This project investigates the effects of forest encroachment in alpine regions for the Rocky Mountain Apollo butterfly, a species restricted to habitat above treeline. Using historical aerial photography documenting past encroachment, habitat mapping, and tree ring dating, areas above treeline that are and are not subject to forest encroachment will be determined at three sites in the front range of the Rocky Mountains. These data will be combined with existing long-term population data for the butterfly to predict if continuing forest encroachment will affect the butterfly, and if so, when these populations may begin to see effects.

This research addresses an important question for conservation as well as for ecological and evolutionary research: Does habitat change in alpine systems necessitate extinction or will local refugia be sufficient to permit persistence? Currently, the elevation of treeline is rising in many alpine areas throughout the world, potentially threatening organisms restricted to alpine habitats. The project will provide training for one graduate student, three to nine undergraduates and one postdoctoral researcher. The investigators participate in the WISE and McNair programs and the Girl Scout summer program and have a strong record of outreach to diverse groups. The project has been featured in park visitor centers and magazine and newspaper articles.

Project Report

We collected data examining past (aerial photographs) and current (location of seedlings) forest encroachment in the front ranges of the Rocky Mountains in an effort to understand if and how future forest encroachment into alpine habitats would affect the alpine specialist Rocky Mountain Apollo Butterfly and its host plants Lance-leaved Stonecrop and Ledge Stonecrop. Analyses of aerial photographs showed considerable loss (72.5%) of unforested habitat between 1953 and 2008. Most of this reduction appears to be due to recovery from fire. Analyses of current encroachment revealed that encroachment is affected by local soil conditions and snow cover. Based on factors affecting where seedlings currently occur, forest encroachment is predicted to reduce alpine habitat by an additional 9.7%. Thus, it appears that forest encroachment has neared its maximal extent at the sites examined. Past forest encroachment has reduced the size of butterfly populations and limited their movement among alpine habitat. Future enrichment will continue to reduce the number of butterflies and their movement, but will not result in their or their host plants loss, locally. This research contradicts the common notions that that forest is generally limited by climatic conditions and that climate change will result in a predictable loss of alpine habitat. Rather, forest encroachment into alpine meadows in the front ranges of the Rocky Mountains has been aided by fire suppression, but is limited by soil and geologic conditions. Alpine specialists may be directly affected by climate change; however, indirect effects of climate change due to habitat loss and fragmentation from future forest encroachment are less important than previously envisioned. This research trained 24 undergraduate and eight graduate students. The results of this research have been presented to a range of groups from the scientific community to the general public.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Saran Twombly
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University of Cincinnati
United States
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