How often must foliage be trod upon before what can be defined as a visible ‘trail’ starts to form?
A natural trail? First define that.
I’ve trails behind my house, some made by me just from walking.
There are other trails of course, made by the local critters. I follow them as well. A natural trail will be created by water and food available. They can be hard to find and follow but are there.
Mostly made just by walking, not by taking a hoe or rake and intentionally clearing a pathway.
It doesn’t take that much. A single person can create an obvious and recognizable trail through the woods or grassland just by walking through it semi-regularly. I created lots of them when I was growing up on a large rural property and I have never seen established rural properties that didn’t have some of their own. They even exist deep in the woods because animals like deer help mark them as well.
People and many animals are really good at finding the most efficient route between two points without even thinking consciously about it. Once those trails begin to get established, they tend to get used more and that creates a reinforcement loop. Most young plants are quite fragile and cannot tolerate people or animals trampling them when they are most vulnerable so the trail will never become completely overgrown with larger growth once it has even a modest amount of traffic using it somewhat consistently.
As an aside, there is a related phenomenon it comes to designing the sidewalks for meandering spaces like parks or college campuses. It is extremely difficult to design the paths in advance. Predetermined designs almost always end up with people cutting across the grass and killing it making an unsightly mess that the groundskeepers have to constantly combat. A better solution is to not to lay any permanent sidewalks at all when the grounds are first built. You just let people walk where they want. They will do it in remarkably consistent paths that become obvious over time. After those are well established, you can pave them properly and people will continue to follow them because that is the was always the intuitive route.
I have two tiny yapper dogs that have clearly blazed a trail in my yard from my door to the fence next to my neighbor who shamelessly feeds them treats all day, in just a few months.
My data point is that a rat infestation took just a couple of weeks to make a track in my lawn between my wood pile and the hole in the fence that lead to the neighbor’s chicken feed. I killed about 20 rats (that I found) when I started putting out poison pellets everywhere around their holes.
This case really surprised me because I’d always thought of trails as being made by much heavier animals. Cows, people, deer, etc. all look big enough to make a trail It’s hard to imagine rats (even rats as big as the ones in my yard) trampling anything down, but there you go.
This is a very interesting explanation. I’d once heard it expressed less scientifically by a landscaper as “Don’t fight it, pave it” but I always kind of dismissed the idea as expressing frustration more than wisdom. The way you describe it actually does make a lot of sense.
I know that when I was living on campus in Montana, I always tried to be one of the first out after each snowfall, so I could make sure that the trails through the snow were in the places convenient for me. With snow, it really only takes 1-3 trips along a path to establish it.
Ants excepted. They seems to find the most outrageously circuitous paths to establish their ant trails sometimes.