A time series of urban forestry in Los Angeles

Using historical oblique aerial imagery from the 1920s through 1960s and more recent vertical aerial imagery from 2006, changes in tree density over time were measured for three Los Angeles areas: the San Fernando Valley, Hollywood, and the Los Angeles basin. The results showed a significant, nearly linear increase in total tree density in the San Fernando Valley and LA Basin, but not in Hollywood, where tree density peaked in the 1940s. An analysis of city council districts shows that most districts have increased their tree density over time but with wide variation in the actual amounts. The authors conclude, based on the results for private vs public property, that LA’s Million Tree Initiative will have to rely heavily on private property owners to achieve its planting goals.