This page has been archived. Only use for reference purposes.

2021 AmeriFlux Annual Meeting Talks

For talks and breakout discussions, we will use zoom. For the times, please see the agenda page.

click here to jump to Day 2 – Session: Natural Climate Solutions
click here to jump to Day 3 – Session: Open Science

Sept 20 – Session: Water

Keynote Talk: Transpiration of trees and forests using the SAPFLUXNET database: from species-level water use strategies to the quantification of ecosystem transpirationprofile picture of Rafael Poyatos

Dr. Rafael Poyatos López, SAPFLUXNET initiative, Centre de Recerca Ecològica i Aplicacions Forestals, Universitat Autònoma de Barcelona

Transpiration is a major component of global water balance and a key process underlying vegetation function and dynamics. However, estimating ecosystem transpiration, partitioning the contribution of different species, and quantifying species-specific variation in transpiration regulation in response to environmental variation are challenging with the common methods applied to quantify land evaporative fluxes. SAPFLUXNET ( provides the first harmonized global database of sap flow measurements, designed to investigate the spatiotemporal dynamics of whole-tree transpiration, and encompassing 202 datasets and 175 species. Here, I will provide some examples of how SAPFLUXNET is being used to address key questions about plant drought responses and forest transpiration quantification.

Trends and developments in water flux partitioning at ecosystem scale

Jacob A Nelson, Max Planck Institute for Biogeochemistry

Methodologies for estimating the individual components of total ecosystem evaporation, such as transpiration, soil evaporation, and evaporation of canopy intercepted water, has seen rapid developments in recent years. Advances in both empirical and proceased based methods for estimating component fluxes, as well as strategies for validation given the limited availability of ground truth datasets, have produces a rich landscape of tools to study ecohydrology. This presentation outlines key recent advances in water flux component estimates, as well as potential future developments and links to remote sensing which will allow for the link from ecosystem to global scale.

Thermal remote sensing for terrestrial ecosystem science

Mallory L. Barnes *[1], Martha M. Farella [1], Joshua B. Fisher [2,3]

[1] Indiana University Bloomington [2] Hydrosat Inc. [3] Chapman University

Recent and emerging advances in thermal remote sensing data resolution, availability, and analytics present a timely opportunity for scientists studying carbon and water fluxes. Remote sensing in the thermal infrared (TIR) domain can offer novel insights into the impacts of changing surface temperatures on vegetation and associated ecosystem responses at multiple levels of organization. At the leaf-level, TIR can be used to derive stomatal behavior, identify plant traits, and differentiate between species. Remotely-sensed temperature anomalies at the canopy-scale can identify plant stress in near real-time. Regionally and globally, TIR remote sensing help address open questions related to photosynthetic acclimation, water use efficiency, and evapotranspiration in a warming world. Scaling leaf traits, canopy structure, and regional patterns requires an integrated understanding of both process and technology. We introduce a unifying framework to link leaf to globe through thermal remote sensing, outlining specific opportunities where thermal imagery could complement eddy covariance measurements of carbon and water fluxes. Incorporating thermal data into flux syntheses and upscaling efforts could be especially important to advance understanding of the impacts of climate change on vegetation from leaf to globe.

Combining ECOSTRESS, CubeSats and footprint modelling to improve the estimates of evaporation in Corn and Alfalfa fields

Camilo Rey-Sanchez*[1,2], Kaniska Mallick[1,3], Tianxin Wang[1], Joseph Verfaillie[1], Daphne Szutu[1], Dennis Baldocchi[1]

[1] Department of Environmental Science Management and Policy. University of California, Berkeley [2] Department of Marine, Earth and Atmospheric Sciences. North Carolina State University [3] Luxembourg Institute of Science and Technology, Luxembourg

The increasing availability of high-resolution (spatial and temporal) remote sensors provides important information for evaporation models. In particular, CubeSats offer information on vegetation biophysical status at the daily scale and at 3 m spatial resolution. In this study we evaluate the improvement of evaporation estimates from the ECOSTRESS mission by assimilating data at three different spatial scales, 30 m from Landsat, 10 m from Sentinel, and 3 m from CubeSats. We evaluate the estimates against latent heat flux measurements from 2 eddy covariance towers, at a corn and alfalfa site, and further assessed the necessity of using footprint-weighted averages of evaporation at the different spatial resolutions. We also developed improved model parameterizations of radiation partitioning thanks to detailed field measurements of intercepted photosynthetically active radiation at both alfalfa and corn fields. In addition, we conducted analysis of the scale of the coefficient of variation across multiple scales to identify the adequate resolution to capture the most relevant scale of spatial heterogeneity. Our study revealed that information at the Cubesat level is important to detect small differences in photosynthetic capacity within homogeneous crops such as crop and alfalfa. We also found that the phenology of corn establishes a hysteresis in the growing season spectral response detected by high resolution vegetation indices, such as NDVI, EVI and NIR. The results of this study can be used to achieve precise estimates of evaporation at the diurnal and seasonal scale, relevant for modelling and crop irrigation management.

