Will planting trees get us out of our climate pickle? Not entirely. But it could increase the world’s natural drawdown of atmospheric carbon by 25%.
Most mornings when I get up I check the weather. I’d like to know what it will be doing so I can plan my day around that.
Even after all these years of observing patterns, I am often surprised. I will walk out on my deck and look at the mercury and it reads ten or fifteen degrees below what my Apple Watch tells me the temperature should be. The watch gets its data from a local weather sensor, likely somewhere near the Post Office in town. The thermometer on my deck is reading its temperature 20 feet above ground in an oak forest.
Inside, during the heat of the day, the air will be ten degrees below even the forest because I have a living roof and the green mossy cover works exactly the same way a refrigerator does, dropping coolth into the enclosure as overnight dew is wicked and evaporated.
Transpiration is one of the cooling effects of a forest. So is photosynthesis. A single oak tree may have one million leaves and a solar collecting area of two acres. Using sunlight for energy, it draws carbon dioxide from the sky, reserves the carbon and sends the oxygen back. We are all told as children that this is a reciprocity arrangement we have with plants because we are air breathers and need that oxygen. We mammals draw in oxygen, add carbon from our bodily wastes, and then exhale the CO2. Trees gratefully accept that carbon and add girth.
The tree has carbon waste too. Some of the CO2 it inhales, as it were, goes into leaves, bark, branches and roots, but nearly half — more than 90 percent in the case of a bamboo forest — is excreted into the soil. In a bamboo forest that carbon pool is very shallow because bamboo’s roots do not run very deep. In an oak forest like mine, the roots extend down until they hit bedrock or perhaps as deep as the tree is tall if there is no rock encountered. That carbon pool — the sugar “exudates” the tree exchanges with root nematodes and soil microbes for calcites, nitrates, sulfates, and trace minerals the tree needs — is in a labile form of carbon and so will move through the soil food web, some returning to the surface and possibly being released by bacteria and fungi to the sky, and…