Impact of prescribed fire on plant and insect communities in a roadside prairie planting

Four years after seeding the U.S. Hwy-52 roadside to native prairie north of Decorah, Iowa, there has not been successful establishment of native grasses and forbs.  The successful establishment of native tallgrass prairie species along U.S. Hwy-52 would likely lead to increased abundance and species richness of native butterflies and ground beetles by providing suitable host plants for plant-insect interactions.  In the spring of 2013, a late spring prescribed burn was used to control both Bromus inermis and Phalaris arundinacaea, which are the primary invasive grass species present.  Five 200-m long plots, each paired with an unburned control plot, were burned in an attempt to increase native plant and insect diversity.  There was a slight increase in forb productivity and a reduction in grass productivity and leaf litter in burned plots.  However, the late spring burns did not significantly reduce the abundance of either B. inermis (P=1.0) or P. arundinacaea (P=0.182).  Species richness (P=0.496) and diversity (H’) (P=0.556) of plants were not significantly different between burned and unburned plots.  Butterfly (Lepidoptera: various families) and ground beetle (Coleoptera: Carabidae) abundance and species richness were also surveyed in both burned and unburned plots.  Butterfly and ground beetle abundance were both affected by fire.  Butterfly abundance was significantly higher in unburned plots (P=0.014) likely because fewer flowers were blooming in the burned plots due to the late spring burn.  Carabid abundance was significantly greater in burned plots (P=0.05), due to the reduction of leaf litter that restricts ground beetle activity.  Species richness in burned plots were not significantly different from unburned plots for either butterflies (P=0.688) or ground beetles (P=1.0).  Repeated use of prescribed fire may be necessary to control the invasive grasses and stimulate the growth of native species.