The Science
Remote sensing has become a critically important tool for researchers who study Earth’s ecosystems and minerals. In particular, imaging spectroscopy – or the measurement of many, continuous spectral channels across visible and non-visible wavelengths – and thermal infrared imagery are essential for inferring plant health, ecosystem function, biodiversity, and solid earth research. Reviewing the requirements of the NASA Surface Biology and Geology (SBG) Designated Observable, a proposed global imaging spectroscopy and thermal infrared Earth Observing satellite, over 130 scientists reviewed the current state of imaging spectroscopy algorithms and state-of-the-art methods for remote sensing of surface, terrestrial and aquatic ecosystems.  

The Impact
Regular monitoring of the state, functioning and biodiversity of Earth’s terrestrial, freshwater, and coastal aquatic ecosystems is essential for understanding the impacts of severe weather, disturbance, and climate change on natural resources, potential feedbacks to climate and the management of resources, and defining policy. Remote sensing technologies are essential for large-scale monitoring, but current satellite platforms are insufficient to fill this need. The SBG Designated Observable, a novel combination of high spatial resolution spectral and thermal infrared imagery, is uniquely designed to address these challenges and provide key observations for studying hydrological, ecological, weather, climate and solid earth dynamics.  

Summary
Monitoring Earth’s diverse natural resources and managed ecosystems is a significant challenge but essential for balancing the maintenance of health, diversity and resource utilization. Vegetation plays a key role in regulating climate and weather, while the state and health of freshwater and coastal ecosystems impacts global circulation patterns, as well as fisheries and recreation. Scientists and policy makers require tools to provide the information needed to understand how the Earth is changing and to define management strategies for the maintenance of biodiversity. The 2017-2027 National Academy of Sciences Decadal Survey, Thriving on our Changing Planet, identified the critical need for a global imaging spectrometer (IS) combined with a multi-spectral thermal infrared (TIR) imager with a high spatial resolution (~30 meters for the IS and ~60 meters for the TIR) and sub-monthly temporal resolution. The Surface Biology and Geology (SBG) Designated Observable is designed to meet the needs for regular mapping of the state and changes in Earth’s resources. A team of more than 130 scientists synthesized applications and methods for using SBG to provide the observations needed to inform science and management strategies. The team also identified the necessary next steps needed to prepare for an operational SBG-like satellite to monitor Earth.  

Contacts
BER Program Manager: Daniel Stover, U.S. Department of Energy Office of Science, Office of Biological and Environmental Research, Earth and Environmental Systems Sciences Division (SC-33.1), Environmental System Science, Daniel.Stover@science.doe.gov
Brian Benscoter, U.S. Department of Energy Office of Science, Office of Biological and Environmental Research, Earth and Environmental Systems Sciences Division (SC-33.1), Environmental System Science, Brian.Benscoter@science.doe.gov
Principal Investigator: Shawn P. Serbin, Scientist, Brookhaven National Laboratory, sserbin@bnl.gov (+1 631-344-3165)

Funding
Support to the lead authors (Cawse-Nicholson and Townsend) was provided by NASA Headquarters and the Jet Propulsion Laboratory, California Institute of Technology. This study was also supported by the Space-based Imaging Spectroscopy and Thermal (SISTER) pathfinder, part of the Surface Biology and Geology (SBG) project, a NASA Earth Science Designated Observable. Adam Erickson’s contribution was supported by an appointment to the NASA Postdoctoral Program at NASA Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASA. Robert Frouin was supported by NASA’s Ocean Biology and Biogeochemistry Program under various grants. The contribution of Michael E. Schaepman is supported by the University of Zurich Research Priority Programme on Global Change and Biodiversity (URPP GCB). Shawn Serbin was supported by the Next-Generation Ecosystem Experiments in the Arctic (NGEE-Arctic) and tropics (NGEE-Tropics) that are supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science, and through the U.S. DOE contract No. DE-SC0012704 to Brookhaven National Laboratory. The authors thank the other members of the SBG Algorithms Working Group, constituting more than 130 researchers, who participated in telecons and webinars to contribute to the contents of this paper. Two anonymous reviewers provided invaluable insight and recommendations, and we are grateful for their time and suggestions. Part of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. © 2021 California Institute of Technology. Government sponsorship is acknowledged.  

