The Mānoa Cliff Trail is an easily accessible hike that is still great for observing native plants. The vegetation along the Mānoa Cliff Trail ranges from Lowland Mesic Shrub land to Lowland Mesic Forest. Sadly, native vegetation along the trail has been observed to be in rapid decline.
Our restoration work aims to protect and promote native plant growth:
In 2005, with the assistance of the Conservation Council of Hawai’i, we received a permit from the Na Ala Hele program to restore a section of the Mānoa Cliff Trail between its junctions with the Pu’u ‘Ōhi’a and Pauoa Flats Trails. The land is owned by the State of Hawai’i.
Our effort involves manually controlling alien weeds and replacing them with native plants. We have good success such as:
- Koa and mamaki natural regeneration after opening the canopy
- Clermontia kakeana and Bidens asymmetrica from spread seed
- Olona (Touchardia latifolia) and papala (Charpentiera ovata) propagation and outplanting
A fence to keep out feral pigs was constructed in late 2009 by DLNR around 6 acres of the site. We have achieved great success with our work to date.
At the site, our efforts have begun to significantly turn back the decline of native plants. The decline of these native plants has at least two major causes:
- Competition for light and space by quick growing alien plants (weeds) such as cinnamon, guava, bamboo, ginger and others
- The disturbance and destruction of native seedlings and groundcover species by pigs rooting for worms. For example, before the installation of the fence, māmaki (Pipturus albidus) seedlings and a patch of ‘ala ‘ala wai nui (Peperomia leptostachya) were eliminated by pig rooting in one section of the restoration area that had been cleared of weeds
This decline has also been well documented:
- Recent surveys and our own observations have documented approximately 110 native plant species (as well as at least 115 non-native species) present along the trail or in the vicinity (Mt. Tantalus area), but based on numerous historical records dating back to the late 1800s (Bishop and Smithsonian museum records), 94 other native species are now missing from the area.
- Evidence for rapid decline has also been observed in the population of ‘oha wai (Clermontia kakeana), a native shrub in the Lobelia family. In 1980-1983 Coleen Cory, a biology graduate student at California State University, located 104 ‘oha wai (Clermontia kakeana) plants along the trail as part of her study in pollination biology. When we started this project in 2005 we were only able to locate 16 ‘oha wai plants in the area.
For more detail, see information presented at the 2010 Hawaii Conservation Conference that provides an overview of our work HCC-conference-2010 (pdf 5mb)