Photo: David Gilkey/NPR
Droughts kill trees. That much we know. But beyond the simple concept of "trees die without water," scientists actually don't know much about how heat and droughts affect trees. How long can they go without water? Which ones will die first?
Ecologists at the Los Alamos National Laboratory in New Mexico want to help trees survive droughts, but first, they have to learn how to kill them:
Nate McDowell runs what you might call a "tree torture" lab. It's actually outside in the desert, near the national lab. He's growing a group of pinon and juniper trees, about 15 feet high. Plastic gutters keep rain away from the tree roots, to simulate drought. The trees themselves are growing inside clear plastic chambers — tubes with no tops. Silvery hoses carry heated air into the chambers.
We climb in through a hole in the chamber where you can immediately feel the heat. It's about 7 degrees hotter than the outside, roughly the increase predicted by computer models of climate change over the next 80 years or so.
McDowell is simulating drought and a warmer climate. He measures how the trees respond — there are instruments stuck into and all over the trees. Even wrapped around the stem.
"Every few minutes they measure the diameter of that tree," he explains. The trees look like patients in intensive care — wired up with tubes coming out of the stems. All to see what it takes to kill it. "Everyone knows it gets hot and dry; you know, beetles show up, the trees are dead," McDowell says, "but we don't really understand it."
Christopher Joyce of NPR's Weekend Edition has the fascinating story: Link