It's harmless, till I accidentally introduce an invasive species. Which you think would be easy to avoid. But I have some useful trees that are invasive in parts of the US, but apparently not in Europe (so far). I can't find out why that is the case. I'd like to do something good, but it's not easy even achieving harmless. 
There's a patch of oak forest on Dartmoor which is a remnant of the forest that presumably covered the whole place till it was denuded to it's current bleakness. The trees are ancient and knarled and twisted and hanging with moss and lichen. Between the trees are big round boulders. It looks like a movie set, and seems spooky even on a bright sunny day. I know they wanted bent oaks for ships ribs, but I guess they gave up when they got to this patch of trees (Wistman's wood, if you pass this way). Mind the adders, which are all over the place.
