Preserves can be many things and serve a variety of purposes. Perhaps the most apt description in NTBG’s case is to view a preserve as a refuge for nature. This means first creating a safe haven for endemic species threatened by invasive plants and animals, and sometimes from real estate development. The next step is the active intervention by NTBG staff to improve the habitats by restoring the ecologies that sustain and preserve native plant communities. Preserves are a resource for the NTBG staff to develop and test conservation protocols in a range of ecosystems beyond those that exist in the gardens.
Each of NTBG’s preserves has different characteristics, and some have been more successful than others. The important point is that the work done in each preserve has been productive in terms of the experience provided and the lessons learned. In 2005, the NTBG developed a matrix to evaluate future land acquisition opportunities. Comprehensive criteria include such considerations as whether the land in question contains significant biodiversity, whether the ecosystems are unrepresented in NTBG’s other properties, distance from Garden facilities, challenges to physical access, and whether operational funding accompanies any gifts of land.
Limahuli Preserve (acquired in 1994)
Limahuli Preserve is located on the northern coast of Kaua‘i in a lush tropical valley that contains an almost pristine Hawaiian stream with a waterfall that plummets nearly 800 feet into the lower valley. This isolated area is surrounded on three sides by precipitous ridges 2,000 feet high. Within this spectacular setting are three separate ecological zones and many ancient Hawaiian archaeological sites. Botanical surveys have indicated that although much of the lower valley has been modified in the past, it remains an invaluable resource for native plant and animal species.
The unique topography in Limahuli Valley has resulted in two distinct management areas. These are: 1) The Upper Preserve, which is a "hanging" upper valley that extends to an elevation of over 3,000 feet at its highest point near the Alaka'i Swamp, and 2) the Lower Preserve, which is the part of the valley that is located below the waterfall.
Lower Limahuli Preserve
The Lower Limahuli Preserve contains approximately 600 acres of land. It is not open to the public and access is rugged and only by foot. The unspoiled Limahuli Stream has never been highly degraded by human impact, although the ancient Hawaiians did use its waters to irrigate their lo`i kalo (taro patches), which were located throughout the Lower Preserve as well as on the plain in front of the valley. Today, the stream has a full complement of native fauna, including fish and crustaceans that are found only in Hawai‘i.
Over the past 100 years the Lower Preserve has seen a major decline in the population of native plants, primarily due to the introduction of feral cattle in the late 1800s. The consequence has been not only the loss of native species, but also the establishment of many alien species of plants that are aggressive and able to out compete most of the native plant species.
Ten years ago, in an effort to restore this unique area to a more natural state, the Limahuli Garden staff began an aggressive plant-community restoration program. Efforts have been directed at three important plant communities – the mesic lowland forest, wet forest, and riparian plant communities. The results of these innovative restoration projects have garnered national recognition, demonstrated the importance of restoration projects in Hawai‘i, and proven our ability to turn the tide of retreating plant communities. They serve as models for newer projects.
Upper Limahuli Preserve
The Upper Limahuli Preserve encompasses approximately 400 acres of land above Limahuli Falls and extends from about 1,600 feet at the top of the falls to 3,330 feet at the summit of Hono O Napali. At upper elevations, the vegetation is characteristic of montane rain forest, while at lower elevations it is characteristic of lowland rain forest.
The Upper Preserve is remote, requiring the use of a helicopter to gain access. Historically, this area has suffered from different environmental pressures than those exerted on the Lower Preserve. Surveys have indicated that it was never intensely cultivated or modified by the ancient Hawaiians and it was isolated from the impacts of the cattle that did so much damage in the Lower Preserve. As a result, the Upper Preserve was still considered to be a pristine ecosystem with very few non-native species until the early 1980s. In 1982, and again in 1992, this unspoiled area was severely damaged by two powerful hurricanes. These devastating storms not only denuded the vegetation, but also spread aerial-borne alien weed seeds through much of the area. In the past 20 years the area has also been subject to increased pressure from expanding populations of feral pigs.
Since 1992, staff has increased management activities in this remote area in an effort to mitigate the decline of this once pristine ecosystem. Restoration and management programs today are focusing on control of the worst of the invasive plant species and control of the feral pigs. Given time and adequate resources we hope to begin returning this area to its original condition.
Ka‘upulehu Preserve (acquired in the early 1970s)
The Ka‘upulehu Preserve is a nearly six-acre fenced enclosure located north-northeast of Kailua-Kona on the west side of Hawai‘i Island. It was designated a State forest preserve in the 1950s, and was fenced to prevent further damage from grazing by cattle and feral goats which are prevalent in the region. In the early 1970s management of the preserve was taken over by NTBG on a 40-year lease. Ka‘upulehu Preserve is covered by remnant dryland forest dominated by lama (Diospyros sandwicensis) and harbors a high concentration of listed endangered plant species.
This preserve is situated at an elevation of roughly 2,000 feet on rough flows of block lava (a‘a) with geologic ages of 1,500 to 3,000 years. Annual rainfall ranges from about 1-1/2 to as much as 40 inches, but averages over 16 inches. The rough, rocky surface has relatively shallow gravelly soils confined to pockets. Kau‘pulehu Preserve is an important site to test methods in restoration ecology because of its diversity of dryland forest species and the fact that it has been fenced for over 50 years.
Beginning in 1973, NTBG botanists have conducted floristic inventories of the preserve. At one time 87 native and non-native vascular plant species were growing at Ka‘upulehu. Although large animals can be fenced out effectively, invasive plants, and small animals, cannot be. Fountain grass (Pennisetum setaceum), an invasive alien weed from Africa, has replaced the native herbaceous species, choking out seedlings of native plants and posing a severe fire hazard throughout the North Kona area. In addition, rats eat seeds of many native plants, preventing their regeneration. In 1995 NTBG initiated a three-year project to demonstrate the feasibility of restoring and regenerating the dryland forest by controlling the fountain grass and rodents. Results show that control of fountain grass does allow native plants to regenerate when rainfall is adequate, but new weeds also often appear in its place. Beginning in 2005 and continuing into 2006, Conservation staff began a more active management program at this preserve. NTBG is in the process of replacing the 50-year old rusted fence with a new one designed to keep the abundant feral goats out of this valuable area.
Awini Preserve (acquired in 1975)
This preserve is located in a remote area on the Awini Plateau in the Kohala Mountains of Hawaii Island. Because of its challenging location, the only practical access to the Awini Preserve is by helicopter. Surveys done in the 1970s indicated that eighty-five native and non-native species were recorded growing at Awini. The vegetation is primarily characteristic of a stunted and highly disturbed wet forest dominated by ‘ōhi‘a (Metrosideros polymorpha) spread over boggy ground. Feral pigs and cattle have greatly damaged the area, allowing alien plant species such as strawberry guava (Psidium cattleianum) and broom grass (Andropogon virginicus) to become established. Due to the remote nature of this preserve, active management of the invasive species is not possible and NTBG’s future use of this site in unclear.