As Earth’s climate warms, the shrubs of alder, birch, and willow that grow on arctic tundras are becoming taller and more numerous. Although the trend yields demonstrably more food for reindeer, its other ecological implications, good and bad, are less clear. Now, a large collaboration led by Mark Olson of the National Autonomous University of Mexico has identified a potential threat: Taller plants are more vulnerable to droughts, freezes, and other climatic shocks.
As their maximum height increases, plants in regions that become warmer and wetter develop wider vessels to transport water from their roots to their leaves. Such an adaptation is shaped by the physics of capillary hydraulics. Wider vessels can harvest more water more efficiently. But the wider a vessel, the more vulnerable it is to developing flow-blocking gaps of vapor during periods of drought or freezing. If the gaps persist, the supply of liquid water to the...
