There is interesting science behind deciduous trees losing their leaves.

http://treephys.oxfordjournals.org/content/18/8-9/537.full.p...

Deciduous trees have an important role in urban environments.

http://www.sustland.umn.edu/maint/trees.html

http://extension.usu.edu/forestry/HomeTown/Energy_TreesandEn...

This link caught my eye because the source was National Public Radio in the United States, in the northern temperate zone (Northern Hemisphere). As I expected, the original date of the article was October (2009). At this time of year (April 2011), deciduous tree leaves are mostly falling only in the Southern Hemisphere.