Like "cold case" detectives digging up clues from the past, University of Illinois scientists sifted through the genetic clues in living spruce trees and have come closer to solving some of the mysteries of how trees adapt to climate change.
LAS researchers analyzed chloroplast DNA from 24 spruce forests in Alaska and Canada. They have determined that trees cannot migrate in response to climate change as quickly as originally thought. What's more, there is now strong evidence that trees survived the height of the last glacial period 17,000 to 25,000 years ago in the ice-free areas of Alaska.
"In the face of global warming, we need to study how plant and animal populations have responded to climate change in the past to better predict what will happen in the future," says Lynn L. Anderson, lead author of the DNA survey and a U. of I. doctoral student in ecology and evolutionary biology.
Chloroplast DNA offers "compelling evidence" that white spruce trees survived the last glacial period within favorable "microhabitats"-ice-free refuges in the harsh environment dominated by glaciers, Anderson says. As the climate warmed, DNA evidence suggests that the trees then migrated from these refuges, advancing from at least two directions, she adds.
This helps solve a long-running controversy, says Feng Sheng Hu, U. of I. professor of plant biology and geology. According to Hu, some scientists believed that the trees had been restricted to areas south of the ice sheets covering North America during glacial periods. Then, as the climate warmed, they rapidly migrated north. However, the U. of I. evidence shows that the trees were not restricted to the south. Some of them survived in these northern, ice-free refuges.
The data indicate that the trees may not have migrated as rapidly as once thought. Hu says earlier estimates of the rate of tree migration, based on fossil pollen records, may have been too high. "Additional analysis of fossil pollen in sediments, as well as DNA data from living trees, could help pin down the actual rate of tree movement over time," he says.
The researchers' findings reveal the great resilience of the white spruce-and perhaps other tree species-to climate change. They show that isolated populations of trees might be able to persist in certain habitats even after regional climatic conditions have become unfavorable as the result of rapid global warming. This resilience might reduce the probability of species extinction with global warming. Or maybe not.
"Our study looked at the past, before humans had made any significant impact on climate," says Hu. "In the future, both human and natural disturbances will likely interact with climate change to reduce resilience and trigger larger ecological shifts."
This study was published in the Proceedings of the National Academy of Sciences USA. Contributors included Ken Paige, Professor of Animal Biology, David Nelson, Postdoctoral Fellow of the Institute of Genomic Biology, and Remy Petit of the French National Institute of Agronomy.
