Pinyon-juniper woodlands are a common sight in a large portion of Utah and especially the Canyonlands region. However, it turns out that these two species differ in their water use and that may impact their long-term survival.
“We found that pinyon may continue to decline, and juniper may continue to expand in the coming decades,” said Faraz Rehman, a master’s student at Utah State University. His research looks below ground, focusing on how trees access and use water in dry ecosystems, where water often determines whether plants live or die.
“Pinyon and juniper have been coexisting species from millions of years, but now one is declining and one is expanding,” he said.
Although pinyon-juniper woodlands are widespread across the state and often encroach on other habitats, the two species fare differently under extreme weather. For example, where the two species coexist, junipers continue to expand, while pinyon pines show signs of vulnerability under increasing drought.
Rehman was interested in why that is, and he deduced, understandably, that it must be due to their water absorption — but what he found was surprising.
“What we expected to find is that juniper has better water uptake strategies, but on the contrary, we found that pinyon has better water uptake strategies,” he said.
Rehman found that pinyon pine has more flexible rooting behavior, allowing it to move roots through the soil to capture water after small rain events. Juniper, by contrast, tends to keep its roots more consistent. Yet despite pinyon’s ability to access more water, it is still losing ground, leading him to one major conclusion.
“Water uptake is not the answer for these species,” Rehman said.
Instead, Rahman believes that the key difference lies in how each species uses water. Pinyon follows a faster growth strategy that demands higher water use, while juniper is far more conservative. As temperatures rise and droughts become more frequent, that difference matters.
“This strategy was successful in the past, but not now, while temperature is increasing and droughts are more frequent,” he said.
Rather than how much water a tree can access, Rehman said the study shows it is how efficiently that water is used that may determine which species persist in a changing climate.
