Global team of scientists determine ‘fingerprint’ for how much heat, drought is too much for forests – Watts Up With That?

The authors conclude that limiting global warming will determine the survival of many of the Earth’s forests.

Peer-reviewed publication

UNIVERSITY OF FLORIDA

IMAGE: TAKEN IN 1993, THIS PHOTO SHOWS THE MORTALITY OF HISTORIC ATLAS CEDAR FORESTS IN MOROCCO. see more
CREDIT: MÁTYÁS CSABA, PROFESSOR EMERITUS, SOPRON UNIVERSITY, HUNGARY

How hot is too hot and how dry is too dry for Earth’s forests? A new study by an international team of researchers found the answers by looking at decades of dying trees.

Just published in the magazine 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 covers all forested continents, then compares that information with existing climate data to determine conditions climatic conditions of heat and drought that caused these documented episodes of tree mortality.

“In this study, we’re letting Earth’s forests do the talking,” said William Hammond, a plant ecophysiologist at the University of Florida who led the study. “We collected data from previous studies documenting where and when trees died, and then looked at what the weather was like during mortality events, compared to long-term conditions.”

After performing climatic analysis of the observed forest mortality data, Hammond noted, a pattern emerged.

“What we found was that, on a global scale, there was this consistently warmer and drier pattern, what we call a ‘warmer drought fingerprint,’ which can show us how unusually warm or dry it has to be for forests to be in risk. of death,” said Hammond, an assistant professor in the UF/IFAS department of agronomy.

The fingerprint, he says, shows that forest mortality events consistently occurred when the typically hottest and driest months of the year became even hotter and drier.

“Our hottest drought fingerprint revealed that global forest mortality is related to intensified climate extremes,” Hammond said. “Using climate model data, we estimated how often these previously lethal climate conditions would become with increased warming, compared to the pre-industrial climate: 22% more frequent at plus 2 degrees Celsius (plus 3.6 degrees Fahrenheit), to 140% more frequent at plus 4 degrees Celsius (plus 7.2 degrees Fahrenheit).

Those higher temperatures would more than double the frequency with which forests around the world experience tree-killing droughts, it adds.

“Plants do a phenomenal job of capturing and sequestering carbon,” Hammond said. “But not only does the death of plants prevent them from performing this critical carbon sequestration function, the plants also begin to release carbon as they decompose.”

Hammond says that relying, in part, on trees and other plants to capture and sequester carbon, as some proposed climate solutions suggest, makes it critical to understand how hot is “too hot” and how dry is “too dry.” “Otherwise, mortality events, such as those included in our database, can wipe out planned carbon gains.”

One of the study’s co-authors, Cuauhtémoc Sáenz-Romero of the Universidad Michoacana de San Nicolás de Hidalgo in Mexico, offered an example of how recent weather patterns affected a Mexican temperate forest.

“In recent years, the hot dry season from March to May is even drier than usual, but also hotter than ever,” he said. “This combination is putting a lot of stress on the trees ahead of the next rainy season from June to October. 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 Niña Pacific Ocean current resulted in drier and warmer conditions; a deadly combination that favored plague outbreaks.”

Hammond has also developed an interactive application on the International Tree Mortality Network website to host the online database and allow others to submit additional tree mortality observations to the database.

EXPLANATIONS

‘Georeferenced’

Using maps or aerial images, scientists assign real-world coordinates to them.

‘ground verified’

Information confirmed or validated by direct observation and measurement. In the case of machine learning, it refers to verifying the accuracy of the results.

The organization, founded and coordinated by co-author Henrik Hartmann of the Max Planck Institute in Germany, among others, is a collaborative effort between scientists from all forested continents and aims to coordinate international research efforts on forest extinction events. Hammond is the group leader for network data management.

“We hope that this paper will create a bit of urgency around the need to understand the role of warming in forest mortality,” Hammond said. “In addition, we hope that our open access database will enable further studies, including other climate fingerprints from local to regional scales. Today’s remote sensing and climate modeling research communities need ground-verified datasets to validate their predictions of important processes such as forest mortality. One of the really important elements of this study was bringing all this data together for the first time, so that we can ask a question like this on a planetary scale.”

The paper, “Global Field Observations of Tree Death Reveal Fingerprints of Hotter Drought for Earth’s Forests,” will be available at nature.com/articles/s41467-022-29289-2. In addition to Hammond, Sáenz-Romero, and Hartmann, he is also a co-author with A. Park Williams, University of California, Los Angeles; John Abatzoglou, University of California, Merced; Henry D. Adams, Washington State University; Tamir Klein, Weizmann Institute of Sciences; Rosana López, Polytechnic University of Madrid, Spain; David D. Breshears, University of Arizona; and Craig D. Allen, University of New Mexico.

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DAILY

nature communications

DOI

10.1038/s41467-022-29289-2

RESEARCH METHOD

Data/statistical analysis

OBJECT OF INVESTIGATION

Does not apply

ARTICLE TITLE

Global field observations of tree dieback reveal fingerprint of hottest drought for Earth’s forests

ARTICLE PUBLICATION DATE

5-Apr-2022

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