Arctic forest thawing every so often north of America (5)
I believe the answer is:
taiga
'arctic forest' is the definition.
'taiga' can be an answer for 'forest' (type of forest). I am not sure about the 'arctic' bit.
'thawing every so often north of america' is the wordplay.
'every so often' means one should take alternating letters.
'north of' means one lot of letters go next to another (in a down clue, some letters go above others).
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
The alternating letters of 'thawing' are 'taig'.
'taig'+'a'='TAIGA'
Can you help me to learn more?
(Other definitions for taiga that I've seen before include "Boggy forest" , "Swampy forest south of tundra" , "Marshy pine forest" , "swampy forests" , "Arctic coniferous region" .)