Essentially, disallow campsite in these mountains (4)
I believe the answer is:
alps
'these mountains' is the definition.
(European mountain range)
'essentially disallow campsite' is the wordplay.
'essentially' says to take the centre.
'disallow' becomes 'bar' (barring is a kind of disallowing).
'campsite' becomes 'lps' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The central letter of 'bar' is 'a'.
'a'+'lps'='ALPS'
'in' is the link.
Can you help me to learn more?
(Other definitions for alps that I've seen before include "high points" , "South-central European mountain system" , "High mountains" , "Slap (anag.)" , "Mountain system, highest peak Mont Blanc" .)