Masters Theses

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The utility of high-diversity prairie mixtures as bioenergy feedstocks.  by Jessica E. Abernathy.  2015.


Two of the more pressing, yet opposing, ecological challenges that we face at the global-scale are the loss of biodiversity and rising demand for energy. Many ecological experiments have shown the importance of biodiversity for ecosystem services and functions, but simultaneous demand for energy has led to greater conversion of natural landscapes to low-diversity energy crops (e.g., corn for ethanol). One potential solution to these seemingly opposing issues would be to grow diverse native vegetation for bioenergy. Native tallgrass prairie produces large amounts of aboveground biomass but also provides great habitat for wildlife and other ecosystem services. In this study, we compared the productivity, yearly biomass variability, and invasion resistance of four potential bioenergy feedstocks with contrasting diversity: 1 species - a switchgrass monoculture; 5 species - a mix of C4 grasses; 16 species - a mix of grasses, forbs and legumes; and 32 species - a mix of grasses, sedges, forbs, and legumes. Each diversity treatment was replicated four times on three different soil types (clay loam, loam, and sandy loam) for a total of 48 plots (0.33-0.56 ha each). We compared productivity by harvesting all plant material in 10 randomly placed 0.3m2 quadrats per plot. Species composition was compared using basal area sampling of 10 randomly placed 0.1m2 quadrats per plot. Across soil types, the 1-, 16-, and 32-species treatments produced the same amount of aboveground biomass over the 5-yr study, with the 1-species treatment producing more biomass than the 5-species treatment. Although the overall productivities of the 1-, 16-, and 32-species treatments were similar, the relative ranking of the four diversity treatments varied between soil types. Weed biomass was higher in low-diversity treatments than high-diversity treatments. Year-to-year variation in productivity did not differ between treatments. My results show that diverse mixes of native perennial vegetation are as productive as a switchgrass monoculture over a 5-yr period suggesting that they are reliable source of biomass for bioenergy. However, differences in the relative ranking of the four diversity treatments, between soil types suggest that bioenergy seed mixes must be tailored to site characteristics to maximize productivity and stand success.

Biodiversity and ecosystem function and the design of tallgrass restorations for biomass production.  by Dustin R.J. Graham.  2015.


Biodiversity and ecosystem function research (BEF) suggests species richness may provide high levels of ecosystem functions. However, few studies have applied a BEF perspective of restoration, which utilizes biodiversity to achieve increases in ecosystem functions. In this study, we test the application of the BEF perspective of restoration in the design of tallgrass prairie plantings as a biomass crops. Specifically, we examine the effects of planted species richness on biomass production, resistance to disturbance, and resistance to invasion by weeds.

Four seed mixes which range in species richness (1, 5, 16 and 32 species) were established in four, field-scale (0.33-0.55 ha) plots on three soil types. Over four years, the seed mixes produced similar amounts of biomass (8.27 ± 0.65 to 7.46 ± 0.65 Mg/ha). Seed mixes had relatively high yields compared to estimates from fertilized monocultures of perennial crops in the region. Species rich planting (16-32 species) may produce more biomass than less species rich plantings in years without flooding or drought. However, the effects of species richness on productivity are complicated by soil type. The mix with the highest species richness (32 species) had the lowest biomass production on the Waukee loam soil, but the highest biomass production on Spillville-Coland clay loam soil. Plantings with higher species richness were also less resistant to drought. However, species rich mixes (16 and 32 species) produced similar amounts of biomass compared to less species rich mixes (5 species) with the same dominant species. Finally, I found that increased species richness increased resistance to invasion by weeds and as few as five species may provide high levels of resistance to invasion by weeds. The study suggests that the application of the BEF perspective of restoration may lead to weed resistant crops which are as productive, or more productive than low diversity crops.

Butterfly and floral community dynamics at a native prairie agrofuel research site.  by Benjamin J. Hoksch.  2015.


Agrofuel production in the Midwest has historically relied upon monoculture food crops (Zea mays and Glycine max) that do little to support biodiversity or maintain soil and water quality. The University of Northern Iowa’s Tallgrass Prairie Center is investigating the feasibility of establishing and harvesting diverse mixes of native prairie vegetation for use as a sustainable agrofuel. In 2009 48 research plots were established on three soil types, on land with a >30 year history of row crop production in Black Hawk County, IA. Each plot was seeded with one of four native prairie agrofuel crops: (1) Switchgrass1, (2) Grasses5 (5 warm season grass species), (3) Prairie16 (16 species of grasses, legumes, and forbs), or (4) Prairie32 (32 species of grasses, legumes, forbs, and sedges). Research plots were actively managed with a three-year rotation (establishment/no management, burn, harvest), and in 2013 and 2014 a significant portion of the research site experienced early summer flooding. I monitored floral and butterfly communities present on site from 2010 through 2014 and hypothesized that more diverse floral communities would support more abundant and diverse butterfly communities. Butterflies were ~3.6 times more abundant, ~1.4 times more species rich, and more diverse in Prairie16 and Prairie32 than Switchgrass1 and Grasses5; however butterfly abundance, richness and diversity in Prairie16 and Prairie32 did not diverge as the site matured as predicted. Sown flowers were more species rich and diverse, but not more abundant in Prairie32 than Prairie16. Flooding frequency and duration was a strong predictor of sown floral abundance, richness and diversity; which in turn influenced butterfly abundance. My research suggests that the widespread adoption of diverse assemblages of native prairie plants as agrofuel crops would provide higher quality habitat for butterflies than native, grass-only agrofuel feedstocks.

