Sunday, February 9, 2014

The Invasive Australian Tree Fern

Although the Australian fern (Cyathea cooperi) is being sold in Hawaii at many commercial plant nurseries, it is invasiveAccording to Dr. J.B. Friday with CTAHR Extension, Department of Natural Resources and Environmental Management, it is fast growing and aggressively outcompetes native plants in the forest understory. It is a threat to the forests and eventually displaces the native ferns, including the slower growing hapu’u.  

Dr. Friday suggests cutting out the Australian fern and removing it while wearing long sleeves and gloves since the hairs are irritating.The best diagnostic characteristic is the hairs on the leaf stems. With the Australian tree fern the hairs are broad and white. On the native hapu’u they are either fine and red-brown for hapu'u pulu (Cibotium glaucum) or fine and black for hapu'u i'i (C. menziesii). 
                                                                    C. cooperi

The Australian tree fern grows to 40 feet tall. It tolerates full sun in cool wet areas. Their spores are spread by wind and can travel over 7 miles from the parent plant.

In comparison, the Hawaiian tree fern, or Hapu’u is native to most of the Hawaiian Islands. Although once common, hapu’u stands have been reduced due to a large number of ferns being harvested for orchid media and landscape use. The last remaining large stands of native hapu’u are found on the Big Island.

The Hawaiian hapu’u  are very slow growing; the young ones grow at about 3.5 inches per year while the older plants grow even more slowly, eventually growing to  15-20 feet tall.  The unfurled fronds are covered with silky, red-brown wool -like fibers called pulu.  In the past, pulu was used for stuffing pillows and mattresses and for dressing wounds. 

The Hawaiian tree ferns are relatively easy to grow. They grow best in well drained slightly acid soils and partial shade; they will tolerate full sun in cloudy upland areas. They need a steady supply of water and occasional light applications of a complete, slow release fertilizer. Old and injured fronds should be pruned. It is illegal to ship tree ferns or products from the ferns internationally. 

Photos by Forest and Kim Starr