Ferns of the rainforest

Skyrail Nature Diary: June 2011

The Wet Tropics rainforests of Tropical North Queensland have an abundant plant life. One plant commonly found in rainforests and vital to rainforest ecosystems, is the fern.

Ferns are a characteristic feature of rainforests due to their love of moist conditions. As any ardent gardener knows, ferns don't like wind and often need watering. This dependency on water has led to some interesting adaptations to the dry season.

Ferns will often lose their green leaves when the humidity drops and will go into hibernation. Once the rain starts, they can often go green overnight. Typical for the epiphytic ferns, those growing on top of trees, is their tendency to grow in the lee of the wind on the branches.

Ferns are ancient plants and have a life cycle consisting of two distinct plants. The plant we generally think of as the fern is in its asexual stage. Spores are produced under the leaves in clusters and are carried away by the wind. If they land on a good spot they germinate and become a tiny heart shaped plant, two cell layers thick, that reproduces sexually. This stage only lasts for a few weeks and is rarely seen by most people. Once fertilized, the plant is in its asexual stage and will grow on top of its dying parent, feeding off the remains.

Tree Ferns (Cyathea spp. Cyatheaceae) are unusual tree shaped ferns only found in Australia, New Guinea, Indonesia, Philippines, New Zealand and some of the South Pacific islands. Tree Ferns are not true trees. Their stems are underground and what appears to be the stem is in fact several layers of compressed frond bases. If you cut off the top of the fern and plant it, the fern will continue growing. There are two species of Tree Ferns in Barron Gorge National Park (Tropical North Queensland): the Scaly Tree Fern (Cyathea cooperi: Cyatheaceae) and the Black Tree Fern (Cyathea rebeccae: Cyatheaceae).

Basket Ferns (Drynaria rigidula: Polypodiaceae) are the most common fern spotted in the Barron Gorge National Park. They are epiphytic and grow on top of trees, just below leafy branches. The falling leaves become compost and nest in the basket shaped structure of the fern. Because of this structure, these ferns capture and absorb lots of water. The largest Basket Fern ever recorded weighed close to 2000kg. Each Basket Fern contains a whole ecosystem of insects and earthworms that aerate the compost. Over 500 species of Basket Ferns have been recorded. Strangler Figs (Ficus spp.: Moraceae) often start their lives inside a Basket Fern.

King Ferns (Angiopteris evecta: Marattiaceae) are considered to be the most primitive fern still around today. King Ferns also have the largest fronds of any plant known, growing up to seven metres long. These ferns never develop a trunk but stand out on the rainforest floor nonetheless. King Ferns normally shun full sun and do best in dappled sunlight.