Brazil nuts, the traditional Christmas snack, are threatened by overharvesting, researchers say.

Conservationists say at least a few of the brown nuts need to be left behind to grow into trees to save the stocking stuffers.

Unlike other commercially available nuts, Brazil nuts are grown exclusively from wild trees in the Amazon.

Since the trees can live 500 years or longer, harvests won't decline soon. Mature Brazil nut trees can produce hundreds of softball-sized fruit containing 10 to 25 seeds or "nuts."

In fact, scientists encourage people to buy the nuts, since the industry depends on rainforest preservation, not destruction.

The key is to ensure more Brazil nuts grow into young trees, the researchers found.

"It's a very simple message," said tropical forestry Prof. Karen Kainer of the University of Florida. "If you collect too many seeds, you're not going to have seedlings."

Kainer and her colleagues at the Wildlife Conservation Society and the University of East Anglia in Britain surveyed tree populations.

Scientists measured 23 natural Brazil nut tree populations in Brazil, Bolivia and Peru and compared the results to a century of historical data.

They found populations that were heavily harvested for decades were dominated by older trees with few young ones. Computer models supported the observations.

The pattern suggests the trees' normal regeneration cycle has been disrupted, according to a study in Friday's issue of the journal Science.

The researchers suggest:

  • Closer monitoring of the tree populations.
  • Managing the annual seed quota.
  • Rotating harvest areas.
  • Planting seeds or seedlings.
  • Controlling herbivores to give the seeds a chance to germinate.

They concluded intensive harvesting is a concern but more immediate problems such as deforestation pose a greater threat to Brazil nut trees.