UPDATE: Mystery solved - it's "Twig Girdler Beetles". :)
What's been girdling my trees? I'm not an expert, but it does not look like beetle damage (too regular and straight) or nibblin' critters (no teeth marks, and again, too perfectly straight). The black stuff looks bacterial, that makes sense, but the damage itself is very strange. I was out there a week ago, and didn't have any reason to inspect them closely but at least noticed that the two short ones were upright and unbroken at that time. Any thoughts?