This case is unusual, but the strongest piece of advice that I can give to everyone in similar landowner situations is that ‘Jumps are bad, m’kay’
Over fifteen years almost every incident of landowner conflict, crackdown, exclusion, bad press, ban, bulldozing, blockage or restriction has been prompted by jump digging. (I can count on one hand the number of times that this wasn’t the flare point, two were scheduled ancient monuments, one was nightjar, one was ancient woodland, this is the fifth)
If you want to keep your trails, kill the jumps, dead – most particularly gap jumps, and then exert peer pressure to stop people digging more (I find putting the word round the local shops helps)
Then google ‘forestry commission wild trail management guidelines’ and read them