Natural Resources

In 2020, inventory reports for Honouliuli National Historic Site identified the vegetation and wildlife found at the Park. The reports outlined both the native and invasive plants and animals found in the Park along with the potential for rare or endangered plants. Due to the Park's strong cultural history and location within the Hono‘uli‘uli Ahupua‘a, the park service wishes to maintain the natural resources of the site and protect the native species that have potential to flourish on its grounds.

Honouliuli National Historic Site is characterized by the gulch in a valley with Honouliuli stream flowing across the center, and the elevation range of 64-165m places it in the most endangered of all native Hawai‘i vegetation types (native lowland dry shrub and lowland dry forest vegetation).

Floral Resources

Invasive Plants
More than 90% of the plants at Honouliuli National Historic Site are invasive. The two main non-native plants are guinea grass (Panicum maximum) and koa haole trees (Leucaena leucocephala), which are both found along the steep sides of the valley, the base of the gulch, and along the historic aqueduct and Honouliuli stream. Guinea grass was introduced to the Hawaiian Islands as feed for cattle, but quickly spread due to its fire tolerance, quick-growing nature, and wind-based seed dispersal. These invasive plants pose a threat to the cultural sites left behind from the sugar plantation and camp days.

The park is currently testing different vegetation management methods that are sustainable and long-term. The koa haole will prove harder to mitigate due to its location on the hillsides, thick trunks, and root systems. These plants create dry environments that increase fire risk. It is important to reduce that risk by regular clearing and upkeep at the park.

In total, there are 50 plant species at Honouliuli that are categorized as non-native or as noxious weeds.

Native Plants
Only six native plant species were found at Honouliuli, including the endemic wiliwili tree (Erythrina sandwicensis). The other five are the ‘ilima (Sida fallax), aridland peperomia (‘ala‘ala wai nui, Peperomia blanda ver. floribunda), candlenut (kukui, Aleurites moluccana), milo (Thespesia populnea), and wild leadwort (‘Ilie‘e, Plumbago zeylanica). Competition with invasives, parasitism, and slow growth are threats to the native plant populations on site. At the time of the survey, the native plants were only found in a couple spots around the park in small patches. Two of these plants, the kukui and milo, are Polynesian introduced plants.

Faunal Resources

Although the faunal inventory survey did not capture proof of the Hawaiian hoary bat (‘Ōpe‘ape‘a, Lasiurus cinereus semotus), the environmental conditions of Honouliuli met all the habitat requirements (tall forest cover) for their potential existence within the site.

Depending on the month, as many as 19-22 bird species could be present at Honouliuli with 26 total species observed. The one most commonly seen was the red-vented bulbul (Pycnonotus cafer), followed by the Japanese White-eye (Mejiro) and the Common Waxbill (Estrilada astrid). Other bird species not as populous included shamas, doves, warblers, cardinals, finches, mynas, silverbills, francolins, skylarks, egrets, quails, parrots, grassquits, and laughingthrushes.

Of note was also the potential for the Hawaiian short-eared owl (Pueo, Asio flammeus). Although none were seen during the survey, the surrounding lands around Honouliuli provide adequate habitat for pueo to thrive, indicating they may be present on the site in passing.

Invasive Animals
The largest threat to native birds in Hawai‘i continues to be feral cats, the small Indian mongoose, rats, and feral pigs. These invasive and non-native animals also pose threats to native plants. Mongoose have been frequently observed at Honouliuli and pose threats to ground birds, such as the pueo. Feral animals such as cats and dogs were not seen, but may be present along with rats and mice. Feral pigs have been seen in the park.

Other invasives that don't pose a direct threat to birds include the giant African snail (Achatina fulica), the Erythrina gall wasp (Quadrastichus erthyrinae), and the pink spotted hawkmoth (Agrius cingulata).