This is a holiday which originated in the United States, but is now celebrated internationally. Since this observance is marked by planting trees, the date differs depending on the climate in various locations.
Regular Websites
This non-profit conservation and education foundation offers membership details, programs and a tree store. - Arbor Day Foundation
http://www.arborday.org/
Features the history of Arbor Day as well as a list of dates when each state in the US celebrates. Also offers a list of the types of trees which are normally planted in each location. - Arbor-Day.net
http://www.arbor-day.net/
Presents a list of Arbor Day crafts for kids as well as links to other educational resources about the significance of this celebration. - Kaboose: Arbor Day
http://holidays.kaboose.com/arbor-day/