Mesita del Buey, NM, USA Top Impact Other Impacts |
![]() Piñon trees feature prominently in the landscapes, ecosystems, and Native American cultures of the southwestern United States. The combined effects of rising temperatures, drought, and pests—which are likely to become more severe and extensive as the planet warms—have already caused massive die-offs of the trees. 1 |
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
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 ContextClimate 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 HoldsPiñon 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. Endnotes
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