Poison ivy and culverts have nothing in common except that I had to deal with both in the last two weeks.
I'll answer your first question right away: a culvert is a structure used for crossings generally under 12 feet instead of constructing a bridge. In practice a culvert basically looks like a huge pipe that allows running water to continue along it's natural path. The Pumpkinvine has one such culvert in Shipshewana, for crossing Mather's Ditch, which collapsed a few weeks ago after years of erosion caused by heavy rain.
I have gotten poison ivy twice in the past two weeks and I am scratching the rash on my arms as I type this post. Here's the thing though, poison ivy is meant to be here. Culverts are not.
Poison ivy is a nuisance to humans, and it is generally acceptable to remove this plant despite it's role in the local ecosystem as bird food. Culverts are not naturally occurring, but people utilize them to make nature more human friendly.
So if the Pumpkinvine is a nature trail, what is the efficacy of manipulating the environment in the name of human enjoyment and not ecosystem restoration?
I don't have a good answer for this. The town of Shipshewana had to spend around $12,000 to install a new, more resilient, culvert. We changed nature to better suit our needs.
So shouldn't we reciprocate?