Domestic and wild ungulates can be a major threat to rare and endangered plants in the Intermountain West. When these imperiled plants are restricted endemics that are short-lived biennials and highly palatable, it is vitally important to quantify herbivory pressure and institute effective management strategies to limit herbivory impacts. Such is the case for the clay phacelia (Phacelia argillacea), which was federally listed as endangered on September 28, 1978 (43 FR 44810) with one known population comprised of nine individuals. The property was acquired by The Nature Conservancy and the 8 ac hillside was fenced with a seven-foot game fence to protect the species from threats that included grazing by domestic and/or wild ungulates. However, due to the steep nature of the site and human trespassing, the game fence had fallen into disrepair and the plant population plummeted to a perilously low number of 3 flowering adults in 2016. We quantified herbivory pressure from free-ranging ungulates and plant survival over a four year period and evaluated the effectiveness of small portable plant cages and the larger game fence to reduce herbivory on the clay phacelia. We utilized wildlife cameras to document herbivore presence and plant cages to quantify herbivory pressure before and after the repair of the game fence.
Results/Conclusions
Population and survival levels of the clay phacelia was highly variable in all four years. When the game fence was in disrepair wildlife cameras showed high deer activity throughout the year, and direct evidence of deer eating clay phacelia. We found that caged plants had 25-41% higher survival rates than uncaged plants when the game fence was in disrepair (Χ2=7.19 p=0.02), showing that herbivory is a major threat to clay phacelia. We also found that most of the herbivory was taking place during winter. When the game fence was repaired wildlife cameras showed a drastic reduction in deer activity at the site and caged plants only had 1-16% higher survival rates than uncaged plants (Χ2=2.12 p=0.34). Our results show that wildlife cameras are an effective strategy to monitor herbivore presence and activity, and that both large and small fences can be highly effective strategies for protecting rare and endemic plants. When population levels at a site are stable the use of game fences is advised, while for highly variable populations the use of regular monitoring and portable cages may be a more cost effective strategy.