Browsing by Author "Pearse, William D."

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    Climate and lawn management interact to control C-4 plant distribution in residential lawns across seven US cities
    Trammell, Tara L. E.; Pataki, Diane E.; Still, Christopher J.; Ehleringer, James R.; Avolio, Meghan L.; Bettez, Neil; 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 C.; O'Neil-Dunne, Jarlath P.M.; Pearse, William D.; Chowdhury, Rinku Roy; Steele, Meredith K.; Wheeler, Megan M. (2019-06)
    In natural grasslands, C-4 plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C-3 vs. C-4 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 (delta C-13, index of C-3/C-4 relative abundance) and C-4 cover in residential lawns across seven U.S. cities to determine how climate, lawn plant management, or interactions between climate and plant management influenced C-4 lawn cover. We also calculated theoretical C-4 carbon gain predicted by a plant physiological model as an index of expected C-4 cover due to growing season climatic conditions in each city. Contrary to theoretical predictions, plant delta C-13 and C-4 cover in urban lawns were more strongly related to mean annual temperature than to growing season temperature. Wintertime temperatures influenced the distribution of C-4 lawn turf plants, contrary to natural ecosystems where growing season temperatures primarily drive C-4 distributions. C-4 cover in lawns was greatest in the three warmest cities, due to an interaction between climate and homeowner plant management (e.g., planting C-4 turf species) in these cities. The proportion of C-4 lawn species was similar to the proportion of C-4 species in the regional grass flora. However, the majority of C-4 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, C-4 plants were predominantly imported and cultivated. Elevated CO2 and temperature in cities can influence C-3/C-4 competitive outcomes; however, this study provides evidence that climate and plant management dynamics influence biogeography and ecology of C-3/C-4 plants in lawns. Their differing water and nutrient use efficiency may have substantial impacts on carbon, water, energy, and nutrient budgets across cities.
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    Convergence of microclimate in residential landscapes across diverse cities in the United States
    Hall, Sharon J.; Learned, Jennifer; Ruddell, Benjamin L.; Larson, K. L.; Cavender-Bares, Jeannine; Bettez, Neil; Groffman, Peter M.; Grove, J. Morgan; Heffernan, James B.; Hobbie, Sarah E.; Morse, Jennifer L.; Neill, Christopher; Nelson, Kristen C.; O'Neil-Dunne, Jarlath P.M.; Ogden, Laura A.; Pataki, Diane E.; Pearse, William D.; Polsky, Colin; Chowdhury, Rinku Roy; Steele, Meredith K.; Trammell, Tara L. E. (2016-01)
    The urban heat island (UHI) is a well-documented pattern of warming in cities relative to rural areas. Most UHI research utilizes remote sensing methods at large scales, or climate sensors in single cities surrounded by standardized land cover. Relatively few studies have explored continental-scale climatic patterns within common urban microenvironments such as residential landscapes that may affect human comfort. We tested the urban homogenization hypothesis which states that structure and function in cities exhibit ecological "sameness" across diverse regions relative to the native ecosystems they replaced. We deployed portable micrometeorological sensors to compare air temperature and humidity in residential yards and native landscapes across six U.S. cities that span a range of climates (Phoenix, AZ; Los Angeles, CA; Minneapolis-St. Paul, MN; Boston, MA; Baltimore, MD; and Miami, FL). Microclimate in residential ecosystems was more similar among cities than among native ecosystems, particularly during the calm morning hours. Maximum regional actual evapotranspiration (AET) was related to the morning residential microclimate effect. Residential yards in cities with maximum AET < 50-65 cm/year (Phoenix and Los Angeles) were generally cooler and more humid than nearby native shrublands during summer mornings, while yards in cities above this threshold were generally warmer (Baltimore and Miami) and drier (Miami) than native forests. On average, temperature and absolute humidity were similar to 6 % less variable among residential ecosystems than among native ecosystems from diverse regions. These data suggest that common residential land cover and structural characteristics lead to microclimatic convergence across diverse regions at the continental scale.
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    Homogenization of plant diversity, composition, and structure in North American urban yards
    Pearse, William D.; Cavender-Bares, Jeannine; Hobbie, Sarah E.; Avolio, Meghan L.; Bettez, Neil; Chowdhury, Rinku Roy; Darling, Lindsay E.; Groffman, Peter M.; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Learned, Jennifer; Neill, Christopher; Nelson, Kristen C.; Pataki, Diane E.; Ruddell, Benjamin L.; Steele, Meredith K.; Trammell, Tara L. E. (Ecological Society of America, 2018-02)
    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.