Understanding the historical dynamics of forest communities is a critical element for accurate prediction of their response to future change. In cooperation with international colleagues, Prof. Chuck Cannon of XTBG has presented a spatially explicit model of rainforest distribution through the last million years. The research result entitled “The current refugial rainforests of Sundaland are unrepresentative of their biogeographic past and highly vulnerable to disturbance” has been published in PNAS (Proceedings of the National Academy of Sciences of the United States of America).
The publication illustrates that the current situation, where the islands are separated by the shallow South China Sea, is extremely unusual given the actual history of the region. It demonstrates that the forest dynamics in Sundaland are exactly in the opposite phase as those in the northern latitude, which means that during the ice age, rainforest is at its greatest extent, while during the warm periods, like now, rainforest is at its lowest extent and exist only in refugia.
The paper provides a powerful tool for exploring how refugia are formed. The results also have major conservation implications. The model highlights the fact that the human conversion of Sundaland’s forests is occurring only a few thousand years after a major natural reduction and fragmentation of forest area occurred due to changing climate and rising sea levels. So, all of these endangered species were already at probably historical low in their population and already highly vulnerable to population extinction.
Sundaland is the ‘sub-continent’ of the major islands of Indonesia and Malysia which were joined during previous ice ages but much of which is now submerged due to the high sea levels after the ice melted.
The article is available online at:
http://www.pnas.org/content/106/27/11188.abstract
Abstract
Understanding the historical dynamics of forest communities is a critical element for accurate prediction of their response to future change. Here, we examine evergreen rainforest distribution in the Sunda Shelf region at the last glacial maximum (LGM), using a spatially explicit model incorporating geographic, paleoclimatic, and geologic evidence. Results indicate that at the LGM, Sundaland rainforests covered a substantially larger area than currently present. Extrapolation of the model over the past million years demonstrates that the current “island archipelago” setting in Sundaland is extremely unusual given the majority of its history and the dramatic biogeographic transitions caused by global deglaciation were rapid and brief. Compared with dominant glacial conditions, lowland forests were probably reduced from approximately 1.3 to 0.8 × 106 km2 while upland forests were probably reduced by half, from approximately 2.0 to 1.0 × 105 km2. Coastal mangrove and swamp forests experience the most dramatic change during deglaciations, going through a complete and major biogeographic relocation. The Sundaland forest dynamics of fragmentation and contraction and subsequent expansion, driven by glacial cycles, occur in the opposite phase as those in the northern hemisphere and equatorial Africa, indicating that Sundaland evergreen rainforest communities are currently in a refugial stage. Widespread human-mediated reduction and conversion of these forests in their refugial stage, when most species are passing through significant population bottlenecks, strongly emphasizes the urgency of conservation and management efforts. Further research into the natural process of fragmentation and contraction during deglaciation is necessary to understand. |
