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How Much CO2 Do Trees Absorb? “While trees are generally effective at reducing air pollution, it isn’t as simple as the more trees you have in an urban space, the better the air will be. Some trees are markedly more effective at filtering pollutants from the air than others. To make the most difference in air quality in a street or city, it has to be the right tree for the job.” https://www.bbc.com/future/article/20200504-which-trees-reduce-air-pollution-best Why Size Matters. When it comes to Climate Change not all trees are equal. by Boni Biery Human beings eat to grow/restore themselves. Trees photosynthesize using sunlight to create sugars for growth from carbon dioxide (CO2) and water. In the process they split the water (H2O) and transpire or breathe out oxygen. The underside of tree leaves is covered with tiny pore-like openings called stomata. The stomata act as exchange agents. They take in CO2 from the atmosphere for photosynthesis by the tree. Then they “transpire” the waste products of water vapor and oxygen (O2) out. “Capturing carbon" isn't some abstract concept. When you look at a tree, what you're seeing is basically all the carbon they've captured. The leaves, the bark, the wood.The more stomata, the greater the amounts of clean O2 and cooling water vapor are produced for human benefit. Here are considerations: First – Is the tree evergreen? Evergreen tree canopies are photosynthesizing every day of the year. Deciduous trees, drop their leaves and go “dormant” for a period of months each year. When they have no leaves, they are not cleaning the air. Therefore, evergreens are more beneficial than deciduous trees for air purification. Native evergreens typically grow to have significantly greater canopy leaf area volume, providing greater benefits from CO2 – O2 exchange, summer cooling from shade to transpiration and winter wind protections. Second – If the tree is evergreen, is it broad-leafed or a conifer? Conifers are the cone-producing trees and while their needle-leaves are small they have greater surface area than broad-leafed evergreens like our native Pacific Madrone (Arbutus menziesii). Third – If it is an evergreen conifer, is it mature? Many conifers grow quite large and the larger the volume of the canopy the greater the leaf surface area that can photosynthesize and produce both clean oxygen and cooling water vapor. Mature trees are less vulnerable to drought than smaller, weaker trees. Volume vs. Circumference - The typical way that urban canopies are measured is by flying over the tree canopy and measuring the ground cover. Sadly, this one-dimensional measurement accounts only for the diameter or dripline of a tree. A far more accurate means of assessing tree benefits is to measure the volume of the canopy. This requires knowing the overall shape of the canopy along with its height x width x depth to properly calculate the total volume. Finally - “ . . . adaptation and mitigation strategies will help us as the climate changes. Humans can support plant survival by making sustainable lifestyle decisions, including planting native species, avoiding pesticides and chemicals, and encouraging ecosystem reforestation efforts. Not only are these actions simple to take up, they support our environment as a whole.” https://www.nps.gov/articles/000/plants-climateimpact.htm
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