We get stuff like this all the time in the woods we use, mostly done by Mountain Bikers to make new and unauthorised jumps, thing is they leave 4-5ft high stumps in line with their jumps, so we cut the stumps off on safety grounds, last thing anyone wants is to find a biker pole axed on a 4ft high stump, we then use the wood for bushy stuff, they have also recently taken to making huge jumps on public foot paths, so we knock those jumps down and clear them away from the path and make it safe for walkers to use per the agreement i made with the Estate.
Thing to do Spanit, is to make a positive from the negative, find the landowner, show them the photo's or even take them there and offer to clear the mess up free of charge, well, your payment being, you get to keep the felled timber.