Publications
Cawse-Nicholson, K., P. A. Townsend, D. Schimel, A. M. Assiri, P. L. Blake, M. F. Buongiorno, P. Campbell, N. Carmon, K. A. Casey, R. E. Correa-Pabón, K. M. Dahlin, H. Dashti, P. E. Dennison, H. Dierssen, A. Erickson, J. B. Fisher, R. Frouin, C. K. Gatebe, H. Gholizadeh, M. Gierach, N. F. Glenn, J. A. Goodman, D. M. Griffith, L. Guild, C. R. Hakkenberg, E. J. Hochberg, T. R. H. Holmes, C. Hu, G. Hulley, K. F. Huemmrich, R. M. Kudela, R. F. Kokaly, C. M. Lee, R. Martin, C. E. Miller, W. J. Moses, F. E. Muller-Karger, J. D. Ortiz, D. B. Otis, N. Pahlevan, T. H. Painter, R. Pavlick, B. Poulter, Y. Qi, V. J. Realmuto, D. Roberts, M. E. Schaepman, F. D. Schneider, F. M. Schwandner, S. P. Serbin, A. N. Shiklomanov, E. N. Stavros, D. R. Thompson, J. L. Torres-Perez, K. R. Turpie, M. Tzortziou, S. Ustin, Q. Yu, Y. Yusup, and Q. Zhang. 2021. “NASA’s surface biology and geology designated observable: A perspective on surface imaging algorithms”. Remote Sensing of Environment 257, 112349.[DOI: https://doi.org/10.1016/j.rse.2021.112349]

Related Links
Article URL (open-source article): https://www.sciencedirect.com/science/article/pii/S0034425721000675?via%3Dihub
Article DOI: https://doi.org/10.1016/j.rse.2021.112349
NASA Surface Biology and Geology Designated Observable: https://sbg.jpl.nasa.gov/
Remote Sensing of Plant Biodiversity: https://link.springer.com/book/10.1007%2F978-3-030-33157-3
Serbin S.P., Townsend P.A. (2020) Scaling Functional Traits from Leaves to Canopies. In: Cavender-Bares J., Gamon J.A., Townsend P.A. (eds) Remote Sensing of Plant Biodiversity. Springer, Cham. https://doi.org/10.1007/978-3-030-33157-3_3

The Science
Scientific hypotheses describe how processes might work in the natural world. Computer models are built from mathematical descriptions of these hypotheses. Alternative hypotheses are common, especially in environmental sciences, yet most computer models cannot easily switch among these alternative hypotheses. DOE scientists have developed a new model that can switch between hypotheses and prioritize which process to study further, a “multi-hypothesis model.” Using the model to study common leaf photosynthesis models, scientists found the surprising importance of a process that has previously received little attention. New data were then collected to discriminate among the alternative hypotheses finding support for the more traditional approach.

The Impact
Leaf photosynthesis models simulate the rhythms of CO2 transfer from the atmosphere to plants. This study highlights a key shortfall in photosynthesis modeling and in our general approach to developing and using predictive models of the terrestrial biosphere. Models can reach the same end point in multiple ways. This can lead to models “getting it right for the wrong reasons.” The multi-hypothesis approach will help to identify key processes causing model differences and evaluate alternative hypotheses to describe those processes. Ultimately leading to more robust predictions of terrestrial ecosystems.

