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Canopy: Trees for Palo Alto
Nonprofit center for street, park, and garden trees in Palo Alto, California. Runs planting and education programs.
http://www.canopy.org/
CommunityTrees.Org
Nonprofit promoting the planting and care of trees in urban and community neighborhoods.
http://www.communitytrees.org/
Friends of Trees
Brings neighbors together for tree-planting and tree-care projects along city streets, in urban natural areas, and on school grounds.
http://www.friendsoftrees.org/
Stable Slopes Forever
Dedicated to saving a Redwood forest in the heart of Southern Humboldt County, California.
http://www.stableslopes.com/
Trees Forever
Facilitates planting and care of trees through action-oriented programs that empower people, build community and promote environmental awareness.
http://www.treesforever.org/