BER launches Environmental System Science Program. Visit our new website under construction!

U.S. Department of Energy Office of Biological and Environmental Research

BER Research Highlights


A Challenging Future for Tropical Forests
Published: February 16, 2018
Posted: March 07, 2018

Mortality rates of moist tropical forests are on the rise due to environmental drivers and related mechanisms.

The Science
Moist tropical forests are the largest terrestrial carbon sink in the world and house most of Earth's terrestrial biodiversity. However, climatic and ecological benefits of intact moist tropical forests face the threat of increasing tree mortality due to environmental and biotic changes. A Pacific Northwest National Laboratory scientist led a study to determine the risks of increasing tropical forest tree mortality. In this study, scientists reviewed the state of knowledge regarding moist tropical forest tree mortality. They created a conceptual framework with testable hypotheses regarding the drivers, mechanisms, and interactions that may underlie increasing mortality rates of moist tropical forests. The research team then identified next steps for improved understanding and reduced predictive uncertainty.

The Impact
Researchers found that mortality rates of trees in moist tropical forests are increasing as the drivers and mechanisms of tree mortality—such as temperature, drought, and carbon dioxide (CO2)—continue to rise. These effects are expected to continue increasing under future environmental conditions, with serious consequences to Earth's carbon cycle.

Summary
Tropical forests absorb a significant amount of atmospheric CO2. Tree death reverses this process by shutting off photosynthesis and increasing carbon release (from dead wood), leaving more CO2 in the atmosphere. Increasing tree mortality rates observed over the past few decades in moist tropical forests are associated with rising temperature, vapor pressure deficit, liana (woody vine) abundance, drought, wind events, fire, and possibly CO2 fertilization–induced increases in stand thinning. Most of these mortality drivers ultimately kill trees in part through carbon starvation and hydraulic failure, though the relative importance of each driver is unknown. Ecosystems with greater diversity may buffer tropical forests against large-scale mortality events, but recent and expected trends in mortality drivers are likely to continue or increase. Model predictions of tropical tree mortality are rapidly improving, but they require more empirical knowledge regarding the most common drivers and their subsequent mechanisms. This study identified critical hypotheses, datasets, and model developments required to quantify the underlying causes of increasing mortality rates and to improve predictions of future mortality and carbon storage consequences under environmental change.

Contacts
BER Program Manager
Dan Stover
Terrestrial Ecosystem Science, 23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Nate McDowell
Pacific Northwest National Laboratory
Richland, WA 99354
nate.mcdowell@pnnl.gov

Funding
This manuscript is the product of the workshop “Tropical forest mortality” held in Santa Fe, New Mexico, in 2015. The U.S. Department of Energy Office of Science supported the workshop and the writing of the manuscript as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project.

Publication
N.G. McDowell et al., “Drivers and Mechanisms of Tree Mortality in Moist Tropical Forests.” New Phytologist (early view, February 16, 2018) 219(3), 851–869 (2018). [DOI:10.1111/nph.15027].

Topic Areas:

  • Research Area: Earth and Environmental Systems Modeling
  • Research Area: Carbon Cycle, Nutrient Cycling
  • Research Area: Next-Generation Ecosystem Experiments (NGEE)

Division: SC-33.1 Earth and Environmental Sciences Division, BER

 

BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER

Recent Highlights

Mar 23, 2021
Molecular Connections from Plants to Fungi to Ants
Lipids transfer energy and serve as an inter-kingdom communication tool in leaf-cutter ants&rsqu [more...]

Mar 19, 2021
Microbes Use Ancient Metabolism to Cycle Phosphorus
Microbial cycling of phosphorus through reduction-oxidation reactions is older and more widespre [more...]

Feb 22, 2021
Warming Soil Means Stronger Microbe Networks
Soil warming leads to more complex, larger, and more connected networks of microbes in those soi [more...]

Jan 27, 2021
Labeling the Thale Cress Metabolites
New data pipeline identifies metabolites following heavy isotope labeling.

Analysis [more...]

Aug 31, 2020
Novel Bacterial Clade Reveals Origin of Form I Rubisco
Objectives

  • All plant biomass is sourced from the carbon-fixing enzyme Rub [more...]

List all highlights (possible long download time)