By Katherine Edwards
In a previous post, Jodi Wildy raised concerns about the health of Flooded Gum, on her land in Boyup Brook and elsewhere. George Matusick has shared his ideas about the role of psyllids in the decline, and below Katherine Edwards, on the basis of her master’s studies, pays attention to some other factors that she thinks may be important explanatory factors.
Thank you Jodi for bringing the important issue of Flooded Gum decline into the spotlight! Relatively little research has been conducted into the causes behind the extensive Flooded Gum decline. Research that has been conducted has tended to focus on the role that phloem-feeding insects (PFI) may be playing in the decline. While George has given abundant information on the psyllids, I wanted to comment on the Perthida leafminer, another important PSI that is abundant on Flooded Gum. An important factor of the history between Flooded Gum and the Flooded Gum species of the Perthida leafminer, is that the abundance and distribution of the leafminer seem to have increased since their first records in the late 1800’s according to a study of herbarium collections. The authors of that study suggested that the increases were linked to the governmental changes to Aboriginal fire regimes around that were in place since the 1850’s, the hypothesis being that Aboriginal burning regimes produced more crown scorch which would kill larvae and abscise the leaves that would have been their food source, and the change to the European burning regime reduced this population control mechanism. The Aboriginal fire regime, compared to the European regime, involved frequent burning of bushland areas with intensity sufficient to reach and scorch the crowns. The European burning regime involved an era (1856-1920) of uncontrolled, intense fires caused by settlers, followed by an era (1921-1965) of fire suppression, followed by the current era (1966-present) of wildfire suppression and prescribed burning.
PFI are an important factor in the decline aetiology of Flooded Gum but, from my observations and the research I have read, are one factor in a complex decline. Fire and understory disturbance may also be important but I fear that changes to rainfall may be the main driver behind this decline, causing the stress that renders the species more susceptible to the horde of organisms (PSI’s, Phytophthora species, heart-rot fungi, mistletoe’s, boring beetles, termites, e.t.c.) that feed on this species.
The decline of Flooded Gum presents some exciting opportunities for further research into ecological interactions, the effect that a changing climate is having on South-Western Australian Eucalypts and the primary cause of the decline of an iconic keystone species. This is one species I am not prepared to lose in the shift to the novel ecosystem state, it is far too important!
