Nature – Land-Building Mangroves

Some shores are built by trees. The unique mangroves grow in places where other trees and shrubs cannot survive—in the wet, salty world of tide-washed tropical and subtropical seas. Along such coasts, mangroves have created virtual jungles on stilts.

Most trees produce seeds that do not sprout immediately, even if they are planted. But one of several mangrove species, the red mangrove, produces exceptional seeds—they sprout while they are still attached to the branch. A root bursts through the fruit and forms a long, dagger-like point that may reach nine inches in length. When the seed finally detaches from the branch, it falls, often planting itself upright in the soft, muddy bottom.

A mangrove seedling floats horizontally in the water, like a well-designed canoe. (You may see one drifting along a tropical beach.) The seedling can float for months, unaffected by salt water, scorching sun, and battering waves—and even continue to grow. Its sharp root tip turns downward; if the seedling strikes land, it quickly sends roots into the soil. New roots emerge in tiers that extend out and downward from the trunk, forming arches, called prop roots, that resemble umbrella stays. The prop roots may send up new trunks where they touch the ground. Red mangroves are so well braced that they can usually weather hurricanes that flatten other trees.

In 20 or 30 years, the red mangrove reaches its maximum height of about 30 feet. The profusion of prop roots and new tree trunks form a dense, interlacing mesh that traps sediment, plants, and debris. Soon a swamp is formed at the edge of the sea. Gradually, as more mangroves sprout up, new land is created. Every year, the land advances a few inches into the sea.

There is a definite sequence to the seaward march of a mangrove swamp. In the Florida Keys, where mangroves have built vast areas of new land and new islands, you will see the youngest and smallest red mangroves growing next to the water. Their roots are usually submerged, except during the lowest tides. Behind them, washed only by high tide, are the taller mangroves, which grow to 70 feet. Their thick branches and dark, dense foliage form a nearly solid canopy.

Trees and other plants more typical of the land grow behind the mangroves, but in the swamps, mangroves usually crowd out other vegetation. Numerous animals depend on mangroves for protection and support. Oysters attach themselves to the prop roots, where they are covered by high tides. At night these oyster beds are raided by raccoons. Fiddler crabs burrow in the mud between the roots; starfish move slowly over the muddy surface. High up in the dense canopy, large colonies of pelicans and herons may roost and nest. But even while one mangrove swamp, with its dependent animal life, pushes slowly out to sea, another one may be just beginning where a single seedling washes against a distant shore.

Joy of Nature, Reader’s Digest Association, ©1977, 132, 133.

“The plant grows by receiving that which God has provided to sustain its life. It sends down its roots into the earth. It drinks in the sunshine, the dew, and the rain. It receives the life-giving properties from the air. So the Christian is to grow by cooperating with the divine agencies. … As the plant takes root in the soil, so we are to take deep root in Christ. As the plant receives the sunshine, the dew, and the rain, we are to open our hearts to the Holy Spirit.” Christ’s Object Lessons, 66, 67.