(Photo by Andrew Bernier - KJZZ)

Trees like Redwoods are at risk of a warmer, dryer atmosphere sucking the moisture out of them.

(Photo by Andrew Bernier - KJZZ)

Ponderosa forests in Arizona could be at risk, especially if trees compete for water from a lack of thinning projects.

While the shade of a tall tree may help keep you cool, rising temperature averages from climate change may be causing greater stress for taller trees.

A new report suggests that with warmer and dryer air, taller plants will release more moisture because of greater evaporation. This means when plants open up small holes in their leaves called stomata, to absorb carbon dioxide needed for photosynthesis, even more of the plant’s water is lost to the atmosphere. But now that’s changing.

“The plants close that stomata because they don’t want to dry out," said Nathan McDowell with the Los Alamos National Laboratory. "But the consequence is they can’t photosynthesize. They can’t eat.” 

Using a mathematical equation called Darcy’s Law that measures forces on water flow, McDowell said longer plant tissue and more leaves with more stomata will cause greater stress for taller trees.

“Darcy’s Law shows the plants that are going to be better adapted under this warming atmosphere are shrubs," said McDowell. "How does a big tall tree get shorter? It doesn’t. So that’s why there’s this mortality implication that we predict tall trees are the most vulnerable.”

This adds further challenges to iconic southwestern trees such as Ponderosa Pine and Redwoods as drought conditions continue.