Alison Hoyt is an Assistant Professor of Earth System Science at Stanford. Her work focuses on understanding how biogeochemical cycles respond to human impacts, with a particular focus on the most vulnerable and least understood carbon stocks in the tropics and the Arctic. For more information, please visit her group website here:

Academic Appointments

Stanford Advisees

All Publications

  • Controls and relationships of soil organic carbon abundance and persistence vary across pedo-climatic regions. Global change biology von Fromm, S. F., Hoyt, A. M., Sierra, C. A., Georgiou, K., Doetterl, S., Trumbore, S. E. 2024; 30 (5): e17320


    One of the largest uncertainties in the terrestrial carbon cycle is the timing and magnitude of soil organic carbon (SOC) response to climate and vegetation change. This uncertainty prevents models from adequately capturing SOC dynamics and challenges the assessment of management and climate change effects on soils. Reducing these uncertainties requires simultaneous investigation of factors controlling the amount (SOC abundance) and duration (SOC persistence) of stored C. We present a global synthesis of SOC and radiocarbon profiles (nProfile = 597) to assess the timescales of SOC storage. We use a combination of statistical and depth-resolved compartment models to explore key factors controlling the relationships between SOC abundance and persistence across pedo-climatic regions and with soil depth. This allows us to better understand (i) how SOC abundance and persistence covary across pedo-climatic regions and (ii) how the depth dependence of SOC dynamics relates to climatic and mineralogical controls on SOC abundance and persistence. We show that SOC abundance and persistence are differently related; the controls on these relationships differ substantially between major pedo-climatic regions and soil depth. For example, large amounts of persistent SOC can reflect climatic constraints on soils (e.g., in tundra/polar regions) or mineral absorption, reflected in slower decomposition and vertical transport rates. In contrast, lower SOC abundance can be found with lower SOC persistence (e.g., in highly weathered tropical soils) or higher SOC persistence (e.g., in drier and less productive regions). We relate variable patterns of SOC abundance and persistence to differences in the processes constraining plant C input, microbial decomposition, vertical C transport and mineral SOC stabilization potential. This process-oriented grouping of SOC abundance and persistence provides a valuable benchmark for global C models, highlighting that pedo-climatic boundary conditions are crucial for predicting the effects of climate change and soil management on future C abundance and persistence.

    View details for DOI 10.1111/gcb.17320

    View details for PubMedID 38751310

  • Canal networks regulate aquatic losses of carbon from degraded tropical peatlands NATURE GEOSCIENCE Bowen, J. C., Wahyudio, P. J., Anshari, G. Z., Aluwihare, L. I., Hoyt, A. M. 2024
  • Boreal-Arctic wetland methane emissions modulated by warming and vegetation activity NATURE CLIMATE CHANGE Yuan, K., Li, F., McNicol, G., Chen, M., Hoyt, A., Knox, S., Riley, W. J., Jackson, R., Zhu, Q. 2024
  • Controls on timescales of soil organic carbon persistence across sub-Saharan Africa. Global change biology von Fromm, S. F., Doetterl, S., Butler, B. M., Aynekulu, E., Berhe, A. A., Haefele, S. M., McGrath, S. P., Shepherd, K. D., Six, J., Tamene, L., Tondoh, E. J., Vagen, T., Winowiecki, L. A., Trumbore, S. E., Hoyt, A. M. 2024; 30 (1): e17089


    Given the importance of soil for the global carbon cycle, it is essential to understand not only how much carbon soil stores but also how long this carbon persists. Previous studies have shown that the amount and age of soil carbon are strongly affected by the interaction of climate, vegetation, and mineralogy. However, these findings are primarily based on studies from temperate regions and from fine-scale studies, leaving large knowledge gaps for soils from understudied regions such as sub-Saharan Africa. In addition, there is a lack of data to validate modeled soil C dynamics at broad scales. Here, we present insights into organic carbon cycling, based on a new broad-scale radiocarbon and mineral dataset for sub-Saharan Africa. We found that in moderately weathered soils in seasonal climate zones with poorly crystalline and reactive clay minerals, organic carbon persists longer on average (topsoil: 201±130years; subsoil: 645±385years) than in highly weathered soils in humid regions (topsoil: 140±46years; subsoil: 454±247years) with less reactive minerals. Soils in arid climate zones (topsoil: 396±339years; subsoil: 963±669years) store organic carbon for periods more similar to those in seasonal climate zones, likely reflecting climatic constraints on weathering, carbon inputs and microbial decomposition. These insights into the timescales of organic carbon persistence in soils of sub-Saharan Africa suggest that a process-oriented grouping of soils based on pedo-climatic conditions may be useful to improve predictions of soil responses to climate change at broader scales.

