Mangroves, known to be sensitive to cold, have expanded dramatically on Florida's Atlantic Coast as the frequency of killing frosts has dropped, scientists say.

Between 1984 and 2011, the Florida Atlantic coast from the Miami area northward gained more than 3,000 acres of mangrove forests, researchers from the University of Maryland and the Smithsonian Environmental Research Center in Edgewater, Md., reported Monday.

The study illustrates how changes in the frequency of rare, severe events can determine whether landscapes hold their ground or are transformed by climate change, the university said in a release.

The mangrove forests are edging out salt marshes, UM entomology Professor Daniel S. Gruner, a study co-author, said.

"This is what we would expect to see happening with climate change, one ecosystem replacing another," he said. "But at this point we don't have enough information to predict what the long term consequences will be."

Any change in an area's ecosystem should be the subject of close study, the researchers said.

"Some people may say this is a good thing, because of the tremendous threats that mangroves face," lead study author Kyle Cavanaugh, a Smithsonian postdoctoral researcher, said. "But this is not taking place in a vacuum. The mangroves are replacing salt marshes, which have important ecosystem functions and food webs of their own."

Mangrove forests and salt marshes fill the same ecological niche in calm, shallow coastal waters, the researchers said, with mangroves in the tropics and salt marshes in temperate zones.

Providing valuable ecosystem services including buffering floods, storing atmospheric carbon and building soils, both mangrove forests and salt marshes are in decline nationally and globally, threatened by urbanization, aquaculture, drainage, polluted runoff and rising sea levels, the researchers said.