IRC’s Plant Restoration Efforts Show Early Success in Aiding Butterfly Population Growth

In an effort to keep the butterfly population thriving on the Landmarks, Irvine Ranch Conservancy (IRC) has been working on a project to restore nectar and larval host plants in 11 designated butterfly habitat “islands” in OC Parks’ Limestone Canyon over the past two years. While IRC is still in the early stages of collecting data to evaluate the overall success of the project, initial counts may suggest a positive trend in increasing butterfly numbers in these habitat islands.

For over a decade, IRC staff and volunteers have been monitoring butterfly populations and species in OC Parks’ Limestone Canyon. By leveraging this butterfly count dataset, Restoration & Enhancement developed a plant palette to increase native host plant cover along Limestone Canyon Road in a series of plots, or habitat islands.  This data led IRC to establish a pilot project that involves fostering patches of abundant and diverse native plants that can support populations of 10 butterfly species. Monitoring data from these areas is being compared with data from nearby unenhanced or “control” plots.

Over the past two years, IRC staff and volunteers focused on enhancing plant species in the designated plots before initiating the data collection phase of the project. Starting in June 2024, monthly data collection from both the “enhanced” and “control” plots began, aiming to monitor both plant and butterfly abundance and species richness to evaluate the success of the restoration project.

Early results show that there are improvements in butterfly abundance and number of species in the “enhanced” plots compared to the “control” plots. While it is still too early to tell if the data is significant, initial counts reveal one additional butterfly recorded per plot in the enhanced plots as opposed to the control plots. Furthermore, the richness of butterfly species in the “enhanced” plots showed a 0.4 increase in the number of species detected per plot compared to the “control” plots.

The ongoing process of planting nectar and larval host plants remains an ongoing priority for IRC staff and volunteers, with a focus on enhancing plant diversity in the “enhanced” plots. Plans are underway to continue seeding efforts this winter, followed by planting in the spring. In the future, IRC is planning to emphasize planting milkweed to attract Monarch butterflies which the U.S. Fish and Wildlife Service recently proposed listing as a threatened species. The monitored butterfly species for this project include Monarch, Bernardino Blue, Sara Orangetip and Common Ringlet, among others.