A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
Asian dipterocarps deeply imprint the forest ecology
and economy of the places where they grow. They
constitute prominent elements of the lowland rain forest
(Whitmore 1988) and are also well represented in the
understorey. As a family they dominate the emergent
stratum. Most belong to the mature phase of primary
forest, which contains most of the entire genetic stock
(Jacobs 1988). All species can colonise secondary
forests during the succession phases provided there is a
seed source; seed dispersal is limited, except among
water dispersed species. However, none seems presently
confined to secondary formations. Certain dipterocarps
of the seasonal regions dominate the fire-climax
deciduous forests of northeast India and Indo-Burma.
In Asia, dipterocarps occupy a large variety of habitats
(Symington 1943, Wyatt-Smith 1963) from coastal to
inland, riverine to swampy and to dry land, undulating to
level terrain, ridges, slopes, valley bottoms, soils deeply
weathered to shallow, well-drained to poorly drained, and
rich to poor in nutrients. In Peninsular Malaysia the
altitudinal zonation of their main habitat types ranges
from 0-300 m (low-undulating dipterocarp forest), 300-
750 m (hill dipterocarp forest), and 750-1200 m (upper
dipterocarp forest). Zonation however, differs in Borneo
and Sri Lanka. The freshwater swamps, especially in drier
parts, are rich in species (Corner 1978, in Jacobs 1988)
while true peat-swamp is relatively poor. The dipterocarp
flora is also poor on limestone and riverine fringes.
Asian dipterocarps are limited altitudinally
(Symington 1943) by climatic conditions, and the
conjunction of altitude and other natural barriers, such
as large rivers and watersheds, have obstructed the
distribution of species in Borneo. For example, the
northwest and northeast of Kalimantan, Sarawak, Brunei
and Sabah are much richer in species than the rest of
Kalimantan. The everwet areas are also richer in species
than the seasonal ones as shown in Sri Lanka by the
concentration of species in the southwest quarter, or in
the Thai-Malaysian transition belt, or from Java to the
Lesser Sundas (Jacobs 1988).
Distribution of Dipterocarps and
Related Taxa
The present distribution patterns of dipterocarps are
thought to reflect routes of colonisation and past climatic
conditions (Fig. 1). Living dipterocarps sensu lato are
spread over the tropical belt of three continents of Asia,
Africa and South America. They occupy several
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phytogeographical zones that mainly conform to climatic
and ecological factors. However, in southeast Asia,
Wallace’s line where it runs east of the Philippines and
between Borneo and Celebes, is a major phytogeographic
boundary for dipterocarps. It cannot be explained in terms
of climatic differences but requires the intervention of
continental shelf drift.
Phytogeographical Regions of Living Taxa
The South American region (Fig. 1, Table 4) corresponds
to Guyana, Venezuela and the part of Colombian Amazon
which overlies the Guyana shield.
The African region (Fig. 1, Table 4) includes a
continental area and an insular part in Madagascar. The
former is in two disjunct areas (Aubreville 1976): a) a
narrow strip in the northern hemisphere from Mali on
the west, to Sudan on the east, neither reaching the
Atlantic nor the Indian Ocean; and b) in the southern
hemisphere the Monotes-Marquesia area covers a semidry
region between the two oceans, south of the
Congolese rain forest, most of which is essentially
central and does not reach the Atlantic or Indian Oceans.
The Asian region (Fig. 1, Table 4) corresponds to the
Indo-Malesian area, which concentrates a high number
of genera and species in the equatorial forests. This area
is limited northward by the Himalayan foothills, then
approximately by the borders of Assam, Arunachal
Pradesh (India), Burma, Laos and Vietnam, and
penetrating into south China including Hainan Island. On
the extreme southwest the large belt of Asian
dipterocarps reaches the Seychelles (1 sp. Vateriopsis
seychellarum), and covers India and Sri Lanka. Its eastern
border corresponds to New Guinea. The Sundalands
delimit the most southern part. No dipterocarp species
is found in Australia.
Five main phytogeographical regions are classically
recognised within this distribution area: 1) Malesia:
Peninsular Malaysia, Sumatra, Java, Lesser Sunda Islands,
Borneo, the Philippines, Celebes, the Moluccas, New
Guinea and the Bismarks. The northern frontier of
Peninsular Malaysia delimits this part; 2) Mainland
southeast Asia: Burma, Thailand, Cambodia, Laos,
Vietnam and south China (Smitinand 1980, Smitinand et
al. 1980, 1990); 3) south Asia: India, Andaman islands,
Bangladesh, Nepal; 4) Sri-Lanka; and 5) Seychelles. In
these Asian phytogeographical areas each dipterocarp
group manifests a more or less distinctive pattern of
variation at the species level (Ashton 1982).