Work together in area of land surrounding base (8)
I believe the answer is:
interact
'work together' is the definition.
(to interact is to connect or work together)
'in area of land surrounding base' is the wordplay.
'area of land' becomes 'tract' (tract can mean a piece of land).
'surrounding' means one lot of letters goes inside another.
'base' becomes 'e' (mathematical symbol).
'tract' going around 'e' is 'teract'.
'in'+'teract'='INTERACT'
(Other definitions for interact that I've seen before include "Train etc. (anag.)" , "Show effect on each other" , "Work with others" , "Work closely together" , "Affect one another mutually" .)