Fallen tree trunk around northern pine (4)
I believe the answer is:
long
'pine' is the definition.
(to pine for something is to long for it)
'fallen tree trunk around northern' is the wordplay.
'fallen tree trunk' becomes 'log' (chopped down tree).
'around' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'log' going around 'n' is 'LONG'.
(Other definitions for long that I've seen before include "Thus having been treated by stretcher, perhaps" , "hunger" , "extended period" , "bought in advance" , "dream" .)