Cool clearing! People will def be dancing over the trees roots. Those trees are pretty tall... a Root Protection Area radius can be even as large as the tree's height, but it depends which species.
Fuzzy picture... I'm guessing those are 10m high Scot's pines? I just looked in a tree report I have lying around and the dozen or so trees of 9-11m high had root protection radii ranging from 4-10m. None were pine, but I'm guessing from that that if dancing really does compact soil significantly, then those roots need protecting.
I'm not an arboriculturalist and I only know where you can find info for construction work (and I doubt if there is a document for raves!), but I have seen treemen shouting at trancers on a video before at a busted illegal rave for damaging tree roots so it might be a valid issue. Then again they might just be being overly precious, who knows... but the rules are so restrictive these days for construction that I can believe it might be a genuine issue. I find it hard to believe too, but as I say I'm no expert.
I'm guessing you probably don't know an arboriculturalist but if you know a tree surgeon (a real hippy job so you might!) at least he might be able to give you some free advice. Maybe if you ring up an arboriculturalist and tell ask him if the trees need protecting he might give you some quick free advice over the phone just because he doesn't want to see them damaged. There's a list of them here:
http://www.trees.org.uk/consultants.php
There will be stuff on RPAs and protective coverings for within RPAs in this document:
"BS 5837: 2005 British Standard for Trees in Relation to Construction (An updated BS 5837 was published in September 2005 and is now available from BSI, British Standards (
www.bsi-global.com)"
... but if you ring and ask maybe they actually have a document for events like yours that would be more appropriate, or maybe it's not even an issue and the treemen in the video I watched were wrong. These documents cost about £70 each so again best if you try and get free advice.
My personal view being a libertarian and all is that if that's your land and you want to have a rave without knowing if it could damage or kill your trees, then that's your call. Just be sure to use the wood afterwards if any die so they didn't die in vain. Still might get you in trouble if the trees give 'public amenity' (i.e. the public can see them).
If it's not your land, I'd say it would be selfish to have an event there without checking first that you won't be damaging the trees, and putting down proper protective coverings where necessary.