Browsing by Author "Bacon, AR"
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Item Open Access Boom and bust carbon-nitrogen dynamics during reforestation(Ecological Modelling, 2017-09-24) Parolari, AJ; Mobley, ML; Bacon, AR; Katul, GG; Richter, DDB; Porporato, A© 2017 Elsevier B.V. Legacies of historical land use strongly shape contemporary ecosystem dynamics. In old-field secondary forests, tree growth embodies a legacy of soil changes affected by previous cultivation. Three patterns of biomass accumulation during reforestation have been hypothesized previously, including monotonic to steady state, non-monotonic with a single peak then decay to steady state, and multiple oscillations around the steady state. In this paper, the conditions leading to the emergence of these patterns is analyzed. Using observations and models, we demonstrate that divergent reforestation patterns can be explained by contrasting time-scales in ecosystem carbon-nitrogen cycles that are influenced by land use legacies. Model analyses characterize non-monotonic plant-soil trajectories as either single peaks or multiple oscillations during an initial transient phase controlled by soil carbon-nitrogen conditions at the time of planting. Oscillations in plant and soil pools appear in modeled systems with rapid tree growth and low initial soil nitrogen, which stimulate nitrogen competition between trees and decomposers and lead the forest into a state of acute nitrogen deficiency. High initial soil nitrogen dampens oscillations, but enhances the magnitude of the tree biomass peak. These model results are supported by data derived from the long-running Calhoun Long-Term Soil-Ecosystem Experiment from 1957 to 2007. Observed carbon and nitrogen pools reveal distinct tree growth and decay phases, coincident with soil nitrogen depletion and partial re-accumulation. Further, contemporary tree biomass loss decreases with the legacy soil C:N ratio. These results support the idea that non-monotonic reforestation trajectories may result from initial transients in the plant-soil system affected by initial conditions derived from soil changes associated with land-use history.Item Open Access Estimates and determinants of stocks of deep soil carbon in Gabon, Central Africa(Geoderma, 2019-05-01) Wade, AM; Richter, DD; Medjibe, VP; Bacon, AR; Heine, PR; White, LJT; Poulsen, JR© 2019 Despite the importance of tropical forest carbon to the global carbon cycle, research on carbon stocks is incomplete in major areas of the tropical world. Nowhere in the tropics is this more the case than in Africa, and especially Central Africa, where carbon stocks are known to be high but a scarcity of data limits understanding of carbon stocks and drivers. In this study, we present the first nation-wide measurements and determinants of soil carbon in Gabon, a nation in Central Africa. We estimated soil carbon to a 2-m depth using a systematic, random design of 59 plots located across Gabon. Soil carbon to a 2-m depth averaged 163 Mg ha −1 with a CV of 61%. These soil carbon stocks accounted for approximately half of the total carbon accumulated in aboveground biomass and soil pools. Nearly a third of soil carbon was stored in the second meter of soil, averaging 58 Mg ha −1 with a CV of 94%. Lithology, soil type, and terrain attributes were found to be significant predictors of cumulative SOC stocks to a 2-m depth. Current protocols of the IPCC are to sample soil carbon from the surface 30 cm, which in this study would underestimate soil carbon by 60% and underestimate ecosystem carbon by 30%. A nonlinear model using a power function predicted cumulative soil carbon stocks in the second meter with an average error of prediction of 3.2 Mg ha −1 (CV = 915%) of measured values. The magnitude and turnover of deep soil carbon in tropical forests needs to be estimated as more countries prioritize carbon accounting and monitoring in response to accelerating land-use change.Item Open Access Human-soil relations are changing rapidly: Proposals from SSSA's cross-divisional soil change working group(Soil Science Society of America Journal, 2011-11-01) Richter, DDB; Bacon, AR; Megan, LM; Richardson, CJ; Andrews, SS; West, L; Wills, S; Billings, S; Cambardella, CA; Cavallaro, N; DeMeester, JE; Franzluebbers, AJ; Grandy, AS; Grunwald, S; Gruver, J; Hartshorn, AS; Janzen, H; Kramer, MG; Ladha, JK; Lajtha, K; Liles, GC; Markewitz, D; Megonigal, PJ; Mermut, AR; Rasmussen, C; Robinson, DA; Smith, P; Stiles, CA; Tate, RL; Thompson, A; Tugel, AJ; Es, HV; Yaalon, D; Zobeck, TMA number of scientists have named our age the Anthropocene because humanity is globally affecting Earth systems, including the soil. Global soil change raises important questions about the future of soil, the environment, and human society. Although many soil scientists strive to understand human forcings as integral to soil genesis, there remains an explicit need for a science of anthropedology to detail how humanity is a fully fledged soil-forming factor and to understand how soil change affects human well being. The development and maturation of anthropedology is critical to achieving land-use sustainability and needs to be nurtured by all soil disciplines, with inputs from allied sciences and the humanities,. The Soil Science Society of America (SSSA) has recently approved a cross-divisional Working Group on Soil Change, which aims to advance the basic and applied science of anthropedology, to facilitate networks of scientists, long-term soil field studies, and regional databases and modeling, and to engage in new modes of communications about human-soil relations. We challenge all interested parties, especially young scientists and students, to contribute to these activities and help grow soil science in the Anthropocene. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.Item Open Access Soil production and the soil geomorphology legacy of Grove Karl Gilbert(Soil Science Society of America Journal, 2020-01-01) Richter, DD; Eppes, MC; Austin, JC; Bacon, AR; Billings, SA; Brecheisen, Z; Ferguson, TA; Markewitz, D; Pachon, J; Schroeder, PA; Wade, AM© 2019 The Authors. Soil Science Society of America published by Wiley Periodicals, Inc. on behalf of Soil Science Society of America Geomorphologists are quantifying the rates of an important component of bedrock's weathering in research that needs wide discussion among soil scientists. By using cosmogenic nuclides, geomorphologists estimate landscapes’ physical lowering, which, in a steady landscape, equates to upward transfers of weathered rock into slowly moving hillslope-soil creep. Since the 1990s, these processes have been called “soil production” or “mobile regolith production”. In this paper, we assert the importance of a fully integrated pedological and geomorphological approach not only to soil creep but to soil, regolith, and landscape evolution; we clarify terms to facilitate soil geomorphology collaboration; and we seek a greater understanding of our sciences’ history. We show how the legacy of Grove Karl Gilbert extend across soil geomorphology. We interpret three contrasting soils and regoliths in the USA's Southern Piedmont in the context of a Gilbert-inspired model of weathering and transport, a model of regolith evolution and of nonsteady systems that liberate particles and solutes from bedrock and transport them across the landscape. This exercise leads us to conclude that the Southern Piedmont is a region with soils and regoliths derived directly from weathering bedrock below (a regional paradigm for more than a century) but that the Piedmont also has significant areas in which regoliths are at least partly formed from paleo-colluvia that may be massive in volume and overlie organic-enriched layers, peat, and paleo-saprolite. An explicitly integrated study of soil geomorphology can accelerate our understanding of soil, regoliths, and landscape evolution in all physiographic regions.