Hot Topics in Ecology

Fire-driven loss of obligate seeder forests in the Alps

Synthesis by Prof. David Bowman and Dr Lynda Prior, University of Tasmania
  • Since 2003, multiple high-severity wildfires in short succession have locally eliminated obligate-seeding alpine ash forests in parts of the Australian Alps.
  • Aerial seeding of burnt areas can re-establish alpine ash in the winter following fire, but it is costly and depends on harvested seed stores: seed supplies are probably negatively affected by climate change.
  • Regenerating forests are vulnerable to wildfire, made more likely under climate change.
  • Protecting surviving mature forests must be a management priority.
Alpine ash forest, burnt three times since 2003, in the Australian Alps.

Alpine ash (Eucalyptus delegatensis) and the related mountain ash (E. regnans) are tall forest trees endemic to the mountains of southeastern Australia. Unlike most eucalypts, they do not readily resprout following fire. They regenerate from seed (i.e. obligate seeders), typically after high-severity fires, but have no long-term soil seed bank. They require around 20 years to reach reproductive maturity, and are vulnerable to local extinction if another fire occurs before the young trees set seed.

A series of wildfires throughout the Australian Alps in 2003, 2006 and 2009 burnt over 87% of the Victorian distribution of alpine ash. These fires, ignited by lightning, initiated regeneration, but some regenerating stands were reburnt by the later fires, causing population declines or local extinction. In some areas where regenerating alpine ash was killed, the species has been re-established by aerial sowing of seed. However, this intervention is impractical over large areas of forest because of costs of aerial sowing and limited availability of seed. Most alpine ash populations are currently in an immature state after these fires, rendering them vulnerable to local extinction if reburnt. Regenerating stands of alpine ash could also be more fire-prone than mature stands, but the effect of stand age is small relative to that of climate on the frequency of high-severity fires.

A projected warming and drying climate, possibly with more lightning, is likely to lead to increasingly frequent, severe fires. The hotter, drier conditions will also constrain the capacity of both alpine ash and mountain ash to recover from disturbance, by reducing tree growth, seed production and seedling establishment. Reduced growth, combined with shorter intervals between high-severity fires, will result in ‘interval squeeze’, which can threaten these species’ persistence as the climate changes.

Hot Topic Lead Author: 
Name: Dr Lynda Prior
Email: lynda.prior@utas.edu.au
Phone: 03 6226 1737

ID Title Location Type
8794 Smith A.L., Blair D., McBurney L., Banks S.C., Barton P.S., Blanchard W., Driscoll D.A., Gill A.M. & Lindenmayer D.B. (2014) Dominant drivers of seedling establishment in a fire-dependent obligate seeder: climate or fire regimes? Ecosystems 17, 258-270. Central Highlands, Victoria. Pre-existing gradient
8733 Bassett O. D., Prior L. D., Slijkerman C. M., Jamieson D. & Bowman D. (2015) Aerial sowing stopped the loss of alpine ash (Eucalyptus delegatensis) forests burnt by three short-interval fires in the Alpine National Park, Victoria, Australia. Forest Ecolog Australian Alps. Observational; pre-existing intervention.
8734 Bowman D. M. J. S., Murphy B. P., Neyland D. L. J., Williamson G. J. & Prior L. D. (2014) Abrupt fire regime change may cause landscape-wide loss of mature obligate seeder forests. Global Change Biology 20, 1008-15. Australian Alps. Observational; pre-existing contrasts.
8735 Bowman D. M. J. S., Williamson G. J., Prior L. D. & Murphy B. P. (2016) The relative importance of intrinsic and extrinsic factors in the decline of obligate seeder forests. Global Change Biology. Australian Alps. Modelling and geospatial analyses.
8736 Clarke H. G., Smith P. L. & Pitman A. J. (2011) Regional signatures of future fire weather over eastern Australia from global climate models. International Journal of Wildland Fire 20, 550-62. Eastern Australia. Modelling.
8737 Enright N. J., Fontaine J. B., Bowman D. M. J. S., Bradstock R. A. & Williams R. J. (2015) Interval squeeze: altered fire regimes and demographic responses interact to threaten woody species persistence as climate changes. Frontiers in Ecology and the Env NA. Conceptual model.
8738 Fagg P., Lutze M., Slijkerman C., Ryan M. & Bassett O. (2013) Silvicultural recovery in ash forests following three recent large bushfires in Victoria. Australian Forestry 76, 140-55. Victorian Alps. Observational; pre-existing contrasts and interventions.
8739 Fairman T. A., Nitschke C. R. & Bennett L. T. (2016) Too much, too soon? A review of the effects of increasing wildfire frequency on tree mortality and regeneration in temperate eucalypt forests. International Journal of Wildland Fire 25, 831-48. Victorian forests. Review.
8740 Ferguson I. (2011) Strategic seedbanks to meet fire risks for Victorian ash-type species. Australian Forestry 74, 97-107. Victorian Alps.
8741 Lindenmayer D. B., Hobbs R. J., Likens G. E., Krebs C. J. & Banks S. C. (2011) Newly discovered landscape traps produce regime shifts in wet forests. Proceedings of the National Academy of Sciences of the United States of America 108, 15887-91. Victorian mountain ash forests. Conceptual model.
8742 Mok H.-F., Arndt S. K. & Nitschke C. R. (2012) Modelling the potential impact of climate variability and change on species regeneration potential in the temperate forests of South-Eastern Australia. Global Change Biology 18, 1053-72. Central Highlands, SE Australia. Modelling.
8743 Prior L. D. & Bowman D. M. J. S. (2014) Big eucalypts grow more slowly in a warm climate: evidence of an interaction between tree size and temperature. Global Change Biology 20, 2793-9. Australia, south of the tropics with > 500 mm mean annual rainfall. Meta-analysis of forest growth data.

Further information about this topic contact:

Dr Lynda Prior
lynda.prior@utas.edu.au
03 6226 1737

Chair, Hot Topics Editorial Board
Dr Rachel Standish
R.Standish@murdoch.edu.au