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Mangrove

Mangrove, a highly adaptive plant in tropical intertidal forest communities. Before the rapid post-war development of Singapore, mangroves were found to be growing freely along Singapore's coast, especially in the north and west. The plant's existence is now limited to mainly some offshore islands and the wetland reserves of Sungei Buloh.

Origin and distribution
The term "mangrove" may have been derived from a combination of the Malay word manggi-manggi, for a type of mangrove tree (Avicennia) and the Arabic "el gurm", for the same, to become "mang-grum". As a word, it can be used to refer to a species, plant forest or a community. Dominant genera or plant species include Rhizophora, Avicennia, Bruguiera and Sonneratia.

In the 19th century, mangroves were extensively found along the coastline of mainland Singapore, especially in the northern and western coasts. Growing along intertidal river mouths and along sheltered shores, it covered approximately 13 per cent of the land. Today, however, only 0.5 per cent remains, growing mainly in the northern part of the island, on some offshore islands such as Pulau Tekong and Pulau Ubin, and nature reserves at Sungei Buloh Wetlands Reserve and Pasir Ris Park.

From the founding of modern Singapore in 1819 till the present day, land shortage in Singapore has resulted in mangroves being gradually cleared through land reclamation schemes. Reclaimed land from mangroves were used for other purposes in nation-building such as industry and housing. A classic example is the reclamation of large tracts of mangrove at Jurong, into what is known today as the Jurong Industrial Estate.

Description
Mangrove forests are a type of tropical wetland forests, which include brackish-water, freshwater and peat swamp forests. It is directly influenced by seawater, existing in an intertidal zone between mid-tide level and the highest spring tides. At high tide, the roots of the mangroves are fully immersed in sea water, while at low tide, rain or river water may wash out the salt, or evaporation concentrates the roots further.

Mangrove soils are fine-grained and rich in organic matter (detritus). They are alluvium, transported as sediment and deposited by rivers and the sea. Mangrove soils are made up of sand, silt and clay in different combinations. The soil is typically anaerobic or lacking in oxygen. Soils are usually soft and unstable, and become semi-fluid when flooded. Mangroves have special adaptations to survive the extreme environmental conditions of high and fluctuating salinity, submergence in inter-tidal seawater and fine silt that is deficient in oxygen. In order to adapt to the high saline conditions, mangroves are especially salt-tolerant. All species secrete salt to some extent through their roots. Some mangrove species, such as Api-Api (Avicenna) and Sea Holly (Acanthus) secrete salt through their leaves, through special glands. Salt crystals form on the leaf surface which are then removed by the wind and rain. The saline condition also makes this a 'physiologically' dry environment. Thus, to reduce water loss, most species have thick walled and waxy leaves.

The root systems of mangroves have special features to the adapt to the unstable anaerobic soils. Specialised aerial breathing roots, known as pneumatophores, provide air supply for the underground root system. Pencil or finger-like breathing roots of the Avicenna and Sonneratia protrude up through the soil surface, from the base of the plant. Some trees, such as Bruguiera and Ceriops have "kneed-roots", horizontal roots growing just below the soil surface grow vertically upwards and then immediately loop downwards to resemble a bent knee. To anchor the trees to the unstable soil, stilt roots are developed in bakau (Rhizophora) trees, with branched, looping roots that arise from the trunk and lower branches. Nyireh bunga (Xylocarpus granatum) trees grow plank roots. These are horizontal roots which grow vertically upwards on its upper side above ground.

Another adaptation to the mangrove habitat is vivipary. This is a condition where the fruit germinates while still attached to the plant. This is found in Bruguiera, Ceriops, Kandelia and Rhizophora species. For example, in bakau kurap (Rhizophora mucronata), the seedling grows till a metre in length before it falls from the tree. When mature, the seedlings fall and are dispersed by the tide to grow at some distance from the parent tree. Avicenna seeds have a long spear-like extension that embeds itself when it falls to the muddy ground.

Usage and potential
Mangroves are areas rich in flora and fauna and have always been important, not only in providing humans with food and all manner of product, but also in stabilising the land. The presence of mangroves along coasts cuts down on coastal erosion. Plant roots trap silt flowing out from rivers to the sea and stabilise the coast. Mangrove areas are rich in anthropoids (insects), crustaceans (crabs, prawns, barnacles), chelicerates (spiders, mites, horseshoe crabs), molluscs (snails, mussels, clams, cockles, squids) and vertebrates (fish, amphibians, reptiles, birds and mammals).

Its trees can be used for scaffolding in construction sites, and mangrove wood is used historically to make charcoal in Southeast Asia. Leaves of some mangrove trees, like the Tumu leaves, are edible or medicinal, like the Sea Holly leaves. Mangroves are home to the flying fox, the largest fruit bat in the world, which is responsible for pollinating wild and cultivated fruit trees. Mud lobsters that can grow up to 30 cm. are commonly found alongside mudskippers, snakes and a large variety of other fauna.



Author
Nureza Ahmad



References 
Chuang, S.H. (Ed.). (1973). Animal life and nature in Singapore (pp. 133-137). Singapore: Singapore University Press.
(Call no.: SING 500.95957 CHU)

Nature Society, Singapore. (2003). Singapore waters (pp. 45-56). Singapore: Author.
(Call no.: SING q578.77095957 SIN) 

Ng, P. K. L., & Sivasothi, N. (Eds.). (1999). A guide to the mangroves of Singapore 1: The ecosystem and plant diversity. Singapore: Singapore Science Centre.
(Call no.: RSING 577.69809595 GUI)

Ng, P. K. L., & Sivasothi, N. (Eds.). (1999). A guide to the mangroves of Singapore II: Animal diversity. Singapore: Singapore Science Centre.
(Call no.:RSING 578.7698 GUI)

Wee, Y. C., & Corlett, R. (1986). The city and the forest: Plant life in urban Singapore (pp. 34-49). Singapore: Singapore University Press.
(Call no.: RSING 581.95957 WEE) 

The information in this article is valid as at 2004 and correct as far as we can ascertain from our sources. It is not intended to be an exhaustive or complete history of the subject. Please contact the Library for further reading materials on the topic.

Subject
Nature>>Plants
Mangrove plants--Singapore
Mangrove swamps--Singapore
Science and technology>>Botany>>Plant ecology

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