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1 April 2015 Initial Vegetation Response to Fuel Mastication Treatments in Rare Butterfly Habitat of the Spring Mountains, Nevada
A. Nalleli Carvajal-Acosta, Scott R. Abella, Daniel B. Thompson
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Current dense forests in the Spring Mountains, Nevada, attributed to land management practices including fire exclusion, are considered to provide sub-optimal habitat for the rare endemic Mount Charleston blue butterfly (Plebejus shasta charlestonenesis). To reduce fuel loads in these forests, managers have used various treatments, including tree thinning and mechanical mastication. This study analyzed potential negative and positive effects of deposition of masticated slash (post-tree thinning material such as branches and logs) on host plants within Mount Charleston blue habitat. We manipulated depth of woodchip beds in 1-m2 quadrats at a Pinus ponderosa (ponderosa pine) site and monitored understory vegetation and butterfly host-plant response to the treatments. We also performed a germination experiment on seeds of the butterfly larval host plant Astragalus calycosus var. calycosus (Torrey's milkvetch) by applying various treatments combinations which included shading, liquid smoke, cold stratification and scarification. We found no significant effect (P>0.05) to any of the plant community variables (e.g., species richness, plant cover, and A. c. var. calycosus density, cover, and flowering) from forest-floor treatments during the first reproductive season after treatments. Cover and leaf number of A. c. var. calycosus declined over all treatments, suggesting that the pine tree canopy inhibited butterfly host plants, despite thinning of the pine canopy, or other factors limited the host plant. In the germination experiment, scarification significantly increased germination but all other treatment effects were not significant (P>0.05). The lack of a short-term response of the plant community to forest-floor manipulation is consistent with experiments in other P. ponderosa forests (including longer-term research) and indicates that these treatments did not substantially alter the vegetative characteristics of butterfly habitat. Given the potential detrimental effects of wood chip deposition on butterfly habitats, this small-scale experiment indicates that such effects will not result in short-term changes in Mt. Charleston blue butterfly host plants in wood chips layers less than 5 cm in depth.

A. Nalleli Carvajal-Acosta, Scott R. Abella, and Daniel B. Thompson "Initial Vegetation Response to Fuel Mastication Treatments in Rare Butterfly Habitat of the Spring Mountains, Nevada," Journal of the Arizona-Nevada Academy of Science 46(1), 6-17, (1 April 2015).
Published: 1 April 2015
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