Key Facts

Rising temperatures are worsening the effects of drought in the Four Corners region of the U.S. Southwest, threatening regional ecosystems and global biodiversity.^2,3,6

• More than 90 percent of the centuries-old piñon pines around Mesita del Buey, NM, died in a 2002-2003 drought.⁶
• This recent drought was warmer than a previous drought in the 1950s, and there is evidence that the recent piñon die-off was significantly more extensive.⁶
• In a warming climate, scientists expect drought to cause even more rapid and extensive die-off of trees on a regional scale.⁶

Details

The Madrean Pine-Oak Woodlands in the U.S. Southwest are home to 44 of 110 global species of pine trees—the greatest such diversity in the world.² However, only isolated patches of these woodlands remain, mostly on mountaintops in New Mexico, southern Arizona, and West Texas.³

These woodlands are one of two designated "biodiversity hotspots" in the U.S. Southwest. Although together all 34 biodiversity hotspots account for a little more than 2 percent of Earth's land area, about half of the world's plant and land animal species live only in these places.³ What these 34 biodiversity hotspots also have in common is that they have already lost more than 70 percent of their native vegetation.^3,4,5

The Global Context

Climate change is adding to pressures on the Madrean Pine-Oak Woodlands, such as from logging, clearing of land for agriculture, and urban development.³ And because of the extraordinary biodiversity of these woodlands, the implications are global.

Rising temperatures, for example, are worsening the effects of drought in the Southwest. One study examined the die-off of piñon trees in a 4,600-square-mile (12,000-square- kilometer) area of the Four Corners region.^3,6

The study found that these tall trees of the forest canopy died in 2002-2003 as a result of drought and associated infestations of the bark beetle. This recent drought was warmer than a previous drought in the 1950s, and there is evidence that the recent piñon die-off was significantly more extensive across all ages and sizes of trees. The 1950 drought, in contrast, primarily affected trees over 100 years old.⁶

Mesita del Buey experienced some of the most severe effects in the 2002-2003 drought—more than 90 percent ofthe New Mexico state tree, the piñon pine, died.⁶ Scientists concluded that warmer temperatures associated with that drought may account for the apparently greater mortality by drying out the soil and increasing water stress on the trees.^3,6

What the Future Holds

Piñon nuts are an important food source for people, birds, and small mammals in the Four Corners region, and scientists say their supply may decline over an extensive area in the future. Die-off of the tree canopy on a regional scale also rapidly changes the area's type of ecosystem, the ecosystem's properties, and land surface conditions for decades. Implications include a potentially large loss of carbon stored in trees, as well as more near-ground solar radiation and water runoff, and faster erosion.⁶

In a warming climate, scientists expect drought to cause even more rapid, severe, and extensive die-off of trees on a subcontinental scale⁶—with dramatic effects on regional ecosystems and global biodiversity.

Credits

Endnotes

1. Photograph : Tsankawi, Bandelier National Monument, New Mexico. Courtesy of the National Parks Service. Available online at http://www.nps.gov/ band/ planyourvisit/ tsankawi.htm. Accessed 3 November 2010. ↑
2. Farjon, A., and C.N. Page, eds. 1999. Conifers: status survey and conservation action plan. IUCN/SSC Conifer Special Group. Gland, Switzerland, and Cambridge, UK: International Union for Conservation of Nature and Natural Resources. ↑
3. U.S. Global Change Research Program. 2009. Global climate change impacts in the United States. Edited by T.R. Karl, J.M. Melillo, and T.C. Peterson. Cambridge University Press. ↑
4. Myers, N., R.A. Mittermeier, C.G. Mittermeier, G.A.B. daFonseca, and J. Kent. 2000. Biodiversity hotspots for conservation priorities. Nature 403(6772):853-858. ↑
5. Mittermeier R.A., P. Robles Gil, M. Hoffman, J. Pilgrim, T. Brooks, C. Goettsch Mittermeier, J. Lamoreux, and G.A.B. da Fonseca. 2005. Hotspots revisited: Earth's biologically richest and most endangered terrestrial ecoregions. Washington, DC: Conservation International. ↑
6. Breshears, D.D., N.S. Cobb, P.M. Rich, K.P. Price, C.D. Allen, R.G. Balice, W.H. Romme, J.H. Hastens, M.L. Floyd, J. Belnap, J.J. Anderson, O.B. Myers, and C.W. Meyer. 2005. Regional vegetation die-off in response to global-change drought. Proceedings of the National Academy of Sciences 102(42):15144-15148. ↑