As promised in an earlier email, here is what I know about Australian Aboriginal boundary trees and scarred trees.
Boundary trees were created by tying gum tree branches (or in the case of very young trees, entire trunks) together with kangaroo sinews. With time the branches or trunks would knit together to form a very distinctive shape == undoubtedly man-made. Such trees signified the boundaries between various tribes and clans. Sometimes they were also marked by carving various symbols into the bark.
Scarred trees (usually just called "scar trees") were created by cutting a piece of bark off a gum tree to use as a shield or other tool, or even a canoe. Usually an oblong-shaped piece of bark would be cut. As the tree grows the scar grows, sometimes as much as 10 to 12 feet in length.
The bark would be cut so that if you stood against the tree with your back to the scar, you would be looking in the direction of something significant, such as a water hole, burial ground, boundary tree, river, mountain, "women's business" or "men's business" site (sacred stuff, this).
Boundary trees and scar trees formed a system of signage throughout the Australian landscape. Aborigines would read the trees just as we read street signs and traffic lights. Unfortunately, European settlers cut down many of these trees and so there are now big gaps in the system.
I'm sure this information is well documented in various texts in Australia, but I got it from some young Aborigines who were generous enough to share it with me when I travelled down under.
Melissa Dennison (email@example.com)
(((bruces remarks: One can only speculate about the extreme age of this practice of using vegetation as media. As Note 30.2 suggests, it may pre-date humanity.)))