A review of dipterocarps - Center for International Forestry Research

Conservation of Genetic Resources in the dipterocarpaceae 52
Species Level Research
First, we have to identify species that are endangered or
threatened with extinction. In some instances, populations
of species themselves might be large, but the types of
forests in which such species occur may be disappearing
at a very rapid rate. Examples are the moist seasonal
evergreen forests on the western slopes of western Ghats
in India and throughout Indochina, the mixed dipterocarp
forests in the southwest region of Sri Lanka, and the
dipterocarp forests in Philippines. Fortunately, due to the
work of Ashton (1982, 1988) and others, as compared to
other tropical families, there is far more information
available on the geographical ranges of various species
and the type of habitats and soil types occupied by these
species. More recently, P. Ashton has reviewed the
conservation status of all Asian dipterocarps for the World
Conservation Monitoring Centre at Cambridge, UK. All
this information along with other data on land use patterns,
fragmentation, and deforestation should be combined in
a geographical information system to provide easily
comprehensible graphical information on the current
status of distribution of species and the conservation status
of the forests in which they occur. Such a database would
be particularly useful because, in many cases, information
on the conservation status of family members is equivalent
to information on conservation status of dipterocarp
forests, the most important and dominant vegetation in
very large areas of south Asia and southeast Asia.
Second, we need to identify centres of taxonomic
diversity and active speciation in the family. Centres of
taxonomic diversity, of course, are known on the basis
of morphological criteria (Ashton 1982, 1988). Molecular
techniques, however, provide means to rapidly assess
species relationships and to elucidate patterns of
speciation. For example, within section Doona of Shorea,
molecular data indicates that the ‘Beraliya’ group is
evolving at a higher rate than the remaining species (S.
Dayanandan, personal communication).
Third, comparative studies of genetic diversity in
species that occupy centres of diversity and those that
occur away from zones of diversification may provide
further insights into patterns of genetic diversity. As
mentioned earlier, Murawski and Bawa (1994) observed
an unusually high level of genetic variation in natural
populations of Stemonoporus oblongifolius. The genus
is endemic to Sri Lanka and has undergone active
speciation in a small region in the southwest region of
the island. The high diversity observed by Murawski and
Bawa may be due to the fact that this species is found in
a region which is the centre of active speciation.
Similarly, comparative studies of related common and
rare species, or species in different ecological zones
may provide additional insights into patterns of genetic
diversity among species.
Fourth, there is an urgent need to study the effects of
logging on genetic diversity and other population genetic
parameters such as inbreeding and gene flow. Gene
Resources Areas that are being established in Malaysia
(Tsai and Yuan 1995) may provide excellent opportunities
for such comparative research.
Fifth, we need a better understanding of the
importance of chromosomal variation, apomixis, and
hybridisation in diversification at the species level and
infraspecific levels. We know the species and genera in
which these processes occur. However, our knowledge
with respect to the incidence and ecological and
evolutionary importance, particularly, of apomixis and
hybridisation is very limited. Again, molecular
techniques now offer new opportunities to assess the
significance of these processes.
Finally, information on breeding systems and
pollination mechanisms is required for many taxa to
characterise genetic factors maintaining genetic variation.
Such information is available for only a few species. Many
large genera such as Dipterocarpus and Hopea remain
unexplored.
Intraspecific Level Research
First, the most urgent need is the characterisation of the
patterns of genetic variation in important species.
However, in addition to ecosystem dominants and species
of commercial importance, we also need to analyse the
genetic structure of rare species. A better understanding
of the spatial organisation of genetic variation is critical
to the assessment of the effects of deforestation and forest
fragmentation on genetic diversity.
Second, comparative studies of gene flow in
contiguous and fragmented forests can provide
information about the effective size of populations,
microevolutionary forces responsible for genetic
differentiation among populations, and the potential
effects of deforestation and fragmentation on genetic
isolation of populations that were once contiguous.
Third, comparative studies of central and peripheral
populations may be useful in revealing pockets of high
genetic diversity. Populations in the centre of a species