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For the last quarter century, Michael Ross, a landscape ecologist at Florida International University, has been visiting the same stand of mangroves on southern Biscayne Bay, year after year, taking students to record the recovery of a forest wiped out by Hurricane Andrew.
Today, the destruction of a quarter century ago is invisible to passing boaters and nobody else in their right mind — aside from Ross and his students — would willingly endure the agony of hiking here on foot. It means muscling through the head-high thickets of mangroves, sinking into knee-deep muck and slapping at clouds of salt marsh mosquitoes.
But what Ross has documented over the years has been dramatic — the little-known cycles of a vital South Florida ecosystem healing itself from what looked like a fatal wound. Everywhere, the coastal forest lay dying, trees amputated at their bases. There were years of rot, the slow sprout of seedlings, then the biggest growth spurt ever recorded in a mangrove forest, along with a see-saw shift in species, before everything balanced out again. But at a only one-third of the coastal forest’s orginal height.
Cat 5 Andrew transformed the way people live and worked in South Miami-Dade, but that natural disaster also altered the landscape in ways Ross is still working to understand.
It’s what keeps drawing him out to the same spot on a quest to understand what happens when a forest goes away, comes back and then faces a new threat, like sea rise.
“Right now all you can say is there hasn’t been enough time for them to get that large. I can’t go any further than that,” said Ross, who has produced a number of published studies from the mangrove forest research.
What he learns matters because mangroves are disappearing faster than any other tropical ecosystem, including coral reefs and rain forests, but play an increasingly vital role in saving South Florida from the perils of climate change, not to mention more hurricanes. They not only prevent erosion, but cool the planet and suck up huge quantities of carbon. A 2016 study valued that service at between $2 and $3.4 billion. Coastal communities are also taking a closer look at including mangroves in sea rise resiliency efforts.
Ross first visited the South Dade coastal forest south of the C-102 canal as a National Audubon scientist studying the damage done by South Florida’s massive drainage system on the Everglades.
Before the landscape was carved up by canals in the 1950s and 60s, water streamed across marshes, or transverse glades, in sheets into Biscayne Bay, replenishing freshwater tidal creeks and freshening the shallow coastal waters. But afterward, the canals dumped water in single big, damaging gulps. Over the years, the sawgrass was replaced by a forest of dwarf mangroves that began depositing layers of peat.
Ross wanted to test whether it was better to restore flows “in 100 little places or five to six strategic places where it can stay a long time.” But just after he and his partner, Jack Meeder, negotiated a contract with the South Water Management District to start work, Andrew hit.
The hurricane knocked down 95 percent of the towering trees but left the dwarf forest nearly completely intact.
“The dwarf trees still had leaves on them,” he said.
At first, assessing damage was almost impossible, with trees splintered and strewn amid the rubble in twisted piles.
“It was very difficult to get a real good perspective of the whole landscape, which species were where, because it was impossible to work very extensively,” he said. “If you were trying to walk to the ocean from the L-31e, you had to walk over these piles of trees that were 10 to 15 feet high.”
When he and Meeder finally got the project underway in 1993, the only thing growing were seedlings that had already taken root before Andrew.
“They were the tallest thing out there,” he said.
Since he hadn’t had a chance to begin his work before the storm, Ross measured downed trees, finding some between about 65 and 75 feet tall. For the next nine years, he and other FIU scientists carefully documented growth rates and which species fared better, erecting a tower to hoist themselves up to the tallest trees.
“We’d tie ourselves in and go up,” he said. “When you get in that environment, it’s like nothing you’ve ever seen. The insects are like nothing you’ve even seen before. Just being in a canopy like that is really awesome and that was when it was only [16 to 20 feet] high….There’s definitely a whole suite of things that live in it and it hasn’t been explored very much.”
They also dragged two-by-fours through the mangroves to build boardwalks so they could run experiments without stumbling in the muck and tangle of roots. During eight-hour shifts, day and night, they measured water heights at every tide, hunching over burning mosquito coils to ward off swarms of marsh mosquitoes. They also mapped out plots, and labeled every seedling they could find.
“So this was either a triumph or a nightmare,” Ross said. “Some people hated it and thought it was boring. I always liked it.”
By 1996, the red mangrove forest that thrives in shade was beginning to be replaced by more white mangroves. But once it grew high enough to provide a canopy, red mangroves quickly caught up and once again dominated.
Over the next year, the forest experienced the fastest regrowth ever recorded anywhere. And while the reds got hit the hardest, and initially rebounded the slowest, Ross discovered Mother Nature has a way of hiding her cards. In the understory of the old forest, a seed bank lay in waiting. Ten years after Andrew, they grew into the new forest that while smaller than the forest before it, still functions as a mature forest.
Andrew also offered a rare glimpse into the impenetrable forest that scientists have always struggled to monitor. There’s a reason trails don’t go through mangrove forests. In the dwarf forest, the floor, a muck of shoe-sucking peat, is covered with water stained dark brown by root tannins. As the trees get taller, so do their roots, becoming an obstacle course of arching thigh-thick trunks. There’s a quiet beauty to enjoy standing still. But movement is work. On a July outing with five students, three turned back as Ross splashed down a tidal creek of black water, stumbling chest-deep into sinkholes hiding who knows what.
Up until Andrew set the clock back, scientists typically had to approximate how a young forest behaved. Watching it recover, gave them a more nuanced view.
Ross is now keeping an eye on sea rise, the latest slow-motion threat to South Florida. Since the 1920s, sea levels around South Florida have risen about six inches, causing saltwater to creep inland. He’s already starting to see the effects in the Keys’ pine rocklands and along the Shark River in Everglades National Park, where mangroves on the move are overtaking freshwater marshes. Since Andrew, the water management district has installed pumps to put more water back in the coastal marshes while it awaits completion of an Everglades restoration project in 2021. Fixing the water flow may stem the damage, but so far it’s not yet clear how much.
“To reverse the whole process,” Ross said, “will probably take a lot more freshwater than they have now.”