Biomes of Sundaland

During the last ice age the world was dryer and slightly cooler as much of the water was locked up in ice-sheets. Sundaland had a range of biomes, from mountain jungles to swamps and tropical shrub and grasslands.

Here's a vegetation map from WikiPedia of the world during the last ice age. Click the image for a bigger view so you can read the legend.

Two maps from http://atlantisjavasea.blogspot.com/

From a research paper:

Borneo and Indochina are Major Evolutionary Hotspots for Southeast Asian Biodiversity

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

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