Vast treeless plane (6)

I believe the answer is:
tundra
'vast treeless plane' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tundra that I've seen before include "Arctic plain with permafrost" , "Treeless Arctic region" , "Vast treeless plain in the arctic regions" , "Vast area" , "Cold northern region" .)