Sept 21 – Session: Natural Climate Solutions

Keynote Talk: Translating terrestrial carbon cycle science from the field to federal policy: challenges and
opportunities for nature-based solutions to advance meaningful climate mitigationheadshot of Caroline Normile

Dr. Caroline Normile, Bipartisan Policy Center

As atmospheric carbon dioxide mixing ratios continue to climb, there is increasing recognition among researchers, policymakers, and the public that meeting climate targets will require a broad suite of mitigation and removal strategies. The urgency of meeting these goals was underscored by the Biden Administration announcement earlier this year of an economy-wide target to reduce net greenhouse gas emissions by 50-52% below 2005 levels by 2030. Within this suite of strategies—and included in the new U.S. emissions target—is the category of natural climate solutions (NCS) that includes carbon sequestration and storage in agricultural, grassland, and forest landscapes. The World Resources Institute estimates that soil carbon sequestration in the U.S. could total roughly 200 million metric tons CO 2 per year; U.S. forests could sequester up to 360 million metric tons per year. To make this potential a reality, innovative policies and programs—and changes to existing conservation programs—are needed to enhance implementation of effective NCS. Policy innovation is also required to cultivate long-term revenue streams for land management practices that result in increased carbon storage, reduced emissions, and environmental co-benefits like improved air quality, water quantify and retention, and biodiversity. Despite a vast body of research that underpins our current understanding of land- atmosphere carbon exchange and carbon stock quantification, there remains a disconnect between the established science and the needs of carbon market players. To generate revenue streams that incentivize conservation practices, carbon credit purchasers must be confident that their investments are truly additional to “business-as-usual,” can be monitored to guarantee long-term permanence, and are not canceled out by changes in practices elsewhere (leakage). Reliable quantification of NCS is also needed to ensure that corporate purchases of offsets made in support of ambitious net-zero goals are
legitimate. This talk explores (1) emerging research on technical and policy opportunities for scaling verifiable, equitable NCS in the U.S. and (2) strategies to ensure that federal policies are informed by the best available science, including eddy covariance data from the invaluable AmeriFlux network.

Team Talk: Promoting forest carbon cycling resilience to disturbance: Lessons learned and management recommendations from the US-UMB and -UMd Ameriflux sites

Christopher M. Gough[1]*, Gil Bohrer[2], Cameron Clay[1]*, Christoph S. Vogel[3]*, Jeff W. Atkins[1]*, Ben Bond-Lamberty[4], Robert T. Fahey[5], Maxim S. Grigri[1], Lisa T. Haber[1]*, Laura Hickey[1]*, Kayla C. Mathes[1]*, Kerstin Niedermaier[1]*, Ellen Stuart-Haëntjens[1], Peter S. Curtis[6]
1-Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary St., Richmond, VA 23284
2-Department of Civil, Environmental and Geodetic Engineering, Ohio State University, 2070 Neil Avenue, Columbus, OH 43210
3-University of Michigan, Biological Station and Department of Ecology and Evolutionary Biology, Pellston, MI 49769
4-Joint Global Change Research Institute, Pacific Northwest National Laboratory, 5825 University Research Ct, College Park, MD 20740
5-Department of Natural Resources and the Environment & Center for Environmental Sciences and Engineering, University of Connecticut, 1376 Storrs Road, Storrs, CT 06269
6-Dept of Evolution, Ecology, and Organismal Biology, Ohio State University, 318 W 12th Ave, Columbus, OH, 43210

