title: Living on the Edge: Assessing the Effects of Catastrophic Fire on Plants Utilized by Two Endemic Subspecies of Spring Mountains Butterflies
Creators: name: Herrmann, Charles Ryan
Publisher: name: University of Nevada, Las Vegas
Year: 2017

description: In the past few decades there has been an increase in catastrophic, high-intensity, large-scale wildfires globally due to the combination of climate warming with more than a century of fire suppression policy. One region that has been drastically affected is the Western United States, as there has been an increase in ‘mega-fires' in the past few decades. The 2013 Carpenter 1 Fire in the Spring Mountains, Nevada was the largest fire in recorded history in these mountains, spreading out over 11,137 hectares. Catastrophic fire like the Carpenter 1 Fire can have potentially devastating effects on endemic species inhabiting refugia on ‘sky-islands.' The understory response to this catastrophic fire was measured using 52-1m2 plots in a burn area that supports two endemic butterfly subspecies, the Mount Charleston blue butterfly and Morand's checkerspot, to test for resistance and resilience of sky-island species to catastrophic fire. Plots were placed in unburned, low severity burn, and high severity burn areas. The species richness of the understory was measured in the varying degrees of burn severity, while the specific nectar and larval host plant abundances of the two butterflies were measured to determine if the fire increased habitat by opening up high pre-fire tree density areas. Three years post-fire I found total species richness of understory vegetation to be greatest in unburned areas, only one species less in low severity burn areas, and significantly less in high severity burn areas. The plant community that existed pre-fire was found to have a legacy effect, as areas of high pre-fire tree density, resulting in high severity burns, were biased towards shade-tolerant plants. In contrast, areas of low pre-fire tree density, resulting in low severity burns, were biased towards plants that occur in more open, sunny conditions. The nectar plants of both butterfly species, Erigeron clokeyi and Hymenoxys lemmonii, recovered past plant densities capable of supporting the butterflies in the low severity burn. However, only Hymenoxys lemmonii has recovered enough to support the butterflies in high severity burn areas. Two of the three larval host plants of the Mount Charleston blue butterfly, Astragalus calycosus and Oxytropis oreophila have surpassed unburned densities in the low severity burn. However, only Astragalus calycosus has recovered in sufficient plant densities to support the butterfly in the high severity burn. Neither larval host plant for the Morand's checkerspot, Castilleja martinii and Penstemon leiophyllus have recovered in either burn severity in sufficient plant densities to support the butterfly. The larval host plants of the Morand's checkerspot may be later successional species, as Castilleja martinii occurs in old burn areas. Grasses have not surpassed unburned densities, which is important for the butterflies as high densities of grasses can impede flight behavior. Non-native species were absent throughout the study in all burn severities. These results provide insight into the resistence and resiliency of sky-island refugia to catastrophic fire.