Increased heat and drought stunt tropical trees, a major carbon sink


Date:
March 31, 2022
Source:
University of Arizona
Summary:
For a long time, ecologists assumed tree rings to be absent
in tropical trees because of a lack of temperature and rain
fluctuations in the trees' environment. But in recent decades, the
formation of growth rings has been proven for hundreds of tropical
tree species, which are sensitive to drought and usually experience
at least a month or two of slightly reduced rainfall every year.



FULL STORY ==========================================================================
For a long time, ecologists assumed tree rings to be absent in tropical
trees because of a lack of temperature and rain fluctuations in the trees' environment. But in recent decades, the formation of growth rings has
been proven for hundreds of tropical tree species, which are sensitive
to drought and usually experience at least a month or two of slightly
reduced rainfall every year.


==========================================================================
When scientists better understand how tropical trees respond to unusually
dry and warm conditions, they can better predict how these trees will
be affected by climate change.

A new study, co-authored by University of Arizona researchers and
published in Nature Geoscience, has found that tropical trees' trunk
growth is reduced in years when the dry season is drier and warmer
than normal. The study defines the tropics in a way that also includes
the subtropics -- or anything between 30 degrees north latitude and 30
degrees south latitude.

The researchers also found that the effect of drier and warmer years is
more dramatic in more arid or warm regions in the tropics. This suggests
that climate change may increase the sensitivity of tropical trees to
climatic fluctuations. Temperatures at the study sites are expected to
increase by half a degree Celsius per decade in the future.

The results of the study help explain the large fluctuations in carbon
uptake by tropical vegetation globally. Model simulations show that during hotter or drier years, tropical vegetation grows less and therefore takes
up less carbon dioxide from the atmosphere. But actual measurements of vegetation growth have been lacking until now.

Research shows that slower growth increases the risk of topical tree
death, so tropical vegetation may more frequently become a source of
carbon dioxide instead of absorbing this greenhouse gas that causes
climate change.



========================================================================== "These (tropical) tree rings contain a wealth of information on the growth history of trees," said lead study author Pieter Zuidema of Wageningen University & Research in the Netherlands. "In this study, we exploit
that potential. For the first time, we get a pantropical picture of how tropical tree growth reacts to climate fluctuations." The study was an international collaborative effort that included University of Arizona dendrochronology Valerie Trouet, a professor in the Laboratory of Tree-
Ring Research, and Flurin Babst, an assistant research professor in the UArizona School of Natural Resources and the Environment. The findings
are based on a new global network, created by the collaborators, of over
14,000 tree-ring data series from 350 locations across 30 tropical and sub-tropical countries.

The authors were surprised to find that during the dry season, climate
had a stronger effect on tree growth than during the wet season.

"We know that photosynthesis and wood production of tropical trees
generally peak during the wet season," Trouet said. "So, why do
year-to-year fluctuations in trunk growth depend on the dry season? That surprised and puzzled us. Our explanation is that water is available
for a longer period of time during years with wetter or cooler dry
seasons. Put simply, the growing season is longer.

This then leads to more trunk growth." The study also fills an important
gap in tree-ring data.

"World maps showing the locations of tree-ring studies typically have a
hole in the middle, in the tropics," Zuidema said. "Our network fills
that tropical data gap." The tree-ring data from more than 100 study
locations has been uploaded to the International Tree-ring Databank,
the global database for tree-ring data.

"In this way, the tree-ring data we've put together will be freely
available for everyone," Zuidema said.


========================================================================== Story Source: Materials provided by University_of_Arizona. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Pieter A. Zuidema, Flurin Babst, Peter Groenendijk, Valerie Trouet,
Abrham Abiyu, Rodolfo Acun~a-Soto, Eduardo Adenesky-Filho,
Raquel Alfaro- Sa'nchez, Jose' Roberto Vieira Araga~o, Gabriel
Assis-Pereira, Xue Bai, Ana Carolina Barbosa, Giovanna Battipaglia,
Hans Beeckman, Paulo Cesar Botosso, Tim Bradley, Achim Bra"uning,
Roel Brienen, Brendan M. Buckley, J. Julio Camarero, Ana Carvalho,
Grego'rio Ceccantini, Librado R.

Centeno-Erguera, Julia'n Cerano-Paredes, A'lvaro Agusti'n
Cha'vez-Dura'n, Bruno Barc,ante Ladvocat Cintra, Malcolm
K. Cleaveland, Camille Couralet, Rosanne D'Arrigo, Jorge Ignacio
del Valle, Oliver Du"nisch, Brian J.

Enquist, Karin Esemann-Quadros, Zewdu Eshetu, Ze-Xin Fan, M. Eugenia
Ferrero, Esther Fichtler, Claudia Fontana, Kainana S. Francisco,
Aster Gebrekirstos, Emanuel Gloor, Daniela Granato-Souza, Kristof
Haneca, Grant Logan Harley, Ingo Heinrich, Gerd Helle, Janet
G. Inga, Mahmuda Islam, Yu-mei Jiang, Mark Kaib, Zakia Hassan
Khamisi, Marcin Koprowski, Bart Kruijt, Eva Layme, Rik Leemans,
A. Joshua Leffler, Claudio Sergio Lisi, Neil J. Loader, Giuliano
Maselli Locosselli, Lidio Lopez, Mari'a I.

Lo'pez-Herna'ndez, Jose' Lui's Penetra Cerveira Lousada, Hooz A.

Mendivelso, Mulugeta Mokria, Valdinez Ribeiro Monto'ia, Eddy Moors,
Cristina Nabais, Justine Ngoma, Francisco de Carvalho Nogueira
Ju'nior, Juliano Morales Oliveira, Gabriela Morais Olmedo, Mariana
Alves Pagotto, Shankar Panthi, Gonzalo Pe'rez-De-Lis, Darwin
Pucha-Cofrep, Nathsuda Pumijumnong, Mizanur Rahman, Jorge Andres
Ramirez, Edilson Jimmy Requena- Rojas, Adauto de Souza Ribeiro,
Iain Robertson, Fidel Alejandro Roig, Ernesto Alonso Rubio-Camacho,
Ute Sass-Klaassen, Jochen Scho"ngart, Paul R. Sheppard, Franziska
Slotta, James H. Speer, Matthew D. Therrell, Benjamin Toirambe,
Mario Tomazello-Filho, Max C. A. Torbenson, Ramzi Touchan, Alejandro
Venegas-Gonza'lez, Ricardo Villalba, Jose Villanueva- Diaz, Royd
Vinya, Mart Vlam, Tommy Wils, Zhe-Kun Zhou. Tropical tree growth
driven by dry-season climate variability. Nature Geoscience, 2022;
DOI: 10.1038/s41561-022-00911-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220331134223.htm

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