From
http://connexionsandcontradictions.blogs…

The city of Vancouver has plans to plant trees - a lot of trees.

Tree-starved blocks could gain some colour, as the city develops an urban forest management plan and begins planting a planned 150,000 trees by 2020....I think it’s really good to do trees,” Prof. Condon said. “It would be better if they were thought of as a direct way to infiltrate stormwater and sequester pollutants.” http://www.theglobeandmail.com/news/brit…
Why is this good news?

Since a tree is half carbon, trees represent one of the best ways to extract carbon (which enters the tree as CO2) from the air. The Kyoto Protocol recognizes this and recognizes afforestation for sequestration (absorption) purposes. http://www.treecanada.ca/site/?page=prog…
Not only do trees sequester carbon, and therefore mitigate climate change, urban forests:

are dynamic ecosystems that provide needed environmental services by cleaning air and water helping to control stormwater, and conserving energy. They add form, structure, beauty and breathing room to urban design, reduce noise, separate incompatible uses, provide places to recreate, strengthen social cohesion, leverage community revitalization, and add economic value to our communities. http://www.fs.fed.us/ucf/program.html

Forests also improve our health - including our mental health.

The study, which will appear in a forthcoming issue of the Journal of Affective Disorders, found that volunteers suffering from depression who took a 50-minute walk in a woodland park improved their cognition, as measured by the ability to remember a random string of digits and repeat them in reverse order, compared to those who took a walk through city streets. An earlier study found similar results in subjects who weren’t depressed. http://www.theglobeandmail.com/life/heal…

Heart rate variability analysis indicated that the forest environment significantly increased parasympathetic nervous activity and significantly suppressed sympathetic activity of participants compared with the urban environment. Salivary cortisol level and pulse rate decreased markedly in the forest setting compared with the urban setting. In psychological tests, forest bathing significantly increased scores of positive feelings and significantly decreased scores of negative feelings after stimuli compared with the urban stimuli. http://www.publichealthjrnl.com/article/…

So - Vancouver 's trees will sequester carbon; help control rainwater runoff; reduce energy use by moderating climate (think of lovely cool shade on a hot day); reduce noise; improve air quality; improve human health; add wildlife habitat; provide food (Vancouver is planting some fruit and nut trees); and improve and enhance our connection to our environment. Money well spent!