NGEE-Tropics is a ten-year, multi-institutional project funded by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research (BER) and focused on transforming the way Earth system models function to depict how tropical forests will respond to changing environmental drivers on timescales of hours to centuries, and from tree leaves to entire canopies, and individual trees to entire regions. The project’s grand deliverable is an advanced tropical forest ecosystem model–the Functionally Assembled Terrestrial Ecosystem Simulator (FATES)–that will enable modeling these ecosystems at the scale and resolution of a next-generation state-of-the-science Earth System Model (ESM). An integral part of DOE’s Energy Exascale Earth System Model (E3SM), FATES enables modeling of the evolution and feedbacks of tropical ecosystems from bedrock to the top of the vegetative canopy-atmosphere interface in a changing Earth system at the scale and resolution of a next generation Earth System Model (ESM) grid cell, particularly DOE Energy Exascale Earth System Model (E3SM).
NGEE Tropics work in Phase 1 revealed several high-priority areas for model development, evaluation, and parameterization. This work has led to three Research Focus Areas (RFAs) for Phase 2 (2020-2023) to advance understanding and E3SM-FATES representation of processes at the individual (RFA1), community to regional (RFA2), and regional and global scales (RFA3). The science within these three RFAs is organized into 12 model-experimental integration (ModEx) Work Packages (WP). Each WP is tightly integrated to existing model code within E3SM-FATES, or is focused on new process representation to enable coordinated model development and evaluation. E3SM-FATES resides at the center of this organizational structure and serves as the unifying platform for the project, enabling integration of scientific advances across the three RFAs toward addressing our key science questions and hypotheses.
Over the next few years during Phase 2 the project team will further develop and strengthen our use of FATES within E3SM as the central modeling framework integrating our research. Continued FATES-model development and testing will be motivated by several high-priority model uncertainties identified during Phase 1, along with the activities and data required to address those uncertainties. Specifically, we will focus on improving and evaluating the model’s ability to represent key mechanisms predicting tropical forest response to drought, warming, and disturbance. In view of the importance of nutrient limitation for tropical forest dynamics, a new modeling capability for nutrient dynamics will be added to FATES. Model development, testing, and application will take place at sites in Puerto Rico, Panama, and the Amazon Basin, and additional pantropical sites will be utilized to take advantage of logistical infrastructure including canopy access (Lambir Hills and Daintree), an ongoing ecosystem-scale drought experiment (Daintree), and pantropically distributed forest-dynamics plots across the tropics (with our ForestGEO partners).
Three Research Focus Areas, Three Overarching Questions
RFA1: Climate change effects on tree function, stress response, and mortality. How do drought and elevated temperature impact tree physiology and mortality?
RFA2: Forest structure and functional composition along environmental gradients. How do forest structure and functional composition vary in response to plant available water, soil fertility, and disturbance regimes?
RFA3: Tropical forests and coupled Earth system processes. How do precipitation recycling and the seasonal timing of precipitation respond to changes in climate and forest structure?
Within RFA1, researchers are evaluating tropical forest ecosystem processes at the scale of individual plants and plant cohorts, including their varying response to stressors such as drought and temperature as determined by differences in plant functional traits and life-history strategies. RFA2 will be organized around competitive dynamics among cohorts for limiting resources at the site scale that enable simulation of emergent forest communities with functional assembly that varies with changing environmental conditions. The RFA3 level comprises fully integrated processes in E3SM, including linkages among vegetation, soil hydrology, and water-table dynamics; the large-scale forest-atmosphere coupling of water, carbon, and energy; and the potential for biome-boundary transitions (e.g., forest-savanna).
Figure. Describes the organizational work flow of NGEE-Tropics Phase 2 science objectives.
