Modelling the impact of canker disease and fire regimes on the population dynamics and extinction risk of the Critically Endangered and granite endemic shrub

Abstract

Landscape-level processes such as fire regimes, increasing disease prevalence and a drying climate are emerging threats affecting plant groups such as the Proteaceae. Using field derived empirical data and a population simulation model we investigated population-level impacts of canker diseases and contemporary fire regimes on the threatened shrub and granite outcrop endemic Banksia verticillata R.Br. We found the persistence of B. verticillata on granite inselbergs is strongly influenced by fire frequency and extent, as well as the prevalence of canker disease. For populations where canker is present but having a relatively lower impact none of the fire scenarios resulted in extinction over the 100-year simulation, but all scenarios resulted in population decline with the magnitude of the effect increasing with fire frequency and extent (proportion of plants killed). In contrast, higher impact canker disease scenarios resulted in rapid population declines and potential extinction. Small increases in inter-fire adult survival reduced the rate of decline in populations with relatively low canker infestation. Research is urgently needed to understand the role that a warming and drying climate in the South-west Australian Floristic Region may have on the epidemiology of canker disease and the feasibility and effectiveness of treating individuals with appropriate fungicides.