Rainforests contract and expand
Tropical forest repeatedly shrinks to isolated patches, then spreads again — a species pump.
- When
- —
- Duration
- 1.8 million years
- Known to
- ± 200 thousand years
- Era
- Early Pleistocene, Quaternary
Glacial periods are dry as well as cold, and tropical rainforest in Amazonia, the Congo and Southeast Asia repeatedly fragments into isolated refugia separated by savanna, then reconnects during wet interglacials. The refuge hypothesis holds that this repeated isolation and reunion drove speciation and is part of why tropical forests are so diverse. The idea has been heavily criticised and partly walked back, but repeated forest fragmentation itself is well supported.