News

3/13/2017 – Scott Saleska joins 30 Climate Scientists in letter correcting EPA chief Scott Pruitt

30 leading scientists (led by Nobel laureate Mario Molina, and including 3 from U. of Arizona: Scott Saleska, Jonathan Overpeck, Joellen Russell) respond to EPA chief Scott Pruitt’s doubt that human-emitted CO2 is a cause of warming.

The letter notes that “focusing on disagreements over details, or among a few individuals on the margins of consensus, or on the uncertainties that are part of any accurate statement of scientific knowledge, misses the big picture: human beings are changing the Earth’s climate.  This key conclusion follows from the basic laws of physics. Just as there is no escaping gravity when one steps off a cliff, there is no escaping the warming that follows when we add extra carbon dioxide and other greenhouse gases to the atmosphere

See coverage in the Washington Post and Inside Climate News.

The full text of scientists’ letter is here.

3/2/2017: From our friends in Manaus: plant community composition tells of influences of pre-columbian humans on Amazonian forests

Paper in 3 March 2017 issue of Science:  Persistent effects of pre-Columbian plant domestication on Amazonian forest composition

Ph.D. student Carolina Levis and her mentor Flávia Costa, both at Brazil’s National Institute for Amazonian Research (INPA), lead 100+ authors in this novel analysis of the massive database of tree surveys previously assembled by Hans ter Steege and colleagues. Their conclusions (published in the March 3 issue of Science): “modern tree communities in Amazonia are structured to an important extent by a long history of plant domestication by Amazonian peoples”

See the news item in Science:  Hundreds of years later, plants domesticated by ancient civilizations still dominate in the Amazon.

 

 

 

1/26/17 – Rick Wehr’s work with Roisin Commane, using carbonyl sulfide as a tracer of forest canopy conductance & transpiration, is out in Biogeosciences

Dynamics of canopy stomatal conductance, transpiration, and evaporation in a temperate deciduous forest, validated by carbonyl sulfide uptake

by Richard Wehr, Róisín Commane, J. William Munger, J. Barry McManus, David D. Nelson, Mark S. Zahniser, Scott R. Saleska, and Steven C. Wofsy


We used measurements of carbonyl sulfide, a structural analog to CO2 that is also taken up by leaves, as a tracer to validate measurements of the transpiration and evaporation of a whole forest canopy over time.  We discovered, surprisingly, that evaporation peaks at the time of year when the soil is dry and the air is moist. This pattern turns out to make physical sense but is not captured by current ecosystem models. Transpiration and evaporation were extracted from the total ecosystem-atmosphere water vapor exchange using estimates of stomatal conductance obtained by two independent, accordant methods: one based on measurements of the water and sensible heat fluxes coming from the forest, and the other based on the aforementioned measurements of the carbonyl sulfide flux into the forest.

1/3/2017 Rick Wehr’s work on the long-solved problem of the best-fit straight line is out in Biogeosciences

The long-solved problem of the best-fit straight line:application to isotopic mixing lines

by Richard Wehr and Scott Saleska

Scientists in a wide variety of disciplines are commonly confronted with the problem of how to fit a straight line to data points that were measured with uncertainty in both X and Y. Much of the scientific literature gives the impression that this is an unsolved problem, but it was actually solved in 1969 by a geophysicist named Derek York — a fact widely known among geoscientists but almost unknown in other fields. Our paper spreads the news about York’s solution and demonstrates its application in the interesting case of the isotopic mixing line, an analytical tool widely used to determine the isotopic signature of trace gas sources for the study of biogeochemical cycles.

7/6/2016 – Jin Wu’s work on tropical leaf traits, spectra and age out in New Phytologist

Convergence in relationships between leaf traits, spectra and age across diverse canopy environments and two contrasting tropical forests

by Jin Wu, Cecilia Chavana-Bryant, Neill Prohaska, Shawn P. Serbin, Kaiyu Guan, Loren P. Albert, Xi Yang, Willem J. D. van Leeuwen, Anthony John Garnello, Giordane Martins, Yadvinder Malhi, France Gerard, Raimundo Cosme Oliviera, and Scott R. Saleska

Leaf age structures the phenology and development of plants, as well as the evolution of leaf traits over life histories. However, a general method for efficiently estimating leaf age across forests and canopy environments is lacking.  Here, we showed that leaf spectra can predict leaf ages from leaf reflectance spectra across two contrasting forests in Peru and Brazil and across diverse canopy environments.   This work suggests that fundamental rules link leaf traits to leaf environments, and constrain the development of optically-detectable leaf traits and allow for general prediction of leaf age from spectra across species, sites and canopy environments.

