Global team of scientists determine 'fingerprint' for how much heat,
drought is too much for forests
The authors conclude that limiting Earth's warming will determine survivability for many of Earth's forests
Date:
April 5, 2022
Source:
University of Florida
Summary:
A new study has compiled a global database of climate-induced
forest die- off events, from 1970-2018, across 675 locations. After
analyzing the climate conditions at each location during each
event, researchers found a common 'hotter-drought fingerprint'
for Earth's forests, a term that describes the combination of
higher temperatures and more frequent droughts for a lethal set
of climate conditions. Under further warming, this hotter-drought
fingerprint will appear more frequently -- the authors conclude
that limiting Earth's warming will determine survivability for
many of Earth's forests.
FULL STORY ==========================================================================
How hot is too hot, and how dry is too dry, for the Earth's forests? A
new study from an international team of researchers found the answers --
by looking at decades of dying trees.
==========================================================================
Just published in the journal Nature Communications, the study compiles
the first global database of precisely georeferenced forest die-off
events, at 675 locations dating back to 1970. The study, which encompasses
all forested continents, then compares that information to existing
climate data to determine the heat and drought climatic conditions that
caused these documented tree mortality episodes.
"In this study, we're letting the Earth's forests do the talking,"
said William Hammond, a University of Florida plant ecophysiologist
who led the study. "We collected data from previous studies documenting
where and when trees died, and then analyzed what the climate was during mortality events, compared to long- term conditions." After performing
the climate analysis on the observed forest mortality data, Hammond noted,
a pattern emerged.
"What we found was that at the global scale, there was this consistently hotter, drier pattern -- what we call a 'hotter-drought fingerprint'
-- that can show us how unusually hot or dry it has to get for forests
to be at risk of death," said Hammond, an assistant professor in the
UF/IFAS agronomy department.
The fingerprint, he says, shows that forest mortality events consistently occurred when the typically hottest and driest months of the year got
even warmer and drier.
==========================================================================
"Our hotter-drought fingerprint revealed that global forest mortality is
linked to intensified climate extremes," Hammond said. "Using climate
model data, we estimated how frequent these previously lethal climate conditions would become under further warming, compared to pre-industrial
era climate -- 22% more frequent at plus 2 degrees Celsius (plus 3.6
degrees Fahrenheit), to 140% more frequently at plus 4 degrees Celsius
(plus 7.2 degrees Fahrenheit)." Those higher temperatures would more
than double how often forests around the world see tree-killing droughts,
he adds.
"Plants do a phenomenal job of capturing and sequestering carbon,"
Hammond said. "But death of the plants not only prevents their performing
this critical carbon-capturing role, plants also start releasing carbon
as they decay." Hammond says that relying, in part, upon trees and
other plants to capture and sequester carbon, as some proposed climate solutions suggest, makes it is critical to understand how hot is 'too
hot,' and how dry is 'too dry.' "Otherwise mortality events, like
those included in our database, may wipe out planned carbon gains."
One of the study's co-authors, Cuauhte'moc Sa'enz-Romero of Universidad Michoacana de San Nicola's de Hidalgo in Mexico, offered an example of
how recent climate patterns affected a Mexican temperate forest.
==========================================================================
"In recent years, the dry and warm March to May season is even more dry
than usual, but also warmer than ever," he said. "This combination is
inducing a lot of stress on the trees before the arrival of the next June-to-October rainy season. For example, in 2021, more than 8,000
mature trees were killed by bark beetles in the Monarch Butterfly
Biosphere Reserve in Central Mexico. The effect of the La Nin~a Pacific
Ocean stream resulted in drier, warmer conditions; a deadly combination
that favored pest outbreaks." Hammond has also developed an interactive application on the website of the International Tree Mortality Network
to host the database online and to allow others to submit additional observations of forest mortality to the database.
The organization, founded and coordinated by co-author Henrik
Hartmann from the Max Planck Institute in Germany, among others, is
a collaborative effort between scientists on every forested continent
and aims to coordinate international research efforts on forest die-off
events. Hammond is the network's data management group leader.
Glossary 'Georeferenced' Using maps or aerial images, scientists assign
to them real-world coordinates.
'Ground-truthed' Information confirmed or validated by direct observation
and measurement. In the case of machine learning, it refers to checking
results for accuracy.
"We're hoping that this paper will create a bit of urgency around the
need to understand the role of warming on forest mortality," Hammond
said. "Also, we expect that our open-access database will enable
additional studies, including other climate fingerprints from local to
regional scales. Current climate modeling and remote-sensing research communities need ground-truthed datasets to validate their predictions
of important processes like forest mortality. One of the really important elements to this study was bringing all this data together for the first
time, so that we can ask a question like this at the planetary scale."
========================================================================== Story Source: Materials provided by University_of_Florida. Original
written by Kirsten Romaguera. Note: Content may be edited for style
and length.
========================================================================== Related Multimedia:
* Historical_forests_of_Atlas_Cedar_in_Morocco ========================================================================== Journal Reference:
1. William M. Hammond, A. Park Williams, John T. Abatzoglou, Henry
D. Adams,
Tamir Klein, Rosana Lo'pez, Cuauhte'moc Sa'enz-Romero, Henrik
Hartmann, David D. Breshears, Craig D. Allen. Global field
observations of tree die-off reveal hotter-drought fingerprint
for Earth's forests. Nature Communications, 2022; 13 (1) DOI:
10.1038/s41467-022-29289-2 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220405084607.htm
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