Historical distribution of Sundaland’s Dipterocarp rainforests at Quaternary glacial maxima

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 47; pp. 16790 - 16795
• Main Authors: Raes, Niels, Cannon, Charles H., Hijmans, Robert J., Piessens, Thomas, Saw, Leng Guan, van Welzen, Peter C., Slik, J. W. Ferry
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25.11.2014; National Acad Sciences
• Subjects: Biodiversity; Biogeography; Biological Sciences; Climate; Climate change; Climate models; Climatic zones; Dipterocarpaceae; Ecological modeling; Forests; Glaciers; Isoptera; Malaysia; Modeling; Paleoclimatology; Rain forests; Rainforests; Species; Trees; Tropical rain forests; Vegetation; Malaysia; Southeast Asia; Sundaland; last glacial maximum; species distribution model; Dipterocarpaceae; Quaternary
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1403053111

Significance The effect of glacial cycles on Southeast Asian (SEA) rainforest during the Quaternary is unresolved. Some historical evidence suggests rainforests were confined to small refugia during glacial maxima, but dynamic vegetation models suggest evergreen rainforests were widespread. Because Dipterocarpaceae dominate current SEA rainforests, their distributions closely reflect general rainforest extent. Here, we use an extensive georeferenced database of collection records for 317 Dipterocarpaceae species to model their climatic niches, based on current climatic conditions. These distribution models were then hindcast onto historical climatic conditions of the last glacial maximum. The results indicate that central Sundaland, exposed because of lower sea levels at glacial maxima, harbored suitable environmental conditions for Dipterocarpaceae and was probably covered by rainforest. The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present.