There is important nuance here. Mature forests store carbon, but they do not, on balance, capture much from the air. This is because decay balances growth in a mature forest. Forests may be the “lungs of the world” but mature forests produce about as much CO2 as they take it. It has to be this way, else forests would have long since absorbed all the CO2 in the atmosphere and ended life on earth as we know it.
Life giving CO2
We NEED CO2 for life to go on as much as we need oxygen. We just need rather less of it at this time.
How can planting trees take carbon out of the air? The short answer is that – on balance – they can’t. What? A lot depends on the conditions and what happens after.
Coal is fossil wood
Consider how coal was formed. Millions of generations of forests used the power of sunlight to convert billions of tons of CO2 into wood. Wood is about 1/2 carbon by dry weight. The key to forming fossil fuels is that the wood did not decay. Over time, geological forces pressed it into coal. Fossil fuel – coal is wood that did not decay in distant past epochs. When we burned that coal, we released the energy of billions of sunny days and also that carbon that had come with it.
It is a problem, but the thought of coal is awesome and poetic in its own way. What are our current prosaic options?
Forest life cycle matters
A mature forest stores, but does not capture carbon – on balance. I am going to stop saying “on balance,” so please just assume it going forward. A young forest captures carbon but does not store much of it. Most American forests these days are middle aged. They are transitioning from young to old because of the peculiar way they grew. There was a big forest regeneration in the early & middle of the 20th Century. These trees are now reaching maturity. I could go into that interesting story, but I need now to stick to this one. The thing to remember is that America forests have been capturing carbon for the last century but they are at the point where they will stop doing that.
Don’t let nature decide
If we “let nature decide,” nature will choose to release more carbon from our forests, given the age structures. (BTW – there really is not let nature decide option. Our choices are good human choices of bad ones.) But we have a wonderful option open to us, one that will allow carbon to be stored for another century, will keep our forests young growing and healthy and keep them capturing carbon. All the while this is going on, it will make our built environment more ecologically friends and more human friendly.
If we responsibly and regeneratively harvest our forests in ways that respect the forest ecosystem, we can continue to store carbon in roots and soils. This has the added advantage of improving soil texture, making it better able to absorb and hold water helping protect our drinking water and avoiding floods. It also helps us to prevent disastrous wildfires, landslides and just makes everything better.
The next step is to use the harvested timber to replace less environmentally benign options in building, materials like concrete and steel. Let’s be clear. Wood cannot replace these materials in all way, but in a lot of cases it can.
This is a virtuous cycle. There are wonderful benefits and literally no important costs (I will say again here on balance.).
Some references
Environmental costs of concrete
Wood replaces concrete and steel
John Matel's Memorial Blog