Date of Award:
Master of Science (MS)
Eugene W. Schupp
Eugene W. Schupp
A project involving shrub removal was undertaken by the United States Forest Service in the Spring Mountains National Recreation Area (SMNRA) to reduce accumulated woody fuels, which can pose risks to human communities. The SMNRA is also home to a variety of species that occur within these fuel reduction boundaries and are protected under the Multiple Species Habitat Conservation Plan (MSHCP) of Clark County, Nevada. It is unknown how MSHCP covered species will respond to shrub removal. This research focuses on the interactions between shrubs and the herbaceous plant Palmer’s penstemon (Penstemon palmeri), one of many nectar sources for the adults of MSHCP-covered Spring Mountains Acastus Checkerspot Butterfly (Chlosyne acastus ssp robusta). To understand the potential impact of shrub removal on P. palmeri, a series of observations and experiments were conducted. I begin by discussing plant interactions and the management concerns of the SMNRA, hypothesizing that shrubs may be an important component to P. palmeri populations (Chapter 1). I then document the effects of shrubs on P. palmeri performance and its spatial patterning to generate hypotheses about their interactions (Chapter 2). The results suggest that shrubs reduced penstemon emergence but increase seedling survival (a seed-seedling conflict) resulting in a pattern of association in which P. palmeri survive almost exclusively under shrubs. Further, while shrubs had little effect on P. palmeri growth, the results suggest that shrubs inhibited its flowering but improved its fruit maturation. Seed-sowing and seedling transplant experiments suggested that shrub soils may help penstemon populations persist as seeds on the landscape during dry years and that when seedlings emerge, shrub soils also improve their survival (Chapter 3). I then provide a detailed description of the direct and indirect reproductive responses of penstemon to shrubs (Chapter 4). The results suggest that competition with shrubs reduced penstemon seed production, but shrubs simultaneously facilitated penstemon water “sufficiency” and altered its pollinators foraging behavior, indirectly increasing seed production. I conclude by discussing the importance of these studies, and studies of plant interactions in general, for helping land managers balance the objectives of fuel management while protecting desirable species (Chapter 5).
Poulos, Jesse M., "Interspecific Interactions between Penstemon palmeri and Shrubs in the Arid Shrublands of the Spring Mountains, Nevada" (2013). All Graduate Theses and Dissertations, Spring 1920 to Summer 2023. 1966.
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