An alumni explainer: each year hundreds of people flock to two of Tasmania’s national parks to witness the magnificent autumnal display put on by the deciduous beech (Nothofagus gunnii), also known as ‘the turning of the fagus.’ We asked two of our distinguished plant scientists to tell us about the significance of the seasonal display.
Nothofagus gunnii is one of around forty Nothofagus species (the so-called Southern beeches) found in Australasia and South America.
Fossils of pollen grains, leaves and fruit show that it’s one of the last species standing from a group of plants that were once scattered right across all of Australia and indeed pretty much all of the southern hemisphere, including Antarctica. A true living relict of Gondwana, now endemic to Tasmania’s mountains.
Many of the present-day Nothofagus species are evergreen, including the only other Tasmanian species, N. cunninghamii (myrtle), but several lose their leaves in winter. Among Australian species, N. gunnii is the only one that does this, and it is in fact our only “cold-deciduous” plant.
There have been few specific studies of its spectacular autumn display, known as ‘turning of the fagus’, but work on other winter deciduous trees may provide clues to what is happening.
Initially, shortening days signal the shutdown of growth in autumn. Then, when temperatures drop enough to be stressful, energy capture stops altogether, and the plant starts salvaging the cellular machinery in its leaves and storing nutrients for the spring.
The most abundant leaf components are the chlorophylls - the photosynthetic pigments that make leaves green. But leaves also contain other pigments, including yellow-orange carotenoids, and red-purple anthocyanins, that serve different functions.
The changing autumn colours reflect the fact that chlorophylls are the first to be salvaged, and this reveals the others. Variation across species, years, and locations reflect how much of each is present, and their relative rates of loss, which may be influenced by environmental and nutritional factors.
This article was written by two members of our alumni community:
Jim Weller (PhD 1997, BSc Hons 1990) is an Associate Professor in Plant Genetics and former ARC Future Fellow in the School of Natural Sciences.
Greg Jordan (PhD 1993, BSc Hons 1987) is a Professor of Plant Evolution and Ecology in the School of Natural Sciences, and is currently head of the Biological Sciences discipline
Best places to see the ‘turning of the fagus’ in Tasmania.
Image: James Burke