In a finding that one researcher labeled a “huge surprise,” scientists have discovered that as the climate has changed in recent decades, more trees in the U.S. have moved west than have moved north.

With temperatures rising, researchers knew that many trees species already were moving north as climate zones shift. But Songlin Fei, a forest ecologist at Purdue University, discovered that shifts in tree distribution also have been making an unexpected turn to the west. Relying on U.S. Forest Service inventories of 86 types of trees, Fei and his colleagues found that 47 percent of those species had made statistically significant westward shifts in the past three decades at a rate of 15 kilometers per decade. By contrast, 34 percent of the 86 tree species had shifted northward at a rate of 11 kilometers per decade.



A key factor, Fei believes is changing rainfall patterns. Increased precipitation since 1980 in the central United States has probably hastened the westward movement of trees, particularly among flowering trees, known as angiosperms. Reporting in the journal Science Advances, Fei said that most of the northbound trees were gymnosperms, mainly made up of conifers. Angiosperms tend to be faster-growing and more drought-resistant than gymnosperms, and the more robust vascular systems of angiosperms could enable them to move swiftly west into areas where precipitation has increased.