The Old Gum Tree: the Reason for the Eucalyptus Having Flammable Bark may be Found in Game Theory
https://www.kqed.org/science/4209/eucalyptus-california-icon-fire-hazard-and-invasive-species
https://royalsocietypublishing.org/doi/10.1098/rspb.2016.0847
The prisoner’s dilemma is a famous example of a situation in which game theory applies. In the scenario, two prisoners are brought in for questioning by some detectives. The detectives tell the prisoners that they can either confess or remain silent. If one prisoner confesses and the other remains silent, then the one who confessed will be let off and the silent one will go to prison for a long time. If both confess, then both will go to prison for a medium sentence. If both don’t tell the detectives anything, then both prisoners get light sentences. What do you think the prisoners will do? It seems best for both to remain silent and take the light sentence. However, each suspect has no guarantee that the other will also stay silent. Not being able to take the risk of the other prisoner informing on him/her, each will choose to confess. Various examples of the prisoner’s dilemma can be found in real life, from arms races to women wearing makeup, but a really interesting one is the Eucalyptus tree.
The old gum tree. Anybody who lives in a fire-prone environment will know of its danger. The eucalyptus is a genus of tree native to Australia that has managed to proliferate across the globe to places such as India, the Mediterranean Basin, as well as my home state of California. Brought in the mid 19th Century during the gold rush, the eucalyptus, specifically the Blue Gum, can be found throughout California in strands or along roadsides. The danger I spoke about, well that can be found in the tree’s bark. Eucalyptus trees are constantly growing and shedding bark in long strips. In California, it is common to see municipal workers raking up this shed bark, and for good reason. The bark of the gum tree is flammable due to the prevalence of eucalyptus oil.
This doesn’t seem logical. Why would a tree native to a dry climate evolve to have flammable bark? It seems counterintuitive. Well, that’s the point. The eucalyptus have evolved to create a flammable environment on the forest floor so as to burn away the offspring of competing tree species. Eucalyptus release large bunches of seeds after fires, and the seeds actually require fire to germinate, having a protective shell that needs to be burned off. They are not great at germinating in non fire-prone environments where they are outcompeted by other plant species. This relates to the prisoner’s dilemma, because the Eucalyptus has evolved to harm itself to survive, as having a better germinating species outcompete it would result in its obliteration. The eucalyptus would be better off if they didn’t shed flammable bark and have seeds which require fire to grow. There would be less fires, and the trees would have a better chance of thriving. However, as the eucalyptus is slow to germinate, it cannot take the risk of having a competing species proliferate quicker than it and eventually replace it. Thus, the eucalyptus creates a fire prone environment with its flammable shedding bark, releases seeds which only grow after a fire, and grows rapidly following its slow germination. This is known as a trade-off in economics. The eucalyptus sustains some damage from fire, but is among few trees able to germinate following fire.