What Does Long-Term Bison-Grazed Prairie Look Like?

Bison-grazed pastures tend to have higher forb cover and vascular plant diversity in prairie (bison have been there now for 35 years), but what does this look like. I have some pictures from quadrats from field work at in Konza’s N2B watershed (Bison + Fire every other year) taken nine years ago. It’s worth noting that spring burning at Konza is usually conducted between late March to early May, which is mostly/usually well into the growing season there (I used to volunteer, and Baptisa australis was often flowering at burn time), and that large swathes of bison watersheds lack enough fuel to burn when fire is applied (every other year is the frequency of fire application, not actual burning).

The below photos were taken in August. I’m not going to say here whether I like what I see or not. It should be pretty obvious. These are from a reference area of “intact” prairie used for a woody removal study that is in preparation. Another grad-student colleague and I helped by collecting baseline vegetation data. The woody removal did not work in the long-term, because TNC didn’t want cut woody vegetation treated near the stream. It was simply cut and left to resprout. …and woody vegetation removed included a few open-grown chinkapin and bur oaks about 150 years old (I counted rings on the stumps), which had green dragon and wild coffee under their canopies. That’s a tangent, but sometimes the big picture in science misses some of the nuance of what is being studied.

This area is indeed forbier and more diverse than frequently burned Konza watersheds that aren’t grazed, which are over-dominated by the big warm-season grasses, because burning is late (within the growing season) and probably also due to legacies of past broad-leaf herbicide application that would have occurred for warm-season pasture management. Here, the most prominent forbs are western ragweed (Ambrosia psylostachya), Canada goldendrod (Solidago canadensis; or tall goldenrod, Solidago altissima. The former is on the Konza list and I didn’t know the difference in the early 2010s when I did this work), Baldwin’s ironweed (Vernonia baldwinii), stiff goldenrod (Solidago rigida), and hoary vervain (Verbena stricta). These were easy quadrats to do!

Konza is just one site (even if subdivided into pseudo-replicates, which are reasonable at that scale), and results, I’m sure, will very with duration, seasonality, stocking rates, and geography.

I distinctly remember getting out of the truck in a bison watershed on my first tour of Konza before my graduate program began and being struck that this was more or less the vegetation, and I haven’t seen a case yet that struck me differently. This could be Minneopa State Park in Minnesota, for instance. Bison are appropriate at Konza and elsewhere in the western tallgrass and on the Great Plains where they were an important historical presence, but the devil is in the details of fencing them in.

This links to Konza’s bison fact sheet.

Looking into the bison enclosure at Minneopa State Park near Mankato, MN. This is also has a lot of forbs–Erigeron and Artemisia.

A few decades ago there was a debate between Konza researchers and those working on more eastern prairies about what the context of and results from Konza mean for prairie management–and simply what maintains prairie. See the Bioscience article and response. It’s worth a look.

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