Mix of red trees -- when wild land has been this? (10)

I believe the answer is:

reforested

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'wild land has been this?' is the definition.
The definition suggests a singular noun but the answer is not.

'mix of red trees' is the wordplay.
'mix' indicates an anagram.
'of'+'red'+'trees'='ofredtrees'
'ofredtrees' with letters rearranged gives 'REFORESTED'.

'when' acts as a link.

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I've seen this clue in The Telegraph.

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