San Francisco Chronicle: The bigger the fir, the more it would be worth to Smith. But not as lumber – as carbon. Tree 10525 is part of the Garcia River forest in Mendocino County, one of two privately owned California forests that have been recruited into the war against climate change as certified sources of carbon offsets. Carbon offsets – which have become popular among environmentalists over the past several years – are voluntary payments made to initiatives that reduce the level of carbon …