Rising temperatures are drying out forests in the western US. As temperatures increase, so does the atmosphere’s demand for water, a relationship known as the vapor pressure deficit. Numerous studies have shown that as vapor pressure deficit increases with climate change, the amount of water stored in both live and dead vegetation decreases. In fire-prone forests, this means that the fuel loads in these systems are becoming drier making them more available to burn when wildfire occurs. This is because the amount of water stored in live and dead vegetation (known as fuel moisture content) controls the amount of time and energy needed to vaporize that fuel moisture before ignition can occur. As fuels dry out, they burn more readily, and as a result we have seen an exponential increase in the forest area burned in the western US.

Climate change has increased drought frequency and severity as well as insect outbreaks which has resulted in widespread tree mortality. The substantial tree die-off from these mortality events increases the total amount of dead fuels available in the forest, which are inherently drier than live trees. Because fuel moisture content regulates the amount of heat energy that is released during wildfire, fires that occur where there is a surplus of dead fuels may release a significant amount of energy as heat. Consequently, the combined effect of rising temperatures and widespread tree die-off on fuel moisture content may in part be responsible for the unprecedented wildfire behavior we have seen in recent years.

In our recent study, we assessed how the combined effects of tree mortality and rising temperatures increased fuel availability and potential heat energy release in the areas where two megafires occurred: the Creek Fire in the southern Sierra Nevada of California and the Cameron Peak fire in the Rocky Mountains of Colorado. Both fires occurred during the 2020 fire season and were preceded by widespread tree mortality. The Creek Fire was one of the largest in modern California history and burned in an area where the 2012-2016 drought and bark beetle outbreak resulted in widespread tree mortality. The Cameron Peak Fire, which was the largest in Colorado history, burned through forest with large numbers of bark beetle-killed trees.
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In our study, we used temperature and fuel moisture content data to calculate changes in fuel availability in these two forests over the past three decades. Additionally, we calculated how this influenced the amount of heat energy that could be released during these wildfires and how the transition of trees from live to dead fuels influenced potential energy release. We found that tree die-off in these two forests transitioned substantial amounts of biomass from live to dead fuel pools.

​This transition, coupled with reductions in fuel moisture content from rising temperatures, resulted in substantial increases in fuel availability and the amount energy available for release in the areas where these two fires occurred.

​For example, in the footprint of the Cameron Peak fire, we estimated that higher temperatures coupled with dead fuel loading from beetle mortality resulted in a 55% increase in fuel availability and a two-fold increase in potential energy release. Because heat energy release drives fuel ignition and wildfire spread, our results suggests that the combined effects of tree mortality and rising temperatures likely play a role in the unprecedented fire behavior that has characterized modern wildfires. Fires that occur where there is surplus of dry, dead fuels may be perpetuated not only by available fuels, but also by the substantial amounts of energy they release.

The number of wildfires and acres burned by wildfires are the most common metrics used to report current fire season statistics. When an especially large fire is burning, it captures media and public attention. However, fire size is a poor measure of impact.
 
Large wildfires represent only 2-3% of all wildfires in the US but burn over 90% of the area. As such, they have a disproportional impact on firefighting costs and ecosystems. Extremely large fire events (> 40,000 acres), sometimes termed megafires1 are mostly associated with extreme fire weather and impacts. Not all large fires are equally impactful on society. For example, the 2011 Wallow Fire burned over 500,000 acres in Arizona and New Mexico with property damage estimated at $109 million. The 2018 Camp Fire, which burned just over 150,000 acres, caused an estimated $16.6 billion in losses and killed at least 85 people. 
 
Fire Severity and Ecosystem Impacts
Historically, large fires were a common occurrence throughout the western US. Due to fuel buildup from long-term fire deficits in the 20th century, fires are burning much more severely today with severe consequences to human communities and ecosystems.
 
