Climate Change Reduces Forest Regrowth After Wildfires

https://doi.org/10.1111/ele.12889

Stevens-Rumann, C.S., K.B. Kemp, P.E. Higuera, B.J. Harvey, M.T. Rother, D.C. Donato, P. Morgan, and T.T. Veblen. 2018. Evidence for declining forest resilience to wildfires under climate change. Ecology Letters 21: 243-252.

Who Will Speak for the Trees?

The wildfire that swept through northern California this past November was one of the deadliest and most destructive in the state’s history. Wildfires can consume everything in their paths, and forever change the local communities and the lives they leave in their wake. While it may take a long time for these communities to rebuild after these natural disasters, what is often missed is how the forest will rebuild itself. It turns out forests are struggling to come back, and climate change might have something to do with it.

Figure 1: Camp Fire, 90 miles north of Sacramento, CA on November 8th, 2018.
Source: https://en.wikipedia.org/wiki/Camp_Fire_(2018)#/media/File:Camp_Fire_oli_2018312_Landsat.jpg 
How to ‘Start the Fire’

A fire needs three things in order to sustain: fuel, oxygen, and a heat source. Wildfires in the Western United States are already pretty common, due to heat, drought, available fuel sources, and thunderstorms creating ideal wildfire conditions. Drought and warm temperatures in this part of the country dry out vegetation. Dried out trees, shrubs, and grasses can easily become fuel sources for fires once ignited with a heat source, such as lightning, burning campfires, or cigarettes. Air then supplies the oxygen needed with winds helping to grow and spread the blaze into a full-blown wildfire. Wildfires can move nearly 14 miles per hour and can clear 4 to 5 million acres of land in the U.S. each year!

Natural Wildfires

It’s important to remember that wildfires naturally occur in the environment, and play an integral role in the ecosystem. Fires burn up dead or decaying organic material (which can be dangerous!) but help to break down and recycle this material back into the soil. If some plants in the forest have diseases, or there’s parasitic insects hurting the trees, fires act as a disinfectant and wipe out those causing the damage. Wildfires also help to break up the top layer of the tree line, known as the canopy, to allow sunlight to reach the forest floor. This gives new seedlings a chance to grow and start a new generation of trees in the forest.

Figure 2: Lodgepole pine forest 23 years before (above) and 10 years after a wildfire (below) in Yellowstone National Park (1988). Notice all the dead trees and organic material cluttering the forest (above), and all the new growth that was able to take its place after the wildfire cleared it out (below).
Source: https://en.wikipedia.org/wiki/Pinus_contorta
How Does Climate Change Play a Role?

So why are forests struggling to come back after wildfires? One research team wanted to see if tree seedlings were struggling because of climate change, which has made this region’s climate warmer and drier in the last decade. This intensifies those ideal wildfire conditions, while potentially straining a tree seedling’s ability to establish itself and grow.

Dr. Camille Stevens-Rumann and her colleagues studied nearly 1,400 sites in the US Rocky Mountains, from Colorado to norther Idaho and Montana, from 1988 and 2011. In this region, climate data confirmed that the decade after 2000 was drier and warmer than the decade before. This enabled the team to investigate how well trees regrew after wildfires during a wet/cool decade compared to a dry/warm decade.

The Struggle IS Real

Trees in this region struggled mightily to regrow after wildfires during the dry/warm decade compared to the wet/cool decade. During wet/cool years, a large majority (70%) of the sites saw tree saplings reestablish themselves at numbers that met or exceeded the forest density before wildfires. During warm/dry years, not even half of the sites saw saplings reestablish themselves to pre-fire numbers. 19% of sites during wet/cool years saw no tree regrow, whereas that number nearly doubled during dry/warm periods. The team also noticed less tree regrowth across all forest types during dry/warm years compared to cool/wet years. Tree seedlings were just not able to reestablish themselves during dryer, warmer weather as successfully as they did during wetter, cooler weather.

Figure 3: Lodgepole pine in Anacortes Community Forest Lands, Washington.
Source: https://en.wikipedia.org/wiki/Pinus_contorta#/media/File:Pinus_contorta_28263.JPG
Unless Someone Like You Cares a Whole Lot …

Dr. Seuss’s ‘The Lorax’ spoke for the trees, and it appears someone needs to speak for them now more than ever. Fewer trees were able to recover and regrow after wildfires in the Rockies during the last decade, a period of warmer and drier climate conditions. Increasing temperature and water stress may not be creating a suitable environment for young tree seedlings to establish themselves and regenerate the forest. So as wildfires rage and climate change intensifies, a forest’s ability to bounce back may be in trouble.

As climate change continues, these stressors become more severe, and could result in the ecosystem shifting from a forest to some other ecosystem, such as a field filled with grasses or shrubs. This change in ecosystem type would impact the types of plants and animals that live there, the associated food web, and the services the forest provides people (hiking, hunting, lumber, etc.).

Let’s not forget that there are ways to mitigate the destructive damage done by wildfires! Firefighters are trained to fight wildfires, but hikers, naturalists, and outdoors-enthusiasts can remain vigilant to potential wildfire causes, such as smoldering campfires or dropped cigarettes. These practices can help to mitigate or stop wildfires before they turn into larger disasters. However, it appears that climate change may be a large driver of wildfires, a main deterrent to forest regrowth, and our main focus moving forward if we wish to save the trees.

References:

“California’s Camp Fire Deadliest In State History.” CBS Los Angeles, CBS Los Angeles, 12 Nov. 2018, https://losangeles.cbslocal.com/2018/11/12/californias-camp-fire-deadliest-in-us-history/.

Stevens-Rumann, C.S., K.B. Kemp, P.E. Higuera, B.J. Harvey, M.T. Rother, D.C. Donato, P. Morgan, and T.T. Veblen. 2018. Evidence for declining forest resilience to wildfires under climate change. Ecology Letters 21: 243-252. https://doi.org/10.1111/ele.12889

“Wildfires Information and Facts.” Climate 101: Wildfires, National Geographic, www.nationalgeographic.com/environment/natural-disasters/wildfires/.

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Nick Iraola

Nick has a Master of Science in Marine Science from UNC Wilmington. He has worked in the Aquatic Ecology Laboratory since 2015, and which monitors the water quality in the Lower Cape Fear River Basin. His master's thesis research pertained to eutrophication and nutrient cycling within a freshwater lake in Wilmington, NC. When he's not sciencing, Nick enjoys running, swimming, cooking, sailing, and catching up with friends and family. His favorite candy is Reese's pb cups, because what is there not to like!?

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