Shifting patterns of Nothofagus cunninghamii (Hook.) Oerst rainforest in the late quaternary of southeastern Australia: Evidence from pollen

An attempt is made to identify the location and nature of areas in which the cool temperate rainforest tree Nothofagus cunninghamii may have survived the glacial period, using fossil pollen data from sites at different altitudes in the Central Highlands of Victoria, Australia.

At one high altitude site Nothofagus has been recorded consistently through the latter part of the Pleistocence including the height of the last glacial. There was a postglacial expansion at most sites to a maximum extent in the early to middle Holocene, followed by a decline at all sites and elimination from two of the lower altitude sites.

The persistence of Nothofagus pollen through the height of the last glacial in a sheltered high altitude site supports the concept of glacial refugia, and leads to the query as to how Nothofagus survived the glacial under winter temperatures several degrees lower than those supporting the tree today. Evidence from evolutionary history, clinal variation in morphology and physiology along altitudinal or environmental gradients, and recent work on leaf physiognomy and ecophysiology contribute to possible explanations.

Elimination of Nothofagus from lower altitude sites after the middle Holocene raises the possibility of a shifting pattern of distribution, with long term survival dependent on the continued existence of locations suitable for the tree through the range of glacial and interglacial conditions. Fossil pollen data provide support for the occurrence of such locations in mountainous areas in sheltered gullies protected from fire.