Little Bighorn Battlefield National Monument vegetation composition, structure, and soils: 2009–2016 status and trend, revised September 2019

Borgman, Erin

In 2006 the Rocky Mountain Inventory and Monitoring Network began an effort to determine status and trends in upland vegetation structure, species composition, and soil condition in Little Bighorn Battlefield National Monument (NM) in order to help inform park management. The upland vegetation and soils protocol directly addresses two high priority vital signs in the network’s small parks: 1) vegeta-tion composition, structure, and soils, and 2) invasive/exotic plants. The protocol is also linked to three other vital signs: 1) landscape dynamics, 2) weather and climate, and 3) wet and dry deposition. This report summarizes results from upland monitoring at Little Bighorn Battlefield NM from 2009 to 2016. We provide park- and subpopulation-scale estimates of condition and trend for several specific indicators and provide summary statistics of several other indicators. Sites fall within 3 subpopulations based on ecological site and soil types: upland (relatively flat areas); gulley1 (ravines in the Custer unit); and gulley2 (ravines in the Reno-Benteen unit). We monitor vegetation community structure and composi-tion by documenting native species richness and the cover of native grasses, forbs, and shrubs. We monitor invasive exotic species by documenting annual brome cover and dominance and the cover of other exotic species. And we monitor soil chemistry and erosion potential by documenting soil stability and the cover of litter and bare ground. In order to interpret results in a way that is both scientifi-cally defensible and relevant to the management of Little Bighorn Battlefield NM, we assign condition categories to each indicator. These categories are: in reference condition (“good”), out of reference condition (“poor”), and in inter-mediate condition. The categories are based on assessment approaches and terminology modified from Stoddard et al. (2006), Bennetts et al. (2007), and Mitchell et al. (2014). We define these categories using assessment points from several sources, including Natural Resources Conservation Service Ecological Site Descriptions and the Annual Brome Adap-tive Management project. Where no assessment points exist, we develop our own based on our data or data from nearby mixed-grass prairie systems, ecological knowledge, and park input. Results demonstrate that the condition of vital sign indica-tors in Little Bighorn Battlefield NM range from good to poor and warrant concern (Table 1; Table 2). Native species diversity and soils in Little Bighorn Battlefield NM are in reference, or good, condition. However, several vegeta-tion indicators are out of reference condition and warrant significant concern: native grass cover is low while exotic annual brome (cheatgrass and Japanese brome) cover and dominance is high. Native forb and shrub cover is in an in-termediate state (as is litter cover), which warrants moderate concern. Our analysis of trends indicates that vegetation and soil conditions in the park are unchanged between 2009 and 2016, after accounting for short-term variations in weather and a change in the botanist. Since several important indicators, especially annual brome cover and dominance compared to native grass cover, are out of reference condition, we believe the overall condi-tion of vegetation and soils in Little Bighorn Battlefield NM warrants significant management concern and continued monitoring. Moreover, available moisture was an important source of variation for several indicators, like annual bromes and native grasses. This suggests that these resources may be sensitive to future climatic change. The summary condition table on the next two pages provides a brief description of results.

Little Bighorn Battlefield National Monument vegetation composition, structure, and soils: 2009–2016 status and trend, revised September 2019

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