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