2019 North American Prairie Conference

The Nature Conservancy’s Broken Kettle Grasslands Preserve occupies 3,300 acres (1335 ha) of Plymouth County, Iowa near the northern terminus of the Loess Hills.   In anticipation of observing the impact of bison and other management practices on ecosystem restoration, 30 long-term vegetation monitoring plots were established in August 2008.  Vascular plant species sampled within the plot quadrats were recorded, and plots ranked using a floristic quality index.  Plots were also digitally photographed.  In October 2008, 28 bison were released on 139 acres (56 ha) of the Preserve. By summer 2018, the herd had grown to 240 and had an expanded access to 1,900 acres (769 ha).  In August 2018 the 30 plots (25 open to bison grazing) were resurveyed.  Whereas the floristic quality indices based on total species encountered during 2008 and 2018 were similar, the 2018 individual plot indices were typically lower than those in 2008.  The occurrence of leafy spurge (Euphorbia esula) remained relatively unchanged, yet another invasive, crown vetch (Coronilla varia), exhibited a noteworthy increase.  Eight of the 25 original plots open to bison grazing contained evidence of grazing in 2018.  Comparison of plot photographs from 2008 and 2018 documented a reduction of red cedar (Juniperus virginiana) and other woody species on open prairie concurrent with an expansion of deciduous forest from protected valleys.