Image: Grasshopper on seedling
Paul V.A. Fine  /  University of Utah
A grasshopper sits on a tree seedling in a white-sand forest in the Allpahuayo-Mishana National Reserve, near Iquitus, Peru.
updated 7/29/2004 5:17:35 PM ET 2004-07-29T21:17:35

Insects chowing down on trees may not be such a bad thing after all, at least in tropical areas where they can help increase plant diversity.

That’s the conclusion of a new study that found insects help keep some faster-growing trees from taking over and driving out slower-growing trees, thus helping preserve the diversity of the forest.

The report, by doctoral student Paul Fine and biology professor Phyllis Coley of the University of Utah, is being published in Friday’s issue of the journal Science.

“The battle between plants and insects increases the number of habitats in the rainforest,” thus increasing the diversity of trees living there, Fine said in a statement.

The researchers studied trees growing in the Amazon jungle of Peru, comparing trees in nutrient-poor white sand soil with those in rich red clay soil.

They transplanted trees from each type of soil to the other, using nets to protect some trees from insects and allowing others to fend for themselves.

Trees transplanted from red clay to white sand did well — even better than trees normally growing in white sand — but only when protected from insects. They did poorly when cicadas, beetles and other plant-eaters were allowed to chomp on them.

The researches said that indicates that if not for the insects, these trees would be able to outgrow other trees and dominate both habitats.

Trees from the white sand soils, which invested more energy in defending themselves from insects, grew slowly in both habitats, but protecting them from insects made little difference.

“A plant can’t be extremely well-defended from insects and grow very fast,” said Fine. “It’s similar to why you can’t have the heaviest, safest car and the fastest car.”

While trees that normally grow in the rich red clay also are attacked by insects in their normal areas, the soil is so rich that the trees grow faster than they are consumed. Plus, other insects and birds in the red clay forest help control plant-eating insects.

In a commentary on the paper, Robert J. Marquis of the University of Missouri at St. Louis, who was not part of the research team, said the study provides strong support for the idea that herbivores, such as insects, contribute to maintaining species diversity, though they are probably not the only factor.

The research was funded by the U.S. National Science Foundation.

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