Biosphere 2 experiment shows how fast heat could kill drought-stressed trees

EurekAlert: Widespread die-off of piñon pine across the southwestern United States during future droughts will occur at least five times faster if climate warms by 4 degrees Celsius, even if future droughts are no worse than droughts of the past century, scientists have discovered in experiments conducted at the University of Arizona's Biosphere 2.

Their study is the first to isolate the impact of just temperature on tree mortality during drought. The temperature effect is usually confounded by varying weather and bark beetle and other pest attacks. Quantitative information on how sensitive drought-stressed trees are to hotter temperatures is critical for predicting drastic, sudden and widespread die-offs, the scientists said.

University of Arizona researchers and their colleagues transported 20 reproductively mature piñon pine trees from New Mexico to Biosphere 2's glass-enclosed 3.14-acre living laboratory near Oracle, Ariz., for the experiment. Half the trees were kept in an area at temperatures normal for piñon pine. Half were kept in an area warmer by 4 degrees Celsius, or about 7 degrees Fahrenheit. Once the trees were established, researchers deprived some of them of water.

Drought killed the trees at the higher temperature 28 percent faster than it killed the trees at the cooler temperature. When the researchers extrapolated this temperature effect to the region's 100-year historical drought record, they found that widespread piñon pine die-offs can be predicted to occur five times more frequently because of the higher temperature alone, without factoring in predictions for worsening drought, insect attack or other consequences of climate change….

Biosphere 2 in Tucson, Arizona, shot by Daderot