A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
or ruptures of continental drifts: a) by lack of marine
influence the Permian continental block (Fig. 2 (A), 3)
would have been drier than the previous split continents
of the Carboniferous with its luxurious Cryptogamic
flora; b) the split of Gondwanaland during the Secondary
would have permitted marine humidity to enter the
fragmented lands (Fig. 2 (B, C) and probably the first
Angiosperm ancestral forms to originate; c) the supposed
late Cretaceous - early Eocene (Renous 1989, Dercourt
et al. 1992) connection of India with Eurasia (Fig. 2 (D)),
between -65 and -40 million years, and later that of Africa
(Fig. 2 (E)), would have created new dry and humid zones
and corresponded to the differentiation of Angiosperms
(and dipterocarp ancestors?).
According to these reconstituted changes, the flora
of past continents from Permian (Primary) to Miocene
(Tertiary) times had a very ancient common history (land
and climate). Later on the future southern part of the
Eurasian southeast zone first separated from the rest of
Eurasia (Fig. 2 (B): Triassic: hatched area, Fig. 3) and
then (the upper Jurassic) connected with it (Fig. 2 (C, D,
E)). Wallace’s line corresponds to the separation between
lands of different origins: the two Gondwanan shelves,
the Indian on the west and the Australian on the east (Fig.
2 (C)).
For long geological periods (lower to extreme upper
Cretaceous period, Secondary) the Indian-Seychelles-
Sri Lanka part of the Gondwana shelf remained under an
insular situation. For similar long periods the present
regions of mainland southeast Asia, China and Malesia
pro-parte remained separated from the Indian island, but
perhaps intermittently connected to Eurasia. The Indian
collision with Eurasia produced huge changes (land,
climate, flora) as well as possibilities (or difficulties)
of colonisation and species evolution for both types of
flora (the insular-Indian flora and the continental-Asian
flora) in the new territories.
Paths of Possible Flora Migrations
Four main land connections are thus suggested for
eventual migrations of the ancestors of the dipterocarps,
at different periods after the Gondwana split: a) India-
Sri Lanka-Madagascar-Africa-America-Eurasia (Fig. 2
(C)); b) the putative eastern archipelago northeast of
Gondwana to Eurasia (Fig. 3); c) later, India-Sri Lanka-
Eurasia (Fig. 2 (C, D)); and d) finally northeast Africa -
Southeast Eurasia (Fig. 2 (E)). Because of the distances,
land dimensions and climate history, the first connection
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could have favoured the success and survival of species
with small winged fruits, the second could have aided
species with water dispersal, while the third could have
permitted the persistence and establishment of more
diverse biological types. Perhaps excessively dry
climates did not favour dipterocarp migrations in the
fourth case.
These geological events bring light to the present
distribution over three continents and the paucity east
of Wallace’s line. They explain certain endemic aspects
such as the Monotes kerstingii disjuncted area in Africa
(survival at the periphery of the rain forest newly
established in the previously drier area of Monotes).
They could justify Upuna in Borneo, and localisation of
Vateriopsis, Vateria, Stemonoporus and Doona in the
Indian island zone. These events underline the existence
of a very long past of successive modifications, and help
to explain the real difficulty in finding primitive features
in present flora. If characters evolved independently
from each other, a single present taxon might have
retained some primitive aspects and modified others;
these latter preventing consideration as an ancestral form.
Endemicity of Dipterocarps Sensu Lato
As expected, the higher endemicity is located at the
extremes of the geographical area of distribution. It is
due to monospecific genera westward in south America
(100%: 2 sp.), Madagascar (100%: 1 sp.) and Seychelles
(100%: 1 sp.). Endemicity is of different intensity (Table
7) eastward in Sri Lanka (98%: 43/44 spp.), south India
(85%: 11/13 spp.) and in New Guinea (73%: 11/15 spp.),
and with a much lower proportion in Borneo (58 to 55%:
158 to 155/267 spp. of which 1 is a monospecific
endemic genus), north Peninsular Malaysia (49%: 23/
47 spp.) and the Philippines (47%: 21/45 spp.) and north
India (40%: 4/13 spp.). A certain endemicity also exists
in the other Malesian areas but the values rapidly
decrease: Celebes (29%), Java (20%), Peninsular
Malaysia (17-18%), Moluccas (16%). Peninsular
Malaysia, Sumatra and Borneo only separated 10,000
years B.P. and, if taken as one biogeographic region, its
endemicity is 293/345 species or 85% when the
boundary is determined by the Kangar/Pattani line, 303/
345 species or 87% when the boundary is the Isthmus
of Kra.
Endemicity is very reduced on a country to country
basis (Vietnam 9%, Laos 5%), or absent in the mainland
southeast Asian phytogeographical area (Burma, Thailand,
Cambodia; however, for Indo-Burma as one
biogeographic region it is high), and totally absent from