Agronomy and Horticulture Department


First Advisor

John A. Guretzky

Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor John A. Guretzky. Lincoln, Nebraska: January, 2018

Copyright (c) 2018 Josiah D. Dallmann


Historically, disturbances shaped prairie ecosystems both directly through events like fire and soil moving by animals, as well as indirectly through dynamic rainfall patterns and periodic flux in seed availabilities. We hypothesized that the implementation of several distinct disturbance events in Nebraska Sandhills upland prairie would have measurable effects on plant community composition. We implemented mid-spring fire, soil disturbance in the form of disking, seed addition of native forbs on disked plots, as well as early summer supplemental watering (to mimic minor rainfall events during abnormally dry periods) during 2016 and 2017. Plant community response during the first and second growing season post-disturbance was quantified through measurements of June forb density as well as August percentage cover and herbage mass. In the first season, fire increased the cover of warm-season rhizomatous grasses as well as perennial forbs, such as western ragweed (Ambrosia psilostachya DC.), and reduced the cover of annual forbs and species richness. Fire had positive interactive effects on the cover of warm-season grasses in both seasons and on forb density in the second season. Perennial forb seedling establishment from spring seed addition was poor, possibly due to species-specific dormancy and abnormally dry June conditions. Seed availability did play a minor role on cover of seeded leguminous species, although temporary and year-dependent. Water addition (two 0.64-cm events) and burning, however, improved seeded forb establishment. Disking had generally negative effects on plant cover. Minor water additions had both positive and negative interactive effects on various species, with the underlying drivers of this often unknown. We documented ecological interactions between disturbance events, as fire mediated the negative effect of disking on warm-season grasses and water mediated its negative effect on grasses as a whole. Overall, distinct disturbance events significantly altered plant composition of Sandhills prairie over two growing seasons.

Advisor: John A. Guretzky