Most of Susan Island was cleared long ago - logged for timber, grazed, even used for Grafton's first rifle range. What survived, on the western end, is the largest remnant of lowland subtropical rainforest left in the entire Clarence Valley, a rare patch of an ecosystem now listed as endangered. It is an unlikely survivor. Built on alluvial soil laid down by the river's floods, it gets only about 1,080 millimetres of rain a year - marginal for rainforest, which is why botanists describe it as a "dry" form of the type. Inside grow more than ninety species of rainforest trees: huge Moreton Bay figs, the fearsome Giant Stinging Tree, tulipwood and black bean. Red cedar, logged to exhaustion by the 1920s, was reintroduced in 2001 and is now quietly thriving and reseeding itself.

The island's great spectacle is its flying foxes. Grey-headed flying foxes use it year-round as a roost and, crucially, as a maternity camp - a nursery where mothers carry and raise their young. In a normal summer the colony numbers in the thousands; when the nearby eucalyptus forests burst into blossom, it can swell past 100,000, and in exceptional years beyond 300,000, swollen by waves of little red flying foxes chasing the flowering hardwoods. These are not vermin but pollinators and seed-carriers, stitching the region's forests together on their nightly flights. Above them wheel other rarities: white-bellied sea eagles, ospreys, the jewel-bright wompoo fruit-dove and the shy noisy pitta that hunts snails on the forest floor.

Long before any of this was mapped or protected, Aboriginal people came to the island to fish, to gather food and medicine from the forest, and to collect fibre for nets and bags. To the Gumbaynggirr, Susan Island carries a deeper meaning still: it is a women's site, a place of ongoing cultural significance to the Aboriginal women of the Clarence Valley, who are recognised as its cultural custodians. That standing is not merely informal - the island is officially acknowledged as an Aboriginal Place under New South Wales law. Custodial women still make trips here, where the bats, the rainforest and the women's heritage are bound together as one living landscape.

Keeping the remnant alive has been a long, patient fight against weeds rather than chainsaws. From the late 1980s, parks staff and volunteers began clearing the invaders that smother northern rivers rainforest - camphor laurel, broad-leaved privet, and the curtain-forming exotic vines like cat's claw creeper and Dutchman's pipe that blanket the canopy until it sags and collapses, dragging the trees down with it. Early on, crews had to hack through dense prickly pear just to reach the forest at all. Decades of steady regeneration have slowly expanded the rainforest and let the natives recover, the reintroduced red cedar now reseeding itself among figs that predate the town. The reward is an island that still works as nature intended: a rare endangered ecological community, a wildlife nursery, and a place of deep cultural meaning, all within sight of a country town's main street.