Carolyn Beans

PNAS December 26, 2018 115 (52) 13138-13141

Ilka Feller has a penchant for mangrove hunting. Since the early 2000s, Feller, an ecologist at the Smithsonian Environmental Research Center, has periodically gone road-tripping in search of the northernmost mangrove tree in Florida. The red mangrove, Rhizophora mangle, has draping roots that hold fast in the tide. But all three of Florida’s mangrove species anchor themselves and whole ecosystems—protecting the shoreline from erosion, forming nurseries for fish, and sequestering carbon.

Globally, mangroves are threatened by coastal development and shrimp farming. “More than half of the world’s mangroves have already been destroyed,” says Feller. Yet in Florida, Feller kept finding new mangroves farther and farther north, “solitary plants that are out there in this forever saltmarsh.”

As part of a 2014 study, Feller’s then postdoc, Kyle Cavanaugh, analyzed satellite images taken from 1984 to 2011 and saw that mangroves were indeed advancing northward (1). The spread was associated with a reduced frequency of extreme cold events. Climate change, it seemed, was replacing marshland, an important temperate ecosystem, with mangroves, an important subtropical and tropical one. But had they really revealed a trend pointing in one direction, or was the recent expansion of mangroves part of a continual cycle of mangrove and saltmarsh replacing one another? Feller needed more than just conventional scientific data to find out.

So she dug into Florida’s past using tools more typical of historians. She found mangroves mentioned in the texts of famed naturalist John Muir, uncovered data in tourist photos, and parsed the writings of war surgeons and beekeepers.

Feller and a growing group of ecologists are piecing together historical records to understand how ecosystems have changed over timescales that extend beyond the memories of the current generation of researchers and residents. These portals to the past can help researchers better predict and plan for the future. But as historians already know well, ecologists first have to figure out how to find these records and whether to trust them.

See more: https://www.pnas.org/content/115/52/13138

Figure: Ecologist Ilka Feller used archival records to investigate whether mangroves in Florida, like these in Indian River Lagoon, are expanding into new territories or returning to a historical range. Image credit: Ilka Feller.