A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
Geographical Patterns in Biological
Characters
There is a relation between shapes and structures and
the biological processes they permit. It is thus necessary
to try to understand how the morphological or biological
characters (which constitute the base of the taxonomic
divisions and systematic affinities) are related to the
survival of plants in a given habitat, particularly under
eventual modifications. During the past geological time,
climatic and/or geographic variations predominated,
while presently the transformations by human beings
predominate. This type of information is not yet available
for the American and African putative dipterocarp taxa.
Most importantly, some characters (which are
essential in establishing phylogenies and classifications)
are ancestral and do indeed constrain the ecological
range of species; but others are plastic, derived and
adaptive to ecological circumstances. This distinction
still requires classification among dipterocarps. For
Ashton, the greater the number of correlated/independent
character states, the more ancient, conservative and
phylogenetically important they are, thus this point
should be a major basis for assessment of phylogenetic
generic delimitation. However, Kostermans strongly
disagreed with this approach when presenting his case
for Sunaptea.
Biological Groups
All the African taxa, except one, fit into monospecific
formations of savanna woodland or dry deciduous
forests, under seasonal climates. Marquesia excelsa, a
residual species of the Gabonese rain forest is close to
the other savanna species of the genus, and the new South
American genus Pseudomonotes which appears closely
related to Marquesia, present the opposite situation.
Pakaraimaea is abundant but not monospecific and
could multiply both through coppicing and sexual
reproduction. However in the laboratory the germinative
potential of seeds was low and the survival of young
seedlings in USA and France nearly impossible (Maguire
and Steyermark 1981, Maguire and Maury unpublished).
Most Asian dipterocarps remain in evergreen forests
(some in seasonal regions, most in aseasonal areas). A
few species of Dipterocarpus and Shorea live in fireclimax
savanna woodlands, though closely allied to rain
forest species.
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There is a sharp discontinuity in Asian dipterocarps
in ecological and geographical ranges of the family
Dipterocarpaceae between the evergreen forest and the
fire climax dry dipterocarp woodlands (Ashton 1979a).
The species of the latter group present characters which
are unusual within the family: thick, ruggedly fissured
bark, some seed dormancy, cryptocotylar germination,
easily coppicing, seedlings with prominent taproots as a
result of frequent burning.
The dipterocarp flowering (and consequent fruiting)
phenology also changes: in seasonal areas species flower
annually with varied intensities each year; in aseasonal
regions sporadic flowerings occur each year in riparian
species for example, but large gregarious flowerings
happen at intervals of 3 or 4 years (Sri Lanka) or 5 or 10
years (aseasonal Malesia) (Ashton 1988, 1989). The
gregarious flowerings are synchronous within
populations and occur over several months for the whole
family (Ashton 1969, Chan 1977, 1980, 1981, Ng 1977).
Certain understorey Stemonoporus and Shorea however,
do not follow this timing. The climatic boundaries closely
coincide with the boundaries of the regions of exceptional
dipterocarp diversity. The abundance of species and
gregarious flowerings both occur in aseasonal west
Malesia.
Detailed information on these aspects is needed for
the American and African taxa.
Morphological Trends Related to Biological
Patterns
Deciduousness is mainly connected to seasonal areas
while evergreen trees are more frequent in the aseasonal
zones (Ashton 1979a). Degree of hairiness decreases
from seasonal to aseasonal; the extreme expression of
glabrousness is in understorey taxa such as certain Vatica
and many Hopea. The tomentum disappears first from
leaves, then from twigs, followed by the young shoots
and finally the inflorescence and floral parts. Similar
trends exist in Africa with Marquesia species from the
open savanna forests and the only species from the rain
forest, Marquesia excelsa.
Flower and fruit characters have strongly influenced
dipterocarp classification. Flower size seems constant
within genera and Shorea sensu lato subdivisions, except
in Dipterocarpus. The larger flowered taxa have their
crowns in or above the canopy. This is the case for
Vateria, Vateriopsis, Dipterocarpus, Anisoptera,
Parashorea, Shorea section Shorea (Ashton’s sub-