The passage of a cyclone makes the land more vulnerable to fires

Oct. 13 () –

The strong winds and torrential rains that accompany a cyclone cause enormous damage to ecosystems, and this damage can make them more prone to future forest fires.

Given the forecast that intense cyclones will become more frequent around the world, a team of researchers examines in the journal ‘Trends in Plant Science’ the links between cyclones and wildfires, how they feed off each other, and why we might see fires in unlikely places in the future.

“Tropical forests, for example, are humid by definition, which makes them resistant to fire. But when they are disturbed by cyclones, can allow fire to spread in those ecosystems. For a fire to break out, three things are needed: fuel to burn, a sufficiently dry microclimate, and an ignition source, explains lead author Thomas Ibáñez, a plant ecologist at France’s National Research Institute for Sustainable Development who works with the University of Montpellier–. Cyclones can affect all three elements“.

Cyclones are storms that originate in the South Pacific or Indian Oceans and, like hurricanes in the Atlantic or typhoons in the Northwest Pacific, cause heavy rains, storm surges and gale-force winds. Strong cyclones can have wind speeds well in excess of 200 kilometers per hour, which can damage forests and fuel forest fires.

“When the wind from a cyclone blows, it damages the trees, knocking many leaves, twigs, branches and trunks to the ground, which are great fuel for future fires,” Ibáñez points out. “The wind also opens the canopy, bringing more light to the undergrowth, which can promote the growth of grasses or shrubs that are also good fuel. Also, when the canopy opens up, it makes the understory drier, because the canopy tends to shade the sun and lock in moisture.”

Cyclones can also indirectly increase human-generated ignition events by turning forests into promising places for agriculture. “This phenomenon is common in places where people depend on slash-and-burn agriculture or forest resources for their livelihoods,” he continued. “After cyclones, damaged forests can be burned to provide ash beds for planting new crops and to facilitate access to forest resources“.

Cyclones not only make fires more likely, but fires can also change the way cyclones affect forests. “Of course, fire can’t directly affect the likelihood of cyclones, because cyclones originate in the oceans, but they can affect the ecosystem’s response to cyclones,” he explains. “A fire can cause trees to be weaker to withstand cyclone winds or it can kill trees and promote regrowth of less cyclone-resistant trees.

In some regions that have historically had strong cyclones and fires, these events are a natural part of maintaining the land. “In cyclone-prone regions, there are also ecosystems that are adapted to frequent cyclones and fires, and the interactions between these disturbances actually maintain original and species-rich ecosystems,” Ibáñez recalls. “In these ecosystems, activities actions that reduce fire, such as land use change and fire suppression, can threaten ecosystem stability and cause biodiversity loss.”

But as climate change increases the intensity of extreme weather events like cyclones and temperatures continue to rise, storms are expected to reach places they haven’t in the past. Ibáñez and his colleagues hope to continue studying the interactions between cyclones and fires.

“We would like to better understand how this phenomenon varies depending on the place. In this way we could predict, with climate change, which places will be most affected by these changes,” he says. “An important component of global change is that ecosystems do not face to a single disturbance, but to a mixture of several, and the interaction between new disturbances can give rise to unexpected effects”.