Massive city tree planting campaigns have invigorated the urban forestry movement, and engaged politicians, planners, and the public in urban greening. Million tree initiatives have been launched in Los Angeles, CA; Denver, CO; New York City, NY; Philadelphia, PA, and other cities. Sacramento, CA even has a five million tree program. These planting campaigns - and urban forestry programs in general - are justified by models that estimate and monetize the environmental and socioeconomic benefits of trees. These ecosystem services, defined as "the benefits that humans derive from nature," play a major role in urban natural resource management. However, realizing the ecosystem services associated with planting depends on tree survival. Despite the major focus on city tree planting over the past few decades, Nowak and Greenfield found that overall canopy cover levels in major US cities have been declining.
Roman, Lara A. 2014. How many trees are enough Tree death and the urban canopy. Scenario Journal. Scenario 04. 8 p.