A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
section Shorea), Pentacme, Doona and Anthoshorea
which form a full complement of supraspecific taxa
exclusively confined to canopy in the Asian seasonal
tropics (Ashton 1979a). But many other emergent
Shorea, especially the Richetioides group, have small
flowers, whereas Vatica and Stemonoporus (many of
which flower beneath the canopy) have large flowers (as
big as Parashorea or Anthoshorea).
The anther and stamen sizes broadly follow the same
trend: a) in the seasonal area the anthers are large,
elongate and bright yellow for Vateria, Vateriopsis,
Dipterocarpus, Parashorea, and Pentacme; and b) the
same type of anthers also characterise certain taxa
confined to aseasonal regions: Dryobalanops,
Cotylelobium, Neobalanocarpus, Stemonoporus,
Ashton’s Shorea section Rubellae, and Doona. In the
other taxa, such as Anthoshorea and Ovalis, anthers are
smaller, white and subglobose to ellipsoid; Richetioides
presents the smaller ones. The African taxa seem to
possess numerous stamens of medium size (drawings
of Verdcourt 1989).
The number of stamens (Ashton 1979a) is often 15:
Vateria, Vateriopsis, most Dipterocarpus species,
Anisoptera section Anisoptera, Dryobalanops, Shorea
sections Shorea and Rubellae, 6 species of Anthoshorea
all in seasonal sites, Ovalis, 1 species of Brachypterae,
1 species of Richetioides, and 3 species of Hopea (2 of
which are in seasonal sites). Ten species have less than
15 stamens: 10 stamens in 6 species of Hopea and 3
species of Richetioides, 5 stamens in 2 species of
Stemonoporus and 1 species of Vatica.
Large flowers produce large pollen grains (Muller
1979). Flower and pollen dimensions will interfere with
potential pollinators. Clear relations have been
demonstrated between ovary shapes and sizes within
Shorea sensu lato subgroups and pollinator size or
taxonomical group (Chan and Appanah 1980, Appanah
and Chan 1981, Appanah 1990). Bees pollinate large
yellow elongate anthers while thrips pollinate small,
white anthers. Bees prevail in seasonal tropics and Sri
Lanka. Pollination changes during geological to present
times probably explain much of the present aspect of
dipterocarps. This is an important point to consider when
planting trees outside their original areas. Forest
degradation may result in the absence of tree
reproduction by extinction of pollinators.
The biggest fruits are in taxa with large flowers, and
more frequently in species producing wingless-fruits
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than in species with winged fruits. There is also a relation
between large dimensions and the development of a
protective thickening of pericarp and/or calyx base to
prevent dehydration of the embryo and sometimes
permit floating of the fruit (Maury 1978, Maury-Lechon
1979b, Maury-Lechon and Ponge 1979). Thickened sepal
bases are a defining character of Shorea sensu Ashton,
but do not occur in Anisoptera, Upuna, Cotylelobium
or Sunaptea. Pericarp thickenings characterise
particularly the Pachynocarpus and Vatica groups of
genus Vatica and genera Stemonoporus and Vateria. The
thickening is of different type in Monotoideae and the
case of Dipterocarpus remains apart because of the
variously thickened calyx ornamentations (tubercules,
simple or folded wings). The protective thickenings
mainly develop in the group of taxa forming 15 elongate,
large, yellow anthers. Large fruits are produced in smaller
numbers, and they represent an investment which lowers
risks in weakly lit places. The increased size of seedembryo
probably demonstrates a trial for better survival
in unpredictable habitats with irregular supply of light
and nutrients (and water) during the germination period
of non-dormant seeds. However, fewer fruits are
produced, so that investment is in fewer high-cost seeds
bearing other risks of probably lower intensity. Animal
predation is mainly by insects and seeds do germinate
and develop normal seedlings in spite of insect larvae
which continue their development within the fleshy
cotyledonary limbs; human predation is more drastic and
mainly corresponds to traditional and industrial oil
extraction.
The 5-winged fruits of Pakaraimaea, Monotes and
Marquesia clearly disperse in open and windy habitats,
as probably do that of Pseudomonotes (detailed
information not yet available). In these taxa pollen and
nuts show evident adaptations to the dry conditions of
their seasonal climates: thick layers and protected
apertures, while the thin coriaceous pericarp of the ripe
fruit of Marquesia excelsa is an exception (Maury et
al. 1975a, b, Maury 1978, Maury-Lechon 1979a, b,
Maury-Lechon and Ponge 1979). In Asia the wingedlight
fruits of Sunaptea and Cotylelobium, of certain
species of Hopea, Shorea (Ashton sensu lato) and
Upuna present thin pericarps, even in seasonal regions.
Asian taxa have developed winged fruits in seasonal
and aseasonal regions. In closed forests these fruit wings
have limited possibilities for dispersal. However, over
the canopy and at forest borders, storms and very strong
winds at the beginning of the rainy season may transport