I hadn't knowingly seen it much, and only learned the name a couple years ago, but this year,
Should we be concerned about either example of this nonnative rampancy? I sent an inquiry to a couple listserves of land managers, and received a tepid response. Birdsfoot trefoil is mostly a roadside weed, was the sentiment. It only gets a couple feet high, so will likely just stay in the background rather than stifle native species.
But I have a vivid memory of a prairie walk I went on last year at the Kishwauketoe nature preserve in my home town in Wisconsin. At one point, leading us through a gloriously restored prairie, the botanist spotted a birdsfoot trefoil and immediately went over and pulled it out. Was it merely a pet peeve, or was his determination rooted in past observations of dramatic consequences if birdsfoot trefoil is allowed to spread?
This short video shows how birdsfoot trefoil can alter the appearance, if not necessarily the composition, of a meadow:
This is an invasion that's in the very early stages, and could be easily nipped in the bud. For instance, I found a grand total of three plants on the middle school grounds. Five minutes of spot spraying with a selective herbicide now is all it would take to stop an infestation that will otherwise become intractable.
Another reason to take action is that it is poised to invade the new native meadow planting in the detention basin next to the tennis courts. In this photo, a few plants of birdsfoot trefoil grow just across the parking lot from the new native planting. Does the school want a native meadow, or a meadow that is thick with a nonnative species that appears capable of outcompeting many of the native grassland plants?
Now, while the extent of the spread is limited, would be the time to take proactive action.