Could the environment limit dispersal between Sunda and Sahul?

Prepared by Liam A. Trethowan

Dry riverbed and drought-prone forest of Sumbawa. Photo credit: Liam A. Trethowan.

The West (Sunda) and East (Sahul) of the Southeast Asian archipelago used to be much further apart. As the Asian and Australian plates came together, the islands we see today uplifted and the plant communities began to form. The historical separation of the continents is thought to underpin which species exist where. There are, however, many environmental variables that could shape the distribution of species across the islands.

(1) The islands at the western and eastern extremities of the archipelago have large expanses of lowlands – this is not the case for the islands in the middle which are often small and mountainous. (2) There are relatively more regions of heavy metal rich ultramafic soils on the islands at the centre of the archipelago. (3) Sea currents flow toward drought-prone habitat in the south (photo above). (4) I tentatively suggest that forests at the centre of the archipelago are shorter (photo below). All these differences dictate plant distributions in other parts of the world – but do they in Southeast Asia?

Stunted forest over heavy metal rich ultramafic soils on Wawonii island, a satellite island of Sulawesi at the centre of the Southeast Asian archipelago. Photo credit: Liam A. Trethowan.

I carried out a preliminary analysis to see if this is the case, and the results suggest that they do. I incorporated plant height into this analysis and called for more trait data to be gathered for Southeast Asian plants. This, alongside our increasing understanding of evolutionary relationships amongst Southeast Asian plants, plus more boots on the ground fieldwork to get a proper picture of which plants are where, should allow us to understand the drivers of the current (and future!) make up of vegetation.

This is a plain language summary for the paper of Liam Trethowan published in the Journal of Vegetation Science (