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IV. Carbon Storage and Sequestration <br />Climate change is an issue of global concern. Urban trees can help mitigate climate change by sequestering <br />atmospheric carbon (from carbon dioxide) in tissue and by altering energy use in buildings, and consequently altering <br />carbon dioxide emissions from fossil -fuel based power sources (Abdollahi et al 2000). <br />Trees reduce the amount of carbon in the atmosphere by sequestering carbon in new growth every year. The amount <br />of carbon annually sequestered is increased with the size and health of the trees. The gross sequestration of City of <br />Pleasanton trees is about 333.2 tons of carbon per year with an associated value of $56.8 thousand. See Appendix I <br />for more details on methods. <br />40 <br />35 <br />- 30 <br />0 <br />0 25 <br />m <br />W 20 <br />Z <br />915 <br />10 <br />5 <br />PS e <br />°a5°jc�a <br />o <br />(CA valley oak) species <br />Qea` atm <br />E � <br />7 <br />6 <br />5 <br />v� <br />4 C <br />0 <br />3 -c <br />W <br />2 0 <br />1 <br />0 <br />Figure B. Estimated annual gross carbon sequestration (points) and value (bars) for urban tree species with the <br />greatest sequestration, City of Pleasanton <br />Carbon storage is another way trees can influence global climate change. As a tree grows, it stores more carbon by <br />holding it in its accumulated tissue. As a tree dies and decays, it releases much of the stored carbon back into the <br />atmosphere. Thus, carbon storage is an indication of the amount of carbon that can be released if trees are allowed <br />to die and decompose. Maintaining healthy trees will keep the carbon stored in trees, but tree maintenance can <br />contribute to carbon emissions (Nowak et al 2002c). When a tree dies, using the wood in long-term wood products, <br />to heat buildings, or to produce energy will help reduce carbon emissions from wood decomposition or from fossil - <br />fuel or wood -based power plants. <br />Page 11 <br />73 of 219 <br />