ESCANABA — Forest carbon’s role in climate change mitigation is a hot topic these days, at least in the forestry world. As with many issues, a confusing miasma of information floats around the media.

The planet possesses a beaded string of inter-connected cycles involving many atmospheric components. The carbon cycle is one of them. In the atmosphere, carbon exists married to oxygen. Carbon dioxide contains one carbon molecule and two oxygen molecules. CO2 makes up about 0.04 percent of the atmosphere. Oxygen, in the form of O2, comprises about 21 percent, but there is additional oxygen in CO2, water, and other forms. However, enough about chemistry.

The Earth’s carbon cycle consists of four major pools, each with a described amount of carbon: the air, the biota, the waters, and the soil. Carbon circulates among these pools in amounts well-measured by scientists. The flow rates vary with seasons, biomes, and other factors. All is well and good, until fossil carbon enters the picture and inflates the size of the pools, especially that in the air. Fossil carbon has been latent for many millions of years and does not belong in the carbon cycle. This is an important fact when considering climate change and forest management.

Focusing more narrowly on forests, trees and associated forest vegetation “sequester” a lot of carbon. However, the rate of sequestration greatly varies depending upon several factors, especially the season and the age/health of the forest.

Forests both sequester carbon and release carbon through processes called photosynthesis and respiration. Photosynthesis (PNS) captures carbon in sugar molecules, among other functions. Respiration (RSP), the same process as in humans and animals, releases carbon in the form of CO2. The balance between the two processes is a ratio, the PNS:RSP ratio. Why does this matter in forestry? Good question, and here it goes.

This forest-based PNS:RSP ratio can be measured and has been repeatedly done by scientists. A young forest has a high ratio, meaning a lot more PNS is happening than RSP. This is good in that it draws greater volumes of carbon from the atmosphere, something considered critical in many quarters.

As a forest ages, the ratio declines and, sometimes, can become negative, meaning more carbon is released than captured. Changes in this ratio, over decades, can be expressed as a simple curve. The line gradually rises, then ascends sharply, flattens out, then declines, sometimes rapidly. The upshot is that older forests generally have lower carbon sequestration rates than middle-aged forests. This is an important consideration if forests are managed with carbon as a high priority.

However, there’s another curve, and that’s the one that depicts the gross amount of carbon stored in a forest system. That curve also starts out slowly, picks up speed, then flattens out. Carbon storage, keeping more carbon out of the atmospheric pool of the carbon cycle, is an objective in using forests as climate mitigation tools. But wait a moment!

That carbon does not necessarily need to be stored in a slowly sequestering forest. When trees are harvested, they’re manufactured into products that also have long storage potential, such as houses and other buildings. Even disposable wood products, such as paper, wind up being stored in landfills. Now, landfills may not be the wisest endpoint for this carbon, but that’s where much of our long-term forest carbon resides.

Additionally, wood products have the smallest environmental footprint of any raw material.

If forests are to be managed for carbon sequestration, or the long-term removal of carbon from the atmosphere, then forests ought to be managed where sequestration rates are highest, rather than when they are low, or even negative. And if we, as a society, want to be strategic, we should schedule more acreage of forestland to reach this sequestration peak around the year 2050, when climate scientists predict the need will be greatest. That means we should be harvesting more today, socking-away that carbon into wood products, and then letting the forest machinery remove as much atmospheric carbon as possible.

The best part of this process, perhaps, is that it doesn’t cost money. In fact, it generates revenue far down the supply chain.

What might this mean for forest-owners, both public and private? Well, if the forest is aging into the senescent phase of succession, where sequestration rates and the PNS:RSP ratios are low, then that forest is not doing much to advance climate mitigation efforts. As monetary carbon programs are offered on the market, consider whether they’re better serving Wall Street or climate mitigation. If carbon program protocols push forests into that flat-line, senescent phase, then something fishy might be going on.

Of course, carbon management, and revenue, is only one objective in forestry. There are many others, all of which are better served through active management of the forest, rather than benign neglect.

And, the 20+ million acres of Michigan forest is highly diverse in terms of forest types, ages, and ecological conditions. The issues surrounding forest carbon are best considered on a large managed landscape basis, which means most ownerships ought to look beyond their personal boundaries, as well as into their own inventories. After all, our individual forestlands are a part of the much larger ecosystem community, whether we like it or not.