Fire tolerance for Xanthorrhoeas or Grasstrees will differ between species according to Borsboom (2005). Even though they are highly combustible they do have the ability to accumulate a significant amount of fuel usually in the form of starch to help them survive fire and droughts. Post-fire stored starch tends to reduce as resources are used to push growth of new leaves, and phosphorus becomes immobilized from the trunk towards the crown according to Lamont et al. (2004).
But there seems to be a limit to burn-offs depending on species with some adult plants and also seeds dying during intense or frequent fires.
Xanthorrhoea deaths by fire have not been shown for species growing in Queensland, Australia. More research still needs to be done into the fire tolerance and frequency of burning off of Queensland species.
In general the recommendation is that grasstrees need to be given between 3 - 13 years of fire-free periods to help maintain Xanthorrhoea populations all over Australia. Burning plants younger than 4 years of age may seriously impact on seedling survival and adult plants may still be fire-affected by as much as 25 years after fire. At the same time, according to the Environmental Sciences Division of QLD, "young seedlings have a contractile primary root which helps to draw the vulnerable apical meristem below ground to provide some protection from fire".
It is clear that the burning off of grassplants is a skilled and timed-procedure, perfected by our Aboriginal ancestors.