6/29/2016 – Rick Wehr’s research on isotopic partitioning of NEE is out in Nature

Article title:  Seasonality of temperate forest photosynthesis and daytime respiration

Overturning textbook knowledge, Rick Wehr from the Saleskalab, working with colleagues from Harvard University, Woods hole, and Aerodyne research, discovered that the trees “exhale” (or respire) less carbon dioxide during the day than previously thought, and that forest photosynthesis doesn’t decline over the course of the summer. The results close a longstanding gap in our understanding of the carbon cycling between terrestrial ecosystems and the atmosphere and could be useful in making more accurate models to predict the long-term effects of global climate change. Our superb team on this paper included Bill Munger and Steve Wofsy from Harvard University, Eric Davidson from University of Maryland, and Barry McManus, David Nelson and Mark Zahniser all from Aerodyne Research.

To read the article here (or click on the title above): http://www.nature.com/nature/journal/v534/n7609/full/nature17966.html

EurekAlert!, June 29, 2016: http://www.eurekalert.org/pub_releases/2016-06/uoa-waf062716.php

 

3/17/2016: We debate Doug Morton & Co in Nature on “Dry-season greening of Amazon forests”

Our bottom line:  “the primary substantive finding of Morton et al. of consistent canopy structure and greenness is incorrect.”  (Saleska et al., 2016)


Two years ago, Morton et al (2014) published “Amazon forests maintain consistent canopy structure and greenness during the dry season” in Nature, criticizing as an artifact the remote sensing observation that (as we wrote in an article led by Alfredo Huete in GRL in 2006) “Amazon rainforests green-up with sunlight in dry season“.

Our position:  Technical corrections for artifacts adjust the magnitude of Amazon forest seasonality downwards, relative to what they used to be, but on the basic ecology, Huete et al (2006) was basically right, and Morton et al (2014) is basically wrong.  See the latest round of our debate in the March 17, 2016 issue of Nature (including Morton et al’s response) under the heading “Dry-season greening of Amazon forests” in the “Brief communications arising” section here (paywall).

Want to know more?  See our article published in Science last month (February, 2016):  Wu, Albert et al. (2016) Leaf development and demography explain photosynthetic seasonality in Amazon evergreen forests.

 

2/26/2016: Saleska Lab gets the cover of Science with paper by Jin Wu, Loren Albert, et al.

Screen Shot 2016-02-26 at 1.38.35 PMArticle title: Leaf development and demography explain photosynthetic seasonality in Amazon evergreen forests.  The analyses are reported in this week’s issue of Science (Feb 26, 2016) in a paper led by recent Saleska Lab graduate, Dr. Jin Wu, current graduate student Loren Albert, and INPA (Manaus) student Aline Lopes (advised by our INPA collaborator Bruce Nelson).

We used special tower-mounted cameras to discover that synchronization of the birth and death of leaves in evergreen forest trees across broad areas of the Brazilian Amazon is the cause of strong seasonal increases and decreases in overall tropical forest photosynthesis. These findings about how forests regulate their seasonal “breathing in” of atmospheric carbon dioxide will help scientists better understand how climate influences these forests and more accurately predict how these forests will respond to future climate change.

Our fantastic team included 5 other current and former Saleskalab members — Natalia Restrepo-Coupe, Kenia Wiedemann (now a post-doc at Harvard), Scott Stark (faculty at MSU), Brad Christoffersen (post-doc at Los Alamos lab), and Neill Prohaska (Ph.D. student) — and an international collaborators from Brazil led by Rodrigo da Silva (UFOPa, Santarem) and Paulo Brando (IPAM).

 

Find the article here: http://science.sciencemag.org/content/351/6276/972

Report in the University of Arizona news: https://uanews.arizona.edu/story/seasonal-changes-in-amazon-photosynthesis-explained

Relatório em Português no site do INPA (Instituto Nacional de Pesquisas da Amazônia): http://portal.inpa.gov.br/index.php/component/content/article?id=2410

Report by the National Science Foundation: http://1.usa.gov/1Ta8Qcj