Australian tree fern threat to native Hawaiian plants
By Heidi Bornhorst
By Heidi Bornhorst
Q. I found out that the ferny plant my landscape architect planted in our new garden is a noxious alien weed. It's called Australian tree fern and looks so innocent. But I believe in protecting our native Hawaiian environment. Why is this plant such a pest? What can I plant in its place that will give me the same lush, green refreshing look in my treasured garden?
— D.H., Wai'alae Nui
A. Ferns spread by tiny, carried-by-the-winds spores. This is how native Hawaiian ferns got to the Islands in the first place.
Australian tree ferns are aggressive and fast-growing — that's one reason why they are planted, for their "instant" effect. However, they produce a lot of spores, which our Hawaiian breezes carry far and wide. They can invade and take over pristine Hawaiian rainforest, growing in big patches, shading and crowding out native plants. The ferns keep producing spores, making more of their own kind to outgrow native Hawaiian forest plants.
Years ago, Australian tree ferns were found in the rainforest in Kipahulu, Maui. My friend Paul Higashino warned me about them, and we started getting the word out to akamai, caring gardeners. I yanked them out of my garden and stopped selling them to a garden shop in Wahiawa.
Christy Martin, of the Coordinating Group on Alien Pest Species, in a presentation to the Hawaii Island Landscape Association, showed us pictures taken from a helicopter above the Alaka'i Swamp on Kaua'i. There, in a pristine bog, by a waterfall, were big choking Australian tree ferns.
So we should not plant these ferns in our gardens. Nurseries should not sell them. Those already in landscapes should be cut down, double bagged and tossed in the trash. We also need to watch for other ferns, especially big or thorny ones that might escape our gardens and harm the native forests.
Landscape maintenance gardeners dislike the Australian tree fern for other reasons. They are itchy and nasty to deal with when you have to trim the old fronds. Unlike our Hawaiian hapu'u, the Australian tree fern has a hard trunk on which nothing else can grow.
Hapu'u, known as the "mother of the forest" because of its soft, welcoming fibrous trunk, is a great substitute. Hawaiian plants such as 'ohi'a lehua, 'olapa and 'ie'ie often get their start in life by growing on the welcoming hapu'u trunks. They also are a good living "green sponge" for our watersheds, our forests that catch, filter and purify our water.
Erin Lee, director of landscaping for the Four Seasons Hualalai, also suggests the dwarf date palm Phoenix roebelinii, a native of Indochina, as another substitute for the Australian tree fern. It is slow-growing and the seeds don't pop up everywhere. The hotel also uses hapu'u extensively in its verdant and well-tended landscapes.
Ape or giant elephant ear (Alocasia) is another suggestion, offered by Christy Martin.
'Ama'uma'u is another Hawaiian tree fern that could be used. The fern is very pretty and has a striking new leaf or frond which is bright pink or orange when it emerges. The frond unfurls, keeps the protective bright color for a short time and then toughens up to green. We saw this in an attractive entry landscape planting at the Kamehameha Preschool in Waimea on the Big Island.
So let's be conscious of what we plant in our gardens, and what we might want to weed out permanently. Grow native Hawaiian!
Heidi Bornhorst is a sustainable landscape consultant. Submit questions to firstname.lastname@example.org or Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802. Letters may be published or distributed in print, electronic or other forms.