They were known as the Spade Brigade: thousands of volunteers, from different walks of life, armed with garden tools. Together, they transformed Tiritiri Matangi from a virtually birdless, treeless island to a world-renowned forest sanctuary in the Hauraki Gulf.

For a decade from 1984, people from forest and bird groups, tramping clubs, church groups, schools and families would make the sometimes testing boat trip to the island off the end of the Whangaparaoa Peninsula to dig - planting around 300,000 native trees and shrubs.

The Spade Brigade's toil became a model of community conservation other groups still replicate, not only in the Gulf and mainland Auckland but around the globe. Today, Tiritiri Matangi is held up as one of the most successful conservation projects in the world.

For more than a century, the 220ha island was a working farm, stripped of almost all its native flora and fauna, bar a few tui and bellbirds and a scattering of pohutukawa trees along clifftops.

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In 1970, it became a recreation reserve in the Hauraki Gulf Maritime Park, but it wasn't until John Craig, a young zoology lecturer at the University of Auckland, visited the island, that its unique restoration plan was born.

With the help of botanist Neil Mitchell, Craig organised some of his students to carry out scientific research on Tiritiri and came up with a remarkable strategy to replant a forest; their vision was to see thousands of native birds (some on the verge of extinction) repopulate the island and people walking among them.

Ray Walter, the last keeper of Tiritiri's grand lighthouse, managed the restoration project when it began in 1984, growing trees from seedlings in his nursery. His wife Barbara organised Spade Brigade volunteers.

Three decades on, 65 per cent of the island is covered in bush, rats have been eradicated and the canopy has closed over. Native birds, reptiles, and now insects, are thriving; the Supporters of Tiritiri Matangi, an evolution of the brigade, has 1600 families as members. Chairman John Stewart says he is continually amazed by what they have achieved by creating an open sanctuary.

"But there's still so much to do - it's hard to persuade people that 25 years is nothing in the life of a forest. It's a 100-year project and things will still be changing even in a century's time," he says.

Matt Rayner in the field. Photo / Supplied
Matt Rayner in the field. Photo / Supplied

Volunteers are being asked to bring their spades back again. Part of the island's biodiversity plan is to attract burrow-nesting seabirds, once prolific in the Gulf. It would mean digging artificial burrows into Tiritiri's hard banks - topsoil has been lost through erosion - and installing loudspeakers to play the seabirds' calls.

Other community groups have followed Tiritiri Matangi's lead - including the Motuora Restoration Society who have also planted 300,000 trees on Motuora Island, now used as a "kiwi creche" by Operation Nest Egg. Friends of Maungawhau band together for the protection and conservation of Mt Eden's volcanic cone, while Friends of the Whau in West Auckland work to restore the Whau River's natural ecology.

There is still some way to go, says Matt Rayner, curator of land vertebrates at Auckland Museum. "There's a serious mismatch with how we use the environment and how we value it, which stems from our settler legacy - that the environment is something to be consumed.

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"In New Zealand, we're still riding the crest of our wave of damage."

Bold steps needed

"The [Hauraki] Gulf has undergone an incredible transformation over two human lifespans. That transformation is continuing in the sea and around the coast, with most environmental indicators either showing negative trends or remaining at levels which are indicative of poor environmental condition. Further loss of natural assets will occur unless bold, sustained and innovative steps are taken to improve the management and utilisation of its resources, and to halt progressive environmental degradation." - State of our Gulf, 2011