Summary
Leaf photosynthesis models are the beating heart of global carbon cycle models. These photosynthesis models simulate the rhythms of CO2 transfer from the atmosphere into plants and terrestrial ecosystems. The reigning king of photosynthesis models is the Farquhar model published in 1980. However, despite its almost ubiquitous use, there are a number of variations in how the mechanics of various component processes are mathematically described, i.e. there are various mathematical hypotheses that describe some of the sub-processes within the overarching Farquhar model. The consequences of these alternative choices have never been formally investigated. In part this is because methods to formally investigate model sensitivity to variation in how processes are represented have only recently been developed. Novel multi-hypothesis modeling methods were applied to investigate the influence of 14 parameters and four processes with alternative representations in photosynthesis models, finding the surprising dominance of a process that has not been extensively evaluated with data. Running the alternatives of this dominant process in global models resulted in a difference in photosynthesis equivalent to annual human CO2 emissions. This multi-hypothesis model evaluation identified as important two alternative hypotheses for photosynthetic limiting rate selection. Novel, high-resolution photosynthesis measurements were designed and undertaken to discriminate among these hypotheses. General support for the original Farquhar implementation was found and is recommended for use to reduce uncertainty in global photosynthesis simulations.

Contact: Anthony Walker, Senior Scientist, Oak Ridge National Lab, walkerap@ornl.gov

Funding
U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research: Next Generation Ecosystem Experiments-Tropics, ORNL Terrestrial Ecosystem Science SFA, university grant DE-SC0019438. National Science Foundation support for National Center for Atmospheric Research.

Publications
Walker, A. P. et al. “Multi-hypothesis comparison of Farquhar and Collatz photosynthesis models reveals the unexpected influence of empirical assumptions at leaf and global scales.” Global Change Biology 27, 804–822 (2021). [DOI: 10.1111/gcb.15366]

Related Links
Huntingford, C. & Oliver, R. J. “Converging towards a common representation of large-scale photosynthesis.” Global Change Biology 27, 716-718 (2020).

The Science
Tall trees are key drivers of ecosystem processes in tropical forests, but what controls the distribution of the very tallest trees remains poorly understood. The recent discovery of giant trees over 80 meters tall in the Amazon forest requires a reevaluation of current thinking.

The Impact
We found that changes in wind and light availability drive giant tree distribution as much as precipitation and temperature, together shaping the forest structure of the Brazilian Amazon. The location of giant trees should be carefully considered by policymakers when identifying important hot spots for the conservation of biodiversity.

Summary
In this study, we employed the largest airborne lidar data collection in the Amazon to contribute to the understanding of (a) how resources and disturbances shape the maximum height distribution across the Brazilian Amazon, and (b) what drives the occurrence of giant trees (taller than 70 m). We conducted an extensive analysis relating environmental variables to the maximum height recorded in the lidar transects (Figure 1). Common drivers of height development are fundamentally different from those influencing the occurrence of giant trees. We found that changes in wind and light availability drive giant tree distribution as much as precipitation and temperature, together shaping the forest structure of the Brazilian Amazon. Ultimately, the association between environmental conditions and mechanisms of natural selection are key to understanding the complexity of this process in a changing climate.

Contacts (BER PM): Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact: Eric Bastos Gorgens, Universidade Federal dos Vales do Jequitinhonha e Mucuri – UFVJM – Brazil, eric.gorgens@ufvjm.edu.br

Funding
Funding was provided by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Brasil (CAPES; Finance Code 001); Conselho Nacional de Desenvolvimento Científico e Tecnológico (Processes 403297/2016‐8 and 301661/2019‐7); Amazon Fund (grant 14.2.0929.1); National Academy of Sciences and US Agency for International Development (grant AID‐OAA‐A‐11–00012); Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM); and Instituto Nacional de Pesquisas Espaciais (INPE). D. Almeida was supported by the São Paulo Research Foundation (#2018/21338‐3 and #2019/14697‐0). B. Gimenez, G. Spanner, and N. Higuchi were supported by INCT‐Madeiras da Amazônia and Next Generation Ecosystem Experiments‐Tropics (NGEE‐Tropics), as part of DOE’s Terrestrial Ecosystem Science Program – Contract No. DE‐AC02‐05CH11231. T. Jackson and D. Coomes were supported by the UK Natural Environment Research Council grant NE/S010750/1. M. Nunes was supported by the Academy of Finland (decision number 319905). J. Rosette was supported by the Royal Society University Research Fellowship (URF\R\191014).

