(n.) overgrown plants and grasses on a riverbank or at a lakeside
To shirp something is to cut or trim it—while shirpings are the overgrown, untrimmed plants that grow on lakesides and riversides.
That’s a dialect term first recorded in the late 1800s, but likely (like a lot of dialect terms) in use a lot longer than that. Etymologically, it’s little more than a dialect variation of the standard verb sharp—but if it derives from a verb meaning to cut, and came to mean ‘to cut’ itself, why are shirpings areas of uncut vegetation?
The English Dialect Dictionary sheds some light on the conundrum. While shirp means to cut, shirpings are plants that, because of their position on a riverbank, “cannot be mown with the scythe, and have to be cut afterwards with a sickle.” So effectively, shirpings are plants that are noticeably difficult to shirp.