BELEM, Brazil — A frenzy overtakes the teeming harbor here as a wooden-hulled riverboat chugs into port.

“It’s here!” cries an expectant buyer, one of many shoving his way toward the craft in a sweaty mercantile crush. “The gold! The purple gold!”

The cargo is acai (pronounced ah-sigh-EE), the unassuming fruit of a jungle palm that has gone from Amazonian staple to global wonder-berry: a much-hyped ingredient in smoothies, sorbets, nutrition bars and countless trendy treats from Los Angeles to London to Tokyo.

Acai’s cachet derives not only from the berry’s antioxidant traits but from its green pedigree: It has been acclaimed as a renewable resource that provides a livelihood for tens of thousands of subsistence harvesters without damaging the expanses of the Amazon.

With acai a global sensation, however, some fear the berry’s runaway success may spell trouble for the rain forest.

International conglomerates are elbowing their way into the acai trade, while traditional cultivators are intensifying production at the expense of other trees. Conservationists worry that acai could succumb to the destructive agribusiness model.

“There’s a kind of ‘green deforestation’ to plant acai,” says Alfredo Homma, agronomist with the Brazilian Company for Agricultural Research, a publicly funded institute. “They don’t bring down all the trees and leave the area deforested. They bring down diverse forests and replace them with one single culture — acai.”

For generations, men such as Domingos Bravo Rosa have harvested the berry in the dense forests across the river from downtown Belem, a onetime rubber boomtown that is now the capital of the Amazonian state of Para.

“We don’t destroy the forest,” says Rosa, 44, a lifetime acai harvester. Rosa knows where to find the acai; a single palm is often hidden among a score or more of other trees.

A different model of acai harvesting is found on neighboring Murutucu island. Here, Ben-Hur Borges, a forest engineer turned acai entrepreneur, proudly displays the 1,350 acres of elegant groves that supply his firm, Amazon Fruit, a major exporter of acai to the United States and Europe.

The sprawling plantation resembles the kind of acai “mono-culture” that is anathema to conservationists. But Borges argues that his success demonstrates how more than one version of acai production can thrive, with both environmental and social benefits.