Soil Degradation and Food Production
Prepared by: Mary Silfven
Soil Degradation and Wildfire
Wildfires have many effects on our health and the health of our planet. One specific after-effect of wildfires is soil degradation, or the decline in the physical, chemical, and biological quality of soil (Santín & Doerr, 2016).
Healthy soil is important for many reasons; it’s one of our most important natural resources.
Benefits of Healthy Soil
Biological Diversity: Soil preserves biodiversity, referring to "the variety of living species on Earth, including plants, animals, bacteria, and fungi" (National Geographic, n.d.).
Water Benefits: Soil helps purifies water.
Food Production: Soil produces healthy food.
Carbon Storage - acts as a carbon sink, which keeps carbon out of the atmosphere and limits "greenhouse effects" that can warm the Earth.
Healthy soil consists of organic matter, a diverse population of microorganisms, and an abundance of nutrients. Nutrients move from healthy soil into the plants we eat (Silver et al., 2021).
However, soils impacted by intense wildfires have meaningful changes including loss of nutrients, microorganisms, and organic matter. In the worst case fires can lead to desertification, which is the loss of all biological productivity of what was once fertile land (Neary & Leonard, 2021).
Aren’t Fires Good for the Soil?
Fire is one of the oldest tools humans have used to cultivate and manage the environment. Controlled burns are still used today in forest management to reduce combustible material in a forest and prevent larger uncontrolled fires.
The burning of crop residue on agricultural lands is still a fundamental practice worldwide and is used to control pests and weeds, increase crop yields and minimize tilling (Santín & Doerr, 2016). So, it’s true that not all fires are bad for the soil. Some fire can be a useful tool.
When is Fire Bad for the Soil?
The main distinction between good fires and bad fires in terms of soil health comes down to the intensity of the fire.
Most controlled and planned fires are low-intensity. That means these fires don’t burn super-hot or for very long.
On the other hand, medium and high-intensity fires burn much hotter and for longer which has very different effects on the soil. With these more intense burns biomass like seeds and roots as well as microbes in the soil parish, soil pH changes, chemical properties change, and even physical properties in the soil change. These changes can lead to soil erosion or loss of topsoil (Santín & Doerr, 2016).
Effects on Soil
Physical Changes in the Soil
Physical changes in soil can occur with less intense fires, though the most severe changes happen when smoldering fires burn for long periods of time. When this happens, organic matter (i.e., decomposing plants, bacteria, insects, or anything formed by living organisms) can be depleted, which leaves the top of the soil in a condition of water repellency. Other physical changes are a loss in the soil structure and an increase in the soil density. This means water runs off of the soil and does not soak in. This leads to soil erosion or loss of topsoil, the soil most necessary for vegetative growth (Neary et al., 2005).
Chemical Changes in the Soil
Organic matter is lost when fires burn at medium to high intensity. Organic matter is important to the chemical structure of soil because it plays an important role in nutrient cycling in soils. Organic matter stores important nutrients such as nitrogen, the essential element plants need to grow. The stored nitrogen is easily volatilized and lost into the atmosphere after a fire. After this chemical change, any vegetation including crops will no longer be able to grow from this soil until the organic matter is restored. Unfortunately, it can be difficult and, at times, impossible to restore nitrogen in soils (Neary et al., 2005).
Desertification
Due to climate change, fires are starting earlier in the season, lasting longer, spreading more, and burning hotter. These factors lead to high-intensity fires which have severe effects on the soil, with the most severe being desertification. Desertification is the loss of all biological productivity of what was once fertile land. Computer models have predicted that the Western United States is one of the hot spots for high-intensity fires. Additionally, it seems as though fires are now burning in areas that are still recovering from fires from long ago in areas known as “fire scars”. Fires burning in fire-scared areas accelerate desertification. As a result, we are starting to see the desertification of once fertile and abundant land (Neary, 2018).
Effects on Food
Almost all (97%) of the world’s food supply comes directly from land used to grow crops. This process is reliant on healthy and complex soil. As the world’s population continues to grow, we will continue to need healthy soil. The world’s soil is under threat from many aspects of human life. Soil fertility is declining, topsoil is eroding, and desertification is expanding (Gupta, 2019).
As fires continue to plague the world, and specifically the Pacific Northwest, desertification and the loss of fertile soil will continuously threaten our food supply. Wildfires are intensifying as climate change continues to impact our world. Now 75% of fire-affected areas in the United States are in non-forested lands including urban areas and croplands (Powell, 2021).
As of right now, the United States is lucky enough that we have not experienced direct threats to our food supply that are specifically linked to soil degradation as a result of wildfires. However, our soil is in jeopardy due to increasing high-intensity wildfires and other human activities.
The state and federal governments are working together to protect farmers, crops, and soil, all of which are under threat from wildfire. Farmers are on the front line of protecting our food supply and soil health and, in recent years, have also become some of the people most impacted by wildfires (USDA, 2022).