Publications
Gorgens, E. B., Nunes, M. H., Jackson, T., Coomes, D., Keller, M., Reis, C. R., Valbuena, R., Rosette, J., Almeida, D. R. A., Gimenez, B., Cantinho, R., Motta, A. Z., Assis, M., Pereira, F. R. S., Spanner, G., Higuchi, N., Ometto, J. P. (2021). Resource availability and disturbance shape maximum tree height across the Amazon. Global Change Biology, 27(1), 177-189. https://doi.org/10.1111/gcb.15423

The Science
Tropical forests play a critical role in the global carbon cycle. Yet, there is a high level of uncertainty on how these forests will respond to ongoing global environmental changes. This uncertainty is partially attributed to the poor representation of tree mortality in Vegetation Demographic Models. We designed a standardized field protocol to evaluate tree vigor, biomass loss, and factors likely to be associated with future tree death. Advancing the mechanistic inclusion of mortality in vegetation models is a research priority to enable more accurate estimates of terrestrial carbon budgets and predictions of future carbon cycle-climate feedbacks.

The Impact
Although key to predict forest response to global changes, much uncertainty remains on causes and consequences of tropical tree mortality. This study proposes a rapid, repeatable, and inexpensive assessment of individual tree death and damage. It minimizes the effort required at each tree to allow the frequent assessments of more trees. A comprehensive assessment of tree damage coupled with the identification of factors associated with tree death will lead to an improved understanding of the causes of tree mortality and estimates of biomass fluxes in tropical forests.

Summary
Tree mortality drives changes in forest structure and dynamics, community composition, and carbon and nutrient cycles. Since tropical forests store a large fraction of terrestrial biomass and tree diversity, improved understanding of changing tree mortality and biomass loss rates is critical. Tropical tree mortality rates have been challenging to estimate due to low background rates of tree death, and high spatial and temporal heterogeneity. Furthermore, the causes of mortality remain unclear because many factors may be involved in individual tree death, and the rapid decomposition of wood in the tropics obscures evidence of possible causes of tree mortality. We present a field protocol to assess tree mortality in tropical forests. The protocol focuses on the rapid, repeatable and inexpensive assessment of individual tree death and damage. The protocol has been successfully tested with annual assessments of >62,000 stems in total in several ForestGEO plots in Asia and the Neotropics. Standardized methods for the assessment of tree death and biomass loss will advance understanding of the underlying causes and consequences of tree mortality.

Contact: Daniel Zuleta, Forest Global Earth Observatory, Smithsonian Tropical Research Institute, dfzuleta@gmail.com

Funding
This research was supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
Arellano, D. Zuleta & S.J. Davies, “Tree death and damage: a standardized protocol for frequent surveys in tropical forests”. Journal of Vegetation Science (2020).  [https://doi.org/10.1111/jvs.12981]

Related Links
Frequent Tree Damage and Death Assessment, Forest Global Earth Observatory, Smithsonian Tropical Research Institute.

The Science
Whether trees are in the canopy or not has long been recognized as a critical determinant of tree performance. However, the structural complexity of many tropical forests makes it difficult to determine canopy positions. The integration of remote sensing and ground-based data enabled this determination and measurements of how canopy and understory trees differ in structure and dynamics in the Central Amazon. Researchers found that canopy trees constituted 40% of the inventoried trees with diameter at breast height > 10 cm, and accounted for ~70% of aboveground carbon stocks. Diameter growth was on average twice as large in canopy trees as in understory trees and the size distribution also differed.

The Impact
The combination of high-resolution drone imagery and ground-based field work has great potential to improve the understanding of the structure and dynamics of old-growth tropical forests having dense understories. These results help scientists understand the proportion of trees in canopy and understory in relation to tree size, the contributions of canopy and understory trees to carbon stocks and wood productivity, and differences in stem growth and size distributions between canopy and understory trees.