The deciduous forests of North America are increasingly affected by disturbances from insects, pathogens and extreme weather, resulting in an uncertain future for this century-long carbon (C) sink. Our student-led group presentation will draw from over two decades of research, including multiple experimental disturbance manipulations, at the University of Michigan Biological Station’s US-UMB and US-UMd Ameriflux Core sites to ask: how resilient are deciduous forests to partial disturbance and what characteristics of a forest support C cycling and sequestration resilience following disturbance? We will also discuss how our findings could revise forest carbon management practices and help to prioritize disturbance mitigation. Among our most surprising findings is the observation that deciduous forests can experience high tree mortality of >50% without compromising their capacity to sequester C. In the short term, this resilience is tied to offsetting patterns of C uptake and loss and, in the longer-term, an increase in resource-use efficiency followed by a rapid replacement of vegetation loss. Secondly, we found that more complex and biodiverse deciduous forests exhibit greater levels of C cycling resilience, even at relatively high disturbance severities. Lastly, continuous decades-long observations show that a transition from early to mid-late successional canopy tree species increases, rather than decreases, forest C sequestration, a finding that is counter to popular theory. In practice, these findings suggest that forest managers should: recognize that disturbances have variable effects on C cycling resilience, with some effects short-lived; enhance C sequestration stability by cultivating biodiverse compositions and complex forest structures; and, preserve old forests as a way of sustaining the region’s C sink and maintaining other critical goods and services tied to natural climate solutions.

Combining Remote Sensing Models and Eddy Covariance to Monitor Natural Climate Solutions in Agricultural Production Systems

Susanne Wiesner *[1, 2], Alison J. Duff [3], Kristine Niemann [3], Stefan Metzger [4], Ankur R. Desai [2], and Paul C. Stoy [1,2]
[1] Department of Biological Systems Engineering, University of Wisconsin – Madison, 460 Henry Mall, Madison, WI, 53706 USA
[2] Department of Atmospheric and Oceanic Sciences, University of Wisconsin – Madison, 1225 W Dayton St Madison, WI, 53706 USA
[3] U.S. Dairy Forage Research Center, USDA Agricultural Research Service, 1925 Linden Dr, Madison, WI, 53706 USA
[4] National Ecological Observatory Network Program, Battelle, 1685 38th Street, Boulder, CO 80301, USA

Natural climate solutions (NCS) are at the forefront of climate crisis debates, demanding change in ecosystem management to reduce and/or mitigate greenhouse gas emissions. Monitoring the success of such strategies, specifically changes in ecosystem carbon stocks, is subject to high uncertainty and often constrained by regional climate, soil type and management intensity. We tested if the combination of eddy covariance (EC) and remote sensing (RS) techniques could be used to improve NCS monitoring in agroecosystems by overcoming limitations of spatial and temporal resolution via RS and financial costs via EC. We used the environmental response function (ERF) approach to test if EC net ecosystem exchange of CO2 (NEE) measurements can constrain RS gross ecosystem exchange (GEE) and ecosystem respiration (Reco) models by updating model parameters like the maximum quantum yield of photosynthesis (φm). Daily EC NEE sums matched Landsat RS results when daytime data were compared (slope and R2 increased from 0.34 to 0.77 and 0.8 to 0.88, respectively), as Landsat measures during daytime periods. Daily EC NEE, GEE and Reco were in good agreement with RS models (R2 0.78-0.94, 0.86-0.95 & 0.74-0.89), however EC Reco & GEE were 60-115% of RS estimates, suggesting that both fluxes are generally overestimated using RS during the day. Soil respiration and Reco comparisons were in good agreement but EC Reco was again of lower magnitude (slope 0.5 versus 0.8 from RS). Nevertheless, annual biomass budget predictions from RS and EC fusion improved for all crop types when compared to field harvest biomass estimates (R2 = 0.6 and slope improved from 1.09 to 0.98). Our results suggest that EC RS fusion products can help improve the monitoring of NCS on much larger spatiotemporal scales compared to EC and RS methods alone but key uncertainties in Reco still need to be addressed.

Team Talk: Examining Climate Mitigation Practices at the Ecosystem Scale: Carbon Cycling, Methane Uptake, Evapotranspiration and Phenology Responses to Compost Application in a Grazed Grassland

Thomas Fenster*[1], Housen Chu [2], Isabel Torres [3], Patty Oikawa*[3]
1-Department of Soils and Biogeochemistry, UC Davis, Davis, CA, USA
2-Climate and Ecosystem Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA, USA
3-Department of Earth and Environmental Sciences, Cal State East Bay, Hayward, CA, USA

