Wildfire smoke certainly affects vegetation, but the specific impact on agricultural crops is yet to be fully understood.
By Jackie Clark
In 2021, while many farmers were already dealing with devastating drought and the lingering impacts of the COVID-19 pandemic, Mother Nature threw another curveball: wildfires.
Across western provinces and northern Ontario, fires filled the skies with smoke. Even in southern Ontario, city dwellers snapped photos of the hazy, red sunsets, commenting on their unique beauty before being informed that the visual effect was another impact of wildfire smoke.
The impact of burn on vegetation growth has been studied for many years in regions where wildfires are common. Smoke impacts on human health have also been researched. Less studied is the specific impact of the smoke on vegetation growth, particularly when it comes to agricultural landscapes.
Wildfire risk research is a relatively new field of study in Canada, according to a February 2020 assessment led by Lynn M. Johnston, forest fire research specialist at Great Lakes Forestry Centre.
However, some models predict a variety of consequences from increased wildfire activity across the country.
For example, the number of lightning fires in Ontario is predicted to increase by 24 per cent by 2040, and 80 per cent by 2090, according to a 2005 publication from Canadian Forest Service (CFS). The number of fires caused by people is expected to increase by seven and 26 per cent by 2040 and 2090 respectively. This predicted increase is a result of higher temperatures and drier forest floors, due to climate change.
These estimates are conservative, according to the CFS and will result in more fires escaping initial management efforts, and increased fire management costs.
We can expect to see more smoky skies in our future.
Impact on Canadian ag
Canadian perspectives on how wildfire smoke is impacting agricultural crop development are currently mostly anecdotal. Agronomists from western provinces and Ontario share their experiences.
In 2018, wildfire smoke filled the skies in Western Canada in late August, James Oberhofer, a private agronomy consultant in Marwayne, Alta., tells Better Farming.
“In 2021 the wildfires occurred a little earlier in the growing season. In the middle of July, we were seeing heavy smoke,” he explains. “This year was a very hot and dry year, so most of the Prairies were in the middle of drought stress. When you have excessive heat, especially temperatures over 30 C, you typically see flower blasting in Canola. That’s the plant aborting its flowers.”
However, “the smoke actually came as somewhat of a blessing because we were going through such intense heat and the canola plant was under heavy stress. The smoke actually helped protect the plant, give it a bit of a break from the intense UV light and excessive heat and temperatures cooled off a bit because of the cloud cover,” he says.
In both 2018 and 2021 the impact on canola was similar in that the plants ‘shut down’ and didn’t progress in the growth cycle. In 2018, the farmers were eager to get the crop to mature so they could harvest, so the delay was detrimental. This year, however, “it actually, I think, was somewhat welcome,” Oberhofer says.
Though wheat, barley, peas and corn also grow in his region, the impact was most evident in canola, because it’s “one of those plants that really show stress easily,” he adds.
The smoke cover may have actually mitigated the yield hit crops would have taken from the drought, Oberhofer says. “If we didn’t have the break that the smoke gave the plant to recover for a few days, I think the yield impact would have been worse.”
Doug Moisey, a Pioneer Seeds agronomist for Corteva AgriScience, saw the same stasis of canola crops in northeastern Alberta.
“Basically, the smoke put the crop into what we call suspended animation because the smoke particles actually plug the stomata opening of the plants, causing a hormone response which shuts the plant down,” he explains.
He also noted the difference between 2018 and 2021.
“Back three years ago, you couldn’t see 100 feet past your nose, we went from 25-degree days to highs of 12 and 13,” he says. “This year, we were under intense heat and lack of moisture and the smoke and cooling helped.”
Moisey’s customers say that “the smoke this year actually was a help to our crop, it wasn’t a detriment. The plants were actually able to hold their own until the heat finally left,” he explains.
“When that smoke came in, you could almost see the canola plants breathe a sigh of relief,” he adds. The heat and drought are particularly hard on the crop “because canola cannot completely close its stomata opening, it has a tough time keeping moisture in the plant.”
When rain came along, the canola crop was able to grow again, Moisey says. The “smoke cooled things down enough that the plant could actually do something with the moisture they had.”
Wheat yields didn’t seem to be impacted by smoke, he added.
In Ontario, agronomists and growers observed a similar impact on canola crops.
