To continue the discussion I would like to add my observations regarding arches and tree breaks (I purposefully ignore tree structures presently, because they are much more complex, and I feel their manufacture involves more complexity).
Last summer, after observing many tree breaks and arches that appeared to me to be due to other than natural causes, I began to photographically document and record their GPS x-y locations.
Some observations in mixed coniferous montane forests (pine, spruce, fir, aspen trees at elevations of 8500 – 11,000 feet) over the last few years:
Tree Breaks
67 tree breaks described.
All involved Aspen trees.
Range of tree diameter at break = 2.6 - 6.2 inches.
Breaks occur from 2.2 to 15.7 feet above the ground level (median just above 8 feet).
About 2/3 of the breaks exhibit obvious left rotation of a few to many degrees (max about 15* - most a few degrees only).
All the observed breaks are within 100 yards of a human trail – some next to a trail, some within view from a trail, some well removed from a trail (but not far).
65 of the 67 breaks lean toward the trail – usually within 10-15* directly toward the trail (I have observed only 2 breaks that lean in the 180* azimuth away from a trail).
I am including a few photos of some breaks.
One of the included breaks has with it a personal story that I will relate if a discussion ensues.
Arches
34 arches have been described (many more have been observed).
The arches are what I say are graceful curves with a fairly consistent radius.
All arches involved Aspen trees – thin saplings in every case (2 – 5 inch diameter near base).
Arches were made (or occurred) while the saplings were alive and supple, although most are now dead and brittle.
About half (16) have their tips anchored into the ground and then pinned with a branch (usually a short aspen branch) inserted at a low angle over the arch tip.
One arch in particular was pinned in a much more complex way – see my photos in an earlier post in this thread.
Once the aspen arch sapling has died the pinning branch can be removed with the arch remaining in place, so some of the older arches may have had pins removed by natural or other forces (I see no way to have determined this). In other words, all arches may have been pinned at one time.
Aspen arches made during the current summer growing season (2018) rebound to some degree if they are unpinned.
As a general observation – I have hiked through numerous aspen groves that do not contain a single break or arch (or other structure) that I would consider anomalous. Then, in some of those groves, it seems like I have crossed a sharp boundary and entered a zone with numerous breaks and arches (and structures and tangled, intertwined aspens – like a fence) that appear anomalous.
Wind and snow certainly work in wondrous ways!