Issue with creating forest

Hi.

I am trying to make a map. I used the files from east coast USA as a base and deleted everything and created new terrain. All is going well atm but whenever I create a new forest I get the old forest from ECA and I want an empty forest to work with. Is there a way I can clear the forest without having to manually delete it with the brush (It takes forever).

Thanks!

 

Here you go

 

Awesome thanks worked perfectly!