Any gravitons regularly missing trees? (6)
I believe the answer is:
Here is my best explanation:
'missing trees?' is the definition.
'ngaios' can be an answer for 'trees?' (I've seen this before). I'm not sure about the 'missing' bit.
'any gravitons regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'anygravitons' are 'ngaios'.
(Other definitions for ngaios that I've seen before include "New Zealand trees", "Southern Hemisphere trees" and "Trees".)