Some timber reserves the diaries (8)

I believe the answer is:

logbooks

'the diaries' is the definition.
(a logbook is a diary or journal)

'some timber reserves' is the wordplay.
'some timber' becomes 'log'.
'reserves' becomes 'books' (booking is a kind of reserving).
'log'+'books'='LOGBOOKS'

(Another definition for logbooks that I've seen is " Record volumes".)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.