You can find most publications (and presentations) at Tim’s Google Scholar page. Peer-reviewed publications are listed below, followed by a very short summary of each publication. You can see a word cloud of the text from publication abstracts in the image adjacent to this paragraph, where words used more often are larger. The three studies most relevant to current work are in bold and press coverage is indicated with a *.
Summary: Cattle are grazing the same percentage of stems of common and showy milkweed species as of big bluestem grass in the same field (as determined by repeatedly monitoring the same milkweed stems throughout the growing season), and this is not having any noticeable effect on cattle health. This milkweed grazing appears to decrease common and milkweed abundance because adjacent ungrazed fields contain on average 74 fold (74x) as many common and showy milkweed stems as fields that have been grazed by cattle for at least the previous 10 years.
*CoolGreenScience (stories from The Nature Conservancy)
Summary: Spatial variation in productivity data within Nutrient Network sites was affected by nutrient addition differently depending on the alpha-, beta-, and gamma-diversity within sites.
Summary: We collected soil samples from the longest running burning and mowing study in North America, located at UNO. We extracted DNA from soil samples to examine the 16S rRNA region for bacterial and archaeal communities and the internal transcribed spacer region for fungal communities. Our findings show that both bacterial and fungal communities were different between burned and mowed prairie.
Summary: The Nutrient Network data on nutrient addition and herbivore exclusion were used to determine whether herbivores consume the additional biomass produced after fertilization. Results indicate that wild herbivores consume some additional biomass but only in rare situations, such as the presence of domesticated livestock, was all additional biomass consumed.
Summary: Plant production is not significantly different between spring and autumn burning in ungrazed Nebraska tallgrass prairie, but composition is strongly affected with annual spring burns significantly increasing C4 grass abundance and annual autumn burns significantly increasing forb abundance.
Summary: I measured the effects of spring, summer, and autumn burning and mowing on soil temperature and plant production during three periods of the growing season and found that autumn and spring burning and mowing similarly increased spring plant production, but only autumn and spring burning increased soil temperatures.
Summary: Disturbance increases beta-diversity when dispersal is limited but decreases beta-diversity when dispersal is increased via seed addition, and changes in beta-diversity due to treatments do not appear to be due to the identity of plant species.
Summary: Bombus bees are the best observed pollinators at moving pollinaria between flowers of the self-incompatible Asclepias meadii, even though the nectar chemical composition of A. meadii does not appear well suited to Bombus bees.
Summary: Harvesting twice during a growing season (in summer and autumn) decreases biomass production in a low diversity prairie, as compared to a single autumn harvest, but does not affect biomass production in a high diversity prairie.
Summary: Agriculturally realistic bioenergy plantings in southern Michigan do not produce more biomass with increased planting diversity, in part because seed cost limits seed density and therefore most species in high diversity plantings are seeded at low seed density, which limits their potential production.
Summary: Switchgrass and prairie bioenergy plantings are able to support many more bird, bee, insect, plant, and soil microbial species than corn, and this added species diversity provides ecosystem services such as increased predation on agricultural pests and reduced methane output from soils.
Summary: We experimentally removed clonal species and fertilized in a factorial design, and we found that tall clonal species severely reduce the abundance and richness of all other species whereas tall non-clonal species reduce abundance and richness of other species much less severely.
Summary: Surprisingly, the stability of grassland community composition (and total aboveground biomass production) was not directly related to mean annual precipitation nor the coefficient of variation of annual precipitation, but was instead indirectly related to these variable through their effects on species richness and covariance between species abundances.
Summary: Tall highly-clonal species increase in biomass after fertilization but cause the biomass of all other growth forms to decrease, thereby driving decreases in plant species richness.
Summary: Average turnover of species from year to year in grasslands is quite high (nearly 50% per year), and is especially high in sites with low mean annual precipitation and a high proportion of annual species.
Summary: Invasive plants species produce much more biomass with a three week head start in germination than do native plants and strongly reduce diversity (lead to plant communities not significantly different from monoculture).
Summary: Shade limits plant species richness in wetter years but actually increases richness in drought years, and fertilization decreases richness in both wetter (light limiting) and drought (light not limiting) years.
Summary: A larger species pool causes plant communities to diverge more in response to higher fertilization rates.
Summary: Insect removal doubles the seed production of the most common plant in the North American tallgrass prairie, Andropogon gerardii (big bluestem), by reducing consumption of flowers and seed embryos.
Summary: The presence of the invasive plant, Melilotus officinalis (yellow sweetclover), strongly decreases plant diversity and causes a 5x increase in nitrogen in plant biomass.
Summary: Seeding lower rates of tall grasses into prairie restorations allows more forb species to establish and greatly increases forb abundance.
*Tallgrass Prairie Center Newsletter
Summary: Higher evenness of plant litter, but not higher richness, generally leads to greater decomposition, but environment and species identity play the largest roles in controlling litter decomposition rates.
Summary: Low productivity grasslands are open to new colonists and therefore dispersal and seed addition can increase plant richness, but high productivity grasslands are largely closed to new colonists and these sites must be disturbed if they are to be restored.
Summary: Native prairie vegetation is more resistant to vehicular disturbance than is vegetation dominated by the introduced cool-season grass, Bromus inermis (smooth brome).
Summary: Larger species pools increase plant species richness and biomass production; but these responses are contingent upon resource availability, with stronger effects of species pools in irrigated and disturbed sites.
Summary: Along a topographic productivity gradient, larger species pools increase plant species richness much more at lower productivity.
Summary: High diversity sites are more open to new species (more invasible) than low diversity sites, but this relationship is due to both diversity and invasibility being driven by environmental factors rather than direct effects of diversity on invasibility.
Summary: One square meter quadrats do not provide a good measure of mussel species richness and density under realistic replication, whereas spatially larger samples can provide good measures of these variables (Tim wrote this paper as an undergraduate).