Fire is an integral part of many ecosystems and is even a requirement for certain organisms’ life cycles. Anthropogenic climate change has increased the severity and frequency of fire with consequences for natural systems and human populations. This has been magnified by high profile fires in the Amazon, Australia, and California. More severe fire has been attributed to warmer temperatures and more fuel from fire suppression by land management. But how exactly does this happen? More importantly, how has increased fire affected wildlife populations and what will impacts look like under future climate scenarios? We’ll examine these questions from recent literature researching the impacts of changing fire regimes on ecosystems and the integrated services they provide to humans.
Pyrophytes and Fire Cycles
Many species of trees and plants require fire to complete their life cycles and reproduce. Famous examples of such trees include the Giant Sequoia of Yosemite fame, the lodgepole and jack pines of the Boreal forests, and sand plain gerardia and wood lily of Eastern habitats.
The trees have serotinous cones protected by thick waxy coatings, that require the heat of a fire to release seeds. Fires are part of natural ecosystem cycles that pave the way for new growth, increase biodiversity (pyrodiversity), and naturally manage the health of the forest. Fires open up space and quickly regenerate soil nutrients for new trees (whose seeds have just been released by fire) and plants to germinate. They also clear old growths dominated by few species (or invasives) to open up meadows and grassland spaces, and animal deaths from fire become food for scavengers or detritus for further nutrient cycling. Fire has been a natural event in ecosystems for a long time and organisms are well-adapted to it.
So, what’s the problem?
Problems, really if we want to answer this truthfully. To quote the musical “Hamilton”, you should “look arou-nd, look arou-nd…”
The number, severity, and frequency of fires has increased significantly in the last half century in the Western U.S. and this has impacted human civilizations and wildlife populations. While huge individual fires that have burned towns to ash, caused plumes of smoke to drift across the United States, and turned urban skies eery shades of orange get the most media attention, it is the patterns of these events that matter more and give us context.
Interestingly, fire regime change from climate impacts globally is difficult to assess and shows less of a clear pattern (though more updated research is needed). This is due to the dynamics of climate change such as increased atmospheric moisture from warmer temperatures and less fuel that can reduce fires in some areas (tropics and deserts) while increasing fire rates elsewhere (arid grasslands and upper latitude climes.)
Why have fires increased in the Western U.S.?
This has been a subject of much study because there are many factors involved in pinpointing the causes of increased fire. For people that do not want to put the climate change stamp on the fire increase, the reasons are to do with forested land management, increased proximity of human settlements to forests, and natural climate variations.
Humans have indeed decreased the fuel clearing fires (fire suppression) that naturally occur and so lots of detritus and organic matter (read: wood) has built up in forests while the fires that do occur, are closer to human settlements that have encroached onto previously uninhabited land. So is this the reason fires have increased?
While more fuel from fire suppression certainly is part of the equation, that wood has to burn first. What increases the likelihood of that wood burning is how dry it is (fuel aridity). What has been found is that increasing drought, which has been part of a long-term “mega drought” in the Western U.S., and rising temperatures caused by anthropogenic climate change (ACC) have increased the aridity of the air and decreased atmospheric vapor pressure across Western US forests. While natural climate variability does account for some of the observed drying out, ACC was found to be responsible for the majority (~55%) between 1979 – 2015. The study’s authors also found that ACC contributed 4.2 million more hectares of forest burned, nearly twice as much as would have otherwise occurred between 1984 – 2015, and double the average number of days of the fire season between 1979 – 2015.
In addition, a great deal of the fuel from fire suppression has also come from dead plant matter as a result of drought and wood-boring beetle outbreaks (themselves wrought by changing climate conditions, see image below). Drought, likely exacerbated by ACC, has caused the die-off of many forest plants and contributed to the increase in fire fuel. Fire suppression in the 20th century certainly provided more fuel for the increased fire regime and has modulated the fire data, but the effects of ACC to dry out and add to that fuel has led to much of the increases in fire we see in the present.
How have increases in fires affected wildlife?
While it is true that natural ecosystems are well-adapted to fire cycles, conditions wrought by ACC are negatively impacting wildlife directly and indirectly. The obvious impact of more frequent fires is that some wildlife populations are lost directly from the fire itself (which has also claimed many human lives). Some of these populations were already vulnerable due to habitat loss and other ACC caused stressors such as invasive or pest species impact. The well known bark beetle outbreaks that have killed large stands of forest have an interesting relationship with fire as some of the wood-boring insects can survive fires and subsequently attack fire damaged trees.
In order for wildlife to survive a fire and be part of natural cycles, they must be able have unburnt refuges to thrive in while the burnt habitat recovers (which takes time). With habitat loss and higher intensity of fires which burn more completely, refuges are smaller with fewer available resources, handicapping organism capacity of surviving with a fire cycle. Another worrying impact of fire on wildlife is the loss of non-pest insects and the ecosystem services they provide for humans as well as nature, mainly in the form of pollination.
