LOS ALAMOS, N.M., Sept. 29 (UPI) -- A new study shows larger trees are more vulnerable to drought. The pattern, researchers say, is consistent in a variety of ecosystems across the globe.
The research also confirms the ecological importance of trees, suggesting a climate with more and longer droughts will damage the type of trees most beneficial to the climate.
The new study, published in the journal Nature Plants, included the analysis of 40 drought events at 38 forest locations, including field observations from a range of wooded environs -- from semi-arid woodlands to tropical rainforests.
"Previous studies at a few sites had shown that large trees suffer more than small trees during and after droughts, and our theory suggested this should be a globally consistent pattern, but this project was the first to test this hypothesis globally." study co-author Nate McDowell, a forest ecologist and plant physiologist at the Los Alamos National Laboratory, said in a press release.
Analysis by McDowell and his colleagues -- which included scientists from the Smithsonian's Conservation Biology Institute and Tropical Research Institute, the University of New Mexico and the U.S. Geological Survey -- showed that rates of tree deaths increased with widening trunk diameters.
Larger trees are more vulnerable to prolonged droughts because their high number of leaves and surface areas leave them more exposed to evaporation. They require more water to stay hydrated, and their more expansive hydraulic system is more easily overworked when water supplies run short. Their taller canopies are also more exposed to hotter, more drying levels of solar radiation. Furthermore, larger trees are typically targeted more aggressively by invasive insects.
Because of the important role trees play in pulling CO2 from the atmosphere and cooling the planet, the new study's findings are worrisome. When larger trees die, they go from being a carbon sink to a new source of carbon. But more than just climate savers, large trees play a vital role as shelter, food source and indirect benefactor to a variety of plant and animal species.
Unfortunately, a climate with drier soils, longer and more frequent droughts and high temperatures will further stress some of the planet's most valuable ecological resources.