Pearse William D.

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Pearse
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William D.
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  • Article
    Climate and lawn management interact to control C4 plant distribution in residential lawns across seven U.S. cities.
    (Ecological Society of America, 2019-04-01) Trammell, Tara ; Pataki, Diane E. ; Still, Christopher J. ; Ehleringer, James R. ; Avolio, Meghan L. ; Bettez, Neil D. ; Cavender-Bares, Jeannine ; Groffman, Peter M. ; Grove, J. Morgan ; Hall, Sharon J. ; Heffernan, James B. ; Hobbie, Sarah E. ; Larson, Kelli L. ; Morse, Jennifer L. ; Neill, Christopher ; Nelson, Kristen ; O'Neil-Dunne, Jarlath ; Pearse, William D. ; Roy Chowdhury, Rinku ; Steele, Meredith K. ; Wheeler, Megan M.
    In natural grasslands, C4 plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C3 vs. C4 photosynthetic pathways. However, in lawns, management decisions influence interactions between planted turfgrass and weed species, leading to some uncertainty about the degree of human vs. climatic controls on lawn species distributions. We measured herbaceous plant carbon isotope ratios (δ13C, index of C3/C4 relative abundance) and C4 cover in residential lawns across seven U.S. cities to determine how climate, lawn plant management, or interactions between climate and plant management influenced C4 lawn cover. We also calculated theoretical C4 carbon gain predicted by a plant physiological model as an index of expected C4 cover due to growing season climatic conditions in each city. Contrary to theoretical predictions, plant δ13C and C4 cover in urban lawns were more strongly related to mean annual temperature than to growing season temperature. Wintertime temperatures influenced the distribution of C4 lawn turf plants, contrary to natural ecosystems where growing season temperatures primarily drive C4 distributions. C4 cover in lawns was greatest in the three warmest cities, due to an interaction between climate and homeowner plant management (e.g., planting C4 turf species) in these cities. The proportion of C4 lawn species was similar to the proportion of C4 species in the regional grass flora. However, the majority of C4 species were nonnative turf grasses, and not of regional origin. While temperature was a strong control on lawn species composition across the United States, cities differed as to whether these patterns were driven by cultivated lawn grasses vs. weedy species. In some cities, biotic interactions with weedy plants appeared to dominate, while in other cities, C4 plants were predominantly imported and cultivated. Elevated CO2 and temperature in cities can influence C3/C4 competitive outcomes; however, this study provides evidence that climate and plant management dynamics influence biogeography and ecology of C3/C4 plants in lawns. Their differing water and nutrient use efficiency may have substantial impacts on carbon, water, energy, and nutrient budgets across cities.
  • Article
    Homogenization of plant diversity, composition, and structure in North American urban yards
    (John Wiley & Sons, 2018-02-15) Pearse, William D. ; Cavender-Bares, Jeannine ; Hobbie, Sarah E. ; Avolio, Meghan L. ; Bettez, Neil D. ; Roy Chowdhury, Rinku ; Darling, Lindsay ; Groffman, Peter M. ; Grove, J. Morgan ; Hall, Sharon J. ; Heffernan, James B. ; Learned, Jennifer ; Neill, Christopher ; Nelson, Kristen ; Pataki, Diane E. ; Ruddell, Benjamin L. ; Steele, Meredith K. ; Trammell, Tara
    Urban ecosystems are widely hypothesized to be more ecologically homogeneous than natural ecosystems. We argue that urban plant communities assemble from a complex mix of horticultural and regional species pools, and evaluate the homogenization hypothesis by comparing cultivated and spontaneously occurring urban vegetation to natural area vegetation across seven major U.S. cities. There was limited support for homogenization of urban diversity, as the cultivated and spontaneous yard flora had greater numbers of species than natural areas, and cultivated phylogenetic diversity was also greater. However, urban yards showed evidence of homogenization of composition and structure. Yards were compositionally more similar across regions than were natural areas, and tree density was less variable in yards than in comparable natural areas. This homogenization of biodiversity likely reflects similar horticultural source pools, homeowner preferences, and management practices across U.S. cities.