Re-Establishing Native Host Plants to Recover Butterfly Populations Along the Southern California Coast

Volunteer habitat rehabilitation efforts in drought-stricken Southern California have proven helpful in recovering butterfly populations threatened by weeds, which have crowded out butterfly host plants. Host plant re-establishment represents just one aspect of full habitat restoration, but without preservation efforts on the Palos Verdes Peninsula (Peninsula), extinction of two rare subspecies of blue butterflies—the El Segundo blue and Palos Verdes blue—is likely.

Host Plant Establishment

Host plant establishment may allow butterfly population numbers to increase to levels that could withstand further population loss due to future drought and climate change. To help these unique blue butterflies recover from dangerously low population numbers, Erin Bergman, a Dudek biologist and arborist, has led a group of volunteers on a year-long project on the Peninsula to re-establish blue butterfly perennial host plants, which are less susceptible than annuals to drought.

Recovery in Action

Before weeding

Bergman said that weeding is the first step to host plant establishment. Recently germinated weeds are scraped, reducing their growth and helping native species replace the weeds within the seedbank. Weather forecasts are monitored for rain, and if over a 50% chance is expected, recently weeded areas are seeded with native species, focusing on host plants for the threatened species. Once a plot has been cleared, host plants from the Palos Verdes Peninsula Land Conservancy (Conservancy) nursery are planted throughout the plot.

At this point, proper irrigation is critical to ensure the success of the transplanted plants. Grey water is directly applied to the native seedlings through a gravity irrigation system every two weeks. This drought-friendly method only uses approximately one cup of water per plant.

Bergman and her team have gradually increased the size and density of plots, and the container plants have grown to almost a foot tall with more than a foot-long fibrous root system. “It is amazing how land can recover native species if you just get rid of the weeds.” Bergman said of their efforts. Early signs of success are already visible, with native dove weed filling in areas where non-native species once occurred.

Community Collaboration

After weeding

Several groups from the local community are helping with varying aspects of the restoration and propagation process. Efforts include:

  • propagation of Palos Verdes blue butterflies by Moorpark College for release in June 2016;
  • host plant growing by the Palos Verdes Peninsula Land Trust Conservancy (Conservancy);
  • planting and butterfly release on restoration sites by local high school students; and
  • fundraisers and donations arranged by the Conservancy to fund seedling plantings in the local greenhouses.

The volunteer efforts have so far been successful in re-establishing host plants for both blue butterfly species. With continued propagation and planting of native host species, as well as a comprehensive habitat restoration effort, butterfly population recovery on the Peninsula is possible.

Re-established host plant

Erin Bergman is a biologist and certified arborist with over 11 years’ experience in biological research and ecology, specializing in botany, weed mapping/monitoring, rangeland science, agricultural studies, and rare species. For more information, contact her at