Strangler fig

The first thing to learn in a rainforest is a tree that does not begin as a tree. A strangler fig starts life as a single seed wiped from a fruit-pigeon’s gut onto a high fork of some other tree, dozens of metres up. On the Blackall Range it is most often the Watkins’ fig, Ficus watkinsiana. There is a reason for the peculiar address. The floor of a closed rainforest is one of the dimmest places in nature, and a seedling that germinates down there faces years of waiting in the dark for a gap to open overhead. The fig refuses to wait. By starting high, in a pocket of leaf litter trapped in a fork, it stands in the light from its first day. It is choosy about its host, too, favouring big, rough-barked trees whose furrows cradle the litter and moisture a seedling needs. From there it sends slender roots groping down the trunk toward the soil far below.

The moment those roots touch the ground, the fig begins to grow in earnest. It thickens, branches and fuses into a lattice, wrapping its host in a living cage of its own roots that tightens and shades a little more each year, until the original tree, starved of light above and girdled at the trunk below, dies and rots away inside. What remains is the fig: a hollow woven cylinder, a tree-shaped absence where another tree used to be. It is a patient killing, and it can take a century.

For all that drama, the fig can manage none of it alone. It leans, at both ends of its life, on partners it cannot do without. It needs an animal to deliver its seed aloft, because a seed that merely drops to the ground has landed in the wrong place; without a frugivore to carry it up into a fork, the strangler has no way to begin. And it needs its own particular wasp. Each species of fig is pollinated by one species of tiny wasp, an obligate connection tens of millions of years old and sealed in the dark inside the fruit: no wasp means no fig seed, and no fig means no wasp. (The wasp’s side of that connection belongs with the coast’s other great partnerships.) The most ruthless tree in the forest turns out to be one of the most dependent.

And what the forest gets back for hosting such a tenant is a larder. A big fig in full fruit ranks among the rainforest’s most important food sources, feeding wompoo and rose-crowned fruit-doves, nomadic flocks of topknot pigeons, bowerbirds and flying-foxes all at once — the animals that carry the forest’s seed between trees, and between one patch of forest and the next. Better still, figs keep no common calendar: different figs, and different individual trees, come into fruit at different times, so a forest with its figs intact almost never has a month when nothing is bearing. That steady, out-of-season fruit is the reason the strangler is counted a keystone. Lose it, and the forest’s seed-carriers lose a mainstay they cannot easily replace.

The strangler cheats the darkness of the closed forest, climbing to the light on another tree’s back, then spends the rest of its life at the mercy of a pigeon and a wasp. A killer, and the tree the forest can least afford to lose.