Like a giant mass of cuckoo spittle on the trunk of a tree on a remote part of a private estate. It looked like fairy liquid suds (approx 20-25 cm top to bottom). I have no idea what it might be.
No interactions present.
A slime mould - but I'm sure you have already considered that.
There is a variation to the "paintball" game that uses a type of foam-shooting water pistol. Any aficionados in your part of the world?
We did wonder about Fairy Liquid!!! It was found on a large private estate, so paintballing could be a possibility, but in that case I would have expected to see more than just one occurrence. Also, the Estate Owner was keen that we shouldn't disturb the pheasants, so it's unlikely that he would have allowed paintballing.
I was just reading about bacterial wetwood (also called slime flux). Maybe it is that?
Interesting. I had never heard of slime flux. Should it not have gone brown on contact with the air, though?
I had never heard of it either. Seemed to be lots of pics of it as white though if you look on other sites.
This does not look like a fungus to me. It appears rather 'foamy' on the image.
Another suggestion: Could this have been produced by insects? Members of the Aphrophoridae, for example, produce such foamy structures (I think they protect their larvae with it, but not sure).
Lat/Lng: 54.5, -5.6
OS grid ref: NW7020