Migrating Trees May Find Their Way Barred by Geology

By Nathanael Massey, E&E reporter
4/15/2013 9:12:43 AM

The trees are on the move. From the tropical Andes to the maples of New England and far beyond, warmer temperatures are pushing species upslope and away from the equator as climatic regions shift around the globe. The process has been underway since the close of the last ice age but has accelerated over the last century with the rapid rise of human-caused warming.

Photo by James Gaither

That migration may be checked, however, by geologic and geomorphic factors that have proved less susceptible to the influence of climate. A new study from the University of Calgary finds that, in certain cases, a shifting climate is pushing trees into less-than-ideal habitats.

"The scientific community's been very confident in its assessment that trees are moving around with climate change," said Edward Johnson, a professor of biological sciences at the University of Calgary. "We haven't been asking the right question, though, and that question is: Will there be appropriate habitats for those trees to move into?"

Among living creatures, trees win no awards for speed. Migration occurs only at the pace that new seedlings can take root in previously uninhabited -- but climatically and ecologically suitable -- territory. Given the growth rate of trees, it can take decades for a forest to shift even a few meters.

Geologic change, however, can take much longer. Plants require viable soil to grow, meaning rocks must erode and organic matter must decay. "Given time, most new territories will geomorphically weather to become suitable for trees to move in," said Johnson. The problem, he said, is that with the current rapid pace of migration under climate change, there is often not enough time for that process to occur.

Rising temperatures and unfavorable terrain

To demonstrate and measure the importance of geology on forest migration, Johnson and colleague Marc Macias-Fauria of Oxford University designed a simulation incorporating regional and climate models alongside remote sensing and on-the-ground investigation of the Marmot Creek Research Watershed, located west of Calgary, Alberta. They ran their model through high-powered computers at Oxford's Supercomputing Centre in England.

Their results were stark. "As far as we can tell, there doesn't seem to be any movement upslope," Johnson said.

"There are lots of places in the present alpine where the conditions are simply not suitable for trees," he said. "Between 6 to 18 percent of the present alpine area is either too steep, has bedrock, cliffs and talus or some other local terrain conditions that will limit trees being established."

The section of the Canadian Rockies under study is characterized by thrust faults where sedimentary rock has pushed up against itself, he said. Some of this rock is shale, which weathers quickly, but much of it is limestone and dolomite, which does not, he added.

Similar concerns have been raised about North American tree species that have moved north to keep pace with higher temperatures. A study last year found that maple trees in New England may be moving into rockier and less hospitable territory in Nova Scotia.

As forests are squeezed between unfavorable climates on one side and inhospitable terrain on the other, scientists worry that biodiversity may be at stake -- particularly in the Andes, where an area as narrow as 20 meters can span a complete bio-region, home to unique sets of plants and animals (ClimateWire, Feb. 13, 2012).

The University of Calgary researchers are looking to expand their models to include a wider range of geologic factors to better understand why trees do and do not migrate to certain regions, as well as identify possible "eco-niches" where species could be sheltered.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.

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