“We definitely had some days of overcast smoke cover,” says Terry Phillips, an agronomist Certified Crop Advisor for Co-op Regionale in Nipissing-Sudbury.
“For some crops, like canola, we actually had a benefit of reduced heat at flowering,” he explains. “Unfortunately, some crops, like soybeans, actually thrive from the combination of heat and sunlight.”
It was already a challenging year for soybeans in northern Ontario, with a late May 28 frost. Many farmers had to replant and “the smoke didn’t help,” says Phillips. However, “overall, talking to counterparts in the West, the effect wasn’t as pronounced as it could have been.”
Other farming effects
Smoke’s impact on agricultural crops is nuanced, highlights an Aug. 4 report from the University of Minnesota Extension. The impact will vary depending on ozone damage sensitivity, cloud cover, and aerosol properties.
“There are very few studies about the impacts of wildfire smoke on crops, and they are mostly on global scales, so we can’t translate this directly to say how much these wildfires will impact vegetable growth,” says the report. “In places like California and Australia where wildfires are much more common, people have cited problems like ash settling directly on crops, creating a physical barrier on the leaves, which prevents access to light.”
Wildfire smoke composition can vary considerably, the report adds. If plants are directly in the path of smoke instead of under a cloud cover of wildfire smoke, the impact may be more severe, says Dr. Lew Feldman, professor at the University of California, Berkeley and garden director at Berkeley Botanical Garden.
“Short-term exposure to smoke, as little as 20 minutes, has been reported to reduce photosynthesis by as much as 50 per cent,” he said in an October 2020 report. Impact is “a consequence of both the destruction of chlorophyll, the light-capturing green pigment, and in impeding the movement of carbon dioxide into the plant through stomata.”
Smoke can impact the quality of grapes used in wine production, Jacob Powell said in a Jul. 12 report. He’s the general agricultural extension agent for Sherman and Wasco Counties, affiliated with Oregon State University.
Finally, though the impact on crops is not yet well-researched, the impact of smoke on human health is understood, says the University of Minnesota report.
“Health effects of wildfires include burning eyes, runny nose, chest pain, fatigue, coughing, difficulty breathing, and rapid heartbeat,” the report says. If the air quality index (AQI) reaches over 151, respirators should be worn outside, and work schedules altered to include more rest. In his region of Alberta, farmers didn’t have trouble working in the smoke, says Oberhofer.
The way “we work is a lot different than what it used to be,” he explains. “Now we’re in pretty nice tractor cabs.”
Only individuals with pre-existing respiratory conditions were more wary of working in the smoke, say Oberhofer. When asked how the smoke impacted people in the areas, Moisey was also only aware of individuals with pre-existing conditions avoiding working in the smoke.
Further research
Scientists found that aerosolized particles in wildfire smoke increased the diffusion of photosynthetically active radiation (PAR) by almost one third, while minimally reducing overall PAR, during wildfires in California in 2018.
“These conditions caused nearly a doubling of light use efficiency over the range of diffuse fraction observed, with the highest sensitivity to diffuse fraction exhibited by corn and alfalfa crops,” according to the study published in JGR Biogeosciences. Kyle Hemes from the Department of Environmental Science, Policy and Management at the University of California, Berkeley, was the lead author.
Essentially, smoke can scatter sunlight and increase the efficiency of plant canopy photosynthesis, which, in some circumstances, can increase productivity. However, the scientists also found there were potential drawbacks in reduced total light and co-pollutants such as ozone.
Indeed, a 2018 study on the impact of air pollution from fires found that the overall impact of smoke negatively impacted plant productivity, according to authors Dr. Xu Yue from the Institute of Atmospheric Physics, Chinese Academy of Sciences and Dr. Nadine Unger, professor of atmospheric chemistry at the University of Exeter in the U.K. Their study was published in Nature Communications and used data from 2002-2011 to model the impact of fire pollution.
“Surface O3 damages vegetation photosynthesis through stomatal uptake, while aerosols influence photosynthesis by increasing diffuse radiation,” they reported. “The net negative impact of fire pollution poses an increasing threat to ecosystem productivity in a warming future world.”
Their research didn’t look specifically at ag species, however. More research would help determine how wildfire smoke impacts production in different context. BF
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