A review of dipterocarps - Center for International Forestry Research

Conservation of Genetic Resources
in the Dipterocarpaceae
K.S. Bawa
Introduction
The biological and economic importance of
Dipterocarpaceae lies in the extraordinary dominance of
its members over vast areas in forests of southeast Asia.
With approximately 510 species and 16 genera, the family
may not be particularly large among tropical woody
groups. Other families such as Euphorbiaceae,
Myrtaceae, Rubiaceae, Annonaceae, and Lauraceae have
more taxa than the Dipterocarpaceae, however, they are
pantropical in distribution. Although members of
Dipterocarpaceae are also found in the African and
American tropics, 13 out of 16 genera and 470 out of 510
species are largely restricted to Asia, and there, restricted
primarily to south and southeast Asia. In Malaysia, it is
certainly among the six largest families that are
predominantly woody, the others being Euphorbiaceae,
Myrtaceae, Rubiaceae, Annonaceae, and Lauraceae.
Moreover, the members of the family are exceedingly
abundant in lowland forests of southeast Asia, for
example, in many areas, 80% of the emergent individuals
and 40% of understorey trees are dipterocarps (Ashton
1982). Thus, when one considers the relatively restricted
distribution of the family, both diversity and abundance
are its main attributes.
The diversity of the family is under assault from
deforestation and habitat alteration. Effective in-situ and
ex-situ conservation strategies are required to conserve
the existing genetic resources. To conserve genetic
resources, it is essential not only to maintain existing
diversity, but also to understand the ecological and
evolutionary processes that have been responsible for the
origin, evolution, and maintenance of diversity at
intraspecific and higher taxonomic levels. This chapter
has two broad objectives. One is to review genetic
mechanisms responsible for the origin and maintenance
of diversity. The second is to identify areas of research
that may elucidate patterns and processes of diversity and
Chapter 2
a more complete understanding of factors regulating
diversity. It is assumed that a better understanding of
diversity and the mechanisms maintaining diversity may
be helpful in developing effective strategies for
conservation of genetic resources. The chapter ends with
a brief commentary on the institutions involved in
research related to the conservation genetics of the family.
Diversity
Genetic mechanisms responsible for diversification at
intraspecific and specific levels are considered and then
patterns of genetic variation within and among
populations are described.
Chromosomal Differentiation
Information about chromosome numbers is available for
9 out of 15 genera and 68 out of 510 species of the family
(Jong and Kaur 1979, Ashton 1982). Species and genera
are remarkably uniform with respect to chromosome
number. Perhaps all species in the genera Dryobalanops,
Hopea, Neobalanocarpus, Parashorea, and Shorea have
x=7 as the basic number. Anisoptera, Dipterocarpus,
Upuna, and Vatica seem to have x=11 as the basic
number. Several species in the genera with x=7 as the
basic number have a somatic chromosome number of 20,
21 and 22. Thus, x=11 may have been derived from x=7
through alloploidy.
Polyploid species are known in only two genera:
Hopea and Shorea. In Hopea, polyploidy has been
reported in 5 out of 9 species and in Shorea in 3 out of 36
species. Five of these polyploid species are triploids
(2n=21; also 2n=20 and 22) and one (2n=20) seems to
be an aneuploid derivative of a triploid. Many of the
triploids are apomictic (see below).