Destructive Ornamental Plants Threaten Ko‘olau Forests
Hawaiʻi residents enjoy thousands of plants from around the world that provide beautiful landscaping and tasty food. Most of these are not invasive. However, a small percentage of introduced plant species easily escape cultivation and spread rapidly, resulting in the loss of our unique Hawaiian forests and the cultural traditions that depend on native species.
The plants featured on this page are just a few of the plants that are commonly found in local stores and gardens that are invading our native forests. None of these plants have yet been listed as noxious weeds in Hawai‘i, but all are invading and damaging our native forests. Please remove these plants from your yard and help spread the word. Choose native or other non-invasive plants for landscaping.
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Octopus tree (Schefflera actinophylla) is spreading like wildfire in O‘ahu’s forests. The problem can easily be seen from a car on the windward side of H-3 around Hirano Tunnel, where the tree dominates a large area. Octopus tree is able to invade even undisturbed native forests. Its fruit is eaten by birds, which then disperse the seeds to surrounding areas. Both Schefflera actinophylla and Schefflera arboricola (dwarf umbrella plant, which is also invasive), can grow upon and kill other trees. Octopus tree is native to Australia and New Guinea, and can reach 40 feet or more in height.
Kāhili ginger, white ginger, and yellow ginger
Kāhili ginger (Hedychium gardnerianum), white ginger (Hedychium coronarium), and yellow ginger (Hedychium flavascens) were introduced to Hawai‘i for their showy scented flowers, but began escaping from gardens and are now serious invasives in Hawaiian forests. The plants form thick stands that choke out native vegetation. Keiki of native plants find it difficult or impossible to germinate and grow in a ginger thicket. Gingers also block stream edges, altering the flow of water. Small root fragments of various gingers will re-sprout if pulled up, making these plants challenging and costly to control.
Strawberry guava (Psidium cattleianum) is a small tree up to 20 feet tall. This species is native to South America and is believed to have been introduced to Hawai‘i as early as 1825, probably for its edible fruit. Pigs and introduced birds eat the fruit and spread the seeds in their waste. As a result, this plant has become one of the state’s worst weeds, occurring on all of the main islands except Ni‘ihau and Kaho‘olawe. Strawberry guava forms dense stands where little else can grow, and has replaced thousands of acres of native forest.
Native to Brazil, Christmas berry (Schinus terebinthifolius) is a shrub or small tree that grows up to 23 feet tall. The species escaped into the wild in Hawai‘i in the early part of last century and has now invaded all the main islands except Ni‘ihau and Kaho‘olawe. It is a serious weed in mesic native forest and shrubland, particularly in habitats that have been disturbed (such as by grazing animals or fire).
African tulip tree
African tulip (Spathodea campanulata) is one of the most popular landscape trees in Hawai‘i, grown for its large orange flowers. As the common name suggests, the species is native to tropical Africa. However, it has escaped into the wild, and now occurs in lowland mesic and wet forests on all the main islands except Lana‘i, Ni‘ihau, and Kaho‘olawe. African tulip has light seeds that are easily dispersed by wind, increasing its ability to spread into new areas.
Everyone can help by using more of our beautiful native plants in their landscaping!
Sources of native plants for landscaping:
Plants should not be collected from the wild. State of Hawaiʻi Department of Land and Natural Resources rules prohibit the removal of plants from forest reserves without written permission. Instead, buy them from plant sales and nurseries.
Learn more about planting natives:
- Five Easy Native Hawaiian Landscaping Plants
- Native Hawaiian Plants for Landscaping, Conservation, and Reforestation(pdf)
- Best Native Plants for Landscapes(pdf)
Learn More About Invasive Ornamentals
The Oʻahu Invasive Species Committee (OISC) is a voluntary partnership of state, federal, and private agencies. OISC works to prevent the establishment of new alien pests, controls incipient pests, and provides community education and volunteer activities.
Destructive Animals Threatening Ko‘olau Forests
Feral pigs are a common problem in Hawai‘i’s natural areas, agricultural lands, and suburbs. Their rooting and wallowing damages stream beds and increases mud, silt and erosion in the forest and downstream. Pigs break open the native forest understory, allowing invasive weeds to gain a foothold. They spread weed seeds into new areas as they move around the forest. They destroy young native trees, preventing important species like ʻōhi‘a and koa from reproducing successfully.
Feral pigs are also very costly to local farms and other businesses. A small group of feral pigs can wipe out a long-awaited crop in a single night.
Feral pigs are a game animal in Hawai‘i. However, they reproduce so quickly that hunting is not enough to prevent damage to our natural areas and farms. Remote native forests can be protected from pig damage only by fencing the pigs out.
KMWP supports fencing in important watersheds and coordinated hunting and trapping to manage feral pigs in agricultural and other easily accessible areas.
Feral goats, like feral pigs, end up roaming the watershed when they escape from farms or are released by people who don’t want to care for them or want animals to hunt. Also like feral pigs, feral goats are considered one of the most invasive species on the planet, being especially harmful on oceanic islands with limited resources and vulnerable native plants. Goats cut trails into steep slopes that promote landslides and eat the vegetation down to the dirt, causing terrible erosion. Hawai‘i has many infamous and highly visible examples of goat damage, such as the condition of Kaho‘olawe, or Waimea Canyon on Kaua‘i. If you see wild goats in the Ko‘olaus, please call KMWP at 808.453.6110.