Writer: Aaron Hoover
Source: Francis Putz, (352) 392-1486, firstname.lastname@example.org
GAINESVILLE, Fla. --- When University of Florida researchers first looked into Florida west coast residents' complaints of dying palms, they thought the cause was a disease.
But in a landmark study recently published in the journal Ecology, a team of UF and U.S. Geological Survey researchers concluded the cabbage palms and many other coastal trees are falling victim to saltwater exposure tied to global sea level rise. The phenomenon may be a more immediate threat to coastal forests on Florida's west coast than commonly recognized, partly because small increases in sea level can affect large areas of extremely flat coastline on the west coast, and partly because development and farms impede forests from growing anew on higher ground further inland, the researchers say.
"What this does for me is bring home the global problem of sea level rise," said Francis Putz, a UF professor of botany and member of the team that worked on the project.
The research team launched the project seven years ago at the Waccasassa Bay State Preserve south of Cedar Key in Levy County, dividing forested islands with differing elevations into 400-square-meter plots. They tagged and counted all the trees and seedlings and monitored groundwater salinity and tidal flooding. Over the next three years, they returned to the sites periodically to note changes to the tree populations and correlate them with measurements of tidal flooding and changes in groundwater salinity.
Despite the relatively short duration of the study, many trees died by the end of the field research. Although some of the deaths were attributed to the 1993 Storm of the Century, some occurred before the storm.
"Trees died during the course of the study in several island plots, changing community composition ... Southern red cedars were lost from two of the four most frequently flooded stands, leaving cabbage palms as the only tree species in three plots," the study said, noting that the cabbage palms were usually the last trees to die.
Perhaps more worrisome, the researchers also found even when older trees and palms survived, they often failed to produce new seedlings, effectively making them the last generation of trees on the once densely forested islands.
"Elimination of tree regeneration may precede the death of established trees by many decades," the study says. "For cabbage palms ... the stand with fewest surviving trees is estimated to have suffered complete regeneration failure around 80 years ago."
Kimberlyn Williams, a member of the research team and former assistant professor at the UF department of botany, said researchers do not have enough information yet to determine whether the tree die-off rate and forest retreat is faster now than in the past. She noted that sea levels have been rising for the past 10,000 years but that many scientists fear global warming has sped up the process in recent years. She added that rising sea levels may not be the only contributor to the demise of the coastal forest.
"Things such as drought and a reduction in freshwater flow to the coast may have accelerated the process -- we can't tell yet, but it's definitely a possibility," she said.
Whatever the case, the process is happening relatively quickly, especially by the standards of geologic time. Sea levels are rising an average of about 1.5 millimeters each year globally, a seemingly small increase. But on the large areas of Florida's west coast which have little or no slope, this small increase is converting as much as 2 meters of forest to salt marsh annually, Williams said.
The forest retreat threatens many coastal parks and nature reserves, such as Waccasassa Bay State Preserve, because the reserves are sandwiched between the ocean on one side and residential areas or farms on the other, Putz said. If Florida wants to have coastal forests, it should plan ahead and buy forested areas now inland of the reserves, he and Williams said. Putz added that sea level rise also is likely to be killing trees on Florida's east coast, but that the area is harder to study because of tidal fluctuation.
In addition to Putz and Williams, the research team consisted of Katherine Ewel, a former UF professor in the school of forest resources and conservation; Richard Stumpf, a researcher at the U.S.G.S. Center for Coastal Geology and Regional Marine Studies in St. Petersburg; and Thomas Workman, formerly a UF graduate student.
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