2017 ASHS Annual Conference

In Hawaii’s roadside areas, non-native weed pressure leads to the colonization of exposed soil by invasive species before native pioneer species are able to establish. The current practice for erosion control in roadside remediation is to hydro-seed with exotic grass species. As these non-native species establish, ecological damage such as the alteration of native soil chemistry and the make-up of microorganisms within the soil can result. Additionally, there is increased risk that these exotic species spread into nearby native forest where they may out-compete and endanger rare species. As an example remediation project, we used a series of horticultural techniques to transform a sloped plot of exotic grass into a native Hawaiian fern landscape. The trial was conducted as part of a protocol development program for large scale roadside restoration using native Hawaiian ferns, funded by the Hawaii State Department of Transportation. We harvested spores from the Harold L. Lyon Arboretum (Honolulu, HI) and wild populations in the southern Koʻolau mountain range (Honolulu, HI). We then germinated the spores on petri dishes containing a solidified agar medium. Germination occurred after approximately one month. After two to three more months in solid media culture, we transferred the gametophytes to a liquid flask culture containing higher levels of nutrients. We grew the gametophytes in liquid culture for approximately one month during which time they increased wet weight by an average of 464%. We prepared the ~65 sq. ft. trial site located at the University of Hawaii Shidler College of Business (Honolulu, HI) by eradicating the exotic grass with a non-selective herbicide, allowing weeds to grow back, and then covering with weed mat (repeated 1x). We combined the gametophytes from liquid culture in a hydro-mulch slurry containing water, wood mulch, and tackifier (slope adhesive). The slurry was spread by hand on the sloped plot. This experiment was successful in the mass out-planting of the native fern Microlepia strigosa (Thunb.) C.Presl., which had a success rate of ~1 established sporophyte per sq. ft. per gram of gametophytes, as well as the native ferns Nephrolepis cordifolia (L.) K. Presl, and Nephrolepis exaltata (L.) Schott subs. hawaiiensis, which had a combined success rate of ~1 established sporophyte per 3.3 sq. ft. per 10 grams of gametophytes. This trial provides an example protocol for the mass production of three native Hawaiian fern species, subsequent slope remediation using weed removal techniques, and mass out-planting with a hydro-mulch slurry.