For anyone who is interested, I've found some information about tree management on the airport's website.
It looks like they've been actively reducing tree heights and felling on lots of areas south of the runway, with Marlhill Copse next on the list. According to the website the airport bought the land there last year.
This seems like a very positive development for the airport, with a runway 20 starter extension and a climbout cleared of many of today's obstacles it would appear that much of the existing performance limitations at SOU would disappear.
https://www.southamptonairport.com/a...-safeguarding/