What Can be Done?
Seeding and Mulching
The first essential step in preserving and restoring soil is to prohibit the growth of invasive weeds. To do this, reseed the soil with the appropriate plants (Moench & Fusaro, 2012). For farmland, this could be crop cover and planted seed not intended to produce food but rather specifically intended for enriching and improving soil health. This will slow erosion, smother weeds, and bring water back into the soil (Clark, 2022).
The second step is mulching with weed and seed-free straw or hay to add a proactive layer to the seeds. Mulching helps to reduce erosion and create the ideal environment for seed germination (Moench & Fusaro, 2012).
Reduce Runoff
There are several strategies to reduce water runoff. When soil has been affected by fire it becomes hydrophobic, meaning water does not easily seep into the soil. This can aid in erosion. By making contoured log terraces on slopes water will run down the hill but be slowed down by the alternating logs which will give the soil more time to absorb the water.
Additionally, silt fences made with wire and fabric can catch sediment that is being washed away. Lastly channeling water runoff into streams by making water bars, rounded mounds of soil held in place with logs (Moench & Fusaro, 2012).
Help in Oregon
In the past in Oregon, different government and nonprofit agencies have implemented ways to help farmers and landowners preserve soil health after fires. The USDA has assisted with finical assistance specifically aimed at soil health by providing funds for crop cover and mulching.
Additionally, the Environmental Quality Incentives Program has provided funds and assistance for agricultural producers to reduce soil erosion and sedimentation after fires (United States Department of Agriculture, n.d.)
References
Beyers, J. (n.d.). An example of a failure of check dams with straw bales and wattles following an extreme rain event. Post-fire erosion. U.S. Forest Service. Retrieved December 11, 2022, from https://www.fs.usda.gov/psw/topics/fire_science/ecosystems/erosion.shtml.
Bracewell, A. (n.d.). Prescribed fire at the Revolutionary War-era Saratoga National Historical Park in New York is used to maintain an historic landscape. Wildland Fire: What is a Prescribed Fire? National Park Service. Retrieved December 11, 2022, from https://www.nps.gov/articles/what-is-a-prescribed-fire.htm.
Clark, A. (2022, May 12). Cover crops for sustainable crop rotations. SARE. Retrieved November 14, 2022, from https://www.sare.org/resources/cover-crops/
Dirt to Dinner. (2019). Farmer stands on his tractor with a smoky fiery sky in the background. California Megafires and the Effects on Agriculture. Retrieved December 11, 2022, from https://dirt-to-dinner.com/california-megafires-and-the-effects-on-agriculture/.
Gupta, G. S. (2019). Land Degradation and Challenges of Food Security. Review of European Studies, 11(1), 63–. https://doi.org/10.5539/res.v11n1p63
Iverson Family Farms. (2020). Iverson Family Farms fields under a ruddy red sky. What Impacts Do the West Coast Wildfires, Smoke Have on Crops? Civil Eats. Retrieved from https://civileats.com/2020/10/13/what-impacts-do-the-west-coast-wildfires-smoke-have-on-crops/.
Moench, R., & Fusaro, J. (2012). Soil Erosion Control after Wildfire. [Fact sheet]. Colorado State University. https://extension.colostate.edu/topic-areas/agriculture/soil-erosion-control-after-wildfire-6-308/#:~:text=Mulching,sprayed%20with%20a%20tacking%20agent.
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Neary, D. G. (2018). Wildfire contribution to desertification as local, regional, and global scale. Chapter 8. In Squires V., & Ariapour A. Desertification. Nova Science Publishers.
Neary, D. G., & Leonard, J. M. (2021). Soil conservation after wildfires: Challenges, failures, and successes Chapter 2. In Vieira A., & Gonçalves A. Soil conservation: Strategies, management and Challenges. Nova Science Publishers.
Neary, D. G., Ryan, K. C., & DeBano, L. F. (2005). Wildland fire in ecosystems: Effects of fire on soils and water. https://doi.org/10.2737/rmrs-gtr-42-v4
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Santín, C., & Doerr, S. H. (2016). Fire effects on soils: the human dimension. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 371(1696), 20150171. https://doi.org/10.1098/rstb.2015.0171
Silver, W. L., Perez, T., Mayer, A., & Jones, A. R. (2021). The role of soil in the contribution of food and feed. Philosophical Transactions of the Royal Society B: Biological Sciences, 376(1834), 20200181. https://doi.org/10.1098/rstb.2020.0181
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U.S. Department of Agriculture. (2013). This is an example of soil water repellency damage from the Rim Fire. Burned Area Emergency Response (BAER) Flickr Album. Retrieved December 11, 2022, from https://www.flickr.com/photos/41284017@N08/10020904195.
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