The most damaging long-term impact to ecosystems after wildfire is soil erosion. Restoring landscapes after wildfire depends on the severity of damage and time of year. A timely and proactive response to wildfire will prevent further damage and accelerate the recovery of your home landscapes.
Soil Erosion and Recovery
Erosion is a natural process through which soil moves. The rate and scale of erosion is typically driven by local geology, topography, vegetation, climate and weather. In post-fire situations, the loss of soil stabilizing roots and vegetative cover often accelerate the rate of erosion, which can sometimes lead to debris flows and flooding. Not only can erosion happen immediately after fire, it can continue over several years as root systems of burnt vegetation decay.
Erosion Areas
In general, all drainages in steep, hilly areas are especially vulnerable after a wildfire. Areas burned at moderate to high severity are of greatest concern due to lack of cover and the development of water repellent layers. Even areas with low erosion hazard ratings can experience rill and gully erosion if there is a lack of vegetation or if exposed to a high intensity storm.
Types of Erosion
Debris flows and avalanches are dramatic forms of erosion that can deliver huge amounts of sediment and debris downslope. Surface erosion can also occur and result in gradual loss of soil as well as declines in water quality. If you live on or near a slope, in a draw or ravine, or along a stream or river, you need to be aware of the extent of wildfire damage upslope or upstream. If most or all of the vegetation has been burned off of these areas, the chance for erosion is significantly greater and can result in mass movements of soil and water downhill or downstream from the damaged areas.
Addressing the Impacts of Wildfire on Water Resources is necessary in maintaining the health and vigor of the local rivers and streams. Understand how Wildfire and Its Effects on Streams and Rivers can severely impact local watersheds and ecosystems are another important step in addressing and combating wildfires.
Mitigating Erosion
If addressed quickly, you can minimize the negative impacts of erosion. There are several common methods of controlling erosion:
- Mulching: mulch covers the soil, reducing rain drop impact, overland flow, and soil particle movement and offsets the effects of water-repellent soils. Mulching is the only treatment that consistently and significantly reduces erosion rates by immediately increasing the percentage of ground cover. Types of mulch include certified weed-free straw, slash, and geotextile fabrics.
- Barriers: barriers are installed on hill slopes and in streams to slow water flow, increase infiltration, and trap sediment. Types of barriers include log barriers, straw wattles, sandbags, silt fences, and straw bale check dams.
- Seeding and Revegetation Grass: seeding is the most commonly used erosion control treatment after a burn. Grass is seeded to burned sites from the ground or by air to increase vegetative cover during the first few critical years after a fire.
There are several methods of erosion control you can implement on your property following a wildfire:
Post-Fire Home Garden Soil Management
After a wildfire, soils can be impacted in a number of ways, including chemical and heavy metal contamination, alteration of nutrients, organic matter content, and pH, an increase in erosion hazard, and altered water holding capacity. The cumulative effects of these changes can modify soil productivity and biological diversity, as well as pose health risks to humans and animals. Urban soils are at an increased risk for chemical and heavy metal contamination post-fire because urban environments tend to have features and materials that release these contaminants when burned. After a wildfire, assess, test, and remediate your home garden soils to reduce the likelihood of exposure to potentially harmful contaminants.
It is important that you understand the history of your gardening site to determine possible sources of contamination. Next, testing is critical to understanding how wildfire may have affected your soil. Laboratory soil testing is recommended, especially if the soil is currently being used or is going to be used for urban agriculture. DIY soil testing kits are not recommended for this kind of testing because they cannot test for many contaminants or heavy metals that are of concern post-fire.
After determining the history and state of your soil, the next steps will depend on what your soil testing results indicate. If your soil test indicates that no contaminants have been found exceeding acceptable levels, no immediate action is required for contaminant remediation. If your soil testing indicates that contaminants have been found at or exceeding acceptable levels, consider working with your existing soil, using raised beds or other containers, or removing contaminated soil.
Best Management Practices for Near-Home Garden Soil
If you are concerned about inhaling or ingesting chemical contaminants from plants, produce, or soil, use the following best management practices for interacting with soil that has been potentially affected by wildfire:
- Wear gloves, boots, eye protection, a long-sleeved shirt and long pants when interacting with contaminated soil to prevent ingestion and direct contact.
- Use raised garden beds and import clean soils to avoid inhalation, ingestion, and plant intake of contaminants over time.
- Amend soil with clean, high-quality compost to improve soil health. Be mindful to use the appropriate amount of compost.
- Use mulch to cover the soil to prevent airborne soil and dust up-splash.
- Promote good drainage and use drip irrigation to prevent up-splash, particularly at the bottom of slopes that burned and after long wet periods. Contaminants can accumulate in these areas under wet conditions.
- Be mindful not to track contaminated soil into your home.
- Wash hands before and after harvest and rinse produce before it is consumed.
References and Resources
After the Fire: Home Garden Soil Management
Erosion Control
- Barkley, Erosion Control after a Wildfire, University of Idaho Extension
- Barkley, Erosion Potential After Wildfire, University of Idaho Extension
- Barkley, Using Barriers to Control Erosion after a Wildfire, University of Idaho Extension
- Deak, Post-Fire Erosion Control: Mitigating Hillslope Erosion Following Wildfire (2023), UC Cooperative Extension Forest Stewardship
- Waskom et al. (2013) Addressing the Impacts of Wildfire on Water Resources, Colorado State University Extension