Lāwa‘i Forest Restoration
At one time in Hawai‘i, dry forests occupied much of the leeward lowlands of all the main islands and were a center of high diversity for native tree species. Dry forests were considered by early botanists to be the richest forest type in terms of number of tree species. But they had been all but totally eliminated by agriculture, livestock grazing, and development by the 1950s. Less than 10 percent of Hawaiian dry forests remain today. The remnants that still exist of this once vast ecosystem are scattered in only a few leeward sites across the state. On Kaua‘i, dry-mesic forests are believed to have most likely once existed within Lāwa‘i Valley.
The Lāwa‘i Forest Restoration Project is innovative and strategically significant because it allows us to recreate a type of forest plant community that has been nearly eradicated in Hawai`i. By developing a dry-mesic forest restoration site, we are creating a habitat for at least 100 native plant species that can eventually be planted there. Many of these species are Threatened and Endangered dry forest species that no longer have a viable home in the wild on Kaua‘i. By establishing this restoration site we will be able to offer long-term protection in a managed habitat for reintroduced populations of many species. In addition to enabling us to recreate the rarest and most species-rich Hawaiian forest type, the dry-mesic forest restoration will complement the current palette of NTBG restoration sites that include coastal, wet forest, and mesic forest sites.
The site of this restoration project is located directly below the NTBG Headquarters on the west slope of the Lāwa‘i Valley. The site is approximately 10 acres. Introduced species of brush and grasses currently dominate the area. Conditions on the site are optimal for both dry and mesic forest species.
When completed, the restored site will feature three to four distinct dry forest types based on variations once found throughout Hawai‘i. We will achieve these variations utilizing Kaua‘i species only. The forest will contain mixed assemblages of tree species with individual species grouped in small stands.
Lāwa‘i Stream Restoration
Lāwa‘i Stream is typical of streams found on volcanic islands throughout Oceania. Although watersheds are small by continental standards, the streams cross steep gradients between their sources and the ocean. Lāwa‘i Stream drains an area of only 4,200 acres, yet drops 1,800 feet from its headwaters to the sea. Due to the high-intensity rainfall, small drainage basin, steep stream slope, and little channel storage, this stream subject to flash flooding; it can rise and fall about 40 inches over a few hours in response to a storm event.
Land use practices in the watershed above the gardens severely impact the natural flow regime and water quality. Soil disturbance associated with upstream activities generates surface runoff carrying fine-grained clay particles into the stream. The native fish species, which require sufficient stream flow to provide clean, cool, fresh water, are unable to maintain populations under such degraded conditions.
The Lāwa‘i Stream Restoration Project is addressing this with a coordinated program of conservation measures and management strategies. Implementation of the stream corridor restoration was preceded by careful planning and the collection of baseline data. This was followed by the establishment of efficient monitoring parameters, methods for sampling and sample processing, and a statistical framework.
Site clearing consisted of setting the geographic confines of the stream, removing undesirable plant species, addressing site drainage issues, and protecting and managing desirable existing vegetation. Large boulders, removed during the plantation era, are being reintroduced to increase surface variability in the streambed and to improve water velocity in the wide, shallow reaches. Cuttings and nursery-grown specimens of native riparian vegetation are being planted to stabilize stream banks and provide shade to maintain cooler water temperature in the stream.
NTBG is uniquely positioned to carry out this watershed improvement program in the Lāwa‘i Stream. Since 1996 a collaborative research project on Limahuli Stream (one of the few remaining pristine streams in Hawai`i, which runs through NTBG’s Limahuli Garden and Preserve) has helped us understand the ecological functioning of streams in relation to riparian zones, watersheds, estuaries, and near shore marine habitats. The project allowed us to refine technologies for monitoring ecological components of Hawaiian streams, initiate a model community-based stream monitoring program, and create a Geographical Information System (GIS) to evaluate the effectiveness of stream resource management efforts. Employing the Limahuli Stream project as a model, we are applying the expertise, methods, and techniques developed to the restoration project in Lāwa‘i Stream.