|
|
Dipterocarpaceae Family
|
Dipterocarpaceae is the defining family for our South East Asian Dipterocarp forests and the trees of this family are large, commercially valuable and dominate the forest as many are emergent species standing above the canopy of surrounding forest. The life and times of Dipertocarps also makes for an interesting story, from their method of fruiting to Seed dispersal and how they came to be distributed across Africa and Asian continents to the high level of diversification in South East Asia.
Dipterocarp seed dispersal involves a winged nut falling from the mother tree, with the only lateral movement made possible by whatever prevailing breeze is available beneath the canopy. At best these seeds will fall obliquely perhaps one or two crown widths during fruiting on a windy day. It is also known that
the fruits of Dipterocarpaceae are generally intolerant of salt water and because of this, sea boundaries are a major obstacle to dispersal. If you consider this mind numbingly slow
linear rate of dispersal plus the time it takes for a seedling to
become a mature reproductive tree you may realize that there is no way
this family could have the breadth of distribution it enjoys simply through
terrestrial seed dispersal. Scientific studies have identified correlations between distribution and diversification of Dipterocarp species with tectonic plate movements and the currently accepted theory of distribution involves the family originating in Africa and deploying to South East Asia via these plate movements.
The family is considered to have its origins in Gondwanaland (the great southern continent) and crossed onto the Asian continent during he Tertiary period. The animation shown on the left is one of many that are available from the United States Geological Survey that address the subject of historical plate movements. This particular animation follows the African continent and the Indian sub-continent can be seen breaking away and moving north-east towards its current location.
More recently (in the past 11,000 years) and more locally, the Sumatra, Malay Peninsular and Borneo land masses were part of one single land mass with a major river valley separating east and west portions. It is apparent from the current distribution of Dipterocarps in the South East Asian region that extensive regional speciation occurred within this extensive system.
Interestingly South East Asia can be shown (see map below) to be the centre of diversification for Dipterocarpaceae and this is attributed to the favourable bio-geographical conditions that prevail here, e.g. the absence of annual drought resulting in high survival rates for seedlings, supra-annual flowering and mast fruiting which overwhelms the seed predators to the extent that there are sufficient remaining seeds after the predators have become fat to achieve a higher rate of successful germination compared to that which could be achieved if fruiting occurred independently.
|
|
|
Distribution map of the Dipterocarp family adapted from The Foresters' Manual of Dipterocarps by C.F. Symington
Shaded areas indicate extent of the family, graduated symbol indicates diversity, label indicates number of genus/species.
|
Since this web site is all about the flora of Singapore, we must now abandon global matters and attend to the issue of Dipterocarp diversity on this small island located at the southern tip of the Malay Peninsular. The fact is that since Singapore is an island separated from the main peninsular by a few hundred metres of sea water and by additionally accounting for small and perhaps imperceptible variations in climate, we can reasonably expect that the diversity of Dipterocarps on the island of Singapore be something different to and less than that of the main land. This is in fact the case with some 14 genera and 160 species attributed to the Malay Peninsular, whereas the Singapore Nature Reserves currently enjoy the company of only 5 genera and approximately 30 species.
|
Dipterocarpus (Keruing) Genus
| The Dipterocarpus genus is distributed from India through Malaysia to the Philippines. There are some 69 described species out of which 31 are known from the Malay peninsular. For Singapore there are 7+ native species of the Dipterocarpus genus. Dipterocarpus is generally recognized by the scaly bark, the leaves are larger than other Dipterocarpaceae genera and are generally crenate with the lamina folded between the secondary veins. Some hybridization between Dipterocarpus species has been observed. |
Hopea (Merawan) Genus
The Hopea genus consists of over 100 species, 32 of which are known in Malaysia however only 3 are known from Singapore. The genus is divided into four groups described as the Smooth Barked group, Mata Kucing group, Fissure Barked group and Scaly Barked group. In Singapore our three species are distributed in three groups with Hopea sengal belonging to the Scaly Barked group, Hopea mengarawan belonging to the Fissure Barked group and finally Hopea griffithii belonging in the Smooth Barked group.
|
Shorea (Meranti) Genus
|
Dipterocarps belonging to the Shorea genus are the most commercially valuable members of the Diptertocarp family and they are distributed from India east to the Philippines and from North Malaysia south to the Wallace Line. For Peninsular Malaysia, there are some 58 described species however for Singapore Island there are 12+ species only with some considered rare and critically endangered.
The Shorea genus is considered to be made up of five distinct groups, they are known as the Balau group, Temak Batu group, Meranti Pa'ang group, Meranti Damar Hitam group and the Red Meranti group. With the exception of Shorea gratissima which belongs to the Meranti Pa'ang group, all of the remaining Shorea species found in Singapore belong to the Red Meranti group. |
Vatica (Rasak) Genus
|
From some 23 species of Vatica, only 3 species of this Genus are known from Singapore.
|
|
|
