network website.

Article created by the Heartland Network, 2024.