Areas in the wake of cyclone-strength winds and torrential rain are more likely to subsequently suffer from forest fires
The strong winds and torrential rains that accompany a cyclone do tremendous damage to ecosystems, and this damage can make them more prone to future wildfires, researchers have found.
As intense cyclones are projected to become more frequent worldwide, the team of researchers examined the links between cyclones and forest fires, how they fuel one another, and why we may see fires burning in unlikely places in the future.
Thomas Ibanez is a plant ecologist at the French National Research Institute for Sustainable Development working with the University of Montpellier, and lead author of the research.
He said: “Rainforests, for instance, are wet by definition, which makes them resistant to fire. But when they are disturbed by cyclones, it can allow fire to spread into those ecosystems.
“To have a fire, we need three things: fuel to burn, dry enough micro-climate, and a source of ignition; 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 north-western Pacific, they deliver heavy rains, storm surges, and gale-force winds.
Strong cyclones can have winds with speeds well over 200km/h, which can damage forests and prime them for forest fires.
Ibanez said: “When the wind from a cyclone blows, it damages trees, bringing down a lot of leaves, twigs, branches, and logs to the ground, which make great fuel for future fire.
“Wind also opens the canopy, bringing more light into the undergrowth, which can promote the growth of grasses or bushes that also make good fuel.
“Also, when the canopy is opened, it makes the undergrowth drier because the canopy usually shades it from the sun and locks in moisture.”
Cyclones may also indirectly increase the instances of human-generated ignition by rendering forests promising places to conduct agriculture.
Ibanez added: “This phenomenon is common where people depend on slash-and-burn agriculture or forest resources for livelihoods.
“After cyclones, damaged forests may be burned to provide ash beds for planting new crops and for easier access to forest resources.”
Not only do cyclones make the likelihood of fire greater, but the fires may also change the ways that cyclones affect forests.
“Of course,” Ibanez said, “fire cannot directly affect the likelihood of cyclones, because the cyclones originate from oceans, but they can affect the response of the ecosystem to cyclones.
“If you have a fire, it can make the trees weaker to resist cyclone winds or it can kill trees and promote the regrowth of trees that are less resistant to cyclones.”
In some locations that have historically had strong cyclones and fires, the events are a natural part of maintaining the land.
Ibanez explained: “In cyclone-prone regions, there are also ecosystems that are adapted to frequent cyclones and fires, and interactions between these disturbances actually maintain original and species-rich ecosystems.
“In these ecosystems, human activities that reduce fire, such as land use change and fire suppression, can threaten the stability of the ecosystem and cause biodiversity loss.”
But, as climate change increases the intensity of extreme weather events like cyclones and wind speeds and temperatures continue to rise, the storms are projected to reach locations that they haven’t in the past.
Ibanez and his colleagues hope they can continue to study cyclone-fire interactions.
“We would like to better understand how this phenomenon varies by location. We could then predict with climate change which places would be more likely to be affected by these changes.
“An important component of global change is that ecosystems do not face just one disturbance, but a mix of several disturbances, and the interaction between new disturbances can result in unexpected effects.”
The research is published in Trends in Plant Science.
Image: Fire in crown of downed pine, Thomas County, Georgia. © William J Platt.