The genetic and demographic impacts of contemporary disturbance regimes in mountain ash forests [article]

Brenton Von Takach Dukai, University, The Australian National, University, The Australian National
2019
Timber harvesting, frequent wildfires and a changing climate are influencing ecosystem composition, structure and function globally, with resulting losses to biodiversity and economic indicators. In south-eastern Australia, these factors are causing the rapid ecosystem collapse of montane forests. Here, I characterise and quantify the demographic and genetic impacts that changing environments are having on mountain ash (Eucalyptus regnans), a foundation species and one of the world's tallest
more » ... es. To test whether mountain ash populations exhibit variation in susceptibility to increasing fire frequency, I investigated the response of growth rates and seed production to stand age under different environmental conditions. My results show that environmental factors determine the age of maturation, in turn affecting the time taken for populations to develop reproductively viable amounts of seed. This suggests that reduced fire return intervals may result in niche contractions of obligate seeders such as mountain ash. Next, I conducted a range-wide analysis of mountain ash population genetic structure to determine the extent of hybridisation with messmate stringybark (Eucalyptus obliqua), and investigate how genetic diversity parameters are influenced by hybridisation. I found that hybrid occurrence was not distributed evenly across environmental gradients or populations, and after accounting for admixture, mountain ash showed very little population genetic structure, with a small effect of isolation-by-distance and low global FST (0.03). This suggests that decisions around provenancing for restoration may depend on knowledge of how admixture influences population genetic structure, and that for some species there may be little benefit in planning conservation strategies around environmental adaptation of seed sources. Fire and silvicultural practices may be modifying patterns of within- and among-population genetic diversity and fine-scale spatial genetic structure, across a mountain ash-dominated landscape. As chlor [...]
doi:10.25911/5d820ac04e269 fatcat:6y44s6t7fra6zcwgzbfixi2fdm