Do Mangrove Trees Walk?

In this zone where fresh water meets salt water between high and low tides are found close to some 30,000 hectares of mangroves. This area is neither liquid nor solid, rather a slow reclamation of land from the sea. How does this happen? The development or expansion of a mangrove region is most unique. How does a single mangrove become a village of walking stilt trees? Mangrove seeds are shaped like plumbs bobs that germinate while hanging from the tree. First, a flower blooms for several weeks followed by the fruit which then spawns the seedling shoot. The shoot grows up to a foot long before falling to the ground or water. If it falls at the low tide, it drops like a dart into the mud and puts out roots immediately. If instead it falls into water, it may float, scouting for a new habitat even 100 miles away. It can survive in the water for up to a year, waiting to touch the muck rich sand. Again, roots are sent out immediately and growth begins. By the third year the spidery root system arches upward and within 10 years a whole new surrounding colony has formed. By claiming the mucky silt the man-grove gradually claims the land back from the sea.

What is the mud composed of? The very fine mucky soil is made up of guano, algae, rich tiny marine organisms and carbon deposits 50 times greater than that found in tropical rain forest floors. One square mile of mangrove has as much carbon as 50 square miles of rainforest habitat. This is potentially vital for mitigating climate change. Because of the salt content, it is not a good medium for edible plants.

For a mangrove forest to evolve, two unusual requirements need to be met: First, the ability to overcome the salinity of the water which saturates the ground and the Second, the ability to grow in the absence of oxygen. Trees that can master these two issues evolve into mangrove trees. They are not necessarily of the same species. In Costa Rica, seven species of mangrove trees have evolved from four plant families. Each has evolved a root system that allows for aeration and a filtering system to filter out the salt from the ocean water.

The salt filtering ability is handled differently by different mangrove trees. Some secrete salt through their roots and or leaves, some store the salt in old leaves which eventually fall off and some seem to be able to tolerate salt.

The soil base of the mangroves is an acrid very fine gained mud, devoid of oxygen. Hence the mangrove tree does not send down roots deep into the mud, but sends out instead aerial roots, like arching spider legs. The mangrove ecosystems of this eco-region serve as wildlife refuges, nursery and spawning areas, wildlife habitat, nutrient and sediment retention areas and shoreline protection areas as well as areas of expansion. These features build upon each other to attract many different species of wildlife to the eco-region for the purpose of attaining important resources such as food and shelter. The roots serve as well as nurseries to many species of marine life and havens for water birds. The cage-like root systems protect small marine animals from larger predators.

Unfortunately, in Costa Rica and the rest of the world, mangrove forests are being destroyed and their sites converted to fish pens, rice paddies, salt-drying ponds, cattle pastures, tourist developments and human settlements. Mangrove wood makes good fuel and excellent charcoal, but over-harvesting has contributed to their demise. Additionally, the red mangrove is an important source of tannin (used in processing leather), but the stripping of the bark to get the tannin kills the individual trees.

All mangroves in Costa Rica are protected by law, but there is not always someone around to enforce the law. Many species of wildlife are attracted to the eco-region for the purpose of attaining important resources such as food and shelter. This destruction of mangrove ecosystems has caused a decline in available habitat and the resulting decline in species numbers. The Terraba-Sierpe mangrove region is one of the greatest remaining concentrations of mangroves in the world. It forms the northern border of the Osa Peninsula, habitat to some of the greatest bio-diversity on the planet.

Rosemary MacGregor is an enthusiastic promotor of Eco-tourism in Costa Rica. Her interest extends from Eco lodge promotion, preserving the archeological findings to training the young and educating the peoples in the rural villages.