THAT OVERNIGHT GLOBAL FOREST? SPLAINED.

'DOCTOR WHO'
"IN THE FOREST OF THE NIGHT"

I don't think the Doctor actually knows that the Earth (known as "Earth Prime-Time" here at Toobworld Central) is a super computer built by the Magratheans to the specifications of the computer known as Deep Thought.  When he showed the formation of the planet to Donna Noble, he made no mention of the robot barges that must have been attached to the rocks in order to guide them into place.

 

Had he known that the Earth was an artificial construct, he might have realized that the sudden overnight growth of world-wide forests (which would protect the planet from a massive incoming solar flare) was nothing more that an automatic safety program to protect the computer from harm. 

 As for the "fae", those firefly-like lights - "thoughts" as Maeve called them - which pestered the little girl and finally spoke through her, they are the manifestation of the computer's brain, its memory banks and mainframe.  They interfaced with Maeve in order to communicate with the Doctor.  They were the "Interfae" if you wll and even if you won't.

It might seem fortuitous that they just happened to pick her and the Doctor just happened to be there, but I think there must be thousands of people all over Earth Prime-Time who have been conditioned to be the spokesmen for the computer if need be.  And how could it not be Maeve - the Queen of the Fairies was a "Maeve" derivative and her last name was Arden (as in the Forest of Arden.)

It could be that the computer known as Earth steered generations of people to each other in order to mate so that a girl like Maeve would be born.

Nice use of a "tool" that shouldn't have even been on the planet in the first place according to Deep Thought's original plans!

BCnU!