By observing the water flow in Iao Stream, Ray Neilson can tell what the weather is like six miles away, high in the mountains of Iao Valley on Maui.

“;Since this morning, the water level has gone up by about a third,”; he says as we stand beside the stream on the grounds of the 35-acre Hawaii Nature Center. “;It's a bit murkier, and there are leaves floating in it, which indicate it's raining up there. If a flash flood is coming, you'll see a lot of debris, the water will be running fast and as deep as four feet, and it'll be the color of chocolate milk because heavy rains are washing soil into it. It'll also have a strong earthy smell.”;

Neilson is my guide for the center's Rainforest Walk, which spotlights dozens of native and introduced plant species, including guava, hala and kukui, Hawaii's state tree. All along the 90-minute, 1.5-mile tour, he shares tidbits about the greenery, which grows so thick in some areas it blocks the sun.

THE EARLY Hawaiians wove the leaves of the ukiuki into cordage and used its berries to dye tapa. Awapuhi flowers yielded a fragrant substance for shampoo and perfume. From ohia ai trees came succulent mountain apples and strong, straight poles for houses. Dancers gathered palapalai ferns for adornments and offerings to place on altars dedicated to Laka, goddess of the hula.

Kahuna lapaau (healers) brewed dried mamaki leaves into a tea that purportedly lowers blood pressure. “;Today there are still Hawaiian practitioners who rely on the power of plants to heal,”; Neilson says. “;They and their families have been coming to Iao Valley for generations to gather medicine.”;

He plucks a fruit from the papala kepau tree and asks me to touch it. It's as sticky as glue.

“;Bird catchers would put the sap on the favorite perches of birds in the forest,”; he says. “;When the birds landed on those branches, they would be stuck there, enabling the bird catchers to remove the feathers they wanted for capes, cloaks, helmets and other items worn by the alii (royalty). They used kukui nut oil to clean the birds' feet.”;

Unfortunately, coffee, thimbleberry, banana poka, basket grass and other invasive introduced plants are threatening the natives. “;We're engaged in an ongoing battle here,”; Neilson says. “;Volunteers ranging from kindergartners to kupuna (elders) are participating in our service project to remove the invasive species and replant the natives.”;

As one ninth-grade group from Kamehameha Schools' Maui campus was uprooting a big patch of thimbleberry last year, they discovered a lone mamaki shrub making a valiant stand in the middle of it. “;That showed the kids how the invasives are overwhelming the natives and absorbing all the nutrients and sunlight,”; Neilson says. “;We're trying to help the natives reclaim their place in the forest, but it's been a tough, uphill fight.”;

In olden times alii were laid to rest throughout Iao Valley. Although this lush, tranquil sanctuary was considered sacred and kapu (off limits) to most commoners, there were a few exceptions. Kahuna (priests), farmers and cultural practitioners were allowed in the valley to prepare the burials and tend the taro loi (patches) that provided them with food.

OVER THE past two years, hundreds of volunteers have been clearing the ancient loi and auwai (irrigation ditches) as part of Loiloa (Long Kalo or Taro), a joint project of the center and cultural advisers from Maui's Hawaiian community. The first taro crop was planted in July, and will be ready to harvest early next year.

According to Jay Franey, the nature center's Maui programs manager, the oldest evidence of human activity in Iao Valley dates back to A.D. 900. It's not known when the loi were built, but scholars believe they have not been used for more than a century.

“;We envision restoring three acres of loi as an outdoor classroom to teach the Hawaiian model of sustainability,”; Franey says. “;I've supervised many groups there, using the restoration work as an opportunity to point out the skills and insights the Hawaiians had for utilizing the precious resource of water.”;

The goal of the center's programs is to provide a positive outdoor experience for participants. Doing that, Franey believes, will inspire them to become dedicated stewards of the environment.

“;It's natural for people to want to protect something they enjoy,”; he says. “;If visitors leave the center embracing the notion of malama aina (caring for the land) not only in Hawaii, but wherever they live, we'll feel we've accomplished our mission.”;