This picture here does look like pieces of pipe, but also pieces of trees/logs so it's an odd mixture in my mind. Somebody of course could have stacked the pieces on top of each other to better represent "trees".Actually those bottom set of pictures don't look like trees at all to me anyways. They look exactly like furred up pipes. Or more accurately the inside of furred up pipes which has dried out and cracked in the fashion you show. What material the pipe was if it were a pipe I cannot tell but the furring was always bad on steel, lead and cast iron pipes in my experience with terracotta and plastics coming next.