    View details for DOI 10.1111/gcb.17089

    View details for PubMedID 38273490

  • Relating mineral-organic matter stabilization mechanisms to carbon quality and age distributions using ramped thermal analysis. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences Stoner, S., Trumbore, S. E., González-Pérez, J. A., Schrumpf, M., Sierra, C. A., Hoyt, A. M., Chadwick, O., Doetterl, S. 2023; 381 (2261): 20230139


    Organic carbon (OC) association with soil minerals stabilizes OC on timescales reflecting the strength of mineral-C interactions. We applied ramped thermal oxidation to subsoil B horizons with different mineral-C associations to separate OC according to increasing temperature of oxidation, i.e. thermal activation energy. Generally, OC released at lower temperatures was richer in bioavailable forms like polysaccharides, while OC released at higher temperatures was more aromatic. Organic carbon associated with pedogenic oxides was released at lower temperatures and had a narrow range of 14C content. By contrast, N-rich compounds were released at higher temperatures from samples with 2 : 1 clays and short-range ordered (SRO) amorphous minerals. Temperatures of release overlapped for SRO minerals and crystalline oxides, although the mean age of OC released was older for the SRO. In soils with more mixed mineralogy, the added presence of older OC released at temperatures greater than 450°C from clays resulted in a broader distribution of OC ages within the sample, especially for soils rich in 2 : 1 layer expandable clays such as smectite. While pedogenic setting affects mineral stability and absolute OC age, mineralogy controls the structure of OC age distribution within a sample, which may provide insight into model structures and OC dynamics under changing conditions. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

    View details for DOI 10.1098/rsta.2023.0139

    View details for PubMedID 37807690

  • How well does ramped thermal oxidation quantify the age distribution of soilcarbon? Assessing thermal stability of physically and chemicallyfractionated soil organic matter BIOGEOSCIENCES Stoner, S. W., Schrumpf, M., Hoyt, A., Sierra, C. A., Doetterl, S., Galy, V., Trumbore, S. 2023; 20 (15): 3151-3163
  • Processes Controlling Methane Emissions From a Tropical Peatland Drainage Canal JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Somers, L. D., Hoyt, A., Cobb, A. R., Isnin, S., Suhip, M., Sukri, R. S., Gandois, L., Harvey, C. 2023; 128 (3)
  • Soil carbon stocks in stable tropical landforms are dominated by geochemical controls and not by land use. Global change biology Reichenbach, M., Fiener, P., Hoyt, A., Trumbore, S., Six, J., Doetterl, S. 2023


    Soil organic carbon (SOC) dynamics depend on soil properties derived from the geoclimatic conditions under which soils develop and are in many cases modified by land conversion. However, SOC stabilization and the responses of SOC to land use change are not well constrained in deeply weathered tropical soils, which are dominated by less reactive minerals than those in temperate regions. Along a gradient of geochemically distinct soil parent materials, we investigated differences in SOC stocks and SOC (Delta14 C) turnover time across soil profile depth between montane tropical forest and cropland situated on flat, non-erosive plateau landforms. We show that SOC stocks and soil Delta14 C patterns do not differ significantly with land use, but that differences in SOC can be explained by the physicochemical properties of soils. More specifically, labile organo-mineral associations in combination with exchangeable base cations were identified as the dominating controls over soil C stocks and turnover. We argue that due to their long weathering history, the investigated tropical soils do not provide enough reactive minerals for the stabilization of C input in either high input (tropical forest) or low-input (cropland) systems. Since these soils exceeded their maximum potential for the mineral related stabilization of SOC, potential positive effects of reforestation on tropical SOC storage are most likely limited to minor differences in topsoil without major impacts on subsoil C stocks. Hence, in deeply weathered soils, increasing C inputs may lead to the accumulation of a larger readily available SOC pool, but does not contribute to long-term SOC stabilization.

