Piles of garbage left by humans thousands of years ago may have helped form tree-covered biodiversity hot spots in the Florida Everglades, according to a new study. The authors say the findings show that human disturbance of the environment doesn't always have a negative consequence.

The so-called tree islands of the Everglades are patches of relatively high and dry ground that rise from the wetlands. They stand between 1 and 2 meters higher than the surrounding landscape, can cover 100 acres or more, and host two to three times the number of species living in the surrounding marsh. Besides providing habitat for innumerable birds, the islands offer refuge for animals such as alligators and the Florida panther during flood season.

Previously, scientists had presumed that many of the larger tree islands, which have a veneer of peaty soil, formed atop topographical high spots in carbonate bedrock underlying the Everglades. But research reported today at a meeting of the American Geophysical Union in Santa Fe suggests that the real foundation for some of these islands may be prehistoric trash heaps, known as middens....