Short-lived but severe climatic events, such as droughts, can trigger cascades of ecosystem change that last for centuries, according to a recent study.
According to the United States Department of Agriculture, more than 40 percent of the western U.S. is in a drought that is deemed "severe" or "exceptional." The same was true in 2013. In 2012, drought even spread to the humid east.
Researchers found that some of the most compelling evidence of how ecosystems respond to drought and other challenges can be found in the trunks of trees. They found that climatic events can cause seemingly stable forests to abruptly change within the next century.
"Trees are great recorders of information," Dave Orwig, an ecologist at the Harvard Forest and co-author of the new study, said in a statement. "They can give us a glimpse back in time."
For the study, investigators analyzed tree rings spanning 300,000 square miles and 400 years of history in the eastern United States. The tree records in the study show that just before the American Revolution, across the broadleaf forests of Kentucky, Tennessee, North Carolina, and Arkansas, the simultaneous death of many trees opened huge gaps in the forest -- prompting a new generation of saplings to surge skyward.
"There's no historical evidence that the dead trees succumbed to logging, ice storms, or hurricanes. Instead, they were likely weakened by repeated drought leading up to the 1770s, followed by an intense drought from 1772 to 1775," researchers said.
The final straw was an" unseasonable and devastating frost in 1774 that, until this study, was only known to historical diaries like Thomas Jefferson's Garden Book, where he recounts 'a frost which destroyed almost everything'," according to researchers.
"Many of us think these grand old trees in our old-growth forests have always been there and stood the test of time," Neil Pederson, lead author of the new study, said in a statement. "What we now see is that big events, including climatic extremes, created large portions of these forests in short order through the weakening and killing of existing trees."
Researchers said that as climate warms, increasing drought conditions could easily expose eastern forests to the kind of conditions that changed them so abruptly in the 17th and 18th centuries.
"We are seeing more and more evidence of climate events weakening trees, making them more likely to succumb to insects, pathogens, or the next severe drought," Orwig said.
The findings were recently published in the journal Ecological Monographs.