Summary
Canopy trees constituted 40% of the inventoried trees with diameter at breast height (DBH) > 10 cm, and accounted for ~70% of aboveground carbon stocks and wood productivity. The probability of being in the canopy increased logistically with tree diameter, passing through 50% at 23.5 cm DBH. Diameter growth was on average twice as large in canopy trees as in understory trees. Growth rates were unrelated to diameter in canopy trees and positively related to diameter in understory trees, consistent with the idea that light availability increases with diameter in the understory but not the canopy. The whole stand size distribution was best fit by a Weibull distribution, whereas the separate size distributions of understory trees or canopy trees > 25 cm DBH were equally well fit by exponential and Weibull distributions, consistent with mechanistic forest models.

Contacts (BER PM): Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact: Jeffrey Chambers, Lawrence Berkeley National Laboratory, jchambers@lbl.gov

Funding
The study was financed by the INCT – Amazonian Woods (FAPEAM/CNPq) and by the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract DE-AC02-05CH11231. Fellowship support for the first author was provided from Coordination for the Improvement of Higher Education Personnel (CAPES).

Publications
Araujo, R.F., J.Q. Chambers, C.H.S. Celes, H.C. Muller-Landau, A.P.F. dos Santos, F. Emmert, G.H.P.M. Ribeiro, B.O. Gimenez, A.J.N. Lima, M.A.A. Campos, N. Higuchi (2020), Integrating high resolution drone imagery and forest inventory to distinguish canopy and understory trees and quantify their contributions to forest structure and dynamics. PLoS ONE 15(12): e0243079. [DOI:10.1371/journal.pone.0243079]

The Science
Soil moisture plays a key role in hydrological, biogeochemical and energy budgets of terrestrial ecosystems. Accurate soil moisture measurements in the Amazon are difficult due to logistical constraints. Realistic soil moisture data in the Amazon are greatly needed for improving our understanding of ecohydrological processes within tropical forests and for improving models of these systems in the face of changing environmental conditions.

The Impact
1. First Time Domain Reflectometers (TDR) soil moisture calibration in an old-growth forest in the Central Amazon.
2. Interannual thirty-minute observations of soil moisture up to 14.2-m depth.
3. The Topp model underestimated volumetric water content by 22 to 42%.
4. Dry season morning-night fluctuation of soil moisture were observed

Summary
Depth-specific Time Domain Reflectometers (TDR) were calibrated using local soils in a controlled laboratory producing a novel calibration. The sensors were later installed to their specific calibration depth in a 14.2 m pit. The widely used Topp model underestimated the site-specific volumetric water content (θv) by 22-42% indicating significant error in the model when applied to these well-structured, clay rich tropical forest soils. The calibrated wet- and dry-season θv data showed a variety of depth and temporal variations highlighting the importance of soil textural differentiation, root uptake depths, as well as event- to seasonal-precipitation effects.

Contacts (BER PM): Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact: Robinson Negron-Juarez, LBNL, Robinson.inj@lbl.gov

Funding
This research was supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, under contract number DE-AC02-05CH11231. Laura Borma would like to acknowledge Go-Amazon (2013/50531-2) for retrofitting the pit structure.

Publications
Negrón-Juárez, S. Ferreira, M. Mota, B Faybishenko,  M. Monteiro, L. Candido, R. Ribeiro, R. de Oliveira, A. de Araujo, J. Warren, B. Newman,  B. Gimenez, C. Varadharajan, D Agarwal, L. Borma, J. Tomasella, N. Higuchi, J. Chambers. Calibration, Measurement and Characterization of Soil Moisture Dynamics in a Central Amazonian Tropical Forest. Vadose Zone Journal, 2020.  DOI:10.1002/vzj2.20070

Related Links
Data available at http://dx.doi.org/10.15486/ngt/1602141