Margaret Cheasebro

Wildfire smoke tends to have harmful particles and gases in it. People are often told to stay indoors to avoid breathing in those things. Trees, which have no way of going inside or moving somewhere else, have their own way of holding their breaths to reduce smoke intake.

In an Aug. 5, 2024 article in Atlas Obscura, authors Delphine Farmer and MJ Riches explained that plants have pores on the surface of their leaves called stomata. Delphine is a professor of chemistry at Colorado State University, and Riches is a postdoctoral researcher in environmental and atmospheric science at CSU.

The authors explained, "These pores are much like our mouths, except that while we inhale oxygen and exhale carbon dioxide, plants inhale carbon dioxide and exhale oxygen. … Unlike humans, however, leaves breathe in and out at the same time, constantly taking in and releasing atmospheric gases."

A scientific study of trees in heavily polluted areas in the early 1900s revealed something interesting about the tree leaves. Those that had been chronically exposed to pollution from coal burning had pores clogged with black granules.

Because there weren't instruments available to explore the chemistry of those granules back in the early 1900s, scientists weren't able to study the granules. And they weren't able to discover what affects the granules had on the plants' photosynthesis.

Then, as now, wildfire smoke sometimes travels long distances. When it does, exposure to the heat of sunlight can chemically change the smoke. In addition to the effects of sunlight, smoke becomes mixed with volatile organic compounds and nitrogen oxides. Together, they make ground-level ozone which can cause breathing problems in humans, Farmer and Riches wrote.

The ground-level ozone "can also damage plants by degrading the leaf surface, oxidizing plant tissue, and slowing photosynthesis," according to the authors.

All those things make wildfire smoke a growing concern. A study in 2020 of ponderosa pines and other plants in the Rocky Mountains of Colorado focused on the plants' leaf-level photosynthesis. The results showed that the tree's pores were completely closed. That meant they weren't breathing in the carbon dioxide they needed to grow, and they weren't breathing out oxygen along with the chemicals that the oxygen usually released. The trees, basically, were holding their breaths to keep from breathing in the wildfire smoke.

No one is certain how frequent wildfire smoke will affect trees and other plants. Time and additional studies may help to answer those questions. Perhaps the results will help scientists discover ways of protecting trees and people from the smoke.

As we venture into 2021, coming out of 2020 full of grief, worry, frustration and a boatload of other emotions, it can be hard to feel hopeful.

Even so, there are reasons to keep our hope alive and to look forward to positive change. When I worry that more people I know could get very sick with Covid-19 and its emerging virus strains, I think about trees.

What could trees teach us? They have weathered all kinds of challenges, from invasive beetles to the possibility of being cut down, and they've faced a whole host of other threats from many different sources. What keeps them going?

They are rooted to one spot. They can't run away from danger. But they can draw on strengths. They change their behavior as needed to stay healthy.

In the winter, trees go dormant. As some animals hibernate during the winter, trees slow down their metabolism. That helps them to conserve the food they have stored. They want it to last since they don't make food in the winter. That's the season when they slow down their energy consumption and growth. Many trees shed their leaves in the winter because they don't need the leaves to help them form simple sugar, their kind of food, in the presence of sunlight, a process called photosynthesis. That sugar helps to give them energy, but in winter they take a rest.

Just as trees go into a dormant state during the winter, in this time of Covid-19, we need to slow down our activities by staying indoors more, not gathering in large groups, and shopping in stores only for essentials. If we wear masks, keep at least six feet from other people, and wash our hands frequently, we also reduce the chance of getting the virus. Those are all activities that slow us down and make us practice different behavior than we normally would. It can be frustrating and downright maddening to have to change our behaviors. But it gives us and others a better chance to remain healthy.

Trees know how to be dormant. They do it naturally. They slow their activity level to stay healthy during the winter. If trees can adjust their behavior during winter to keep themselves safe, perhaps it doesn't seem quite so limiting to adjust our behavior too.

Trees also do something called respiration. In this process, they convert energy stored in the form of glucose, the sugar that leaves and sunlight produce during photosynthesis. That energy is needed to carry out the tree's metabolic reactions, which occur even in winter. During respiration, carbon dioxide oozes through the trees' pores. Carbon dioxide is essential to create the energy trees need to keep themselves healthy. They get a lot of that carbon dioxide from animals, including humans, when we breathe out that gas. In return, trees give off oxygen, which is toxic to them, but we would die without enough of it.

No matter how challenging life may be for them at times, trees continue to create the carbon

dioxide they need and to get rid of the oxygen that we need. If they didn't keep doing what they need to do to survive, we wouldn't be able to survive ourselves.

When I look at trees, I don't often think about the chemical reactions that happen within them. I just enjoy their beauty, the shade their provide, and the habitat they offer for birds and other critters.

I'm glad trees remain committed to doing what comes naturally to survive. It helps me think that, even though it's not easy to wear a mask, social distance, and wash my hands often, it is helping to give me and others a better chance to stay healthy. That gives me hope.