The mayor joined scores of volunteers who turned out at Roding Valley Park in Redbridge at the start of a mass tree planting which aims to plant 10,000 new trees in one week.
The locally sourced young trees include oak, ash and hazel.
Mayor Boris Johnson said: "Trees immeasurably improve our quality of life and I am determined to boost their numbers."
Johnson is supporting the project as part of City Hall-backed campaign Re:Leaf London, run by the Forestry Commission, Woodland Trust and Trees for Cities which aims to encourage businesses, communities and individuals to plant more trees across the capital.Trees for Cities chief executive Sharon Johnson said:
"The creation of this new 10,000-tree urban woodland in just one week is Trees for Cities’ largest project to date and sees 2011 off to a flying start."
Johnson added: "The project couldn’t be achieved without the support of our volunteers who are working alongside local people to create this new woodland for future generations to enjoy."