Since, the IUCN (2012) assessed 46 species of Dipterocarpus under different threatened categories; where 1 species listed as Extinct, 34 species as Critically Endangered, 6 species as Endangered, 1 species as Vulnerable and 4 species as Least Concern category.
Since dipterocarps are only found in SE-Asian forest ecosystems they should not be considered on a global base. On more regional terms you might consider them as such.
Substantial areas of forest in Southeast Asia are dominated by Dipterocarpus and can be regarded as hot spots of global biological diversity (Cao et al., 2006). The genus is ecologically dominant and also economically significant (Ashton, 2002). Even, Dipterocarpus species account for 80% of timber exports from the region providing a major source of revenue for many developing country (ITTO 2008). The long-term resilience and conservation of the supported biodiversity depends on the existence of these Dipterocarp forests. Because, besides major sources of potential timber, Dipterocarpus species plays important ecosystem roles in the form of suitable habitat for many threatened wildlife and also act as source of livelihood of the forest dwellers.
Sorry, with "only" I did not mean insignificant but restricted to SE-Asia. I Agree with all you statements also based on my own observations in Borneo. Compared to other parts of the world, e.g. Amazonia, there is nothing to compare with this dominance and significance of only one plant family in dipterocarp forests.
Hi Koushik, you might like to consult a special Issue of Biotropica we produced in 2012 http://onlinelibrary.wiley.com/doi/10.1111/btp.2012.44.issue-5/issuetoc
This might help answer your question. A point of detail, 'Dipterocarpus' is just one genus in the family of Dipterocarpaceace. Do you mean Dipterocarp species more generally, which I think can be described as Keystone species in lowland dipterocarp forest, or specifically 'Dipterocarpus' species?
I think the answer to the question depends partly on your objectives.
A 'flagship' species is one which we decide to nominate for attention because it will appeal to the public in a conservation campaign. Dipterocarps are often magnificant trees and have appeal for this reason. Nevertheless, conservation campaigns are more often built around mammals, which tend to have more public appeal than other taxa.
An 'umbrella' species is one which, if protected, will result in the protection of many other species too. Since dipterocarps provide the foundation for some tropical forest ecosystems, if we choose to protect one particular species, then it could have a more general effect, but if we select a species that is rare then the effect is quite limited because trees are immobile. Mammals and birds tend to be more effective as umbrellas because they can be rare, wide-ranging and dependent on a large area of habitat even when rare.
A 'keystone' species is one which has a much larger effect on the ecosystem in which it is found than its numbers or biomass would indicate. Trees are rarely 'keystone' simply because they are so massive and their ecological significance is generally due to their abundance. For this reason, it is better to use the term 'foundation species' (rather than 'keystone species') for trees like dipterocarps, because they commonly form the base upon which tropical forest ecosystems are built.
In light of this, I think you could build an international conservation campaign around a rare dipterocarp species as a 'flagship', and make use of the argument that the species has the capacity to build the foundation of entire ecosystems which will be lost if the species itself is lost. In a sense, large trees are always umbrellas because they always have many other species associated with them due to the long periods of time over which they have been present in the places where they reside. For these reasons, I think you could build a conservation campaign around the idea that ancient dipterocarps provide the irreplaceable foundation for unique ecosystems which are of global significance.
I remember seeing an old dipterocarp on a small Indonesian island. It was the only big tree on the island and was valued by the local community as a shade tree and for its inherent value due to its age. There were some young ones too, but I don't know whether the community had selected any for retention as a future replacement.
You also have to take the current IUCN assessments for the Dipterocarpus with a grain of salt. In many cases their assessments are too high. For example Dipterocarpus applanatus is listed CR and as only occurring in Kalimantan, Indonesia but it well represented within the PA network in Sabah, Malaysia (e.g. Sepilok, Imbak, Tawau Hills Park, etc.). This is why most are listed as needing upgrading
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