|Image by Lanare Sevi|
Each species commonly grouped together under the mangrove lifestyle has differing tolerances to saltwater; they use various strategies to block absorption or to excrete dangerous salt from their tissues. They also grow in slightly different environments. Mangroves don’t need saltwater to live, they just tolerate it much better than other plants. It’s a great advantage and an evolutionary strategy that rids them of competitors. Some must have primarily freshwater or water that is only slightly brackish to survive.
Other mangroves are found closer to
the sea, and some can grow in pure seawater. Many mangroves excrete excess salt
via pores along the undersides of their leaves or from their twigs, while
others have impermeable leaf surfaces that physically block the salt.
|National park Service/Image by G. Gardner|
Mangrove forests are imperiled worldwide due to coastal development, harvesting for timber and fuel, and the catastrophic effects of increasingly powerful hurricanes. Mangroves have declined in most areas due to human activities, but the warming climate is allowing them to colonize places that, until recently, were too cold for them to survive.
|National Park Service/Image by G. Gardner|
The forests historically covered much of coastal South Florida, its offshore barrier islands, and the Keys. Rising sea levels will allow them to grow on land that was last submerged 2.5 million years ago. Drive along U.S. highway 41, the Tamiami Trail, west of the Big Cypress Swamp to see stunted Red Mangroves, the recent pioneers of a swamp that is gradually turning salty.
Sometime within this century, most, if not all, of low-lying South Florida will once again become submerged by a shallow sea, as it has been at least four previous times in the geological history of North America.
Pinecrest Gardens’ artist-in-residence, Xavier Cortada, has developed a conceptual project to remind us of this. As part of The Mangrove Project, he has distributed mangrove seedlings, painted a Garden mural depicting Red Mangroves, and collaborated with the Gardens to plant the world’s first upland mangrove forest. Hundreds of Red, Black, and White Mangroves have been installed adjacent to the mural. It’s thought that the cultivated mangrove forest will survive to grow, in the future, in the newly-returned sea.