Dry area with 500 sick trees (6)

I believe the answer is:

desert

I'm a little stuck... Click here to teach me more about this clue!

'dry area' is the definition.
'desert' can be an answer for 'area' (desert is a kind of area). I am not sure about the 'dry' bit.

'with 500 sick trees' is the wordplay.
'with' means one lot of letters go next to another.
'500' becomes 'd' (Roman numeral for 500).
'sick' is an anagram indicator.
'trees' with letters rearranged gives 'esert'.
'd'+'esert' is 'DESERT'.

Can you help me to learn more?

(Other definitions for desert that I've seen before include "Abandon in wasteland" , "Wild" , "Run away (from army)" , "Abandon; barren waste" , "Run away; desolate area" .)

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

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