Anyone who has spent much time in Hawaii can easily find themselves daydreaming state-side of the islands’ fragrant-scented nights, the thousands of diamonds in the sky that get washed out back home by the urban glow, the caressing trade winds. How could you have left this, you ask yourself?
Of course, Oahu, home to Honolulu, Pearl Harbor and Diamond Head, is the most built up of the islands, the most inhabited and the least pristine. Here, perish the thought, you actually have Miami-esque high rises on the beach, a freeway, traffic and a mall!
Man’s encroachment upon the land is such that the Hawaii DOT has been working with University of Hawai’i at Manoa plant specialists to select and plant native groundcover along bare areas of the state roadways instead of the low-cost, effective, and decidedly nonnative, Bermuda grass.
LASN asked Christopher Dacus, RLA, with Hawaii DOT, about this project. Mr. Dacus explains the majority of Oahu’s roads are in low-lying areas close to the ocean and have been devoid of all native plants long before the highways were built. Say it isn’t so! In fact, says Mr. Dacus, “Most areas below 2,000 feet altitude are nonnative in Hawaii.”
University of Hawaii horticulturist Dr. Joe DeFrank is also interested in Mau'u aki aki (Fimbristylis cymosa), as a groundcover. Mature seed heads of Mau'u aki aki are doing well at this demonstration planting off Interstate H1 at the University Avenue interchange on Oahu. The plastic sheeting prevents weeds from growing, but also allows seed collecting for this native sedge.
Photo by Dr. Joe DeFrank and graduate research assistant Orville Baldos
Because of the dearth of native plants in the lower elevations, HDOT contacted the University of Hawaii five years ago to develop hydroseed protocols for two grasses: Akiaki grass (Sporobolus virginicus) and Pili grass (Heteropogon contortus).
Hydroseeding highway areas is significantly less expensive than hand planting. Prof. Joe DeFrank, PhD, and graduate research assistant Orville Baldos have been conducting the research for what it simply calls “Native Hydroseed Experiment for Future DOT Roadside Projects.” Dr. DeFrank, a horticulturist, administers the Magoon Agricultural Research and Instruction facility on campus and is the graduate faculty chairman. His research specialty is chemical and cultural techniques to control weeds in turf and ornamentals.
The dominant grass in Hawaii prior to nonnative grasses was probably Pili grass, explains Mr. Dacus. “HDOT needs a number of grasses in its toolbox to address the various situations. Pili grass is low rainfall 10-40 inches of annual rainfall and will become the standard grass for DOT since most of our roads are fairly close to the ocean and receive 20-40 inches of annual rainfall. Pili grass has an ornamental quality and DOT will not be mowing or herbiciding Pili grass. Akaaki grass is a salt-tolerant grass and HDOT will be hydromulching Akiaki grass for roads adjacent to the sandy beach areas and possibly for roads that use nonpotable water. Nonpotable water in Hawaii tends to have higher salinity.”
“Mau'u aki aki does well near the ocean and thrives in rocky areas, so (we) will be using it for riprap, rocky areas,” explains HDOT landscape architect Christopher Dacus.
Dr. DeFrank is also interested in Mau’u aki aki (Fimbristylis cymosa).
“Mau’u aki aki does well near the ocean and thrives in rocky areas, so DOT will be using Mau’u aki aki for riprap /rocky areas,” Mr. Dacus adds.
None of the native groundcovers being researched will require permanent irrigation or mowing. The benefits are multiple: reduced maintenance, no gas emissions from mowers, blowers, soil erosion prevention, keeping out invasive species and no use of chemical herbicides.