Mangroves Matter

As seen from the water, mangrove trees may look as tangled as a backlash on a rusty reel. There's nothing to look at, really, just a dense welter of green and brown shrubbery, garnished with white bird poop and swarming with nervous little crabs.

 

 

Where a drifting propagule finds anchorage, a new tree grows.

Still, their ecological importance can't be overstated. Ninety percent of the gamefish and shellfish caught in South Florida waters depend on mangroves at some point in their life cycles. Mangrove leaf litter, falling at an average annual rate of three and a half tons per acre, sustains fungi, bacteria, protozoans, marine worms, copepods, amphipods, shrimp, crabs, mollusks, striped mullet, and, ultimately, much of Florida's economy.

 

The red mangrove, Rhizophora mangle, is the most familiar of Florida's mangroves. It's the one with long, stiltlike “prop roots” projecting from the trunk and branches, arching into the sea like inverted antlers. Its prop roots trap sand and sediments and discourage erosion by the waves and winds. They're also a natural daycare center for larval fish, forming labyrinthine underwater sanctuaries that larger predators can't penetrate.

 

The black mangrove, Avicennia germinans, colonizes upper reaches of the intertidal zone, surrounded by thousands of cigarlike “breathing tubes,” called pnuematophores, that project from the sand, from its shallow, radiating root system. Like the red mangrove, the roots of the black are well-suited for anchoring the soil against tidal erosion and boat wakes.

 

The white mangrove, Laguncularia racemosa, is typically found a little farther inland, at slightly higher elevations.

 

Aerial surveys and mapping of Florida's mangrove wetlands weren't systematically conducted until the 1960s. Before then, no accurate estimates existed of the total area they covered. And since we don't know how many acres we had, it's impossible to say how many we've lost. Some put the figure at 150,000 acres, minimum. Dredging, filling and waterfront development account for most of the loss; altered salinities and declining water quality for much of the rest. Surprisingly, despite the application of modern mapping techniques, how much is left still depends on who you ask; estimates vary from 400,000 to 650,000 acres.

 

Although scattered populations occur as far north as Cedar Key and Cape Canaveral, 90 percent of Florida's mangrove forests are concentrated in Lee, Collier, Monroe and Dade counties. In 1985, the passage of the Mangrove Protection Rule strictly curtailed trimming, removal or defoliation of Florida mangroves. For 10 years it was the subject of bitter complaints from developers and waterfront property owners who found it too restrictive. In 1995, the Florida legislature passed the controversial Mangrove Trimming and Preservation Act, which eases regulations regarding the trimming and management of mangroves, particularly those occurring in “narrow riparian fringes” (mangrove thickets less than 50 feet wide measured perpendicular to the shoreline) on privately and publicly owned land. For ecologists and environmentalists, the revision of the original Mangrove Protection Rule was bitter medicine. Even so, Florida's mangrove habitats are still the most regulated and best protected in the world.

 

Mangroves are hardy trees, generally speaking, and they'll recolonize vigorously under the right conditions. In coastal communities throughout South Florida, a number of mitigation and replenishment projects are successfully undertaken each year, offsetting losses to development. But they're expensive, even on a small scale, and cost effectiveness is always an issue.

 

There's a whole lot more to a restoration project than clearing a site and planting trees. In fact, mangrove replenishment often doesn't involve planting trees at all. On the southwest coast of Florida they take a kind of “Field of Dreams” approach. If you build it—prepare the site properly, that is—the plants, including mangroves, will come. But first you have to clear out the exotics, like Brazilian pepper and Australian pine, repair the site's altered hydrology, lay down a mud or fine-grain sand substratum, and establish topographic elevations conducive to successful colonization by native plants.

 



Rather than plant juvenile mangroves, which are expensive and might be wiped out by an unforeseen freeze, southwest coastal habitat restorations typically involve the planting of “nurse plants,” like spartina, more popularly known as cordgrass. At the Fish and Wildlife Conservation Commission's Port Manatee Fish Hatchery Ponds, where redfish and snook are raised for restocking programs, an extensive spartina grow-out pond is maintained and made available for use by different agencies for various projects. Planted on 3-foot centers, the grasses spread quickly. Within two years they coalesce into dense communities, stabilizing the carefully graded slopes of wetland restoration sites and creating ideal conditions for tide-born mangrove propagules to settle and take root.

