A Program to Eradicate Twenty-Four Nonnative Invasive Plant Species from Santa Cruz Island

Abstract

Santa Cruz Island, California, has been free of nonnative vertebrates since 2007, but nonnative invasive plants remain one of the most significant threats to the recovery of the island’s native ecosystems. Just over one-fourth of the island’s flora is comprised of nonnative, naturalized plant species. In 2007, an island-wide invasive plant survey indicated that several species were candidates for eradication based on factors such as their distribution, abundance, invasiveness, and known or projected harmful impacts on the native biota. In 2008, The Nature Conservancy (TNC) and Native Range, Inc., initiated a program to eliminate 15 invasive plant species from TNC’s portion (76%) of the 246-km2 island. An additional 9 species were targeted in subsequent years. As of 2012, a total of 882 populations of 24 weed species have been mapped and treated, and 73% of these populations are considered inactive (dead), with no above- ground living biomass. The majority of the remaining active infestations are due to resurgence from the soil seed bank. Continued monitoring and annual follow-up treatments of invasive plants will be required. Utilization of a small heli- copter provides surveyors and herbicide applicators with efficient access to remote infestations and a platform from which to treat populations and detect individual plants. Most important in achieving project success is consistent treat- ment from year to year, which prevents reproduction and recovery of infestations. Long-lived soil seed banks for some species will be a management issue for years to come. Continued commitment to eradicating these weeds and the ability to detect incipient infestations and respond rapidly to eliminate them will be key determinants of success of this program.