Niels Raes of the Naturalis Biodiversity Center, in Leiden, The Netherlands joins with 6 colleagues to publish Historical distribution of Sundaland’s Dipterocarp rainforests at Quaternary glacial maxima in the journal PNAS. Dipterocarps in SE Asia were great forest-formers and still would be if we were not cutting them all down. Biodiversity and conservation of that biodiversity depends upon a sound knowledge of the Quaternary period. 317 species currently form the full extent of dipterocarp rainforest, ever since the LGM or last glaciation maximum of the Quaternary. The ice would be further south and the climate colder, to prevent the forests from extending beyond their refugia in Sunda. Sundaland consisted of the whole SE Asian area around Borneo, Sumatra, Java, Bali and the Malay peninsula, now sunken and not connected as they once were.
Species distribution models illustrate that the climate then was suitable, with a trans-equatorial savannah corridor very unlikely. Mammals and termites are especially useful to show up the forest distribution while isotopic surveys of vascular plant fatty acids join those of carbon isotopes in cave guano.
What appears is a lower species richness under the stress of the LGM. Current island locations had the highest number of dipterocarp species, along with the emergent Sunda shelf. This means many species were able to migrate and interbreed during transitions. For example, between the LGM and the present time, the warmth has facilitated several migrations of forest tree species. The richness of NW Borneo and on Bangka Island (east of Sumatra and full of tin mines!) remain despite all of the interference.
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