COS 181-5 - High severity fires, positive fire feedbacks and alternative stable states in Athrotaxis rainforest ecosystems in western Tasmania

Friday, August 11, 2017: 9:20 AM
E145, Oregon Convention Center
Andres Holz, Geography, Portland State University, Portland, OR, Sam Wood, Biological Science, University of Tasmania, Michael Fletcher, University of Melbourne, Feli Hopf, Australian National University, Carly Ward, University of Tasmania, Thomas T. Veblen, Geography, University of Colorado, Boulder, CO and David Bowman, School of Plant Science, University of Tasmania, Hobart, Australia

Recurrent landscape fires present a powerful selective force on plant regeneration strategies that form a continuum between vegetative resprouters and obligate seeders. In the latter case, reduction of the interval between fires, combined with factors that affect plant traits and regeneration dynamics can drive plant population to local extinction. Here we use Athrotaxis selaginoides, a relict fire-sensitive Gondwanan tree species that occurs in western Tasmania, as model system to investigate the putative impacts of climate change and variability and human management of fire. We integrate landscape ecology (island-wide scale), with field survey and dendrochronology (stand-scale) and sedimentary records (watershed and landscape-scales) to garner a better understanding of the timing and impact of landscape fire on the vegetation dynamics of Athrotaxis at multiple scales.


Across the species range sedimentary charcoal and pollen concentrations indicate that the recovery time since the last fire has consistently lengthened over the last 10,000 yrs. Stand-scale tree-age and fire-scar reconstructions suggest that populations of the Athrotxis have survive very infrequent landscape fires over the last 4-6 centuries, but that fire severity has increased following European colonization causing population collapse of Athrotaxis and an associate shift in stand structure and composition that favor resprouter species over obligate seeders. Overall our findings suggest that the resistance to fires and postfire recovery of populations of A. selaginoides have gradually declined throughout the Holocene and rapidly declined after Europeans altered fire regimes, a trend that matches the fate other Gondwanan conifers in temperate rainforests elsewhere in the southern Hemisphere.