Trash mounds left behind from human settlements that date to about 5,000 years ago could have triggered the development of the islands, elevated above the Everglades enough for trees to grow and provide nesting sites for alligators and a refuge for birds, panthers, and other wildlife, a release by the American Geophysical Union said Monday.
Dotting the marshes of the Everglades, tree islands are typically 3 to 4 feet high.
Ancient trash piles, a mixture of bones, food discards, charcoal, and human artifacts such as clay pots and shell tools, would have provided an elevated area, drier than the surrounding marsh, allowing trees and other vegetation to grow.
Bones would have provided phosphorus, a nutrient for plants that is otherwise scarce in the Everglades, researchers say.
"This goes to show that human disturbance in the environment doesn't always have a negative consequence," said Gail Chmura, a paleoecologist at McGill University in Montreal, and one of the authors of a study being presented at an AGU conference in Santa Fe, N.M., on Tuesday.
The researchers warn that humans are now threatening many tree islands by cutting down trees whose roots keep the islands bound together and by artificially maintaining high water levels year-round in some water control systems.