By Bill Kleiman

We recently heard from Emily Wedel who worked on her doctorate at Konza Biological Station, looking at shrub encroachment in seldom and frequently burned units. Konza has been studying and pondering the shrubs which have established on their plots that have had infrequent fire. Emily showed us a slide where the infrequently burned unit was full of top killed shrub stems, shrubs that would all re-sprout come spring. On the other side of the fire break was an annually burned prairie that had no shrubs.

Emily showed us maps of shrub encroachment that showed that a 20 year fire return interval looks to have the same heavy shrub encroachment as the 4 year fire return interval. To me this suggests that the fire return interval should be one, two or three years. The unit with annual fire had essentially no shrubs even though just across a mowed fire break was a 20-year fire unit full of shrubs.

The above photo is at Nachusa Grasslands in our East Heinkel Unit, due north of Schafer Knob. On the left is a prairie planting that is about a decade old and frequently burned. It established well and is handsome this time of year with pale purple coneflowers and white baptisia. My photo does not do it justice. It has essentially no shrubs and has been burned every year or every other year since its planting in 2013.

On the right of the photo is a fallow prairie pasture that the former owner sprayed with broadleaf herbicide a number of times and then grazed horses on it. The prairie was nearly vanquished, but some diversity remains. This herbicide sprayed field likely supported shrub establishment. Notice all the shrubs in it. Abundant are smooth sumac, various Rumex briars, some multiflora rose, honeysuckle, cherry, and black oak.

This unit with shrub buildup has not been burning enough to top kill all the shrubs. It is on a gentle north slope which may lower fire intensity. We had shrub buildup in there before bison, and we have the shrub thickets now, ten years after bison have had access to it. The grazing at times makes the fires patchy with low intensity, which has benefits, but likely supports the shrubs.

This winter we hope to brush mow the unit to see if that later helps the fire come across the unit and top kill the shrubs. We work to keep shrubs and trees out of our open prairies to leave some habitat as full open prairie.