Tree deaths linked to rise in sea level

Rising sea levels threaten to kill coastal forests around the world.

October 20, 1999
Web posted at: 12:46 p.m. EDT (1646 GMT)

Coastal forests in developed areas around the world are threatened by rising sea levels, according to research published in the September issue of the journal Ecology.

The research was conducted along the extremely flat west coast of Florida where the average 1.5 millimeter annual rise in sea level turns two meters of forest to salt marsh each year.

"What this does for me is bring home the global problem of sea level rise," said Francis Putz, a professor of botany at the University of Florida and co-author of the study.

Rising sea levels expose coastal forests to increasing amounts of salt water. In the same manner that a human cannot hydrate from seawater, trees cannot survive either, said Putz. "You get disruption of biochemical processes."

While sea levels have gone through periods of rise and fall over the years, the development of homes and farms along the coastline impede forests from growing anew on higher ground further inland.

"With all the development, forests are stuck between the devil and the deep blue sea," said Putz. And the developers — i.e., humans — are most likely to blame for the global warming that has sped up the process of sea level rise in recent years.

Researchers note the death of trees in a coastal forest due to sea level rise

Putz and his colleagues began the project seven years ago at the Waccasassa Bay State Preserve south of Cedar Key, Fla. They divided forested islands of differing elevations into 400-square-meter plots. They then 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.

"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 researchers write in Ecology.

The researchers also found that 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.

The study shows how sea level rise threatens coastal forests around the world where the forests are sandwiched between the ocean on one side and residential areas or farms on the other, said Putz.

While the flatness of Florida's west coast enabled the researchers to drive home the problem of sea level rise, the same thing is happening around the world. If people want to have coastal forests in the future, they should ensure that there is space for the forest to renew itself inland, said Putz.

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