Effects of Light, Flooding, and Weeding on Experimental Restoration of an Endangered Hawaiian Fern



Conservation of rare plants can be accomplished by the restoration practice of reintroduction, but subsequent management is often required. In species with narrow habitat requirements, it is especially difficult to predict which management methods will be successful at new locations. Marsilea villosa is an endangered endemic Hawaiian fern with only seven remaining populations in ephemerally flooding drylands. Among its uncommon traits are long-lived sporocarps, a requirement of flood and drought to complete its sexual life cycle, and the potential for extensive vegetative growth. An experiment was performed to determine which restoration techniques might best facilitate growth of outplanted M. villosa. The following effects were tested in a split-plot factorial design: flooding (once/none), light (50% shade/full sun), weeding (bi-monthly/none), and all interactions. We hypothesized that flooding would have the largest single-factor effect and that there would be interactions among treatments. As hypothesized, flooding had the greatest positive effect on percent cover and sporocarp production. However, shade also increased cover over full sun when the plants began to experience drought. There was an interaction of light × flooding because M. villosa grew best in flooded, shaded plots. Weeding had no significant effect except in combination with flooding. Beyond protected status, current management of M. villosa only includes weed management at some populations. This study shows that if reintroducing new populations, the need for labor-intensive weed management might be reduced if M. villosa is planted under conditions of flooding and moderate shade.