Genetic and demographic impacts of contemporary disturbance regimes in Mountain Ash forests

Ignition Grant Round 4 (March 2015)

Mountain Ash (Eucalyptus regnans) is the world’s tallest flowering plant and hardwood, and one of just a few obligate seeder eucalypts. It is killed outright by high-intensity fires and a canopy seedbank provides the only source of natural regeneration.

Unfortunately, contemporary logging practices and changes to climate-related regeneration niches may be combining to produce a fire regime that could cause the abrupt and permanent collapse of vast tracts of Mountain Ash forest. Abrupt shifts in ecosystem state such as this are becoming apparent in different scenarios around the world, and present a real challenge to management agencies trying to lengthen ecosystem viability.

Our pilot project will be the initial step towards using Mountain Ash forest as a model system for predicting how forest ecosystems dominated by obligate seeders will respond to contemporary disturbance regimes.

To make such predictions, we will need to identify and characterise life history traits and population demographic parameters that influence the species response to disturbances. It also requires determining any potential adaptive responses that Mountain Ash may invoke as a result of contemporary disturbance regimes, which could influence its susceptibility as a community.

This pilot study will help to clarify the most effective sampling regimes, preparation techniques and genotyping methodologies to conduct a landscape genomics project involving Mountain Ash. Specifically, the pilot project will be used to determine whether the dispersal kernel for Mountain Ash seeds is likely to be within the range suggested by the historical literature (< 150 m), and whether parent-pair analyses are possible using trees killed in the 2009 Black Saturday fires.

Forty leaf samples will be taken from each of two monotypic stands of Mountain Ash forest (approximately 5 km apart), where all individuals are in the same age cohort. Samples will be collected in a T-shape with two trees sampled every 20 m, to create transects 180 m long.

We will use high-throughput sequencing methods to genotype these samples, and then calculate genetic relatedness between individuals (to determine pairwise ‘kinship’ coefficients) of known distance from one another, based on random genes. This will give us the knowledge of spatial genetic structure we require to be able to conduct broader genomic analyses in the future.

Additionally, we will use wood samples taken from the sapwood of 40 adult trees (20 from each site) killed in the 2009 fires to determine whether parent-pair analyses are possible in such stands. As the DNA of the wood is likely to be highly degraded, we will pick a sample of SNPs (evenly distributed across the genome) that we identified during the relatedness investigation, and genotype these individuals using a Fluidigm assay or other suitable platform. We will then conduct analyses to relate the dead parent trees to the leaf samples.

This pilot project will use novel genetic approaches to gain an understanding of population demographics of an Australian keystone species, and will provide us with the knowledge and methods required to carry out large-scale landscape genomic analyses of Mountain Ash over the next three years.