There's bats passing over the heart of the forest (5)
I believe the answer is:
trees
'the forest' is the definition.
(a forest is made up of trees)
'there's bats passing over the heart' is the wordplay.
'there's' means one lot of letters go next to another.
'bats passing' becomes 'tr' (I am not sure about this - if you are sure you should believe this answer much more).
'over' is a reversal indicator.
'the heart' becomes 'see' (see is a kind of heart).
'see' back-to-front is 'ees'.
'tr' put next to 'ees' is 'TREES'.
'of' is the link.
Can you help me to learn more?
(Other definitions for trees that I've seen before include "Components of forest" , "Woods" , "Large plants" , "Elms, pines etc" , "Steer into the plants" .)