Warmer Temperatures Could Boost Plant Growth on Rangelands

By CIRCulator Editorial Staff

Reprinted from: The Climate CIRCulator

EAST OF THE CASCADES, hundreds of thousands of cattle graze the vast rangelands. This economically vital agricultural region of the Pacific Northwest could become more productive as a result of climate change, a new study finds. Climate models show that rangelands in the interior West — including eastern Oregon and Washington as well as southern Idaho — would experience the greatest increases in productivity, according to the study by the Rocky Mountain Research Station of the U.S. Forest Service.

Matthew Reeves and colleagues compared the conversion of CO2 into plant growth under four climate scenarios as measured by “net primary production” (NPP) of rangelands across the continental United States. Specifically, the study estimated that production would initially decrease in the first half of the 21st century but rebound and increase by more than 25 percent from historical levels by century’s end.

These gains in net primary production seem to result from projected increases in “CO2 fertilization” — that is, enhanced growth resulting from higher concentrations of carbon dioxide in the atmosphere. Lab studies have attributed this extra growth to greater efficiency of water use. In other areas of the United States, precipitation is the most likely driver of increased growth, particularly in the prairies of Montana and the Dakotas to the north; Nebraska, Kansas and Oklahoma to the south; and Iowa, Missouri and Arkansas to the east. In the Southwest rangelands, on the other hand, increasing temperature is likely to drive losses of production.

What this may mean for rangeland management, particularly for grazing, is unclear. The paper cites other studies suggesting that increased NPP could raise carrying capacity for grazing in areas of Australia by more than 40 percent, while other studies contend that overall carrying capacity could decline even with increased NPP because of other limiting factors such as plant nitrogen production. Also note that the study does not consider other factors impacting rangelands, including how pests (such as grasshoppers) or invasive species (such as cheat grass) will respond to future climate conditions.

Reference:

Reeves, M.C., A.L. Moreno, K.E. Bagne (2014) Estimating climate change effects on net primary production of rangelands in the United States, Climatic Change, 126:429. Online Access

A version of this story originally appeared in the November/December issue of The Climate CIRCulator.