- - Soil Health

What Fire Does to Soil

A near-record 10 million acres burned in wildfires across the United States last year. In much of the American West, fires increasingly cause widespread damage to homes and businesses. Many of the fires occurred in agricultural areas, as well, leaving farmers devastated.

In October, about 20 wineries across Napa and Sonoma Valley in California experienced damage from a series of 250 wildfires blazing through northern California. An estimated 245,000 acres in total were burned.

And in December and January, the Thomas Fire scorched another 280,000 acres across Southern California, in the nation’s primary avocado and lemon-producing region. It was the largest fire ever to be recorded in the state.

Just north of Los Angeles, Ventura County’s agricultural industry sustained more than $170 million in damages from the Thomas Fire, according to the county’s Agricultural Commission. Avocado groves were hit hardest; around 4,030 tons of avocados were lost, totaling $10.1 million. And nearly 7,600 tons of lemons were lost, at an estimated total loss of $5.8 million. Those numbers don’t account for lost wages of agricultural workers.


Photo courtesy of NASA/Randy Bresnik. Plumes of smoke rising from wildfires, photographed Dec. 8, 2017, from the International Space Station flyover of Southern California.

For farmers dealing with crop destruction, fire can be a nightmare. But from the perspective of the land itself, fires can play an important role in the health and fertility of soil.

In fact, American Indians used fire to manage their land for thousands of years. “Native peoples throughout North America actively managed their environments, playing key roles in determining the structure and composition of forest and grassland ecosystems across the continent,” the Oregon History Project writes about the Kalapuya of the Willamette Valley.

Today, there’s a debate over the best way to manage the growing number of—and ever-more costly—fires across the nation. How can we square fire’s ecological benefits with the extraordinary damage it can cause to farms and other property?

History and Policy

For the first half of the 20th century, the U.S. federal policy was to quickly extinguish any wildfire, whether natural (such as from lightning) or from human error (such as from dropped cigarettes, machinery sparks, or even arson). But by the 1960s, scientists began to change their tune, recognizing fire as often a natural process that can benefit the environment.

Today, federal policy generally encourages fire to be used as a tool, such as through controlled—also called prescribed—burns. An increase in developed land as well as fragmented land from large-scale agriculture means natural burns are suppressed. The Forest Service, a branch of the U.S. Department of Agriculture, says the absence of low-intensity fires over many years actually increased the risk of large fires and has negatively impacted the health of forests.

That’s especially important now, as climate change and increased development in rural areas have raised the stakes when it comes to the threat of destruction from fires. Higher population density means a higher chance of fires starting to begin with, and settlement in wildfire-prone areas increases risk even more.

In 2017, the federal government spent a record $2.9 billion suppressing fire—up $1 billion from the year prior and up from just $240 million in 1985. In California alone, Cal Fire spent $700 million during the 2017 fiscal year, a number far exceeding the approximately $426 million the agency had budgeted for fire suppression. The California Governor’s Office reported in April that the state had removed nearly 1.7 million tons of debris since last year’s devastation.

In March 2018, the U.S. Congress added an update to the federal budget that secures stable funding both for fighting wildfires and for fire prevention and forest health projects. Now, Congress can pay for fire suppression with emergency funds, freeing up resources for things like forest thinning, the removal of dead and downed trees and underbrush, and controlled burns. Experts say those activities can make fires more manageable and the environment better for forests. Without them, it becomes more likely that larger and more severe fires will burn out of control, leading to high levels of destruction with little benefit for the environment.

Climate change and increased development in rural areas have raised the stakes when it comes to the threat of destruction from fires.


How Fire Regenerates Soil

The effects of fire on soil depends largely on a fire’s intensity. High-intensity fires that scorch the earth—such as those that caused destruction across the West last year—can be destroy crops. But low-intensity fires that do not grow out of control can benefit wildlands and provide a habitat for flora and fauna.

The Forest Service calls fires “nature’s way of recycling”—low-intensity fires decompose and convert the nutrients found in dead plant matter on the soil’s surface, returning them to the soil. That can ultimately lead to greater soil fertility.

Microbial activity in soils has been shown to increase after a fire. This is likely a result of increased levels of decomposable carbon and increased pH, the conversion of nutrients to soluble forms, increased soil temperature, and increased water availability to microbes due to lesser demand from plants.

Fire also improves flowering, seed, and fruit production, increasing the availability of these foods for wildlife. And fire actually allows established trees to grow stronger and healthier. Overall, fire is a “catalyst for promoting biological diversity and healthy ecosystems,” according to the Pacific Biodiversity Institute.

For farmers, this is especially useful at the end of a harvest, or before planting a new crop. Each spring, farmers and land managers across the world will use controlled burns to prepare their land for planting. For farmers, fire serves the purpose of clearing land, removing weeds, disposing of waste, and controlling disease.

However, many states have permit requirements for such activities and suggest varying cropping or weed reduction strategies to reduce the need for a burn, which can have a negative impact on local air quality and the environment.

Low-intensity fires decompose and convert the nutrients found in dead plant matter on the soil’s surface, returning them to the soil. That can ultimately lead to greater soil fertility.

The Path Forward

Controlled fires are now seen by many experts as essential to avoiding disastrous wildfires in the future, and to improving the long-term health of forests and other natural lands. Ideally, when wildfires do start they remain low-intensity, burning grasses and vegetation on the ground but causing less damage to trees and property. For farmers, clearing brush from any forest floor on their property can help prevent the damaging wildfires that spread out of control, such as those seen during last year’s fire season.

Farmers who do experience disastrous fires have a long road of paperwork and recovery to follow the destruction. Nearly 45,000 insurance claims totaling some $12 billion in losses were filed in California alone after last year’s season. The fires damaged and destroyed more than 32,000 homes, 4,300 businesses, and 8,200 vehicles, plus water and farm vehicles and other equipment.

Many farmers are still assessing damages. Jason Cole of Cole Ranch lost some 200 acres, or 30,000 avocado trees, in the Thomas Fire. That was one-third of his supply. As he sifted through the debris, he told reporters at the time that it could take him a decade to recover.

The U.S. Department of Agriculture’s Farm Service Agency (FSA) assists farmers and ranchers who lost livestock, grazing land, fences, or eligible trees, bushes, and vines as a result of wildfire. The FSA’s safety-net programs include the Livestock Indemnity Program, the Tree Assistance Program, and the Emergency Conservation Program. In April, the USDA announced it would implement up to $2.36 billion to help agricultural producers recover after the historic 2017 wildfires. Sign-up for the new program will begin no later than July 2018.