Population monitoring protocol for Lemhi penstemon (Penstemon lemhiensis) and spotted knapweed (Centaurea stoebe) in Big Hole National Battlefield: Narrative version 1.0

Rodhouse, Thomas; Stucki, Devin; Lyon, Jason; Lonneker, Meghan; Lonneker, Jeffrey; Dicus, Gordon

Lemhi penstemon was identified as a vital sign for BIHO because it is a rare regional endemic forb thought to be at risk of extinction from habitat loss stemming from weed invasion and altered fire regimes, and, over a longer time frame, from changes in climate and extreme weather (e.g., drought) patterns. The Lemhi penstemon species inventory and pilot monitoring conducted in the Battlefield by the NPS has provided clear evidence that BIHO supports the largest reported population of Lemhi penstemon anywhere within its restricted range, making the park globally significant in terms of Lemhi penstemon conservation. Unfortunately this early survey effort has also established that spotted knapweed invasion poses a serious threat. Lemhi penstemon is thought to be dependent on early-seral, bare-soil microsites for successful seed germination and therefore possibly easily lost from ecosystems in which fire or other soil-disturbing processes are interrupted. This dependency creates both an opportunity and a challenge for aligning Battlefield cultural and natural resource management. Prescribed fire has been used in the past to maintain the open hillslopes of the Battlefield cultural landscape. These hillslopes host the core of the Lemhi penstemon population but, in the absence of fire, they are also prone to encroachment from the adjacent lodgepole pine forest and densification of native sagebrush and bunchgrasses. More recently, spotted knapweed has heavily infested some portions of these hillslopes, creating an additional threat to Lemhi penstemon persistence and to the historical and ecological integrity of the Battlefield in general. This infestation complicates the potential utility of using prescribed fire in the future if this invader also responds vigorously to fire. Monitoring the Lemhi penstemon and spotted knapweed populations in BIHO over time will provide information critical to effective Battlefield resource management decision-making. It also provides an important opportunity for NPS to contribute knowledge about biological conservation in protected-area cultural landscapes more generally. This is a targeted, hypothesis-driven monitoring program, closely integrated with Battlefield management. The fundamental working hypothesis is that Lemhi penstemon population persistence in the Battlefield is dependent upon recruitment of germinants, and increased survival and reproductive vigor of established plants in bare-soil microsites where sunlight, water, and soil nutrients are available in adequate supply. The corollary is that encroachment of lodgepole pine and increasing density of native steppe vegetation and spotted knapweed will reduce the number and size of these microsites and cause a decline in the penstemon population through resource competition. When natural processes and Battlefield management activities, including fire, downslope soil movement, and herbicide application, create microsites and suppress competitive vegetation, we expect that the Lemhi penstemon population will respond with increased reproduction and survival. We have developed monitoring objectives and corresponding survey and analytical methods that will allow us to test these hypotheses. Both the monitoring itself and Battlefield management will be adaptive and incorporate knowledge about the ecological system as it is acquired through monitoring over time, reflected in updated versions of this protocol. There are several important sources of uncertainty that may obfuscate some of the clarity of information generated through monitoring. Most importantly, monitoring will be done against a complex backdrop of varying climatic processes. Initial results from the inventory and pilot monitoring suggest that fluctuations in precipitation and temperature patterns prior to and during the growing season may influence variation in spotted knapweed and Lemhi penstemon counts from year to year. Climate information from weather stations near...

Population monitoring protocol for Lemhi penstemon (Penstemon lemhiensis) and spotted knapweed (Centaurea stoebe) in Big Hole National Battlefield: Narrative version 1.0

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