    View details for DOI 10.1111/gcb.16622

    View details for PubMedID 36847151

  • Extensive global wetland loss over the past three centuries. Nature Fluet-Chouinard, E., Stocker, B. D., Zhang, Z., Malhotra, A., Melton, J. R., Poulter, B., Kaplan, J. O., Goldewijk, K. K., Siebert, S., Minayeva, T., Hugelius, G., Joosten, H., Barthelmes, A., Prigent, C., Aires, F., Hoyt, A. M., Davidson, N., Finlayson, C. M., Lehner, B., Jackson, R. B., McIntyre, P. B. 2023; 614 (7947): 281-286


    Wetlands have long been drained for human use, thereby strongly affecting greenhouse gas fluxes, flood control, nutrient cycling and biodiversity1,2. Nevertheless, the global extent of natural wetland loss remains remarkably uncertain3. Here, we reconstruct the spatial distribution and timing of wetland loss through conversion to seven human land uses between 1700 and 2020, by combining national and subnational records of drainage and conversion with land-use maps and simulated wetland extents. We estimate that 3.4 million km2 (confidence interval 2.9-3.8) of inland wetlands have been lost since 1700, primarily for conversion to croplands. This net loss of 21% (confidence interval 16-23%) of global wetland area is lower than that suggested previously by extrapolations of data disproportionately from high-loss regions. Wetland loss has been concentrated in Europe, the United States and China, and rapidly expanded during the mid-twentieth century. Our reconstruction elucidates the timing and land-use drivers of global wetland losses, providing an improved historical baseline to guide assessment of wetland loss impact on Earth system processes, conservation planning to protect remaining wetlands and prioritization of sites for wetland restoration4.

    View details for DOI 10.1038/s41586-022-05572-6

    View details for PubMedID 36755174

  • Reviews and syntheses: The promise of big diverse soil data, moving current practices towards future potential BIOGEOSCIENCES Todd-Brown, K. O., Abramoff, R. Z., Beem-Miller, J., Blair, H. K., Earl, S., Frederick, K. J., Fuka, D. R., Santamaria, M., Harden, J. W., Heckman, K., Heran, L. J., Holmquist, J. R., Hoyt, A. M., Klinges, D. H., LeBauer, D. S., Malhotra, A., McClelland, S. C., Nave, L. E., Rocci, K. S., Schaeffer, S. M., Stoner, S., van Gestel, N., von Fromm, S. F., Younger, M. L. 2022; 19 (14): 3505-3522
  • Climate change-induced peatland drying in Southeast Asia ENVIRONMENTAL RESEARCH LETTERS Dadap, N. C., Cobb, A. R., Hoyt, A. M., Harvey, C. F., Feldman, A. F., Im, E., Konings, A. G. 2022; 17 (7)
  • Drainage Canals in Southeast Asian Peatlands Increase Carbon Emissions AGU Advances Dadap, N. C., Hoyt, A. M., Cobb, A. R., Oner, D., Kozinski, M., Fua, P. V., Rao, K., Harvey, C. F., Konings, A. G. 2021; 2 (1): 1-14

    View details for DOI 10.1029/2020AV000321

  • An open-source database for the synthesis of soil radiocarbon data: International Soil Radiocarbon Database (ISRaD) version 1.0 EARTH SYSTEM SCIENCE DATA Lawrence, C. R., Beem-Miller, J., Hoyt, A. M., Monroe, G., Sierra, C. A., Stoner, S., Heckman, K., Blankinship, J. C., Crow, S. E., McNicol, G., Trumbore, S., Levine, P. A., Vinduskova, O., Todd-Brown, K., Rasmussen, C., Pries, C., Schadel, C., McFarlane, K., Doetterl, S., Hatte, C., He, Y., Treat, C., Harden, J. W., Torn, M. S., Estop-Aragones, C., Berhe, A., Keiluweit, M., Kuhnen, A., Marin-Spiotta, E., Plante, A. F., Thompson, A., Shi, Z., Schimel, J. P., Vaughn, L. S., von Fromm, S. F., Wagai, R. 2020; 12 (1): 61–76
  • The landscape of soil carbon data: emerging questions, synergies and databases Progress in Physical Geography Malhotra, A., Todd-Brown, K., Nave, L. E., Batjes, N. H., Holmquist, J. R., Hoyt, A. M., Iversen, C. M., Jackson, R. B., Lajtha, K., Lawrence, C., Vindušková, O., Wieder, W., Williams, M., Hugelius, G., Harden, J. 2019

    View details for DOI 10.1177/0309133319873309

  • Satellite soil moisture observatins predict burned area in Southeast Asian peatlands ENVIRONMENTAL RESEARCH LETTERS Dadap, N. C., Cobb, A. R., Hoyt, A. M., Harvey, C. F., Konings, A. G. 2019; 14

    View details for DOI 10.1088/1748-9326/ab3891