Modex Work Package for Each RFA
We recognize that developing models to produce robust predictions of tropical forest response to global change will require strong collaborations between modeling and measurement scientists, as exemplified by the concept of model-experimental integration (ModEx). ModEx requires that experiments and observational studies are designed to address specific modeling gaps, and that evaluation of those new model structures inform additional measurement activities in an iterative manner. This approach will be central to the NGEE-Tropics enterprise, focused on those processes where uncertainties most strongly control model response, and are most critical for determining the fate of the tropical forest carbon sink over the next 100 years.
Phase 2 research is structured into a set of three Research Focus Areas (RFAs), each with associated ModEx Work Packages (WPs) which constitute sets of tasks with clearly identified milestones and deliverables, and associated science advances. This structure, with each WP linked to specific FATES or E3SM code to be developed or tested, is designed so that integration within and among RFAs will result in a number of high-impact outcomes. As appropriate, activities within WPs will apply emerging E3SM-FATES capabilities to high-priority science questions, model evaluation at site to regional scales, and new model developments required to enable future science advances. WPs also include data processing and synthesis tasks, and field and laboratory activities to generate essential new data.
NGEE-Tropics has a pantropical scope, engaging in research and data collection across the globe, with specific research activities during Phase 2 underway at three primary locations: Puerto Rico, Panama, and the Amazon Basin, and additional pantropical sites, including a network of forest dynamics plots, to supplement these sites with essential datasets. Site selection balances scientific needs with logistical and infrastructural requirements including canopy access and ongoing ecosystem-scale manipulations.
Puerto Rico: Sabana, El Verde, Icacos
Panama: Barro Colorado Island (BCI), Parque Natural Metropolitano (PNM), San Lorenzo (SLZ) [Formerly Fort Sherman (FTS)], Agua Salud (forest and pasture catchments)
Brazil: National Institute for Amazon Research (INPA) ZF2 site
Malaysia: Lambir Hills
Australia: Daintree Rainforest Observatory
French Guiana: Paracou
Modeling and Integration Framework
During Phase 1, we developed FATES as a vegetation module within DOE’s Energy Exascale Earth System Model (E3SM). FATES is a size-structured vegetation model that represents the dynamics of cohorts of trees grouped by plant functional type (PFT), size, and successional age, and resolves disturbance processes vital for the maintenance of functional diversity and forest structure. At the plant cohort level, FATES resolves key physiological processes of photosynthesis, respiration, phenology, carbon allocation, root water uptake, water transport through the plant, and transpiration. At the community level, the model simulates light and water competition among cohorts of different tree sizes and PFTs, with forest composition and function as emergent properties. At the regional scale, coupled E3SM-FATES enables us to explore climate feedbacks from forest structure and functional changes.
By enabling size structure representation of forest demography in this way, FATES can explore ecological dynamics at scales up to that of the planet, but informed by data at the scale of individual trees and the ecosystem. During Phase 1, key goals included building and testing the FATES basic framework, and developing a plant hydrodynamic module (FATES-Hydro, now integrated into FATES) for testing process representation directly against measurements made during NGEE-Tropics field campaigns. For Phase 2, we will continue working to test FATES against observations, improve process fidelity, further explore and test FATES ecological dynamics, build new process representation with a particular focus on vegetation nutrient cycling, and explore the use of E3SM-FATES to address science questions of the coupled vegetation-atmosphere system across multiple scales.
Data Synthesis and Management Framework
NGEE-Tropics is committed to publicly sharing our data and model code following our data and software policy. The primary objective for NGEE-Tropics’ Data Synthesis and Management Framework is to provide support for team members to share and preserve their data for use within the project to a lasting publicly available legacy of NGEE-Tropics data, while complying with DOE’s Climate and Environmental Sciences Division and DOE Office of Science Digital Data Management Requirements. Data generated by the NGEE-Tropics project will need to be properly managed, and the NGEE-Tropics Archive is designed to provide curation, QA/QC, and archiving and public release of project data. Data will also be stored in a long-term repository (ESS-DIVE) using standardized formats to preserve the data legacy of NGEE Tropic beyond the lifetime of the project and enable data reuse.