Increases in fire frequency, severity, and longevity may have long lasting impacts on natural ecosystems. Forest trees may see their ranges shift (due both to climatic factors and fire), fire-dependent species may thrive in some areas, but ultimately this will depend on fire frequency. If fires are too frequent to permit growth, than slow growing pyrophytes such as sequoias will not have sufficient time to grow past the juvenile stage. This scenario could lead to current forested areas being left treeless. This rapid change in primary production source has implications for the entire ecosystem, which could lead to rapid die-offs of communities or migrations of species that are dependent on forests.
The future outlook of fire disruption is highly biome-specific. Global models have shown that certain regions of the world expected to receive higher precipitation levels or that expect to have less vegetation (due to drought / desertification) may be less fire prone. Other regions, such as boreal forests, tundra, and mountain grasslands may be at much higher risk especially as the intensity and frequency of drought from ACC and continued levels of arid fuel are present.
The increase in fire season length and intensity along with the impacts that follow will continue in these areas as the climate continues to warm and as long as there is fuel to burn. The obvious long-term solution is part of the challenge of climate change in general which is to reduce planet-warming carbon emissions. Other short-term solutions may involve mitigating the impact of these more frequent fires. These short term solutions could include adjusting forest management to increase prescribed burns, using integrated pest management to control some bark beetle outbreaks, limiting human settlements to reduce direct impacts from fire, and to target fire support to critically endangered populations during fire seasons (such as using fire repellents around stands of endangered tree populations).
These short term solutions will be for nothing however if the longer term of goal of reducing carbon emissions to prevent further warming and its consequences are ignored or not taken seriously. We already know the impact of climate change and the projected outlook for the future will be looked at through smoky, orange colored (not rose colored) glasses.
Sources and Further Reads:
Abatzoglou, John T., and A. Park Williams. “Impact of Anthropogenic Climate Change on Wildfire across Western US Forests.” Proceedings of the National Academy of Sciences, vol. 113, no. 42, 2016, pp. 11770–11775., doi:10.1073/pnas.1607171113.
Akaike, H., et al. “Forest Ecosystems, Disturbance, and Climatic Change in Washington State, USA.” Climatic Change, Springer Netherlands, 1 Jan. 1974, link.springer.com/article/10.1007/s10584-010-9858-x.
Aponte, Cristina, et al. “Forest Fires and Climate Change: Causes, Consequences and Management Options.” CSIRO PUBLISHING, CSIRO PUBLISHING, 4 Aug. 2016, http://www.publish.csiro.au/wf/Fulltext/wfv25n8_fo#R8.
Aponte, Cristina, et al. “Forest Fires and Climate Change: Causes, Consequences and Management Options.” CSIRO PUBLISHING, CSIRO PUBLISHING, 4 Aug. 2016, http://www.publish.csiro.au/wf/Fulltext/wfv25n8_fo#R11.
Canada, Natural Resources. “Government of Canada.” Natural Resources Canada, / Gouvernement Du Canada, 7 July 2020, http://www.nrcan.gc.ca/our-natural-resources/forests-forestry/wildland-fires-insects-disturban/forest-fires/fire-ecology/13149.
Flannigan, Mike D., et al. “Implications of Changing Climate for Global Wildland Fire.” CSIRO PUBLISHING, CSIRO PUBLISHING, 10 Aug. 2009, http://www.publish.csiro.au/wf/WF08187.
Goss10, Michael, et al. “IOPscience.” Environmental Research Letters, IOP Publishing, 20 Aug. 2020, iopscience.iop.org/article/10.1088/1748-9326/ab83a7/meta.
“The Long-Lasting Impact of Wildfires on Wildlife, WWF Explains.” PBS, Public Broadcasting Service, http://www.pbs.org/wnet/nature/blog/wildfires-wildlife-wwf/.
Moritz, Max A., et al. “Climate Change and Disruptions to Global Fire Activity.” The Ecological Society of America, John Wiley & Sons, Ltd, 12 June 2012, esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES11-00345.1.
“What’s the Deal With a Lack of Water in the West?” What’s The Deal With…, 26 Apr. 2015, understandhistorynow.wordpress.com/2015/04/26/whats-the-deal-with-a-lack-of-water-in-the-west/.
“A Rare Species of Tree Was Saved from Australia’s Wildfires. And Something Else Happened.” Bulletin of the Atomic Scientists, 27 Aug. 2020, thebulletin.org/2020/01/a-rare-species-of-tree-was-saved-in-australias-wildfires-and-something-else-happened/.