Adapting to a fiery world

Australia. California. Mediterranean Europe. Alaska. Greenland. Each week there are news reports describing unprecedented fire events in another part of the world. These reports are often associated with heated debate about the causes of these fire events. Are they exacerbated by the climate emergency? What about fuel management? Are patterns of urbanisation and land-use change problematic? Is fire becoming more frequent or extreme?

Understanding the changing place of fire in the earth system is a key question for global change science. Changes in any part of the fuel-oxygen-heat ‘fire triangle’ are likely to alter patterns of fire activity. A challenge in understanding how environmental change will influence fire is that its drivers are deeply intertwined in complex webs of feedbacks. So, what is happening to patterns of fire activity?

Fire as a natural component of ecosystems
Plants colonised the land potentially more than one billion years ago, and charcoal has been present in the fossil record since atmospheric oxygen levels became sufficient to support combustion (the oldest known charcoal dates to some 440 million years ago). Because of fire’s long history in the biosphere, it has been important in the evolution of plants and animals. Plant species show a range of adaptations to fire: thick insulating bark, cones designed to release after fire, seeds whose germination is triggered by smoke, underground storage organs that re-sprout after fire, and more. In short, fire is a natural part of many ecosystems and in some plays an important role in maintaining local biodiversity.

How does climate affect fire activity?
Fossil pollen and charcoal show that past changes in climate have been associated with changes in fire activity. As conditions become drier and warmer, fire is expected to become more frequent and potentially change in its seasonality. A recent analysis of nearly 500 of the most intense (high energy release) fire events using remotely sensed data, concluded they were consistently associated with extreme fire weather (prolonged hot, dry, windy conditions).

The relationship between climate and fire is not simply the former driving the latter. Biomass burning is an important source of emissions associated with climate warming. Alongside CO2, fires release brown carbon and black carbon, which are effective agents of warming and have been dispersed across the planet as far as the ice-fields of the poles (where they reduce the reflective properties of those surfaces). Burning also changes terrestrial albedo (reflectance of the land surface) with further implications for climate due to the absorbance of heat.

However, the contribution of biomass burning to climate emissions varies with environmental context; although fire activity is concentrated in Africa, burning of peat in SE Asia and in some boreal regions, is a key contributor to burning emissions. The interactions between climate and fire are complex and dynamic, and many remain uncertain.

Changing vegetation influences fire activity
Vegetation is changing in many ecosystems, which can either increase or decrease fire risk. In parts of the southwest USA invasive grasses have transformed shrub lands by connecting isolated plants which helps fires to spread. Elsewhere changes in vegetation and land-use have also resulted in shifts in fire activity. The global decline in fire activity over the past 20 years is believed to be, in part, the result of urbanisation in Africa with associated changes in vegetation and the use of fire as a land management tool. The relationship between fire and vegetation is not just one-way. In some ecosystems the vegetation that appears following fire is more flammable, potentially setting up a ‘fire begets fire’ cycle. This type of dynamic, for example in shrub lands invaded by grasses, is an important component of loss of tropical rain forest in Amazonia and southeast Asia, and is associated with landscape transformations in parts of Patagonia and New Zealand.

In some ecosystems, such as New Zealand, these invasive plants carry fire adaptations absent in native flora that give them distinct advantages as fire activity increases. On the other hand, recent work has shown the potential for green firebreaks –that is, strips of low flammability vegetation positioned to impede the spread of fire and provide habitats. Likewise, homeowners can help to reduce fire damage by maintaining low flammability ‘defensible spaces’ around their properties.

Changes in patterns of ignition
Lightning is the most important natural ignition source, and its prevalence varies across the globe, with some areas of Africa and South America receiving more than 200 strikes per km2 per year, and others fewer than one (parts of New Zealand). In many parts of the world, humans are the prime source of ignition, whether deliberate (land clearance or arson) or accidental. These patterns of ignition, human and non-human, are likely to differ in time and space, and this affects patterns of fire activity. Climate change may also influence ignition. While the effects of climate change on lightning frequency are debated, there are ecosystems where lightning patterns seems to be shifting. For example, the devastating 2016 fire events in the World Heritage area of Tasmania - so severe they burned soils that took millennia to accumulate - were caused by a period of very high frequency dry lightning events. Likewise, large wildfires in Alaska in 2015 have been attributed to increased lightning activity. Changes in human activity and behaviour will also affect ignition patterns.

A fiery future?
For humans, the wildfires of most immediate concern are those threatening human life, well-being and infrastructure. A recent analysis suggests these events are clustered in south-eastern Australia and the western USA where extreme fire conditions are predicted to become between 20 and 50 percent more frequent under climate change. However, fires are also likely to occur at times and places where they have been rare in the past.

In 2016 a nearly 2000ha fire burned the Port Hills of Christchurch. Although small on the global scale, it equated to nearly 50 percent of the long-term annual burned area in NZ. In 2017 Greenland experienced the largest fires ever recorded there, including the 2500ha event north of Sisimiut in peatland rendered flammable as permafrost thawed. Again, not a large area on a global scale, but unprecedented for this region. Likewise, the catastrophic fires we are seeing in Australia occurred earlier in the fire season than historically the case, and have resulted in unprecedented burn sizes.

Whether individual events are the direct outcome of climate change is impossible to determine, but changes in average climatic conditions and in climatic variability make such events much more likely.

Adapting to a ‘fierier’ world will be challenging. Simply managing fire out of the landscape is not feasible, and may have unexpected and perverse ecological and social outcomes. While there is a place for management interventions such as fuel thinning and fuel reduction burning (prescribed fire) they are unlikely to be in themselves sufficient in the face of the current climate emergency and changes in urbanisation and land-use practices. Thus, fire management approaches need to be expanded to address the climate emergency, habitat loss and invasive species.

If we are to meet the challenges fire poses, we need to foster a flexible and forward-looking social and ecological resilience, and accept that in many landscapes changes in fire activity mean historic ecosystem conditions may not be able to be maintained.

A longer version of this article is on the University of Auckland’s Big Q website: How can we adapt to a fierier world?