|Remains of a stand of mangroves, Cardwell|
|Shredded remains of roots cover much of the surface|
|What the stand would have looked like before the cyclone|
|New roots growing out from the stilt root|
This root structure is entirely different to that of trees that live on the same sand just above the tidal zone. Most species of trees have roots that are like cables and these roots run for distances of many metres and branching is generally simple dichotomous branching where the root divides into two similar sized branches. Strand trees have shallow root systems which run through the top soil which is where the fertility is. Their roots also seem to stay above the water table which can be close to the surface near a beach. Calophyllum trees, beach she-oaks and paperbarks have this pattern.
|A giant Calophyllum tree toppled by Cyclone Yasi reveals cable-like roots|
|Scaffold roots and secondary tap roots of a Beach Almond (Terminalia catappa)|
Mangroves are also putting a huge amount of carbon below the ground surface where it may be retained indefinitely. Growing mangroves may be a way of stripping some carbon from our atmosphere. Sewage plants usually discharge into the mangroves and in many coastal towns, the surrounding mangroves have grown taller and denser as a result of the lower salinity as treated sewage dilutes the seawater and irrigates the mangroves in the dry season. Some carbon is already being captured due to this accidental process. Perhaps we can use mangroves to sequester carbon? Conversely, clearing mangroves releases carbon into the atmosphere. When cane farmers cleared mangroves to grow cane, the soils firstly became acid and poisonous but as the carbon in the soil oxidised and disappeared into the atmosphere, the ground surface fell sometimes by a few metres and some areas ended up useless and permanently underwater. Clearing of mangroves is no banned in Australia for this and other reasons.
More info on carbon sequestration in mangroves