To assess fire impacts to ecosystems and important values - recreation, clean water, carbon sequestration and timber production – we need information about how severely fires burn. The Monitoring Trends in Burn Severity program uses pre- and post-burn satellite imagery to map changes in the reflectance of soils and vegetation following fire. Changes in reflectance have been calibrated with fire severity and are generally classified as high, moderate, low, and unburned/low severity.
 
Recent trends in forest fire severity are alarming2,3. Many of our nation’s old and mature forests are burning in large high severity fires. On dry sites, high severity fires may be wiping forests permanently off the map to be replaced by grasslands or shrublands. On many sites throughout the western US, tree regeneration is challenged by warm and often drier summers.
 
Appropriate Metrics for Wildfire Impact
Viewing wildfires in terms of impacts to communities and ecosystem services is a better way approach to differentiating between wildfires that have negative impacts for society and those that have little impact to society and are good for ecosystems. Recommended terms:

• Number of residents evacuated
• Number of homes destroyed
• Acres of high-severity fire
• Amount of a watershed severely burned
• Air quality index and smoke impacts to communities
• Hospitalization rates due to smoke

References:
1 Linley, G.D., Jolly, C.J., Doherty, S. et al. 2022. What do you mean, ‘megafire’? Global Ecology and Biogeography. https://doi.org/10.1111/geb.13499
 
2 Parks, S. A., and J. T. Abatzoglou. 2020. Warmer and drier fire seasons contribute to increases in area burned at high severity in western US forests from 1985–2017. Geophysical Research
Letters.’ https://doi.org/10.1029/2020GL089858
 
3 Hagmann, R.K., Hessburg, P.F., Prichard, S.J. et al. 2021. Evidence for widespread changes in the structure, composition, and fire regimes of western North American Forests. Ecological Applications 31: e02431.  https://doi.org/10.1002/eap.2431
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Job Description:
We are hiring 5 field technicians to work at the Teakettle Experimental Forest for the 2022 summer field season. The Teakettle Experimental Forest is a 1300 ha old-growth, mixed-conifer forest located 80 km east of Fresno, CA in the southern Sierra Nevada. The 2022 field season will focus on collecting pretreatment data for a catchment wide prescribed burn. The crew will be tasked with establishing experimental plots, mapping forest structure using a surveyor’s total station, basic tree measurements, and conducting fuels transect surveys. Additionally, the crew will be tasked with conducting understory vegetation surveys and identifying the local flora to the species level.  The crew will also assist visiting scientists with their projects as needed. These projects may include basic soils work (coring, soil moisture, etc.), seedling inventories, and tree coring. Desired skills include plant identification, use of a total station, basic knowledge of tree measurements, and previous experience working as a crewmember. The facilities at Teakettle are rustic due to the remote location of the station. The cabin has solar power, bathrooms, a kitchen, and common space. Individuals will spend the summer sleeping in tents. The nearest town for supplies is Shaver Lake, CA, approximately a 1-hour drive from the field station. There is no WIFI or cellphone service at the field station but there is a landline.
The pay rate is $16/hour and crew members will work four 10-hour days each week with 3-day weekends. The field season will run for 12 weeks from the middle of June to early September. The official start date will be determined in late April.
 
Preferred Qualifications:
Preference will be given to applicants who have spent at least one season working on a field crew or have experience working at a remote field location. Preference will also be given to applicants who have prior experience with plant identification, basic tree measurements (i.e., DBH), line-intercept sampling or use of a total station. Please note that an up to date COVID-19 vaccination is required for this position.
 
How to Apply:
To apply, you will need to apply through the University of New Mexico’s Job Portal. First, go to UNM Jobs (https://unmjobs.unm.edu/) and select “Search for a Job”. In the search bar, search “req18591”, “Field Research Tech”, or “Teakettle”. Once the listing has appeared, select “Apply Now”. Review of applications will begin on February 14, 2022. Applications will be reviewed until all positions have been filled. Please note that a New Mexico Driver’s License IS NOT REQUIRED for this position.
 
Contact Information:
If you have any questions regarding the application process or about the Teakettle project, please contact Marissa Goodwin at mjgoodwin@unm.edu.

Go here more information about the field site.