It’s been fire season again down here in Australia, with all that that entails. But the threat to life and property is not the only aspect of bushfires, and it’s interesting to see how the Australian ecosystem has evolved over millennia to make use of fire. For instance, the native orchid Pyrochis nigricans, shown in this article in The Conversation, flowers in response to fire.
Then there’s the eucalyptus, so characteristic of Australian landscapes. Many eucalypts shed their bark in ragged sheets that hang from the trunk, which draws fire up the trunk to the highly volatile canopy, which literally goes up like a bomb, spreading seeds widely – this works to create a broad gene base in a region, which helps ensure robustness.
But that’s only part of the story: the seeds of some trees require both fire and smoke to germinate. In fact, scientists in Western Australia have identified the gene which responds to smoke.
After a fire, eucalypt forests regenerate quickly, sprouting rapidly from protected tissues in the stem and roots. This survival mechanism, however, is dependent on bushfires in these areas maintaining current intensity and frequency, as eucalypts tend to do best with fires occurring about once every 10 years, with a relatively low intensity. Climate change will undoubtedly affect both intensity and frequency, which will in turn affect our landscape. In fact, according to University of Tasmania Professor David Bowman, one result of climate change may be to wipe out our giant gums.
In an area that has mixed acacias and eucalypts, the eucalypts will dominate if fires occur frequently (around every 10 years). If there are no fires, or fires occur less frequently, the acacias will dominate and tend to crowd out the eucalypts.
Then there’s the role of ants: we wrote in an earlier post about how the process of myrmechacory (seed dispersal by ants) provides a better chance of speciation for plants. What’s more interesting is that there’s reason to believe that some plants have evolved in ways that take advantage of the specifics of seed burial by ants. Specifically, the depth at which ants bury seeds in their stores may be optimal in terms of protecting seeds from fire, yet ensuring that they get enough heat to break the seed dormancy and allow it to germinate. The results aren’t confirmed, but it’s interesting to consider what millennia of evolution can get you (hat tip Kieren Beaumont of Flinders University for this).
Of course, the adaptation of Australian ecosystems to dry conditions and frequent fires depends on those conditions remaining relatively unchanged, which makes the introduction of invasive plants a threat to the current fragile balance. One invader in particular, gamba grass, has already started to drastically reshape the savanna areas of northern Australia. This grass grows up to 4 metres high, and can produce up to 5 times the biomass of Australian grasses. This means that Australian savanna trees, adapted to high-frequency, low-intensity fires that stay low to the ground, are now subjected to much more intense fires that reach higher.
Professor David Bowman recently wrote an article in The Conversation that suggested importing elephants to graze the gamba grass as a way of preserving the native savanna. While the suggestion was somewhat tongue in cheek, Professor Bowman was quite serious that we need to consider all options to solve our problems, rather than simply picking a short-term solution for one problem that exacerbates others or creates new ones further down the road.
And after all, we have the lesson of the cane toad to show where that leads.