Is it ok to let leaves, bark and twigs accumulate on a roof?

Question

So. Cal; asphalt shingle roof with a slight pitch; debris is from a eucalyptus tree

Answer 1

They will damage the roof remove them!

Answer 2

No, the debris will start to break down, providing a perfect growing medium for what ever will grow there. This starts to destroy the asphalt shingles below or in contact.  

Answer 3

Nope. They should be removed periodically. Accumulations of debris hold moisture on a roof, and moisture encourages the growth of moss and algae, and neither one are what you want on your shingles. Another problem is that they can actually form little dams that can cause water to back up under the shingles, and that's bad news, too.

If you don't take care of a roof the shingles will fail prematurely. Here are some signs of a failing roof:

http://www.thisoldhouse.com/toh/asktoh/q...