Mangrove forests (also called mangal) are a type of wetland rainforest formation that has its own unique characteristics not found elsewhere. Occurring in coastal regions near the equator, the trees in mangrove forests are all adapted to deal with a highly saline environment that would normally be uninhabitable for other kinds of trees.
Globally, mangrove diversity have been arbitrarily divided into two groups, the Old World and New World groups, with the Old World group having by far the richest diversity of tree species, with the mangrove forests in South East Asia (such as in Malaysia) amongst the most floristically developed, in terms of species richness and structure, compared to mangrove forests elsewhere in the world. Therefore, they are of great interest for scientists and naturalists alike.
Mangrove forest types
Mangrove forest is often classified based on the frequency of tidal inundation from the sea, which affects the species that grow in these zones. The main genera of mangroves (at least in the Old World) revolves around the genus Avicennia, Bruguiera, Rhizophora, Sonneratia, Ceriops, and Lumnitzera. Further inland in the brackish intertidal zone, this is a zone dominated by the Nipah palm (Nypa fruticans). Due to their dispersal mechanism by seawater, many mangrove plants and animals are widely distributed and have broad ranges spanning many countries, and even continents.
Mangrove trees have special adaptations to enable them to colonize their environment, such as leaves that can excrete salt, viviparous breeding (fruits that germinate while attached to the parent tree), stilt and buttress prop roots to support them in the muddy substrate, and pneumatophore roots (aerial roots that can breathe).
Various factors contribute towards a type of zonation pattern that is recognizable, especially in the larger mangrove swamps. At the waterfront directly facing the sea (lower intertidal zone), the mangrove forest is often dominated by Avicennia and Sonneratia species. Here, the mud layer is pretty deep, and both Avicennia alba and Sonneratia alba are especially common here.
Avicennia is recognizable from its pencil-like pneumatophore roots, while Sonneratia have thicker, triangular-shaped pneumatophore roots. The Avicennia-Sonneratia consociation is generally regarded as the front line colonizer belt of the mangrove forest, if the mud is soft and the terrain is exposed. On firmer soil at the mangrove seaward front, Rhizophora tends to dominate, where they occur as dense thickets.
A bit further from the front of the mangrove, the common types of forest are the Avicennia-Bruguiera, Rhizophora-Bruguiera, and mixed forest zone. Avicennia officinalis, Avicennia marina, Rhizophora apiculata, Rhizophora mucronata, Bruguiera cylindrica, and Bruguiera parviflora, are some of the common species found here. Rhizophora can be identified from their stilt roots, while Bruguiera can be identified from their protruding knee-like pneumatophore roots.
In larger mangrove swamps, a type of tall, mature Rhizophora or Bruguiera dominated forest may be found, such as can be seen at the Matang mangrove forest reserve in Perak. Further back up the intertidal zone where it is drier, other mangrove forest trees that now thrive include species of Ceriops, Lumnitzera, Heritiera, Xylocarpus, and Nypa. The Nypa fruticans belt may extend for several kilometers inland along rivers, where the coastal mangrove has long given way to dryland mangrove forest, dominated by Xylocarpus, Pandanus, Intsia, and Ficus spp.
The factors that affect mangrove zonation are quite varied, and researchers believe that salinity levels, tidal fluctuation, sapling predation, soil conditions, competition between species, nutrient concentration, and water sulfide levels all can affect the species of mangrove trees that can grow or thrive in any one area.
Wildlife is abundant in the mangrove forest. Long tailed macaques, silvered leaf monkeys, otters, monitor lizards, dugongs, eagles, kingfishers, storks, egrets, herons, mudskippers, mud crabs and lobsters, mangrove snakes, and saltwater crocodiles are just some of the diverse fauna that inhabit mangrove forests. Caution needs to be exercised where saltwater crocodiles are found; these animals can be a real hazard in Borneo, but in Peninsular Malaysia, such crocodiles are very rare as to be considered practically extinct. Borneo is also home to the Proboscis monkey, a rather specialized mangrove/coastal forest inhabitant, and endemic to that vast island.
A fact not widely known is that the Malaysian mangroves are home to fireflies, and the spectacle of them lighting up the mangrove trees at night is a sight to behold. It’s been said that the firefly population in the area upstream of the Kuala Selangor mangroves is one of the “wonders of the world”, due to the high density of the firefly population there. The fireflies congregate mainly on a type of mangrove tree (Sonneratia caseolaris) at night.
Importance of mangrove forests
Mangrove forests are the spawning ground for various species of fish and shellfish. When the mangroves go, so will the fish and seafood that we often take for granted. Mangroves act as sponges to absorb the impact of tidal waves during storms or tsunamis, and they also protect the coastline from erosion. The wood from mangrove trees is used for construction works, firewood, and charcoal; in this context, the Matang mangrove forest has been sustainably logged and managed for about a century now. It’s clear that mangrove forests are very important!
Despite their huge value, mangroves have been cleared a lot. Not only that, pollution is a serious problem affecting mangrove ecosystems. Toxic effluents discharged into the rivers and rubbish end up in the mangroves, and may then wind up in the food chain as well.
The mangrove forests of Malaysia used to occupy quite extensive swathes of coastline, but have now been largely reduced in extent. True virgin mangrove forest in Peninsular Malaysia is now largely limited to a few locations (e.g. Pulau Kukup, Johor, Langkawi Islands, parts of the Klang islands, and parts of Matang forest reserve, Perak).
Fortunately, mangrove regeneration and colonization is relatively rapid, which means that mangrove forests can be replanted and regenerated, even on degraded coastlines. Most of the mangrove forest cover in Peninsular Malaysia is on the West Coast due to it being more sheltered from strong winds and waves, while the East Coast (exposed to the more turbulent South China Sea) is largely dominated by sandy beaches, and possesses relatively little mangrove forest.