Tree ferns are a characteristic feature of the New Zealand bush, thriving in the cool moist climate. There are 10 species in New Zealand, with five growing in the park. The two most common are mamaku or black tree fern—with black leaf stalks—arguably the largest tree fern in the world, and ponga, or silver fern, named for the silver underside to the leaf and New Zealand’s unofficial national emblem (first used by the Māori rugby tour of Britain in 1888).
Another, much rarer species, is gully tree fern which is like a tall slender mamaku. These three are Cyathea medullaris, C. dealbata and C. cunninghammii, respectively, and name Cyathea Cove. You may also see a smaller, harsher tree fern called whekī, Dicksonia squarrosa.
Tree ferns grow by forming the very strong woody trunk at the tip, but do not increase in width year by year. However, they do produce new roots from the trunk and can build up a thick fibrous base. Many other plants grow in this fibrous tissue which soaks up water, making tree ferns very important sites for regeneration. The crown of leaves also enclosed a cup-like space that is a favourite nesting place for bellbirds.
Tree ferns usually grow in wet gullies but can also form almost pure forest on shaded slopes. Ponga likes drier places and can form a dense understorey beneath kānuka forest here in the park. As new leaves form older leaves die and fall off so that the ground beneath tree ferns can be devoid of other plants for many years. Eventually however, taller trees take over and shade the tree ferns out and they stand like dead posts covered with other plants and vines.
There is a Māori saying “as one frond dies, another unfolds”: a metaphor for human life. The unfolding tree fern leaf is one of the masterpieces of the plant world.