Historical land use couples with host density to affect myrtle rust impacts in a wet sclerophyll forest community in Eastern Australia

Abstract

Non‐native plant pathogens such as Austropuccinia psidii , the causal agent of myrtle rust, pose a significant threat to native forests. Myrtle rust is wind dispersed and its impacts are influenced by its ability to move through landscapes. Understanding the connection between land clearing processes and susceptible species dynamics is a crucial step towards developing targeted plant disease management strategies. We hypothesised that patches of wet sclerophyll forest with greater disturbance—particularly land clearing—would show higher densities of susceptible species in the subcanopy layer and therefore higher myrtle rust impacts.
To test this, we surveyed 21 patches of wet sclerophyll forest in eastern Australia, varying in land tenure and level of historical land clearing. We explored relationships between species abundance, susceptibility and myrtle rust impacts.
We found a positive interaction between historical land clearing, the abundance of susceptible species and myrtle rust impacts. Sites where susceptible species, particularly Archirhodomyrtus beckleri , were more abundant also showed more severe disease impacts.
Practical implication : Plant pathogens worldwide continue to spread outside of their native ranges into new habitats. Our results highlight the importance of investigating variable processes like land use legacy that can correlate with impacts of non‐native plant pathogens. Our findings suggest that forest patches regrown after disturbance are more vulnerable to myrtle rust because of the composition of their subcanopy layer. Several management implications stem from our study. For example, formerly heavily cleared sites would benefit from monitoring for weeds that may establish in openings created by the death of susceptible trees. Less disturbed areas should receive targeted conservation to protect healthier individuals of species threatened by myrtle rust.