Downhill Mountain Migrations

While most scientists envision forest plants and animals retreating up mountainsides to avoid the effects of global warming, researchers studying the ranges of Northern California are finding trees and other vegetation growing in the opposite direction.

In the face of widespread warming since the 1930s, while average annual temperatures over California increased 0.6 degrees Celsius (1 degree F), trees and other northern forest plants were migrating downhill an average of 80 meters (87.5 yards), the researchers report in the new issue of the journal Science.

The study points up the powerful effects of another important, although less widely recognized feature of our changing climate -- the regional shifts taking place in precipitation patterns.

The images of California above, courtesy of Science, illustrate the statewide warming trend (left) and the increases in precipitation in the North (right) from the 1930s to the present. The precipitation changes are part of larger regional patterns toward wetter conditions in the Pacific Northwest and drier conditions in the Southwest.

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In the Coast Range, the Cascades, and the Sierra Nevada of Northern California, forest scientist Shawn Crimmins of the University of Montana and colleagues report that the benefits of wetter soil conditions have outpaced the drying effects of higher temperatures.

While the pattern of uphill migration of plants and animals still holds true for much of the globe, the researchers would not be surprised to find other areas of downhill migrations of plants in places where heightened precipitation patterns have occurred.

The scientists write:

"Most locations north of 45° latitude have experienced increased precipitation over the past century, and at continental scales, global climate models generally predict those locations to become wetter over the next century. If increases in precipitation outpace increases in evaporative demand in these regions, we can expect downhill shifts by species to occur."

IMAGES: Science Magazine