The most common and most likely answer to this crossword clue is the 5 letter word MAPLE
I've seen this crossword clue in The Guardian
M
A
P
L
E
More clues leading to the result MAPLE
- Treasure finally found under different palm tree
- Fellow must keep quiet in wood
- Tree feller around middle of copse
- Plot with hollow lime tree
- Fellow with inner power is the symbol of a nation
- West’s sheltered place for shrub
- Destroyed ample plant
- Sleuth Jane, not seeing river, finds wood
- Man that must take pee in wood
- Old man in one sort of tree has to climb another
Buddy explains!

The straight part
We know that "timber" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case timber = maple.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MAPLE mean?
MAPLE noun- A tree of the Acer genus, characterised by its usually palmate leaves and winged seeds.
- The wood of such a tree, prized for its hardness and attractive appearance