Plant community composition and structure monitoring for Knife River Indian Villages National Historic Site: 2011-2016 summary report

Davis, Christopher; Ashton, Isabel

The Northern Great Plains Inventory & Monitoring Program and Fire Effects Program have been monitoring vegetation in Knife River Indian Villages National Historic Site for over 18 years. While methods have changed slightly, this report summarizes data from 57 locations from 1998-2016. Below, we list the questions we asked and provide a summarized answer. For more details see the Results and Discussion section. We conclude with a Natural Resource Condition Table (Table ES-1) that summarizes the current status and trends of a few key vegetation metrics. 1. What is the current status of plant community composition and structure of KNRI grasslands (species richness, cover, and diversity) and how has this changed from 1998 to 2016? A long history of agriculture and a change in the natural disturbance regimes at KNRI has led to low native species richness when compared to more intact mixed-grass prairies in the region (Table ES-1), but diversity is spatially variable. In general, sites within the northern prairie area support a diversity of native species typical of intact mixed grass prairie. We found no significant trends in native diversity or evenness from 1998 to 2016, but both are threatened by the large abundance of smooth brome and Kentucky bluegrass. Smooth brome has not increased over time (Figure 6), but where it is present there are very few native species. Kentucky bluegrass, on the other hand, has been increasing since the 1990s (Figure 6). Continued control efforts will be necessary to maintain native prairie and reduce exotic species cover within KNRI. 2. How have plots in restored and reseeded areas changed over time? Several long-term monitoring plots were located in sites that were reseeded with native grass and forb species in 2004 or 2010. Since this time, exotic species cover has declined in these areas. Native graminoid cover increased from 2007 and 2010 in both sites and native species richness remained consistent during this period. These observations suggest that seeding has increased native grass establishment and abundance in these areas, potentially preventing an increase in Kentucky bluegrass cover that has been observed in other areas of the park. 3. What, if any, rare plants were found in KNRI long-term monitoring plots? Three rare plants were observed in NGPN monitoring plots: blue wildrye (Elymus glaucus), maiden blue-eyed-Mary (Collinsia parviflora), and upright carrionflower (Smilax ecirrhata). We recommend close examination and collection of voucher specimens for these species when encountered in future field seasons so their identification and location can be confirmed. 4. What is the composition and structure of riparian forests at KNRI? The riparian forest in KNRI is a dominated by green ash and box elder trees. Cottonwood and willow species are rare. Future range expansion of the emerald ash borer into North Dakota could have large impacts on these forests because it can cause rapid mortality of green ash trees. Seedlings of many tree species are common, but it is unclear whether these will survive to maturity because many are covered by thick layers of smooth brome. Exotic forbs are common in the understory of the forest, particularly Canada thistle and dame’s rocket, and continuing control efforts will be necessary to prevent their spread. Revisiting these forested sites in 2019 will provide a better picture of how these forests may be changing over time.

Plant community composition and structure monitoring for Knife River Indian Villages National Historic Site: 2011-2016 summary report

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