Originally Posted by
webtwo
I worked in a state park during my college summer breaks. People hanging things on trees will kill them or make them more susceptible to disease and pests. The living tissue of a tree lies just beneath the bark. Tie a tourniquet around one of your limbs for 8 hours and see how it feels. I agree that enforcement will be minimal at best, so you can decide for yourself how much or how little you care.
Try standing still outside for a few years and you might realize that you're not a tree.
While abrasion and scouring of bark can certainly hurt a tree, "tourniquetting" a tree trunk larger than 6" diameter will cause absolutely no harm. Most hammocks hang from webbing which is at least a half inch thick which helps prevent them from rubbing off any bark. A tire swing rubbing back and forth for a few years might hurt a tree (and there are plenty of those that have been up for decades), a hammock for a night is not doing any harm.