A study recently published in the journal Science Advances reveals that forests in the eastern United States are being altered by climate change. By using empirical data, researchers have found that tree species commonly found in eastern American forests have been shifting their population centers westward since 1980. They’ve also found that many tree species have moved northward. Their research can give us some food for thought on the impacts of climate change on tree populations and associated ecosystems.
Population Shifts of Deciduous and Coniferous Trees
The study has found that different tree species are responding to climate change differently. In general, coniferous/evergreen trees are moving northward while deciduous/broad-leaf trees are moving westward. The researchers worked with the hypothesis that changes in the climate have caused temperatures to rise across the eastern United States and have altered rainfall patterns and totals. From an ecological perspective, it’s logical to presume that plants adapted to colder climates will move farther north and at higher elevations. However, scientists were surprised to the see the westward shift of tree populations over the last three decades.
They’ve found that approximately three-quarters of common tree species in eastern American forests have shifted their populations westwards since 1980. Some of these species include white oaks, sugar maples and American hollies. During the same period of time, over half of the tree species studied were also moving north. This study is one of the first to use empirical data to see how these eastern forests are being affected by climate change.
Reasons for the Shift
The results of a westward movement were more surprising to the team of scientists than the northward movement. One of the authors of the study is Songlin Fei, a professor of forestry at Purdue University. According to Fei, “the results seem to show that moisture plays a much more significant role in the near-term, which is very intriguing”. Researchers have noticed that the north eastern United States has received more rainfall since 1980 than it did the century prior. The south eastern region, on the other hand, has received less rainfall. States in the Great Plains region (such as Oklahoma and Kansas) now have more precipitation than historically normal.
The group of researchers argue “that at least 20 percent of the change in population area is driven by changes in precipitation, which are heavily influenced by human-caused climate change.” Other potential reasons for the westward shift include: land use changes, frequency of wildfires and the introductions of blights and pests.
Food for Thought
The study conducted by Fei and his colleagues was an eye opening experience. Loïc D’Orangeville, an ecologist at the Quebec Forest Research Center, believes that “this is a very cool study, with results that seem to raise more questions than they can provide answers for.” It remains unclear whether trees will continue to shift westwards or if they’ve reached their peak movements. The research team is now concerned with the ecological health of forests in the eastern United States since tree species are moving away from the region. How will these forest communities adapt? Will they start to collapse with the absence of these trees?
According to D’Orangeville, “… trees are highly dynamic organisms, constantly moving in response to climatic shifts like recent glaciations or other disturbances. Their actual range does not reflect conditions that are optimal for their growth”. The empirical data shows that forests in the eastern United States are being reshaped by climate change. Will ecosystems have the ability to keep up and adapt to the Earth’s fast changing climate?