A global team of scientists determines the "footprint" of how much heat and too much drought for forests

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

How hot is too hot, also how dry is too dry for the world's forests? A new study by an international team of researchers has found the answer - looking at trees that have been dead for decades.

The study, just disseminated in the journal Nature Communications, compiles the first global database of properly georeferenced deforestation events at 675 sites from the hot climate conditions and drought of 1970 that led to this documented case of tree death.

"In this study, we let the world's forests do the talking," said William Hammond, a plant ecophysiologist at the University of Florida who led the research. "We collected data from previous studies documenting where and when trees died and then analyzed the climate during death versus long-term conditions.

Hammond noted that after climate analysis of observed forest mortality data, a model emerged.

What we've found is that there are models of getting hotter and drier globally - what we call the "Heater Drought Trail" - that can show us how unusually hot or dry it puts forests at risk of dying out.", Hammond said, assistant professor in the UF/IFAS Department of Agronomy.

Fingerprints, he said, show that deaths continue to occur in the forest when typically the hottest and driest months of the year become warmer and drier.

"Our fingerprints of hotter droughts have shown that global forest mortality is associated with increased extreme weather conditions," Hammond said. "Using climate data, we calculated how common these pre-fatal climatic conditions were with additional warming compared to pre-industrial climates 22% more common at plus 2 degrees Celsius (plus 3.6 degrees Fahrenheit). Up to 140% more common at temperatures plus 4 degrees Celsius (plus 7.2 degrees Fahrenheit).