trees | blue
Mangrove trees have
become specialized to survive in the extreme conditions of
estuaries. Two key adaptations they have are the ability
to survive in waterlogged and anoxic (no oxygen) soil, and
the ability to tolerate brackish waters.
Some mangroves remove salt from brackish estuarine waters through ultra-filtration in their roots. Other species have special glands on their leaves that actively secrete salt, a process that leaves visible salt crystals on the upper surface of the leaves.
All mangrove species have laterally spreading roots with attached vertical anchor roots. These roots are very shallow. Because the soil in shallow areas of mangal forests is typically flooded during high tides, many species of mangrove trees have aerial roots, called pneumatophores, that take up oxygen from the air for the roots. Some species also have prop roots or stilt roots extending from the trunk or other roots that help them withstand the destructive action of tides, waves, and storm surges (Smith and Smith, 2000).
Many mangrove trees also have a unique method of reproduction. Instead of forming seeds that fall to the soil below and begin growing, mangrove seeds begin growing while still attached to the parent plant. These seedlings, called propagules, even grow roots. After a period of growth, these seedlings drop to the water below and float upright until they reach water that is shallow enough for their roots to take hold in the mud (Northern Territory Government, 2000).