Rudbeckia colors the north side of  Bob’s Prairie in July.  Although switchgrass, big bluestem and  Indian grass are present across the site, the grasses grow taller and in greater density on the south.

When Bob purchased the site in 1959 it was uniformly covered by the usual mixture of native and non-native plants typical of abandoned fields and pastures in the Upper Midwest. That cover remained undisturbed until September 2009 when herbicide was applied to kill the existing vegetation.  How the site might have been used before 1959 is unknown.

The company hired to prepare the site burned the herbicide-killed cover in April 2010, and disked the soil.  They applied more herbicide in May to kill plants that had emerged since the burn.  After disking the site again in June, they seeded the area and mulched it with prairie grass hay. 

The unequal distribution of broad-leaved plants and grasses is even more evident in August when Monarda fistulosa on the north contrasts with grasses flowering on the south.

                               Puzzle: Why do Broad-leaved Plants Dominate One Side of Bob’s Prairie?

Seeds of the native prairie plants germinated and grew very well in 2010 and 2011, so well that the fledgling prairie was burned in 2012.  The contrasting north-south distribution of wildflowers and grasses, evident since the seeds germinated, is especially noticeable now that the flowers and grasses have come into full bloom

The site slopes gently from north to south, so it’s possible that nutrients and soil moisture are greater on the south side.  If so, does greater moisture and fertility necessarily favor grasses?

Analysis of soil conditions and a fuller understanding of the site’s history might resolve the puzzle, but until then, the stark north-south demarcation of forbs and grasses on Bob’s Prairie remains a mystery.