An international team of researchers carried out a study to determine the heat and moisture threshold for Earth’s forests. Published in Nature Communications, the study answers “how hot is too hot” and “how dry is too dry” for forests. To do this, researchers compiled the first global database of georeferenced forest die-off events at over 675 locations dating to the 1970s.
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The study covered all forested continents and compared the information to existing climate data to determine the climatic conditions behind three major mortality episodes. Lead author William Hammond, a University of Florida plant ecophysiologist, says the analysis allows the forests to speak for themselves based on historical occurrences. “In this study, we’re letting the Earth’s forests do the talking,” said Hammond “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.”
According to Hammond, an analysis of the previous forest mortality events revealed a pattern. The pattern shows that Earth’s forests face the highest mortality risk during extremely hot periods. “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.
While every year has hotter months and colder ones, some years are much hotter than others. During these hotter years, Earth’s forests face higher risks of combustion.
“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).”
One finding showed that as the planet warms, the frequency of such extremes increases. This increase further threatens forests’ safety. Especially considering trees’ roles in carbon sequestering, monitoring forest temperatures could help prevent them from getting dry enough for destruction.
Lead image via Pexels