Plant community composition and structure at Jewel Cave National Monument: 2011–2017 summary report

Ashton, Isabel; Davis, Christopher; Swanson, Daniel

This report presents the results of vegetation monitoring efforts at Jewel Cave National Monument (JECA) by the Northern Great Plains Inventory and Monitoring Network (NGPN) and the Northern Great Plains Fire Ecology Group from 1998-2017. Field crews collected data relating to species richness, herb-layer height, and abundance of individual native and non-native species, ground cover, seedling and tree densities, and site disturbance at 27 plots and across 97 plot visits. We compared our findings to the range of natural variability seen in other grasslands and management targets to develop summaries of natural resource condition (Appendix C). We also explored how key metrics have changed over time from 1998 to 2017. In addition to annual monitoring, we also surveyed forest condition in 2011 and 2016 at 60 randomly located plots. We collected data on tree and seedling density, tree condition, disturbance, and the presence of exotic species of management concern, such as smooth brome and Canada thistle. Our findings can be summarized as follows: Monitoring crews identified 274 vascular plant species, and overall native plant diversity was in good condition, with an average of 12 native species occurring within any given 1 m2 quadrat sampled. Grasses and sedges make up the majority of plant cover, and non-native species comprise about 14% of total plant cover. Grasses and sedges were the most commonly observed plants, and slender wheatgrass (Elymus trachycaulus), a native species, was the most abundant plant observed with more than 25% absolute cover. Exotic species comprise 14% of total vegetation cover, which exceeds the management target level of 10% or less. The majority of this cover (8.9%) is comprised of Kentucky bluegrass (Poa pratensis), a common non-native species in the Black Hills. Species cover and diversity of both native and non-native plants was relatively stable from 2013–2017 with no significant increases or decreases detected. Forests are dominated by ponderosa pine (Pinus ponderosa) trees, which were observed in 77% of forest monitoring plots. Ponderosa pine density in JECA is similar to that of historic forest records, though on average, trees are smaller now than those observed in in the past, likely the result of the Jasper wildfire in 2000 which resulted in the death of approximately 50% of the park’s trees. Encouragingly, between 2011 and 2016 we observed an increase in the frequency of plots with ponderosa pine seedlings present as well as an increase in the number of pine seedlings observed in each plot, suggesting that pine forest regeneration is slowly progressing after the fire. The most frequently observed exotic species of management concern in forest plots was Canada thistle (Cirsium arvense), occurring in 72% of plots in 2016. Woody fuel loads in the park are high, averaging about 21 tons per acre, which exceeds the fire management program’s target range of 2– 12 tons per acre. Overall, the park’s vegetation seems to be in good condition, though exotic plants pose a significant challenge to park management.

Plant community composition and structure at Jewel Cave National Monument: 2011–2017 summary report

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