You may have heard by now that the Amazon rain forest has been burning this summer. The internet quickly filled with quotes about the Amazon being the lungs of the earth, providing the earth with 20% of its oxygen. This article by PBS Newshour does a good job of explaining why oxygen production and loss is not a primary concern when addressing the Amazon fires. In short, we have a huge reserve of breathable oxygen which is barely impacted by the oxygen output of plant matter. The most significant threats posed by Amazon fires are much more significant and dire: regionally the loss of biodiversity, and globally the destruction of massive carbon sinks.
Trees, and more broadly forest ecosystems provide countless ecosystem services, but the most notable are carbon sequestration, natural habitat, oxygen production, and water management. In healthy forest ecosystems trees ‘sink’ carbon, meaning they absorb more than they produce. The total of carbon processed during photosynthesis is more than the amount released through fires and decomposition. Carbon can be stored more permanently in wood products (think wooden houses, furniture, and more), but also in the soil, and the biomass of the forest itself (plants and animals). Healthy forests can have forest fires, even significant ones, and still, sequester or sink more carbon than they release. The problem in the Amazon, and other forests, however, is that fires reduce the capacity for carbon storage. When a large tree burns, a certain amount of carbon is released, but the tree also becomes incapable of photosynthesis and stops sequestering carbon. In our National and State forests, trees reemerge naturally or are replanted, giving the land a chance to store carbon again. In the Amazon, these burned areas are likely to be replaced with pasture or cropland, significantly reducing their capacity to sequester carbon. Even in areas where trees are replanted, young, immature trees sequester much less carbon than large trees. Using the PA treemap we can see that a 20-inch London planetree (Platanus acerifolia) sequesters 630 pounds of carbon per year and has sequestered 1900 pounds over its lifespan. A 40-inch London planetree, however, sequesters 1400 pounds per year and has sequestered 11,350 pounds in its lifespan. In short, the 40-inch tree sequesters almost as much in one year, as the 20-inch tree sequestered in its life to that point. For greater perspective, the trees we typically plant are 2 inches in diameter and sequester less than 20 pounds of carbon in their first few years.
If you repeat that millions of times over, replacing large trees with seedlings, or in the case of the amazon with no trees at all, huge amounts of carbon go un-stored. This is the opposite of the math in a recent study which showed that planting millions of trees could be a long-term solution to climate change. By replacing unplanted and unused areas with trees we can create long-term carbon sinks in more areas. Of course, the study didn’t account for the loss of the Amazon rain forest, and like all tree planting efforts it will take years, and millions of dollars in maintenance to bring enough trees to maturity to begin to see impacts. It is still most beneficial to preserve the remaining large trees we have, but we can always increase planting efforts.