According to the Wikipedia, beginning in March 2023, and with increased intensity starting in June, Canada has been affected by an ongoing, record-setting series of wildfires. As the worst wildfire season in recorded Canadian and North American history, Big Burn 2023 surpasses the record held by the 2020 California wildfires.

Canadian Wildfires: Neither Gone Nor ForgottenThe 2023 burn season has impacted 11 provinces, from Alberta to Nova Scotia. Forest fire-based smog has, at some point, blanketed all the states bordering Canada, even reaching as far south as South Carolina.

On June 25, the Canadian Interagency Forest Fire Centre declared 2023’s wildfire season to be the worst in Canada’s recorded history. As of July 16, 4,147 fires had torched almost 39,000 square miles of forest in Canada – an area approximately equal to that of the state of Virginia. International aid helped reduce the impact of the fires. Smoke emitted from the wildfires caused air quality alerts and evacuations in Canada and the U.S. In late June such smoke crossed the Atlantic, reaching Europe.

Canadian Minister of Public Safety Bill Blair pointed out that due to these weather-related anomalies, average temperature readings have been warmer and drier, raising wildfire risk as vegetation tends to become tinder under these conditions. Wind from a passing cold front during the week of May 18 intensified the problems.

The big question, agriculturally, is how this type of misbehaving climate affects crop production. Crop researchers at Purdue in Indiana answered that question with another: How does wildfire smoke impact corn growth?

In a newsletter published July 10, Dan Quinn, agronomy professor at Purdue, wrote that in late June, air quality warnings were issued throughout Indiana due to smoke caused by Canadian wildfires. Such smoke, which resulted in a noticeable haze and reduced direct sunlight, also became a human health concern. It caused many farmers to ask how this uninvited smoke might harm their crops. Quinn answered that haze and reduced air quality from wildfire smoke can result in both negative as well as positive impacts on crop growth.

The first negative impact is a reduction in light availability, which can reduce crop photosynthesis. During the week of June 26 – when local air quality concerns were the greatest – average weekly solar radiation was decreased by 32% compared to the week prior (June 12) and the week after (June 30) at their main campus at West Lafayette, IN.

Atmospheric wildfire smoke can reflect portions of incoming sunlight, reducing the total amount available to plants. Reductions in light availability from wildfire smoke are more likely to impact corn than soybean. This is due to corn being a C4 photosynthesis crop, having a higher light saturation point – at which further (ultraviolet) light increases do not benefit photosynthesis. Quinn explained that soybean is more susceptible to changes in carbon dioxide.

Photo by Paris Reidhead

The second negative impact caused by wildfire smoke is increased ground-level ozone, which can be harmful to both human health and crop growth. Wildfires can emit various air pollutants which can form ozone when reacting with sunlight. Ozone can harm both corn and soybean by entering the plant through the stomates, causing harm to plant tissue during respiration. Since both reductions in sunlight and increases in ozone can cause photosynthesis reductions, corn may also be inclined to remobilize carbohydrates from the stalks later in the season to satisfy grain fill requirements, thus increasing the potential for weak stalks and lodging prior to harvest.

Quinn further explained that, despite reduced sunlight and increased ozone, wildfire smoke in the atmosphere can also have positive effects on crop growth. One positive effect is that not only can wildfire smoke reflect sunlight, it can also scatter sunlight. Scattering can allow light to penetrate deeper into the crop canopy and increase plant photosynthesis. Furthermore, when light is scattered and direct sunlight is reduced, this can also lower leaf surface temperatures which can benefit crops under drought stress. Lower leaf temperatures can reduce the amount of transpiration (water movement and evaporation from the plant) needed to cool the plant and reduce overall water stress.

Overall, corn is more susceptible to the negative effects of wildfire smoke during the grain fill stages; the good news is that the majority of corn in Indiana (and, for that matter, the Northeast) was in the vegetative stages during the smoke barrage in June and early July. Therefore, minor or no yield loss is expected in these regions.

However, much is still needed to be learned about the impacts of wildfire smoke on crop growth. As these events are unfortunately expected to become more frequent, it will be important to pay attention to them in the future. Thinking that climate change aggravation might become even more commonplace, some crop researchers even recommend that plant breeders develop corn varieties that are less susceptible to reduced solar radiation – like when wildfires hijack it.

On June 6, I was traveling through southern Madison County, NY, during what was officially declared by climatologists to be the peak of the Canadian wildfire smog inundation (at least as far as New York and New England were concerned). The air outside my truck was thick with haze, and it smelled of good old-fashioned hardwood smoke. But inside my truck what I breathed smelled more like hot brakes. I got out of my truck and carefully touched the driver’s side hub, which appeared to be normal temperature. Listening to TV news reports that night, I learned that a lot of other things besides timber are being incinerated in Canada. Some of those things’ emissions were serious pollutants which medical professionals advise babies and old folks not inhale – some say I’m in that latter category.