Once clear cutting had commenced, and the fields were subsequently abandoned by the nomadic farmers, birch trees and similar species grew in their place (Curwen and Hatt, 1953).
(clear cutting; had commenced; T:Once) (the fields; were abandoned; by the nomadic farmers, birch trees and similar species; T:subsequently)
clear cutting the fields
had commenced were abandoned
T:Once
by the nomadic farmers, birch trees and similar species T:subsequently