1. Biofuel production from cellulosic feedstocks may increase during the next century.To be sustainable, this production should protect environmental quality and biodiversity. Fertilized mixed-species prairie can deliver substantial quantities of cellulosic ethanol per unit land area with minimal losses of NO 3 -N in drainage water, but the long-term maintenance of biodiversity in such systems has been uncertain.2. We report how nitrogen, phosphorus, and potassium fertilizer application, precipitation, and time affected the species composition and productivity of reconstructed prairie communities harvested annually as biofuel feedstocks over a 9-year period.3. Results indicated that both precipitation and fertilizer application drove aboveground biomass production, with the greatest response to fertilizer occurring in wetter than average years. Fertilization reduced species richness, but increased species evenness. Consequently, Simpson's diversity index did not differ between the fertilized and unfertilized communities, though it declined in both communities over time. 4.A total of 59 plant species was recorded, with eight of them explaining most of the differences in vegetation cover between the fertilized and unfertilized treatments.After 9 years, the high fertility community was dominated by the C4 grass Andropogon gerardii, the C3 grass Elymus canadensis, and the non-leguminous forbs Heliopsis helianthoides, Helianthus maximiliani, and Monarda fistulosa, whereas the low fertility community was dominated by the C4 grasses A. gerardii and Sorghastrum nutans, the C3 grass E. canadensis, and the non-leguminous forb M.fistulosa. Fertilization increased the abundance of flowering forbs available to pollinators in the early, middle and late portions of the growing season. Synthesis and applications.Results of our study suggest that maintenance of reasonably high levels of productivity and biodiversity are possible in fertilized prairie communities harvested annually for bioenergy, with plant cover more evenly distributed among different functional groups. In the future, if policy and markets favour biofuels and better delivery of ecosystem services from harvested land, prairie-based feedstocks could become part of a renewable energy portfolio that fosters biodiversity and contributes to the provision of floral resources for pollinators. K E Y W O R D Sbiofuel, cellulosic ethanol, community dynamics, prairie vegetation, productivity, soil fertility, species diversity, succession | 331Journal of Applied Ecology KORDBACHEH Et Al.

Cool-season cover crops have been shown to reduce soil erosion and nutrient discharge from maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] production systems. However, their effects on long-term weed dynamics are not well-understood. We utilized five long-term research trials in Iowa to quantify germinable weed seedbank densities and compositions after 10+ years of cover cropping treatments. All five trials consisted of zero-tillage maize-soybean rotations managed with and without the inclusion of a yearly winter rye (Secale cereal L.) cover crop. Seedbank sampling was conducted in the early spring before crop planting at all locations, with three of the five trials having grown a soybean crop the preceding year, and two a maize crop. Two of the trials (both previously soybean) showed significant and biologically relevant decreases (4,070 and 927 seeds m−2, respectively) in seedbank densities in cover crop treatments compared to controls. In another two trials, one previously maize and one previously soybean, no difference was detected in seedbank densities. In the fifth trial (previously maize), there was a significant, but biologically unimportant increase of 349 seeds m−2. All five trials' weed communities were dominated by common waterhemp [Amaranthus tuberculatus (Moq.)], and changes in seedbank composition from cover-cropping were driven by changes in this species. Although previous studies have shown that increases in cover crop biomass are strongly correlated with weed suppression, in our study we did not find a relationship between seedbank changes and the mean amount of cover crop biomass produced over a 10-years period (experiment means ranging from 0.5 to 2.0 Mg ha−1 yr−1), the stability of the cover crop biomass production, nor the amount produced going into the previous crop's growing season. We conclude that long-term use of a winter rye cover crop in a maize-soybean system has the potential to meaningfully reduce the size of weed seedbanks compared to winter fallows. However, identifying the mechanisms by which this occurs requires further research into processes such as seed predation and seed decay in cover cropped systems.

Historic, wide-spread destruction of native prairies in Minnesota was caused by conversion to agricultural land, disruption of disturbance regimes, and loss of key species. Attempts to restore tall-grass prairies have resulted in a new ecosystem type on the Midwestern landscape, with novel assemblages of both plant and animal species. The mammalian herbivore community, once dominated by bison, is now primarily comprised of white-tailed deer (Odocoileus virginianus), Eastern cottontail rabbits (Sylvilagus floridanus), and small mammals such as meadow voles (Microtus pennsylvanicus). The role of this assemblage of herbivores in restored prairies is not well understood. This study characterizes patterns of mammalian herbivory on five legume species in restored prairie in southern Minnesota. Legumes were sampled along transects that varied in their distance from the prairie-forest boundary and time since prescribed burning. Herbivore selectivity was determined for each legume species using an electivity index based on the total number of stems of each species and the percent of stems grazed. Herbivory was highly variable among legume species: Desmodium canadense was strongly preferred, Dalea candida and Dalea purpurea were moderately preferred, and Amorpha canescens and Lespedeza capitata were avoided. Both Dalea species and Lespedeza experienced increased rates of herbivory in burned sites. Avoided species were characterized by either low tissue nitrogen content or a high proportion of recalcitrant carbon relative to preferred species. These results suggest mammalian herbivores have an important functional role in prairie communities with potential consequences for community dynamics and the success of prairie restorations.

The student author, whose presentation of the scholarship herein was approved by the program of study committee, is solely responsible for the content of this thesis. The Graduate College will ensure this thesis is globally accessible and will not permit alterations after a degree is conferred.

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