Can Multiple Exchange Co-exist in a single forest

Hi,

I am working on unifying my companies infrastructure. My current model looks like this:

Prod Forest:
DC1
DC2
Exchange 

Dev Forest 
DC
Exchange

QA Forest 
DC
Exchange

Support Forest 
DC
Exchange

What we want is to merge the forest of DEV, QA and Support together and have 3 domains in it with their respective exchange. 
I wanted to know if these exchange servers can co-exist in a single forest. We cannot merge the exchange coz it will disrupt a lot of settings.

Thanks

KV