Yes, Trees are a Global Warming Solution for 3 Reasons
As Californians watch their hills become golden earlier in the year, and wrestle with response to the drought, trees have come under relentless pressure. Now, more than ever we need to be thoughtful about protecting trees and managing the water that sustains them.
Trees in the ground must be a significant part of mitigating climate change. Focusing solely on carbon misses a crucial broader point: Trees benefit the entire ecosystem and once established take surprisingly little water to maintain. Donald Hodel of University of California’s Cooperative Extension (UCCE), wrote “Selecting the right tree for the situation, and then planting and maintaining it properly are critical to conserving water” in The California Drought and Landscape Water Use Hodel’s study found that parks, sports fields, public landscaping used less than 6% of California’s total water supply.
During the day, tree canopy provides coveted cool shade. Each night as temperatures drop, these cooler areas are more likely to reach the dew point, where water vapor condenses into liquid. The tree canopy increases the likelihood of reaching the dew point and offers surface area on which condensation can occur. Thus, trees create their own microclimate, which helps sustains them
Children learn that water evaporates, travels long distances as water vapor and drops as rain or snow. Fourth graders identify this as the large water cycle. Recent research shows trees play a significant role in local precipitation, the small water cycle. As much as 60% of rainfall is directly tied to local vegetative ground cover, plant respiration and trees.
Above ground, trees offer shade, ground cover and water. What goes on below ground is just as important as above it. Soil is made of rocky material, dirt and organic matter — decomposed leaves, roots, plant extrudates and soil microbes, dead and alive. Photosynthesis from green leaves pulls CO2 from the air — and uses the carbon to build the leaves upon which the dew precipitates. Tree roots anchor soil and prevent erosion.
Most of the carbon is extruded through the roots as sugars and enzymes, which feeds soil microbes. Healthy soil has a complex community with broad biodiversity. Soil microbes, like all life, need food and water. The dew, rain and extrudates feed the bacteria and fungi which, in turn, are eaten by protozoa, which cycle the nutrients the tree or plant needs to survive. Nitrogen, for example, makes up 80% of the atmosphere. Bacteria can pull nitrogen from the air, but it remains unusable by plants until processed by protozoa. Nutrient cycling is the effect of a complex community of soil microbes. Each 1% increase in organic matter increases the soil’s water-holding capacity by 20,000 gallons.
While each component of the soil’s microbiome is important, fungal strands, known as hyphae, pull water and nutrients into the tree roots. These hyphae, and their bacterial coating, is the mechanism for carbon storage, where carbon from the air is put into the soil on a permanent basis.
Trees and other plants may come and go, but the glomalin of the bacteria that coat the fungal strands is formerly atmospheric carbon, now sequestered in the soil. Glomalin changes the texture of dirt, giving soil structure which allows plants to deepen their roots. Trees, more than grasses and annual plants, need fungi to live. Trees are the major contributor to the sequestering of carbon and mitigating climate change.
Trees also make us feel better. Biophilia, the effect of plants on human neurology, is measurable. Trees and green spaces enhance emotional well-being as well as health.
At 100,000 Trees for Humanity, we’ve seen how planting a tree makes the planter feel better. The physical activity engages the volunteer with contributing a solution. These positive emotions are reinforced as the planter passes the tree. Our projects have 100% recidivism. That is, all of our volunteers return to plant more trees.
But there is more. Low levels of serotonin are known to be a factor in depression and anxiety. A common soil bacterium, mycobacterium vaccae, stimulates serotonin production. It’s been shown to reduce anxiety — and increase joy — in cancer patients as well as gardeners. Mycobacterium are only one component in healthy soil’s microbial biodiversity, which trees promote.
Trees make us feel better, cool communities and contribute to mitigating climate change. Being water wise includes maintaining trees in our streets and parks.
Amos White is the founder and Chief Planting Officer at 100,000 Trees for Humanity and member of the Advisory Board of California Urban Forests Council. Elizabeth Pearce, is the founder and CEO of SymSoil Inc. and an adviser to RegenIowa
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