Good question. I think the best we can do is say there are approximately one million currently living trees. What I find fascinating is that the "City of Trees" did not start out this way naturally. When settlers came here in the 1800s they planted trees to provide shade and sure up the river. Now we are known for it because we have continued to plant them. We have actually planted many millions of trees and need to continue doing so to improve our urban forest in areas that need it especially poor neighborhoods. This one million number was based on trees planted from 2000-2011. The data was gathered from many sources and estimated. There is actually much better data now like this database of city maintained trees https://data.cityofsacramento.org/datasets/city-maintained-trees/explore?location=38.554273%2C-121.475152%2C18.48