Uncovering and mitigating the impacts of invasive crystalline iceplant (Mesembryanthemum crystallinum) on San Nicolas Island

Summary

This study at three sites located across San Nicolas Island revealed that crystalline iceplant (Mesembryanthemum crystallinum) reduced either invertebrate species richness or invertebrate functional diversity, or both. Crystalline iceplant significantly changed invertebrate composition to favor tiny litter-feeding invertebrates over the larger flies, beetles, ants, and moths that native habitat supports and which are in turn important prey of the rare San Nicolas Island fox. A restoration experiment was undertaken to determine if a one-year effort of weed control and hydro-seeding could recover significant native diversity and cover. Findings showed that grow-kill treatments, where watering releases the weed seed bank and then hoeing removes those weeds, was more successful than herbicide treatments at controlling crystalline iceplant and, together with hydro-seeding, benefitted plant richness and cover. A longer-term effort in non-drought conditions would be needed for substantial and lasting recovery, however. With these results, the U.S. Navy has been pursuing biological control of crystalline iceplant on San Nicolas Island.