Browsing by Author "Pouyat, Richard V."

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    Heterogeneity in soil chemistry relates to urbanization while soil homogeneity relates to plant invasion in small temperate deciduous forests
    (Landscape Ecology, 2022-02-07) Trammell, Tara L. E.; Pouyat, Richard V.; D ’Amico, Vince III
    Context: Soil heterogeneity versus homogeneity patterns are observed within and across urban landscapes at multiple scales. To fully evaluate human-mediated influences on soil properties and processes, we need to understand spatial patterns and variation in soil characteristics within a single ecosystem patch type (e.g., forests) in and near cities. Objectives: Our research objectives were to: (1) identify soil characteristics important in driving variation in soil chemistry within urban forests, and (2) examine whether urbanization and invasion gradients were related to variation in soil chemistry within these forests. Methods: We measured soil chemical properties within 36 forests across the U.S. mid-Atlantic. The forests are spatially distributed across an urbanization gradient and comprise a gradient of non-native plant invasion. Results: Urbanization was related to more variation in soil chemistry, whereas plant invasion was related to less variation in soil chemistry within our forests. Soil Ca and Mg concentrations increase with plant invasion yet are less variable within invaded forests most likely due to invasive plants taking up and concentrating these elements. Soil pH, Ca, Mg, Zn, and Cu increase in forests surrounded by greater urbanization, however, these elements are more variable within urban forests likely due to edge effects altering element deposition. Conclusions: Our results demonstrate that while urbanization and invasion can increase soil chemical concentrations, they differentially alter variation in soil chemistry within urban forests. Plant invasion and urban environmental conditions need separate consideration in future conceptual models of urban ecological theory since non-native invasive plants influence soil chemistry independent of other urban factors.
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    Soil nitrogen cycling in forests invaded by the shrub Rosa multiflora: importance of soil moisture and invasion density
    (Biogeochemistry, 2024-03-23) Moore, Eric R.; Pouyat, Richard V.; Trammell, Tara L. E.
    Invasive plants often alter ecosystem function and processes, especially soil N cycling. In eastern United States forests, the shrub Rosa multiflora (“rose”) is a dominant invader, yet potential effects on N cycling are poorly understood. Moreover, invasive plant management can impact soil N cycling by decreasing plant N uptake and disturbing the soil. The objectives of this study were to evaluate N cycling along a gradient of rose invasion (observational) and investigate potential changes to N cycling (manipulative) under four different management strategies: (1) do nothing (the control), (2) invasive plant removal, (3) removal followed by native seed mix addition, (4) removal, native seed mix, and chipped rose stem addition. We selected three forest sites experiencing a Low, Medium, or High amount of shrub invasion, and measured N cycling in the early (June) and late (September) growing seasons. We found N was immobilized in June and mineralized in September. One year after experimental management, removal alone had no effect on N cycling compared to control plots, but addition of native seed mix and chipped stems reduced early-season nitrification in our Medium invasion site. Our findings suggest that rose invasion may increase N cycling rates when soils are dry, which may occur more frequently with future climate change. In addition, N cycling responds differentially to management in the year following invasive plant removal, but most noticeably under moderate rose invasion.
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    Spatial variability and uncertainty of soil nitrogen across the conterminous United States at different depths
    (Ecosphere, 2022-07-27) Smith, Elizabeth M.; Vargas, Rodrigo; Guevara, Mario; Tarin, Tonantzin; Pouyat, Richard V.
    Soil nitrogen (N) is an important driver of plant productivity and ecosystem functioning; consequently, it is critical to understand its spatial variability from local-to-global scales. Here, we provide a quantitative assessment of the three-dimensional spatial distribution of soil N across the United States (CONUS) using a digital soil mapping approach. We used a random forest-regression kriging algorithm to predict soil N concentrations and associated uncertainty across six soil depths (0–5, 5–15, 15–30, 30–60, 60–100, and 100–200 cm) at 5-km spatial grids. Across CONUS, there is a strong spatial dependence of soil N, where soil N concentrations decrease but uncertainty increases with soil depth. Soil N was higher in Pacific Northwest, Northeast, and Great Lakes National Ecological Observatory Network (NEON) ecoclimatic domains. Model uncertainty was higher in Atlantic Neotropical, Southern Rockies/Colorado Plateau, and Southeast NEON domains. We also compared our soil N predictions with satellite-derived gross primary production and forest biomass from the National Biomass and Carbon Dataset. Finally, we used uncertainty information to propose optimized locations for designing future soil surveys and found that the Atlantic Neotropical, Pacific Northwest, Pacific Southwest, and Appalachian/Cumberland Plateau NEON domains may require larger survey efforts. We highlight the need to increase knowledge of biophysical factors regulating soil processes at deeper depths to better characterize the three-dimensional space of soils. Our results provide a national benchmark regarding the spatial variability and uncertainty of soil N and reveal areas in need of a better representation.