Compost amendments to grasslands could be an important tool for climate change mitigation, accounting for ~9% of the cumulative greenhouse gas (GHG) reductions required for CA state’s ambitious goal of 147 MMTCO2e by 2030. Previous studies in compost-amended rangelands showed elevated soil respiration that was offset by increased net primary productivity and bulk soil organic carbon. Compost amendments had no significant effect on CH4 emissions, but generally increased soil water holding capacity. While these previous studies show promising results for compost amendments as a climate mitigation practice, more studies are needed to determine how compost applications function in diverse grasslands and at larger scales. Our team applied a one-time compost application to 1.6 ha of grazed grassland in 2020. An eddy covariance tower (US-CGG) monitored the grassland for the year before and following the amendment. Soils were sampled in both years and are being processed for bulk soil C and N. Static soil chambers were used to monitor soil surface CO2 and CH4 flux within the footprint of the tower. The compost amendment stimulated high GPP, however high Reco offset all enhanced CO2 uptake resulting in no significant difference in annual NEE between the 2 years. Phenocam data show that the compost amendment changed the phenology of the ecosystem leading to earlier green-up relative to control areas. Finally, compost-amended soils had significantly greater CH4 uptake compared to control soil. We hypothesize that higher soil moisture and nutrients in amended soils facilitates a larger methanotroph community. Future work will include analyses of the soil bulk C and microbial community as well as implications of changing soil moisture content for ET. These data will help inform the scale-emergent properties of soil amendment applications, an important climate mitigation practice that is planned to be used at large scales in CA and beyond.

Sept 22 – Session: Open Science

Priorities for synthesis in ecology and environmental scienceProfile picture of Ben Halpen

Dr. Ben Halpern, National Center for Ecological Analysis and Synthesis

Synthesis research generates new understanding, advances theory, and supports management strategies by linking data, ideas, and tools. We convened a virtual workshop to examine how and where synthesis can address key questions and themes in ecology and environmental science in the coming decade, and thus provide a strategic vision for the future of synthesis in these disciplines. Seven priority topics emerged for the focus of future synthesis research: 1) Justice, Equity, Diversity, and Inclusion (JEDI), 2) scale, 3) universality, 4) actionable and use-inspired science, 5) system design and resilience, 6) human and natural systems, and 7) predictability. Additionally, two related issues regarding the practice of synthesis emerged: the need for increased diversity in those who conduct synthesis, as well as increased data and knowledge brought to bear. These topics and practices provide a blueprint for the future of synthesis in ecology and environmental science.

Team Talk: Urban eddy-covariance: Why, how and where?

Kenneth Davis[1]*, Natasha Miles[1]*, Scott Richardson[1], Alex Zhang[1], Samantha Murphy[1]*, Claire Jin[1]*, Matthew Berzonsky[2], Eli Vogel[3]*, Kai Wu[4]*, Sharon Gourdji[5], David Allen[5], Lucy Hutyra[6], Kevin Gurney[7], Geoff Roest[7], Jocelyn Turnbull[8]
[1] The Pennsylvania State University
[2] St. Francis University
[3] University of Maryland Baltimore County
[4] University of Edinburgh
[5] National Institute of Standards and Technology
[6] Boston University
[7] Northern Arizona University
[8] GNS Science

Eddy-covariance has been used to study land-atmosphere fluxes for decades. Flux towers are typically deployed in relatively homogeneous ecosystem settings. Flux towers have been deployed in urban and suburban settings, but their integration into emerging efforts to quantify urban greenhouse gas (GHG) emissions with urban atmospheric inversions has been limited. We present the logic and methodology for flux tower deployments as a component of urban GHG studies. We present a synthesis of results that demonstrate these methods, drawing from the Indianapolis Flux Experiment (INFLUX) and Northeast Corridor (NEC) study. We present decomposition of total CO2 fluxes into anthropogenic and biogenic components using CO : fossil CO2 ratios, flux footprint decomposition at high spatial and temporal resolution to evaluate urban flux models in regions of heterogeneous emissions, and targeted observations of regional ecosystem fluxes. We show applications of these methods to quantify traffic-related flux changes resulting from the spring 2020 COVID lockdown. We describe how urban flux towers can be a valuable element of the overall “bottom-up” approach to determining urban GHG fluxes. We also illustrate the utility of these observations for improving the simulation of boundary layer turbulence required for urban atmospheric inversions.

