Fire, Ecosystems, Climate: It’s Complicated
USGS is disentangling the interwoven fire-ecosystem-climate relationship to better understand and predict how it will change into the future.
Fire is Fundamental
Fire is fundamental to humanity. Without it, civilization as we know it wouldn’t be possible. Using fire, people can do many things, like cook food we couldn’t eat otherwise. Harnessing fire opened a world of technological possibility when people began using it to smelt metal, without which our advanced, industrialized society wouldn’t exist.
But before people started using fire as a tool, fire was already foundational in ecosystems. The presence or absence of fire, how frequently and when an area burns, and the intensity of fire—collectively known as the fire regime—contribute to and are affected by the type of ecosystem in an area. In turn, fire regime and ecosystem type are interconnected with an area’s climate.
The relationship between fire, ecosystem, and climate is interwoven and complex. Each part in this triad of factors influences and is influenced by the other two parts.
People are included in this relationship, too. USGS scientists are at the forefront of studying changes to the fire-ecosystem-climate relationship and predicting what those changes mean for ecosystems and people. They study this relationship in every biome across America, providing science that gives land and fire managers tools so they can better understand and manage for changes at a range of different scales.
Studying a Changing Relationship
Ecologist Ellis Margolis studies the interactions between forest ecosystems, fire, climate and people's use of land over the last millennium. Specifically, he uses the evidence from tree rings to help reconstruct fire, climate, and ecosystem interactions and changes before 1900, when written records were few, but fire was a frequent, normal event in many forests.
The centuries-old fires that Margolis studies are particularly helpful to fire and land managers, because in many of the ecosystems they are managing, people have used fire as a tool, often to influence ecosystems, for thousands of years.
In the southwestern U.S., Margolis and others found that, on a local scale, indigenous fire management was able to buffer the influence of climate on fire, which enabled societies to persist at the ancient wildland urban interface for centuries in regions that, today, are experiencing an increase in devastating fires.
The USGS has a large portfolio of science on the interactions between fire, climate, and invasive species, especially in the sagebrush biome where the introduction of a slew of invasive annual grasses has created a self-perpetuating cycle.
Here, the invasive grasses dry early in the growing season and are adapted to more frequent fires than the dominant native vegetation, sagebrush, which are adapted to much less frequent fires. They also grow more quickly than sagebrush after fire, so not only are they more resilient to the fire they help fuel on the landscape, they spread much faster than the native plants can keep up with.
Fire ecologist Doug Shinneman and his team produce science that directly informs land and fire managers so they can effectively manage ecosystems, including in the sagebrush biome. Their work includes studies on the effectiveness and impacts of fuel breaks, or spaces managed to contain less burnable material, to reduce fire spread in the sagebrush biome. Using field-based studies of fuel break conditions and modeling research, the team assesses potential fuel break effectiveness across large portions the Great Basin region.
As people use fire to burn fossil fuels, they increase the amount of greenhouse gases in the atmosphere, which is affecting climate on a global scale. Of course, changes in the climate piece of the fire-ecosystem-climate relationship impact ecosystems and fire behavior.
Climate change is stressing many ecosystems making them less resilient to extreme disturbances, like fires.
Ecologist Adrian Das has seen this bear out in his studies on forest health. Using a 40-year dataset, he tracked extreme change in forests in Sequoia and Kings Canyon national parks—home to some of the largest trees on the planet, giant sequoias, which can live well over 3,000 years—as the climate in the region has shifted and become drier.
The plants in these forests are fire-adapted and often the ecosystem is fire-dependent, meaning fire is a regular and necessary feature of this ecosystem. However, just like in other regions, people actively suppressed fire from burning this landscape for over a century and a lot of fuel built up as a result.
When the insult of uncharacteristically severe fire is added to the injury of immense fuel build up and climate change-induced drought, the forest ecosystem can both literally and figuratively go up in flames.
Forests that once were maintained by fire are now being obliterated by it.
Das’s work, and that of other USGS scientists, will help to characterize and predict ecosystem change so that we can better prepare for and manage climate change-impacted ecosystems.
Finally, with the changes in precipitation and temperature caused by climate change, fire behavior itself is changing. Fires are burning hotter and moving faster and all of this makes postfire recovery in an ecosystem different than what it was before climate change.
Das and colleagues track the amount of fuels on the landscape and monitor the change in vegetation and fuels after a fire. For many reasons, shrublands and other ecosystem types are now replacing the forests Das studies and scientists are uncertain if the forests will recover or return.
Shinneman also studies how fire and other disturbances affect ecosystem health and resiliency. Their work focuses directly on understanding the dynamics of the past, present and potential future fire-ecosystem-climate relationship.
Shinneman’s work extends to tracking the changes in wildfire size, count, and area burned over time. Scientists and fire and land managers can use the Wildfire Trends Tool to view the changes and track trends in wildfire in the American West over the last century. While this tool is not predictive of future fire, it is informative of how much has changed in the fire-ecosystem-climate relationship over the last century.
USGS fire science is disentangling the interwoven fire-ecosystem-climate relationship to better understand and predict how this relationship will change into the future. With this information in hand, fire and land managers are better prepared to conserve ecosystems and protect people and the ecosystem services that societies depend upon.
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