Trees will likely be smaller and capture less carbon in future forests

A new study published in the journal Global Change Biology discusses the future of forests.

Researchers from the University of Arizona have combined tree-ring data from the U.S. Forest Service with inventory data on ponderosa pines in Arizona to model the drivers of future tree growth. They predict a 56 to 91 percent decline in individual tree growth, decreasing each tree's individual capacity to remove carbon from the atmosphere.

"While Arizona's forests are relatively small in terms of their contribution to the total U.S. carbon sequestration, our approach can be used to make the same predictions for forests around the world," said lead study author Kelly Heilman, a postdoctoral research associate in the University of Arizona Laboratory of Tree-Ring Research.

Many factors influence the size trees will grow to, but the increasing temperature is the main factor in the case of the ponderosa pines. Trees have to transport water to their tops against gravity, and the system to transport water is put under more pressure as temperature increases. This effect is more pronounced the larger the tree in question.

"The third interaction is between forest density and the climate variables. These interactions show that denser forests fare worse when it's hotter and drier, which is generally what we'd expect for the species, but this is concerning given the recent densification of these forests," said Heilman.

"Foresters can't influence the climate, but they can change forest density to reduce competition for the remaining trees. If you have both an overly dense forest and climate warming happening at the same time, that's a double whammy. But if you thin the forests, you can remove one source of stress," said study co-author Margaret Evans, assistant professor of dendrochronology in the tree-ring lab.

You can read more from the study here.