 

The effect a mass planting of spartina has on the local ecology is sudden and dramatic. And that's part of the goal. According to Dr. Brandt Henningsen, Senior Environmental Scientist with the Southwest Florida Water Management District, “The faster I can get the plant community to become a component of the food web, the better.” Henningsen has supervised and participated in many of SWFWMD's most extensive habitat restorations. The object is not just to get the site up and running, that is, stable and functional, but to do it as quickly as possible. Then, as he puts it, “You can set it free and let natural processes take place.” Recently he helped the non-profit organization Tampa BayWatch coordinate one of the largest spartina plantings ever undertaken at a Flo

rida restoration site. At Hillsborough County's Fred and Idah Schultz Preserve, 400 volunteers from an international workshop hosted by General Electric planted 14,000 plugs of cordgrass in 35 minutes. The result: instant salt marsh.

 

Down around Miami on the Atlantic coast, different conditions mandate a different approach. Because of the subtropical climate, restoration projects can be undertaken year-round. Land is at a premium and restoration sites are often smaller. Here, projects can involve the planting of red mangrove propagules, or one-year-old nursery-grown adolescent trees, as well as nurse plants like spartina.

 

 

Red mangrove propagules.

But mangrove restoration isn't just large-scale projects, involving the coordinated efforts of multiple agencies and scores of volunteers. It can take place on an individual level with one tree and one consciousness at a time. At least, I'd like to think so.

 

Next time you're out working your favorite stretch of mangrove fringe, you might try the following little exercise: find a break in the trees and stick a red mangrove propagule into the sand, a few inches above the high tide line. Make sure it's a healthy one, green with a brown tip. If you're unsure which end should be down, drop it in the water first. It should float vertically. Now plant it in the same position.

 

For the next year or two, check on it periodically. Maybe it'll survive, maybe not. Either way, there's something to be learned. (continued)

 

Walking Trees Versus a Trio of Storms

 

November 30th came and went, Otto spun itself out in the North Atlantic, and Floridians breathed a collective sigh of relief. While we're still assessing the damage, 2004 will almost certainly be remembered as the most costly and destructive hurricane season in the state's history. The devastation wreaked by four of these storms in a 6-week period may have exceeded even that of Hurricane Andrew in 1992.

 

 

Black mangroves and "breathing tubes."

It's tough to quantify all of the destruction to homes and property, but it's even tougher to weigh the damage done to Florida's environment. A short drive through the heart of the state reveals hundreds of pines snapped in half, massive oaks uprooted and acres of orange trees stripped of fruit.

 

Although mangrove forests on the east coast suffered extensive losses from both Jeanne and Frances, some of the worst devastation occurred on August 16, when Charley slammed ashore at Punta Gorda.

 

According to Jon Iglehart, Acting Director of District Management for the Florida Department of Environmental Protection, South District, severe damage occurred on Sanibel, Captiva and portions of Pine Island. The southern terminus of the Peace River took a grievous hit as well, with many black mangroves snapped off and denuded. Says Iglehart: “This is the most damage we've had since Hurricane Donna in 1960. Our experience with Hurricane Andrew showed us that the negative impacts from a storm (like Charley) may be long lasting, and we still haven't seen them all. We'll probably lose most of the big trees.” In other words, we can expect a decline in Charlotte Harbor's black mangrove population over the next several years. The environmental and economic consequences of this die-off are impossible to predict.

 

Despite the destruction, no new mangrove replenishment projects are scheduled for publicly owned areas. The DEP plans to let most restoration occur naturally. Private efforts, however, are being fast-tracked, with some permits issued immediately, on-site. For DEP to circumvent a process that can take months—and mounds of red tape—is unusual, to say the least. But these are special circumstances, and the agency is responding with due diligence.

FS