Estimating a net carbon balance involves the accounting of carbon accumulations and losses. The carbon balance of urban trees includes many factors, many of which are difficult to estimate. The net balance is positive when your tree stores more carbon from the atmosphere than is lost to the atmosphere through tree care and decomposition.
Carbon accumulations:
- Growth: This includes the carbon fraction of the tree mass (~50% of tree dry weight) including stem, leaves, branches, and roots.
- Products: Any carbon that is stored in products made from the tree (i.e., building materials, wood carvings, etc.)
- Energy Conservation: Any avoided energy consumption directly related to services provided by the tree (i.e., shade, evaporative cooling, windbreak, etc.)
- Soil Carbon: Any carbon fraction of partially decomposed tree material (leaf litter, root turnover, wood decomposition) that is stored in the soil.
Carbon losses/emissions:
- Decomposition: Microbial respiration releases the carbon in decomposing organic material, including trees, as carbon dioxide during decomposition.
-
Fossil Fuel Emissions: Fossil fuel combustion is the main source of usable energy. When burned, these fuels release carbon dioxide. Sources of these emissions that relate to your urban tree include:
- Energy use by the nurseries growing commercial trees from seed.
- Transportation involved in bringing the tree or maintenance crews, and tools to the site.
- Energy used to power equipment and tools during planting, maintenance, and removal.
- Energy used to move water, mulch or other materials to the site.
- Energy used to produce fertilizer used for the tree.
- Soil Carbon: Trees can also decrease soil carbon on site by disturbing soil during planting, maintenance, or removal. Soil disturbance causes an increase in microbial respiration and can also cause soil erosion from the site if care is not used.