Drought-induced decoupling between tree growth and carbon uptake impacts forest carbon turnover time

Steven A. Kannenberg*[1], Antoine Cabon[1], Flurin Babst[2,3], Soumaya Belmecheri[3], Rossella Guerrieri[4], Nicholas Delpierre[5], Justin T. Maxwell[6], Frederick C. Meinzer[7], David J.P. Moore[2], Christoforos Pappas[8,9,10], Masahito Ueyama[11], Danielle E.M. Ulrich[12], Steven L. Voelker[13], David R. Woodruff[7], William R.L. Anderegg[1]
[1]School of Biological Sciences, University of Utah, Salt Lake City, UT, USA
[2]School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA
[3]Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ, USA
[4]Department of Agricultural and Food Sciences, University of Bologna, Bologna, Italy
[5]Ecologie Systématique Evolution, Univ. Paris‐Sud, CNRS, AgroParisTech, Université Paris‐Saclay, Orsay, France
[6]Department of Geography, Indiana University, Bloomington, IN, USA
[7]USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR, USA
[8]Département de géographie, Université de Montréal, Montreal, QC, Canada
[9]Centre d’étude de la forêt, Université du Québec à Montréal, Montreal, QC, Canada
[10]Département Science et Technologie, Téluq, Université du Québec, Montreal, QC, Canada
[11]Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Japan
[12]Department of Ecology, Montana State University, Bozeman, MT, USA
[13]SUNY College of Environmental Science and Forestry, Syracuse, NY, USA

The ability of forests to withstand, and recover from, drought stress is a critical uncertainty regarding the impacts of climate change on the terrestrial carbon (C) cycle. Quantifications of drought resistance and resilience are largely based on either direct measurements of tree growth or broader-scale proxies for C uptake, but it is unclear how drought responses scale from individual trees to forests. Understanding the nature of this scaling is crucial to quantify the degree to which drought impacts the C cycle through changes in uptake versus turnover time. Here, we document a widespread decoupling in drought responses across C cycle processes, whereby gross primary productivity (GPP) was relatively resistant to drought despite highly sensitive co-located tree-ring chronologies. For example, annual GPP was infrequently significantly reduced due to drought, while tree ring width decreased on average by 25% during the drought year, and 20% in the year after drought. By modeling whole-forest C turnover time, we show this decoupling has important ramifications for the forest C cycle, especially if C is allocated towards foliar or non-structural pools with short residence times. Indeed, our modeled decreases in forest C turnover due entirely to allocation shifts represent a sizeable fraction of the current trend in turnover due to tree mortality. Our results demonstrate that quantifications of drought impacts that rely on C uptake are missing this fundamental pathway through which drought alters the forest C cycle.

Team Talk: The FLUXNET Coordination Project: A new initiative to support global network-enabled science

Trevor Keenan*[1,2] Kyle Delwiche*[1,2] Kim Novick*[3] David JP Moore*[4]
[1] Department of Environmental Science, Policy and Management, UC Berkeley, Berkeley, CA, USA
[2] Climate and Ecosystem Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA, USA
[3] O’Neill School of Public and Environmental Affairs, Indiana University, Bloomington, IN, USA
[4] School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA

Global ecosystems provide services that sustain society, including provisioning of food, ber and timber, and water cycle regulation. Understanding ecosystem-atmosphere interactions, and the response of these to ongoing environmental change, is thus an urgent challenge. The FLUXNET Coordination Project will ll fundamental knowledge gaps in science, engineering, and societal issues associated with ongoing changes in ecosystem function and the related cycling of carbon and water. FLUXNET is a global network of regional networks, consisting of scientists measuring the exchange of carbon dioxide, water, energy, and other greenhouse gas fluxes between ecosystems and the atmosphere. Such measurements have proven essential for understanding ecosystem function, calibrating space-borne observations, and developing models used to project future climate. The project links over ten existing national and international networks focused on continuous observations of ecosystem-atmosphere interactions at over 1000 locations around the world. Through multiple research and training opportunities it will help develop the next generation of the FLUXNET network-of-networks to be a self-sustaining global collaboration focused on supporting early career scientists, expanding the diversity of scientists, biomes, and climate regions involved, and empowering international collaboration. The central goals of the FLUXNET Coordination Project are to provide novel training and exchange opportunities, develop strong international collaborations, and build tools and protocols that ensure continued growth of FLUXNET beyond the life of the project. To do so, the project will develop both data-focused processing protocols and pipelines, and people-focused education and exchange opportunities. Here, we give an overview of the project, including various opportunities for involvement and activities planned for the coming year.