Variation in mineral content of prairie forb species and content changes over winter related to slagging potential.  by Jennifer Nyla Wahl Rupp.  2015.


Coal fired power plants are responsible for more than 75 percent of the energy produced in Iowa. Burning coal releases large amount of carbon dioxide and other chemical compounds into the atmosphere.

A variety of types of biomass, including prairie vegetation, are being proposed as biofuel alternatives for electrical generation. Tilman et al. (2006) determined that biofuels from mixtures of prairie vegetation of increasing diversity provide more usable energy, reduce greenhouse gases and produce less agriculture pollutants. The Prairie Power Project of the Tallgrass Prairie Center is testing four mixtures of prairie species for maximum production of biomass. A primary concerns regarding burning prairie biomass for electrical generation is the potential for slag production from trace metals and other minerals during the combustion process (Skrifvars et al. 1998). Adler et al. (2006) observed that the mineral content of switchgrass declined from summer to fall harvest and dropped further the following spring. Little is known about the slagging potential of prairie forbs.

This study examined the concentration of three minerals, potassium, sodium, and silicon, in nine prairie forb species in relation to their potential for slagging. Samples of the prairie forbs were collected during late fall and early spring-near the beginning and the end of the winter dormancy period from five different prairie sites. Mineral concentrations of the prairies forbs were compared to determine whether some species had higher potential for slagging than others. Also, concentrations of the minerals were sampled fall and spring to determine if there were changes during the winter dormancy period that would affect slagging potential of the plants.

The energy production per unit weight was similar for all the species. The slaginducing chemicals in the prairie forbs varied from species to species. Solidago canadensis, Solidago rigida and Silphium laciniatum exhibited high potential for slagging and should be avoided as biofuels. Desmodium canadensis showed low potential for slagging. Concentrations in Monarda fistulosa, Lespedeza capitata, and Heliopsis helianthoides declined during the winter dormancy. Delaying harvest until spring would improve their candidacy for biomass production.

Bird use of heterogeneous native prairie biofuel production plots.  by Jarrett D. Pfrimmer.  2013.


Changing land use practices and agricultural intensification have driven the loss of >90% of native grassland habitats in the Midwestern U.S.A. Consequently, grassland birds have declined more drastically than any other North American guild. Current biofuel production systems in the Midwest rely on high input monoculture crops that provide little habitat value to most grassland birds. The Tallgrass Prairie Center at the University of Northern Iowa is exploring the feasibility of growing and harvesting diverse mixes of native prairie vegetation for use as a sustainable biofuel in a manner that also provides high quality bird habitat. In 2009, 48 research plots on three soil types were seeded with one of four treatments of native prairie vegetation: 1) switchgrass monoculture, 2) a 5-species grass mix, 3) a 16-species biomass mix, or 4) a 32-species prairie mix. In subsequent years, I conducted visual surveys of breeding birds and monitored bird nesting attempts in the biomass production plots. I hypothesized that more diverse plant communities would support more abundant and diverse bird communities with higher nest densities and nest success rates. Results indicated that bird species richness and abundance were significantly greater in the biomass and prairie mixes compared to the low diversity grass plots; however, there were no differences between the biomass and prairie mix plots nor between the switchgrass and grass mix plots. Three grassland birds classified as “species of greatest conservation need” in Iowa successfully nested in the biomass production plots during my study, but nest density did not vary significantly among treatments or soil types. My results suggested that establishment and management of diverse native prairie vegetation for biomass production on marginal lands could have positive impacts on the maintenance of bird populations in agricultural landscapes.

Early avian colonization in a prairie biofuel project.  by James T. Mason.  2012.


The steady decline of grassland bird populations has been attributed to agricultural intensification. The establishment of native prairie vegetation for biomass fuel has potential to reverse this decline. The Tallgrass Prairie Center at the University of Northern Iowa is investigating the potential of perennial native vegetation as a biofuel feedstock. In the spring of 2009, research plots located in seven previously row cropped fields in Black Hawk County, Iowa, were seeded with one of four treatments of native vegetation: 1) switchgrass monoculture, 2) five native warm-season grasses, 3) 16 native species, and 4) 32 native species. Treatments were replicated four times across three soil types in 48 research plots.

To assess avian colonization of the site, I conducted visual strip transect surveys of birds using the research plots. Beginning at the time of seeding during the 2009 breeding season, I sampled in four periods; breeding season, fall migration, winter, and spring migration, concluding after the 2010 breeding season. To provide a comparison with the surrounding landscape, I sampled plots in adjacent row crop fields during the 2009 fall migration and 2010 breeding season.

I did not detect differences in avian abundance, species richness, or diversity between the biomass production plots until the second growing season. During the 2010 breeding season, the combination of treatments and soil types provided a mosaic of habitat types that together supported greater species richness and diversity than any of the habitat types alone. In general, differences were detected between two treatment groups, Grasses (treatments 1 and 2) and Forbs + Graminoids (treatments 3 and 4) and two soil type groups (dry and mesic to wet). Avian abundance, species richness, and diversity were significantly greater in Forbs + Graminoids than Grasses and, in turn greater in Grasses than row crops. Generally, avian community composition on all but the driest soil type varied significantly between Grasses and Forbs + Graminoids. Regional avian species richness and diversity would be maximized by planting a variety of native biofuel feedstock mixes on a variety of soil types. Further research on a broader scale is required to verify this assessment.