An experimental study of pinon pines at Biosphere 2 in Arizona shows that an increase in temperature makes the species more susceptible to die-off during drought. When temperatures were increased by 4 degrees Celsius (7.2 degrees Fahrenheit), the piñon pines died 28 percent faster than trees which experienced drought-conditions at current temperatures, according to a new study published in Proceedings of the National Academy of Sciences (PNAS).

The researchers transplanted mature piñon trees pinus edulis (also known as the Colorado Pinyon) to the Biosphere facility. As the researchers simulated drought-conditions on the trees, one set of trees experienced average temperatures while the other set received temperatures 4.3 degrees Celsius higher.

“All drought trees in the warmer treatment died before any of the drought trees in the ambient treatment,” the researchers write. “Our results imply that future warmer temperatures will not only increase background rates of tree mortality, but also result in more frequent widespread vegetation die-off events.”

Relating their findings to historic occurrences of drought across the Southwestern United States, the scientists predict tree die-offs in the region will occur five times more frequently than in the past. However the authors write, “this projection is conservative because it is based on the historical drought record and therefore does not include changes in drought frequency, which is predicted to increase concurrently with warming.”

With the likelihood of more droughts and continued stress from pests, like the bark beetle, the outlook for trees in America’s southwest, and possibly elsewhere, is troubling at best.

More tree die-offs is likely to increase the region’s carbon output as well. When trees die they release their stored carbon back into the atmosphere, at the same time massive declines in trees means less carbon storage. According to the authors, tree die-offs could also lead to losses in wildlife habitat, changes in the water cycle, increased opportunities for alien species, and a loss of ecosystem services.

The scientists suggest that similar research should be done on other tree species. In addition, they write, “the temperature sensitivity we document highlights the need to improve model predictions and could profoundly alter assessments of climate change impacts, which continue to reveal increasingly dangerous risks.”

Related articles

Plant communities changing across the globe, says scientist Sasha Wright

(03/29/2009) Having studied plant communities across three continent and within widely varied ecosystems—lowland tropics, deciduous forests, grasslands, and enclosed ecosystems on hill-tops—graduate student Sasha Wright has gained a unique understanding of shifts in plant communities worldwide as they respond to pressures from land use and global climate change. “Plant communities are certainly changing,” Wright told Mongabay.com in a March 2009 interview. “These changes are undoubtedly affected by an increased occurrence of extreme weather events, temperature fluctuations, atmospheric CO2 concentrations, human land use, and in some cases urbanization of populations.”

Could engineering rainforests save the planet from global warming?

(01/21/2009) At the Smithsonian symposium entitled “Will the Rainforests Survive?”, leading tropical biologists vigorously debated current threats to the rainforest and what the future may hold. While climate change was identified as a leading threat to rainforests, many of the scientists argued that the tropics may also be the key to mitigating the impact of global warming.

20% of the Brazilian Amazon’s tree species to go extinct

(08/11/2008) A new study estimates the number of trees that will go extinct in the Brazilian Amazon due to habitat loss.

Global warming causes plants to move to higher elevations

(06/26/2008) Global warming has caused many plant species to move to higher elevations, report researchers writing in the journal Science.

Global warming threatens California’s native plants

(06/24/2008) Two-thirds of California’s native plants could suffer an 80 percent or more reduction in geographic range by the end of the century due to changing climate warns a study appearing tomorrow in the open-access journal PLoS ONE.

New discoveries about past forest changes may help predict future ones in a changing climate

(06/12/2008) There is no better method to understand the future than to look to the past. Several new studies of the earth’s glacial history are transforming the way scientists look at tree behvaior during extreme changes in climate. Scientists Remj Petit, Feng Sheng Hu, and Christopher Dick described such changes in relation to current global warming in the new issue of the journal Science. They report that already “in some parts of the world, tree species have started to shift their distributions in response to anthropogenic climatic warming”, thus raising the stakes for understanding how tree species will adapt to coming changes.